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whelming effect of a volcanic eruption, in a region 

 where the aborigines of the soil have not wandered far 

 from their primaeval haunts, may, as Sir Charles Lyell 

 has well remarked, put an end to others, and so effect 

 the separation of their allies from the central stock. 

 And, lastly, the intervention of man, with all the various 

 concomitants which civilization, art, and agriculture 

 bring in his train, is the most irresistible of every 

 agency in the extensive (though often accidental) demo- 

 lition of a greater or less proportion of the animate 

 tribes. 



The whole of these ultimate assortments, however, are 

 dependent, as it were, for their outline, upon contingency 

 or chance ; and we must not deduce our ideas of genera 

 from the examples which they supply. We should 

 rather reflect, that it is no matter of mere speculation, 

 that many organic links, now absent, have, through the 

 crises and occurrences to which we have just drawn 

 attention, become lost. On the contrary, indeed, we 

 know that, in the common course of things, it must 

 have been so; and therefore we are induced to regard 

 those cases as exceptional, and as in no way expository 

 of Nature's universal scheme. The more we look into 

 the question, whether by the light of analogy or the 

 evidence of facts, the more are we convinced that lines 

 of rigid demarcation (either between genera or species, 

 though especially the former) do not anywhere, except 

 through accident, exist. And hence it is that we ascend, 

 by degrees, to a comprehension of that unity at which I 



