218 E. B. BRANSON ORICxIN OF RED BEDS OF WESTERN WYOMING 



about 35 miles northwest of Lander and examined the exposures about 

 15 miles north of Rawlins, and in the summers of 1911 and 1913, when 

 tlie studies were continued from about '25 miles south of Lander to near 

 Dubois, a distance of about 100 miles; but the investigations on the Red 

 Beds were incidental to other work. In the main the discussion in this 

 paper is confined to the western outcrops. 



Historical 



Darton says of the Red Beds in Wyoming : 



"In the latter part of tbe Carboniferous time, and probably during the Per- 

 mian also, there was a widespread emergence, resulting in shallow basins with 

 very wide mud-flats which occupied a large portion of the Rocky Mountain 

 province. In these regions were laid down the last deposits of the Pennsyl- 

 vanian division and the great mass of red clay and sands constituting the 

 Chugwater formation. These beds probably were deposited by saline water 

 under ai-id climate conditions and accumulated in a thickness of 1,000 feet or 

 more. The waters were shallow much of the time, and there were wide, bare, 

 wash-slopes and mud-flats, as is indicated by the frequent mud cracks, ripple- 

 marks, and impressions of various kinds on many of the layers throughout the 

 formation." " 



With this the writer agrees, but in western Wyoming the mud-flats 

 appeared only two or three times. 



Schuchert says:^ "The marine Triassic of California, Oregon, and 

 T^Tevada early in this period extended into Idaho and as continental de- 

 posits continued thence into eastern Wyoming." Referring to the Wy- 

 oming Triassic, he says: "Farther to the east all the Triassic appears to 

 be devoid of marine strata." Schuchert's maps in his Paleogeography 

 of North America show all of the Wyoming Triassic as of continental 

 origin, but in continuous connection with the marine formations of 

 Idaho, Nevada, and California. 



Description of Red Beds of western Wyoming 



For about 60 miles along the eastern slope of the Wind River Moun- 

 tains the outcrops of the Red Beds are almost continuous and the beds 

 reappear in a small anticline 10 to 15 miles east of the main outcrops, 

 though they are never exposed to the bottom in the anticline. Darton's 

 map* shows their distribution in a general way. 



The Red Beds on the Little Popo Agie River, 15 miles south of Lander, 



2 Bull. Geol. Soc. Am., vol. 19, 1008, pp. 465-466. 

 •^Bnll. Geol. Soc. Am., vol. 20, p. 579, pis. 86 and 87, 

 *Bull. Geol, Soc. Am., vol. 19, pi. 22. 



