348 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



from the Cambrian to the Tertiary. Each period of sub- 

 sidence, local or wide-spread, has been followed by a 

 period of elevation in which the continent resumed approxi- 

 mately its former shape and extent. Whatever may have 

 been the development of the other continents, North 

 America has been a unit since its history began to be 

 recorded in the Pre-Cambrian sediments laid down in the 

 first sea that covered its surface. 



The Lower Trias. 



The Lower Trias of Idaho. Many years ago Dr. A. C. 

 Peale discovered in southeastern Idaho and southwestern 

 Wyoming a series of fossiliferous beds lying below the 

 Red Beds and above the Carboniferous limestone. The 

 fossils found in this formation were described by Dr. C. A. 

 White (40), and assigned to the Lower Trias. Cephalo- 

 pods were found at but two places: Locality No. i, in 

 southeastern Idaho, sixty-five miles north of Utah, eighteen 

 miles west of Wyoming, and five miles west of John Gray's 

 Lake: locality No. 2, fifteen miles east of south from 

 locality No. i. 



The section at locality No. i, according to Dr. C. A. 

 White, is as follows : 



A. (Uppermost beds). Limestones and shales, with 7>r^dr«^?//a \ 



setnisimplex White, T. angiistata Hall, Aviculopecten ida- \ 

 hoensis Meek Viooo ft. 



B. Limestones, with Eumicrotis curta, and Aviculopecten ida- I 



hoettsis Meek / 



C. Greenish and reddish shales and sandstones, with Aviculo- \ q r. 



pecten pealei White / 



D. Bluish gray limestones, fossiliferous near the base, with \ 



Meekoceras gracilitatis White, M. mushbachanuni White, 700 ft. 

 Arcestes ? cirratus White ' 



E. Reddish and greenish sandstones 400 ft. 



F. Dark blue sandstone ) g^^ ^^ 



G. Quartzite ' 



H. Massive gray limestone 400 ft. 



At locality No. 2 were ioun^ Meekoceras gracilitatis White 

 and M. a^lanatiim^\{\\.t.^ in limestone similar to that marked 



