16 RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY. [CH. 



botanical affinities, which has reached the last stage in its natural 

 life. The Mammoth trees of California (Sequoia sempervirens 

 Endl., and >Si. gigantea Lindl. and Gord.) afford other examples of a 

 parallel case. The North American Tulip tree and other allied 

 forms are fairly common in the Tertiary plant beds of Europe, but 

 the living representatives are now exclusively North American. 

 Such differences in distribution as are illustrated by these 

 dicotyledonous forest trees in Tertiary times and at the present 

 day, have been clearly explained with the help of the geological 

 record. Forbes, Darwin, Asa Gray^ and others have been able 

 to explain many apparent anomalies in the distribution of 

 existing plants, and to reconcile the differences between the 

 past and present distribution of many genera by taking account 

 of the effect on plant life of the glacial period. As the ice 

 gradually crept down from the polar regions and spread over the 

 northern parts of Europe, many plants were driven further south 

 in search of the necessary warmth. In the American continent 

 such migration was rendered possible by the southern land 

 extension ; in Europe on the other hand the southerly retreat 

 was cut off by impassable barriers, and the extinction of several 

 genera was the natural result. 



The comparatively abundant information which we possess 

 as to the past vegetation of polar regions and the value of such 

 knowledge to geologists and botanists alike is in striking 

 contrast to the absence of similar data as regards Antarctic 

 fossils. Darwin in an exceedingly interesting letter to Hooker 

 a propos of a forthcoming British Association address, referring 

 to this subject writes as follows : — 



" The extreme importance of the Arctic fossil plants is self- 

 evident. Take the opportunity of groaning over our ignorance 

 of the Lignite plants of Kerguelen Land, or any Antarctic land. 

 It might do good I" 



In working out any collection of fossil plants, it would be 

 well, therefore, to bear in mind that our aim should be rather 

 to reproduce an accurate fragment of botanical history, than to 



1 Vide Hooker, J. D. (81), for references to other writers on this subject; 

 also Darwin (82), eh. xii. 



2 Darwin (87), vol. iii. p. 247. 



