DERIVATION OF BRITISH COLEOPTERA. 167 



vaguely guess. Further back than this we cannot go, the 

 Geological record as regards insects is extremely fragmen- 

 tary and discontinuous, and we really have not the slightest 

 evidence as to when, where, or how the differentiation of 

 existing specific forms among the Coleoptera, or indeed of 

 any other order of insects, took place. 



But we are not now considering the origin of insects, 

 but their distribution in Britain and immediate derivation, 

 and we cannot get far into the subject before we discover 

 that any theories we may form on the matter will depend 

 ultimately on the view we take of that vast secular catas- 

 trophe known as the Glacial Age. 



How intense was that cold? Did an ice sheet cover the 

 whole of the British Islands as to-day it does Greenland ? 

 Can we regard the almost entire submergence of this 

 country during or at the close of the glacial epoch as 

 incontrovertible ? In short, were the climatic and other 

 conditions such that the whole of the preceding Tertiary 

 fauna of Great Britain must have been extirpated and 

 destroyed? Was such a clean sweep made of the whole of 

 antecedent life that when the great refrigeration passed, or 

 when the land stood once more above the waters, there 

 was presented a tabula rasa, and an empty stage on 

 which the actors in our present drama of life might appear 

 for the first time ? 



These are the questions which, at the outset of our 

 enquiry, confront us, questions you will observe so very 

 much more easily asked than answered. For it appears 

 that opinion on these points is not quite uniform, and, 

 indeed, seems recently to have become, as regards the 

 severity of this refrigeration, somewhat modified. 



Many great authorities, however, hold extreme views. 

 Thus, Dr. Wallace says — "The submergence destroyed 



