20 GEOLOGICAL SURVEY OF THE TERRITORIES. 



following extracts from Chapter X, commencing at the bottom of page 

 85. I have quoted the chapter without corrections, that it may be com- 

 pared with tlie more careful observations which were made by the party 

 the past season. Only one prominent error occurs, and that is the state- 

 ment that the central portion of the Teton Range is composed of erupted 

 rocks, whereas Professor Bradley has sliown that they are formed mostly 

 of gueissic strata, penetrated here and there by dikes. 



'■''June 1. — On the west slope of the Wind Eiver Mountains we met with 

 a thick deposit of drift material, which, as we descended to Gros Ventres 

 Fork, soon expanded into a great thickness of recent strata, evidently 

 quite recent Tertiary. The baulcs of the Gros Ventres Fork present high 

 blufi's, some 300 to 000 feet high, but I should think that this formation 

 had been deposited after the surface of the country had attained, for the 

 most part, its present configuration. The strata consist of loose fine 

 arenaceous clays, the layers containing more or less arenaceous matter, 

 which does not effervesce, and layers of harder rock, a fine-grained and 

 coarse sandstone, and sometimes an aggregation of grains of quartz 

 with ferruginous matter and particles of mica. The materials are all 

 evidently derived from the vicinity. Some of the masses of rock i^resent 

 a compact fine siliceous structure and effervesce feebly. 



'■'■June 4. — To-day the Tertiary strata begin to assume a good deal of 

 importance. AVe have the brick-like materials which result from the 

 burning out of the lignite beds. There were also masses of indurated 

 clay, covered with vegetable remains and impure lignite beds ; indeed, 

 all the indications which the lignite Tertiary beds present on the east 

 side of the mountains. The beds are also much disturbed, inclining at 

 various angles. The following section of the lignite beds was taken 

 here, which will serve to show their resemblance to those on the eastern 

 side of the mountains : 



9. A yellow fine-grained sandstone and a dark gray limestone, with a 

 parting of clay. The limestone is quite brittle, breaking into 

 thin lamina3,and contains impressions of dicotyledonous leaves and 

 a distinct species of Unto. 15 feet ; inclination, 28^". 



8. Light yellow sandy marl. 15 feet. 



7. Impure lignite. 4 feet. 



6. A series of marly clays which, when saturated with water, forms a 

 thick paste, variegated in color. Near the summit, just below the 

 lignite, is a thin seam, four to six inches, of hard-shell limestone, 

 with the shells iu the most comminuted condition. I recognized 

 Unios, Viviparas, &c., sufficient to show that the deposit is fresh 

 water. 150 feet. 



5. Alternate dark gray and brown-yellow gray, fine sandy and clay 

 layers, with some calcareous matter and a few seams of incoherent 

 sandstone, sometimes assuming a concretionary character. 200 

 feet. 



4. Iminire lignite aiul clay. 8 inches. 



3. Yellowish-gray clay. 4 feet. 



2. Impure lignite. (5 inches. 



1. Yellowish clay, with some calcareous matter. 



The general inclination of all these beds was about 20°. 



June 5. — We ascended a high ridge, from which we could see to a 

 great distance. Looking to the dividing crest of Wind River Mountains, 

 we find the exposed belt of granite to be not more than four or five miles 

 in width, and gradually lost iu the basaltic or eruptive range, which 

 also renders itself conspicuous. The Tertiary beds seem to reach fully 



