136 DISCUSSIONS IN CLIMATOLOGY. 



of deposits containing organic remains, indicative of a 

 superior mildness of climate having obtained during 

 early interglacial periods, cannot certainly be regarded 

 as satisfactory evidence against the conclusion just 

 referred to. When we consider the enormous pressure 

 and destructive power of an ice-sheet some 2000 or 

 3000 feet in thickness grinding down the face of a 

 country, our surprise is that so much evidence remains 

 of even the last interglacial period. That so few relics 

 of the flora and fauna of preceding interglacial periods 

 have been preserved, is a conclusion which we might 

 a priori anticipate. This fact has been clearly pointed 

 out by Mr. Wallace himself, who says : — " If there have 

 been, not two only, but a series of such alternations of 

 climate, we could not possibly expect to find more 

 than the most slender indications of them, because 

 each succeeding ice-sheet would necessarily grind down 

 or otherwise destroy much of the superficial deposits 

 left by its predecessors, while the torrents that must 

 always have accompanied the melting of these huge 

 masses of ice would wash away even such fragments 

 as might have escaped the ice itself." * 



When we pass beyond the limits reached by the 

 ice-sheets of the Glacial Epoch, we may expect, of 

 course, to find the remains of many of the plants and 

 animals which lived during the earlier interglacial 

 periods. But here, again, we encounter another diffi- 

 culty ; for we have in this case seldom any means of 

 determining the age to which these remains belong. 

 Unless in relation to overlying and underlying boulder- 

 clays, there seems in many cases no way of knowing 

 to what interglacial period they ought to be assigned ; 

 or, in fact, whether they are really interglacial. or not. 

 If the remains in question indicated a condition of 



* " Island Life," p. 118. 



