OCR Text |
Show 220 Dakota groups have been collected within 35 feet vertically and one-half mile horizontally. The material of this deposit 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, iu most cases, owing to the presence of iron, in the condition of oxide and silicates. Sometimes poor limonite is seen. In some places, in every county where it abounds, it affords a good building- material. It is frequently interstratified or overlaid by clay- shales, of almost all 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 the farmers as feeding- troughs for hogs and cattle. In a few localities they assume the form of tubes of various sizes, some being 3 inches in diameter and 3 to 8 feet in length. These concretionary deposits are sometimes glazed and distorted, as if they had been subject to the action of fire; but the cause is the oxidation of iron, and not any application of heat. Such specimens of sandstone frequently inclose well- preserved dicotyledonous leaves. The fossils of the Dakota are very unequally distributed over its area. In searching for the marine mollusks, we have found but two localities, both in the western part of Saline County, in the vicinity of Bavaria. In one of these spots, covering a few acres, we procured twelve species new to science. These are figured and described in Professor Meek's work on the Invertebrates, now in press. The other locality furnished a less number. In collecting fossil leaves, we have frequently examined every visible outcrop for fifteen or twenty miles without finding a specimen; then perhaps a single square mile would present several good localities. In this irregular manner we have collected specimens from Washington County to Fort Larned, a distance of one hundred and fifty miles. The fossil plants are usually obtained from thin layers, or strata, extending in a horizontal position along a ravine or around a hill. They may occur at several places in the same vicinity, but usually without any connection. The fossil flora is almost entirely represented by leaves, though a few specimens of fruit, imperfectly preserved, have been collected; also some poor fragments of wood and bark. The leaves, however, are usually in excellent preservation, the veins and veinlets as they lie imprinted on the stone being frequently as clearly visible in all their outlines as those just taken from the living tree. Professor Lesqnereux has recently made a report, issued by the Department of the Interior, on the Fossil Flora of the Cretaceous Dakota Group, which is one of the most valuable monographs published in our country. He describes one hundred and thirty- two species, distributed among seventy- two genera and twenty- three orders, of which one hundred and seven species of nineteen orders and fifty two genera are dicotyledonous plants. Of these, more than one- half have been collected in Kansas; and about twenty of the new species were described by Professor Lesqnereux from specimens discovered by the writer. To these are to be added twenty- six new species described by the same author in a recent bulletin ( VII of Xo. 5, second series) of Hayden's reports. Additions to these are constantly being made. They are found at all depths in the Dakota, from within 35 feet of the Permian to within 40 feet of the Fort Hays limestone. Although all the species are extinct, yet nearly all the of genera are now existing, and all are of marked modern type. There are eight species of conifers, five of poplar, six of willow, eight of oak, six of platanus or |