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). [3] Notes on the geology of the survey for the extension of the Union Pacific Road E. D. from the Smoky Hill to the Rio Grande, by John L. Leconte, M. D. Philadelphia, 1868.