GEOLOGY 



ization, and because their shells were so constituted as to record 

 their progress. 



The earliest fauna was markedly restricted. This may be more 

 apparent than real on account of the imperfection of the acces- 

 sible record; but it was doubtless real in some measure, and due to 

 the physical limitations already sketched. At the same time, there 

 was an increase in differentiation. The conditions which repressed 

 the life, reducing the number of individuals, species, and genera, 

 forced them to diverge more and more, in order to accommodate 

 themselves to the conditions inhospitable to life. This is shown 

 best in the development of the land and fresh-water life, but to 

 some extent also in the marine life. 



The geographic suggestions of the faunas. A great group of 

 ammonites, embracing more than 200 species, formed the leading 

 features of the early Indian fauna. The alliance of the Indian 

 forms with those of North America is so close as to indicate that be- 

 fore the close of the early Trias, migratory connections had been 

 established between India and western America. 



Somewhat later in the early Trias there appeared in the Siberian 

 region (Olenek River) a fauna having some of the same genera as 

 the Indian. Closely related species are found in Idaho. If there 

 was connection between the Indian and Siberian regions, it would 

 be possible for Indian species to reach America either by way of 

 Siberia and the Arctic coast, or by the Pacific sea-shelf, and slight 

 changes, involving submergence or emergence in the region of 

 Bering Strait might change the combination of the faunas. 



The Indian and Siberian provinces seem to have been distinct 

 from the Mediterranean province throughout the earlier Trias<ir: 

 but in California a few fossils have been found which are character- 

 istic of the earlier Triassic of southern Europe. 



The early Triassic faunas of central Europe were very variable. 

 a part being developed apparently in fresh water, a part in isolated 

 seas, and a part perhaps in dependencies of the ocean. The marine 

 life was scanty, and its origin and relations uncertain; but it seems 

 to have been largely independent of the Mediterranean basin. 



By the middle of the Triassic period the faunas had be.min to 

 intermingle, and to lose their provincial characteristics. The Med- 



