1 882.] Central Region of the United States. 183' 



THE WASATCH. 



In lithological character, the Wasatch consists of a mixed 

 arenaceo-calcareous marl, alternating with beds of white or rusty 

 sandstone. The more massive beds of sandstone are in New 

 Mexico, Colorado and Wyoming, 'at the base of the formation. 

 The marls readily weather into the fantastic forms and canon 

 labyrinths of bad-land scenery. The marls often contain concre- 

 tionary masses of a highly silicious limestone, which cover the 

 banks and slopes of the bluffs with thousands of angular frag- 

 ments. It is characteristic of this formation that the marls con- 

 tain brightly colored, usually red strata ; and in many localities 

 the colors are various, giving the escarpments a brilliantly banded 

 appearance. 



Petrographically this formation has two divisions, the Wasatch 

 proper and the Green River beds ; the latter name having some- 

 times been given to the entire formation as well as the former. 



Of the few vertebrate fossils known from the Green River 

 division, some are identical with those of the Wasatch, while at 

 least one genus of fishes is common to the Bridger. 



The Wasatch beds proper are much more widely distributed 

 than those of the Green River. They appear first in the south in 

 Northwestern New Mexico, and extend thence into the adjacent 

 parts of Colorado. They are exposed over extensive areas of 

 Colorado west of the Rocky mountains, and reappear in South- 

 western Wyoming. They extend along the western portion of 

 the Green River valley, whose northern portion they entirely 

 occupy. On the eastern side of the Wind River mountains it 

 has, according to Hayden, an exposure of from one to five miles 

 in width for a distance of one hundred miles, from the source of 

 the Wind river to the Sweet Water river. North of this point it 

 fills the extensive basin of the Big Horn river to the borders of 

 Montana. It does not occur east of the Rocky Mountain range. 

 The thicknesses given by geologists are the following : 



Northwestern New Mexico (Cope). 



Red striped marls 15°° 



Reddish-brown sandstone 1000 



Rio San Juan, Colorado (Hoi 



Coarse yellowish sandstones, alternating with \ 



White and Yampa Reservations (Endlic 



Chiefly yellow and reddish sandstones, alternatii 



