ARBAL DISTRIBUTION OF THE LIGNITIC FORMATIONS. 9 



come in contact, the former is superimposed to the latter; and that really 

 the White River group formed a vast basin subsequent to the existence of the 

 great lake on which the Lignitic sediments were deposited." He adds: — 

 "We find also, by examining the White River group along the base of the 

 mountains, that the Laramie Range formed a barrier that prevented it from 

 extending into the Laramie Plains; but the evidence is clear that at the time 

 of the existence of the great Lignitic lake or sea, this barrier did not pre- 

 vent the water communication with the Laramie Plains. Indeed, the evi- 

 dence seems quite clear that, with the exception perhaps of some isolated 

 peaks rising above the waters, there was no mountain barrier where we have 

 now the Laramie Range. Therefore, with the exception of the Bear River 

 and Coalville group, we may connect the coal-bearing beds of the Laramie 

 Plains and Colorado with the vast group in the Northwest." 



The southern basin, generally named the Colorado Basin, is followed, 

 nearly without interruption, from a few miles soutii of Cheyenne to New 

 Mexico. It is continuous to the Soutli Platte below Denver, where it is 

 covered by a ridge of hills, the Monument Creek group, and then reappears 

 near Colorado City. On the Arkansas River, near Canon City, outlayers of 

 the Lignitic have been left upon the Cretaceous, which by denudation is 

 exposed over nearly the whole valley; and south of the Arkansas, or from the 

 Spanish Peak the belt becomes continuous again to the Raton Mountains, in 

 New Mexico, with outlayers or isolated patches appearing as far south as 

 Albuquerque. 



The southern Lignitic covers, therefore, an extensive area. It cannot 

 be estimated, however, for the reason that it is cut by more recent deposits 

 at some places, as south of Denver, and by erosions along the Arkansas River, 

 and especially because its width from the mountains to the east is unknown. 

 The upheaval of the mountains has exposed the edges of the Tertiary strata 

 with those of the underlying formations, throwing them up into a series of 

 hogbacks, which pass very abruptly from an inclined, even vertical, position, 

 in the proximity of the mountains, to a horizontal direction toward the plains. 

 All along the mountains, the Lignitic is at the upper stage, and therefore it is 

 covered merely in passing to ihe plains by the more recent deposits of the 

 surface. But how far it extends, or it is accessible for coal, has not yet been 

 ascertained. Shafts have been sunk east of Denver about ten miles, and thick 

 beds of coal or lignite have been reached at a moderate de[)th. Other 



