CHAP, h] 



PHYSICAL GEOGRAPHY. 



11 



tlie islands were upniised from beneath the ocean, or WLTt- 

 sBparatcjd 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. Tlie depth of sea 

 produced by such subsidence will therefore generally be 

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

 organic fonna have undergone is a measure of time. 

 When we make proper allowance for tlie continued in- 

 troduction of new animals and plants from surrounding 

 conntries, by those natural means of dispei'ssil which have 

 been so well explained by Sir Charles Lyell and Mr. 

 Darwin, it is remarkable how closely these two measures 

 correspond. Britain is sepamted i'roiti the coiilinent by 

 a very shallow sea, and only in a vei'}* few cases have our 

 animals or plauts begun to show a diflbrence 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 stmit, differs more 

 markedly, so that most of its productions are of distinct 

 and peculiar species; while Madagascar, divided from 

 Atiica by a deep channel three hundred miles wide, pos- 

 sesses so many peculiar features as to indicate separation 

 at a very remote antiquity, or even to render it doubtful 

 whether the two countries have ever been absolutely 

 united. 



Returning now to the Malay Archipelago, we find that 

 all the wide expanse of sea wldch divides Java, Sumatra, 

 and Borneo from each other, and from Malacca and Siam, 

 is so sliallow that ships can anchor in any part of it, since 

 it rarely exceeds forty fathoms in depth ; and if we go as 

 far as the Une of a hundred fathoms, we shall include the 

 Philippine Islands and Bali, east of Java. If, therefore, 

 these islands have been separated from each other and 

 the continent by sul)sidcnce of the intervening tracts ol 

 land, we should conclude that the separation has been 

 comparatively recent, since the depth to winch tlie land 

 has subsided is so small. It ib also to be remarked, that 



