CRETACEOUS UPLIFT OF BITTER CREEK. 231 



Black Butte Station, where there is distinct non-conformity between the 

 beds at the base and those which form the summit of the bluff, and again 

 to the north of Point of Rocks Station, where the discrepancy of angle is 

 only 2°. The finding of fossils, of distinctly fresh- water types, in the 

 vicinity of marine and brackish- water forms, may be explained by a non- 

 conformity of erosion, where fresh- water Tertiary beds, of similar lithologi- 

 cal character, have been deposited in valleys eroded out of the rocks of the 

 Laramie group. 



From Black Butte Station to Point of Rocks, the course of Bitter 

 Creek winds through low sandstone ridges, following, in general, their 

 trend. The rocks exposed are grayish- white and rusty-reddish sand- 

 stones, with intercalated beds of sand}^ clays and carbonaceous shales, the 

 latter frequently opening out into well-defined coal seams. The coal seams 

 are not, however, continuous for any great distance, and do not, therefore, 

 afford a means of tracing a correspondence of geological horizon. In many 

 cases, the carbonaceous shales have, in former times, become ignited, and, 

 having burned out, left a rusty-red ash-material in their place. The highest 

 coal seams observed are those in the bluff's to. the east of Black Butte Sta- 

 tion and at Hallville, of which the former has a thickness of about 4^ feet, 

 and the latter 6 feet ; in either case capped by a well-defined clay seam. 

 In this clay, above the Hallville coal, were found numerous remains of 

 fresh-water fossils, among which were recognized Corhicula fracta, Cor- 

 hicula crassatelliformis, and Unio (sp.?). Similar, and, in some cases, iden- 

 tical forms have been found b}'' Professor Meek in the beds overlying 

 the coal at Black Butte Station. These facts, taken together with the 

 evidences of displacement observed at the Hallville coal-mine, render it 

 probable that the two belong to the same horizon, and that the overlying 

 beds, and, possibly, even the coal seam itself, if it be true, as reported, that 

 coal has been discovered in the Vermillion Creek beds to the west of Rock 

 Springs, may belong to the overlying Tertiary. The discovery by Pro- 

 fessor Cope, since the completion of our field-work, of the remains of a 

 saurian, in the neighborhood of Black Butte Station, proves the existence 

 at the surface of well-defined Cretaceous strata as far east as this point. 

 Great quantities of leaf-impressions and plant-remains are found also in 



