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.