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chain ; whilst he whose lot has been cast amidst island 

 groups, will have become even more conscious than the 

 former of the permanency of those impediments which 

 have been placed (in this instance by the broad arms of 

 the mighty ocean) as checks upon a too rapid system of 

 diffusion. 



But if the sea and mountain ranges, when of a suffi- 

 cient age in situ, are amongst the most effectual of 

 Nature's barriers against the self-dispersion of the 

 animate tribes ; it follows that, if the two could be (as 

 it were) united, we should have found the greatest ob- 

 stacle which physical conditions can ordinarily present 

 against the wandering capabilities of the latter. The 

 question therefore arises, Is it possible for them to be 

 so joined ? Undoubtedly it is : and hence we arrive at 

 the conclusion, that a mountain island should afford us 

 the minimum of size, as regards the areas its species 

 have overspread, which any country is able to furnish. 



Madeira is a mountain island, its highest peaks 

 rising, although resting on so small a base, to an alti- 

 tude of more than 6000 feet. Yet it is only partially a 

 case in point; for, although it was a mountain mass, 

 and perhaps a very elevated one, when its endemic 

 beings made their first appearance upon its surface, we 

 have already intimated that it has become isolated since 

 that epoch : so that, whilst one of the natural barriers 

 against dispersion which it involves (namely, mountain 

 ridges) may be considered as primary ; the other (to wit, 

 the sea, as it now obtains) has played, as an agent of 



