Studies for Students. 



DISTINCT GLACIAL EPOCHS, AND THE CRITERIA 

 FOR THEIR RECOGNITION.^ 



I. Introduction. 



It has long been evident that writers on glacial geology are 

 not at one concerning some of the important questions which 

 underlie the interpretation of the history of the glacial period. 

 Certain recent publications have served to emphasize the differ- 

 ences between them. There are two questions, at least, concern- 

 ing which there must be agreement, or at any rate a common 

 understanding, before existing differences can be eliminated or 

 justly evaluated. When the answers to these questions have 

 been agreed upon, or when the positions of the contending par- 

 ties are clearly understood, it may be found that some of the 

 apparent antagonisms have no better basis than differences in 

 definition. Stated interrogatively, the two questions referred to 

 are these: i. What constitutes a glacial epoch as distinct from 

 other glacial epochs ? and 2. W^hat are the criteria for the recog- 

 nition of distinct glacial epochs, if such there were? 



II. The Idea of a Glacial Epoch, 



It is conceivable that, after the development and extension 

 of a continental ice-sheet, it might be wholly wasted away. 

 The maximum extension of such an ice-sheet would mark the 

 culmination of a glacial epoch. If subsequently another ice- 

 sheet of considerable dimensions were accumulated, its develop- 

 ment and extension would constitute a second glacial epoch. 

 These successive ice-sheets might be so related to each other in 



' Read before the American Geological Society at Ottawa, Dec, 1S92. 



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