STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 139 



in Montana it is divided by shales into subordinate wedges, and 

 these " fingers " disappear toward the east, giving place to marine 

 shales. Coal seams are confined to the areas of sandstone and 

 shale, there being none in the fine-grained marine shales, which 

 extend from the longitude of central Colorado to the eastern border 

 of the Cretaceous, except in the sandy strip along the southern 

 border in New Mexico. In the sandstone wedges, land and marine 

 conditions alternated, the former continuing for long periods at 

 m.any localities, long enough to permit accumulation of thick coal 

 seams. At the same time, the distribution of coal is indefinite. 

 In the southern basin within New Mexico, the coal seams are im- 

 portant locally, but they are irregular and there are broad spaces, 

 which are altogether barren. The story is similar in the Uinta 

 Basin; coal seams are very numerous in the IMesaverde, but they are 

 not persistent ; portions of the column showing workable seams in one 

 district are apparently without trace of coal in others. The fea- 

 tures are the same in the Green River Basin ; an extensive coal field 

 in Sweetwater County of Wyoming has many lenses yielding coal 

 of excellent quality, but at the same horizons in other counties there 

 is either no coal or the seams are mere streaks. Farther east, the 

 sandstones thin away and all traces of coal disappear. Elsewhere 

 in Wyoming the distribution of coal is certainly capricious ; here 

 and there one finds a seam thick enough to be digged for local 

 supply, but such exposures are separated by intervals of many 

 miles. In Montana, coal occurs only in scattered spots, while the 

 intervening spaces seem to be barren. Seams of workable coal are 

 more numerous in Alberta and the lenses are larger ; conditions 

 favorable to coal accumulation existed in a large area. But there, 

 as in the United States, the sandy coal-bearing formation thinned 

 away toward the east and was replaced with shale, in which no coal 

 is known. 



The sandy deposits, containing Benton coals, reach only to the 

 109th meridian, aside from an isolated deposit in Colorado near the 

 loSth. The most westerly localities at which coal has been found 

 are in southwestern Utah, where the conditions are not in accord 

 with the assertion that coal is present only in association with pre- 

 vailingly coarse materials. In those fragmentary fields, the rocks 



