PLIOCENE.
The Pliocene group of the Tertiary is seen only in the northwestern portion of the State. The northwesterly boundary of the Pliocene begins in the north of Phillips and Smith counties, running irregularly southwesterly to the divide between the head waters of the Saline and Smoky Hill rivers, and thence into Colorado. Detached portions are seen on the high grounds to the southeast of this line. (See geological map).
The strata composing this deposit are very irregular, and can not be traced to any great distance from any given point. This makes it very difficult to calculate its thickness after the lower portions have disappeared under the streams. Every examination has, however, induced me to add to my previous estimates of its thickness, and my present impression is, that in the extreme northwestern part of the State its thickness cannot be less than fifteen hundred feet. It dips slightly to the northwest, and its lowest beds disappear gradually underneath the streams. This gives a good opportunity to study the dividing line between the Cretaceous and Tertiary formations. On the North Fork of the Solomon, for a distance of twenty miles, the hilltops and higher grounds are covered with the sandstone of the Pliocene, while the streams are cutting their beds in the limestones and shales of the Niobrara.
Even the best known portions of this geological area have been but little examined, and consequently our knowledge of its local features is quite limited. Professors Cope and Marsh have, in their visits to the Cretaceous, made some casual notices of the southern portion, without spending time in searching for its fossils.
During the summers of 1874, '75 and '76 we spent much time along the line of its union with the Niobrara, and made some excursions across it, thus becoming acquainted with its outlines and a few of its fossils. The line of demarkation, at most points between it and the Cretaceous, is clear and well defined. In numerous places we have found the fossils of the mammalia of the Pliocene within ten vertical feet of the marine shells and vertebrates of the Cretaceous; and in slides we frequently found them intermingled. The contrast is remarkable, as hardly a single type is common to both, the one being marine and reptilian, the other land fossils, and the bones those of mammals.
The material of the Pliocene deposits consists of sandstone of various shades of gray and brown, occasionally whitened by a small admixture of lime. The lower strata are usually composed of finer sand than the upper, and are looser and more friable in their texture. The over-lying beds are of coarser ingredients, consisting of water-worn pebbles of metamorphic rocks — quartz, greenstone, granite, syenite and sometimes fragments of fossil wood from an older formation. The polishing action of water is not so thorough as in the Drift. These portions of the deposits when crumbled and the finer parts washed away, have much the appearance of Drift, and have been mistaken for it. This formation, down to a recent period, must have covered the whole of the Cretaceous, as we find the coarser pebbles scattered, to a greater or less extent, over the western half of the State. It appears to have been subjected to later movements of water-currents, as it assumes the form of altered drift, and sometimes includes the remains of the mastodon, elephant, and horse of the later Quaternary age.
The sandstone is usually friable, crumbling on exposure to the atmosphere. When more compact its mechanical construction is so irregular as to render it almost unfit for a building material. When firmly consolidated, it forms the hill-tops of the table-like eminences along the boundary line of the Pliocene and Cretaceous formations.
At Breadbowl Mound, Phillips county, it is about 200 feet above Deer creek, and at Sugarloaf Mound, in the western part of Rooks County, it is about 300 feet above the Solomon river. In these hills, as in many others, the upper strata belong to the Pliocene, while the bases belong to the Niobrara. Farther west it forms the whole of the visible outcrop, and the mounds are not so prominent.
In the southern portion of the Pliocene, in the vicinity of Fort Wallace and Sheridan, the hill-tops are covered with a stratum about eight feet in thickness, very hard and silicious. The material varies from coarse flint-quartz to chalcedony. The latter mineral shades from milk white to transparent, sometimes presenting a semi-opal appearance. The so-called moss-agate is found in the upper few inches of the stratum. This cap-rock is interesting to the mineralogist by showing the moss-agate in its various stages of formation. The lower portion of the eight feet indicates an imperfect chemical solution of the silica and black oxide of manganese; therefore, the crystallization of the latter is imperfect. As we examine the stratum from the bottom to the top, we find the chemical conditions more favorable and complete, so that the distinct quartz, chalcedony and manganese of the bottom, become more commingled towards the upper inch or half inch, where the silica must have been sufficiently fluid to allow the manganese* to assume the form of sprig crystals. This peculiar deposit is common on all the high hill-tops of Wallace county, but the best locality is the cap rock of the two buttes, two miles southwest of Sheridan, and half a mile from the line of the Kansas Pacific Railway. They form a notable land-mark to travelers. The total thickness of the Pliocene can not be less than 1,500 feet. It may prove more.
* On a chemical test by Prof. W. K. Kedzie, some iron was found with the manganese.
Over a considerable portion of the Pliocene no fossils are to be seen, but at other points they are somewhat abundant. They are of modern type, represented by bones of deer, beaver, a large animal of the ox kind, two species of the horse, one less in size than the small Indian ponies, a wolf, ivory from the elephant or mastodon, bones of the rhinoceros and camel, and also remains of an undetermined character. In addition to these mammalia, we find the bones and carapace of a large fresh-water turtle five feet in length besides several species or a smaller size. Also a few species of mollusks, of fresh and brackish water types, and some of scarce fossils which have puzzled our best paleontologists.
All the bones are firmly fossilized and many of them changed to a hard, compact silica. The most interesting of these is the ivory. In the process of petrifaction the tusk must have been so softened as to admit the intermixture of black oxide of manganese in solution, which then crystallized in delicate sprigs.
The ivory was next silicified into nearly pure quartz with the usual hardness of that substance. The ivory was thus converted into the so-called moss agate. Some fragments could not be detected, by an ordinary observer, from the usual specimens of that gem.
The ivory is found in fragments in the extreme upper portions of the deposit, and we were at first inclined to call it Post-Tertiary; but the peculiar fossilization, similar to some of the other bones, induces me to think that it belongs to the close of the Pliocene.
The remains of the horse are apparently most common, the teeth and jaws being found from Smith county to the vicinity of Ellis, in Ellis county.
One is a species of the celebrated three-toed horse, having three hoofs coming to the ground. In the northern part of Ellis county, our party, in 1875, found the feet, with the three toes in excellent preservation. In most cases the bones are badly broken and much of the skeleton missing, but sufficient to show that it was of small size. In the same geological horizon I have also found the remains of a horse about the size of the present hog horse, and in the skeleton, and markings of the teeth, very closely allied to it.
At one locality in Norton county, I found the jaws of both on the same level, within ten feet of each other. The mastodon bones were rather frequent. My attention was recently called to the fragment of one on the farm of Mr. S. Decker, near Spring City, Norton county, where it was associated with the vertebrates above named, and several species of brackish water shells. On searching the outcrops within half a mile, I found the fragments of three other individuals represented by ribs, vertebrae, teeth and tusks. All of these were geologically in the lowest part of the Pliocene, and within forty vertical feet of the Cretaceous limestone. In Trego county, in the Saline Valley, I obtained a few bones from two other mastodons in the same geological horizon, and within less than twenty feet of the Cretaceous. These were all so low that if it should be proved that there is any Miocene in Kansas, they must be credited to that epoch.
All the six specimens were so fragmentary that it was difficult to decide the species. But one femur was nearly entire, and strikingly resembled Mastodon Giganteus. Had I found it in the alluvium I should have had no hesitancy in assigning it to that species. Its great age, however, induces us to assign it to a different species. These bones were fossilized with lime and consequently not nearly as hard as those of the later portion of the Pliocene, near the moss-agate beds. A full and careful examination of the Pliocene of Kansas will undoubtedly furnish some valuable fossils, illustrating the mammalia of the period, and give to science some new species, as it has in fact already done. The Eocene and Miocene have not yet been discovered in Kansas, unless the specimen of the three-toed horse, found in Ellis county, should prove to be the anchitherium of the Miocene. It was embedded in the lowest part of the deposit, within ten feet of the Niobrara limestone. As at this locality the sandstone is quite distant from the other Tertiary beds this is more likely to be Miocene than any other stratum that I have discovered. Further examination of this formation is desirable.
