The Dakota group includes all the Cretaceous east of the Fort Benton. As no fossils of the Triassic or Jurassic have yet been discovered after ten years' search, we conclude that the Dakota rests directly on the Permian. While the dividing line has not usually been very well defined, yet, in a few instances, the fossils of the Permio-Carboniferous and Dakota groups have been collected within thirty-five feet vertically and one-half mile horizontally.
The material of these deposits is formed very largely of brown and variegated sandstone of all degrees of compactness, from that which crumbles in the handling to that which requires a sledge hammer to break it. This extreme hardness is, in most cases, owing to the presence of iron, in the condition of oxide and silicates. Sometimes poor limonite is seen. In every county where it abounds, it affords, in some places, a good building material. It is frequently overlaid or interstratified by clayshales of various colors. Many ledges give concretions of fanciful forms, sometimes hollow or with the center filled with loose sand. Some of the hollow concretions are sufficiently large to be used by farmers as feeding troughs for hogs and cattle. Others utilize them as flower vases for the lawn or garden. In a few localities they assume the form of tubes of various sizes, some being three inches in diameter and three to eight feet in length. These concretionary deposits are sometimes glared and distorted, as if they had been subject to the action of fire; but the cause is the oxidization of iron, and not any application of heat. Such specimens of sandstone frequently inclose well preserved dicotyledonous leaves. Had they been subjected to volcanic heat these fossils would have been destroyed.
The white portions of the sandstones are occasionally found in hard concretions. These are of a disk shape, sometimes measuring six or eight feet across, and from two to three feet in thickness. When capping softer layers they assume the form of toadstools; the softer portions becoming the stone to support the disk, Fremont noticed them in his early explorations, when passing over Kansas. Our engraver gives us several illustrations. "Pulpit Rock," near Alum creek, Ellsworth county, Fig. IV, is fifteen or eighteen feet high and ten feet across the top; "Rock City," Fig. V, and "A Settler of Rock City," Fig. VI, are seen near Minneapolis, Ottawa county. "Table Rock," Fig. VII, in Lincoln county, consists of two pillars supporting a tablet-like concretion.
FIG. IV. PULPIT ROCK, (Alum Creek, near K. P. R. R., Ellsworth Co.) |
FIG. V. ROCK CITY, (Ottawa County). |
FIG. VI. A SETTLER OF ROCK CITY, (Ottawa County). |
FIG. VII TABLE ROCK, (Lincoln County). |
The average width of the Dakota is less than fifty miles, being somewhat less than that in the north part of the State, and more, on the Smoky and Arkansas rivers. The dip is to the northwest and very slight. It is difficult to decide the amount, but it does not appear to be on the average more than five feet to the mile. It is conformable to the Fort Benton group above it. It corresponds very nearly to the Cretaceous of Swallow's Report, page 9, and also to Nos. 2 and 3 of his Triassic.* The maximum thickness of this formation may be five hundred feet. It is difficult to estimate the thickness, as the larger portion of the material consists of sandstone, much of which was originally thrown down in oblique deposits.
* The other numbers of his Triassic belong to the Permio-Carboniferous.
As this group is composed, to a very large extent, of silicious sandstone, the first impression would be that the soil would naturally be poor and sandy. This is not the case. The best material of the soil must have come from the later divisions of the Cretaceous above it. We find the Fort Benton limestones and lime-shales overlying the western portion of the Dakota formation, and other indications go to prove that formerly they overspread the whole of it. At the rate at which these lime-deposits are now being disintegrated by rain, frost and other natural agencies, such action prevailing for a long period would have commingled lime with the sand and produced a fertile soil.
The farms on the Dakota formation show as much natural fertility as any portions of the State. The moderately sandy subsoil furnishes a natural drainage, even better than usual, and in the spring frequently gives the grasses and winter grains from twelve to fifteen days earlier start than the farms of the adjoining Permian. No soil in the State is so easy to work and so free from baking or the ill effects of drought. The eastern half embraces the best wheat land in the State. It is also an excellent fruit district. The iron in the sandstone uniting with other good materials makes it particularly favorable to pear culture.
The total thickness of the Cretaceous in Kansas we estimate to be nine hundred and sixty feet.
