STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 99 



it could not be found. At one locality, a seam belonging at or near 

 to this Dry Hollow horizon underlies a bed of oyster shells, 20 feet 

 thick. The quality of the Dry Hollow coal is good, but the bed 

 is too variable, so that no mines of any importance were in opera- 

 tion at the time of Wegemann's examinations. 



No coal of economic importance has been reported from the 

 Pierre of Uinta County in Wyoming, but in southern Sweetwater 

 County, where Gale" recognized Lewis, Mesaverde and Mancos, he 

 saw in one exposure two seams, 8 and 10 feet thick, separated by 

 only 25 feet. The coal is not persistent and, within a short distance, 

 it becomes black shale with coaly streaks. The lower seam is sepa- 

 rated by one foot of bone from a thick white sandstone. Farther 

 north in the same county is the Rock Springs coal field, intersected 

 by the Union Pacific Railroad. There Schultz''' recognized the 

 Lewis shale, without coal, and the Mesaverde, consisting very largely 

 of sandstone with important coal seams. The " Laramie " of 

 Schultz is not everywhere conformable to the underlying Pierre. 

 The unconformity is especially marked on the south and west sides 

 of the Rock Springs Dome, where the " Laramie " rests on the Rock 

 Springs coal group, a hiatus of fully 2,500 feet ; but the succession 

 is complete and conformable throughout on the west side of the 

 Dome. Elsewhere there appears to be no unconformity. 



The important coal seams are in the Almond and Rock Springs 

 groups, separated by 800 to 1,000 feet of mostly massive sandstone, 

 more or less conglomerate in the upper third with pebbles of gray 

 and black quartz. The Almond coal group, 700 to 900 feet thick, 

 contains many seams of coal and of carbonaceous shale. The seams 

 are variable, though less so than are those in the Ro^k Springs 

 group, but the coal is comparatively poor and no works were in 

 operation at the time of Schultz's examination. 



The coals of the lower or Rock Springs group are black, with 

 distinct bedding planes and do not slack on exposure. The coal- 

 bearing portion is about 1,275 ^^^t with 37 seams containing in all 

 somewhat more than no feet of coal. Five seams have been opened 



" H. S. Gale, Bull. 341, pp. 310-314. 



'« A. R. Schultz, Bull. 341, pp. 256-382; Bull. 381, pp. 214-281. 



