120 THE ENTOMOLOGIST. 



this ; but it does not, to my mind, wholly explain the total 

 absence even of mountain species. 



Mr. WoUaston, in his work on the variation of species, 

 suggests that this remarkable difference between one moun- 

 tain district and another has its explanation in geological 

 movements of subsidence and elevation. He says : — " 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 other of these 

 extremes does almost constantly obtain. And, although I 

 would not wish to dogmatize on phenomena which may in 

 reality be explicable 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. Where the gradual lowering 

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

 accumulation of life on its loftiest pinnacles — for, even 

 allowing a certain number of species (which even formerly 

 were only just able to find a sufficient altitude for their 

 development) to have perished, we shall have concentrated 

 at that single elevation the residue of all those which have 

 survived from the ancient elevations above it. But if, on 

 the other hand, an area, already peopled, be in parts greatly 

 upheaved, there will be either a universal dying out, from 

 the cold, of a large proportion of its inhabitants, or else an 

 instinctive striving amongst them to desert the higher 

 grounds on which they have been lifted up, and to descend 

 to their nornial altitudes ; in both cases, however, the 

 present summits will display the same feature — namely, 

 utter desolation." (Pp. 115, 116). 



So far as the Wicklow mountains are concerned, the facts 

 seem to accord with this hypothesis, the upheaved granite 

 being almost devoid of insect life, though it must be 

 admitted that the amount of elevation of these hills is com- 

 paratively trilling, and it is somewhat difficult to consider it 



