16 THE MALAY ARCHIPELAGO. [chap. i. 



though closely resembling other kinds found in the nearest 

 parts of the American continent. 



Most naturalists now admit that these facts can only 

 be explained by the greater or less lapse of time since 

 the islands were upraised from beneath the ocean, or were 

 separated from the nearest land ; and this will be generally 

 (though not always) indicated by the depth of the inter- 

 vening sea. The enormous thickness of many marine 

 deposits through wide areas shows that subsidence has 

 often continued (with intermitting periods of repose) 

 during epochs of immense duration. The depth of sea 

 produced by such subsidence will therefore generally be 

 a measure of time ; and in like manner the change which 

 organic forms have undergone is a measure of time. 

 When we make proper allowance for the continued in- 

 troduction of new animals and plants from surrounding 

 countries, by those natural means of dispersal which have 

 been so well explained by Sir Charles Lyell and Mr. 

 Darwin, it is remarkable how closely these two measures 

 correspond. Britain is separated from the continent by 

 a very shallow sea, and only in a very few cases have our 

 animals or plants begun to show a difference from the 

 corresponding continental species. Corsica and Sardinia, 

 divided from Italy by a much deeper sea, present a much 

 greater difference in their organic forms. Cuba, separated 

 from Yucatan by a wider and deeper strait, differs more 



