of the Yellowstone Parle. 447 



sediments, nor are there any beds derived wholly, or in part, 

 from volcanic material of later age other than the eruptive 

 masses of the Archean. On the other hand, as will be shown 

 later, closely following and possibly coincident with the Lara- 

 mie uplift, came the first outpouring of igneous rocks, which, 

 beginning in late Cretaceous time, continued throughout a long 

 period, lasting till near the close of Tertiary time. With the 

 blocking out of the mountains, which accompanied the post- 

 Laramie movement, a largely increased continental land area 

 was formed. Coincident with this elevation of the land, denu- 

 dation of the continental mass began, and deposition of fresh 

 sediments uncomformable to the uplifted Laramie took place. 

 Within the park region such sediments, if deposited, were 

 either carried away by erosion or buried beneath outflows of 

 later igneous rocks. 



Along the northern slopes of the Snowy range, about 45 

 miles north of the park, these post-Laramie sediments were 

 deposited several thousand feet in thickness under conditions 

 singularly favorable for their preservation. 



The lowest rocks resting directly upon these upturned sedi- 

 mentary beds, are largely composed of friable sandstones 

 derived from the degradation of the Laramie strata. They 

 are soon followed by sands, conglomerates, clays, aud grits, 

 varying greatly in texture in different localities, and consisting 

 mainly of material derived from the disintegration of igneous 

 rocks. In places, they consist almost wholly of coarse, acid, 

 andesitic agglomerates, which attain a development of nearly 

 2,000 feet in thickness. 



The volcanic nature of the great body of this material was 

 recognized by Mr. Walter H. Weed,* who first carefully 

 studied it, and this view has been generally accepted by all 

 geologists who have since visited the region. According to 

 Mr. Weed, the beds reach a maximum development of nearly 

 7,000 feet. He has proposed to designate them as the Liv- 

 ingston formation, after the town on the Yellowstone river 

 where they are well exposed. 



Since their deposition the Livingston beds have been uplifted 

 and now lie inclined, dipping away from the mountains, hav- 

 ing taken part in subsequent orographic movements which 

 elevated the Rocky Mountains. The limited invertebrate fauna 

 obtained from these beds is as yet too restricted to be of any 

 special value in determining the geological position of the 

 terrane. As regards the flora, however, the collections which 

 have been made from time to time, are more satisfactory and 

 definite as regards specific characters, and Prof. F. H. Knowl- 



*The Laramie and Overlying Livingston Formation in Montana, U. S. Geol. 

 Survey Bull., JOG. 



