86 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



the Black Hills on the Wyoming border. No coal, aside from some 

 insignificant lenses, has been seen in this northern extension of the 

 Fox Hills ; and the conditions are the same in Alberta. ^^ 



The Pierre Formation. 



Thus far the tracing has been comparatively simple. The Lara- 

 mie and Fox Hills mark the closing portion of the Cretaceous and 

 conditions appear to have been much the same in each throughout 

 the whole region. But during the Pierre, conditions near the source 

 of sediments were wholly different from those in the great area 

 beyond. On the eastern side, the rocks are almost wholly shale and 

 without coal, while on the western and southern sides there are 

 great deposits of sandstone and sandy shale with, in some areas, 

 important coal seams at several horizons. At the east, the fossils 

 are marine but at the west and south there are marine and brackish 

 as well as fresh-water horizons. The offshore and strand conditions, 

 marking strife between advancing land and the sea, are evident from 

 the recurrence of a fauna allied to that of the Fox Hills as well as of 

 sections showing a succession like that of Fox Hills and Laramie, 

 a gradual transition from marine to continental deposits. In the 

 description of widely separated areas, local terms based on litholog- 

 ical features became necessary, but the resulting confusion has been 

 removed by the labors of the students listed on an earlier page and 

 the relations are now well understood, though in some areas there 

 still remains uncertainty as to the planes of separation. 



In Alberta, Montana and northern Wyoming the Pierre is di- 

 vided into Lewis or Bearpaw shale, Judith River formation, Clag- 

 gett shale and Eagle sandstone: the last, overlying shale. This 

 order, descending, is distinct from the Bighorn Basin of Wyoming 

 northward into Alberta, but, at a short distance westward, where one 

 approaches the western limit of Cretaceous deposition, some modifi- 

 cations in nomenclature and grouping become necessary. Farther 

 south in W^yoming, Colorado and New Mexico, the succession is 

 given as Lewis shale, Mesaverde formation and Mancos shale. The 

 terrn, Mesaverde, is indefinite ; it is the sandstone member of the 

 Pierre and is more or less coal-bearing. In some extensive areas it 



'•'^'E. Stebinger, Bull. 621-K, 1916, p. 125; Prof. Paper go-G, p. 62. 



