54 GEOLOGY. 



a group of ammonites not found in the other provinces, while the 

 ceratite genera named above were wanting or very rare in it. 



In California (Santa Ana Mountains) a few fossils have been found 

 which are characteristic of the earlier Triassic of the Alpine province. 

 If further discoveries should prove that the Mediterranean province 

 sent emigrants to the California coast, or received immigrants from 

 it, while Idaho, though in communication with Siberia and India did 

 not receive Mediterranean emigrants, an interesting question as to 

 the respective routes would be raised. The question is indeed raised 

 on other data in a later epoch. 



The faunas of the central basin of Europe in the early Trias had 

 very uncertain shifting characters, a part being apparently developed 

 in fresh water, a part in isolated seas, and a part perhaps in dependen- 

 cies of the ocean. The salt-water life was scant, and its origin and 

 relations uncertain. It seems to have been largely independent of 

 the Mediterranean basin. 



The middle Triassic faunas. — By the middle of the Triassic period 

 the provincial faunas had begun to intermingle extensively, and to 

 become composite faunas. The Mediterranean fauna gained access 

 to the Indian basin and to our western coast, and counter-migrations 

 were of course made possible. In western Nevada (Star Peak), species 

 are found that belong to the Muschelkalk horizon of the Alps. With 

 these are forms that are found also in the Siberian province, but the 

 Siberian and Mediterranean faunas, curiously enough, do not seem 

 to have directly mingled. The Mediterranean fauna is found on the 

 shore of the sea of Marmora, which suggests its line of connection with 

 the Indian basin, and representatives are thought to have been found 

 in the vicinity of Vladivostok, suggesting that its route to our western 

 coast lay along the north Pacific sea-shelf. The Siberian connection 

 may have been along the Arctic sea-shelf, in the main, but having com- 

 munication with the Pacific border at some point north of Nevada ; or 

 the Nevada and Idaho basins may have been in communication with 

 one another at this time. The fauna was very rich in ceratites. 

 Stephanites superbus, Ceratites binodosus, and C. trinodosus of the Hima- 

 layas are characteristic types which give name to their respective 

 horizons. 



In the Nevada embayment the fauna embraced certain cephalo- 

 pods that are unknown in the Siberian Trias, but have been found in 



