Dr. Croll's Theory of Glacial and Warm Periods, ioj 



a strange thing is this ! If the so-called glacial age has 

 been a recurring one in all geological time, assuredly we 

 ought to find at every horizon not merely evidence, but 

 unmistakeable proof. We have not to do with fragile 

 materials which could be destroyed by denudation, but with 

 tough boulders, with rounded land-surfaces on crystalline 

 rocks, etc., etc. Nowhere, except as I have mentioned, 

 is this forthcoming, but the contrary. The evidence of 

 the animal and vegetable debris again, of which we have so 

 much from every horizon, is perfectly consistent with that of 

 the lithology and consistent in protesting against a theory 

 which makes so many demands on our credulity, and 

 especially is this true, as has been well observed, of the 

 Tertiary beds and the vast period of time they cover. It 

 is quite true that certain traces have been found in some 

 Permian beds, which have been quoted by Ramsay and 

 others, and which seem to point to ice action, but ice action 

 •does not mean the existence of a glacial period. Glaciers 

 probably always existed as they exist now where the land 

 was sufficiently high, and we ought to find traces of them 

 in the geological record. What is wanted, however, is not 

 testimony to sporadic glaciers or local ice action, but to 

 widespread glacial phenomena such as would witness an 

 ice age. 



On this question let me quote two authorities of the first 

 rank : — 



Sir Charles Lyell, after examining the evidence in some 

 detail, concludes thus : " If it be asked whether in the entire 

 miocene series there are no indications of intercalated spells 

 of colder climate like the glacial episode intervening 

 between the older pliocene and the modern era, I may 

 reply that there are none which can at present be estab- 

 lished on organic evidence." {Principles, 1867, 204.) 



Again, speaking of the same kind of evidence, he says 

 some indications seem also to have been discovered of 



