62 G. R. Mansfield — Triassic and 



the names Higham grit, Deadman limestone, and Wood 

 shale respectively, and the name Nngget sandstone is 

 restricted to the "main sandstone member" of the 

 author's earlier paper. This sandstone has the charac- 

 teristic lithology and position of the upper division of 

 Veatch's Nngget, the conspicuous sandstone at Nugget 

 station, Wyoming, the type locality of the formation, and 

 corresponds also to the Nugget as mapped by Boutwell. 



The term Ankareh shale cannot be retained in south- 

 eastern Idaho without confusion and is therefore dropped 

 from the classification of that area. The name Timothy 

 sandstone, which is taken from Timothy Creek in the 

 Freedom and Lanes Creek quadrangles, is introduced for 

 the sandstone that lies between the Portneuf limestone 

 (top of Thaynes) and the Higham grit, and which in 

 the earlier paper was called the "Ankareh sandstone." 



Triassic and Permian. — The relations of the Triassic 

 to the Permian in this region are not definitely known. 

 As first described in the Park City district the Wood- 

 side, Thaynes, and Ankareh were all assigned to the 

 Permian. Later studies have demonstrated the Triassic 

 age of the Thaynes group and have pointed strongly to 

 the base of the Woodside as the probable base of the 

 Triassic system. The marked lithologic and faunal 

 change at that horizon makes this interpretation easy to 

 express cartographically. 



The field relations suggest conformity between the two 

 systems, for the boundary between the Woodside and the 

 underlying Phosphoria is marked by great regularity 

 wherever shown and the attitudes of the two formations 

 correspond quite closely. There is, too, no conglomeratic 

 development at the base of the Woodside or evidence of 

 erosion in the Phosphoria preceding the deposition of 

 the Woodside, unless the somewhat variable thickness of 

 the Phosphoria be so considered. Nevertheless the 

 striking faunal and lithologic differences above noted 

 point to very different conditions of deposition for 

 the two formations and indicate a stratigraphic break 

 (unconformity) of some magnitude. 



Age determination. — The Lower Triassic age of the 

 Woodside, Thaynes, and Timothy is based upon ammonite 

 zones which occur 1,000 to 2,250 feet above the top of the 

 Paleozoic formations. The fossils of the overlying 3,000 

 feet or more of sediments are less distinctive and the 



