JURASSIC PERIOD 581 



and 600 feet. In Wyoming it is known as the Sundance formation, and 

 is correlated by Stanton 228 with the Oxfordian, "and perhaps the Callo- 

 vian, in whole or in part/' The latter, according to De Lapparent, is the 

 base of the Upper Jurassic. The distribution of this fauna and sea was 

 first mapped by Logan. 229 



The Great Plains submergence was of short duration, and vanished 

 early in the Upper Jurassic before the Aucella fauna appeared in Alaska 

 in the higher Naknek. This Upper Jurassic Aucella fauna is clearly of 

 boreal origin and spreads south to California, "where it characterizes the 

 Mariposa slate and equivalent formations, continuing through a great 

 thickness of strata to the top of the Jurassic, and passing without any 

 striking change into the Lower Cretaceous." The earlier Upper Jurassic 

 of California "had a different, though imperfectly known, fauna more 

 closely related to middle European faunas/' 230 



During the later Upper Jurassic times elevation again set in with local 

 volcanic activity, and the Pacific extensions were reduced to marginal 

 seas. This movement was the introduction to the birth of the Sierra 

 Nevadas. 



Mexico. — Shortly after the retreat of the boreal or Logan sea all of 

 eastern Mexico began to subside, — a region that, with the exception of the 

 short and local Upper Triassic invasion, had apparently been land since 

 the Proterozoic. This Mexican subsidence is correlated by Burckhardt 231 

 with the Kimmeridgian and Portlandian of the late Upper Jurassic. The 

 faunas are unlike those of California and have decided southern European 

 connections, since of the 85 species of ammonites described by Burck- 

 hardt 232 no less than 10 are identical with those of Central Europe (7), 

 boreal Eussia (1), and India (2). Boreal species present here are an 

 abundance of Aucella pallasi mexicana and Perisphinctes nikitini. In 

 addition, there are 11 other forms more or less closely related to forms of 

 central Europe, showing that the Gulf of Mexico was in direct communi- 

 cation with the western end of the Mediterranean. Burckhardt states 

 that in both areas "above the Lower Kimmeridgian there are deposits with 

 a great development of Haploceras filiar and Oppelia of the group 0. flex- 

 uosa. In the two regions the remarkable genus Waagenia also appears in 

 the higher beds, and these in turn are overlaid, in Mexico as well as in 

 Prance, by the zone with Oppelia litliograpliica and by the Lower Port- 



228 Stanton : Journal of Geology, 1909, p. 411. 



229 Logan : Journal of Geology, 1900, p. 245. 



230 Stanton : Journal of Geology, vol. 17, 1909, p. 412. 

 23 i Ibidem, 1909, p. 412. 



232 Burckhardt : Bol. 23, Instituto Geologico de Mexico, 1906. 



