5 l6 JAMES P ERR IN SMITH 



From the close of the Coal-measures the land encroached on 

 the basin-sea by a progressive westward uplift, and the brackish 

 water and basin deposits take a successively higher place in the 

 geologic column towards the west. Thus somewhere in the eastern 

 part of the Great Basin region marine intercalations of Lower 

 Trias may be expected to be found in the Red Beds. Indeed, 

 this formation in southeastern Idaho lies above and conformably 

 upon the marine limestones with a Lower Triassic fauna. It is, 

 then, in the upper part of this Red Beds formation, in the fresh 

 and brackish-water deposits and its rare marine facies, that we 

 are to seek for the transition from Paleozoic to Mcsozoic. 



C. A. White ^ has described from the Aspen Mountains of 

 Idaho a marine fauna older than any Trias known up to that 

 time in America, and younger than any known Permian. The 

 Meekoceras beds in which this fauna was found he assigned to 

 the Lower Trias. According to A. C. Peale^ this formation lies 

 conformably upon the Carboniferous, and below the Red Beds. 

 The Meekoceras fauna was found near the base of the series, which 

 here has a thickness approximating three thousand feet. The 

 Carboniferous limestone below contained Prodiictus multistriatus 

 Meek, which has been found by the writer in the uppermost 

 Paleozoic beds of California, and has been cited as a character- 

 istic fossil of the Permian of northern Europe. 



Since that time Professor Alpheus Hyatt and the writer have 

 visited the Meekoceras beds, and their joint collections yielded ; 

 Meekoceras gracilitatis White, M. (^Gyroriites) aplaiiatum White, 

 M. {^Ko?iinc kites) mushbachaniitn White, Aspidites, Flemingites, 

 Pseudosageceras, Ussuria, Ophiceras, Clypites, Danubites, Nannites, 

 and a number of new genera. 



The writer^ has previously described the Ceratite limestone 

 of the Lower Trias of Inyo county, California. During the past 



'Twelfth Ann. Rep. U. vS. Geol. and Geog. Siirv. Terr., Part I (1880). Triassic 

 Fossils from Southeastern Idaho. 



'Bull. U. S. Geol. and Geog. Surv. Terr., Vol. V., No. i (1879). Jura-Trias 

 Section of Southeastern Idaho and Western Wyoming, p. 119. 



3 Jour. Geol., Vol. VI, No. 8, 1898. Geographic Relations of the Trias of Cali- 

 fornia. 



