472 THE TERTIARY FLORA OF AUSTRALIA, 



have caused its extinction everywhere else but in the Australian 

 region 1 Surely it should now be growing naturally somewhere 

 on the confines of the deserts and drier districts of Asia, Africa, 

 or America if droughty conditions help it along. On the other 

 hand, different species of Eucalypts have adapted themselves in 

 Australia to all conditions of moisture and dryness, heat and cold, 

 and there is certainly nothing in the climate of other parts of the 

 world to show why the genus should have been killed out in 

 every corner, especially as quite a large number of species have 

 been tried and have been found to flourish in New Zealand, at 

 the Cape, on the Pacific Coast and elsewhere in America, and on 

 the Mediterranean. 



The probability of the former existence in Europe of any forms 

 now characteristic of Australia is in like manner extremely small, 

 and it requires the very strongest evidence — not the mere opinions 

 of men however eminent— to establish such a fact. On the other 

 hand, the probability of their having been evolved in the region 

 where they now most abound is very great. A glance at the 

 geological history of the past will be found instructive. 



At the end of the Devonian and beginning of the Carboniferous 

 periods, the Lepidodendron flora was in full vigour and apparently 

 distributed throughout the world. Then took place a remarkable 

 change in the Southern Hemisphere. Arctic or glacial conditions, 

 or such at least as produced all the phenomena attributed to 

 glaciation, set in. The Lepidodendron flora was swept away 

 from a large area of the surface of the globe and the Glossopteris 

 and Gangamopteris flora took its place. This area included what 

 we now know as South Africa, Australia, the southern extremity 

 of South America and Southern India. Judging by the identity 

 of the flora throughout and its dissimilarity to that of the rest of 

 the surface of the earth, this area must have contained land 

 surfaces more or less continuous and altogether separated by some 

 important barriers from the world outside. This land has been 

 named by Suess " Gondwana Land." 



It is evident, therefore, that at the end of the Paheozoie Age 

 lands now widely separated by the ocean must have been con- 



