164 ON BIO-GEOLOGY. [vn. 



younger botanists, that they may work it out after our 

 work is done. 



Of course these plants introduced by man, if they 

 are cut out, must be cut out of only one of the floras, 

 namely, the European ; for they, probably, came from 

 the south-east, by whatever means they came. 



That European flora invaded us, I presume, imme- 

 diately after the glacial epoch, at a time when France 

 and England were united, and the German Ocean a 

 mere network of rivers, which emptied into the deep 

 sea between Scotland and Scandinavia. And here I 

 must add, that endless questions of interest will arise 

 to those who will study, not merely the invasion of 

 that truly European flora, but the invasion of reptiles, 

 insects, and birds, especially birds of passage, which 

 must have followed it as soon as the land was sufficiently 

 covered with vegetation to support life. Whole volumes 

 remain to be written on this subject. I trust that 

 some of your younger members may live to write one of 

 them. The way to begin will be : to compare the flora 

 and fauna of this part of England very carefully with 

 that of the southern and eastern counties ; and then to 

 compare them again with the fauna and flora of France, 

 Belgium, and Holland. 



As for the Atlantic flora, you will have to decide 

 for yourselves whether you accept or not the theory 

 of a sunken Atlantic continent. I confess that all 

 objections to that theory, however astounding it may 

 seem, are outweighed in my mind by a host of facts 

 which I can explain by no other theory. But you 

 must judge for yourselves ; and to do so you must 

 study carefully the distribution of heaths both in 

 Europe and at the Cape, and their non-appearance 



