512 REPORT UNITED STATES GEOLOGICAL SURVEY. 



In 1871 the survey travelled northward through Cache Valley and 

 Marsh Creek and the Lower Portneuf Valley, in the western part of the 

 district, en route to the Yellowstone National Park, and in the following 

 autumn on returning from the field the party came through the Upper 

 Portneuf Valley to the bend of Bear River, and thence via Pear River 

 Valley and Bear Lake to Evaustou, where the expedition disbanded. 



Although the work done was somewhat general in its character it was 

 essentially correct, and all that has been added during the season of 1ST 7 

 is in the matter of detail and in tracing its geological connection with the 

 formations of the surrounding country. 



In 1872 the Snake Biver Division of the survey passed northward from 

 Ogden via Malade Valley and the Portneuf to the Snake Biver plains. In 

 1872 also, Prof. E. D. Cope took a small party over the southwest corner of 

 the Green Biver Basin, visiting Fontenelle Canon. (See Report for 1872.) 



In 1873 an expedition to the Yellowstone National Park under pant. 

 W. A. Jones went from Fort Bridger to Camp Stambaugh over the route 

 via Big Sandy, &c, followed by Hayden in the reverse direction in 1870. 

 Prof. Theo. B. Com stock acted as geologist for the party and has colored 

 a geological map which includes the southwestern part of the Wind 

 River Mountains and the adjacent portion of the Green River Basin. 

 All that falls within the limits of our district is incorrectly colored, and 

 the explanation is found in the fact that Professor Comstock never visited 

 the portions thus colored. On the southwestern slopes of the Wind 

 River Mountains formations from the Lower Silurian to Carboniferous 

 are colored as showing between the granites of the range and the Green 

 River beds of the Green River Basin, whereas the fact is that the Ter- 

 tiary beds (Wahsatch formation) are directly superimposed on the granitic 

 rocks, the line of junction being frequently concealed by accumulations 

 of morainal material. 



Professor Comstock also colored an area of volcanic rock as extending 

 southward east of John Day's River between it and the Green River 

 Basin. This area is occupied by what we have named the Wyoming 

 Range,* which is composed almost entirely of Carboniferous rocks. A 

 large portion of the area represented by him as occupied by the Green 

 River Group has the underlying Wahsatch Group as the surface forma- 

 tion. The map of the Green River Basin published by the Survey of the 

 Fortieth Parallel in the western northern portion slightly overlaps our 

 southern line in the eastern part of our district. Portions of this region 

 were not visited by the Fortieth Parallel Survey, and therefore it was not 

 thoroughly explored by thein.t The map colored by them, as regards 

 these parts, although generally correct, differs in a few minor details from 

 the map as colored by us especially in the eastern portion. 



DRAINAGE, MOUNTAINS, ETC. 



Drainage. — The drainage of the district belongs to three systems, viz : 

 Green River, Snake River, and the Great Basin. 



It is not proposed here to go into the details of the drainage, as it falls 

 more properly within the province of the topographer. All the details 

 necessary for the elucidation of the geological structure of the district 

 will be presented in the subsequent chapters. 



The district is naturally divisible for the purpose of description into 



-*In the map accompanying his report, the name Wyoming is given to the mount- 

 ains that previously were known as the Gros Ventre Mountains. We have transferred 

 the name to the range just south, which was unnamed. 



t Report U. S. Geol. Expl. 40th Parallel, vol. ii ; p. 251. 



