512 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



In 1871 the survey travelled uortliwarcl tlirongli Cache Valley and 

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

 district, en route to the Yellowstone IS'ational Park, and in the following 

 autumn on returning from the field the party came through the Ui)per 

 Portneuf Valley to the bend of Bear Eiver, and thence via Bear Iliver 

 Valley and Bear Lake to Evanston, 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 1877 

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

 formations of the surrounding country. 



In 1872 the Snake Eiver Division of the survey passed northward from, 

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

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

 the Green Eiver Basin, visiting Fontenelle Canon. (See Eeport for 1872.) 



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

 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. Comstock acted as geologist for the party and has colored 

 a geological map which includes the southwestern part of the Wind 

 Eiver Mountains and the adjacent portion of the Green Eiver 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 

 Eiver Mountains formations from the Lower Silurian to Carboniferous 

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

 Eiver beds of the Green Eiver 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 bv accumulations 

 of morainal material. 



Professor Comstock also colored an area of volcanic rock as extending 

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

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

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

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

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

 tion. The map of the Green Eiver 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 them.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. 



DEAINAGE, MOUNTAINS, ETC. 



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

 Green Eiver, Snake Eive?, 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 divis ible for the purpose of description into 



*Intlie map accompanying Ms 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. 



