152 DAVID WHITE 



flora, has arisen in the wake of retreating ice, though it is not really 

 a glacial flora. It probably originated in a great region, the " Gond- 

 wana land" of Suess, from which the Stephanian flora had been more 

 or less completely expelled by the rigorous climate, and to which it 

 had not yet been able to return, presumably on account of either 

 temperature or isolation. 



The dominant characteristic types are Gangamopteris, Glossop- 

 teris, and its rhizome Vertebraria, Neuropteridium, Noeggerathiopsis, 

 Phyllotheca, Schizoneura, Ottokaria, and Derbyopsis. The distri- 

 bution and the relations of this flora to the Northern or Cosmopolitan 

 flora have already been discussed in this journal.' The geographical 

 extension of this flora in Paleozoic time, as also the distribution of the 

 northern or cosmopolitan Permian flora, are shown on the Permian 

 map, Fig. 2. 



Distribution. — The uniformity of the Gangamopteris flora is so 

 nearly complete as emphatically to indicate freedom of migration 

 between all the areas in which it dominated; but whether Australia 

 communicated with South i\frica by way of India and Arabia, or by 

 connection through an Antarctic land mass is a matter of opinion. 

 The former is perhaps more probable. South America was almost 

 certainly made accessible either to Africa or Australia by route 

 over Antarctic land. 



Gondwana climate. — The Gondwana climate following the glacia- 

 tion was not too severe for the early return at distant points of a few 

 of the presumably hardiest representatives of Psaronius, Sigillaria, 

 Lepidophloios, and Lepidodendron, and at a higher stage, Voltzia 

 Psygomophyllum, and Pterophyllum, both in Africa and South 

 America. The early return of a climate not so widely different from 

 that of the western Permian is further shown by the fact that though 

 the early Gondwana woods found in beds more or less closely asso- 

 ciated with the bowlder beds in Australia and South Africa show 

 annual rings indicative of sharp seasonal changes, the woods from the 

 higher portion of the series in South America show nearly continuous 

 growth with but slight trace of seasonal differences. 



Ability of types to mingle in later Permian and early Mesozoic 

 environments. — This amelioration of temperature harmonizes, firstly, 



I Jour. Geol., Vol. XV (1907), p. 615. 



