320 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



line of drift trends off to the northwest, and lias not as yet been recog- 

 nized along the Yellowstone valley. 



Cretaceous strata form the greater part of the surface rocks all the 

 way from the -lames Valley to the mountains. The divisions of the 

 Cretaceous system recognized on the Great Plains and along the base 

 of the mountains in Dakota and Montana are: 



Series. Subdivisions. 



Livingston. 



Laramie . . . 



Montana 

 Colorado 



Prevailing rooks. 



Conglomerates, sandstones, and voloanic agglomerates. 

 White sandstones, olays, and shales. 



( Fox Hills 



'l Foi t Pierre. . . 



< Niobrara. Shalesand limestones. 



I Port Benton. . j 

 Dakota | Sandstones and conglomerates. 



The Laramie Cretaceous, the coal-bearing series of the Great Plains 

 and the Rocky .Mountain region, is the prevailing horizon, and only in 

 a few limited areas along the line of travel do the underlying rocks 

 come to the surface east of the Yellowstone River; from Jamestown to 

 Livingston, a distance of over 660 miles (1 } 046 km.), seldom do any but 

 Cretaceous rocks appear at the surface from beneath the drift. 



The Laramie consists of coarse sandstones and shales, the former 

 more abundant at the base of the series, where also most of the coal 

 seams are found. This important series has been traced north and 

 south almost continuously along the Rocky Mountain front within the 

 boundaries of the United States, and in British America has been 

 recognized in the valley of the Yukon River, stretching northward 

 nearly to the Arctic Circle. South of the United States it is less defi- 

 nitely known, but coal seams of Cretaceous age which probably belong 

 to this horizon have been observed at various points in Mexico and 

 also in Central America. Westward, the Laramie Cretaceous extends 

 through the various breaks in the front ranges to the one hundred and 

 twelfth meridian. The Northern Pacific Railway crosses it at one of its 

 broadest expansions. Under varying conditions the coal obtained from 

 the beds of this series range from a dry, porous, non-coking coal of very 

 low specific gravity, through slightly caking coal, to a fairly dense coal 

 affording an excellent quality of coke, and, in limited areas, to an 

 excellent anthracite. Nearly 5,000,000 tons of coal were mined in these 

 beds during the census year 1890. 



Near the base of the mountains the Upper Cretaceous has been 

 divided into two distinct groups which have been designated as the 

 Laramie and the Livingston. The former is mainly a normal white 

 sandstone composed of quartz grains; the latter is made up largely of 



