J. P. Smith — Periodic Migrations. 219 



the Middle Trias a connection was established between these 

 regions through some other way than the Indian branch of the 

 old central Mediterranean, or " Tethys," but we have no way 

 of knowing this passage. It seems possible, however, that it 

 may have been through the Boreal region. The writer* has 

 already given a suggestion of the faunal -change at the end of 

 the Lower Trias, based on his own collections made in Nevada 

 during the summer of 1902. No species are thought to have 

 been absolutely identical with European forms, but many are 

 so similar to species long known from the Alps that some sort 

 of connection is beyond question. 



Upper Trias, Subbullatus beds. — The writerf has brought 

 out several years ago the relationship of the Trias of California 

 to that of the Alps. Further study, in field and museum, has 

 served only to strengthen this hypothesis, and recent work in 

 India has given a means of comparison with that region, show- 

 ing that the same thing is true there also. 



The Karnic horizon, zone of Tropites subbullatus, contains 

 many elements common to the Mediterranean region and west- 

 ern America, and many of these are also found in India. 

 Tropites subbullatus, T. torguillus, Paratropites Sellai, Ento- 

 moceras sandlingense, Sagenites Herbichi, Polycyclus Henseli, 

 and Halobia superba are common in both California and the 

 Tyrolean Alps, and many other species are very closely related. 

 Most of these are represented in India by forms that may be 

 identical with them, although complete publication of recent 

 geologic explorations in India must be awaited before a final 

 decision can be made. 



Now it is well known that the Tropitidse appeared as immi- 

 grants in the Mediterranean and the western American regions 

 in the Upper Trias, without local ancestors. They also 

 appeared at the same time in India, but since we do not yet 

 know the faunas of the upper part of the Middle Trias in that 

 region, there is still a possibility that the Orient may have 

 been the source of this part of the fauna, for it is highly prob- 

 able that the Indian province was the connection between 

 Europe and America. This Karnic fauna, however, is not yet 

 known elsewhere in Asia, and the only proof we have of the 

 migration is the occurrence of similar species in the widely 

 separated regions. The path of this migration cannot be 

 traced, for fossils of the zone of Tropites subbullatus are 

 known in America only in California, not having been found 

 at any other place in either North or South America. 



Upper Trias, JVoric horizon. — Fossils of the Noric horizon, 



* Centralblatt fiir Mineral. Geol. und Pal., pp. 689-695, 1902. 

 f The Metamorphic Series of Shasta County, California, Jour. Geol., ii, 

 588-612, 1894. 



