MesozoiG and Ccenozoic Geology and Paloiontology. 33 



grades. The line separating- this group from the Triassic is not 

 clearly defined, and the separation therefore is somewhat arbitrary. 



The group attains its greatest thickness in the region of Big Thomp- 

 son Creek, in Colorado. In Wyoming, along Lodge Pole and Horse 

 Creeks, it is represented by only about 75 feet of strata. Still farther 

 to the northward it expands again to a thickness of 150 feet. On the 

 Laramie Plains west of Antelope Creek the thickness is estimated at 

 200 feet. On Como Ridge, in the extreme northwestern corner of the 

 Laramie Plains, just west of the lOCth Meridian, the Jurassic rocks 

 exhibit all the characteristic st.rata that have been observed in other 

 localities, associated with organic remains, and possessing a thickness 

 of from 175 to 200 feet. Its thickness in the North Park is estimated 

 at from 200 to 250 feet. 



S. F. Emmons* estimated the average thickness of the Jurassic in 

 the Uinta Mountain Region at from 600 to 800 feet, in which the lime- 

 stones are highly fossiliferous, and have a thickness of 200 or 300 feet, 

 the remainder being made up of sandstones, shales and clay beds, re- 

 markable, where well exposed, for their bright, variegated colors. 



In Henry's Fork Basin, a thickness of 300 to 400 feet is observed 

 in the cliffs overlooking Sheep Creek. 



In the Montezuma Range, Nevada, the shales have a thickness of 

 between 3,000 and 4,000 feet, and rest directly upon granite. North of 

 Indian Pass, and at Antelope Peak, they reach a development of 4,000 

 feet. 



F. B. Meekf described, from the Triassic at Buena Vista Canon, 

 Nevada, Splicura whitneyi, Modiomorplia ovata, Modiomorplia lata, 

 Gymnotoceras rotelliforme, Arcestes perplanus, A. gabbi, Acrochordi- 

 ceras hyatti, Eutomoceras laiibei, Eudiscoceras gabbi. Hall and 

 Whitfield, from the Trias of Pah-Ute Range, Nevada, Spirifera alia, 

 Edmondia myrina. 



Prof. E. D. Cope,]; from the Trias at Phoenixville, Pa., Palaeoctonus 

 appalachianus, a gigantic carnivorous dinosaurian, P. aulacodus, now 

 Suchoprion aidacodus, Clepsysaiirus veatJeianus, Siichoprion cypho- 

 don, Thecodontosaurus g ibbidens^^ and Palaeosaurus/i'azeramis, from 

 Texas, Eryops niegacephalas; and from Painted Canon, in Southeast- 

 ern Utah,! Dystrophaeus vicemalce. 



* Geo. Sur. 40th Parallel. 



t U. S. Geo. Expl., 40th Parallel, vol. 4. 



t Pal. Bull.. No. 26. 



? Proc. Am. Phil. Soc. 



II Wheeler's Sur. W. 100th Mer., vol 4. 



