166 GEOGRAPHIC DISTRIBUTION. 



carbonaceous shales and lignitic coal obtained from time to time, now here 

 now there, and such shales and coals are found distributed in great profu- 

 sion throughout the entire area which has been studied. In a section made 

 on the south side of the railroad between Lawrence Section House and Rock 

 Springs more than 30 seams and beds of coal are noted. The coals of this 

 horizon in the vicinity of Black Butte Station have been frequently described 

 by other geologists. 



It is not my purpose to discuss the distribution and character of the 

 lignitic coals in this report. 



LOWER GREEN RIVER GROUP. 



In the Flaming Gorge district the Lower Green River Group overlaps 

 the Bitter Creek Group, and farther westward disappears by attenuation. 



The course of the Green River from the northern border of the area 

 embraced on the map to the hogback six miles north of Flaming Gorge is 

 through the beds of this group, and an irregular escarpment of these beds 

 having deep reentrant angles, and spaces broken into low hills, faces the 

 axis of the Aspen Mountain uplift. The escarpment known as Pine Bluffs 

 on the east side of the uplift is of this age. Another outcrop is found north 

 of Dry Mountains and west of the Po Canon district, where their upturned 

 edges are exposed on the border of a basin of displacement or sag due to a 

 downthrow. 



This group is composed chiefly of bituminous shales and impure lime- 

 stones, the latter being both arenaceous and argillaceous; but to the south, 

 near the Uinta uplift, the group is much thickened and the shales are replaced 

 by sandstones, and conglomerates of fine pebbles appear. 



From this fact it is inferred that the beds of this group are derived from 

 the Uinta region, and that the material was supplied from limestones and 

 sandstones of Carboniferous Age. Conditions favorable to the accumula- 

 tion of Carbonaceous shales and lignitic coal are less frequent than in the 

 former period, but a fine bed of coal has been found at the base of this group 

 on the bank of the Green River, about eight miles below the station, and 

 Carbonaceous shales and thin seams of coal have been found at other hori- 

 zons elsewhere. 



