34 LAKAMIE BASIN, WYOMING. 
dark shale, upon which lies the Mo wry member, 100 feet or more in 
thickness. 
A short distance northwest of Medicine Bow the Benton formation 
presents the following section: 
Section of Benton formation northwest of Medicine Bow. 
Feet. 
Shale, gray 200 
Sandstone, gray, partly slabby 40 
Shale, gray 800 
Shales, hard, and fine-grained slabby sandstones (Mowry) 75 
Shales, mostly dark, weathered brownish, and with thin sandstones 
in lower part 250 
Cloverly formation. 
The upper sandstone of the Benton is especially prominent in 
the Rock Creek district, giving rise to a long sinuous ridge which 
is very persistent. (See PI. VI, B.) In the vicinity of old Miser 
station it consists of a 4-foot ledge of buff, massive sandstone. 
It is overlain by 350 feet of shales and underlain by several hundred 
feet of dark shales containing a bed of bentonite and black ironstone 
concretions. Next below these is the Mowry shale. The beds of 
bentonite, which appear extensively in this vicinity, are persistent 
features. The thicker one in the vicinity of Miser averages 4 feet in 
thickness and lies a few feet above the Mowry shale. It is succeeded 
by 15 or 20 feet of nearly black soft shale, at the top of which are 
many ferruginous concretions. On the east bank of Sand Creek, near 
the middle of the north side of sec. 2, T. 13 N., R. 75 W., the ben- 
tonite is 4 feet thick and is underlain by 7 inches of soft gray 
sandstone. 
Fossils.— The principal fossils of the Benton formation are the very 
numerous fish scales in the Mowry shale member and a few fragmen- 
tary molluscan remains, fish bones, and teeth which occur at various 
horizons. In the upper sandstone, near the foot of Jelm Mountain, 
were found Inoceramus fragilis, together with fish teeth apparently 
of Ptychodus and Lamna. The upper sandstone afso contains 
Prionocyclus, a fossil which is characteristic of the upper portion of 
the Benton (Carlile) in a wide area of the Rocky Mountain and 
Great Plains provinces. 
NIOBRARA FORMATION. 
The Niobrara formation outcrops at intervals from the foot of 
Sheep Mountain northeastward nearly to Wyoming station, in the 
hills east of Lake lone, along the sides of the various flexures east of 
Medicine Bow, in the Freezeout Hills, and along both sides of the 
Centennial Valley. A wide outcrop zone extends up the valley of 
Little Medicine Bow Creek in Tps. 24, 25, 26, and 27 N. Small 
exposures appear at the south end of Sheep Mountain, in the valley 
