33* 



SCIENCE PROGRESS 



our conception of the glacial epoch : it was evidently no un 

 broken reign of ice, it was not a single episode, but a repeated 

 alternation of contrasted episodes. There were periods of 

 predominant snowfall, when the ice attained its maximum de- 

 velopment, and the rivers were impoverished ; and alternating 

 with these were periods of predominant rainfall, when the 

 accumulated ice of centuries melted away, and, adding its 

 volume to the general drainage, gave birth to swollen streams 

 far surpassing in magnitude those with which we are familiar 

 in the existing Alps. 



The great ebb and flow of temperature was at least four times 



Depot Mlo* 



Deposition. 



>«MtOTK0^2£6U»7iCra?i2£U2au»<OUA>ttf&- 



Fig. 3. 



repeated ; four times have the glaciers enlarged their bounds, and 

 four times have they been driven back into their mountain home. 

 Such then is the hypothesis which arises from our con- 

 templation of the river terraces ; there is much that is attractive 

 about it, and it has the additional advantage of completely 

 explaining the facts, so far as they are known. Yet we must 

 not omit to point out that its author, Prof. Penck, admits it was 

 suggested by the writings of Prof. James Geikie, who in turn 

 was inspired by the theory of Adhemar, as advocated by Croll. 

 At the present day, however, there are few who accept the 

 theory of Adhemar, and consequently the explanation is dis- 

 credited at its source. 



