Davis.] 54 [May 3, 



to two thousand feet deep, while a little farther up stream their 

 valleys were but slightly modified, as Ramsay himself claims. In 

 Lago Maggiore, near its deeper parts, the Borromeo Islands rise 

 to the surface. The glacier of the Rhone failed where it had 

 great thickness to cut away the hills at Sion, and yet after it had 

 lessened its thickness and slackened its motion by spreading out 

 upon the plain, it is supposed to have cut out the basin of Lake 

 Geneva ; this lake is not in the line of the thickest part of the 

 glacier, and it is deepest where its rocks are hardest. Lakes 

 Neuchatel and Bienne are distinctly in the marginal area of the 

 ice-sheet, where it had little erosive power; in the former, there 

 is a rocky reef that rises to within a few feet of the surface, hav- 

 ing in some remarkable way escaped destruction. To explain 

 the glacial origin of Lake Constance, one must suppose that the 

 glacier of the Rhine waited till it emerged from its narrow moun- 

 tain valley before beginning its erosive work ; and then while its 

 eastern half moved quietly over the low grounds with but little 

 destructive effect, its western half ploughed out the lake basin to 

 a depth of nine hundred feet. 



C. 6. Detail of Glaciated Surfaces. A close examination of 

 glaciated regions will generally discover rock-forms that are diffi- 

 cult to explain on the supposition that glaciers have materially 

 denuded the surface on which they moved. Angular surfaces of 

 rock remain where it is impossible to suppose that they could be 

 preserved if the general surface had been considerably eroded. 

 Tors never require much erosion in their preparation, and often 

 show that but little has been possible. 



Tyndall claims that the rocky hills found in valleys and lakes are no 

 evidence against glacial erosion, for they may have been worn down " thou- 

 sands of feet." (Hours of Exercise in the Alps, 1871, 240). But this over- 

 looks the observations presented in A. 3. 



T. G. Bonney describes certain forms in the valleys above Lake Como 

 that seem quite inconsistent with severe glacial erosion. (Notes on the 

 Upper Engadine and the Italian Valleys of Monte Rosa, and their Relation 

 to the Glacial Erosion Theory of Lake-Basins. Geol. Soc. Journ., xxx, 

 1874, 479-488.) 



A. Heim says that the careful study of any (Swiss) valley will show that 

 glaciers have only rounded off sharp forms, and that often only on the 

 " stossseite," or here and there rubbed out shallow troughs, but never es- 

 sentially altered the valley-form ; whoever has examined these localities 



