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Mississippi State Geological Survey Bulletin 28
The Geologic History of the Vicksburg National Military Park Area |
DESCRIPTIVE GEOLOGY
In the lower part of Mint Spring Bayou, in reality a valley, at northern edge of the City of Vicksburg, the stream has uncovered nine or more feet of gray marl which is a slightly indurated or consolidated mass of marine shell fragments. It has been named the Mint Spring marl by C. Wythe Cook.1
1Washington Acad. Sci. Jour., vol. 8, No. 7, p. 195, 1918.
Directly overlying the Mint Spring marl is an interval of 12.8 feet of limestone extending to the brink of the falls. It, too, is a gray marl not fully indurated, but possibly sufficiently so to be called a limestone. It belongs to the basal part of the Glendon formation.
Section of the waterfalls in Mint Spring Bayou
| Feet | Feet | ||
| Glendon formation | 12.8 | ||
| Limestone, gray, or marl, indurated, forming the most nearly vertical part of the rock beneath the falls | 10.3 | ||
| Limestone, gray, or marl, indurated, forming also a part of the nearly vertical portion of the falls | 2.5 | ||
| Mint Spring marl | 9.0 | ||
| Marl, gray, only slightly indurated | 9.0 | ||
| Base of exposure is 8 or 12 feet above water level in pool | |||
These layers of limestone in the basal part of the Glendon formation are harder than the other beds of the Glendon or of the other formations of this vicinity. Consequently, they stand out in the steep parts of the valleys, whereas the less indurated beds are commonly covered with mantle rock. For this reason the limestone is exposed in the bluffs of the old Mississippi, north of the business section of the city.
Perhaps the most readily accessible section of fairly well exposed beds in the Vicksburg region is along the side of the roadway extending from Waltersville southward up the hill past the north wall of the National Cemetery. It is given in details in the following section.
Section of the beds along the Waltersville-National Cemetery Road
| Feet | Feet | ||
| Loess | 21.0 | ||
| Loess, grayish-buff, contains Gastropod shells and breaks into vertical columns | 21.0 | ||
| Citronelle (provisionally referred to this formation) | 14.0 | ||
| Clay, pinkish-gray, tenaceous, which has sand and gravel in its upper inch. Both its upper and lower contacts are irregular, and, hence, its thickness is not uniform. Top surface has slickensides | 3.0 | ||
| Gravel and sand mixed in the most confusing way, after the manner of the Citronelle, to which it is provisionally referred. Both upper and lower contacts are irregular, and, consequently, its thickness is not uniform | 11.0 | ||
| Catahoula formation | 26.0 | ||
| Sand and clay in rather indefinite layers. Some of the clay is light in color, and some of it, especially in the basal parts, contains dark films of lignite or lignitic clay. It is slightly covered at the base | 26.0 | ||
| Byram marl | 44.5 | ||
| Marl, gray, certain beds of which are extremely fossiliferous, especially in the lower part of the interval | 37.5 | ||
| Marl, bluish-gray. The top and basal intervals, each of 1.5 feet, are exposed, the median interval of 4.0 feet is covered | 7.0 | ||
| Glendon formation | 17.0 | ||
| Limestone at top, which forms the small falls along the roadway. The lower part is marl 3.5 Interval, covered | 5.5 | ||
| Limestone at top, which forms the small falls in the small gulley opposite the roadway bridge. The rest is fossiliferous marl | 8.0 | ||
| Undetermined | 3.0 | ||
| Interval, covered to Washington Street and Illinois Central Railroad tracks | 3.0 | ||
Although neither the Mint Spring falls section nor the Waltersville-National Cemetery road section extends down to clearly exposed beds of the Forest Hill formation of the Vicksburg series of rocks, exposures elsewhere show the Forest Hill formation to consist of cross-bedded siliceous sand and some clay. It also contains lenses of lignite and lignitic clay.
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Last Updated: 18-Jan-2007