Twentieth Annual Meeting. 



case is the main seam fifty feet below the base of the Benton, and it may always be 

 relied upon, when present, within one hundred feet below the lowest Benton ledges 

 of limestone. In some cases the lignite is within twenty or thirty feet of Benton 

 limestones, but usually the shale over the coal gradually loses its carbonaceous and 

 acquires calcareous qualities upwards for forty or fifty feet before a limestone ledge 

 is fully developed. In a few cases, notably on the Smoky river and Coal creek, south- 

 west of Wilson, a ledge of sandstone from 20 to 24 inches thick is developed over the 

 main lignite seam. But even here other thin seams of lignite occur above this sand- 

 stone ledge, and the inclosing shales shade upward into the Benton. 



The Benton limestones have a decided faunal character {Inoceramus probleniati- 

 ciift, Belemnites and Nautilus being characteristic), and the slaty shales show this 

 sometimes before the limestones are reached. In places the highest ( the two feet 

 above mentioned) sandstone ledge has the characteristic Dacotah leaves. Salix has 

 been found in this ledge on Saw-Log creek in Hodgeman county. There is a shell 

 bed over the lignite in Barber county that appears to belong to the Benton, but a 

 shell bed in a similar position in Hamilton county and one in Lincoln county appear 

 to belong to the Dacotah by lithologic as well as paleontological characters. 



It is certain, then, that this lignitic horizon is in the highest part of the Dacotah 

 Group. As to its vegetable origin, we regard it as altogether belonging to the Da- 

 cotah; but it would appear as if the sinking of the land areas at this period became 

 more rapid, and that the waters soon became the Benton seas that overflowed the 

 old Dacotah forests, and through sandy and carbonaceous shales shaded off the Da- 

 cotah formations into limestones of the Benton. The Benton ledges lie so horizon- 

 tal, and form such a marked feature of the topography of that region, that they are 

 the best guides to the position of the lignitic horizon. Find the lowest of these 

 ledges, and the lignite, if jjresent, will be found within one hundred vertical feet be- 

 low it. 



The elevations between the valleys of the rivers rise from two to three hundred 

 feet above the bed of the streams, and in Lincoln, Ellsworth, Mitchell and Republic 

 counties the lowest ledges of the Benton show high up on the slopes, a greater thick- 

 ness of this group being developed upward as we go west. In the valleys, the lower 

 elevations have rounder and smoother outlines, being formed upon the sandstones 

 and shales of the Dacotah, flanked by the more superficial deposits. In places the 

 sandstones of the Dacotah are weathered into fantastic forms of caps, pulpits and 

 pinnacles, but the general outline of the low hills is smooth and round. As we go 

 np the valley of the Saline the upper, massive sandstone of the Dacotah approaches 

 more nearly the bed of the stream, and between it and the Benton is situate the lig- 

 nite horizon. Erosion has cut out the lignite from any place in the main valley in 

 Saline and Lincoln counties. It has a very slight development some four or five 

 miles from the Lincoln county line, where the valley is much narrower, in Russell 

 county. It is far back up the valleys of the tributary creeks, where there is a con- 

 siderable thickness of overlying Benton, that the lignite is developed in Lincoln 

 county. The principal mines are located on branches of Spilman creek in the north- 

 west, and on the headwaters of East Elkhorn in the south of that county, and over 

 the line in Ellsworth county. At one of the shaft mines on Spilman creek the bed 

 of coal averages two feet thick, and has above and below it from one to two feet of 

 a stiff carbonaceous clay shale — "draw clay," as the miners call it. This is overlain 

 and underlain by a yellowish-white sandstone, soft and friable, the line of contact of 

 the sandstone and clay being sharp and well marked. This shaft is .57 feet to the 

 coal. In the Spilman creek mines the coal ( lignite) is said to pinch out into the 

 hill. This would suggest a thickening of the seam, and probably of the shales and 

 other soft beds, towards the valleys by virtue of the removal of pressure by erosion. 



