THE CRETACEOUS PERIOD 



751 



this part of the continent. The total amount of coal, chiefly in the 

 Laramie, is perhaps comparable to that in the Pennsylvanian system, 

 though the Laramie coal is not now so accessible, and its quality 

 is inferior. It is estimated that along the east and west bases of 

 the Rocky Mountains there are more than 100,000 square miles of 

 coal-bearing lands, and Colorado alone is estimated to have 34,000,- 



Fig. 507. An outcropping ledge of clay, hardened by the burning of the 

 coal-bed below. Except in the immediate vicinity of the burnt-out 

 coal-bed, the clay is not indurated. Near Buffalo, Wyo. (Blackwelder.) 



000,000 tons of available coal, 1 most of which is Cretaceous. The 

 coal is largely lignite, though in Colorado not a little of it has been 

 advanced to coking bituminous coal, and even to anthracite. 2 

 Anthracite referred to the Laramie also occurs farther south in 

 localities where it has been affected by intrusions of igneous rock. 

 The areas of Laramie coal are indicated in Fig. 438. 



Transition beds between Mesozoic and Cenozoic. There are 

 diverse, more or less local, terrestrial formations in the west which 

 have been referred now to the Cretaceous (Laramie, or more 



1 Storrs, 22d Ann. Kept., U. S. Geol. Surv., Pt. III. 



2 Anthracite-Crested Butte folio, U. S. Geol. Surv. 



