684 JAMES PERRIN SMITH 



* 

 The Middle Triassic faunas seem to have been largely endemic, 



because the waters of that time were stable ; thus there are 

 no horizons that are directly comparable in distant lands. But 

 again the Upper Trias ushered in a period of transgression and 

 invasion, and the faunal zone of Tropites subbiillatus appeared 

 simultaneously in the Mediterranean region, in the Himalayas, 

 and in California, with many genera and species common to 

 these countries, exotic in all, and with no previous record to 

 show their origin. 



The geographic provinces of Jurassic time have been grouped 

 by Neumayr 1 in two great regions, the Boreal and the Central 

 Mediterranean, and further he has traced out the distribution of 

 climatic zones of that time in the Boreal type, the North Tem- 

 perate type, the Alpine or Equatorial, and the South Temperate. 

 The western American province belonged to the Central-Medi- 

 terranean region and to the North Temperate climatic zone dur- 

 ing Lower and Middle Jura, but with the beginning of the Upper 

 Jurassic a great change took place in physical and faunal geog- 

 raphy that connected the western American province for a time 

 with the Boreal region. As a consequence of this the faunal 

 zone of Cardioceras alter nans and Ancella pallasi may be traced 

 through Russia, Alaska, and California. 2 The disturbance that 

 caused this invasion may easily be traced in the transgression 

 eastward of the sea on the land that began in northern Europe 

 already in Middle Jurassic, bringing down from the northwest a 

 cold current that permitted the Boreal fauna to make its way 

 into temperate latitudes on the western coast of North America. 



The study of the distribution of fossil faunas as influenced 

 by climate was begun by Ferdinand Roemer, 3 who recognized 

 the fact that the Cretaceous of western Europe was similar to that 

 of the Atlantic region in America, and that the faunas of south- 

 ern Europe, northern Africa, Texas, and Mexico had much in 



1 Denkschr. K. Akad. Wiss. Wien, 1883, Klimatische Zonen wahrend Jura und 

 Kreidezeit. 



2 J. P.Smith: Jour. Geol., Vol. Ill, 1895, Mesozoic Changes in the Faunal 

 Geography of California. 



3 Kreidebildungen von Texas, 1852. 



