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the level of our imaginary range ? It needs no argu- 

 ment to prove, that one at least would be manifest in 

 the total extinction of those forms which could not 

 adapt themselves to the increased heat. Others, which 

 were able with difficulty to endure the alteration, would 

 in all probability, even though they had now emigrated 

 to the loftiest peaks, nourish less vigorously than before ; 

 and it is not unlikely, moreover, that they would become 

 somewhat modified from their normal states, states 

 which, be it recollected (for this is an instructive lesson), 

 would still exist in more northern zones. 



During my researches in mountain tracts, I have 

 usually remarked, that the highest points of land either 

 teem with life, or else are perfectly barren. My own 

 experience would certainly tend to prove, that, in a 

 general sense, one or the other of these extremes does 

 almost constantly obtain. And, although I would not wish 

 to dogmatize on phenomena which may in reality be ex- 

 plicable on other hypotheses, it would perhaps be worth 

 while to inquire whether the geological movements of 

 subsidence and elevation will not afford some clew to the 

 right interpretation of them. Be this, however, as it 

 may, I can answer, that in many countries, where there 

 are strong indications of the former, the alpine summits 

 harbour an insect population to a singular extent ; whilst 

 in others, where the latter is as distinctly traceable, the 

 upland ridges are comparatively untenanted. Now we 

 have already shown, that where the gradual lowering of 

 a region has taken place, there will be, of necessity, an 



