THE CRETACEOUS PERIOD. 159 



life of the west, perhaps because conditions were not yet favorable 

 for the incoming of the mammalian life from the regions where it 

 originated. 



The Livingston formation of Montana, consisting of brackish- and 

 fresh-water sediments, with some intercalated volcanic agglomerates 

 and breccias, rests unconformably on the (Lower) Laramie, and cor- 

 responds in its general relations with the Arapahoe and Denver forma- 

 tions. Its sediments were largely derived from the older sedimentary 

 rocks which seem not to have contributed to the earlier Mesozoic for- 

 mations, indicating post-Laramie-pre-Livingston deformation in this 

 region. The Livingston flora resembles that of the Eocene, and the 

 formation underlies fresh-water Eocene beds conformably. In some 

 parts of Wyoming, on the other hand, beds thought to have been 

 deposited at the same time as the Denver, Arapahoe, and Livingston 

 formations are said to be a part of the inseparable Laramie series. 1 



The thickness of these formations, especially that of the Livingston, 

 is very great, being estimated at 7000 feet. 2 Even if the sediments 

 accumulated rapidly, as their nature indicates, this great thickness shows 

 that the epoch was a long one. 



Coal. — The Cretaceous is preeminently the coal period of the 

 west. Coal-beds occur in every one of its principal divisions in this 

 part of the continent. The total amount of coal, which is chiefly 

 in the Laramie series, is comparable to that in the Pennsylvania n 

 system, though the Cretaceous 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,- 

 000,000 tons of available coal, 3 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. 4 Anthra- 

 cite 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. 241. 



Stanton and Knowlton, Stratigraphy and Paleontology of the Laramie and 

 Related Formations in Wyoming. Bull. G. S. A., Vol. 8, pp. 127-156. 

 2 Weed and Iddings, Livingston, Mont., folio, U. S. Geol. Surv. 

 8 Storrs, 22d Ann. Rept. U. S. Geol. Surv., Pt, III. 

 4 See Anthracite-Crested Butte folio, U. S. Geol. Surv. 



