530 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Spiriferina cf . lippoldi Bittner. If this identification is correct, the overlying red beds (corre- 

 sponding to the Nugget formation of Veatch and the Teton formation of the Yellowstone Park) , 

 which have by some writers been classified as Triassic, would perhaps find a more suitable resting 

 place in the lower Middle Jurassic. 



The Pentacrinus shaly limestones of Peale, of the Hayden Survey, correspond to the Twin 

 Creek formation of Veatch and the Ellis formation of the Yellowstone Park-Montana district. 

 They are commonly regarded as of Upper Jurassic age. In southeastern Idaho their thickness 

 is much greater than that given by Peale, reaching 3,000 feet or more. 



K 12-13. WYOMING AND ADJACENT AREAS. 



Triassic strata are not generally distinguished in this region, but they are 

 assumed to be represented in the upper part of the red beds, the lower portion 

 being assigned to the Permian. (See pp. 490-492, Chapter XI.) An exception to the 

 general uncertainty is found in the beds near Lander to which Williston applied the 

 name Popo Agie, and in the highest strata of Red Mountain near Laramie, from 

 both of which Williston has described Triassic vertebrates. 



Of the Park City district, Utah, Boutwell ^^^ states: 



Within this district no sediments have been found which carry Triassic fossils. To the 

 north and northwest, however, the Park City formations pass upward through several hundred 

 feet of red shale into brown, red, pink, and white sandstones. These are frequently massive 

 and heavily bedded, in striking occurrences are coarsely cross-bedded, and toward the top are 

 quartzitic. Disregarding possible faulting, they aggregate about 1,550 feet thickness. The age 

 of these sandstones has always been regarded as Triassic, as they overlie Permian and underlie 

 Jurassic. 



In western Wyoming Veatch ^^^'^ distinguished as Triassic (?) the Nugget 

 formation, consisting of red shales below (since correlated by Gale ^^^ with the 

 Ankareh shale) and lighter-colored sandstones above (to which the name Nugget 

 is now restricted) . 



Throughout the Bighorn Basin and Mountains the red beds are known as the 

 Chugwater formation. Both Darton ^^^^ and Fisher ^^' place the formation doubt- 

 fully in the Triassic but cite fossils from the lower portion which suggest Permian. 

 (See p. 495, Chapter XL) Darton ^'^ says: 



Fossils found at various horizons in limestones in the Chugwater red beds do not afford 

 conclusive evidence as to age. Those in the lower limestones in the Bighorn Mountains and 

 other uplifts are believed to be "Permian" in the sense in which the term is used in the Mis- 

 sissippi Valley. Many fossils occur in the limestone 150 feet below the top of the formation, on 

 the east bank of Bighorn River, 3 miles below Thermopolis. According to Dr. G. H. Girty, 

 the principal species is Natica lelia, usually considered diagnostic of the Triassic, but probably 

 it is older. Bakewellia and probably Pleurophorus may also be present, and an Aviculipecten 

 occurs resembling A. curticardinalis , which is characteristic of the Permo-Carboniferous of Utah. 

 Dr. Girty is inclined to correlate the fauna with the Permo-Carboniferous of the Wasatch Moun- 

 tain section. The 150 feet of red shales and sandstones which overlie this limestone may pos- 

 sibly represent part of the Triassic. In the lower portion of the Chugwater formation, 10 miles 

 southwest of Casper, a cast of Schizodus wheeleri was found. This form is usually regarded as 

 Pennsylvanian. 



The Chugwater formation also occurs in the Laramie Basin, where Darton has 

 recognized it and included in it 200 feet of light-colored sandstone not typical and 

 not observed to the northeast. The top of the formation nearly everywhere in 

 this region is the base of the fresh-water IMorrison formation, ^^^ the intervening 

 Sundance formation (Jurassic) generally being absent. 



