1882.] 



19 



[Davis. 



GLACIAL EROSION. 



BY WILLIAM MOERIS DAVIS. 



Statement of the Question and 



2. 



Amount of Drift. 



Answer. 



3. 



Great Boulders. 



Growth of the Idea. 



4. 



Central and Marginal Areas of 



The four Lines of Argument. 





Glaciation. 



A . Action of Glaciers 



5. 



The Alps. 



in general. 



6. 



The Vosges. 



1. Beneath the Glacier. 



7. 



Scandinavia and North Ger- 



2. Advance of Glaciers. 





many. 



3. Retreat of Glaciers. 



8. 



Great Britain. 



4. Transporters, not Eroders. 



9. 



North-eastern America. 



5. Limit of Time. 



10. 



Drumlins. 



6. Subglacial Streams. 



C. 



Topography of Glaciated Re- 



7. Pressure Melting. 





gions. 



8. Where is Ice-erosion most 



1. 



Fjords. 



effective ? 



2. 



Valleys. 



9. Ice, more than Rock, is eroded. 



3. 



Cirques. 



10. Preservation of Soratches. 



4. 



Slope of Valley Sides. 



11. Self-limitation of Glacial 



5. 



Lakes. 



Erosion. 



6. 



Detail of Glaciated Surfaces. 



12. Several Glacial Periods. 



7. 



Included Non-glaciated Dis- 



B. Amount and Arrangement 





tricts. 



of Glacial Drift. 



D. 



Argument from Necessity. 



1. Preglacial Conditions. 



Su: 



tnmary. 



How much was the surface of glaciated countries changed 

 during their occupation by ice ? How far was the form of North- 

 western Europe, Switzerland, and North-eastern America remod- 

 eled in the glacial period ? 



To answer such questions briefly, one should first ask the 

 questioner what authority he prefers, for there is no admitted 

 agreement on the subject among geologists. "We may quote 

 Rutimeyer, a Swiss geologist of high standing, to the effect that 

 the glacial period was a time of rest in the formation of valleys ; 

 Ramsay, the late director of the Geological Survey of Great 

 Britain, considers most of our northern lakes the result of local- 

 ized glacial erosion ; and Tyndall, whom some may take as 

 an authority beyond the limit of his special studies, states his 



