Geological Survey Bulletin 611 Guidebook of the Western United States: Part A

Lake Park is another important town of the lake region, and although no water is visible from the train there are one or two ponds near by, and some of the finest lakes of the region lie a short distance to the south. Lake Park is on the edge of the prairies. The trees are small and are confined largely to the watercourses. Almost all the land is under a high state of cultivation, and fields of wheat and hay abound on every side.

The country here is a gently rolling upland with the valleys cut to a depth of 50 feet or more below the general level. At Manitoba Junction the Northern Pacific line running to Crookston, Minn., Grand Forks, N. Dak., and Winnipeg, Canada, turns to the right (north). At this place the traveler enters the valley of Buffalo Creek and can not see the upland country, which, however, is much the same in character as the country east of the junction—that is, it is rolling, but is cut by the valleys of the larger streams. The railway follows Buffalo Creek through the village of Hawley, but the valley grows deeper toward the west, and little of the country outside of the immediate valley can be seen from the train.

If the traveler had been attempting to cross the continent in the closing stages of the glacial epoch by the route which he is now following, he would have been confronted, when he reached the place where Muskoda now stands (see sheet 4, p. 40), by a vast lake which then occupied the valley of Red River. The only passageway around it would have been by a wide detour to the south, for the lake extended into Canada for several hundred miles and was bounded on the north by the impassable front of the great continental glacier. As the lake has completely disappeared the reader may be skeptical about its existence or wonder upon what evidence its presence in a former age has been determined. Unfortunately the track is so far below the general surface of the upland that there little opportunity to observe details, but if the traveler could carefully examine the ground he would easily recognize the shore of this ancient lake just before he reaches the station at Muskoda. This old shore consists of a ridge of gravel which was heaped up by the waves that beat upon its western side. The large gravel pit which the railroad has excavated in this ridge to procure ballast can be seen from the Muskoda station.

SHEET 4. (click on image for an enlargement in a new window)

The lake was named by the geologist Warren Upham in honor of Louis Agassiz, who was the first to make a systematic study of glaciers and glacial phenomena.¹ The beach at Muskoda is called the Herman beach. It was formed when the water of Lake Agassiz stood at its highest level and consequently marks the line between the unmodified glacial topography above and the smooth surface of the old lake basin below. The difference in the topography may not be noticeable on the east side of the valley because of the unfavorable outlook, but on the opposite side of the valley west of Fargo the difference is very striking and can readily be seen from the train.

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¹Lake Agassiz was a body of fresh water that existed during a late stage of the glacial epoch in the valley of Red River and extended northward (see map on sheet 4, p. 40) from the head of that stream for nearly 700 miles. The area of the lake at the time of its greatest expansion was about 110,000 square miles, exceeding the present aggregate area of the five great lakes tributary to the St. Lawrence.

The shore of this ancient lake is marked by well-defined beaches, and it is from these that the existence and the extent of the lake are known. The beach ridges are built upon typical bowlder clay, and hence it is known that the lake either followed the invasion of the ice or marked the closing stages of that episode.

The next question that arises is, What were the conditions that led to the formation of such a lake? It could not have been held in a landlocked basin, for no such basin exists at the present time, and there is no evidence that the surface features of that time differed greatly from those of to-day. Warren Upham, who has studied this question most carefully, has come to the conclusion that it was held in place by the retreating front of the glacier, which blocked the natural outlet of the water to the north and forced it to accumulate in this basin. The ponding of the water in the Red River valley began as soon as the ice front retreated across the divide at the head of Lake Traverse, and the water found an outlet down the valley of Minnesota River, in a stream that has been called Warren River. Lake Agassiz thus began as a small body of water and expanded northward as the ice melted until it became of great extent.

The water of Lake Agassiz continued to flow through Warren River until the Keewatin (ke-way'tin) ice had melted back northward far enough to permit an outlet eastward, perhaps at first to the Superior basin, but later to Hudson Bay. Recent studies have shown that the growth of Lake Agassiz was dependent upon the retreat of the western ice sheet. (See map opposite this page.) The moraines of this ice sheet that mark the successive positions of the ice border indicate two positions, marked A—A and B—B on the map opposite page 40, with a fair degree of accuracy. The later positions, C—C and D—D, are drawn to correspond with the topography. The western limits of Lake Agassiz have been determined with considerable accuracy, but the eastern limits in Canada are in a forested region that has not been explored sufficiently to determine the extent of the lake. Apparently lower eastward outlets were opened successively as the ice retreated northward, for 31 shore lines were formed as the lake was drawn down to lower levels. All the outlets have not been mapped. It seems likely, however, that there was no discharge to Hudson Bay until the ice had melted back beyond the position C—C, but there may have been an outlet into the Superior basin before the ice had retreated so far north.

The shore lines are inconspicuous, but on the smooth slopes of the lake bed they are generally easily traceable. The best-developed beach ridges of the lake commonly rise 10 to 20 feet above the adjoining land on the side that was next to the water and from 3 to 10 feet on the opposite side. They vary in width from 10 to 30 rods and are composed of interstratified gravel and sand, the gravel prevailing, including pebbles 2 to 4 inches in diameter.

The development of the beaches varies greatly from place to place, depending apparently upon the abundance and character of the materials which were within reach of the waves. Thus where the valley is crossed by the main line of the Northern Pacific Railway three beach ridges are clearly visible on the east side of the valley and two on the west. At Wahpeton (waw'pe-ton), on the Fergus Falls branch of the same road, there are four well-developed ridges on each side of the valley. At Grand Forks there are four ridges on the east, where they are crossed by the Great Northern Railway, and twelve on the west.

The Herman beach, which marks the highest stage of the lake and which is the one most easily recognized, has been traced for a long distance around the south and west sides of the lake, but the lower beaches are not so well marked and can not be traced continuously.

Sand and gravel deltas, so extensive as to be notable features of the topography, were formed by several streams that flowed into the lake while it stood at its highest stages. The Buffalo River delta, down which the Northern Pacific Railway runs immediately west of Muskoda, covers an area about 7 miles long from north to south and 2 to 3-1/2 miles wide from east to west. The delta plain, as shown in figure 4 (p. 34), is terminated about 3 miles west of Muskoda by a steep slope, like the face of a terrace, 25 to 40 feet high.

The floor of this ancient lake is apparently a level plain, although it really has a slight slope toward the middle and a gentle northward inclination of about a foot to the mile.

The several shore lines are not parallel with one another or with sea level, but all show an ascent toward the north or northeast. Thus the upper or Herman beach rises 175 feet between Lake Traverse and the international boundary, but the grade is not regular, being 35 feet in the first 75 miles, 60 feet in the second, and 80 feet in the third. The lower beaches show a similar though less pronounced rise. As these beaches must have been horizontal when they were formed, it is evident that the crust of the earth has been elevated toward the north, and as the beaches show divergence among themselves, it is certain that this upward movement in the earth's crust began when Lake Agassiz was in existence and continued for some time after it was drained.

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Between mileposts 242 and 243 the railway emerges from the now shallow valley of Buffalo River, and the traveler may obtain his first view of the famous Red River valley, which has been referred to frequently as the "granary of the world," but which was once a lake about 50 miles wide at this point and nearly 700 miles long. The silt deposited in this lake gives the valley its wonderfully smooth surface and its great fertility. During the highest stage of the lake Buffalo River built just below Muskoda a delta of considerable size, and it is from this delta that the first view of the valley may be obtained. At a later stage, when the water of the lake was at a lower level, the waves cut away the front of the delta and greatly increased the natural slope of the valley side, as shown in figure 4. The railway engineers found difficulty in getting down this slope without loops and curves, so a long, high fill has been made which gives a uniform grade from top to bottom.¹ The weight of the fill, however, proved to be too great for the soft mud at the bottom of the old lake bed, and it is still settling and throwing up a ridge of the soft material on each side.

FIGURE 4.—Section of Buffalo River delta, Minn. A B, Surface of Lake Agassiz at the Herman stage; E F B, delta profile; C D, level of water at Campbell stage; E D F, part of delta cut away by the waves, leaving the steep westward front (D F).

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¹In the original construction of the Northern Pacific Railway the standard maximum grade adopted was 52 feet to the mile except on the mountain sections, where the standard was 116 feet to the mile. As the traffic developed it was found necessary, for economy of operation and to increase the capacity of the line to handle the business of the country tributary to it, to adopt new standards of 18 and 21 feet to the mile except upon the mountain sections. This change necessitated a reduction in the original grades at many points, involving a large amount of expensive work, which has been going on actively for the last 15 years and is now nearly completed. The fill referred to in the text was constructed in connection with one of these reductions of grade. The grade was reduced from 48 to 18 feet to the mile, and freight-train loads were increased from 2,200 tons with two locomotives to 2,550 tons with one locomotive. Many similar examples of grade reduction will be observed along the line.

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From the high fill the traveler can see something of the great extent of the valley—its level floor stretching mile after mile without the least eminence or depression to break its regularity—and some of the fine farms that have made it famous. Drilling for water has shown that originally the surface of the valley was uneven, much like the country on both sides. At a later date the valley was filled by a great glacier that came down from the north, grinding and scouring away many of the projections and filling the depressions with the waste material; and then as the last smoothing process the fine mud carried by the streams settled in the lake, giving the valley its present smooth surface.

The material laid down in the waters of Lake Agassiz is so soft and fine that it is washed away with great rapidity when it is exposed to the action of the elements. Ordinarily the surface vegetation protects it, but when this is removed disastrous results follow. In 1895 a wagon road was graded east of Red River and a short distance north of the railway near Glyndon for about 6 miles. The farmers at once began to drain their fields into the roadside ditch, which was deepened and widened so rapidly by the consequent erosion that in four years the road had been destroyed for nearly a mile and in its place there was a channel 80 feet wide and 25 feet deep.

Dilworth is a division terminal of the railway, established to relieve the congestion of the yards at Fargo, where the terminal was formerly located. In the Red River valley may be seen some of the magical effects of the mirage that is so striking a feature of an arid or semiarid region. Warren Upham describes it as follows:

The mirage, typical of plains country or the ocean, may be seen in the Red River valley almost any sunshiny day in spring, summer, or autumn. This queer phenomenon makes the high land at the sides of the valley, the tops of the distant trees, and houses appear to be raised a little above the horizon, with a narrow strip of sky between. The more complex and astonishing effect of mirage may be seen from the highland on either side of the lake-bed floor. There, in looking across the valley from one and one-half to two hours after sunrise on a hot morning following a cool night, the groves and houses, villages, and grain elevators loom up to two or three times their true height and places ordinarily hidden by the curvature of the earth are brought into view. Oftentimes, too, these objects are seen double, being repeated in an inverted image close above their real positions and separated from it by a foglike belt. In its most perfect development the mirage shows the upper and topsy-turvy portion of the view quite as distinctly as the lower and true portion.

These appearances are due to refraction and reflection from layers of air of different density, such as are often formed above a wide expanse of level country in warm weather.

The last town in Minnesota through which the train passes is Moorhead, named in honor of William G. Moorhead, a former director of the railway company. Between this town and Fargo, N. Dak. runs Red River, the boundary line between the two States, a deep, sluggish stream that generally is heavily charged with mud derived from soft materials deposited in the ancient lake. This mud gives to the water a brownish-red color.

North Dakota comprises an area of 70,837 square miles. It was admitted to the Union in 1889, and at the census of 1910 it had a population of 577,056. It is primarily an agricultural State, but from time to time, as conditions have changed, there has been a corresponding change in its leading industries. At the time of the first permanent settlement the whole State consisted of one vast open range which furnished grazing in abundance for the herds of wild animals that roamed over it. The white man saw the natural fitness of the region for grazing, and soon cattle, horses, and sheep were feeding in place of the deer and buffalo.

In the Red River valley farming early received a great stimulus from the officials of the Northern Pacific Railway, and before many years this valley, from its head to the Canadian line, was one vast sea of wheat. Farming was also carried on in other valleys to a minor extent, but for a long time the region west of Missouri River was considered suitable only for grazing, as the annual rainfall (16 inches) was thought to be too small for raising crops. The discovery in recent years that by proper methods of cultivation most of the moisture in the soil could be conserved and rendered available for agriculture has worked a wonderful change in the appearance of this country, for now almost all the land is under fence and the region west of Missouri River contains many fine farms and thriving towns.

The principal crops are wheat, oats, and flax, and the raising of domestic animals is still an important industry. According to the census of 1910 the value of all farm products for the year 1909 was $205,000,000, of which $180,000,000 was produced directly from the crops and $14,000,000 from domestic animals. During the same year the value of manufactured products amounted to $19,000,000.

North Dakota is well supplied with lignite. This is a low-grade fuel, but it is of very great value for domestic use on these treeless plains. Almost every section of land in the part of the State lying west of Missouri River is underlain by lignite, and it is estimated that the State contains 697,900,000,000 tons of this fuel. In 1913 the value of the lignite mined commercially amounted to $765,105.

Fargo is the most important town in the Red River valley and the largest in the State of North Dakota. It was named for William G. Fargo, of Wells, Fargo & Co.'s Express. Fargo is the seat of the North Dakota Agricultural College and Experiment Station and is noted as one of the great farm-machinery markets in the United States. The climate of Fargo is about the same as that of the Red River valley as a whole. The winters are frequently severe, the mercury registering 40° below zero, and the summers are hot, ranging from 90° to 105°. The mean annual precipitation is about 20 to 24 inches, compared with 28 inches at St. Paul and 15 or 16 inches in the western part of the State.

The Red River valley, including that part which lies in Canada, was one of the first to be explored in this part of the country. Lake Winnipeg, at its mouth, in Canada, was part of the great highway by which the French voyageurs penetrated the country west of Lake Superior in the early days of the trapper and trader. The earliest authentic record of exploration is that of Verandrye, who made an unsuccessful attempt to cross the continent in 1738-1742. French traders doubtless followed in his footsteps, but they left few if any records of their experiences or of the country traversed. In the early years of the nineteenth century David Thompson and Alexander Henry, of the Northwest Fur Co., pushed their way up the Red River valley into what is now North Dakota and Minnesota; and in 1812 the Earl of Selkirk made the first settlement in the vicinity of Winnipeg. Many French traders probably found their way south into that part of the Red River valley lying in North Dakota, for Lewis and Clark mention their presence on the Missouri as early as 1804.

Not much is known of the rocks underlying the Red River valley, for they are effectually concealed by the glacial drift and by the sediment deposited in Lake Agassiz, but their presence here and there has been revealed by deep drilling. The deepest well which was sunk near Moorhead penetrated lake sediment and glacial drift to a depth of 220 feet, Cretaceous shale with some sandstone for 150 feet, and the underlying granite to a depth of more than 1,500 feet. This region is therefore near the eastern edge of the great mass of Cretaceous strata which extends as an unbroken sheet to the Rocky Mountains and which can be seen at many places along the Northern Pacific Railway. The sea in which these materials were laid down must at some stage of its existence have extended farther east than the Red River valley, for a few exposures of these rocks have been found in the valley of the Mississippi. (See route map, sheet 2, p. 26.)

A few years ago a traveler crossing the old lake bottom just before the wheat harvest would have seen mile after mile of grain, which on a clear breezy day would have looked much like the waves rolling across the water, and he could almost have imagined Lake Agassiz to be still in existence. In recent years the crops in this region have become more diversified and now instead of the unbroken stand of wheat that stretched to the horizon line, the traveler sees interspersed with the wheat other grains and flax, and only here and there is the wheat grown in large areas. The rich black soil extends in almost unbroken regularity across the valley and it is under a high state of cultivation, even to the very edge of the railroad track. Probably there are few regions in the world in which the soil is more fertile than that of the Red River valley. The silt where it is wet and compacted has much the character of clay, but it differs from clay in that it contains fine sand, powdered limestone, and carbonaceous matter, which make it less coherent.

There are some tracts of very compact and heavy soil upon the level bottoms, ranging in area from a few square yards to a few square miles, that are known as "gumbo spots." On account of the impermeable character of the clay, drainage is difficult and in places alkaline salts tend to accumulate.

West of Maple River, which the railway crosses near the village of Mapleton, the land rises steadily westward, but the surface of the old lake bed is so smooth and the ascent so regular that it is scarcely perceptible to the eye. This is a region of great farms, and one of the largest and most noted of these is the Dalrymple farm, between Mapleton and Casselton, comprises acres which 21,000 of cultivated land. As these big holdings were the pioneers in the Red River valley and led directly to its agricultural development, their history may prove to be interesting at this place.

About 1870 the banking firm of Jay Cooke & Co. became the financial agent of the Northern Pacific Railroad Co. and advertised widely the great agricultural possibilities of the region to be traversed by the railway. Its glowing statements were attacked through the press and otherwise, and much skepticism was expressed as to whether or not the country was of any value for agriculture. In order to meet these criticisms, certain members of the Northern Pacific directorate determined that they themselves must furnish incontestable proof that the land could be farmed to advantage. T. H. Canfield purchased 5,500 acres at Lake Park, Minn.; Charlemagne Tower, 3,000 acres at Glyndon, Minn.; and Benjamin P. Cheney and George W. Cass, 6,000 acres at Casselton, N. Dak. These farms were at once put under expert cultivation, and the result of the experiment showed the Lake Park region and the Red River valley to contain some of the finest wheat lands in the world. The demonstration of this fact caused a large and steady immigration to this region in the years immediately following.

The town of Casselton is situated in the heart of the great wheat belt and was named for George W. Cass, a former president of the Northern Pacific Co. In the vicinity of Casselton and westward for some distance many flowing water wells have been drilled. These wells derive their supply from two sources—the glacial drift and the underlying Cretaceous rocks. The water obtained from the glacial drift is of fairly good quality and can be obtained at depths ranging from 40 to 200 feet, but the amount of water varies considerably and several of the wells have ceased to flow. The water from the Cretaceous rocks is slightly salty and not suited for irrigation, but can be used for domestic purposes. The depth of the producing wells ranges from 250 to 500 feet, and the flow of water is more constant than that from the glacial drift. The water-bearing rock is supposed to be the Dakota sandstone, which belongs at the base of the Upper Cretaceous. The water is supposed to enter the Dakota sandstone in Wyoming, where the sandstone is upturned against the Rocky Mountains, or in the region of the Black Hills. It follows the sandstone bed beneath the Great Plains and appears where the sandstone rises and approaches the surface in eastern North Dakota.

The village of Wheatland, appropriately named, is situated at the place where the railway crosses the lowest prominent beach of Lake Agassiz, the houses in the eastern part of the village and a cemetery north of the track being situated on the beach ridge. When the surface of the lake stood at this level the water was 90 feet deep at Fargo, in the center of the valley, and it remained at this height long enough for the waves to heap up a distinct ridge of sand and fine gravel. This is known as the Campbell beach, from the town of that name in Wilkin County, Minn., through which it extends.

West of Wheatland there are, here and there, traces of similar beaches, showing that Lake Agassiz stood at different levels above that of the Campbell stage, but at none of them long enough to form a decided and well-marked beach, except at the highest of the series. This is known as the Herman beach. It can easily be seen from the train just 5 miles west of the Campbell beach, or three-fourths of a mile west of Magnolia. (See fig. 5.) This beach ridge is even better developed than the Campbell beach and is marked by an old gravel pit on the right (north) of the track. The ridge is 15 feet high and about 150 feet wide on top. In the pit the beds of gravel dip about 20° to the west, or away from the open water of the lake, showing that the waves carried the sand and gravel over the top and deposited them on the back slope of the ridge. When Lake Agassiz stood at this level the water at Fargo was about 175 feet deep, but it rose no higher, because at that stage it found an outlet to the Mississippi through the valley of Minnesota River.

FIGURE 5.—Section of Herman beach ridge west of Magnolia, N. Dak., showing the relation of the sand and gravel beds composing the beach to the surface of glacial Lake Agassiz.

From the Herman beach a comprehensive view can be had of the broad expanse of the Red River valley. Above the level of the beach the old surface of till and outwash gravel is in its original condition, not having been smoothed and covered by a coating of mud, as was that of the submerged area.

West of the Herman beach the railway crosses a low, broad ridge by a deep cut in glacial till and sand. This cut is 4 miles long, extending as far as the village of Buffalo, and it affords excellent exposures of the materials transported by the ice. The low ridge through which the cut is made is a faint moraine, marking the position of the front of the glacier¹ that occupied the valley of Red River before it became a lake, as described on page 32.

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¹The glacial features of North Dakota are the result of the invasion of the ice sheet that originated west of Hudson Bay. At the time of its greatest expansion this glacier covered all of North and South Dakota east of Missouri River with ice probably hundreds and perhaps thousands of feet in thickness.

A study of the materials brought down from the north shows that glaciation was not confined to a single stage of growth and decadence of the ice sheets, but that there were several advances and retreats, and that the amount of movement accomplished in the various stages differed greatly. These fluctuations appear to have been due to the fact that at times the climate was favorable for the development and advance of the ice, and that at other times it was milder and the ice wasted away until large tracts previously covered were again in condition for the return of animal and vegetable life. During the warmer epoch soils were developed, and the glacial materials spread over the land were sculptured by newly established drainage systems. The return of colder weather and the advance of the ice over most of the area previously glaciated destroyed many of the new surface features and buried the whole under a new deposit of drift.

The extent of the several ice sheets which invaded the Dakotas during the Wisconsin stage of glaciation is shown on the sketch map on sheet 5 (p. 44). Northeastern Minnesota was covered by ice that came from the direction of Labrador. Sweeping southwestward and southward around the west end of this ice mass came another great glacier from the region west of Hudson Bay, which divided at the head of the Coteau des Prairies (for meaning of the word "coteau" seep. 45), or just south of the South Dakota line, into two great lobes, one of which, known as the Minnesota Glacier, passed southward up the broad valley of Red River and across Minnesota into Iowa as far as the present city of Des Moines, and the other, known as the Dakota Glacier, moved down the James River valley to the Missouri, spreading westward upon the flanks of the Coteau du Missouri. The farthest extent of these lobes is marked by a well-developed ridge, called the Altamont moraine.

The Altamont moraine is crossed by the Northern Pacific Railway between Sterling and Driscoll and from this point recedes far to the east, crossing the line between North and South Dakota about 75 miles east of Missouri River. In South Dakota its outline is somewhat irregular, showing that small lobes of ice pushed out here and there far beyond the principal mass. In general, however, the Altamont moraine bounds Missouri River on the east, and it is probable that the front of the ice and its accompanying moraine were largely instrumental in determining the course of that stream.

The Dakota lobe of the glacier filled all the country between Missouri and Big Sioux rivers, but east of the Big Sioux there was a strip of country free from ice, which extended, as shown on the map, nearly to the North Dakota line.

The marginal deposit indicating the first halt in the glacial wasting and retreat is the Gary moraine, which is crossed by the Northern Pacific Railway just west of Crystal Springs. It lies upon the Coteau du Missouri and is closely associated with the Altamont moraine, the high coteau front serving as a wall or dam which held back the ice in its forward movement. The great amount of material in these outer moraines and the large size of the hills indicate that the edge of the great ice sheet probably remained against the coteau for a considerable time. South of the Northern Pacific Railway the Gary moraine is roughly parallel with the Altamont moraine. In some places they coincide, but in others they are nearly 50 miles apart. The glacier at the time the Gary moraine was built extended as far south as it did during the greatest extension, but the lobe was narrower, averaging not more than 80 miles in width, and the point of division between this lobe and the Minnesota-lobe had receded to the North Dakota line.

The next stage in the recession of the ice front is not marked by a single large and well-defined moraine, but by a belt of more or less disconnected ridges or heaps of morainal deposits, called the Antelope moraine. The number of these ridges indicates that the ice front fluctuated back and forth across the belt. The ridges of the Antelope moraine are crossed by the Northern Pacific line between Spiritwood and Eldridge, but they are not well marked on either side of James River. The glacier at the Antelope substage extended in a long tongue down the James River valley as far as Huron, S. Dak., but the point of division between the two great lobes had not changed its position appreciably from that which it occupied in the Gary substage. The Antelope moraine is here regarded as including the Kiester moraine, which has been recognized only for a few miles south of the Northern Pacific Railway and east of James River.

The next important moraine, which has been called the Waconia, is crossed by the railway between Eckelson and Fox lakes and forms the divide between Hudson Bay and the Gulf of Mexico. It marks the first definite and prolonged halt in the retreat of the ice front after the formation of the Gary moraine. The glacier at this stage of the retreat extended only a few miles across the State line into South Dakota, and its lobe, which at one time extended to the mouth of James River, was so reduced as to be scarcely recognizable and before the next halt had disappeared.

Two more halts in the recession of the western margin of the ice are recorded along the Northern Pacific line, but these were doubtless of slight duration and did not produce separate moraines south of the railway. The moraine marking the earlier of these halts is supposed to be the same as a moraine at Fergus Falls, Minn., and therefore is called by that name. It is well developed in Alta Ridge, 6 miles east of Valley City. The second moraine is the low ridge east of Buffalo. When the ice front retreated east of this moraine, the southern part of Red River valley became flooded with water, and Lake Agassiz was formed.

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