116 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



bed is divided by bands of limestone containing brackish-water 

 mollusks. Another has marine hmestone roof and floor, with marine 

 fossils, but one of its partings has Physa, Planorbis and other fresh- 

 water forms, related to those of ponds and streams. Several of the 

 sandstones are cross-bedded. ^°® 



Liipton examined the Emory coal field in in the southern part of 

 Castle Valley, about 40 miles northwest from the Henry Mountains, 

 which had been studied by Gilbert. ^°^ At approximately 600 feet 

 from the base is the Ferron sandstone, regarded by Lupton as equiva- 

 lent to Gilbert's Blue Gate sandstone. It is 800 feet thick at the 

 southwest but becomes thinner toward the northeast until at north 

 end of the valley it is l)ut 75 feet. This sandstone holds all the 

 Benton coal seams, but these are confined to the southern part of 

 the valley, disappearing toward the north as the sandstone de- 

 creases in thickness. Local unconformities which one must accept 

 as evidence of contemporaneous erosion, occur within this sand- 

 stone. The coal-bearing area is a narrow strip about 33 miles long. 

 Fourteen coal horizons were recognized but the deposits are lentic- 

 ular and correlations are uncertain. The variations are abrupt ; in 

 one case, from one to 20 feet within a very short distance. Many 

 of the seams are injured seriously by partings. The coal is low 

 grade bituminous of very fair quality, with color and streak black, 

 and contains resin. In portions it is thinly laminated, but at times 

 the dull layers are several inches thick and resemble cannel. 



The most easterly locality in the southern part of the Uinta 

 Basin,"" at which the Benton coals have been recognized, seems to 

 be that on the Gunnison River about 60 miles east from the Utah- 

 Colorado line. There Lee found at base of the Benton a succession 

 of sandstone and shale with maximum thickness of about 80 feet. 

 The lenses of coal, a few inches to 3 feet thick, occur in the shales. 

 Near the junction of Gunnison and Grand Rivers, 5 deposits of coal, 

 one to 3 feet thick, were seen, but these lenses are too indefinite in 

 extent and contain too much carbonaceous shale to justify mining. 

 The ash in air-dried coal varies from 6 to 34.5 per cent. The sand- 



108 \Y -p. Lee, Bull. 316, 1907, citations from pp. 361-373. 



109 G. K. Gilbert, "Geology of the Henry Mountains," 1877, pp. 4-10; 

 C. T. Lupton, Bull. 628, pp. 30, 31, 47-74, 78. 



110 W. T. Lee, Bull. 510, 1912, pp. 24, 25, 68. 



