CHAP. XV. BY THE EROSIVE ACTION OF GLACIERS. 313 



says Professor Eamsay, had to descend a slope of about 3° 

 for the first twenty-five miles, and then to ascend for the 

 last twelve miles (from the deepest part towards the outlet), 

 at an angle of 5°. It is for those who are conversant with 

 the dynamics of glacier-motion to divine whether, in such a 

 case, the discharge of ice would not be entirely effected by 

 the superior and faster-moving strata, and whether the 

 lowest would not be motionless or nearly so, and would 

 therefore exert veiy little, if any, friction on the bottom. 



4thly. But the gravest objection to the hj^pothesis of 

 glacial erosion on so stupendous a scale is afforded by the 

 entire absence of lakes of the first magnitude in several areas 

 where they ought to exist if the enormous glaciers which 

 once occupied those spaces had possessed the deep excavating 

 power ascribed to them. Thus in the area laid down on 

 the map, p. 306, or that covered by the ancient moraine 

 of the Dora Baltea, we see the monuments of a colossal 

 glacier derived from Mont Blanc and Monte Rosa, which 

 descended from points nearly a hundred miles distant, and 

 then, emerging from the narrow gorge above Ivi'ea, deployed 

 upon the plains of the Po, advancing over a floor of marine 

 pliocene strata of no greater solidity than the miocene sand- 

 stone and conglomerate in which the lake-basins of G-eneva, 

 Zurich, and some others are situated. Why did this 

 glacier fail to scoop out a deep and wide basin rivalling in 

 size the lakes of Maggiore or Como, instead of merely giving 

 rise to a few ponds above Ivrea, which may have been due to 

 ice-action ? There is one lake, it is true, — that of Candia, 

 near the southern extremity of the moraine, — Avhich is larger; 

 but even this, as will be seen by the map, p. 306, is quite of 

 subordinate importance, and whether it is situated in a rock 

 basin or is simply caused by a dam of moraine matter, has 

 not yet been fully made out. 



There ought also to have been another great lake^ 



