In a former report, I was doubtful whether the Benton was represented in Kansas, but a more careful examination decides that what I provisionally called Fort Hays corresponds very nearly in age to the Benton, though the physical character of the deposits differ from those found by Prof. Hayden, farther north, and the fossils are a little different.
The upper portion of the Benton is formed by a bed of limestone, which, when it has not suffered from erosion, is sixty feet in thickness. It is composed of layers from one to three feet thick, and is usually so soft and fine grained as to be cut with a knife, or sawed by a common wood-saw. Yet it makes a fine building material, sufficiently durable for stores or dwellings. At Hays City, the school house and court house are built of it, and ten miles from that place the Kansas Pacific Railroad opened a quarry for use in constructing piers of bridges and other structures along its line. It also burns to a good quick lime. It is the thickest uniform stratum of limestone in the State. Its massiveness and persistence make it a well defined geological horizon, showing the line of demarkation between the Niobrara and Benton groups.
It is seen (but not in full thickness) as far South as Walnut creek and Pawnee creek, in Ness county, but better developed in the bluffs of the Smoky river, Southwest of Fort Hays, as well as seven miles west of that place. It can be thence traced to the northwest, crossing the Solomon just above the Forks, near Osborn City, and entering Nebraska in the Republican Valley, near where that river crosses the State line.
Under the heavy bed of limestone forming the highest portion of the Benton group, is seen a friable, bluish-black or slate-colored shale. It abounds in concretions or septaria of all sizes, from one inch to six feet in diameter. The body of the concretions is of hard clay marl, with cracks lined with beautiful crystals of calc-spar. These cracks frequently extend to the outside, and are then filled with a light lime, which gives them fanciful markings, inducing several persons to send them to me as "fossil turtles." This stratum is well exposed near the railroad, a few miles west of Fort Hays, and in most places, where the massive limestone lies on the high bluffs. It is about sixty feet in thickness, and frequently contains fine clusters of compound crystals of selenite.
Below this dark shale, the Benton has a thickness of one hundred and forty feet, best seen west of Wilson creek, composed of shales differing in texture and composition interstratified by layers of limestone. The latter are composed largely of Inoceramus problematicus and a few other marine shells. The shales are variable in color, hardness and composition - lime, sand and clay, sometimes one and sometimes another predominating. All portions of the Benton, below the heavy bed of limestone, are variable at the same horizon at different points, containing no thick, persistent stratum of any kind. A section at any particular locality would be of little value for comparison at another portion of the Benton, except to show the variability of the shales.
The Benton affords a few fish and Saurian remains. It is more noted, especially in the Saline and Solomon valleys, for the number and variety of its Ammonites, embracing several species, from one to thirty inches in diameter. The most common is Prionocyclus woolgari. The larger specimens are almost invariably in fragments, although a portion of the original shell-substance, of a bright, pearly lustre, is still to be seen. Forms allied to the Ammonites are also found, as Scaphites, Mortoniceras, etc., and also several Inocerami, one near I. nebraskensis of Owen.
Some of the lower strata give thin, impure beds of lignite, but no plants could be identified from them.
The total thickness of the Benton group is two hundred and sixty feet.
