410 G. B. Wieland — Polar Climate in Time. 



the north — tlie so-called Glossopteris — flora. In this the genus 

 Glossopteris was so extraordinarily abundant as to have sug- 

 gested to Seward in his eloquent presidential address* the idea 

 that it must have monopolized wide areas over large parts of 

 southern South America, Africa, and Australia to the exclu- 

 sion of other plants, just as the Bracken to-day covers sunny 

 hillsides with a carpet of green. The southern origin of the 

 Glossopteris flora is certainly a legitimate assumption, and was 

 doubtless connected in some way with climatic changes culmi- 

 nating in the glacial conditions of the southern Permian. But 

 whilst the Glossopteris flora in reality thus furnishes the first 

 suggestion of the breaking up of ancient generalized tropical 

 conditions by an invasion from the far south, there remains 

 the fact of the immense extent and distribution of more varied 

 northern forms, as well as the return and long persistence of 

 wide-spread uniform conditions during the Trias and Jura. 

 The vertebrates of the later Paleozoic are not as yet under- 

 stood to indicate any differentiation into zoological realms, 

 although a much fuller knowledge of the Permian faunas of 

 Texas, South Africa, and J^orthern Pussia may yet furnish 

 evidence of such. 



Although doubtless increasing in force, polar influences due 

 to eccentricity during Paleozoic time must hence from the 

 nature of the record long or always remain more or less 

 obscure. It is, however, from this period on that the facts of 

 polar origins become clearer and clearer. As soon as we get 

 in the Mesozoic, the fortuitous combination of fairly numerous 

 freshwater strata on the Continental mainlands and the early 

 representatives of the more highly organized vertebrates and 

 plants, which by reason of their organization are easily liable 

 to displacement and extinction, and hence constitute delicate 

 horizon-markers, we become more and more aware of a vast 

 procession of similar series of both animals and plants from 

 north to south on both sides of the Atlantic. To this main 

 line of our discussion let us now yield attention. 



The Argument for Polar Origins as Based on the Verte- 

 brates. — The earlier expression of the north to south move- 

 ment of types originating in the high north consists in the 

 fact that the small and delicate so-called mammals of the 

 Jurassic are much alike in beds on both sides of the Atlantic 

 presumed to be of about the same age. In the Cretaceous the 

 same general fact is true, but in an accentuated form. And 

 throughout the Tertiary the completer the record the greater 

 the parallelism displayed between synchronous faunae of the 

 various European and American horizons yielding vertebrate 

 fossils. 



* British A. A. S. meeting at Southport, 1903, Address to the Botanical 

 Section. 



