86 DESCRIPTIVE GEOLOGY. 



Associated with it, occurs the well-known form, Inoceramus Barrdbini^ 

 which is also abundant in the long sandstone banks on the opposite side 

 of the valley, which dip only 2° to 3° eastward. 



Between Cooper and Rock Creeks, the country presents but little 

 variety in its general features; the nearly horizontal sandstones terminating 

 in abrupt walls toward the plains. At Rock Creek, the Fox Hill beds 

 are well developed on both sides of the valley, lying close up against the 

 Archaean body in flat-topped hills, rising 300 feet above the stream-bed, 

 from which were collected several specimens of the genus Inoceramus. 

 In the Fox Hill sandstones, between Cooper and Rock Creeks, layers 

 of carbonaceous clays and shales occur cropping out along the benches, 

 and carrying several thin beds of lignite. Of these coal outcrops, two 

 have been to some extent explored, — the one known as the Cooper Creek, 

 and the other as the Rock Creek coals. The Cooper Creek coal occurs on 

 the north side of the valley, interstratified in a bed of hard clay, which is 

 both overlaid and underlaid by sandstone. The beds have a gentle dip to 

 the eastward. So far as known, no Molluscan remains have been found in 

 immediate connection with the coal strata, yet it seems quite evident that 

 they underlie beds characterized by Fox Hill species. 



The coal possesses a lustrous black color, a moderately compact text- 

 ure, and resembles that found east of the Colorado Range. An analysis of 

 this coal was made by Dr. F. A. Genth,^ of the University of Pennsylvania, 

 with the following result: 



Moisture - - 9.28 



Volatile matter 39.12 



Carbon 47.04 



Ash, yellowish-brown — 4.56 



100.00 



It contains 1.38 per cent, of sulphur, which is equal to 2.59 per cent. 

 of pyrites. 



The Rock Creek coal is situated about 6 miles southeast from the 



lEeport of U. S. Geological Survey of Wyomiug, Dr. F. V. nayden, 1870, 185. 



