162 ON BIO-GEOLOGY. [vn. 



be most thankful to hear they have solved within the 

 next seven years How is ' it that we find certain 

 plants, namely, the thrift and the scurvy grass, abun- 

 dant on the sea-shore and common on certain mountain- 

 tops, but nowhere between the two ? Answer me 

 that. For I have looked at the fact for years before, 

 behind, sideways, upside down, and inside out and I 

 cannot understand it. 



But all these questions, and especially, I suspect, 

 that last one, ought to lead the young student up to 

 the great and complex question How were these 

 islands re-peopled with plants and animals, after the 

 long and wholesale catastrophe of the glacial epoch ? 



I presume you all know, and will agree, that the 

 whole of these islands, north of the Thames, save 

 certain ice-clad mountain-tops, were buried for long 

 ages under an icy sea. From whence did vegetable 

 and animal life crawl back to the land, as it rose again ; 

 and cover its mantle of glacial drift with fresh life and 

 verdure ? 



Now let me give you a few prolegomena on this 

 matter. You must study the plants of course, species 

 by species. Take Watson's " Cybele Britannica " and 

 Moore's " Cybele Hibernica ;" and let as Mr. Matthew 

 Arnold would say {f your thought play freely about 

 them." Look carefully, too, in the case of each species, 

 at the note on its distribution, which you will find 

 appended in Bentham's " Handbook/' and in Hooker's 

 " Student's Flora." Get all the help you can, if you 

 wish to work the subject out, from foreign botanists, 

 both European and American; and I think that, on 

 the whole, you will come to some such theory as this 

 for a general starting platform. We do not owe our 



