PALEOZOIC STRATIGRAPHY OF ROCKY MOUNTAINS 247 



Correlation with the Pogonip group of Nevada. — The Pogonip 

 group of the Eureka district of Nevada, called Lower Silurian by- 

 Hague 1 and Walcott, 2 probably includes equivalents of the Garden 

 City formation and part or all of the St. Charles formation (Upper 

 Cambrian, Blacksmith Fork). The upper part of the Pogonip 

 group carries a fauna, considered by Walcott 3 to be of Chazyan 

 age, which bears a notable resemblance to the faunas of the Garden 

 City formation. 



Member 3 in Wyoming and Montana.— -In Wyoming the thin- 

 bedded Upper Cambrian-Lower Ordovician( ?) sequence, including 

 flat-pebble conglomerate, is nowhere represented by more than 

 500 feet of strata, but its characters are typical of Member 3 wher- 

 ever it is exposed. In southwestern Montana it forms the highest 

 member of the Gallatin formation. 



The faunas so far collected from this sequence in both Wyoming 

 and Montana are very meager, a fact which has made its correlation 

 a subject of dispute in various localities. In the Bighorn Range, 

 Member 3 constitutes the uppermost part of the Deadwood forma- 

 tion, which is called by Darton 4 Middle Cambrian; but the only 

 species Darton names as coming from the upper 600 feet of the 

 formation (about 1,000 feet thick in all) is Dicellomus politus, which 

 is associated in one locality 5 with fragments of a trilobite resembling 

 Ptychoparia oweni. Some collections from the upper part of the 

 Gallatin formation in western Wyoming, comprising three species 

 of Eoorthis and some fragmentary trilobite remains, have been 

 referred to the Upper Cambrian by paleontologists of the United 

 States Geological Survey. 6 Member 3 probably is represented 



'Arnold Hague, "Geology of the Eureka District, Nevada," U.S. Geol. Survey, 

 Monographs, XX (1892). 



2 C. D. Walcott, "Paleontology of the Eureka District," U.S. Geol. Survey, 

 Monographs, VIII (1884). 



J Op. cit., pp. 3-4. 



<N. H. Darton, "Geology of the Bighorn Mountains," U.S. Geol. Survey, Prof. 

 Paper $1 (1906), p. 26. 



s N. H. Darton, "Fish Remains in Ordovician Rocks in the Bighorn Mountains, 

 Wyoming, with a Resume of the Ordovician Geology of the Northwest," Bull. Geol. 

 Soc. Amer., XVII (1905), 551. 



6 Eliot Blackwelder, personal note. Cf. C. D. Walcott, " Cambrian Brachiopoda," 

 U.S. Geol. Survey, Monographs, XXXI (191 2), 233, Lot 302c 



