204 THE GENESIS AND MIGRATIONS OF PLANTS 



or retreated in its old age to its northern home. There is, of 

 course, much in all this that we do not understand, but the 

 general fact seems certain. 



The early Mesozoic is altogether peculiar. It shows a vast 

 predominance of Cycads, Pines and Ferns, to the exclusion- 

 both of the gigantic Cryptogams of the Palaeozoic and of the 

 ordinary exogenous trees of the modern time. It has a strange, 

 weird aspect, and more resembles that of some warm islands 

 of the southern hemisphere at present, than anything else 

 known to us. It is as if the flora of some southern island had 

 migrated and invaded all parts of the world. The geographical 

 and climated conditions which permitted this must have been of 

 a character difl'erent from those both of earlier and later times. 



As we approach to the termination of the Mesozoic, which, 

 in regard to animal life, is the age of reptiles, a new and 

 strange development meets us. We find beds filled with 

 leaves of broad-leaved plants similar to those of our modern 

 woods, and in most cases apparently belonging to the same 

 genera with plants now living, and this new type of vege- 

 tation persists to the present, though with marked differences 

 of species in successive eras, as in the Middle and Upper 

 Cretaceous, and the Lower, Middle and Upper Kainozoic, or 

 Tertiary. It is noteworthy that while this new vegetation not 

 only altogether supersedes the great Cryptogamous forests of 

 the Palaeozoic, but replaces the Cycads of the immediately 

 preceding eras, the Pines retain all their prominence and 

 grandeur, and even seem to excel in number of species, in 

 breadth of dispersion, and in magnitude of growth their 

 successors in the present world. 



While in the latter Cretaceous and Early Tertiary, the 

 northern hemisphere at least seems to have enjoyed an ex- 

 ceptionally warm climate, the later Tertiary introduces that 

 period of cold known as the Glacial age. While there is no 

 doubt that the intensity of this glaciation has been greatly 



