14:2 MEANS OP DISPERSAL. [Chap. XIL 



in the marine faunas on the opposite sides of almost 

 every continent, — ^the close relation of the tertiary in- 

 habitants of several lands and even seas to their present 

 inhabitants, — the degree of affinity betueen the mam- 

 mals inhabiting islands with those of the nearest conti- 

 nent, being in part determined (as we shall hereafter 

 see) by the depth of the intervening ocean, — these and 

 other such facts are opposed to the admission of such 

 prodigious geographical revolutions within the recent 

 period, as are necessary on the view advanced by Forbes 

 and admitted by his followers. The nature and rela- 

 tive proportions of the inhabitants of oceanic islands are 

 likewise opposed to the belief of their former continu- 

 ity with continents. Nor does the almost universally 

 volcanic composition of such islands favour the admis- 

 sion that they are the wrecks of sunken continents; — if 

 they had originally existed as continental mountain 

 ranges, some at least of the islands would have been 

 formed, like other mountain summits, of granite, meta- 

 morphic schists, old fossiliferous and other rocks, instead 

 of consisting of mere piles of volcanic matter. 



I must now say a few words on what are called 

 accidental means, but which more properly should be 

 called occasional means of distribution. I shall here 

 confine myself to plants. In botanical works, this or 

 that plant is often stated to be ill adapted for wide dis- 

 semination; but the greater or less facilities for trans- 

 port across the sea may be said to be almost wholly 

 unknown. Until I tried, with Mr. Berkeley's aid, a few 

 experiments, it was not even known how far seeds could 

 resist the injurious action of sea-water. To my sur- 

 prise I found that out of 87 kinds, 64 germinated after 

 an immersion of 28 days, and a few survived an imraer- 



