14 H. L. PAIRCHILD— ICE EROSION THEORY A FALLACY 



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Effect of deep waters facing the ice 59 



No erosion in front of zone of deposition 59 



Absence of moraines in the basins 59 



Small volume of the valley- heads moraine 60 



Idea of rock basins an assumption 60 



Convexity of valley sides 61 



Rock cliffs 62 



Islands and capes of rock in Cayuga basin . 63 



Direction of ice flow due to the topography 63 



Transverse valleys 63 



Adverse philosophy 64 



Direct proofs of non-erosion 64 



History of the valleys 66 



Preglacial conditions 66 



Preglacial drainage 66 



Ice invasions 66 



Effects of ice advance 67 



Conditions during maximum extent of the ice sheet 67 



Valley-heads moraine 68 



Effects of ice retreat 68 



Local glacial lakes 69 



Drumlin-belt filling 70 



Buried valleys 70 



Greater glacial lakes 71 



Present lakes 72 



General summary. 73 



Part I — General Theoretical Discussion 



INTRODUCTION 



Divergence of opinion. — Probably there is no subject in geology on 

 which the divergence of opinion is so great while at the same time the 

 observational material is so ample as that of glacial erosion. A few 

 geologists believe that glaciers have excavated valleys and basins thou- 

 sands of feet deep in solid rock, while others think that ice erosion has 

 been inconsequential. There was a time when Joseph Le Conte and 

 John Muir held the opinion that Yosemite valley had been excavated 

 by Sierran glaciers, while J. D. Whitney was not convinced that glacier 

 ice had ever even occupied the valley. Today most students of living 

 glaciers and glacial work deny that glaciers possess great erosive power, 

 while a group of physiographers claim that the peculiar features of Nor- 

 wegian, Alaskan, and other deep valleys, including those of the New 

 York " Finger " lakes, are due to great deepening by ice excavation. 

 With such an abundance of concrete evidence available, it would seem 



