presidext's address. 841 



certain districts only over this large area, can these local condi- 

 tions be considered to have been sufficient to produce a complete 

 change in the flora ? Mr. Dubois in " The Climates of the 

 Geological Past," attributes the alteration to a general raising of 

 the land, but it still seems rather strange that all the land should 

 be raised, and although coal was still formed, no suitable positions 

 should be left for the old flora. He says : — "Just as during the 

 Carboniferous Age an extensive lowland, cut up by the sea into a 

 large marshy archipelago, accounts for the formation of coal over 

 nearly the whole of the northern hemisphere, to such an extent 

 that comparison can only be made with the extensive deposits of 

 Jurassic coal, extending from Western Asia to Australia, it seems 

 that a large mountainous continent ("Gondwana Land" of 

 Suess\ at the south of the equator, has caused extensive accumu- 

 lations of ice in suitable places. A great uniformity of orographic 

 conditions over extensi\ e continental parts of the eai'th's crust 

 seems to have been characteristic of the Coal period. It is thus 

 possible, and even probable, that by a gradual upheaval of such 

 a continent, the changed conditions of existence caused the 

 development of a new flora, which only much latei', in the 

 beginning of the Mesozoic period, should find in Europe, in the 

 higher uphea\al of the ground, conditions it was better fitted for 

 than was the older Pah>?ozoic flora which in consequence would 

 suffer extermination. Traces of glaciation are believed to have 

 been actually found in the Permian formation of Europe. From 

 those high centres of acclimatisation the new flora, accommo- 

 dating itself to a higher temperature, could then have gradually 

 spread over the lowlands." 



Up to quite recently there were, and perhaps even at the 

 present time, there are geologists who hold that the Glossopteris 

 Flora belongs to a much later period of the world's history than 

 the Lepidodendron Flora of the Coal Measures; but representatives 

 of the two floras have been found associated in the same beds, 

 which must be accepted as a final and conclusive proof of their 

 contemporaneous existence. (Rec. Geol. Sur. of India, Vol. xxix. 

 Part 2, p. 58). 



