GLACIERS 231 



6. In what part of a valley glacier should erosion be greatest ? 

 Least? Why? 



7. (1) What will be the effect of the slow degradation of glacier- 

 bearing mountains upon the snowfall they receive? (2) What 

 influence will this have upon the position of the snow line ? (3) How 

 will the facts involved in the two preceding questions affect the 

 size and length of the glaciers ? (4) When will the mountains cease 

 to have glaciers ? 



8. How could one determine in the field the approximate thick- 

 ness of the glaciers which formerly occupied the valleys shown in 

 Figures 234 and 235 ? 



9. What conditions would produce valley trains (1) of high, 

 and (2) of low average gradient ? 



10. Why are eskers usually roughly parallel with the direction 

 of ice movement ? 



11. Compare and contrast typical topographies due to river 

 erosion and to glaciation. 



12. Moraine topography and dune topography are sometimes 

 similar. How might the two be distinguished in the field ? 



REFERENCES 



ALDEN : Drumlins of Southeastern Wisconsin; Bull. 273, U.S. 



Geol. Surv. 

 BRIGHAM : The Fiords of Norway, in Bull. Am. Geog. Soc., Vol. 



XXXVIII, pp. 337-348. 

 CHAMBERLIN : The Rock-Scorings of the Great Ice Invasions, in 7th 



Ann. Kept., U.S. Geol. Surv., pp. 147-248. 

 DAVIS : Glacial Erosion in France, Switzerland and Norway, in Proc. 



Bost. Soc. Nat. Hist., Vol. XXIX, pp. 273-322. 

 - Hanging Valleys, in Science, N. S., Vol. XXV, pp. 833-836. 

 GANNETT : Lake Chelan, in Nat. Geog. Mag., Vol. IX, pp. 417-428. 

 GEIKIE, J. : Land-forms modified by Glacial Action, in Earth Sculp- 

 ture, Chs. X, XI. (New York, 1898.) 

 GEIKIE, SIR A. : Scenery of Scotland, Chs. IV, X, XI, XIV, XVII. 



3d ed. (London, 1901.) 

 GILBERT: Alaska; Glaciers and Glaciation. Vol. Ill of Harriman 



Alaska Expedition. (New York, 1904.) 



NANSEN : The First Crossing of Greenland. (London, 1893.) 

 PEARY: Northward over the "Great Ice." 2 vols. (New York, 



1898.) 

 RUSSELL, : Glaciers of North America. (Boston, 1897.) 



Glaciers of Mount Rainier, in 18th Ann. Rept., U.S. Geol. 



Surv., Pt. II, pp. 349-415. 



