STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 117 



stones are more or less flinty, are cross-bedded, ripple-marked and 

 locally conglomerate. These coals have been placed in the Dakota 

 by several students, but the presence of fossils confirms Lee's refer- 

 ence to the Benton. The Ferron sandstone cannot be recognized 

 in this part of the basin and the coals of Castle Valley are wanting. 



No observer has noted the existence of Benton coals on the 

 northern side of the Uinta Basin within Colorado, but they have 

 been recognized in two outlying fields along the northwestern border 

 in Utah, which have been described by Lupton.^^^ The western or 

 Blacktail Mountain coal field is almost due north from the Emery 

 field. The Mancos formation is about 2,650 feet thick. The upper 

 part, 1,450, consists of shale; the middle, about 250 feet, is chiefly 

 sandstone and has coal seams ; the lower part is sandstone and shale. 

 The shales increase and the sandstone decreases toward the east ; 

 the upper shale is but 800 feet thick in the western part of this field. 

 Four coal seams were seen, 3 to 11 feet thick, but extremely vari- 

 able. The coal is very similar to that from the Mesaverde, though 

 3.500 feet lower in the column ; some of it is very good, with but 

 3 per cent, of ash and 10 per cent, of water in the air-dried coal. 

 In the Vernal coal field, 30 miles farther east, the Mancos is not far 

 from 2,500 feet thick, but the upper or shale division is 2,100 feet 

 and the lower or sandy division is about 400 feet, with some coals 

 near the top. It is quite possible, as suggested by Lee, that these 

 coals are at same horizon with those of the Ferron sandstone. They 

 are irregular but in some cases yield a good coal. 



The Coalville coal field, about 30 miles northeast from Salt Lake 

 City, Ut^h, was examined by Wegemann.^^^ There, at somewhat 

 more than 1,600 feet from the base of the Cretaceous section at 

 Coalville, is the important coal seam known as the Wasatch. The 

 roof is sandstone, locally conglomeratic, with sometimes a thin 

 shale intervening. It appears to be quite regular. The floor is 

 shale or sandstone and is irregular, there being " rolls " which oc- 

 casionally cut out as much as 5 feet of the coal. The coal seam is 

 from 5 to 14 feet thick but as a rule, the variations are not abrupt. 

 The coal as mined at Coalville is of excellent quality. It is stated 



^11 C. T. Lupton, Bull. 471-/, 1912, pp. 13, 35, 44. 

 112 C. H. Wegemann, Bull. 581-ii, 1915, pp. 161-184. 



PROC. AMF.R. PHIL. SOC., VOL. LVI, I, MAY 24, I9I7. 



