Geological Survey Professional Paper 215 Geology of the Southern Guadalupe Mountains, Texas

UPPER PART OF GUADALUPE SERIES

The upper part of the Guadalupe series contains the last Permian deposits laid down under normal marine conditions in the region, and the greatest development of limestone reef deposits. Like the middle part of the series, the upper part consists of three dissimilar but contemporaneous facies composed of various sorts of limestone and sandstone (pl. 7, A). It is succeeded by beds of anhydrite and other evaporite deposits.

In the southeast part of the area studied, beds of upper Guadalupe age are classed as the Bell Canyon formation of the Delaware Mountain group. This formation is 670 to 1,040 feet thick and is composed of sandstone, with some thin, dark-gray limestone beds. Farther northwest, in the Guadalupe Mountains, the Bell Canyon changes into the white, massive Capitan limestone, which forms a reef mass. Here, the unit is 1,500 to 2,000 feet thick, or more than twice the thickness of the equivalent beds to the southeast. The Capitan does not extend far to the northwest, for within a few miles its massive limestones change into the thinner-bedded Carlsbad limestone. Tongues of the highest Carlsbad overlap the Capitan to the southeast and form flat benches on the summits of the Guadalupe Mountains.

The Bell Canyon formation crops out in a belt 5 to 10 miles wide on the east slope of the Delaware Mountains (pl. 3). Farther northwest, the Capitan and Carlsbad limestones spread as a plate over the Guadalupe Mountains and constitute its highest peaks and ridges. The limestones are exposed also in the downfaulted area west of the high mountains, where they form the Patterson Hills.

BELL CANYON FORMATION

The Bell Canyon formation, as here distinguished, is roughly equivalent to the highest part of the Delaware Mountain group described by Beede²⁵ as consisting of "very thick sandstones, alternating with less thick limestones, and rather hard shales." The formation is named for Bell Canyon, which lies in the northeast part of the area studied (pl. 3), heading on the Reef Escarpment of the Guadalupe Mountains and draining eastward 5-1/2 miles to the old route of United States Highway No. 62, where it joins Lamar Canyon. In its course the canyon crosses only the lower part of the formation. The upper part is well exposed in the hills directly northeast of the canyon and is crossed by United States Highway No. 62.

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²⁵Beede, J. W., Report on the oil and gas possibilities of the University block 46 in Culberson County: Texas Univ. Bull. 2546, p. 14, 1924.

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The unit is classed as the uppermost formation of the Delaware Mountain group. Recent work indicates that it is nearly all younger than the typical Delaware Mountain, as defined by Richardson,²⁶ at the south end of the Guadalupe Mountains near El Capitan. It was mapped by Richardson, however, as part of the Delaware Mountain in his reconnaissance of the Delaware Mountains, and this practice has been followed in all subsequent geological reports.

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²⁶Richardson, G. B., Report of a reconnaissance in trans-Pecos Texas north of the Texas and Pacific Railway: Texas Univ. Bull. 23, p. 38, 1904.

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In its outcrop on the east slope of the Delaware Mountains, the Bell Canyon formation forms a belt of rolling country 5 or 10 miles wide, in which the beds dip east-northeast or northeast at angles of a few degrees. Occasional mesas or lines of cuestas rise above their surroundings, and are capped by limestone members. Along the southeast base of the Guadalupe Mountains, large tracts underlain by the formation are covered by Quaternary gravel deposits. A short distance east of United States Highway No. 62, the formation has a measured thickness of 670 feet (sec. 34, pl. 6), but in the Niehaus et al., Caldwell No. 1 well, 35 miles east-southeast of El Capitan, the thickness has increased to 1,038 feet.

In the Guadalupe Mountains, the formation intergrades with the reef mass of the Capitan limestone, the change taking place farther southeast in the upper than in the lower part. The lower members thus extend northwestward for several miles beneath the Capitan limestone. They form ledges along the bases of the Capitan cliffs on the southeast and west sides of the mountains.

The outcrop of the Bell Canyon formation is shown on the geologic map, plate 3. Some of its outcrops in the Delaware Mountains appear in the northeastern part of the map, interrupted by patches of gravel. Larger areas of outcrop, not shown, lie beyond the map area to the east. Outcrops in the Guadalupe Mountains appear as a narrow band along their southeastern and western sides. The structure of the formation in the Guadalupe Mountains is shown on the sections of plate 17.

Views of the outcrops of the Bell Canyon formation on the southeast side of the Guadalupe Mountains appear in the panoramas of plate 4. In plate 4, A, its limestone members can be seen standing in benches, mesas, and cuestas along the base of the Guadalupe Mountains escarpment; the highest member, the Lamar, appears at the extreme right. In the district shown on plate 4, B, erosion has advanced farther, and the members have been worn back to the base of the escarpment, where they project in ledges. The lower members can be seen again in the views of the western side of the mountains, as on plate 12, where they stand in ledges at the bases of the cliffs.

Stratigraphic sections of the formation are shown on the right-hand half of plate 6. Further, stratigraphic details for the area along the southeast base of the Guadalupe Mountains are shown on plate 15.

SANDSTONE BEDS

The sandstone beds of the Bell Canyon formation, like those of the Cherry Canyon, are buff colored and extremely fine grained. Three thin sections of typical specimens were studied under the microscope by Ward Smith, one from the lower part from just above the Pinery member at El Capitan (sec. 18, pl. 6), and the other two from the upper part below and above the Lamar member at its type locality, 15 miles to the east (sec. 38, pl. 6). Their maximum grain size ranges from 0.1 to 0.2 millimeter in diameter. The dominant grains are quartz, microcline, and plagioclase, but in all three specimens the accessory minerals are diverse and fairly abundant, and include biotite, chlorite, tourmaline, zircon, apatite, and staurolite. A fresh surface of the specimen from the lower part shows a faint greenish color which is probably caused by the chlorite grains. In the specimen from above the Lamar member, the grains are finer in some laminae than others, and this structure, with an increase in the amount of clay in the same laminae gives the rock a platy layering. The matrix of the sandstone tends to be calcareous.

Aside from the occasional, persistent limestone members, the sandstones contain few or no calcareous beds or lenses, and there are no interbedded black, shaly layers of the sort found in the Cherry Canyon formation beneath. Some of the sandstones are in layers a few inches thick, some are thinner bedded or even platy, and some are thicker bedded or massive. Most of the beds Show faint, closely spaced, light and dark laminations but these laminations are absent in some of the massive beds. Each of the limestone members is underlain by 50 or 100 feet of very massive sandstone that crops out in prominent ledges bare of vegetation, or in rocky buttes. Most of them are overlain by platy sandstones (sec. 34, fig. 5). Thus, a tendency toward cyclical deposition is indicated.

In the Delaware Mountains, the bedding surfaces of most of the sandstones are straight and smooth. The sandstones contain no channeling or irregular bedding of the sort found at many places in the Cherry Canyon formation, and only a few ripple marks (fig. 11). Ripple marks are found occasionally as high in the unit as the Rader member, but are nearly absent above. Thus, in the extensive exposure of the sandstones extending 100 feet or so below the Lamar member, 1-1/2 miles northeast of the junction of Bell and Lamar Canyons, a careful search showed only one bedding surface with ripple marks, and these marks were faint and shallow. All the other numerous exposed surfaces at this locality were smooth and featureless.

Along the Reef Escarpment of the Guadalupe Mountains, and nearer the Capitan reef, the sandstones have a somewhat different character. In the tongues that interfinger with the Capitan above the Rader member, the sandstones are coarser grained than to the southeast, and contain lenses and tongues of sandy dolomite extending out from the Capitan. A specimen of sandstone from one of the sandstone tongues near the head of Rader Ridge was examined under the microscope by Ward Smith. Its grains are coarser than those in the sandstones to the southeast, reaching a diameter of 0.4 mm., but like them consist of quartz, microcline, and plagioclase, with rather abundant accessory minerals, such as tourmaline and zircon. The matrix is calcite. The sandstones between the Lamar and Rader members at the mouth of McKittrick Canyon are cut by channels at one or two places, and many of the beds are ripple-marked.

LIMESTONE MEMBERS

Four limestone members are distinguished in the Bell Canyon formation. The Hegler, Pinery, and Rader members are closely spaced in the lower fourth of the unit, and are separated by several hundred feet of sandstone from the Lamar member which lies near its top (pl. 7, A). In addition, a thin limestone bed about halfway between the Rader and Lamar members has been mapped but has not been named, being designated merely as "flaggy limestone bed."

The limestone members are thinner, but more persistent, than those in the Cherry Canyon formation, and are separated by sandstones containing few calcerous beds. In the Delaware Mountains, the members are each 10 or 25 feet thick, dark gray to black, fine grained, and mostly thin bedded. They contain few fossils, in contrast to the Getaway member of the Cherry Canyon formation lower in the section with its abundant and diversified faunas. Toward the northwest, nearer the Capitan limestone reef, each limestone member thickens to 50 or 100 feet, and becomes lighter gray, thicker bedded, and more fossiliferous.

HEGLER LIMESTONE MEMBER

The Hegler limestone member, which forms the basal bed of the Bell Canyon formation, is named for the Hegler Ranch at the east end of Rader Ridge; on the hillsides near the ranch its thin ledges are well exposed (pl. 3).

In the southeast part of the area, it consists of 30 or 40 feet of dark-gray, fine-grained limestone in beds a few inches to a foot thick, interbedded with platy sandstone (as shown in sec. 34, pl. 6). The more granular layers contain small chert nodules, and some fusulinids, ammonoids, and brachiopods. Near the D Ranch headquarters and Long Point the limestone forms the caps of small knolls on the surface of mesas and cuestas of the Manzanita member of the Cherry Canyon formation. Northeast of the ranch headquarters, near Lamar Canyon, the bedding surfaces are hummocky and there are some irregular dips and small folds, perhaps of the same character as those in the Bone Spring limestone. In this district, at the junction of Cherry and Lamar Canyons, seams of white clay less than an inch thick are interbedded in the limestone. C. S. Ross states that these seams consist of volcanic tuff, showing good ash structures but partly altered to clay minerals.

At the type locality, and elsewhere along the southeastern edge of the Guadalupe Mountains, the limestones of the member are different, although they lie in the same position, that is, 25 feet or so above the Manzanita member of the Cherry Canyon formation (as shown in sec. 23, pl. 15). They consist of dark-gray, fine-grained limestone, made up of closely spaced lumps an inch or so thick. In most places these limestones stand in two groups of ledges with a total thickness of 12 to 25 feet, separated by a break of sand or marl. The limestones contain poorly preserved ammonoids, and some of the bedding surfaces are crossed by small tracks and trails. In some localities, as at Nipple Hill and on the northeast side of Guadalupe Canyon (sec. 19, pl. 6), the member disappears, and the first limestone above the Manzanita member is the Pinery member.

The following analysis of limestone from the Hegler limestone member was made. The limestone is of lumpy facies, characteristic of the member along the southeast side of the Guadalupe Mountains, and was collected on the south side of Rader Ridge north of Nipple Hill.

Analysis of limestone from the Hegler limestone member
[Analysis by K. J. Murata; note on insoluble residue by Charles Milton]

The Hegler limestone member extends several miles northwestward beneath the Capitan limestone. On the west face of the Guadalupe Mountains below Guadalupe Peak, the lumpy, slabby limestone ledges can be traced northward into light-gray, thick-bedded, sparingly fossiliferous limestones more than 100 feet thick (as between secs. 14 and 15, pl. 6). Still farther north, near the head of Shirttail Canyon, these limestones grade into the Capitan limestone (sec. 9, pl. 6). Similar limestones crop out as inliers in the bed of Pine Spring Canyon near Devils Hall, and along South McKittrick Canyon between the Pratt and Grisham-Hunter Lodges (secs. E—E', F—F', and I—I', pl. 17). At Devils Hall, the member is a dark-gray, hummocky limestone in beds a few inches to a foot thick (sec. 59, pl. 15), and nearby there are interbedded lenses of massive limestone (sec. 60, pl. 15, and fig. 9, C). Near the Pratt and Grisham-Hunter Lodges, the member is dense, light-gray, sparingly fossiliferous, thin-bedded limestone, with some interbedded massive layers in the upper part.

PINERY LIMESTONE MEMBER

The Pinery limestone member includes the main part of the dark-gray, bedded limestone, called the "upper dark limestone" by Girty,²⁷ which crops out beneath the Capitan limestone at the south end of the Guadalupe Mountains. This limestone formed member 2 of Shumard's section.²⁸ The name is taken from The Pinery,²⁹ the old stage station on the Butterfield Trail at the mouth of Pine Spring Canyon. The type section is on the hillside above Pine Spring, a short distance to the north (sec. 21, pls. 6 and 15). The greater part of Girty's "upper dark limestone" fauna was obtained from the lower part of the member at this locality.

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²⁷Girty, G. H., The Guadalupian fauna: U. S. Geol. Survey Prof. Paper 58, pp. 17-19, 1908.

²⁸Shumard, G. G., Observations on the geological formations of the country between the Rio Pecos and the Rio Grande, in New Mexico: St. Louis Acad. Sci. Trans., vol. 1, pp. 273-289, 1858 [1860].

²⁹The names Pine Spring and Pinery date from the first visits to the region by Americans and are mentioned in the earliest publications on it. The names were applied because of the pine trees growing on the floor of Pine spring Canyon in its lower course. According to local tradition, these trees were much more numerous at the time of the first visits than they are now. Shumard (idem, p. 280) refers to Pine Spring Canyon as The Pinery.

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In the southeast part of the area, the Pinery member consists of 25 feet of thin-bedded, dark-gray, fine-grained limestone, with a few sparingly fossiliferous, more granular, thicker beds, and much interbedded platy sandstone. It lies about 75 feet above the Hegler limestone, and crops out less prominently than that member. Its ledges are exposed on the north bank of Lamar Canyon for several miles southeast of its junction with Bell Canyon (sec. 34, pl. 6).

Farther northwest along the base of the Reef Escarpment on the southeast side of the Guadalupe Mountains, the member passes beneath the Capitan limestone, and forms prominent ledges on the slopes below the ragged Capitan cliffs; these ledges are well exposed between Pine Spring and Frijole and are illustrated in the panorama, plate 4, B. Good exposures are found at Pine Spring (the type section), at Soldiers Lookout near Frijole (sec. 65, pl. 15), and on Rader Ridge to the northeast (sec. 23, pl. 15).

Along the base of the Reef Escarpment, the member reaches 150 feet in thickness, and consists of gray, fine-grained limestone in beds a few inches to a foot thick, containing small nodules and sheets of brown chert, many fusulinids, and a few crushed brachiopod shells. Interbedded with the thinner-bedded limestones are lighter-gray, quite granular, thick-bedded to massive layers 5 to 10 feet thick. At Pine Spring, the most prominent massive layers are at the base, but there are several massive layers higher. The lower massive beds are crowded with the silicified remains of bryozoans (such as Domopora), fusulinids, cup corals, small brachiopods, and occasional calyces of small echinoderms (such as Coenocystis). The member is separated from the Capitan above by about 100 feet of interbedded sandstone and limestone.

The following analysis of limestone from the Pinery limestone member was made. The limestone is gray and granular, and is of a facies that is characteristic of the member on the southeast edge of the Guadalupe Mountains. It was collected on the south side of Rader Ridge north of Nipple Hill.

Analysis of limestone from the Pinery limestone member
[Analysis by K. J. Murata; note on insoluble residue by Charles Milton]

Farther northwest, in Pine Spring Canyon, the member changes to lighter gray, the chert disappears, and the sandstones between the member and the Capitan give place to limestones like those below (as shown in sec. 61, pl. 15). The beds of massive limestone increase in number and the thinner-bedded limestones contain lenticular bodies of massive limestone (as shown in figure 9, B). Similar beds are exposed on the west side of the Guadalupe Mountains as far north as Guadalupe Peak, and in McKittrick Canyon, half a mile east of the Pratt Lodge (secs. E—E' and K—K', pl. 17.) Farther northwest, the member is replaced by a part of the Capitan limestone.

RADER LIMESTONE MEMBER

FIGURE 9.—Sections showing lenticular reeflike features in limestone members of Bell Canyon formation adjacent to Capitan reef mass. A, Lamar limestone member, south bank of draw half a mile southeast of entrance to McKittrick canyon; B, Pinery limestone member, southeast bank of McKittrick canyon, a quarter of a mile east of Pratt Lodge; C, Hegler limestone member, northeast bank of Pine Spring canyon southwest of Pinnacle.

The Rader limestone member is named for Rader Ridge,³⁰ a series of benches and mesas that project southeastward from the Guadalupe Mountains northeast of Frijole Post Office. They are capped by outliers of the member (sec. G—G', pl. 17).

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³⁰According to Mr. J. T. Smith, the ridge was named for the Rader family; they were early settlers and had a ranch near it.

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In the southeast part of the area, as at the junction of Bell and Lamar Canyons, the member is 15 feet thick and lies 30 or 40 feet above the Pinery member (sec. 34; pl. 6). It consists of several layers, as much as 3 feet thick, of gray, granular limestone, with numerous rounded pebbles, fragments of bryozoans, cup corals, and fusulinids, and of interbedded, thinner, darker-gray limestone. At several places in this region it contains a bed as much as 2 feet thick of apple-green, silicified volcanic ash. One specimen, from 1 mile east of the junction of Cherry and Lamar Canyons, was studied under the microscope by C. S. Ross, who states that it contains well-preserved ash structures and primary fragments of euhedral orthoclase, plagioclase, and quartz. The original glass has been completely altered to secondary quartz, and perhaps to kaolin. A specimen from another locality, similar megascopically, is said by Ross to contain no grains that are definitely of volcanic origin.

To the northwest, on Rader Ridge and elsewhere near the Reef Escarpment, the member is 30 to 100 feet thick (sec. 23, pl. 15), and consists of rounded ledges of very massive, granular or dense, light gray or white limestone, much like the Capitan limestone in appearance. Some of the beds contain angular limestone cobbles. Fossils are common, consisting mostly of Capitan species, but including numerous bryozoans, a group not common in the Capitan. Occasional lenses of sandstone and dark gray, slabby limestone are found in depressions on the undulatory upper surfaces of the massive beds.

The following analysis of limestone from the Rader limestone member was made. The limestone is light gray and of a facies characteristic of the member on the southeast edge of the Guadalupe Mountains. The specimen was collected from one of the massive beds near the head of Rader Ridge, north of Nipple Hill.

Analysis of limestone from the Rader limestone member
[Analysis by K. J. Murata; note on insoluble residue by Charles Milton]

In the vicinity of Rader Ridge, the Rader limestone member is separated from the Capitan limestone by several hundred feet of sandstone and thin-bedded limestone. When traced to the southwest along the escarpment, the intervening beds are replaced by the Capitan limestone, and about a mile west of Frijole the member itself merges with the Capitan. (These relations can be traced out on the ridges to the left of Smith Canyon illustrated in the panorama, pl. 4, B.)

FLAGGY LIMESTONE BED

About 100 feet above the Rader member in the Delaware Mountains is a 10-foot layer of straight-bedded, fine-grained, gray limestone, in part sandy, forming flaggy beds a few inches thick (as in secs. 32 and 34, pl. 6). The flags have been quarried on the McCombs Ranch and farther southeast, and have been used locally for building purposes. The same bed is present also in the exposures of downfaulted rocks west of the Delaware Mountains.

LAMAR LIMESTONE MEMBER

The Lamar limestone member is a bed of dark limestone lying near the top of the Bell Canyon formation. It crops out in a belt of northeast-sloping cuestas that extend southeastward from the mouth of McKittrick Canyon into the Delaware Mountains. It has been named for Lamar Canyon,³¹ and its type locality is on the escarpment northeast of the El Paso Natural Gas Company's road across the canyon, about 15 miles east of El Capitan and east of the area shown on plate 3. The name Frijole limestone has previously been used for the member,³² but this name is abandoned because the member does not crop out near Frijole Post Office, and the dark limestones there are of Hegler and Pinery age (see sec. 65, pl. 15).

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³¹Lang, W. B., The Permian formations of the Pecos valley of New Mexico and Texas: Am. Assoc. Petroleum Geologists Bull., vol. 21, pp. 874-875, 1937.

³²Blanchard, W. G., and Davis, M. J., Permian stratigraphy and structure of parts of southeastern New Mexico and southwestern Texas: Am. Assoc. Petroleum Geologists Bull., vol. 13, p. 973, 1929.

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The confusion in terminology has perhaps arisen from difficulties encountered by previous geologists in tracing the limestones exposed below the Capitan near Frijole northeastward along the Guadalupe Mountain escarpment toward McKittrick Canyon, where the Lamar member is exposed. Blanchard and Davis, and Darton and Reeside³³ considered the beds at the two places to be the same.

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³³Darton, N. H., and Reeside, J. B., Guadalupe group: Geol. Soc. America Bull., vol. 37, pp. 423-424, 1926.

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Near the type locality, and elsewhere in the southeast part of the area, the member consists of 15 to 30 feet of gray, dark gray, or black, fine-grained limestone, weathering brown and rough-surfaced, and forming beds a few inches thick, with some lenticular, thicker beds (secs. 34 and 38, pl. 6). Some of the rock is thinly laminated and contains small chert nodules. Near the crossing of United States Highway No. 62 over its outcrop, a few feet of platy sandstone is interbedded in the middle. In most of the Delaware Mountains the member is unfossiliferous, but to the northwest, within a few miles of the edge of the Guadalupe Mountains, some ledges contain brachiopods and other fossils.

In the vicinity of United States Highway No. 62, the limestones of the Lamar member are somewhat contorted, in a manner that resembles the contortion of the black limestones of the Bone Spring limestone. Bedding surfaces are undulatory, and some of the less competent beds are twisted and rolled into lenses. Some of the bedding surfaces are fluted and striated in a general north-south direction. These marks are perhaps the "ripple marks" reported by Crandall³⁴ from this vicinity. I did not see the features that he suggested might be mud cracks when I visited the locality.

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³⁴Crandall, K. H., Permian stratigraphy of southeastern New Mexico and adjacent parts of western Texas: Am. Assoc. Petroleum Geologists Bull., vol. 13, p. 933. 1929.

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Farther northwest along the base of the Reef Escarpment on the southeast side of the Guadalupe Mountains, as at the mouth of McKittrick Canyon,³⁵ the member thickens to 150 feet or more, and is lighter gray, more granular, and more fossiliferous (sec. 28, pl. 6). The fossils are strewn abundantly over the bedding surfaces, and many of them are silicified. The shells are closely packed, and the valves of most of the brachiopods are separated, or at least twisted, in a manner suggesting some transportation before burial. By far the most common fossil is a large Squamularia, but there are other brachiopods, mostly of Capitan type, and also some gastropods, pelecypods, bryozoans, and trilobites. Fusulinids and ammonoids are absent. About a mile southwest of the entrance to the canyon on the south side of the stream, the Lamar member contains mound-like, massive limestone lenses up to 10 feet in thickness, which interfinger laterally with thinner-bedded limestones (fig. 9, A).

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³⁵The member at this place has been described previously by N. H. Darton and J. B. Reeside, Jr. (op. cit., p. 424), and by K. H. Crandall (op. cit., p. 933).

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The following analyses of limestone from the Lamar limestone member were made:

Analyses, in percent, of limestone from the Lamar limestone member
[Analyses by K. J. Murata; notes on insoluble residues by Charles Milton]

Northeast of McKittrick Canyon toward Big Canyon, the Lamar member spreads out in a broad area at the base of the mountains (pl. 3), forming low, dark-colored hills, covered by a growth of lechuguilla. Southwest of the canyon for several miles the member forms the cap of benches that project along the base of the Reef Escarpment (as shown on the left side of pl. 18). Beyond, at the head of Rader Ridge (sec. 23, pl. 15, and sec. L—L', pl. 17) and on the ridge northeast of Guadalupe Canyon (sec. J—J', pl. 17), only small remnants of the member are preserved projecting as tongues into the Capitan limestone. They consist of white, platy limestone, containing crushed brachiopod shells.

HIGHEST BEDS OF BELL CANYON FORMATION

Some miles southeast of the Capitan limestone on the Reef Escarpment, well out in the area of the Delaware Basin, the limestones of the Lamar member are overlain directly by thinly laminated limestones and anhydrites that are the basal beds of the Castile formation. This relation of Lamar to Castile was observed also on the outcrops in the downfaulted area west of the Delaware Mountains, at the south edge of the area studied (pl. 3). It is reported also in wells drilled east of the outcrops, as in the Niehaus et al., Caldwell No. 1 well, 35 miles east-southeast of El Capitan (pl. 6).

Farther northwest, within several miles of the Reef Escarpment, the Lamar member is separated from the Castile formation by a small thickness of younger Bell Canyon beds. In the exposures in the Delaware Mountains southeast of United States Highway No. 62, these beds consist of 20 feet of very fine grained sandstone (secs. 34 and 38, pl. 6), whose petrographic character has already been noted (p. 54). The rock is thinly laminated, its bedding surfaces are flat and smooth, and it breaks out in thin, flat plates. The beds are well exposed a short distance southeast of the highway, on the north bank of a creek, half a mile northeast of bench mark 4729 (pl. 3), where their relations to the Lamar below and Castile above can be observed.

Northwest of the highway, and nearer the Reef Escarpment, the beds are thicker, and include some limestone. Between McKittrick and Big Canyon Draws, they are preserved as scattered outliers, which form light-colored knolls on the tops of the darker-colored hills of Lamar limestone. Some of these beds are less than a mile from the base of the Reef Escarpment. The best exposure is on the north side of Big Canyon Draw near the State line, and three-quarters of a mile northwest of the Gray Ranch (pl. 3). Here the Lamar is overlain by 20 feet of fine-grained sandstone, and this by 15 feet of light-gray or white slabby limestone, containing crushed brachiopod shells. This is topped by the basal laminated limestones of the Castile. In other exposures near the Reef Escarpment, the sandstones are thinner, and most of the beds above the Lamar are slabby limestone.

At the base of the Reef Escarpment itself, at McKittrick Canyon and elsewhere, the Lamar member is overlain by a small thickness of massive dolomitic Capitan limestone. This limestone is evidently equivalent to the sandstones and slabby limestones not far to the southeast, but the actual connection between them has been removed by erosion, so that the change cannot be traced from one outcrop to the other.

BELL CANYON FORMATION IN AERIAL PHOTOGRAPHS

In aerial photographs the Bell Canyon formation can be recognized as that belt of outcrop between the back slope of the cuesta of the Manzanita limestone member of the Cherry Canyon formation on the west, and the low, light-colored outcrops of the Castile formation on the east. The outcrops of the Bell Canyon formation form an eastward continuation of the cuesta topography already described as characterizing the upper part of the Cherry Canyon formation.

Cuestas are poorly developed in the lower part of the formation, although the photographs indicate the traces of numerous ledges that belong to the Hegler and Pinery limestone members. The first strong cuesta east of and above those of the Manzanita limestone member is formed by the Rader limestone member. Still farther east is a low but prominent cuesta formed by the flaggy limestone bed. It has a persistent development southeast and south of the area studied, and indicates that this limestone is a continuous and persistent unit. Still farther east is the high and prominent cuesta of the Lamar limestone member. It has a steep west-facing scarp, frayed by erosion into numerous promontories, outliers, and indentations. The sandstones overlying the Lamar can be recognized as far south as Delaware Creek but are indistinguishable beyond. The dark-colored back slope of this cuesta is bordered on the east by lighter-colored outcrops of the anhydrites of the Castile formation.

The Lamar limestone cuesta can be traced 30 miles or more south of the area studied, along the east slope of the Delaware Mountains, or nearly to Seven Heart Gap at the north edge of the Apache Mountains. However, about 20 miles south of the area studied, the ledges and cuestas of the underlying members merge into a nearly continuous succession of ledges, evidently a nearly solid limestone body. This limestone body continues southward to the Apache Mountains.

CAPITAN LIMESTONE

DEFINITION

The Capitan limestone was named by Richardson,³⁶ its type locality being on Guadalupe Peak, about a mile north of the summit here called El Capitan.³⁷ The exposures in the vicinity of the two peaks were first studied by Shumard,³⁸ who set off the white limestone of the formation as member 1 of his section (pl. 1). According to present usage,³⁹ the formation includes the thick-bedded or massive white limestones of reef facies and upper Guadalupe age, that crop out in the Guadalupe Mountains (pl. 7, A).

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³⁶Richardson, G. B., Report of a reconnaissance in trans-Pecos, Texas, north of the Texas and Pacific Railway: Texas Univ. Bull. 23, p. 41, 1904.

³⁷For a discussion of the geographic terminology see Lang, W. B., op. cit., pp. 839-844.

³⁸Shumard, G. G., Observations on the geology of the country between the Rio Pecos and Rio Grande, in New Mexico: St. Louis Acad. Sci. Trans., vol. 1, p. 280, 1858 [1860].

³⁹Lang, W. B., op. cit., p. 163.

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RELATIONS TO BELL CANYON FORMATION

Near the top of the Cherry Canyon formation is the Manzanita limestone member, whose outcrop extends across the Delaware Mountains and into the southern Guadalupe Mountains. Its orange-brown ledges and its intercalated seams of volcanic ash retain the same character over wide areas, and form an unmistakable horizon marker (pl. 6).

The sequence above the Manzanita member in the Delaware Mountains, however, is profoundly different from that in the Guadalupe Mountains (as may be seen by comparing secs. 34 and 14, pl. 6). In the Delaware Mountains, as along United States Highway No. 62, the member is overlain by several hundred feet of sandstones and thin limestones, forming the Bell Canyon formation, and these in turn by the anhydrites of the Castile formation. The Bell Canyon formation crops out northeast of, and down the dip from the Manzanita member in low hills (such as those shown in the center and right foreground of pl. 4, A). In the southeast part of the Guadalupe Mountains, the member is overlain by a few hundred feet of thin-bedded limestones, the Hegler and Pinery members, and these by several thousand feet of massive Capitan limestone. Here, the Manzanita member forms ledges that fringe the bases of lofty cliffs.

Looking northwest from the low hills of the Delaware Mountains near United States Highway No. 62, one can see a steep escarpment that rises in jagged spurs and irregular cliffs 2,000 feet or more above the observer (forming the background of pl. 4, A). This is the Reef Escarpment, which forms the southeastern edge of the Guadalupe Mountains and is composed largely of Capitan limestone. Behind it, the Capitan crops out on rugged canyon walls (some of which are shown on pl. 18). Southeast of it, in the Delaware Mountains, no remnants of the Capitan are present, if indeed they ever existed.

The Lamar limestone member, near the top of the Bell Canyon formation in the Delaware Mountains can be traced northwestward along a line of cuestas to the base of the Reef Escarpment at the mouth of McKittrick Canyon. Viewed from a distance (as shown on pl. 4, A), the member seems to extend beneath the Capitan limestone at the canyon, for the Capitan rises 1,500 feet above the cuestas to the flat benches of Carlsbad limestone which form the rim of the escarpment.

That this is not the true relation is at once evident, however, when one climbs a little distance up the spurs on either side of the canyon mouth (pl. 16, A). Viewed now in cross section, the Capitan limestone is seen to be made up of thick beds which dip to the southeast at an angle of 20°, or at about the same angle as the slope of the escarpment itself. The Lamar member, forming benches of well-bedded limestone at the mouth of the canyon, changes northwestward into thick beds, indistinguishable from the rest of the Capitan, which can be traced up the surface of the escarpment until they lie directly beneath the ledges of Carlsbad limestone on its rim. The greater part of the Capitan limestone which lies beneath these beds is thus clearly older than the Lamar member. These relations have been described by Lloyd⁴⁰ and other authors. They are well illustrated in a diagram by Cartwright.⁴¹

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⁴⁰Lloyd, E. R., Capitan limestone and associated formations of New Mexico and Texas: Am. Assoc. Petroleum Geologists Bull., vol. 13, p. 649, 1929.

⁴¹Cartwright, L. D., Transverse section of Permian basin: Am. Assoc. Petroleum Geologists Bull., vol. 14, fig. 3, p. 978, 1930.

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The structure of the beds shown in the panorama of plate 16, A, is given on the right-hand end of section E—E', plate 17. For a more general view, which shows that the same relation exists on nearby spurs of the escarpment, see the aerial photograph, plate 18.

PLATE 16.—PANORAMIC VIEWS OF McKITTRICK CANYON. For locations, see plate 2. Shows structural features of Capitan limestone and related formations. Qoa, Older alluvial deposits; Pcb, Carlsbad limestone; Pcb (ss), basal sandstone member of Carlsbad limestone; Pc, Capitan limestone; Pc (m), massive beds of Capitan limestone; Pdb, Bell Canyon formation (ss, sandstone bed, 8, Lamar limestone member, 7, flaggy limestone bed); Pg, Goat Seep limestone. A, North wall of McKittrick Canyon from peak on south side at entrance. B, Northeast wall of North McKittrick Canyon from peak on southwest side 1 mile north of Pratt Lodge.

Beneath the Lamar member at the mouth of McKittrick Canyon, several hundred feet of sandstones and some thin, interbedded limestones are exposed (sec. 28, pl. 6). These limestones also crop out here and there along the edge of the escarpment to the southwest. Several miles southwest of McKittrick Canyon, near the head of Rader Ridge, where the beds stand higher and erosion has cut deeper, the sandstones are seen to be underlain by the Rader limestone member (sec. 23, pl. 6). Here, on the point of each spur is a slope carved from the sandstone, but in the ravines between, cut back a little farther into the escarpment, there are no sandstone beds. Instead, limestone tongues appear between the sandstone on the sides of the spurs, and thicken into a continuous succession of massive Capitan limestone along the bed of each ravine. The Rader limestone member itself can be seen to merge with the Capitan limestone a mile or so southwest of Rader Ridge.

The mountain spurs above Rader Ridge can be seen below point 8078 at the right-hand end of the panorama, plate 4, B. Note the manner in which the Capitan limestone ledges dip to the right, down the spurs, to be succeeded at the ends by slopes cut on sandstone. The structure of the spurs is shown on section G—G' and in greater detail on section L—L', of plate 17. The merging of the Rader member with the Capitan can be seen on plate 4, B. Note how, when traced to the left from Smith Canyon, the slope between it and the Capitan disappears, and in the next canyon beyond, the member is the lowest of a continuous series of ledges.

The intergradation of Bell Canyon beds and Capitan limestone, between the Rader and Lamar members is shown also by the stratigraphic sections on plate 6 (between numbers 21 and 32), and in greater detail on plate 15 (right-hand half). The distance in which the change takes place is not as great as that which separates the sections, for the sections show only the sequences on the points of the spurs, and not the very different sequences exposed in the nearby ravines.

At the point where the Rader member merges with the Capitan limestone southwest of Rader Ridge, it is underlain by two other limestone beds belonging to the Bell Canyon formation, the Pinery and Hegler members. These limestones stand in ledges at the base of the escarpment (pl. 4, B). They can be traced southwestward across Pine Spring and Guadalupe Canyons to El Capitan, where they form the pedestal on which the great cliff of Capitan limestone rests. This cliff extends northwestward from El Capitan along the west side of the mountains.

Viewed from below near Bone Canyon (pl. 12, A), the ledges of the Pinery and Hegler members can be traced northwestward along the bases of the cliffs, but near the head of Shirttail Canyon (below summit 8356) they are absent, and the Capitan cliff stands directly on ledges of the Goat Seep limestone. The two members do not pinch out northwestward; instead, as each of their thin dark-colored beds is traced from El Capitan, it becomes lighter colored and thicker, and extends upward along the cliff, merging with the massive Capitan limestone. In this manner, all the Pinery member disappears into Capitan below Guadalupe Peak, and all the Hegler member at the head of Shirttail Canyon. The northwestward thickening and increase in dip of each bed is so great that the stratum equivalent to the top of the Pinery member rises to the summit of the cliff on the north slope of Guadalupe Peak. The Capitan limestone as developed farther northwest is therefore wholly of Pinery and Hegler age.

The structure of the panorama, plate 12, A, is shown on section K—K', plate 17. The change from the Pinery and Hegler members into the Capitan limestone is also shown by the stratigraphic sections on plate 6 (between numbers 9 and 18). Similar relations, worked out in greater detail in Pine Spring Canyon to the northeast, are shown on the left-hand half of plate 15.

These observations show that the Capitan limestone consists, at different places, of beds equivalent to various parts of the Bell Canyon formation (pl. 7, A). Toward the northwest, it is chiefly of Hegler and Pinery age, but farther southeast there are younger, similar limestones of Rader to Lamar age. Only several hundred feet of the highest Capitan and Carlsbad limestones, overlying the Lamar equivalent in McKittrick Canyon, cannot be traced directly into beds of the Bell Canyon formation, because their southeastward extensions have been eroded away. As already indicated (pp. 58-59), these several hundred feet are probably equivalent to the slabby limestones and sandstones above the Lamar member southeast of the Reef Escarpment.

The limestone members of the Bell Canyon formation change into the Capitan limestone by an increase in thickness of each layer, and by a change in color and texture. As the change takes place, the intervening sandstone beds disappear, partly by interfingering with numerous limestone tongues and partly by a change into sandy limestone and thence into pure limestone.

OUTCROP

The Capitan limestone extends northwestward into the Guadalupe Mountains for about 4 miles northwest of its edge along the Reef Escarpment. Farther northwest, its place is taken by thin-bedded limestones of the Carlsbad. Toward the northeast, along the trend of the Reef Escarpment, its extent is much greater. Its outcrop extends for many miles into New Mexico, and it has been recognized in wells farther northeastward. To the southwest, along the same trend, it crops out in the Patterson Hills.

The northwestern and southeastern limits of the Capitan within the area studied are shown by lines B and E on figure 10, and its outcrops are shown on the geologic map, plate 3. The probable regional extent of the belt of Capitan limestone is suggested on figure 14, B. A view of the outcrops of the Patterson Hills can be seen on the left half of the panorama of plate 5, A. Note the contrast in height between the outcrops here and those in the mountains on the right half of the panorama. The structural relations between the two areas are shown on sections B—B' and C—C' accompanying plate 3.

Along the canyons and ridges of the Guadalupe Mountains, the formation crops out as lines of irregular cliffs or as steep, rocky slopes which support a growth of forest in protected places (pl. 18). Along the north side of Pine Spring Canyon, erosion along joints has carved the rock into closely spaced, steep-sided pinnacles; elsewhere it weathers to rounded, bouldery masses. On the west side of the mountains, near Guadalupe Peak and El Capitan, the formation stands in a cliff, 1,000 feet or more high. The form of the cliff is controlled by joints, many of which can be seen traversing it from top to base. Its steepness has been maintained by undercutting of the weaker beds below.

THICKNESS

Within the area studied, the Capitan limestone has a variable thickness, nowhere less than 1,000 feet and nowhere greater than 2,000 feet. On the west face of Guadalupe Peak, where it is underlain by the Hegler member and overlain by the Carlsbad limestone, it is about 1,350 feet thick (sec. 14, pl. 6). At several places in McKittrick Canyon (as in sections E—E' and F—F', pl. 17) there are exposures 1,500 to 2,000 feet high.

The Capitan limestone is, however, a facies that extends irregularly through the upper part of the Guadalupe series, and its top and base are therefore not of the same age at all places. Within the area studied it is everywhere underlain by some beds of the Bell Canyon formation and overlain by some beds of the Carlsbad limestone, the first tending to replace it to the southeast, and the second to the northwest (pl. 7, A). At no place within the area does the Capitan limestone facies extend continuously from the base to the top of the upper part of the Guadalupe series.

Outside the area studied, the Capitan is reported to have a much greater thickness. In the Getty Oil Co., Dooley No. 7 well, in the Getty oil field east of Carlsbad, N. Mex. (for location, see fig. 2), the interval from the base of the Ochoa series downward to the top of the bentonites of the Manzanita member of the Cherry Canyon formation is more than 2,700 feet.⁴² Most of this interval is occupied by a single mass of white limestone, probably of Capitan facies, although some thinner-bedded, or darker, or sandy limestones. are present at the top and base. A similar thickness is present in the Ohio Oil Co., Tracey No. 1 well, drilled a few miles west of the town of Carlsbad.⁴³ It is likely that in the neighborhood of these wells there are more beds in the upper part of the Guadalupe series belonging to the Capitan facies than in a single section at any point on the outcrop.

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⁴²King, P. B., The Permian of west Texas and southeastern New Mexico: Am. Assoc. Petroleum Geologists Bull., vol. 26, fig. 7, p. 585, 1942.

⁴³Bybee, H. B., and others, Detailed cross section from Yates area, Pecos County, Texas, into southeastern New Mexico: Am. Assoc. Petroleum Geologists Bull., vol. 15, pl. 1, p. 1088, 1931.

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LITHOLOGIC FEATURES

The Capitan limestone consists in part of compact, light-gray, cream-colored, or white calcitic limestone, which breaks under the hammer into splinters and conchoidal chips. Some beds contain numerous, beautifully preserved fossil shells. At one locality Mr. H. C. Fountain broke from the limestone several gastropod shells on which the original color markings are still preserved. The calcitic limestones crop out in bouldery masses or smooth-surfaced ledges, and in places stand in smooth, light-gray cliffs.

Associated with the calcitic limestones are dolomitic limestones. They are gray or buff, finely crystalline and contain occasional tiny cavities, which suggest that the process of dolomitization has changed the volume of the rock. Scattered crystals of calcite are embedded here and there, and also irregular bodies of crystalline calcite as much as 6 inches across. The dolomitic limestones contain fossils similar to those in the calcitic limestones, but the shells have been so greatly recrystallized that they remain only as "ghosts". The dolomitic rocks weather to dirty gray, pitted or jagged surfaces, which in many places show a rude exfoliation.

The following analyses of Capitan limestone were made:

Analyses, in percent, of Capitan limestone
[Analyses by K. J. Murata; notes on insoluble residues by Charles Milton]

Both the calcitic limestones and dolomitic limestones are irregularly distributed through the formation. The dolomitic type is somewhat more abundant than the calcitic; it is found at all places, whereas the calcitic limestones disappear in places. On Guadalupe Peak and near the mouth of McKittrick Canyon, the youngest beds of the Capitan, of Lamar or younger age, are mostly calcitic limestone, and are underlain by dolomitic limestone. In the older parts of the formation, the two types are interbedded. Thus, on the trail up the west wall of South McKittrick Canyon near the Grisham Hunter Lodge, there are two 400-foot members of calcitic limestone, separated by a 700-foot member of dolomitic limestone. Here, the Hegler limestone member lies below and the Carlsbad limestone above. Near the Grisham-Hunter Camp, 3 miles to the southwest, richly fossiliferous, calcitic limestones lie at the base of the Capitan and are probably of Hegler age. They are overlain by dolomitic limestones.

In the main mass of the Capitan limestone, none of the beds are sandy, and there is no interbedded sandstone. Along its southeastern edge, a few streaks of sandstone extend back for about half a mile into the limestone from the thicker beds of sandstone of the Bell Canyon formation.

A rich and abundant fauna has been collected from some of the nondolomitized parts of the Capitan,⁴⁴ the most abundant groups being brachiopods, gastropods, pelecypods, nautiloids, and trilobites. Rather extensive collecting by H. C. Fountain and me has convinced us that these fossils occur only in relatively thin, lenticular strata, not differing greatly in lithologic character from the inclosing rock. According to our observations, the greater mass of the formation contains little else than the abundant remains of sponges, a few crinoid stems, and some calcareous masses that may be of algal origin. The dolomitic limestones, which were probably altered from an original calcitic limestone, seem also to contain both the brachiopod-gastropod, etc., assemblage and the sponge-crinoid, etc., assemblage.

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⁴⁴Girty, G. H., The Guadalupian fauna: U. S. Geol. Survey Prof. Paper 58, pp. 15-17, 1908.

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BEDDING

The Capitan limestone consists of beds 15 to more than 100 feet thick, separated by indistinct bedding planes, and with very few interbedded, thinner layers. The bedding planes are well exposed in the cliffs on the west side of the mountains (pl. 12, A), but on the gentler slopes to the northeast they are not as clearly evident (pl. 16).

In the McKittrick Canyon region there are some prominent, quite massive members 100 to 300 feet thick. One of them, approximately of Lamar age, lies just under the Carlsbad limestone along the top of the escarpment near the mouth of the Canyon. Farther northwest are several older members, one of which rises in lines of cliffs along the north and south branches of the canyon. Because it lies above the inliers of the Pinery member in the canyon, and dips downstream beneath the Lamar member, it is approximately of Rader age. Each massive bed grades northwestward within a short distance into the thin-bedded Carlsbad limestone and tends to change southeastward into more steeply inclined, thick-bedded limestone.

The massive member that is approximately of Lamar age can be seen forming a cliff just below point 7058 on the panorama, plate 16, A. Cliffs formed by the member that is approximately of Rader age appear on the farther side of McKittrick Canyon in the aerial view, plate 18. The manner in which the massive members join the Carlsbad limestone farther northwest, in North McKittrick Canyon, is suggested by the panorama, plate 16, B. The massive members are separately indicated on the geologic map, plate 3, and on sections E—E' and F—F' plate 17.

Both on the Reef Escarpment and within the mountains, the bedding planes in the Capitan limestone dip southeastward at angles of 10° to 30° (as shown on the sections of pl. 17). To a large degree, this dip is not shared by the beds beneath. Thus, the summit of El Capitan consists of a number of southeast-sloping surfaces cut on the inclined bedding planes of the limestone, and other inclined beds can be seen on the cliffs below. However, the beds in the lower part of the cliff are less inclined, and the dark limestones of the Pinery and Hegler at the base are nearly horizontal. The underlying bedded limestones at some of the inliers within the mountains have dips of more than 10° (as in South McKittrick Canyon, shown in sec. F—F', pl. 17). Because these beds were deposited near the edge of the Capitan limestone mass, their inclination may have been original.

The inclination of the bedding was caused by the greater amount of deposition in the Capitan area than in the area to the southeast, where the Bell Canyon formation was deposited. Thus, as each bed of the Bell Canyon formation changes into Capitan facies, it swells to several times its previous thickness, and acquires a dip to the southeast, partly from the slope of its own surface and partly from the slope of the overthickened beds on which it was deposited. The face of the Reef Escarpment on the southeast side of the Capitan mass is approximately the surface of the last of the inclined beds deposited, somewhat modified by erosion (fig. 20, B).

The dips were probably accentuated by slight tilting of the rocks at various times after Capitan deposition. The much later Cenozoic uplift of the mountains imparted to all the Permian rocks an east-northeast component of dip. There seems to have been also a pre-Cenozoic southeastward tilting, perhaps of later Permian, post-Guadalupe age, as there is a slight southeastward dip of the well-bedded limestones associated with the Capitan. Thus, the Hegler member at inliers within the mountains lies 1,000 feet higher than on the points of Rader Ridge, 4 miles to the southeast (compare secs. I—I' and G—G', pl. 17), and the Carlsbad limestone on the mountain summits dips southeastward at angles of 3° to 5° (as in secs. E—E' and H—H', pl. 17). The tilted Carlsbad beds are truncated by the upland surface of the mountains, which is probably a peneplain formed before the Cenozoic uplift of the range. At least a part of the dip of the Carlsbad is therefore pre-Cenozoic.

According to Johnson⁴⁵ the Capitan limestone in outcrops near Carlsbad and Carlsbad Cavern can be divided into 1, a reef face, or rough slope along the sea side of the reef, composed of massive, inclined beds of dolomitic limestone; 2, a reef crest, forming a low, narrow ridge at the top of the reef face and rising slightly higher than the reef platform behind; and 3, a reef flat a few hundred to 1,800 feet wide, composed of poorly bedded dolomitic limestones. The reef flat grades in turn into lagoonal deposits of the Carlsbad limestone. No details based on specific localities are given. While these subdivisions correspond in a general way with features observed during the present work, one wonders whether the observations are wholly objective, or are unduly influenced by comparisons with modern reef deposits, some of which may not be justified.

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⁴⁵Johnson, J. H., Permian lime-secreting algae from the Guadalupe Mountains, New Mexico: Geol. Soc. America Bull., vol. 53, pp. 216-217, 1942.

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BRECCIA PHASE OF CAPITAN LIMESTONE

At three places in the mountains the normal Capitan limestone is replaced by a dolomitic, sandy breccia. Exposures are found in South McKittrick Canyon near the Grisham-Hunter Lodge, in Pine Spring Canyon near Devils Hall, and on the nearly inaccessible cliffs on the west side of the mountains north of Guadalupe Peak. At each place the breccia lies on the Hegler limestone member, apparently with unconformable contact, and it seems to have been deposited in deep pockets and on knobs and sharp pinnacles of the underlying limestone. So far as the Capitan beds above the breccia can be traced, they seem to be equivalent to the Pinery member. The breccia somewhat resembles caliche-cemented talus of Quaternary age which in places lies on the Capitan. It is actually distinct and is a part of the Capitan and of Permian age.

The breccia consists of cavernous, sandy, light-buff or pink dolomitic limestone, of tufalike appearance, with irregularly developed, rude bedding. It stands in irregular cliffs and crags, with numerous small caves, and is less jointed than the limestones above and below. Embedded in the sandy dolomitic matrix are tumbled and disordered limestone blocks from six inches to several feet in diameter. Near the Grisham-Hunter Lodge the matrix contains imprints of fossils. The breccia contains lenses of fine-grained, well-bedded, calcareous sandstone, and toward the top it is interbedded with dolomitic limestone. It apparently grades both upward and laterally into the more normal Capitan deposits. The greatest thickness observed is 380 feet.

For general stratigraphic relations of the breccia, see plate 7, A. Its structure in Pine Spring Canyon is shown on section I—I' and on the west face of the mountains on section K—K' of plate 17. A stratigraphic section of the breccia in Pine Spring Canyon is given on plate 15 (No. 58), and on the west side of the mountains on plate 6 (Nos. 12 and 13). Note the manner in which it overlies the Hegler limestone member, and is apparently traceable beneath the Pinery limestone member in the sections to the southeast.

CARLSBAD LIMESTONE

DEFINITION

The name Carlsbad limestone was given by members of the Geological Survey⁴⁶ in 1926 to beds exposed in the vicinity of Carlsbad, N. Mex. Thin-bedded limestones of the Carlsbad facies had been described previously by Tarr,⁴⁷ Richardson,⁴⁸ and Baker.⁴⁹ The rocks at the type locality are thin-bedded limestones of late Capitan age and are of a facies that is extensively developed in the Guadalupe Mountains.

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⁴⁶Darton, N. H., and Reeside, J. B., Jr., Guadalupe group: Geol. Soc. America Bull., vol. 37, p. 419, 1926. Meinzer, O. E., Renick, B. C., and Bryan, Kirk, Geology of number 3 reservoir site of the Carlsbad irrigation project, New Mexico: U. S. Geol. Survey Water-Supply Paper 580, p. 12, 1926.

⁴⁷Tarr, R. S., Reconnaissance of the Guadalupe Mountains: Texas Geol. Survey Bull. 3, pp. 29-30, 1892.

⁴⁸Richardson, G. B., Stratigraphy of the upper Carboniferous in west Texas and southeast New Mexico: Am. Jour. Sci., 4th ser., vol. 22, p. 336, 1910.

⁴⁹Baker, C. L., contributions to the stratigraphy of eastern New Mexico: Am. Jour. Sci., 4th ser., vol. 49, p. 115, 1920.

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The name Carlsbad has been used by some geologists for a tongue of the thin-bedded limestone which in New Mexico projects northward into red beds and evaporite deposits,⁵⁰ now called the Azotea tongue, and by others. for both thin-bedded and massive limestones which correspond to the upper part of the Capitan limestone at its type locality.⁵¹ It seems more proper, however, to apply the name to all the thin-bedded limestones equivalent to the massive Capitan limestone,⁵² and this usage is followed in the present report.

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⁵⁰Fiedler, A. G., and Nye, S. S., Geology and ground-water resources of the Roswell artesian basin, New Mexico: U. S. Geol. Survey Water-Supply Paper 639, pp. 53-55, 1933.

⁵¹Darton, N. H., "Red Beds" and associated formations in New Mexico: U. S. Geol. Survey Bull. 794, p. 224, 1928. Blanchard, W. G., and Davis, M. J., Permian stratigraphy and structure of parts of southeastern New Mexico and southwestern Texas: Am. Assoc. Petroleum Geologists Bull., vol. 13, pp. 983-985, 1929.

⁵²Crandall, K. H., Permian stratigraphy of southeastern New Mexico and adjacent parts of western Texas: Am. Assoc. Petroleum Geologist Bull., vol. 13, p. 938, 1929. Lang, W. B., The Permian formations of the Pecos valley of New Mexico and Texas: Am. Assoc. Petroleum Geologists Bull., vol. 21, p. 868, 1937.

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RELATION TO CAPITAN LIMESTONE

The relations between the Carlsbad limestone and the Capitan limestone are best exposed on the northeast wall of North McKittrick Canyon, which cuts transversely through the upper part of the Capitan limestone mass (pl. 3).

Toward the southeast, at the mouth of McKittrick Canyon, the rim of the northeast wall is formed by a small thickness of thin-bedded, flat-lying Carlsbad limestone, slightly younger in age than the Lamar limestone member of the Bell Canyon formation (pl. 16, A). The flat-lying Carlsbad limestone rests on southeastward-sloping, thick-bedded or massive layers of Capitan limestone. At first view, the difference in dip between the two formations is so striking that they appear to be separated by an unconformity. However, when the Capitan layers are traced up the canyon wall to the northwest, they lose their inclination and change within a short distance into flat-lying, thin-bedded limestones similar to but older than those which form the rim at the mouth of the canyon. These limestones continue northwestward into the mountains, either in a horizontal position or with a low dip to the southeast.

As each bed of the Capitan is traced to the northwest along the wall of North McKittrick Canyon, it changes in this manner into Carlsbad limestone (pl. 16, B). Finally, at the head of North McKittrick Canyon, at the pass which leads down into Dog Canyon near El Paso Gap Post Office (pl. 3), the thin-bedded Carlsbad limestone and its basal sandstone member rest directly on the Goat Seep limestone of pre-Capitan age (pl. 14, A). The ledges of white, thin-bedded limestone that form the walls of Dog and West Dog Canyons beyond contrast greatly with the ragged cliffs of massive or thick-bedded limestone of the same age that form the walls of McKittrick Canyon and its branches a few miles to the southeast.

The two panoramas in McKittrick Canyon, plate 16, A, and B, give a nearly complete cross section through the Capitan and Carlsbad limestones. They join each other at their ends, so that point 7044 on the rim of the canyon appears in both views. In addition, the relations farther northwest are shown on plate 14, A. Note that point 7378 near the head of North McKittrick Canyon, shown at the left end of plate 16, B, appears also in the right-hand part of plate 14, A. The contrast in the appearance of the mountain slopes to the northwest with those to the southeast, both carved from rocks of the same age, can be seen by comparing plate 14, A with plate 16, B.

The structure of the beds shown in the three panoramas is assembled on section E—E', plate 17. On this plate, note the similar transition northwestward from Capitan into Carlsbad limestone shown on sections F—F', H—H', and I—I'. The transition from Capitan into Carlsbad is not represented on section K—K', plate 17, or on the stratigraphic sections of plate 6 because on the west side of the mountains, where the sections were measured, the beds of upper Guadalupe age have been eroded away in the critical area at the head of Pine Spring Canyon between Bush Mountain and Bartlett Peak.

As shown on the walls of North McKittrick Canyon, the southeastern edge of the oldest beds of Carlsbad facies lies northwest of the youngest beds of Carlsbad facies. (The southeast edge of the oldest beds is shown as line B, fig. 10.) The southeastward advance of the Carlsbad limestone, however, does not take place bed by bed. Instead, there is a tendency for groups of beds up to several hundred feet in thickness to change southeastward into the Capitan at the same place. In section E—E' of plate 17, which gives the most complete section through the transition zone, there are 7 such groups of beds. Similar groups of beds, which are possibly equivalent to some of these, are shown on the other sections of plate 17.

THICKNESS

The Carlsbad limestone on the walls of North McKittrick Canyon dips southeastward at angles of a few degrees. Each thin-bedded layer which comes out of the Capitan mass, when traced northwestward is cut off in a few miles by erosion, so that the upland surface of the mountains bevels the gently dipping beds (sec. E—E', pl. 17). Here and elsewhere in the southern Guadalupe Mountains this surface, which is probably an uplifted peneplain of post-Permian and pre-Cretaceous age, cuts off the beds in such a manner that no complete section of the Carlsbad limestone exists. Where the lower part of the formation is exposed, its top is eroded, and where its top is exposed, most of the lower part has changed into rocks of Capitan facies (pl. 7, A).

The greatest thickness measured in the area, 787 feet, is found on the slopes of Lost Peak between Dog Canyon and West Dog Canyon (sec. 3, pl. 6), where the formation rests on the Goat Seep limestone. In the upper course of North McKittrick Canyon as much as 1,000 feet of Carlsbad limestone appears to be present above the Goat Seep limestone. According to Lang⁵³ and others familiar with the region in New Mexico to the north the total thickness of the Carlsbad and the associated Chalk Bluff formation of that area is about 1,000 feet. This amount is about the same as the maximum thickness observed in the area of this report.

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⁵³Lang, W. B., op. cit., p. 820, and personal communication, 1937.

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LIMESTONE OF SOUTHEASTERN EXPOSURES

Where the Carlsbad overlies the Capitan in the southeast part of the area, it consists of thin-bedded, white or gray dolomitic limestone. The straight, smooth bedding planes are a few inches to a foot apart, and some beds are thinly laminated. Many of the layers are crowded with pisolites. These pisolites have been considered by some paleontologists to be of algal origin. They have been described and figured by Ruedemann,⁵⁴ Ackers and others,⁵⁵ Lang,⁵⁶ and Johnson.⁵⁷ They are concentric, subspherical, calcareous bodies ranging in size from that of a pea to that of a ball more than an inch across (pl. 19, A). The pisolites are discussed further on pp. 79-80. Other beds are crowded with fusulinids which are commonly oriented in a northwestward direction, perhaps by waves or currents (fig. 10). The parallel orientation was noted by Girty⁵⁸ on the summit of Guadalupe Peak. The fusulinids and pisolites are found in the same exposures of the formation, but commonly occupy distinct beds. Some of the interbedded layers are barren.

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⁵⁴Ruedemann, Rudolf, Coralline algae, Guadalupe Mountains: Am. Assoc. Petroleum Geologists Bull., vol. 13, pp. 1079-1080, 1929.

⁵⁵Ackers, A. L., and others, Hendrick field, Winkler County, Texas: Am. Assoc. Petroleum Geologists Bull., vol. 14, pp. 932 (figs. 9, 10), 940, 1930.

⁵⁶Lang, W. B., op. cit., p. 869.

⁵⁷Johnson, J. H., Permian lime-secreting algae from the Guadalupe Mountains, New Mexico: Geol. Soc. America Bull., vol. 53, pl. 6, p. 225, 1942.

⁵⁸Girty, G. H., op. cit., p. 15.

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In many of the dolomitic limestones, cross sections of other fossils can be seen, but the rock is so hard and brittle that it generally breaks across them. In occasional calcareous beds a considerable fauna, somewhat resembling that of the Capitan, has been collected. This fauna includes several species of brachiopods; the gastropods outnumber all other groups. Many of the gastropods and fusulinids are coated with a concentric, calcareous growth, possibly made by the same encrusting agent that formed the pisolites. A similar description of these rocks as exposed in New Mexico has been given by Johnson.⁵⁹

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⁵⁹Johnson, J. H., op. cit., p. 217.

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LIMESTONE OF NORTHWESTERN EXPOSURES

In the northwestern part of the area, where the Carlsbad lies directly on beds older than the Capitan, its dolomitic limestones are more compact, thinner-bedded, and with a greater variety of colors than in the southeastern exposures. Fusulinids, pisolites, and all traces of other fossils are absent. The change from one type of rock to the other takes place along a fairly definite line, which passes a short distance north of Lost Peak (line A, fig. 10).

About 460 feet of such beds overlie the Goat Seep limestone a mile north of Lost Peak (sec. 2, pl. 6). They include prominent ledges, consisting of compact, dolomitic limestones, which are separated by slabby, brown, pink, or reddish dolomitic limestone, and some platy sandstone. Some of the slabby limestones are full of round holes up to an inch in diameter, possibly caused by solution of soluble minerals. A layer of brick-red, sandy shale lies 300 feet above the base. The same layer is also recognizable on many of the hillsides between Dog and West Dog Canyons.

The following analyses of limestone from the Carlsbad of the southeastern and northwestern exposures were made:

Analyses, in percent, of Carlsbad limestone
[Analyses by K. J. Murata; notes on insoluble residues by Charles Milton]

SANDSTONE OF SOUTHEASTERN EXPOSURES

Interbedded with the limestones of both the southeastern and northwestern exposures are many sandstone beds. They are thickest and most prominent toward the northwest.

Along the southeast edge of the Guadalupe Mountains, the sandstones form occasional beds up to a foot in thickness, which are difficult to trace because of the heavy cover of forest and brush. One member in the upper part, more prominent than the rest, caps the ridges between North and South McKittrick Canyons, and those near the headwaters of Dog Canyon. It has a thickness of about 50 feet, and contains relatively few, thin, interbedded limestones. This member and a few other beds are separately mapped on plate 3. It may be equivalent to the Yates sandstone,⁶⁰ which has been traced widely in subsurface work in the area east of the Guadalupe Mountains.

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⁶⁰Gester, G. C., and Hawley, H. J., Yates field, Pecos county, Texas, Structure of typical American oil fields, vol. 2, pp. 480-499. Tulsa. 1929.

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The sandstones of the southeastern exposures are brown, fine-grained, in part calcareous, and form slabby beds or rounded ledges. Many of them weather reddish brown, thus giving the false impression that they are red-bed layers. Three specimens of the sandstone, from the region between Pine Spring Canyon and the Grisham-Hunter Cabin, were studied under the microscope by Ward Smith. The maximum grain size varies in the different specimens from 0.15 to 0.50 millimeters in diameter; in the coarsest-grained specimens the spaces between the large grains are filled by finer detrital grains and clay. The principal mineral is quartz. Some of the quartz in one of the specimens shows lines of inclusions and is clearly of igneous origin. Some other grains are microcrystalline. There are also grains of feldspar, zircon, tourmaline, and chlorite. At one locality, a sandstone containing small chert pebbles was noted, but no material as coarse as this was found in other places.

SANDSTONE OF NORTHWESTERN EXPOSURES

In the northwestern part of the area, the sandstone beds in the Carlsbad limestone are thicker and more numerous, and form persistent members 5 to more than 50 feet thick. At Lost Peak the 787 feet of section contains 9 such members; the thickest is at the base (sec. 3, pl. 6).

This basal sandstone member, which lies on the Goat Seep limestone, appears to be a widely traceable horizon. On the escarpments on the east sides of Dog and West Dog Canyons, it is buff, fine-grained, and somewhat calcareous, with some cross-bedding, and occasional limonite nodules. It crops out in prominent, brown-colored ledges as much as 10 feet thick. Southward on the two escarpments, and on Cutoff Mountain, the sandstone becomes more thinly bedded, and is of buff or reddish color. In this vicinity it contains much interbedded, platy, white or pink dolomite. A specimen of sandstone from the member, collected near Cutoff Mountain and studied under the microscope by Ward Smith, consists of quartz and feldspar grains, with a few grains of zircon and clastic calcite, all loosely packed in a calcite matrix. The maximum diameter of the grains is 0.2 millimeter.

When traced toward the southeast along several lines of outcrop the basal sandstone member of the Carlsbad limestone appears to extend either into the basal beds of the Capitan limestone or into beds just beneath it. One line of outcrop is along the west edge of the mountains. Here the thinned equivalent of the sandstone seems to be traceable, near Bush Mountain, into the sandstone break that separates the Goat Seep and Capitan limestones (as suggested by correlation lines between secs. 4 and 11, pl. 6). Another line of outcrop extends from Dog Canyon, near El Paso Gap Post Office, into North McKittrick Canyon. Here also the sandstone thins southeastward, and its equivalent appears to lie near the boundary between the Goat Seep and Capitan (sec. E—E', pl. 17, and pl. 3).

PLATE 18.—AERIAL VIEW OF GUADALUPE MOUNTAINS, LOOKING SOUTHWESTARD FROM McKITTRICK CANYON TOWARD GUADALUPE PEAK. Reef escarpment to left, Texas-New Mexico line near right-hand margin. Pdb, Bell Canyon formation, including Lamar limestone member (8); Pc, Capitan limestone, including massive beds (m); Pcb, Carlsbad limestone. Photograph by Edgar Tobin Aerial Surveys.

PLATE 19.—SOME FOSSILS FROM GUADALUPE MOUNTAINS. All figures are natural size. A, Pisolites, probably in part of algal origin, from Carlsbad limestone. B, Fusulinids (Parafusulina sp.) in sandstone of Brushy Canyon formation, showing tendency toward parallel orientation.

The basal sandstone member of the Carlsbad limestone also is traceable northward along the east side of Dog Canyon into New Mexico. It was studied from distant views, such as that shown on plate 14, A. In this direction the bed seems to rise toward the top of the escarpment and finally to spread over the mountain crest in the vicinity of Queen Mesa (for location, see fig. 2) It therefore may be the same as the Queen Sandstone member of the Chalk Bluff formation, which was described in that area by Blanchard and Davis⁶¹ and by Lang.⁶²

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⁶¹Blanchard, W. G., and Davis, M. J., Permian stratigraphy and structure of parts of southeastern New Mexico and southwestern Texas: Am. Assoc. Petroleum Geologists Bull., vol. 13, p. 972, 1929.

⁶²Lang, W. B., op. cit., p. 859.

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If the correlations just outlined are correct, the Queen sandstone is of early upper Guadalupe age, and is equivalent to beds at the base of the Carlsbad and Capitan limestones. In some earlier reports it has been correlated with much higher parts of the Capitan limestone. Thus, Blanchard and Davis⁶³ state that they have traced the Queen southwestward to within a mile northeast of Guadalupe Peak, and that it lies stratigraphically within 300 feet of the top beds of the peak. According to observations made during the present work, there are many thin sandstone beds at different levels in the Carlsbad limestone near the peak, but no continuous traceable layer. These sandstone beds are here interpreted as lying much higher stratigraphically than the Queen and associated sandstones farther north.

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⁶³Blanchard, W. G., and Davis, M. J., idem, p. 972.

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NORTHERN GUADALUPE MOUNTAINS

In the northern Guadalupe Mountains, which lie in New Mexico, outside the area studied, the Carlsbad limestone interfingers with rocks of another facies, composed of anhydrites and other evaporites, thin dolomites, red beds, and sandstones. These rocks form the Chalk Bluff formation of Lang,⁶⁴ and are of the same age and facies as the Whitehorse group, as that term is used by geologists engaged in subsurface work east of the Guadalupe Mountains.⁶⁵ The beds in the northern Guadalupe Mountains were laid down farther away from the Delaware Basin, and farther within the shelf area, than any beds within the area of this report.

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⁶⁴Lang, W. B., The Permian formations of the Pecos Valley of New Mexico and Texas: Am. Assoc. Petroleum Geologists Bull., vol. 21, pp. 855-857, 859-863, 1937.

⁶⁵De Ford, R. K., and Lloyd, E. R., Editorial introduction [to west Texas Permian symposium]: Am. Assoc. Petroleum Geologists Bull., vol. 24, pp. 8-9, 1940.

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The beds in question are exposed east of the central ridge of the Guadalupe Mountains toward the Pecos River, where they form the Seven Rivers Embayment and the northeastern prong of the mountains (fig. 2). In the embayment and prong area, the Carlsbad and Chalk Bluff formations interpenetrate as a Series of tongues. At the base is the Queen sandstone member of the Chalk Bluff, which extends up over parts of the central ridge (as on Queen Mesa), where it overlies the Goat Seep limestone or its equivalents. Above it is the Seven Rivers gypsiferous member of the Chalk Bluff, consisting mainly of anhydrite and red beds. This member is poorly resistant to erosion, and has been carved into the Seven Rivers Embayment, a low-lying plain, down the dip from and east of the central ridge, and between the ridge and the northeastern prong of the mountains. The embayment is wedge-shaped, with its point to the south, where the central ridge and the prong come together (fig. 2). This topographic relation is a reflection of the southward disappearance of the Seven Rivers member along the outcrop, by intergradation with the more resistant and topographically more prominent Carlsbad limestone.

The northeastern prong of the Guadalupe Mountains, down dip to the east of the embayment, is capped by a sheet of Carlsbad limestone that forms the Azotea tongue of Lang. It partly overlies the Seven Rivers member, but intergrades with it toward the northwest, as exhibited in excellent exposures along Rocky Arroyo, in the gorge cut by it through the prong.⁶⁶ The outcrop of the tongue crosses the Pecos River northwest of Avalon Lake, where the tongue forms a rapidly thinning wedge enclosed above and below by beds of the Chalk Bluff formation.⁶⁷

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⁶⁶First described by C. L. Baker, Contributions to the stratigraphy of eastern New Mexico: Am. Jour. Sci., 4th ser., vol. 49, p. 115, 1920. For detailed description see Bates, R. L., Lateral gradation in the Seven Rivers formation, Rocky Arroyo, Eddy County, New Mexico: Am. Assoc. Petroleum Geologists Bull., vol. 26, pp. 80-99, 1942.

⁶⁷Exposures of the tongue at this locality were described by O. E. Meinzer, B. C. Renick, and Kirk Bryan, Geology of number 3 reservoir site of the Carlsbad irrigation project, New Mexico: U. S. Geol. Survey Water-Supply Paper 580, pp. 12-13, 1926. The overlying beds, which they termed Castile formation, are now known to belong to the Three Twins member of the Chalk Bluff formation.

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Overlying the Azotea tongue of the Carlsbad limestone in the north part of the northeastern prong is a higher tongue of the Chalk Bluff formation, called the Three Twins member by Lang. This tongue intergrades with the Carlsbad limestone a short distance northwest of Carlsbad. According to De Ford and Riggs,⁶⁸ it includes the Yates sandstone of subsurface nomenclature, and an overlying unit, which they call the Tansill formation. As shown by drilling east of the outcrop, the Three Twins member is overlain by the basal beds of the Salado formation, a part of the Ochoa series.

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⁶⁸De Ford, R. K., Riggs. G. D., Tansill formation, west Texas and southeastern New Mexico: Am. Assoc. Petroleum Geologists Bull., vol. 25, pp. 1713-1728, 1941.

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North of the area covered by figure 2, the tongues of Carlsbad limestone wedge out entirely, and all the beds of upper Guadalupe age are of Chalk Bluff type. Still farther north, limestones of middle Guadalupe age, equivalent to the Goat Seep limestone, also disappear, their place being taken by rocks of Chalk Bluff type. In its northern exposures, the Chalk Bluff formation is thus partly of upper Guadalupe age and partly of middle Guadalupe age.

The description of the relations of the beds of middle and upper Guadalupe age in the northern Guadalupe Mountains, as given in this report, is based on nomenclature adopted by the Geological Survey, which emphasizes lithologic units. A different system has been used by petroleum geologists, both in subsurface correlations and surface mapping, which emphasizes time units, regardless of their lithologic variations from place to place. By the latter system, the beds here discussed are termed the Whitehorse group, which is divided from below upward into the Grayburg, Seven Rivers, Yates, and Tansill formations. These formations are delimited and traced in both the Chalk Bluff and Carlsbad facies of present usage. Both systems of terminology have merit and originated for specific needs. The lithologic units are of value for reconnaissance surface mapping, and the time units are of value for subsurface work, such as well-log correlations and the recognition of subsurface structural features.

STRATIGRAPHIC RELATIONS

FIELD RELATIONS

In the Delaware Mountains, the Bell Canyon formation, at the top of the Guadalupe series, is overlain by the Castile formation. In the Guadalupe Mountains, no beds younger than the Guadalupe series are present. The highest beds of that area are the Carlsbad and Capitan limestones of Guadalupe age, which have been deeply eroded. The top of the Bell Canyon formation of the Delaware Mountains lies at a much lower altitude than the Carlsbad and Capitan limestones of the Guadalupe Mountains, with the overlying Castile extending up to the base of the Reef Escarpment. Near the Gray Ranch in Big Canyon Draw (northeast corner of pl. 3) the Castile crops out within a mile of the Reef Escarpment and stands more than 1,000 feet below the crest of the escarpment.

The contact between the Bell Canyon and the Castile in the Delaware Mountains appears to be conformable. The highest sandstones of the Bell Canyon give place abruptly to thinly laminated limestone of the Castile, which grades upward in turn into laminated anhydrite. There is no sign of erosion at the contact.

ALTERNATIVE INTERPRETATIONS

The features just outlined would seem to require some special explanation; they have puzzled geologists since the time of the first work in the region. Three principal explanations have been offered:

1, The Capitan limestone could have been laid down across the Delaware Mountain area but was eroded entirely away before deposition of the Castile, so the Castile was deposited on beds older than the Capitan,⁶⁹ 2, the Castile anhydrites could be the southeastward equivalent of the Capitan limestone, the two deposits grading into each other near the present Reef Escarpment;⁷⁰ and 3, the Capitan limestone could be older than the Castile formation and pass laterally into the Bell Canyon formation, the difference in altitude between the two being the result of irregularities in the original depositional surface.

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⁶⁹Richardson, G. B., Reconnaissance in trans-Pecos Texas north of the Texas and Pacific Railway: Texas Univ. Bull. 23, pp. 43-44, 1904. Darton, N. H., and Reeside, J. B., Guadalupe group: Geol. Soc. America Bull., vol. 37, pp. 420-421, 1926.

⁷⁰Baker, C. L., op. cit., pp. 116-117. This view was widely held by other geologists about 1925, but apparently none of them published their conclusions.

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The present field work indicates that the third explanation is the correct one, and demonstrates that the greater part of the Capitan limestone is of the same age as the Lamar and underlying members of the Bell Canyon formation.

Although the greater part of the Capitan limestone can be traced along the outcrop into the Bell Canyon formation, a few hundred feet of Capitan and Carlsbad limestones that are younger than the Lamar member and form the top and face of the escarpment at McKittrick Canyon cannot be traced southeastward because they are cut off by erosion. Their correlation with the Bell Canyon formation of the Delaware Mountains is thus somewhat uncertain. To the northeast, in New Mexico, greater thicknesses of Carlsbad limestone than at McKittrick Canyon extend to the edge of the escarpment. Some geologists have suggested that although most of the Capitan limestone is equivalent to the Bell Canyon formation the highest beds at McKittrick Canyon are contemporaneous with the Castile formation, and that the thick Carlsbad limestones to the northeast include strata that are younger than those at the canyon.⁷¹

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⁷¹Blanchard, W. G., and Davis, M. J., Permian stratigraphy and structure of parts of southeastern New Mexico and southwestern Texas: Am. Assoc. Petroleum Geologists Bull., vol. 13, p. 985, 1929.

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The youngest Capitan and Carlsbad limestones at McKittrick Canyon and farther northeast are identical in character with those of the older parts of the same formations elsewhere in the mountains. If they were laid down at the same time as the Castile formation, the conditions of their deposition would have been very different from those of the older beds. It seems probable, therefore, that they are equivalent to the 20 to 35 feet of thin sandstone and limestone beds that lie between the Lamar member and the Castile formation southeast of the Reef Escarpment. These beds are much thinner than the limestones on the escarpment, but the older sandstone and limestone members of the Bell Canyon formation are likewise thinner than that part of the Capitan limestone which has been proved to be equivalent to them.

Whether any limestones younger than those at McKittrick Canyon come in to the northeast remains to be proved. In view of the widespread and often abrupt replacement of the Capitan by the Carlsbad limestones, it is probable that the limestones of the two areas are of about the same age.

INFERRED STRATIGRAPHIC RELATIONS

The Castile formation may have been deposited on the highest sandstones of the Bell Canyon formation with little or no break in deposition. The sandstones, it is true, record a time of clastic deposition in a body of water connected with the ocean, whereas the anhydrites indicate deposition caused by concentration of salts in a partly inclosed body of sea water. Both, however, seem to have been deposited slowly in quiet water, and the change in character of the sediments probably resulted from events outside the area, such as the growth of a barrier across the entrance of the Delaware Basin (as suggested in fig. 14, C).

Toward the margins of the basin the stratigraphic relations are probably different. If all the Capitan and Carlsbad limestones are older than the Castile, they formed a mass that projected above the sea bottom of the Delaware Basin in somewhat the manner as the Reef Escarpment now rises above the plains to the southeast of it. Deposits laid down in the Delaware Basin in post-Capitan time probably overlapped the more elevated Capitan deposits. The nonresistant Castile formation has now been entirely eroded from the face of the escarpment, so this relation cannot be proved in the area studied. Farther east, however, where the Capitan and Castile formations pass beneath the surface, the evidence of drill records is interpreted by many geologists to indicate that the Castile does overlap unconformably on the surface of the Capitan at the edge of the Delaware Basin (as suggested in sec. e, pl. 7, B).⁷²

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⁷²Cartwright, L. D., Transverse section of Permian basin: Am. Assoc. Petroleum Geologists Bull., vol. 14, pp. 979-980, 1930. Kroenlein, A. A., Salt potash and anhydrite in the Castile formation of southeast New Mexico: Am. Assoc. Petroleum Geologists Bull., vol. 23, figs. 2 and 3, pp. 1685 and 1687, 1939.

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FOSSILS

The upper part of the Guadalupe series contains abundant fossils at many places. Its faunas were, in fact, the ones best known in the Guadalupe Mountains before the present investigation, because they furnished a large part of the material previously described by Girty⁷³ in his Guadalupian fauna. In addition, collections of this fauna made later by Darton and Reeside,⁷⁴ have been reviewed by Girty.

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⁷³Girty, G. H., The Guadalupian fauna: U. S. Geol. Survey Prof. Paper 58, pp. 15-20, 1908.

⁷⁴Darton, N. H., and Reeside, J. B., Jr., Guadalupe group: Geol. Soc. America Bull., vol. 37, pp. 414-416, 424, 427-428, 1926.

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In the discussion that follows, as in that on the faunas previously discussed, the information on the fossils is largely based on the work of Dunbar and Skinner,⁷⁵ Miller, and Furnish,⁷⁶ and G. H. Girty. In addition, some information is taken from the recent work of Pia⁷⁷ and Johnson⁷⁸ on algae, of Edwin Kirk on crinoids, of L. G. Henbest on Foraminifera, and of N. D. Newell⁷⁹ on pelecypods.

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⁷⁵Dunbar, C. O., and Skinner, J. W., Permian Fusulinidae of Texas: Texas Univ. Bull. 3701, pp. 594-596, 727-731, 1937.

⁷⁶Miller, A. K., and Furnish, W. M., Permian ammonoids of the Guadalupe Mountains region and adjacent areas: Geol. Soc. America Special Paper 26, pp. 11-12, 1940.

⁷⁷Pia, J. V., Bie wichtigsten kalkalgen des Jungpalaozoikums und ihre geologische bedeutung: Compte rondo do deuxième congress pour l'avancement des études Carbonifère, pp. 813-837, Heerlen, 1937; Vorläufige übersicht der kalkalgen des Perms von Nordamerika: Akad. Wiss. Wien, Math-Natuurwiss. Kl., Anz. 9, preprint, June 13, 1940.

⁷⁸Johnson, J. H., Calcareous algae from the Carlsbad limestone of New Mexico [abstract]: Geol. Soc. America Bull., vol. 49, p. 1889, 1938; Ecologic distribution of lime-secreting algae of the Permian Carlsbad reef, Guadalupe Mountains, N. Mex. [abstract]: Geol. Soc. America Bull., vol. 50, p. 1915, 1939; Permian lime-secreting algae from the Guadalupe Mountains, N. Mex.: Geol. Soc. America Bull., vol. 53, pp. 195-226, 1942.

⁷⁹Newell, N. D., Invertebrate fauna of the late Permian Whitehorse sandstone: Geol. Soc. America Bull., vol. 51, pp. 279-280, 1939.

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In the upper part of the Guadalupe series, fossils occur in varying abundance. They are very common in the reef mass of the Capitan limestone and in immediately adjacent parts of the Bell Canyon formation and Carlsbad limestone. In the Bell Canyon formation farther southeast and in the Carlsbad limestone farther northwest they are less common, and in many beds are absent entirely. Like the rocks that contain them, the faunas differ markedly in facies from one part of the area to another, even in contemporaneous beds. The first group of faunas, described below from the limestone members of the Bell Canyon formation, lie in a normal, ascending stratigraphic sequence. The next group of faunas, described from the Capitan and Carlsbad limestones, are from beds of the same age as part or all of the members of the Bell Canyon formation. The fossils from each of these two formations are considered as units and no separate zones have been distinguished in them.

BELL CANYON FORMATION

HEGLER LIMESTONE MEMBER

The Hegler limestone member at the base of the Bell Canyon formation contains fossils at numerous places, but they are never abundant or varied, and many are so poorly preserved that collections made from it are small. According to Girty, "The member has a rather extensive fauna, but most of the species are represented only by a specimen or two in the collections in which they occur. The collections occur in rocks of several distinct lithologic types, but the faunal characters are much the same and the differences do not seem to be significant."

Collections were made from the thin-bedded, granular facies of the member in the Delaware Mountains in the southeast part of the area, and in the downfaulted area to the west. They were made also from the lumpy facies along the Reef Escarpment, on the southeast side of the Guadalupe Mountains, and from the light-gray, bedded facies in McKittrick Canyon.

Fusulinids are rare in the Hegler member, but at a few localities, as at 7622 in McKittrick Canyon, there are specimens of Polydiexodina shumardi Dunbar and Skinner. The genus has not been found below this member in the Guadalupe section.

The cephalopods are represented by ammonoids only, no nautiloids having been found. Collections from the Hegler member have furnished a greater number and variety of ammonoids than were found in any other member of the Bell Canyon formation. Ammonoids are especially common in the thin-bedded, granular facies in the southeast part of the area, but they are found also in the lumpy facies to the northwest, where they are seldom well preserved. From the Hegler member, Miller and Furnish have identified Medlicottia girtyi Miller and Furnish, Paraceltites altudensis (Böse), Pseudogastrioceras altudense (Böse), P. beedei (Plummer and Scott), Xenaspis skinneri Miller and Furnish, Cibolites uddeni Plummer and Scott, Waagenoceras guadalupense Girty, and Timorites schuchert Miller and Furnish.

By far the most abundant type is the Waagenoceras, which occurs in great numbers at all collection localities. Considerably less abundant, but still common, is the genus Pseudogastrioceras. The Timorites occurs at only a single locality (7694), but is of some significance, because Miller and Furnish⁸⁰ have used it to name the Permian ammonoid zone next above the zone of Waagenoceras. Here and elsewhere, however, Timorites and Waagenoceras occur in association in the lower part of the zone of Timorites. That the Hegler member is of later Permian age is suggested by Xenaspis which occurs high in the Permian sequences of the island of Timor (Netherlands East Indies), and of the Salt Range of India.

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⁸⁰Miller, A. K., and Furnish, W. M., op. cit., p. 29.

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Regarding the remainder of the fauna, Dr. Girty reports:

The corals are somewhat more diversified than is common in the Guadalupian faunas, although they cannot at this time be safely identified even generically. A few specimens may belong to the form cited in the collections from lower beds as Lophophyllum sp. There seems to be a second species constructed along similar lines, but forming long, slender coralites resembling Amplexus. Cyathaxonia appears to be present in one collection, and in another the small compound coral described as Cladopora spinulata Girty is not rare.

Bryozoans are fairly well represented and abundant in one collection, but not in the others. In this one collection (No. 7622) Fistulipora is as usual the most abundant genus. The specimens have the form of rather slender cylindrical stems and belong to the species described as F. grandis guadalupensis Girty. A few slender branches are provisionally referred to Batostomella, but a more definite assignment must await study by means of thin sections. Some coarsely silicified fronds belong to Fenestella or Polypora, or both. Acanthocladia guadalupensis Girty is fairly abundant, as are some slender stems belonging to the species described as Domopora ocellata Girty.

Turning now to the brachiopods, we find that the orthoids are distinguished by their absence. The Orthotetinae are represented by a few small and poor specimens whose identification would hardly be profitable. Only one is a ventral valve; it probably belongs to the genus Orthotetes. Chonetes is represented by two species, C. subliratus Girty, and C. permianus Shumard, which is here encountered for the first time.

The productids are much reduced in numbers and variety, and half the species are represented by but a single specimen. Aside from several species that, in the present state of my investigations, are indeterminable, we have here Productus capitanensis Girty, P. popei opimus Girty, Productus aff. P. occidentalis Newberry, and two species which in Professional Paper 58 were distinguished as Productus sp. a and Productus sp. d, and finally I would judge, the species that King described as Avonia walcottiana costata.

Of Aulosteges, there are apparently two species, each represented by a single specimen. One of them, which is fragmentary, may belong to A. guadalupensis Shumard. The other begins with an ornamentation of large, elongated nodes, which farther forward develop into coarse, irregular costae; the species is apparently new.

Prorichthofenia is present at two localities and is fairly abundant at one of them. Pending detailed study, the species may be included under P. permiana (Shumard). Camarophoria is represented, if at all, by a mere fragment. It might belong to C. venusta Girty.

The rhynchonellids of the Hegler limestone are rather abundant and diversified, always remembering that this member is not highly fossiliferous. I recognize Leiorhynchus? bisulcatum (Shumard), L.? bisulcatum seminuloides (Girty), Leiorhynchus? n. sp. Wellerella? shumardiana (Girty), Wellerella? swallowiana (Shumard), and Wellerella? indentata (Shumard).

Only two terebratuloids are present, one an indeterminable species of Dielasma, the other Dielasmina guadalupensis Girty.

The spiriferoids are represented by rather numerous species, but by few individuals. I may name Spirifer mexicanus Shumard, S. sulcifer Shumard?, S. sulcifer var., Spirifer n. sp., Spiriferina billingsi Shumard, and Spiriferina pyramidalis Girty?. This group seems to show marked Capitan affinities.

Composita is numerous at one locality, but few of the specimens are well preserved. Two species can be distinguished, which may be called Composita aff. C. subtilita (Hall) and C. emarginata affinis Girty. Some of the latter are very large. Hustedia is represented by few specimens, but they appear to belong to three species, H. meekana (Shumard), Hustedia aff. H. mormoni (Marcou), and Hustedia aff. H. bipartita Girty.

The pelecypods, following the general paucity of fossils in this unit, are scantily represented, and many of the specimens are not identifiable. There is a doubtful species of Sedgwickia and a doubtful species of Parallelodon. As in the faunas already discussed, the pectenoids are more plentiful and varied than the other groups. I may record Pernipecten? obliquus Girty?, Girtypecten sublaqueatus (Girty)?, Deltopecten n. sp., Camptonectes sculptilis Girty?, and Camptonites? n. sp.

Of the gastropods, the collections afford a single fragmentary specimen, which might belong either to Euomphalus or Omphalotrochus. Lastly, the trilobites are represented by a few fragments, probably belonging to Anisopyge perannulata (Shumard).—Girty manuscript.

In comparison with the fauna of the preceding South Wells member, Dr. Girty notes the reappearance in the Hegler member of bryozoans and spiriferoid brachiopods, which were absent in the South Wells and common in still lower horizons; the absence in both of Enteletes, although it was present in the Goat Seep limestone; and the absence in the Hegler of Meekella and Cryptocanthia, which were present in the South Wells. Chonetes permianus Shumard, which occurs in the Hegler, has not been found at lower horizons. The productids seem to differ considerably from those of the older faunas. Both they and the spiriferoids closely resemble those of the Capitan limestone. According to Girty, "like the South Wells fauna, the Hegler fauna shows an abundance and diversity of rhynchonellids, but the specific representation is different. The South Wells fauna is conspicuous for its large forms, such as Liorhynchus weeksi (Girty), and L. weeksi nobilis (Girty), neither of which occurs here."

PINERY LIMESTONE MEMBER

The Pinery member contains the assemblage described by Shumard and Girty as the "upper dark limestone" fauna. Most of the material on which the earlier descriptions were based came from the hillside above Pine Spring, the type section of the member (Girty's locality 2930). Subsequent collections were made at the same locality by Darton and Reeside⁸¹ (No. 5815) and during the present investigation (Nos. 7420, 7477, and 7703). (See pl. 2.)

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⁸¹Darton, N. H., and Reeside, J. B., Jr., op. cit., p. 416.

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Collections made here and elsewhere along the base of the Reef Escarpment reveal abundant and diverse fossils, constituting a fauna of relatively constant character. Similar fossils, but with a considerable admixture of Capitan species, occur in the lighter-colored limestones of the member farther northwest (as at locality 7412), where the member begins to change over into the Capitan facies. Southeast of the Reef Escarpment, in the Delaware Mountains, however, large numbers of the characteristic elements of the fauna disappear. A collection from this last named region (locality 7643) contained abundant fusulinids, ammonoids, and rhynchonellid brachiopods, a few productids and pelecypods, and nothing else.

Fusulinids occur in nearly all exposures of the member, regardless of facies. According to Dunbar and Skinner, they belong to the large species Polydiexodina shumardi Dunbar and Skinner and P. capitanensis Dunbar and Skinner, and to the small species Lëlla bellula Dunbar and Skinner and Codonofusiella paradoxica Dunbar and Skinner.

Ammonoids are represented by fewer collections than those from the underlying Hegler member, but belong to the same species. From the Pinery, Miller and Furnish have identified Waagenoceras guadalupense Girty, Xenaspis skinneri Miller and Furnish, and Pseudogastrioceras sp. No nautiloids have been found, either in recent or earlier collections.

At several localities along the base of the Reef Escarpment, as at Pine Spring, several minute crinoids have been collected. They may possibly prove to be index fossils of the horizon, for they have been found at no other bed in the section. According to Edwin Kirk, they include Coenocystis richardsoni Girty and Allegecrinus sp. The genus Coenocystis and its species were established by Girty⁸² on the basis of material from a locality in the southern Delaware Mountains (No. 2969). The stratigraphic position of this collection is unknown, but it is probably of the same age as the Pinery member. According to Girty, the Pinery member of the Guadalupe Mountains also contains spines and plates of the echinoid Archaeocidaris.

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⁸²Girty, G. H., The Guadalupian fauna: U. S. Geol. Survey Prof. Paper 58, pp. 108-109, 1908.

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Dr. Girty writes as follows on the remainder of the fauna, the theme of his report being a comparison between his original collection at locality 2930, and the later collections from the same and nearby localities:

The original collections contained two sponges (Polysiphon mirabilis Girty and Steinmannia americana Girty), neither of which has been recognized in the new collections.

Of the corals, five are listed from station 2930, Lindstroemia permiana Girty, L. permiana var., L. cylindrica Girty, Lindstroemia sp., and Cladopora spinulata Girty. The four species referred under Lindstroemia have, in a general way, the structural features of Lophophyllum, and the forms loosely cited in these reports as Lophophyllum? sp. will, when studied, closely represent the same species as the above. They may prove to belong to neither Lophophyllum nor Lindstroemia. In the recent collections I recognize, besides Lophophyllum? sp., both Cladopora spinulata Girty and C. tabulata Girty.

Among the bryozoans, station 2930 furnished a long list, containing no less than 15 species under the genera Domopora, Fistulipora, Stenopora (now Tabulipora), Fenestella, Polypora, and Acanthocladia. The same genera, and probably the same species, occur amongst the bryozoans in the recent collections, although for obvious reasons I have not gone into the matter of specific differentiation.

Among the brachiopods, the original list contained Crania sp., Derbya sp., and three species of Chonetes (C. permianus Shumard, C. hillanus Girty, and C. subliratus Girty). The new collections are more varied. Crania is unrepresented, but in the Orthotetinae I find Derbya nasuta Girty var., Derbya n. sp., Derbya? n. sp., and Streptorhynchus? sp. Chonetes is represented by the same three species as in the original list.

The early collection contained 8 species of Productus, as well as Aulosteges guadalupensis Shumard and Prorichthofenia permiana (Shumard). The productids comprised the following species: Productus capitanensis Girty, P. popei Shumard, F. popei opimus Girty, P. indentatus Girty, P. occidentalis Newberry, P. pileolus Shumard, P. limbatus Girty, and Prorichthofenia sp. d. The newer collections contain most of these (P. limbatus being the most notable absentee), together with P. leonardensis King?, and Productus (Marginifera?) sublevis (King). The species of Aulosteges and Prorichthofenia are likewise present.

The original list included Leiorhynchus? bisulcatum (Shumard), together with its varieties L.? b. seminuloides (Girty) and L.? b. gratiosa (Girty), Wellerella? swallowiana (Shumard)?, W. texana (Shumard), W. bidentata (Girty)?, W.? pinguis (Girty), Wellerella sp. a, and W.? indentata (Shumard). This list is practically duplicated in the new collections, which contain also a few Camerophoria venusta Girty.

Terebratuloids in the original collection were limited to three species: Dielasma spatulatum Girty, Dielasmina guadalupensis Girty, and Notothyris schuchertensis ovata Girty?. The same assemblage occurs in the new collections, except for the species last named.

The spiriferoids in the collection from station 2930 comprised Spirifer mexicanus Shumard var., Spirifer sp. a, Spiriferina billingsi Shumard, S. laxa Girty, S. hilli polypleura Girty, and S. welleri Girty. This group is more generously represented in the recent collections. I provisionally identify Spirifer sulcifer Shumard, S. pseudocameratus Girty, S. mexicanus latus King (which probably covers S. mexicanus var., Spirifer sp. a, and possibly S. mexicanus of the old collection), besides Spiriferina hilli Girty, S. billingsi Shumard, S. laxa Girty, Spiriferina n. sp., and Squamularia sp.

The original collection contained only one Composita, which was identified as C. emarginata Girty. The recent ones contain a large species, apparently the one King figures as C. emarginata affinis Girty.

The brachiopods of the original list included also Hustedia meekana (Shumard), H. meekana trigonalis Girty, H. papillata Shumard, and H. bipartita Girty. The new collections contain the same assemblage, except for the variety trigonalis. Leptodus, not recorded at this horizon before, continues its upward range.

Among the pelecypods, the original collection from station 2930 contained Myalina squamosa Sowerby?, Deltopecten guadalupensis (Girty), and Deltopecten sp. a. The more recent collections have a much better representation of this group, and contain Edmondia aff. E. ovata Meek and Worthen, Parallelodon multistriatus Girty, P. politus Girty?, Parallelodon n. sp.?, a small Myalina having the configuration usually ascribed to M. permiana Swallow, some imperfect specimens of Aviculopecten that are provisionally identified as A. guadalupensis Girty and A. guadalupensis var., Myoconcha costulata Girty, and Pseudomonotis? n. sp.

The gastropods in the original list are represented only by Straparollus sulcifer (Girty) and S. sulcifer angulatus (Girty). In addition to these, the new collections contain a species of Platyceras, one of Omphalotrochus, and a number of indeterminable specimens of Euphemites, besides a miscellaneous lot of indeterminable bellerophontid shells.

Both the old and new collections contain the long-ranging trilobite Anisopyge perannulata (Shumard).—Girty manuscript.

In summarizing the collections, Dr. Girty notes the close resemblance between the Pinery fauna and the underlying Hegler fauna, the main difference being the greater abundance and diversity of the Pinery fauna. In his original work Girty⁸³ made the following comparison between the Pinery and Capitan faunas. Some of the differences mentioned have been removed by subsequent collecting, but most of them persist.

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⁸³Girty, G. H., op. cit., p. 19.

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The Capitan fauna, as exemplified by the collections obtained in its middle portion at station 2926, and the fauna of the "dark limestone" show well-marked differences. * * * Some of the more distinguishing characteristics of the "dark limestone" fauna are the abundance of Fusulina elongata * * *, the greater abundance of cup corals, the presence of Cladopora spinulata, the greater abundance of the Domoporas and other Bryozoa, the presence of Chonetes permianus and C. subliratus, the abundance of small Producti of the semireticulatus group, such as P. popei, P. indentatus, etc., the presence of Aulosteges guadalupensis and Spiriferina laxa, the abundance of the group of Pugnax bisulcata, the presence of Aviculopecten guadalupensis, and of Euomphalus sulcifer⁸⁴ and its variety angulatus, and the abundance of Anisopyge perannulata. An equal number of distinctive forms might be named on the part of the Capitan fauna.

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⁸⁴Equivalent to Straparollus sulcifer of Girty manuscript just above.

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RADER LIMESTONE MEMBER

The Rader limestone member is represented by fewer collections than the underlying Pinery member, and is apparently not as fossiliferous. The largest collections came from the vicinity of Rader Ridge (Nos. 7480, 7600, 7668, and 7693, pl. 2), from light-gray, massive limestone resembling the Capitan facies, or from dark-gray, bedded limestone resembling the Pinery facies. Smaller collections were made farther southeast; one of them from east of the area mapped on the south side of Lamar Canyon contains only ammonoids (No. 7654); another contains only fusulinids (No. 7921); and two others contain only smaller Foraminifera.

The fusulinids, represented in two collections (Nos. 7480 and 7921), have been identified by Dunbar and Skinner as Polydiexodina capitanensis Dunbar and Skinner, and P. shumardi Dunbar and Skinner. This genus is characteristic of the beds of upper Guadalupe age. Smaller Foraminifera were obtained by H. C. Fountain from two localities in the eastern part of the area. They were found in thin marl layers interbedded with the limestone and were separated from their matrix by washing. According to Henbest⁸⁵ the following forms are present:

Foraminifera from Lamar Canyon

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⁸⁵Henbest, L. G., memorandum, May 1938.

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Ammonoids from locality 7654 have been identified by Miller and Furnish as Xenaspis skinneri Miller and Furnish, and Waagenoceras guadalupense Girty. The first genus and species does not range below the upper part of the Guadalupe series, and the second does not range below the middle part. Except for a few fragments, no nautiloids have been collected.

Regarding the remainder of the fauna, most of which was obtained from the localities near Rader Ridge, Dr. Girty writes:

The corals comprise the following: Cladopora spinulata Girty, C. tabulata Girty?, Cladochonus sp. (fragment), Lophophyllum? sp., and Amplexus? sp.

The bryozoans appear to be well diversified but, as many of them require study by thin sections, this group must at present be treated in a cursory manner. The identifications made are subject to revision. Fistulipora is fairly abundant and apparently belongs to a single species, F. grandis guadalupensis Girty. The singular series of forms provisionally referred to the genus Domopora is plentiful and diversified. I recognize D. ocellata Girty, D. terminalis Girty, and D. vittata Girty. Besides these, we have Batostomella? sp., Leioclema? sp., Fenestella (fragment), Acanthocladia guadalupensis Girty, and Rhombopora? sp.

Among the brachiopods the orthoids as is usual in the higher Guadalupian faunas, are unrepresented, and the Orthotetinae are very scarce. There are only a few poor specimens of the genus Derbya, which might be a small variety of D. nasuta Girty. The absence of Chonetes is a noteworthy feature of the fauna.

The productids, together with the related genera Aulosteges, Prorichthofenia, and Scacchinella, are diversified but by no means bountiful in individuals, and the individuals are mostly poorly preserved. They comprise Productus capitanensis Girty, P. popei Shumard, P. popei opimus Girty, P. (Buxtonia?) sp., and the peculiar P. (Pustula?) pileolus Shumard. A number of specimens are more or less closely related to another peculiar form, described as Productus limbatus Girty, and the question again arises without being answered, as to whether this species is not actually an Aulosteges. To the latter genus belong A. guadalupensis Shumard, and possibly a very small, smooth form of doubtful affinities. Prorichthofenia permiana (Shumard) occurs in several collections, and a single small specimen is doubtfully referred to Scacchinella.

Camarophoria continues to be represented, although scantily, by C. venusta Girty, and there is another form, unfortunately not generically determinable, which resembles C. venusta except that it has notably finer and more numerous costae.

The rhynchonellids are diversified and fairly abundant. The outstanding species are Leiorhynchus? bisulcatum (Shumard) and L.? bisulcatum seminuloides (Girty). Wellerella? indentata (Shumard) is also present, with one or two varieties or related species.

The representation of the terebratuloids holds closely to type. I recognize Dielasma spatulatum Girty, D. cordatum Girty, Dielasmina guadalupensis Girty, and a new species of the same genus or possibly a diminutive variety of the same species

The spiriferoids are represented only by the genera Spirifer and Spiriferina. They include Spirifer mexicanus Shumard, another species which may be S. sulcifer Shumard, Spiriferina billingsi Shumard, S. angulata King and S. laxa Girty.

Of Composita, there are several species represented by selected specimens. Besides C. emarginata Girty, we have the variety affinis Girty, a form very similar to C. subtilita (Hall) and another related to C. mexicana (Hall).

The pelecypods are few in number and poor in preservation. Only the following have been recognized: Solenomya? sp., Aviculopecten sp., Fasciculiconcha sp., Pernopectin obliquus Girty, Camptonectes sculptilis Girty, and Myalina permiana Swallow? Gastropods are all but absent. The only forms noted are Bucanopsis sp., together with a few indeterminable bellerophontid shells and Trachydomia? sp. Finally comes the ever-present Anisopyge perannulata (Shumard), and some undetermined Ostracods.—Girty manuscript.

According to Girty, the Rader fauna is similar to that of the Pinery, but (as can be expected from the smaller collections) is much less varied. Among the brachiopods, the fewer Orthotetinae and the absence of Chonetes are notable. Other groups, such as productids, rhynchonelloids, terebratuloids, spiriferoids, and the genera Camarophoria, Composita, Hustedia, and Leptodus are about the same in both faunas.

LIMESTONE BEDS BETWEEN RADER AND LAMAR MEMBERS

In the Delaware Mountains, the several hundred feet of beds between the Rader and Lamar members are all sandstone, except one flaggy limestone bed, and no fossils have been observed in any of them. Along the Reef Escarpment, the interval contains a number of fossiliferous limestone beds which are, in fact, tongues of the Capitan limestone. These beds are represented by three collections, two from the mouth of McKittrick Canyon (Nos. 7608 and 7708), and one from the head of Rader Ridge (No. 7360).

The latter, obtained from beds a few feet above the Rader member, contains fusulinids. They have been identified by Dunbar and Skinner as Ozawainella delawarensis Dunbar and Skinner, and Polydiexodina shumardi Dunbar and Skinner. No cephalopods have been found in the interval.

Regarding the remainder of the fauna, Dr. Girty reports as follows:

Sponges are represented by a specimen of Amblysiphonella? sp., another species of doubtful nature, and Cystothalamia nodulifera Girty?.

The corals are represented by a single specimen belonging to the species described in Professional Paper 58 as Lindstroemia cylindrica Girty. Similar corals have been cited as Lophophyllum? sp. in discussions of underlying faunas. A quite novel type is Chaetetes? sp., which grew upon, but apparently did not form a part of, the sponge cited as Amblysiphonella? sp. It is of doubtful nature, and differs from Chaetetes in that the slender cells do not seem to be closed by tabulae. However, many silicified specimens of Chaetetes fail to show the tabulae that they originally possessed.

The following bryozoans are each represented by a single specimen: Fistulipora sp., Domopora terminalis Girty, D. ocellata Girty, Septopora? sp., Phyllopora? sp., and Acanthocladia guadalupensis Girty.

The brachiopod group of Orthotetinae, which have been abundant and diversified in some of the faunas previously discussed, are represented by a few specimens identified as Orthotetes guadalupensis Girty. Chonetes is absent.

The productids are well represented, but in only one of the three collections under consideration (No. 7608), and the specific representation is not large. It is as follows: Productus capitanensis Girty, P. (Marginifera?) waagenianus Girty, P. popei Shumard, P. popei var., Productus aff. P. (Pustula?) latidorsatus Girty, P. (Striatifera) pinniformis Girty, Aulosteges guadalupensis Shumard, Prorichthofenia permiana (Shumard), and Scacchinella? sp. The generic relations of P. pinniformis, which is rather abundant, are uncertain. Some of my specimens give evidence of having been attached by cementation, and the general configuration suggests that of Aulosteges, but I have been unable to ascertain that a cardinal area is present. Altogether, the productid fauna of this horizon is reminiscent of that of the Capitan limestone.

Camerophoria continues to be represented, although very scantily, by C. venusta Girty.

The rhynchonellid fauna is considerably diversified, but each collection seems to have its own set of species, and most of the species are represented by single specimens. These shells are classified as Wellerella? swallowiana (Shumard), W.? shumardiana (Girty), W.? pinguis (Girty), W.? indentata (Shumard)?, and Leiorhynchus? bisulcatum seminuloides (Girty)?.

Terebratuloids are feebly represented by a single small specimen of Dielasma cordatum Girty, and several indeterminate specimens.

The spiriferoids include a single specimen of Spirifer, possibly S. sulcifer Shumard as identified by King (which is doubtfully the authentic S. sulcifer). Spiriferina is represented by S. welleri Girty, S. billingsi Shumard, and S. evax Girty?. The group also includes Martinia shumardiana Girty and Squamularia guadalupensis (Shumard).

Composita, although by no means scarce, is so poorly preserved that little that is definite can be said about it. C. emarginata Girty is definitely present, and some specimens suggest C. subtilita (Hall), and C. mexicana (Hall). Of Hustedia, the collections contain only two specimens, one referable to H. meekana (Shumard), and the other to H. papillata (Shumard). Leptodus americanus Girty is present in two collections, with one specimen in each.

The few pelecypods present belong mostly to the pectenoids, and few of the forms can be identified. I cite only Aviculopecten n. sp., Fasciculiconcha sp., and Acanthopecten coloradoensis (Newberry)?. Mention should be made here also, but with great reserve, of a fairly large specimen referred provisionally to Pseudomonotis. Only the anterior half is present, and even that is for the most part an internal mold. It is marked by fairly strong plications which are very irregular in size, spacing, and even in direction. Aside from the species cited, there remains only an imperfect specimen provisionally referred to the genus Myoconcha.

The gastropods comprise only a few bellerophontid shells which cannot be determined generically, and Worthenia? n. sp. No trilobites are present.—Girty manuscript.

In summary, Dr. Girty notes that the fauna of this interval is closely related to the underlying fauna. The main differences lie in the closer similarity of the fauna of this interval to that of the Capitan, a fact to be expected in view of the similarity of the facies of the containing beds to that of the Capitan, their close proximity to the Capitan, and their gradational relations with it. Among the Capitan affinities of the fauna is the presence of Calcispongia, of Martinia and Squamularia, and of the productid species Productus (Pustula?) latidorsatus Girty, P. (Striatifera) pinniformis Girty, and P. (Marginifera?) waagenianus Girty, none of which were found in the Rader fauna. By contrast, rhynchonellids of the type Leiorhynchus bisulcatum (Shumard), and also Spirifer and Spiriferina, which were common in the Rader fauna, are absent here.

LAMAR LIMESTONE MEMBER

The Lamar limestone member contains abundant fossils along the Reef Escarpment, near the Capitan reef mass, but they are nearly or completely absent farther southeast. Although they occur in gray or dark-gray, bedded limestone, very different from the Capitan limestone in appearance, Dr. Girty notes that, "taken as a whole, the fauna of the Lamar member is a typical Capitan fauna."

Collections obtained from the member by Darton and Reeside⁸⁶ had been identified by Girty prior to the present investigation. These collections came from the mouth of Big Canyon, in New Mexico. Darton and Reeside erroneously suggested a correlation of the member with the "upper dark limestone" (Pinery). During the present investigation a large collection was made at the mouth of McKittrick Canyon (No. 7401), not far southwest of Big Canyon, and others were obtained in the downfaulted area west of the Delaware Mountains (Nos. 7630, 7647, and 7663, pl. 2).

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⁸⁶Darton, N. H., and Reeside, J. B., Guadalupe group: Geol. Soc. America Bull. vol. 37, p. 424, 1926.

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No fusulinids have been collected from the member on the outcrop, but some have been obtained from the uppermost limestones of the Bell Canyon formation (probably Lamar) in wells drilled east and southeast of the outcrops. In the Ohio Oil Company, Popham No. 1 well, in southern Reeves County, 90 miles southeast of the Guadalupe Mountains, Skinner⁸⁷ has identified Ozawainella, Leella, and Codonofusiella from this horizon.

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⁸⁷Skinner, J. W., personal communication, January 1939.

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The member contains a few nautiloids, one of which was identified by A. K. Miller as Metacoceras sp. Ammonoids occur at a single locality west of the Delaware Mountains (No. 7663), which has yielded three specimens. According to Miller and Furnish,⁸⁸

All these represent only one species, Strigogoniatites fountaini Miller and Furnish. The genus Strigogoniatites has not been found elsewhere in Texas, but in Coahuila [Las Delicias area, Mexico] a rather primitive representative of it occurs in the Capitan horizon. An advanced representative of the genus is known from Timor [Netherlands East Indies], probably from the Amarassi horizon. S. fountaini is the youngest Permian ammonoid known from the United States, but it may be older than Cibolites? sp. of the Las Delicias beds of Coahuila.

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⁸⁸Miller, A. K., and Furnish, W. M., Permian ammonoids of the Guadalupe Mountains region and adjacent areas: Geol. Soc. America Special Paper 26, p. 12, 1940.

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Regarding the remainder of the fauna, Dr. Girty writes:

Of the simpler classes of invertebrate life, this fauna contains an unidentified sponge, the corals Lophophyllum? sp., and Cladopora spinulata Girty, crinoid plates, and the spines, jaws, and interambulacral plates of several species of echinoids.

The bryozoans have been less intensively studied than most other groups. I recognize Fistulipora sp., Domopora terminalis Girty, D. ocellata Girty, Batistomella? sp., Fenestella sp., and Acanthocladia guadalupensis Girty.

Among the brachiopods, the Orthotetinae are varied, comprising Orthotetes guadalupensis Girty (abundant), Streptorynchus gregarium Girty, Geyerella? sp., and Derbya sp. Chonetes is abundant and all but one small specimen have been referred to C. hillanus Girty; it is possible, however, that C. subliratus Girty may also be present.

The productids are rather restricted in numbers and variety. I recognize only the following: Productus capitanensis Girty, P. (Pustula?) latidorsatus Girty, P. popei opimus Girty, and P. (Marginifera?) sp. Besides these there are several species belonging to a small, attached genus that would commonly be called Strophalosia. The persistent Prorichthofenia permiana (Shumard) is also present.

Camerophoria is fairly abundant, and for the present all specimens are referred to C. venusta Girty, although they show so much diversity that further distinctions may be practicable on closer study.

Rhynchonellids are fairly abundant, but many of the specimens are crushed or otherwise in poor condition. All seem to be of the general type of Wellerella osagensis (Swallow) and may provisionally be referred to that genus. They contain no striking types and are only sufficiently diversified to be difficult to classify. For present purposes they have been identified as Wellerella? shumardiana (Girty), W.? shumardiana var., W.? swallowiana (Shumard), and one or two indeterminate forms.

Terebratuloids are only fairly abundant, but they show considerable diversity. I identify Dielasma sulcatum Girty, together with two undetermined species of the same genus, Heterelasma shumardianum Girty, Heterelasma? sp., Notothyris schuchertensis Girty, and N. schuchertensis var.

The spiriferoids are represented by the genera Spirifer, Spiriferina, Martinia, and Ambocoelia. Spirifer itself shows little diversity. I recognize only. S. mexicanus Shumard, and the variety compacta Girty. Spiriferina is much more diversified, being represented by S. billingsi Shumard, S. sulcata Girty, S. welleri Girty, and Spiriferina aff. S. hilli polypleura Girty. Squamularia is abundant, but confined to a single species, S. guadalupensis (Shumard). Martinia is less abundant than Squamularia, but is not rare. Like Squamularia, it is represented by a single species, M. rhomboidalis Girty. Ambocoelia is fairly abundant in one locality, but here again only one species is present, A. planoconvexa guadalupensis Girty.

Composita, as usual, is fairly abundant but the species are poorly characterized. They may be identified as C. emarginata Girty? and C. emarginata affinis Girty. Some of the latter might pass as C. subtilita (Hall).

One of the collections contains several species of Cleiothyrida, a small form resembling the common Pennsylvania species C. orbicularis (McChesney), with which it is provisionally identified. The occurrence is interesting, not only on this account, but also because the genus has not heretofore been recognized in the Guadalupian faunas. It was not known when Professional Paper 58 was published (1908), and it has not been found in any of the faunas so far discussed.

Another genus that is not rare, but affords only a single species is Hustedia, represented by H. meekana (Shumard). Leptodus americanus Girty is fairly abundant, and affords material for further study.

The pelecypods are rare compared with the brachiopods, and they are distributed among the genera Parallelodon, Schizodus, Aviculopecten, Girtypecten, Streblopteria, Pteria, Myoconcha, Myalina, and Cleidophorus.

These collections furnish only three specimens of Parallelodon two indeterminable and one identified as P. multistriatus Girty. Schizodus is represented by a single poor specimen, of which more can hardly be said than that it does not belong to S. securus (Shumard)?, the only one that was recognized in Professional Paper 58.

The pectenoids include Aviculopecten bellatulus Newell, Aviculopecten sp., Girtypecten sublaqueatus (Girty), and Streblochondria? sp.

Pteria is represented by a single indeterminable specimen. Of Myoconcha, I have three forms which are generically doubtful and specifically undeterminable. Finally, we have a doubtful and indeterminable specimen of Myalina and a small form identified as Cleidophorus pallasi delawarensis Girty.

A large, straight scaphopod, provisionally referred to Plagioglypta canna White, is rather abundant.

The gastropods are few end poorly preserved. The bellerophontids are represented by two indeterminable species. The pleurotomariids have as yet not been studied critically. Probably three species can be distinguished, but their preservation is such that they may not be identifiable. There are also a large Eotrochus? (possibly Euconospira), a doubtfully identifiable species of Actaeonina?, Bulimorpha sp. Omphalotrochus n. sp., and an indeterminable species of Naticopsis.

The characteristic Guadalupian trilobite Anisopyge perannulata (Shumard) persists in moderate abundance.—Girty manuscript.

CAPITAN LIMESTONE

The fauna of the Capitan limestone was described in considerable detail in Girty's original publication,⁸⁹ for the material at his disposal was extensive. Most of it was obtained at various points on the east slope of Guadalupe Peak (as at localities 2926 and 2966, pl. 2). The collections made during the present investigation have added somewhat to the details of the fauna as originally described but have not materially changed its broader features. Some of the collections (such as 7405) were made in the vicinity of the older localities, but one of the largest (No. 7417) came from a new area, along the channel of South McKittrick Canyon near the Grisham-Hunter Camp. This collection is probably from an older part of the Capitan than the previous ones, being perhaps of Hegler age, whereas the others are perhaps of Rader or younger age.

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⁸⁹Girty, G. H., The Guadalupian fauna: U. S. Geol. Survey Prof. Paper 58, pp. 15-18, 1908.

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The manner of occurrence of fossils in the Capitan limestone, and the faunal facies represented, have been discussed on page 62.

The Capitan limestone apparently contains considerable numbers of lime-secreting algae, but few observations were made on them during the present investigation. Algae were reported from the Capitan by Ruedemann.⁹⁰ The specimen figured, however, consists of pisolites of the sort common in the Carlsbad limestone. Subsequent observations have failed to confirm the presence in the Capitan of concentric structures of the size and abundance reported by Ruedemann. Some of the algae described by Pia and Johnson from the Guadalupe Mountains may have come from the Capitan limestone. The following species described by Johnson appear, from the localities cited by him, to occur in the Capitan:

Solenopora centurionis Pia
Solenopora sp.
Mizzia velebitana Schubert
Mizzia yabei (Karpinsky)
Diplopora? sp.

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⁹⁰Ruedemann, Rudolf, cited in King, P. B., and King, R. E., Pennsylvanian and Permian stratigraphy of the Glass Mountains: Texas Univ. Bull. 2801, p. 159, 1928; Ruedemann, Rudolf, Coralline algae, Guadalupe Mountains: Am. Assoc. Petroleum Geologists Bull., vol. 13, pp. 1079-1080, 1929.

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Pia suggests that some of the forms described from the Capitan by Girty as the sponge Guadalupia are actually the alga Mizzia.

According to Johnson⁹¹ that part of the Capitan interpreted by him as the reef face (p. 63) contains "filamentous green and possibly blue-green algae with red algae becoming abundant near the crest." The reef crest of his interpretation "is composed almost entirely of encrusting algal material (green and red) with colonies of Solenopora locally abundant on the inner slope. Fragments of Dasycladacae occur." The reef flat of his interpretation contains "encrusting and filamentous algae [and] colonies of Solenopora. * * * Algal pisolites occur."

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⁹¹Johnson, J. H., Permian lime-secreting algae from the Guadalupe Mountains, New Mexico: Geol. Soc. America Bull., vol. 53, pp. 216-217, 1942.

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Fusulinids are fairly common in the Capitan limestone, although not as abundant as in the adjacent parts of the Bell Canyon and Carlsbad formations. From the Capitan, Dunbar and Skinner have identified Polydiexodina capitanensis Dunbar and Skinner and P. shumardi Dunbar and Skinner.

Cephalopods occur at a number of places. Of them, the nautiloids are most abundant. According to observations of Girty and Miller, they generally belong to Metacoceras shumardianum (Girty), but Miller has identified a Titanoceras and Girty an "Orthoceras". According to Girty, the collections also contain fragments that probably represent three or four other species. In addition, a few ammonoids have been collected, especially at locality 7417. According to Miller and Furnish, they all belong to the single species Waagenoceras guadalupense Girty.

Regarding the remainder of the fauna, Dr. Girty makes the following comparisons between the original and the later collections:

The Capitan fauna is noteworthy for the variety of its sponges. In Professional Paper 58, they were classified as Anthracosycon ficus capitanense Girty, Virgula neptunia Girty, V. rigida Girty, V. rigida constricta Girty, Pseudovirgula tenuis Girty, Guadalupia zitteliana Girty, G. zitteliana var., G. cylindrica Girty, G. cylindrica concreta Girty, G. digitata Girty, G. favosa Girty, Cystothalmia nodulifera Girty, Cystothalamia? sp., Steinmannia americana Girty, Sollasia? sp., and Amblysiphonella guadalupensis Girty. I now feel that some of the forms listed were too imperfectly known to have deserved naming. Sponges are also abundant in the new collections, which contain Guadalupia zitteliana Girty, G. cylindrica Girty, Anthracosycon ficus guadalupensis Girty, Amblysiphonella guadalupensis Girty, Amblysiphonella sp., Amblysiphonella? n. sp., besides the usual indeterminata. These determinations are provisional and the original material, which was relatively scanty, is in need of revision.

In the two original collections I recognized but two species of corals, Lindstroemia permiana Girty and Campophyllum texanum Shumard?. In the new collections, corals are also poorly represented. I find Campophyllum texanum and probably the form that was described as Lindstroemia cylindrica Girty. These new specimens, however, show a structure suggesting Chonophyllum, but with a much simpler central zone, in the midst of which is a styliform columella; only the columella and the septa showed in the silicified holotype. Definite relationships cannot be established until these two forms have been closely studied by means of thin sections.

Among the bryozoans, the original collections contained Fistulipora grandis guadalupensis Girty, F. guadalupae Girty, Domopora ocellata Girty?, D. terminalis Girty, Tabulipora polyspinosa richardsoni (Girty), Leioclema shumardi Girty?, Fenestella spinulosa Condra?, F. capitanensis Girty, Acanthocladia guadalupensis Girty, Acanthocladia sp., and Goniocladia americana Girty. The bryozoan fauna of the new collections is much smaller. I find only Fistulipora grandis guadalupensis Girty, F. guadalupae Girty, Tabulipora sp., Leioclema shumardi Girty?, and a few poorly preserved specimens of Fenestella I will repeat that identifications of bryozoans made without the study of thin sections are extremely provisional.

Turning to the brachiopods, a species of Crania found in the original collections has no representative in the ones recently made.

Of the Orthotetinae, Streptorhynchus gregarium Girty, Derbya sp. a, Derbya sp. b, Orthotetes guadalupensis Girty, O. declivis Girty, O. distortus Girty, O. distortus campanulatus Girty, Geyerella americana Girty, and Orthotetina sp. were originally distinguished. The new collections contain only Orthotetes sp., O. distortus Girty?, Derbya sp. a, Plicatoderbya? a. sp., and Meekella n. sp. The differences in this group between the old and new are truly noteworthy. Orthotetes which there was abundant is here scarce, but on the other hand we have here Plicatoderbya? and Meekella, two genera that did not appear in the original collections at all. Meekella is particularly interesting, because it is abundant in the older faunas of the section, but is missing from the Bull Canyon formation.

Only one species of Chonetes was recognized in the original collections and the same species, C. hillanus Girty, is found in those recently made.

The productids, as originally listed, consisted of Productus (Marginifera?) waagenianus Girty, P. capitanensis Girty, P. occidentalis Newberry, P. (Pustula?) latidorsatus Girty, P. (Striatifera) pinnaformis Girty, P. (Pustula?) pileolus Shumard, Aulosteges medlicottianus americanus Girty, and Prorichthofenia permiana (Shumard). Only a few of these species have been recognized in the new collections which, on the other hand, contain a number of forms that are at least allied to some that occur in the Pinery limestone. Under this head I would include Productus popei Shumard?, P. popei opimus Girty?, Productus aff. P. limbatus Girty, and Aulosteges guadalupensis Shumard. Of the species listed from the original collections, the new collections contain Productus capitanensis Girty (abundant), P. (Pustula?) latidorsatus Girty, and Prorichthofenia permiana (Shumard). Besides the species mentioned, there are a few not found in either the Capitan or Pinery faunas as previously described: Productus (Avonia?) n. sp., P. (Pustula) n. sp., and Teguliferina? sp.

Products (Avonia?) n. sp., which is abundant at one locality, may be the form that King identified as Avonia signata (Girty), P. (Pustula) n. sp. may be the form that he identified as Avonia meekana (Girty). The authentic meekana belongs to the subgenus Cancrinella. The form cited as Productus aff. P. limbatus Girty is not as well preserved as could be wished, and I am unable to state its relations. This interesting form has features which suggest Aulosteges magnicostatus Girty, but it is certainly not the same species, and probably does not belong to the same genus. Teguliferina? sp. is problematical; it is apparently related to, or derived from Productus or Teguliferina, but is apparently constructed somewhat after the fashion of Proboscidella. It can hardly belong to the latter genus, however, and is apparently new. As already intimated, the productid fauna of the new collections is perhaps more closely related to the fauna of the Pinery limestone member than to that of the Capitan limestone as originally described. At all events, it is in part a combination of species from each fauna.

The only pentameroid from the fauna of the Guadalupe Mountains, Camerophoria, is represented by the common C. venusta Girty in both the old and the new collections.

The rhynchonellids in the original collections included Leiorhynchus? bisulcatum seminuloides (Girty), Wellerella? swallowiana (Shumard), W.? elegans (Girty), W.? shumardiana (Girty), W.? indentata (Shumard), and Camarotaechia? longaeva (Girty). This group has much the same representation in the new collections, except that the first-named species is absent. Wellerella? indentata and W. swallowiana are reversed in point of abundance, the former being relatively abundant in the new collections and the latter relatively rare, and represented by poor, doubtful specimens. In the new collections there are also several doubtful forms, possibly belonging to new species.

Among the terebratuloids, the old collections contained Dielasma spatulatum Girty, D. cordatum Girty, D. sulcatum Girty, D.? scutulatum Girty, Dielasmina guadalupensis Girty, Notothyris schuchertensis Girty, N. schuchertensis ovata Girty, Heterelasma shumardianum Girty, and H. venustulum Girty. The new collections are less diversified, and contain only Dielasma cordatum, D. spatulatum, D. prolongatum Girty, Dielasmina guadalupensis, and Heterelasma venustulum.

The spiriferoids were represented in the old collections by numerous species of Spirifer, Spiriferina, Squamularia, Martinia, and Ambocoelia. The same genera occur in the new collections, but the specific representation is smaller, Under Spirifer itself, I originally recognized S. mexicanus Shumard and, the variety compactus Girty. In the new collections, I find S. mexicanus, the varieties compactus and latus King, and also S. sulcifer Shumard?. Under Spiriferina, I originally recognized S. welleri Girty, S. pyramidalis Girty, S. billingsi Shumard, S. billingsi retusa Girty, S. evax Girty, and S. sulcata Girty. The new collections contain the first three species named, and also S. laxa Girty (described from the Pinery), and Spiriferina n. sp.

Under Squamularia, I originally recognized S. guadalupensis (Shumard), with the varieties S. g. subquadrata Girty and S. g. ovalis Girty, but I now think the last two hardly deserved varietal names. Only one of the new collections contains shells of this genus, and I am referring all of them to S. guadalupensis. Under the genus Martinia, I originally described two species, M. rhomboidalis Girty and M. shumardiana Girty. In the new collections, the genus occurs at only one locality. Pending more careful study, I am referring all the specimens to M. rhomboidalis. Ambocoelia planiconvexa guadalupensis Girty occurs in both the old and new collections, and is the only representative of this genus.

Composita, in the old collections, was represented only by C. emarginata Girty and the variety affinis Girty. In the new collections, the genus is abundant and decidedly more diversified. Most striking is a very large species which is provisionally compared with C. gigantea Branson. There is also present a species which may be cited as Composita aff. C. subtilita (Hall). C. emarginata is doubtfully identified, save in one collection. Specimens have also been referred to its variety C. e. affinis, and to C. mira (Girty)?

Hustedia, in the old collections, was represented by H. meekana (Shumard) and the variety H. m. trigonalis Girty. The new collections contain only a few specimens of this genus, all of which are provisionally referred to H. meekana.

Leptodus is present in the new collections, as in the old, It is rather abundant, and some of the specimens are of large size. All, however, are for the present referred to L. americanus Girty.

The pelecypod fauna, as originally described, was diversified, although but few of the species were represented by more than a specimen or two. They were classified under Edmondia, Paralleladon, Pteria, Myalina, Schizodus, Camptonectes, Aviculipecten, Euchandria, Pernopecten, Plagiostoma, Limatulina, Myoconcha, and Cypricardinia. Most of the same genera are represented in the new collections, but some of the species are not the same. This suggests that the pelecypod fauna is highly diversified, but poor in individuals. I might add that more than half the pelecypods considered in the following paragraphs occur in a single collection (No. 7417, from older part of formation near Grisham-Hunter Camp).

Allorisma, a genus not found in the old collections, is represented by a single doubtful specimen. It is a fragment of a large shell marked by concentric lirae and fairly strong concentric corrugations, The lirae are covered with small, rounded tubercules set close together.

The old collections contained a small form described as Edmondia? bellula Girty. The new collections contain a species equally doubtful as to generic position, but of large size. It does not belong to the strongly corrugated section of the genus, but is apparently almost smooth and is related to a number of smooth, transverse shells referred to Edmondia, especially to the Mississippian species E. fountainensis Weller. My specimens are few and in poor condition.

Parallelodon had two species in the old collections, P. politus Girty and P. multistriatus Girty, neither of which is notable for its size. This is not true of the specimens recently collected. P. politus has not been definitely identified among them, but there is a finely striated species which may belong to P. multistriatus, although some of the specimens are very much larger than the type. There is another large species (a. sp. b), marked by coarse, strong costae which were apparently crossed by strong concentric lamellae. A third species (n. sp. a) is represented by a single specimen of enormous size, showing at the anterior end (where alone the shell is present) only strong, flaring lamellae which interrupt a few subdued, moderately coarse costae. A fourth specimen of doubtful relations represents the median part of a still larger specimen. The surface is marked by fine, radial striae and rather fine, concentric lirae, together with varices of growth of different size and intensity. In places, especially toward the ventral border, the striae appear to be interrupted and to have the form of pustules, but by their linear arrangement to maintain the appearance of radial costae. To some extent, then, this fragment recalls the one cited as Allerisma? sp., and it is not impossible (although at present it seems improbable), that both may belong to the same species but represent different parts of the shell. One very conspicuous difference is that in this form the ornamentation (including the pustules) is conspicuously radial, and in the other it is conspicuously concentric.

Pteria, represented in the old collections by P. guadalupensis Girty, has not been recognized in the new ones. Myalina squamosa Sowerby? was included in the original fauna, but the genus is represented in the new collections by only two doubtful specimens, neither of which is the same as the species cited. Schizodus was represented in the original collections by a rather small form identified as S. securus Shumard?. In the new collections, the congeneric species is large, and more comparable to S. symmetrica Calvin than to any other of our later Paleozoic species. Three species were described under Camptonectes? in the original collections, C. ? asperatus Girty, C. ? papillatus Girty, and C. ? sculptilis Girty. The specimens in the new collections seem to belong to the first two of the species named.

Under the genus Aviculipecten, the old collections had three species, described under the names A. infelix Girty, A. laqueatus Girty, and A. sublaqueatus Girty. A recent revision of our upper Paleozoic pectenoids redistributes these specimens generically. They thus become Streblochondria ? infelix (Girty), Acanthopecten laqueatus (Girty), and Girtypecten sublaqueatus (Girty). The new collections contain Girtypecten sublaqueatus and Acanthopecten? n. sp. besides two indeterminable species of Aviculopecten. Still among the pectenoids, the old collections contain Euchandria? sp. and Pernopecten obliquus Girty. The new collections contain the latter species, and also a remarkable specimen that suggests the genus Obliquipecten, and may belong to that genus so far as the facts are known. It is somewhat imperfect and the greater part of the shell is missing. At first glance the specimen looks like a left valve of a fair-sized Myalina, of the type in which the anterior outline is strongly concave. On closer examination, however, one sees an incomplete anterior auricle and also a few fine radial costae on the anterior side of the umbo, which is the only part where the shell is preserved. Some irregularities on the internal mold by which the greater part of the specimen is represented suggests the presence of a few coarse, weak costae. I would be disinclined to place this form under Pseudomonotis, which is suggested by the surface characters, because of the configuration, especially because it is so strongly prosogyrate. The shape, on the other hand, corresponds remarkably to that of the ventral valve of Obliquipecten.

To Pseudomonotis, a genus not represented in the early collections. I am referring three species from the new collections. All are decorticated and probably not of use in describing the new species which they apparently represent. One is a large form which is nearly flat, and is smooth except for a few large, loose, marginal plications. It has the general appearance of P. spinosa Sayre, but of course little or nothing is known about the surface characters. The second form is much smaller, with large, strong, irregular plications. A much smaller portion of the umbonal region is relatively smooth. Here again, finer details of the surface are unknown. A third species, represented by a single specimen, is small, narrow, and highly convex. Part of the shell is preserved, showing very strong, rather fine, radial costae, alternating in size and closely arranged. No large irregularities of surface are developed.

The Limidae were represented by two species in the old collections, Plagiostoma deltoideum Girty and Limatulina striaticostata Girty. Only the latter is present in the new collections.

The genus Pinna, not represented in the old material from the Guadalupe Mountains, is represented in the new collections by a single specimen. It is smooth-surfaced, and if the sculpture possessed by most species of Aviculopinna is characteristic of that genus, the specimen in question does not belong to it. On the other hand, it certainly does not belong to Pinna peracuta Shumard, for it is much smaller, and has much more rapidly diverging outlines.

The old collections contain a species described as Myoconcha costulata Girty. The new ones contain a similar, but apparently distinct species. They also contain two other species that are perhaps congeneric. One is small, but considerably larger than M. costulata, and is distinguished from it by being entirely smooth. The third form is large, and represented by a considerable number of specimens. Nevertheless, all of them are more or less imperfect and more study is required before one can reconstruct the original characters. This form may not be congeneric with M. costulata, but wherever it belongs, it is a species new to the fauna.

The old collections contain a species of Cypricardinia (C.? contracta Girty), but nothing of the sort has been found in the new ones. On the other hand, Pleurophorus was not represented in the old collections, whereas one, and possibly two species are found in the new ones. One species is a small and elegant form related to P. occidentalis Meek and Hayden, as usually interpreted. The other is an uncommonly large shell of doubtful affinities. It may prove not to belong to the genus at all.

Before leaving the pelecypods, mention should he made of a remarkable genus which, so far as I know, is new to our American later Paleozoic faunas, if not to science. The shell is fairly large, the valves elongated, oblique, and extremely convex, leading back to an umbo which is compressed and strongly prosogyrate. In fact, the valves, taken separately, resemble one of those platyceroid shells that make only part of a turn and are narrowly rounded across the anterior surface. The only specimen in my collection, however, retains the valves in articulation and half open. Furthermore, the surface is marked by fine, faint, regular radial lirae.

The scaphopods, which are not found in the old collections, occur in one of the new ones in moderate abundance. Only one species is recognized, which attains a rather large size. It is elongated, straight, and gently tapering. The surface seems to be smooth, or at most marked only by incremental lines. So far as the characters are shown, this might be the species that I customarily identify as Plagioglypta canna White. Mention should be made of one remarkable slab in which three of these specimens occur almost in contact, and directed to a common center. Whether they lived in that relation, or were so arranged by current action, is uncertain.

The fauna as originally described contains the following gastropods: Patella capitanensis Girty, Pleurotomaria mica Girty, P. discoidea Girty, P. neglecta Girty, Euconospira obsoleta Girty, Trochus ? sp., and Zygopleura swallowiana (Shumard). The absence from this list of any of the bellerophontids is noteworthy. A few bellerophontids occur in the collections recently made, but their preservation is such that definite generic assignments are impracticable.

The pleurotomaroids are mostly small shells, and their classification requires more careful study and deliberate consideration than it has been possible to devote to them. Without going into details, I may predict that some of the species cited in Professional Paper 58 do not occur in the new collections, but that the new collections contain a number of species not there cited. One species of this family, however, Euconospira obsoleta Girty, is fairly common, and may prove to be the type of a new genus. Some of the specimens of it in the new collections are remarkable for the fact that color markings are still preserved on the surface.

The only other gastropods cited from the Capitan in Professional Paper 58 are a small, indeterminable shell, and Zygopleura swallowiana (Shumard), a species which was described by Shumard, but which I did not recognize in my collections. No species of Zygopleura has been recognized in the new collections, but they contain a number of genera not heretofore known in this fauna. At one locality, fragments that belong to Naticopsis, or some closely related genus, belong to one or more species of relatively huge proportions. Another collection has furnished one, and possibly two species of Naticopsis of more moderate size, provided they are not young specimens of the larger species. A fragmentary specimen from another locality represents an elongate, deeply embracing shell, probably belonging to the genus Meekospira, and the same locality has furnished two imperfect specimens of a form that at first suggests a very large, spreading species of Zygopleura, whose flat, sloping sides bear coarse, transverse plications. The basal surface, however, is flat or even concave, and the columella appears to be perforate. The generic position of this curious species is uncertain for the shell is in large measure destroyed.

The trilobites continue to be represented by the characteristic species Anisopyge perannulata (Shumard), which ranges practically throughout the Guadalupe Mountains section.—Girty manuscript.

CARLSBAD LIMESTONE

The fauna of the Carlsbad limestone was largely unknown before the present investigation. One of Girty's original collections (No. 2905) may belong to the formation, but is hardly typical of its fauna as now known. Another collection, made later by Darton and Reeside⁹² from near Carlsbad Cave and reported on by Girty, is more nearly like the assemblages observed during the present work. The report that follows is based primarily on three rather large collections made by H. C. Fountain (Nos. 7415, 7416, and 7427, pl. 2), all of which came from the summits of the Guadalupe Mountains northeast of Guadalupe Peak. The manner of preservation of the fauna has already been noted (p. 65).

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⁹²Darton, N. H., and Reeside, J. B., Jr., Guadalupe group: Geol. Soc. America Bull., vol. 37, pp. 427-428, 1926.

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The Carlsbad fauna has some resemblances to the Capitan fauna, but the collections reveal marked differences between them. These differences are more startling because collections from the two formations are from rocks of approximately the same age, that lie only a few miles from each other. In particular, as indicated by Dr. Girty's report, a number of characteristic later Paleozoic brachiopod groups and genera are not present, although they occur in all the other rocks of the Guadalupe Mountains section.

Near the Capitan reef, the Carlsbad limestone contains numerous lime-secreting algae, some of which have been identified by Pia and Johnson. Some of the species cited below may have come from the Capitan rather than the Carlsbad limestone, and Johnson cites a number that occur in both formations. From collections near Carlsbad Cavern by G. A. Kroenlein and J. E. Adams, and from my collections in the southern Guadalupe Mountains, Pia lists:

Mizzia velebitana Schubert
Macroporella verticillata Pia
M. calcipora Pia
Solenopora centurionis Pia
Solenopora sp.
Gymnocodium n. sp.

From collections between Carlsbad Cavern and Carlsbad, Johnson lists:

Solenopora centurionis Pia
Solenopora sp.
Mizzia minuta Johnson and Dorr
Mizzia yabei (Karpinsky)
Macroporella sp. ?
Anthracoporella sp. ?
Diplopora sp. ?
Girvanella sp.
Colenella guadalupensis Johnson

The pisolites which occur abundantly in the Carlsbad limestone have been mentioned on page 65, and are considered by some paleontologists to be of algal origin. They are described as follows by Johnson:⁹³

As typically developed the pisolites are spherical or subspherical with flattened base and top. The average size is from 0.6 to 1.1 centimeter, and in many deposits they are surprisingly uniform. In very rare cases they grow much larger, and smaller ones also occur. They are formed of thin layers of material more or less concentrically arranged around a nucleus. In small pisolites and in the central portions of larger ones the layers are concentric, completely enveloping those beneath. As the object becomes larger, however, the layers tend to envelop the mass only partially, and the "pisolites" become flattened and rudely elliptical in cross section. The individual layers are seldom of uniform thickness. The irregularity becomes more pronounced in the outer layers where they thin out toward the margins. The nucleus may be a small gastropod, foraminifer, a segment of a Dasycladacae or a fragment of some other fossil; only rarely is the nucleus of inorganic material.

Microscopic examination shows the layers to be composed of very fine particles of calcium carbonate in most cases. Some show a definitely crystalline structure. This is considered as probably secondary since it is best developed in the outer layers. Even under high magnification no cellular structure could be definitely observed although vague suggestions of a feltlike mat of filaments were occasionally found. A few Girvanella tubes were observed in some of the pisolites. However, these were also observed in about the same abundance in most of the other objects studied, so their presence is considered more or less accidental.

In some localities small pisolites occur which show a structure of fine radiating needle-like crystals with concentric layers absent or poorly developed. Except for size these are like the small oolites present in many of the specimens. These are interpreted as of inorganic origin.

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⁹³Johnson, J. H., Permian lime-secreting algae from the Guadalupe Mountains. New Mexico: Geol. Soc. America Bull., vol. 53, p. 213, 1942.

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The pisolites have been variously interpreted. Johnson considers them of organic origin, whereas Pia believes they are inorganic. Johnson ⁹⁴ states:

The writer believes that the majority of the "pisolites" are of algal origin, representing calcareous material deposited around the outer (growing) layers of colonies of low types of blue-green algae and fine silt and organic debris caught in the outer growing layers of such colonies. The structure suggests growth layers which start as a coating about a small object and grow concentrically until the colony becomes large enough to cut off the light from the basal portion, which, as the mass becomes larger, is more and more likely to be partly buried in the fine debris of the lagoon bottom. It may be that from time to time they were rolled over by tides or storm waves or other causes, and growth continued on the upper surfaces.

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⁹⁴Johnson, J. H., op. cit., p. 213.

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Pia⁹⁵ states:

Johnson (1938) states that he has observed the genus Girvanella in the Carlsbad limestone. I have not seen anything of the sort in my material. It seems probable that Johnson has considered certain pisolites to be Girvanella, perhaps the same ones that Ruedemann called "coralline algae." The commonest of these appear to be approximately spherical forms with fine concentric lamination. The samples of rock at my disposal contain balls from 1 millimeter to 7 centimeters in diameter. * * * Besides these pisolites, there are also irregularly sinuous laminations in the rocks, radiating sinter, and finely tufted growths. All these structures appear in places in the lagoon facies behind the reefs. * * * The chief interest of the structures mentioned lies in their surprising similarity to the well-known concretions in the Magnesian Limestone of Durham, in England. Probably we are dealing in both areas with similar chemical processes. It is noteworthy that such processes took place in two such widely separated regions at approximately the same time, and that they took place in a quantity that has not been recorded from any other part of the section, with perhaps the exception of the Algonkian.

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⁹⁵Pia J. V., Vorläufige, übersicht der kalkalgen des Perms von Nordamerika: Akad. Wiss. Wien, Math.-Natuurwiss. Kl., Anz., 9, preprint, June 13, 1940. Translation by John Rodgers.

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In the same area that has yielded the algae, associated beds contain numerous fusulinids. According to Dunbar and Skinner, they include the large species Polydiexodina capitanensis Dunbar and Skinner, and P. shumardi Dunbar and Skinner, and the small species Leëlla bellula Dunbar and Skinner, Codonofusiella paradoxica Dunbar and Skinner, and Staffella fountaini Dunbar and Skinner.

Regarding the remainder of the fauna, Dr. Girty reports:

The sponges of the formation belong to only one species, provisionally identified as Guadalupia cylindrica Girty. The corals are still present, but are represented by a single specimen which does not show structure sufficiently for even a tentative identification. Bryozoans are without a single representative.

Among the brachiopods, the orthoids are, unrepresented, as they have been in several of the preceding units.

The Orthotetinae are represented by two rather remarkable species Plicatoderbya, n. sp. and Derbya n. sp. besides which one dorsal valve is provisionally referred to Streptorhynchus pygmaeum Girty. Aside from these, none of the other Guadalupian genera are present. The Plicatoderbya is of uncommon size, with a rather highly convex dorsal valve and a rather high ventral valve. The surface is marked by very fine and very irregular radiating lirae. In addition, the surface in varying degree is very uneven, after a somewhat definite pattern. Where most conspicuous, this feature consists of innumerable small pits which necessarily leave short ridges between them. The pits may be fine or coarse, few or very numerous, and in some specimens the pits, in other the ridges, are the most obvious features. The ridges show no linear arrangement, but where an arrangement is slightly apparent, it is rather decussating than radial. The form is referred to Plicatoderbya, in spite of the lack of definite radial plications, for it seems less out of place in that relationship than in Derbya. The internal structure appears to be that of Derbya, the septum reaching to and coalescing with the deltidium, although the plates are considerably thickened and confused with callus. The Derbya n. sp. is small and in shape rather elongate than transverse. The ventral valve is very high and the growth very irregular. It is possible that this Derbya may be an extreme variety of the other species, in spite of the numerous differences shown. This form is represented by only a few specimens, whereas the other is abundant.

Chonetes is unrepresented, and what is remarkable for a later Paleozoic fauna, so are all the tribes of productids. Prorichthofenia, on the other hand, occurs in great abundance. I am not sure, however, that all the specimens belong to the same species, for some are uncommonly large, others uncommonly long and tapering. Provisionally, all of them may be referred to P. permiana (Shumard).

Camerophoria, which has ranged throughout the many units of the section, is unrepresented.

Rhynchonellids still persist, but are reduced in numbers and variety. I recognize two species, Wellerella ? swallowiana (Shumard) var. and Camarotaechia? longaeva (Girty). The first type is distinguished from typical Wellerella ? swallowiana by having two instead of three plications on the fold, and all the specimens in the new collections are of this character. Similar forms have also been observed in the Capitan limestone. The second type is identified on the basis of a single, immature specimen.

Terebratuloids are uncommonly abundant and diversified. The following species are tentatively distinguished: Dielasma? scutulatum Girty?, Dielasma sp., Dielasmina guadalupensis Girty, Dielasmina a. sp. ?, Cryptocanthia n. sp., Notothyris? sp.

The entire family of the spiriferoids is unrepresented.

Composita is represented by two species, or by what one might regard as a small-sized and large-sized variety of the same species. The large form resembles C. ovata Mather, as figured by Dunbar and Condra,⁹⁶ and may be so identified. The small form has the characters of C. mexicana (Hall), where the fold and sinus are strong, and of C. argentea (Shepard) (as identified by Dunbar and Condra), where the fold and sinus are relatively weak. These shells were found at two localities and all of those from one locality are of the small species, and all of those from the other locality of the large species.

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⁹⁶Dunham, C. O., and Condra, G. E., Brachiopoda of the Pennsylvanian system in Nebraska: Nebraska Geol. Survey Bull. 5, 2d ser., pl. 43, fig. 14, 1952.

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Hustedia and Leptodus, both of which have ranged throughout the section, and occur in the Capitan limestone, have not been recognized in the collections from the Carlsbad.

Among the pelecypods, the genus Parallelodon is represented by at least two very distinct species. One is large and marked by very coarse radial costae, cancellated by strong concentric lamellae. This species is clearly allied to the one designated as Parallelodon sp. b of the Capitan fauna, if not identical with it. The other is smaller and much more finely marked. It may be identified as P. multistriatus Girty, which was also found in the Capitan limestone.

The pectenoids, insofar as hinge structure is concerned, are not determinable generically, and as none is complete as to outline and few retain more than patches of the shell, they cannot in some instances be distinguished specifically. For this reason, there is some doubt whether any of the species in this fauna are present in the Capitan limestone. On the other hand, it is certain that some of the Capitan species are not found here. Again, although none of the species is sufficiently well preserved for description, several show enough characteristics to indicate that they have not yet been described.

In this group, I recognize the following: Acanthopecten a. sp. (this is not the same as Acanthopecten? sp. of the Capitan fauna, but is more nearly related to A. carboniferus Stevens; Fasciculoconcha n. sp. (a large form with large costae, which occur in groups of three subcostae, a large one in the middle and a small one on each side, with a still smaller one in the grooves between the costae); Aviculopecten sp. a (a large form with moderately coarse costae, rising abruptly from somewhat narrow striae. The costae are flat on top, with a somewhat faint median groove, and all are crossed by fine, strong, regular, closely spaced crenulations). Besides these three sharply defined species, there are a number of specimens that suggest still other species, but are too poorly preserved for their relations to be determined.

Other pelecypods have been classed as Camptonectes sculptilis Girty, Streblochondria? sp., Pernopecten obliquus Girty, Myalina aff. M. perattenuata Meek and Hayden, Conocardium n. sp., Pseudomonotis? sp., Myoconcha sp. a, Myoconcha sp. b, Pleurophorus aff. P. tropidophorus Meek, Cypricardinia aff. carbonaria Meek. Some of these species have been recognized in the Capitan fauna (Pernopecten obliquus, Myoconcha spp. a and b). Others belong to the same genera but are different specifically (Camptonectes and Pleurophorus). Comments upon two of these species may not be out of place. The Conocardium is a rather small form with a very high, stout carina on the umbonal swelling. Pseudomonotis? sp. is used for a single rather small specimen which is nearly flat and marked only by concentric lines and varices of growth. Similar shells have sometimes been referred to Placunopsis.

Scaphopods seem to be rather abundant, but of course are fragmentary, and most of the specimens are internal molds. They are long, straight, gently tapering shells and where any surface characters are shown at all they consist only of obscure, transverse striae. So far as can be determined this is the same species that occurs in the Capitan fauna, and that one I have identified as Plagioglypta canna White.

The gastropods show a wide differentiation, and are uncommonly numerous.

Bellerophontid shells are numerous, in fact much more so than in the Capitan limestone, but most of them are so exfoliated that their generic relations can only be guessed. Many of them are of large size, and one may be cited as Bellerophon aff. B. giganteus Worthen, although neither Worthen's type nor the Guadalupian shell can be definitely referred to Bellerophon s. s. Bucanopsis and Euphemites can be recognized generically, but the specific relations of the specimens so referred are uncertain, save that they probably belong to species as yet undescribed.

As already mentioned, most of the Guadalupian pleurotomaroids are small shells with fine sculpture. For the detailed study required to classify them intelligently, I have not yet had time. For the most part, therefore, only general remarks can safely be made. Shells of this family are extremely abundant and, as already noted, mostly small. Many specimens are too poor for classification. Pleurotomaria richardsoni Girty, and forms related to it, far outnumber all the other types put together. Besides P. richardsoni there are two or three closely related forms which can be recognized as distinct varieties. Aside from this group there are a considerable number of distinguishable species, all probably new, but many of them represented by material too poor for descriptive purposes. The only large species, the one that was described in Professional Paper 58 as Euconospira obsoleta Girty, is fairly abundant. Its occurrence in the Capitan fauna has already been noted.

One of the outstanding features of the present fauna is the development of naticoid shells. One form which may be designated as Naticopsis n. sp. a, is notable for its size. Even Naticopsis altonensis gigantea Meek and Worthen looks small beside it. Nor, indeed, does it belong to the altonensis group at all, as it has regularly rounded whorls and is marked only by fine incremental lines. The spire is moderately high and the suture recessed. It resembles somewhat N. madisonensis Worthen, but is more spherical in shape. Another species may be cited as Naticopsis aff. N. tayloriana Girty. This species is very abundant at one locality and a few unusually large specimens have been referred to it from another. It has the general configuration of N. tayloriana but is three or four times as large, for the species named is a rather diminutive shell. The species, however, is very much smaller than Naticopsis n. sp. a. The following also belong in this group: Naticopsis aff. N. gracillis Branson (a shell of moderate size with a very low spire), Naticopsis aff. N. hartti Bell (a rather small, elongated shell, consisting of a few volutions, of which the last one comprises most of the height), Naticopsis aff. N. permiana Beede (a species with rather numerous, rounded volutions and a moderately high spire. It is of the same general configuration as Beede's species but differs in its surface characters. All the Guadalupian shells are without surface markings, except for incremental lines). Most, if not all, of these species are probably new and several at least are sufficiently well known for description.

Trachydomia is represented by five species, all probably new. One is related to T. wheeleri (Swallow), T. owenii Knight, and similar forms, but is small, slender, and high-spired. For another, I know of no closely comparable species. The third may possibly belong to the genus Turbonitella. Two may prove to represent an undescribed genus. These shells are large and extremely ornate, with nodes of different sizes, and in addition the surface is crossed by fine, sharp, transverse lirae, which have a very irregular course that follows the nodes decorating the surface. I have never seen any species similar to these in our Carboniferous faunas. This type is fairly abundant, but because of its exceedingly rough surface the shell tends to peel off and leave only internal molds. When the specimens have been sufficiently cleaned from the matrix for close study, it is not unlikely that they will be classified into more than the two species here recorded.

In addition to the forms already discussed, there are various other gastropod types in the Carlsbad. Some of these have not yet been accurately placed as to genera and many of the species appear to be new; some are represented by specimens too poor for a description. At present, they may be listed as follows: Zygopleura of two or three species, Helicostylus sp., Bulimorpha chrysalis delawarensis Girty, another long and slender species of the same genus, Strobeus? sp., Trochus? sp., Eotrochus? sp., Aclisina? sp., Orthonema? sp., and Streptacis? of three species. This last name is employed for slender, high-spired shells with rounded, smooth, and slightly embracing volutions. In no instance has the peculiar character distinctive of the genus been observed; in fact, most of the specimens are in a poor state of preservation.

The cephalopods are represented only by a fragmentary "Orthoceras," possibly "O." guadalupense Girty, and a very small and doubtful ammonoid. The trilobite, Anisopyge perannulata (Shumard), continues to be present, and in one collection is abundant.—Girty manuscript.

In considering the Carlsbad fauna as a whole, and in comparing it with other faunas of the Guadalupe Mountains, Dr. Girty makes the following summary:

The fauna of the Carlsbad limestone offers many contrasts to that of the Capitan limestone, but none are more notable than in the brachiopods. As against nearly 50 species in the Capitan, the Carlsbad contains but 14. What is more remarkable, the two great groups of later Paleozoic brachiopods, the productids and spiriferoids, are unrepresented. Moreover, the genera Meekella, Chonetes, Aulosteges, Camerophoria, Hustedia, and Leptodus are no longer present, and the rhynchonellids are reduced in number. The forms chiefly present belong to the Orthotetinae and the Terebratulidae, but Prorichthofenia continues to be fairly abundant, as it was in the other faunas.

Pelecypods are well represented in both faunas as regards variety, but they are much more numerous in the Capitan which has afforded almost twice as many species as the Carlsbad. Some of the species are held in common by the two faunas, but a number of genera are different, and where the genera are the same the species are sometimes different. For instance, under Camptonectes the Capitan fauna has C. asperatus Girty and C. papillatus Girty, whereas the Carlsbad fauna has C. sculptilis Girty. Again, in Pleurophorus, the Capitan fauna has a species related to P. occidentalis Meek and Hayden, whereas the Carlsbad fauna has a species related to P. tropidophorus Meek. As our knowledge of the two faunas, which at present is but scattering, becomes more complete, it is not unlikely that some of these differences will disappear.

If the Capitan fauna has the most pelecypods, the Carlsbad fauna has the most gastropods, the ratio probably being nearly two to one. It would not be safe to go into details in this matter, for the recognition of genera and species among Paleozoic gastropods requires such close study that any details given now would probably require numerous corrections after the descriptive work was done. It is safe to say that the gastropod fauna of the Carlsbad is much richer in individuals than the Capitan, and also is more varied, and that a marked difference in the pleurotomaroids will be found, and also in the naticoid shells, especially in the large and beautiful shells at present included under Trachydomia.

Neither fauna has any cephalopods to boast of, and the trilobite representation is the same in both.

One more difference between the Carlsbad and Capitan faunas should not be passed over. The calcisponges, which were diverse and abundant in the Capitan, are reduced to a single species in the Carlsbad.—Girty manuscript.

Considerably to the north of the area treated in this report, in the Seven Rivers Hills (fig. 2), the Azotea tongue of the Carlsbad limestone contains a few fossils at localities first discovered by Beede.⁹⁷ This area lay much farther northwest of the Delaware Basin and Capitan reef zone than any part of the area of this report, and most of the rocks of the vicinity, belonging to the Carlsbad and Chalk Bluff formations, are unfossiliferous. The fossils that occur are impoverished in number and variety, and so far as known are not like those in the Carlsbad limestone farther south.

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⁹⁷Beede, J. W., The correlation of the Guadalupian and Kansas sections: Am. Jour. Sci., 4th ser., vol. 30, pp. 135-136, 1910.

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From a locality on the north side of the Seven Rivers Hills, 6 miles southwest of Lakewood, N. Mex., which was originally discovered by Beede, Newell⁹⁸ has collected and identified the pelecypods Dozierella gouldii (Beede) and Pleurophorus albequus Beede. According to Beede, minute gastropods and casts of ostracods occur at the same place. Beede mentions another locality 13 miles west of Carlsbad and 5 miles west of McKittrick Spring, where similar fossils were collected.

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⁹⁸Newell, N. D., Invertibrate fauna of the late Permian Whitehorse sandstone: Geol. Soc. America Bull., vol. 51, locality 11, pp. 279-280, 1939.

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This northern fauna of the Carlsbad is of interest because it closely resembles that of the fossiliferous beds in the lower part of the Whitehorse group in central Texas and southwestern Oklahoma. This relationship was first noted by Beede, and is confirmed by the two species identified by Newell, which also occur in the Whitehorse. The correlation suggested by the fossils has been verified by physical methods, on the basis of subsurface information.

CONDITIONS OF DEPOSITION

REGIONAL RELATIONS

During upper Guadalupe time strata of three contrasting facies were deposited in different parts of the southern Guadalupe Mountains area. To the southeast, in what is now the Delaware Mountains, the Delaware Basin received deposits of sandstone with a few thin limestone beds; farther northwest, on the southeast edge of what is now the Guadalupe Mountains, massive limestone deposits of the Capitan accumulated along the margin of the basin; a few miles farther northwest, these gave place to thin-bedded limestones and associated sandstones of the Carlsbad which were spread extensively over the shelf area (pl. 7, A).

The boundaries of the three facies, marked by the places at which the Capitan limestone changes on the one hand into the Bell Canyon deposits and on the other hand into the Carlsbad deposits, extend in a north-northeast direction across the area (lines B and F, fig. 10). Minor, and seemingly unrelated changes have the same trend so far as they have been traced. Thus, the change from the fusulinid and pisolite-bearing Carlsbad limestone into the unfossiliferous, varicolored northwestern facies (line A), and also the changes in the texture and color of the limestone members of the Bell Canyon formation (lines F and G), all take place along north-northeast-trending lines.

The rocks of the three facies, each representing approximately the same interval of time, have very different thicknesses. The Bell Canyon formation is 600 or 700 feet thick, the Capitan limestone and associated deposits are 1,500 to 2,000 feet thick, and the Carlsbad limestone and associated deposits are 800 to 1,000 feet thick. The deposits along the margin of the Delaware Basin were thus much thicker than those on either side, and the deposits outside the basin were somewhat thicker than those within it.

In reconstructing the form of these deposits of various thicknesses, the same methods have been used as for the similar deposits of the middle part of the Guadalupe series. Observations have been made on the structure of the deposits exposed along escarpments and canyon walls where the effects of later deformation can be accounted for, and deductions have been made, from the nature of the deposits themselves, as to the environments in which they were laid down.

The present structure of the deposits of the upper part of the Guadalupe series is shown by the sections on plate 17, of which F—F' and K—K' are particularly instructive, because they provide long, continuous views of the rocks of the unit, the first covering its upper half, and the second its lower half. Less continuous, but similar views are shown on the other sections, which suggest that the relations are the same in the intervening areas. The observations thus obtained are summarized on plate 7, A, which shows the probable arrangement of the rocks as they existed at the close of Permian time. The probable form of the deposits at the close of Guadalupe time are shown in section d, plate 7, B.

The surface of the deposits at the time of deposition probably consisted of: a broad, shallow sea bottom in the shelf area, where the Carlsbad deposits were laid down; a steep, southeastward slope across the marginal area, where the Capitan reef was laid down; and a deep-lying, more or less level floor in the basin itself, where the Bell Canyon formation was deposited.

The form assumed by the deposits was probably controlled by the differential subsidence of the area, which thereby brought about a set of contrasting environments of sedimentation. As during the preceding stages, the Delaware Basin continued to subside to a greater extent and more rapidly than the surrounding areas. Sedimentation outside the basin and along its margin kept pace with the subsidence, so that its approximate measure is given by the thickness of the beds laid down there. Within the basin, where the deposits are thinner, the influx of sediments was probably slow and the sea floor was not built up to the same height as in the surrounding areas. At the margin of the Delaware Basin, between the areas of greater and less subsidence, the beds were probably flexed down to the southeast in a similar manner, but to a less degree, than the beds were during an earlier period along the Bone Spring flexure.

SANDS OF THE DELAWARE BASIN

The sands in the Bell Canyon formation, which were laid down in the Delaware Basin, are very fine grained, with abundant accessory minerals derived from igneous and metamorphic rocks. The material must have entered the basin very slowly, as only a small thickness of deposit was laid down there, in comparison with the greater thickness of contemporaneous deposits outside the basin. The basin was at this time nearly encircled by higher-standing, more continuous, purer limestone deposits than before (fig. 14, B), which probably acted as a barrier and hindered material from being washed in from the sides. Shorewards from the barrier, however, some sands were being deposited in the Carlsbad limestone which are coarser than those in the basin. At the end of Guadalupe time, deposition of sandstone ended abruptly; the great thicknesses of the succeeding Ochoa series contain no embedded clastic material.

The occurrence of coarse sandstones interbedded with the Carlsbad limestone indicates that clastic material was being washed into the region from the north, and it may be that some of this sand was able to reach the basin through small openings in the surrounding limestone barriers. Where could such openings exist? The Capitan reef is best known along the outcrops in the Guadalupe, Apache, and Glass Mountains, and in the subsurface on the east side of the Delaware Basin (fig. 3). Here the reef is thick and contains no interbedded sandstone. In these areas, it trends in nearly straight lines in several directions (fig. 14, B). These directions may have been controlled by lines of weakness in the underlying rocks that served to outline the edges of the basin. Between these straight stretches, the reef apparently curved from one trend to the other, with little or no structural control. Such places probably exist beneath the Salt Basin southwest of the Guadalupe Mountains, at the entrance to the Sheffield Channel northeast of the Glass Mountains, and in southeastern New Mexico, but their existence cannot be proved because the reef is comparatively little known in these areas. In the areas between the straight stretches, the Capitan deposit may have been less pure, less continuous, or dispersed over a wider area. If so, it is at such places that small openings in the reef existed, through which sands coming from the north were able to reach the basin. It has been suggested by⁹⁹ that the sand in the basin is of such fine texture that it could have been carried there by the wind.

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⁹⁹Adams, J. E., Oil pool of open reservoir type: Am. Assoc. Petroleum Geologists Bull., vol. 20, p. 789, 1956.

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Other possibilities are suggested by the absence of clastic material in the overlying Ochoa series. According to the interpretation here adopted, limestone barriers were no longer growing around the edge of the basin during early Ochoa (Castile) time (fig. 14, C), and any clastic material being washed toward the basin from the north was free to enter it. As very little clastic material did enter the basin in Ochoa time, the lands to the north from which it was derived in Guadalupe time had probably been peneplaned or buried.

The Ochoa series, beginning with the Castile formation at the base, is dominantly of evaporite facies, and was probably deposited in water that was partly shut off from free access to the sea. This closing off probably resulted from the growth of a barrier across the southwestern entrance of the Delaware Basin at the beginning of Ochoa time (fig. 14, C). If any considerable part of the sands laid down in the basin in Guadalupe time had come from this direction rather than from the north, the barrier would have prevented them from entering during Ochoa time. The same barrier that brought about the deposition of evaporites in the Delaware Basin may, therefore, have caused the ending of sandstone deposition in the same area.

The two discontinuous volcanic ash layers in the Hegler and Rader members of the Bell Canyon formation probably had the same source as the more extensive ash beds in the preceding Manzanita member. This source was probably in the volcanic area to the south, in Mexico. The two ash beds in the Bell Canyon indicate less violent eruptions in that area than those of Manzanita time.

Most of the sandstones of the Bell Canyon formation were deposited in quiet water. They are thinly laminated, and their bedding surfaces are flat and smooth. No channeling is found as in the Cherry Canyon formation. Shallow ripple marks are seen occasionally in the lower part of the formation, and indicate a slight movement of the water, but they are missing higher up. Somewhat more disturbed conditions existed at the margins of the basin, along the edge of the Capitan reef mass. Here, the sandstones between the Rader and Lamar members are somewhat channeled, and ripple marks are fairly abundant. Possibly these markings were caused by waves breaking against the face of the higher-standing Capitan reef, and by undertow moving down the surface. There was, therefore, some movement of water at the bottom near the margin of the Delaware Basin, even though the water was fairly deep. The ripple marks have a northeastward trend (fig. 10), indicating that the water movements that caused them were probably alined at right angles to the face of the northeast-trending Capitan mass. The sands near the edge of the Capitan are distinctly coarser than those farther southeast, and the finer material was probably picked up near the edge and carried farther out into the basin by the undertow.

LIMESTONES OF DELAWARE BASIN

The limestone members of the Bell Canyon formation record times when calcareous material spread southeastward from the edge of the Capitan mass over the floor of the Delaware Basin. The members are tongue-like projections from the Capitan limestone (pl. 7, A). but their lithologic character is not like that of the Capitan. They were probably laid down in a very different environment.

Near the southeast margin of the Capitan area, the limestones are better bedded than the Capitan. They are of grayer color because they contain small amounts of bituminous material. Small, lenticular bodies of massive limestone found in them (fig. 9) indicate the occasional existence of Capitan-like conditions. Thick layers of granular limestone that are interbedded seem to have had a clastic origin, and originally may have been calcareous sands spread along the lower edge of the Capitan reef. Some of the clastic, calcareous material may have been derived by wave erosion from the face of the reef itself. The angular pebbles which are common in the Rader member seem to have had such an origin. The fossil shells found in the granular limestones are abraded, indicating they had been transported before they were deposited, and some of them may have been carried in from the Capitan area. This was especially likely during Lamar time, for shells found in this member are nearly all of Capitan species. The Rader and Pinery members, however, contain a fauna similar to, but distinct from the Capitan, including numerous bryozoans, which are uncommon in the Capitan itself. An indigenous fauna thus clearly existed at the foot of the reef and along the edge of the basin, at least in the earlier part of Bell Canyon time. The fauna was adapted to an environment of fairly deep but perhaps clear and agitated water along the outer edge of the higher-standing reef mass.

FIGURE 10.—Map of area studied, showing distribution of facies and other stratigraphic features in beds of upper Guadalupe age (Bell Canyon, Capitan, and Carlsbad formations).

Several miles southeast of the edge of the Capitan reef, the light-gray, thick-bedded, granular, abundantly fossiliferous beds disappear from the limestone members; their place is entirely taken by thin-bedded, fine-textured, bituminous limestones, of dark gray or black color. The boundary between the two facies in Pinery and Lamar time is indicated by lines F and G in figure 10. The environment in which these limestones were deposited was not as favorable to life as that to the northwest, and most of the fossil groups except rhynchonellid brachiopods, fusulinids, and ammonoids are missing. The ammonoids were probably free-swimming, rather than bottom-dwelling forms. Probably the limestones of this area were laid down in quiet water, a condition which would have allowed their thin layers to be spread widely and evenly and would have allowed organic matter to accumulate faster than it could decay or be destroyed by bacteria. They record brief repetitions of the conditions that prevailed during the deposition of the black limestone of the Bone Spring.

In the Bell Canyon formation the sandstones and limestones tend to be repeated in cyclical order. The cycles resemble those in the upper part of the Cherry Canyon formation (p. 52). Limestone members are generally underlain by massive sandstones and overlain by thin-bedded sandstones (sec. 34, fig. 5). In the Section near United States Highway No. 62 (sec. 34, pl. 6), there are 5 such cycles in the 670-foot thickness of the formation.

DEPTH OF WATER IN DELAWARE BASIN

During upper Guadalupe time, the sediments of the Delaware Basin were, on the whole, laid down in quiet water. This fact suggests that the water may have been deep, and this inference is confirmed by the relations of the sediments in the basin to those of the Capitan reef along its margin.

Bedding planes in the Capitan limestone slope southeastward toward the deposits of the Delaware Basin at angles of 10 to 30 degrees. This slope must have been largely original in the deposit, because the Capitan is underlain and overlain by well-bedded limestones which either dip at a much lower angle or lie horizontally. The upper surface of the sloping Capitan beds probably rose nearly to sea level, so that, aside from the effects of later tilting, the height of their upper ends above their lower ends, where they merge with the deposits of the Delaware Basin, would be the approximate measure of the depth of water in the basin at the time of deposition (as suggested on section d of pl. 7, B).

The upper surface of the Capitan deposits thus rose above the deposits of the Delaware Basin much as the Reef Escarpment rises above the plains of the Delaware Mountain area at the present time. Conditions were not exactly comparable, however, for although the present scarp is the exhumed face of the Capitan deposits, it has been considerably modified by erosion (fig. 20, B). As shown by the dip of the overlying Carlsbad beds (sections F—F' and I—I', pl. 17), there has been some southeastward tilting toward the basin after Capitan time. The erosion and tilting make the present scarp higher than the ancient Capitan depositional surface.

Estimates of the original difference in altitude between the upper surface of the Capitan reef and the sea bottom in the Delaware Basin can be made by tracing some single bedding plane through the Capitan limestone and into the Bell Canyon deposits on such profiles as sections F—F' and K—K' of plate 17. Correction for later tilting can be made approximately by assuming that the overlying, southeast-dipping Carlsbad beds were horizontal at the time of deposition. Such estimates indicate that the Capitan reef stood 1,000 feet above the basin floor in Lamar time (as shown on sec. d, pl. 7, B). Less conclusive estimates suggest a slightly smaller figure for early Capitan time. Adams¹ states his belief that "in the center of the basin, the bottom was between 1,800 and 2,400 feet below the level of the Permian sea" at the end of Guadalupe time. This belief may be correct, although evidence is not stated. Under this condition the sea floor in the center of the basin would have been much deeper than along the margin, near the base of the Capitan reef.

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¹Adams, J. E., Oil pool of open reservoir type: Am. Assoc. Petroleum Geologists Bull., vol. 20, p. 789, 1936.

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FORM OF CAPITAN REEF

As shown by its outcrops (pl. 3), the Capitan limestone mass is only a few miles wide, yet it extends northeast-southwest in a belt for many miles following the margin of the Delaware Basin. Southeastward the mass sloped down steeply toward the equivalent deposits of the Bell Canyon formation. There was, however, no corresponding slope toward the northwest. In this direction, where the Capitan grades into the Carlsbad deposits, bedding planes extend almost horizontally from one to the other. The Capitan deposits thus formed a high-standing, shelf-like limestone reef along the edge of the Delaware Basin.²

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²Lloyd, E. R., Capitan limestone and associated formations: Am. Assoc. Petroleum Geologists Bull., vol. 13, pp. 646, 648, 1929.

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The southeastward sloping Capitan beds rest on a foundation of older rocks that dip at angles of a few degrees in the same directions. A part of this dip is of post-Capitan age, because it is shared by the Carlsbad limestone which overlies the Capitan. A part of it, however, such as the surface of the Goat Seep limestone, probably existed at the beginning of Capitan time. It was on this southeastward slope of the Goat Seep limestone that the first Capitan deposits were laid down, evidently because this was a favorable place for the building up of limestone deposits.

At any particular time, the surface that received Capitan deposits was narrower than the final width of the whole mass, as younger parts of both the Capitan and Carlsbad were deposited farther southeast than the older parts (pl. 7, A). The width of the mass in Hegler time is the distance between the northwest edge of the well-bedded Hegler limestone, and the southeast edge of the oldest Carlsbad limestone (lines B and C, figure 10). This width ranges from 1 to 2 miles. The deposits during Lamar time, as seen in McKittrick Canyon, seem to have had a similar width, but the width cannot be determined as easily for the intervening stages between Hegler and Lamar time.

The forward growth of the reef is illustrated by the lines C, D, and E on figure 10, which represent its southeastern edge during successive stages. Because of its forward growth, the edge by Lamar time had advanced 3 miles southeastward from the edge at the beginning of Capitan deposition, in Hegler time. During the earlier stages (from Hegler to Rader time) the advance was rapid, but during the later stages (from Rader to Lamar time), the edge of the mass remained in about the same position, and growth was more in an upward than a forward direction. These two directions of growth, forward and upward, appear to be related to the rate of subsidence of the area. In order to maintain itself, the growing part of the reef had to remain at a relatively constant depth. Without subsidence, such depths could be maintained only by forward growth. With subsidence, upward growth would be necessary. The observed relations suggest that the rate of subsidence was less in early Capitan time than in later Capitan time.

In the McKittrick Canyon region, the Capitan contains a number of very massive limestone bodies several hundred feet thick. Toward the northwest each one grades into thin-bedded Carlsbad limestone, and to the southeast each splits into a number of rudely bedded layers that slope down to the deposits of the Delaware Basin. Each massive body lies farther southeast than the one that preceded it, as a result of the forward growth of the deposit as a whole. The massive bodies seem to have been accumulations of rapidly growing calcareous material. They protected the area to the northwest of them so well from wave attack that thin-bedded deposits could be laid down, as in the lagoon of a modern reef. The sloping beds to the southeast probably were sheets of detrital limestone spread out in front of the growing material.

The breccia found at several places in the Capitan was probably derived from the breaking up of the sloping face of the deposit. The angular form of the fragments, their lack of sorting, and the lack of bedding in the matrix suggest that the deposit was a submarine landslip. The irregular surfaces of the bedded limestones on which they rest may have resulted from the ploughing up of the still unconsolidated sea-bottom deposits at the foot of the slope by the moving material. Such landslips probably resulted from the deposition of limestone on the slope until it reached the angle of rest of the material, and a loosening of the material either by its own weight, or by the force of a great storm or an earthquake. Because all the occurrences of the breccia are in beds of about the same age, storms or earthquakes are the most probable agents because they would affect the whole region at about the same time.

NATURE AND ORIGIN OF CAPITAN DEPOSITS

Why and how was the Capitan limestone deposited? A precise answer cannot be given, because there are a number of possible causes, one or several of which may have dominated. Field evidence so far obtained is not conclusive, and the original structure of the rock in a large part of the formation has been destroyed by subsequent dolomitization. I assume, however, that the dolomitized parts of the formation were originally about the same as the parts that still remain as calcitic limestone.

From a study of the calcitic limestone, it is clear that lime-secreting organisms contributed to the formation of the rock. Brachiopods, various mollusks, and some other groups are very abundant in certain beds. These organisms, however, do not show any special adaptation to a reef environment. There is not, for example, a noteworthy abundance of thick-shelled forms that would thrive in strong currents and pounding waves of the exposed parts of a reef and would, therefore, contribute a considerable amount of limestone to the deposit; instead, the assemblage seems to be a normal neritic fauna, such as would grow in any region of clear, shallow water.

I have already noted the observation by H. C. Fountain and me that these fossils occur only in occasional lenses and are not uniformly distributed throughout the formation. The greater part of the mass of rock contains little else than the remains of calcareous sponges, which constitute a group that is likely to build up colonies in agitated water and make important contributions of limestone to the deposit. It may be that the more varied assemblages of fossils grew in sheltered depressions between the masses of growing sponges.

Other reef-building organisms may have grown with the sponges, but their nature is not as well known. Apparently algae were common, for their remains have been described by several observers. Moreover, a considerable amount of the fine-textured, featureless matrix of the sponge rock was probably a calcareous mud, derived from precipitated algal remains that were later broken up by the waves. Crinoids also may have been abundant, for their stem segments are scattered through parts of the sponge rock. Neither corals nor bryozoans, however, seem to have been very common.

All these different organisms thrive in shallow, agitated water, and therefore, would be likely to find foothold in the shoals on the margins of the Delaware Basin, such as those formed by the older Goat Seep reef mass. In the basin to the southeast, the sea bottom was too deep for their growth. In the area to the northwest, the sea bottom was shallow, but the water was also less disturbed, and probably contained too great a concentration of dissolved salts, as is suggested by the change northwestward of the Carlsbad limestone into the evaporites of the Chalk Bluff formation.

The shoals along the margin of the Delaware Basin were probably also favorable places for the growth of lime-secreting organisms because the waters here were more nearly saturated with calcium carbonate than those to the southeast. The waters to the southeast were deeper, quieter, and perhaps cooler. Those on the shoals were warm and agitated, and therefore would cause the amount of dissolved carbon dioxide to be reduced, thereby diminishing the solubility of calcium carbonate.³ Warm water may actually contain less calcium carbonate than cold water. One should not, however, confuse concentration of a solution with its degree of saturation. With increased warmth of the water, the degree of saturation of calcium carbonate increases, without any increase in concentration. This is largely determined by the fact that the amount of dissolved carbon dioxide tends to decrease in warm water. The concentration of calcium carbonate was probably being increased by the evaporation of sea water in the area to the northwest. Under such conditions, the organisms would find an abundant supply of lime available for building their skeletons, and the saturation of the water would prevent the skeletons from being leached after death; thus there would be an abundance of calcareous remains incorporated in the deposit.

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³Twenhofel, W. H., Treatise on sedimentation, p. 321, 2d ed., Baltimore, 1932.

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Such conditions would favor the direct precipitation of calcium carbonate without the aid of organisms. To what extent this took place is difficult to determine, but probably part of the mass of the Capitan reef was built up by inorganic processes.

The dolomitization of large parts of the Capitan limestone probably took place shortly after the sediments were deposited, in the same manner as it has taken place in modern reef deposits. That it did not take place in later times is suggested by the lack of relation between dolomitic limestones and faults, igneous intrusions, and the present land surface. Chemical analyses indicate that the amount of magnesium carbonate does not exceed 28 percent—far less than that contained in the mineral dolomite. The process of dolomitization thus appears never to have been carried to completion.

Dolomitization of the limestones of the Capitan shortly after deposition implies that the chemistry of the sea water at the time was such that calcium carbonate was a less stable precipitate than calcium-magnesium carbonate. This may have resulted from a saturation of magnesium carbonate in the sea water by proper conditions of atmospheric temperature and pressure, or by a concentration of magnesium carbonate in the water as a result of excessive evaporation.

Johnson⁴ notes that:

Algae were probably responsible for much if not all the magnesium carbonate present in the dolomite as magnesium is an essential constituent in chlorophyll, that green pigment characteristic of plants. * * * The writer believes that the importance of these plants in relation to the origin of dolomite has not been appreciated by geologists.

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⁴Johnson, J. H., Permian lime-secreting algae from the Guadalupe Mountains, New Mexico: Geol. Soc. America Bull., vol. 53, p. 215, 1942.

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Dolomitization of the limestones shortly after deposition implies that they remained unburied, or within reach of the sea water a sufficiently long time for the calcium carbonate to be converted into the more stable calcium-magnesium carbonate. According to Twenhofel,⁵

it is possible that enrichment in magnesium carbonate may be connected with the relation that deposited sediments had to the base-level of deposition. Calcium carbonate deposits built up to this level would be subjected to leaching and replacement for a long time, provided the waters were not already high in calcium carbonate. This might lead to the formation of a magnesium-rock layer at the top of each layer of sediment.

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⁵Twenhofel, W. H., op. cit., p. 348.

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This relation may explain the irregular interbedding of dolomitic limestone and calcitic limestone in the Capitan. The dolomitic beds probably represent deposits that stood for long periods near the base-level of deposition, at times when subsidence was slow or absent. The calcitic limestones are probably deposits laid down during times of more rapid subsidence, when sediments were more quickly buried.

DEPOSITS OF THE SHELF AREA

The shelf area, outside the Delaware Basin and northwest of the Capitan reef, was apparently a shallow sea, because layers of the Carlsbad limestone seem to have been deposited in a lagoonal area at about the same altitude as the top of the Capitan reef. The waters were apparently quiet because the limestones formed thin, widely spread layers; perhaps the area was protected from the force of the waves and currents by the reef barrier to the southeast. Some movement of the water, however, is indicated by the parallel orientation of the fusulinids that occur in many beds. Their dominant trend is northwestward (fig. 10). If they acquired this position by wave motion, the waves must have trended northeastward, parallel to the edge of the reef.

The limestone deposits of the shelf area are generally dolomitic and apparently of two sorts. Toward the southeast, near the Capitan reef, they have a granular texture and contain fossils in moderate abundance; farther northwest they are dense, lithographic limestones, with no traces of life. Those of the first sort were probably deposited originally as limestones and were afterwards diagenetically altered. Those of the second sort were probably direct chemical precipitates of dolomite, formed as a result of extreme evaporation of the sea water, a condition that is proved by the passing of the deposits into evaporites a short distance farther northwest. Chemical analyses indicate that the magnesium content is higher in this second type than in the merely diagenetically altered limestones of either the Carlsbad or the Capitan. The chemical composition of the second type approaches that of the mineral dolomite.

The area extending some miles behind the Capitan reef was apparently favorable to the existence of some forms of life. Fusulinids and algae were abundant, gastropods were common, and some families of pelecypods and brachiopods were present. There is, however, a notable absence of some groups and families of invertebrates that are common elsewhere in the rocks of the mountains, suggesting that they could not exist in the Carlsbad environment. Farther northwest, the concentration of dissolved salts in the sea water resulting from evaporation was probably so great that little or no life could exist.

COMPARISON WITH MODERN LIMESTONE REEFS

The Capitan limestone reef, and other reefs in the west Texas Permian have many resemblances to those that were built up in tropical seas during the Cenozoic time, and in part are still growing in modern tropical seas.⁶ In these seas, as in those of west Texas during Capitan time, there are thick accumulations of limestone, parts of which are elongate reef masses, constructed by colonies of corals, calcareous algae, and numerous other lime-secreting organisms. The reefs generally slope abruptly seaward into deep water and merge landward into flat-lying lagoonal deposits.

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⁶These have been described in numerous publications. see, for example, Davis, W. M., The coral reef problem: Am. Geog. Soc. special Pub, 9, 1928.

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The differences between the modern features and their ancient Permian counterparts seem to result chiefly from their respective geographic settings. The modern features lie mainly along continental margins or on the slopes of oceanic islands. In nearly all of them the sea bottom descends to oceanic depths in front, and the ground surface rises to hilly or mountainous heights behind. In contrast, the Permian features were formed in a nearly land-locked embayment of the sea, bordered in part by a low-lying continental surface. One result is that in the modern examples the lagoonal areas are relatively narrow, whereas in the Permian examples the areas corresponding to the lagoons were very broad. Modern lagoonal deposits are thus dominantly marine, whereas the Permian deposits include broad sheets of evaporites and terrigenous clastic sediments.

Possibly the closest modern analog to the Permian deposits exists in the Bahama Islands, southeast of the United States.⁷ In this region are numerous broad, flat-topped banks, covered by shallow water and rising here and there in low islands. These banks slope abruptly into tongues, sounds, and channels of water many thousands of feet deep and are separated by them. The known surfaces of the banks consist of calcareous deposits, including limestone reefs, and similar rock may extend to great depths. A particularly suggestive comparison can be made between the cul-de-sac of the Tongue of the Ocean, between Andros and New Providence Islands, and the Delaware Basin in west Texas. Unlike west Texas, however, the Bahamas lie a considerable distance from any marginal lands, and their deposits probably include little or no clastic terrigenous sediments.

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⁷Hess, H. H., Interpretation of geological and geophysical observations, The Navy-Princeton Gravity Expedition to the West Indies in 1932: U. S. Hydrographic Office, pp. 38-54, 1933. Schuchert, Charles, Historical geology of the Antillean-Caribbean region, pp. 528-540, New York, 1935.

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