304 Prof. A. C. Ramsay on the Erosion 



of the Brenva and Miage ride over their moraines. I know these 

 glaciers well, and the statement that they do ride on their 

 moraines is perfectly true ; but few geologists, and probably no 

 physical philosopher will rest his reputation on the assertion 

 that, if those glaciers were to increase till they attained their 

 ancient size, when as mere tributary sources they helped to swell 

 the enormous mass that ploughed all down the Val d'Aosta to 

 beyond Ivrea, — will anyone, I say, rest his reputation on the 

 belief that these moraine heaps would lie where they now do, 

 underneath a thousand or thousands of feet of ice, unmoved to 

 all eternity, or at least till the complete decline of the glaciers 

 permitted the loose material to be attacked by running water ? 

 If so, again, whence the muddy glacier rivers, and whence the 

 scratched stones that come from under the glaciers ? Tyndall will 

 not believe in their immobility, nor De Mortillet, nor Gastaldi, 

 nor Darwin, who was the first to show that the larger glaciers of 

 Wales had ploughed the drift out of some of the greater valleys 

 of the country ; and many other geologists of weight will equally 

 shrink from the idea. Has ice no weight ? Do the huge glaciers 

 of Victoria-land and of Greenland exert no pressure on the ground 

 over which they flow ? and are there no stones and no powder of 

 rocks beneath to help the grinding-power ? Rub iron with your 

 finger often and long enough, and it will wear a channel in the 

 metal ; for the skin, like the passing glacier, will be renewed, 

 while the iron has no means of restoration. If yielding water 

 can wear out a channel, which few people will deny, far more, 

 then, must the weight of a thick glacier exercise a prodigious 

 abrading-power ; for surely no one on reflection will be so bold 

 as to assert that 50 feet, or one, two, or three thousand vertical 

 feet of ice with a specific gravity of nearly 0*92 will everywhere, 

 or nearly everywhere, be separated from its floor by a stra- 

 tum of water so complete that the glacier rarely touches the bot- 

 tom. If Agassiz, Forbes, and Tyndall, backed by Studer, 

 Escher, and Gastaldi, were to tell me so (and they would not 

 dream of it), my reverence for authority (and it is great) could 

 not persuade me to believe them. 



If, then, glaciers can waste rocks and deepen valleys, is it 

 possible that the great old glaciers under favourable circum- 

 stances have excavated lake-basins, when rocks of unequal hard- 

 ness came in their course, or when from special causes the 

 pressure of ice was unusually great on certain areas ? Or were 

 they apt to do so by a combination of these causes, when, ceas- 

 ing to flow through valleys of great or of moderate inc ination, 

 they descended into regions that are comparatively level ? 



I will not repeat what I have elsewhere printed about the 

 effect of ice passing over rocks of unequal hardness, nor yet what 



