346 C. SCHUCHERT MARINE INVERTEBRATE EOSSIL FAUNAS 



Jurassic ammonites and followed the Mediterranean forms all along the 

 western coast of South America. It was he who accordingly postulated 

 Gondwana and illustrated it on his widely known paleogeographic map 

 of the world's continents during Jurassic time. Finally we may add that 

 it is this continent of Gondwana that has most of the early Permian 

 tillites widely distributed over it, and that it was the generating and 

 dispersing land for the Glossopteris-Gangamopteris flora, which also at- 

 tained peninsular India, Australia, and even iVntarctica. Later, in Per- 

 mian time, this flora reached the Northern Hemisphere and gave rise in 

 the main to the early Mesozoic plant worlds. 



Boreal Devonian realm. — Just as there is an austral late Lower De- 

 vonian realm, so there is a boreal one in eastern ISTorth America and 

 western Europe. The faunal developments in the two provinces of this 

 boreal realm are, however, not vastly different, since many of the forms 

 were able to pass to and fro along the easy migration route of northern 

 Gondwana into the Mediterranean lands and from here along the shores 

 leading into northern Europe. Thence the Coblenzian faunas of Ger- 

 many and England spread as easily westward along the shore of Eria 

 into the Saint Lawrence embayment of the North Atlantic, or Poseidon, 

 where Clarke has described these biotas in Americanized form from 

 Gaspe, Perce, Dalhousie, and Maine. On the other hand, the route of 

 migration from South America direct to North America Avas far less easy, 

 for the two continents were long separated by the deep, mediterranean- 

 like waters of which the j)resent Caribbean is a modified and reduced re- 

 mainder. We now know, moreover, that the Oriskanian faunas of Gaspe 

 spread south through the Appalachian geosyncline into western Tennessee 

 and Missouri and are to be expected in Arkansas and even in Oklahoma. 

 While the Helclerbergian faunas of Atlantic origin came up the Gulf of 

 Mexico embayment, nothing of the sort occurred during the Oriskanian, 

 for there was land here north of Alabama until early in the Middle De- 

 vonian. Then this waterway was again opened and the Camden faunas, 

 with a South American impress, spread into western Tennessee and south- 

 ern Illinois. 



The Middle Devonian faunas of North America east of the Mississippi 

 Eiver have long been known as constituting an independent but greatly 

 restricted faunal realm. Kayser named this the American province, and 

 it is a generating and dispersing center, but receives most of its migrants, 

 chief among them the tabulate corals and the tetracorals, through the 

 Saint Lawrence portal, while the least number arrive by way of the Gulf 

 of Mexico embaj'ment. 



