THE VEGETABLE KINGDOM 343 



pteridosperms, and a southern flora, without any large 

 trees, but chiefly characterized by Glossopteris and Ganga- 

 mopteris. The former is found over most of the northern 

 hemisphere, both in the Old and New Worlds, the latter 

 is principally found in the southern hemisphere and 

 India. So entirely different are the two, that for a long 

 time many geologists would not admit them to be con- 

 temporaneous, but held the Glossopteris flora as Mesozoic, 

 it having in fact nearer affinities to the European Mesozoic 

 than to the European Carboniferous flora. The discovery 

 of marine strata having an unmistakable Upper Carboni- 

 ferous or Lower Permian fauna, alternating with beds 

 containing the Glossopteris flora, at length gave conclusive 

 proof of the Permo-Carboniferous age of the latter. It 

 appeared, therefore, that there were two continental 

 masses, a northern on which the descendants of the 

 Lower Carboniferous plants continued their evolution, 

 and a southern on which that flora had been exterminated . 

 (possibly by glacial conditions of which there is good 

 evidence), and a new and much less rich flora developed. 

 Later discoveries have shown that there was some 

 geographical overlap of the two floras, Sigillaria having 

 been found in South Africa, and Glossopteris in Russia ; 

 but the exact nature of this overlap remains to be ex- 

 plained. By the Rhaetic epoch a uniform flora had once 

 again established itself over the land-surfaces of the 

 world. 



