The geology of this region has been very partially explored, but appears to be quite simple. The following description of the section along the line of the Kansas Pacific Railroad, will probably apply to similar sections north and south of it. The formations referable to the cretaceous period on this line, are those called by Messrs. Meek and Hayden the Dakota, Benton, and Niobrara groups, as Nos. 1, 2 and 3. According to Leconte,[3] at Salina, one hundred and eighty-five miles west of the State line of Missouri, the rocks of the Dakota group constitute the bluffs, and continue to do so as far as Fort Harker, thirty-three miles farther west. They are a "coarse brown sand-stone, containing irregular concretions of oxide of iron," and numerous molluscs of marine origin. Near Fort Harker, certain strata contain large quantities of the remains (leaves chiefly) of dicotyledonous and other forms of land vegetation. Near this point, according to the same authority, the sand-stone beds are covered with clay and limestone. These he does not identify, but portions of it from Bunker Hill, thirty-four miles west, have been identified by Dr. Hayden, as belonging to the Benton or second group. The specimen consisted of a block of dark, bluish-gray clay rock, which bore the remains of the fish Apsopelix sauriformis (Cope). That the eastern boundary of this bed is very sinuous is rendered probable by its occurrence at Brookville, eighteen miles to the eastward of Fort Harker, on the railroad. In sinking a well at this point, the same soft, bluish clay rock was traversed, and at a depth of about thirty feet a skeleton of a saurian of the crocodilian order was encountered, the Hyposaurus vebbii (Cope).
The boundary line, or first appearance of the beds of the Niobrara division, has not been pointed out, but at Fort Hays, seventy miles west of Fort Harker, its rocks form the bluffs and outcrops every-where. From Fort Hays to Fort Wallace, near the western boundary of the state, one hundred and thirty-four miles beyond, the strata present a tolerably uniform appearance. They consist of two portions; a lower, of dark-bluish calcareo-argillaceous character, often thin-bedded; and a superior, of yellow and whitish chalk, much more heavily bedded. Near Fort Hays the best section may be seen, at a point eighteen miles north, on the Saline river. Here the bluffs rise to a height of two hundred feet, the yellow strata constituting the upper half. No fossils were observed in the blue bed, but some moderate-sized Ostreæ, frequently broken, were not rare in the yellow. Half-way between this point and the Fort, my friend, N. Daniels, of Hays, guided me to a denuded tract, covered with the remains of huge oysters, some of which measured twenty-seven inches in diameter. They exhibited concentric obtuse ridges on the interior side, and a large basin-shaped area behind the hinge. Fragments of fish vertebræ of Anogmius type were also found here by Dr. Janeway. These were exposed in the yellow bed. Several miles east of the post, Dr. J. H. Janeway, Post Surgeon, pointed out to me an immense accumulation of Inoceramus problematicus in the blue stratum. This species also occurred in abundance in the bluffs west of the Fort, which were composed of the blue bed, capped by a thinner layer of the yellow. Large globular or compound globular argillaceous concretions, coated with gypsum, were abundant at this point.
Along the Smoky Hill River, thirty miles east of Fort Wallace, the south bank descends gradually, while the north bank is bluffy. This, with other indications, points to a gentle dip of the strata to the north-west. The yellow bed is thin or wanting on the north bank of the Smoky, and is not observable on the north fork of that river for twenty miles northward or to beyond Sheridan Station, on the Kansas Pacific Railroad. Two isolated hills, "The Twin Buttes," at the latter point are composed of the blue bed, here very shaly to their summits. This is the general character of the rock along and north of the railroad between this point and Fort Wallace.
South of the river the yellow strata are more distinctly developed. Butte Creek Valley, fifteen to eighteen miles to the south, is margined by bluffs of from twenty to one hundred and fifty feet in height on its southern side, while the northern rises gradually into the prairie. These bluffs are of yellow chalk, except from ten to forty feet of blue rock at the base, although many of the canyons are excavated in the yellow rock exclusively. The bluffs of the upper portion of Butte Creek, Fox, and Fossil Spring (five miles south) canyons, are of yellow chalk, and reports of several persons stated that those of Beaver Creek, eight miles south of Fossil Spring, are exclusively of this material. Those near the mouth of Beaver Creek, on the Smoky, are of considerable height, and appear at a distance to be of the same yellow chalk.
I found these two strata to be about equally fossilliferous, and I am unable to establish any palæontological difference between them. They pass into each other by gradations in some places, and occasionally present slight laminar alternations at their line of junction. I have specimens of Cimolichthys semianceps (Cope), from both the blue and yellow beds, and vertebrae of the Liodon glandiferus (Cope) were found in both. The large fossil of Liodon dyspelor (Cope) was found at the junction of the bed, and the caudal portion was excavated from the blue stratum exclusively. Portions of it were brought East in blocks of this material, and these have become yellow and yellowish on many of the exposed surfaces. The matrix adherent to all the bones has become yellow. A second incomplete specimen, undistinguishable from this species, was taken from the yellow bed.
As to mineral contents, the yellow stratum is remarkably uniform in its character. The blue shale, on the contrary, frequently contains numerous concretions, and great abundance of thin layers of gypsum and crystals of the same. Near Sheridan concretions and septaria are abundant. In some places the latter are of great size and, being embedded in the stratum, have suffered denudation of their contents, and, the septa standing out, form a huge honey-comb. This region and the neighborhood of Eagle Tail, Colorado, are noted for the beauty of their gypsum-crystals, the first abundantly found in the cretaceous formation. These are hexagonal-radiate, each division being a pinnate or feather-shaped lamina of twin rows of crystals. The clearness of the mineral, and the regular leaf and feather forms of the crystals give them much beauty. The bones of vertebrate fossils preserved in this bed are often much injured by the gypsum formation which covers their surface and often penetrates them in every direction.
The yellow bed of the Niobrara group disappears to the south-west, west, and north-west of Fort Wallace, beneath a sandy conglomerate of uncertain age. Its color is light, sometimes white, and the component pebbles are small and mostly of white quartz. The rock wears irregularly into holes and fissures, and the soil covering it generally thin and poor. It is readily detached in large masses, which roll down the bluffs. No traces of life were observed in it, but it is probably the eastern margin of the southern extension of the White River Miocene Tertiary stratum. This is at least indicated by Dr. Hayden, in his geological preface to Leidy's extinct mammals of Dakota and Nebraska.
Commercially, the beds of the Niobrara formation possess little value, except when burned for manure. The yellow chalk is too soft in many places for buildings of large size, but will answer well for those of moderate size. It is rather harder at Fort Hays, as I had occasion to observe at their quarry. That quarried at Fort Wallace does not appear to harden by exposure; the walls of the hospital, noted by Leconte on his visit, remained in 1871 as soft as they were in 1867. A few worthless beds of bituminous shale were observed in Eastern Colorado.
The only traces of Glacial Action in the line explored were seen near Topeka. South of the town are several large, erratic masses of pink and bloody quartz, whose surfaces are so polished as to appear as though vitrified. They were transported, perhaps, from the Azoic area near Lake Superior.