232 Cincinnati Society of Natural History. 



terstratified, appear more or less arenaceous, and are reall}- closely allied 

 to true sandstones, only showing considerable diversity in texture and 

 mechanical conditions. Deposits of gypsum are very common in the 

 upper beds. 



The Triassic is exposed along the Laramie river, exhibiting a series 

 of nearly horizontal strata, 1,000 feet in thickness. In one place a de- 

 posit of pure solid gypsum, 22 feet in thickness, occurs, lying between 

 two beds of hard red sandstone. In the North Park the thickness is 

 estimated at 1000 feet. 



S. F. Emmons * found the Triassic in the vicinity of Rawling's Peak, 

 600 feet in thickness. And in the Uinta Mountains, from 3,700 to 

 4,000 feet. At its base is a series of clayey beds, having a thickness 

 of 1,200 to 1,500 feet, about equally diyided by a thin but persistent 

 bed of limestone. This is succeeded b}' the Red Bed Group in a 

 thickness of about 2,500 feet, principally of sandstones. 



In Henry's Fork Basin, which is a narrow valley, extending 15 miles 

 in either direction, east and west from Green river, with a width of 

 about 3 miles, and whose average level is about 300 feet below the cen- 

 ter of the Bridger Basin proper, the Triassic sandstones in Flaming 

 Gorge Ridge, near Green river, are exposed in perpendicular cliffs, about 

 1,200 feet in height, while having at their base an undetermined thick- 

 ness of clay beds. 



In Emigration, Parley and Weber Canons, in Utah, the Triassic is 

 exposed from 800 to 1,000 feet in thickness. The Jurassic is also 

 present, and in some places has aiiestimated thickness of 1,500 to 1,800 

 feet. 



The Triassic, in the Desatoya and New Pass Mountains of Nevada, 

 contains highly fossiliferous calcareous shales and limestones. In the 

 Pah-Ute Range in the region of Dun Glen Pass, fossils indicating Ju- 

 rassic and Triassic ages are found associated together. 



The Triassic is represented in the West Humboldt Range, Nevada, 

 in Cottonwood, Buena Vista, Co3'ote, Bloody and Star Canons. Single 

 sections expose strata 1,500 feet or more in thickness. 



Arnold Hague* estimated the thickness of the Jurassic on the out- 

 lying ridges and foot hills of the Colorado range at 250 feet, down to 

 50 feet and less. The rocks consist of loose friable sandstones, lime- 

 stones, marls, and impure clays, presenting great variety in color and 

 texture, and passing from one to the other by almost imperceptible 



'^'Geo. Sur. 40th Parallel. 



