[NTRODUCTION 11 



Miocene) the climate of Europe was evidently sub-tropical, or hi 

 any rate mild enough for palms and other t ropica] types to flourish. 

 In the Pliocene these give way to trees of northern types, oak 

 beeches, etc. The marine fossils indicate that the ocean was grow- 

 ing colder also. 



The Pliocene floras of the northern hemisphere are well known. 

 and consist of genera which still exist, but with a very different 

 distribution from that of Tertiary times. Many of th< aera, 



and probably some species, have survived to the present. Thi 

 are best represented at present by the forests of Atlantic North 

 America, and those of the Himalayan regions, China and Japan 



in Asia. 



With the pines, firs, oaks, maples, willows and poplars now 

 found throughout the north temperate zone, were mingled other 

 genera, at present more restricted in their range. Such are the 

 giant sequoias of California, the bald cypress (Taxodium) of the 

 Gulf States, hickories, walnuts, magnolias, tulip trees, sassafras 



and others. 



The explanation of the present range of these trees is to be 

 sought in changes of climate, and especially the changes resulting 

 from the series of refrigerations constituting the great Pleistocenr 



glaciation. 



The effects of the extensive glaciation in the northern hem- 

 isphere upon the distribution of both plants and animals w 

 far-reaching, and have been the subject of many investigations. 



In the old world, especially in Europe, the extinction of many 

 types, existing in the Pliocene, was brought about. Such tn 

 as magnolias, hickories, sweet gum and others, still existing in 

 America and eastern Asia, were completely extinguished in 

 Europe owing to the complete glaciation north of the Alp-. 1 heir 

 former existence is evident from abundant fossil remains in the 



Tertiary rocks. 



In eastern America the glaciation extended only to about 

 latitude 40° and many of these trees were able to retreat south- 

 ward, later following the northward recession of the melting I 

 Such characteristic Tertiary trees as the tulip-tree (Iiriodend* 

 sweet gum (Liquidambar), sassafras, walnuts, hickories and oth< 

 still flourish in the Atlantic states and in parts of ( foina and Japan 

 and the Himalayas, but have quite disappeared Iron, Europe, 



