142 MEANS OF DISPERSAL. [Chap. XII. 



faunas on the opposite sides of almost every continent, 

 — the close relation of the tertiary inhabitants of several 

 lands and even seas to their present inhabitants, — the 

 degree of affinity between the mammals inhabiting 

 islands with those of the nearest continent, 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 relative proportions of the 

 inhabitants of oceanic islands are likewise opposed to the 

 belief of their former continuity with continents. Nor 

 does the almost universally volcanic composition of such 

 islands favour the admission 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, metamorphic schists, old fossiliferous and 

 other rocks, instead ofconsisting 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 

 dissemination ; but the greater or less facilities for 

 transport 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 surprise 

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

 immersion of 28 days, and a few survived an immersion 



