308 Prof. A. C. Ramsay on the Erosion 



above alluded to must have been destroyed and renewed over 

 and over again j and as glacier-ice is practically anything but a 

 rigid body, I think it would be easy to show that, just as in Arc- 

 tic regions in winter the more rapid flow of the lower strata of 

 ice, with a temperature of about 32°, shatters the more rigid 

 and slowly-moving upper layers which have a temperature far 

 below that point, so, for other reasons/ the motion of some 2000 

 vertical feet of ice sliding over the basin, would be communicated 

 to the lower strata ; for pressure in ice produces adhesion of parts. 

 I for one cannot conceive a horizontal fracture of 40 miles in length 

 over the area of the Lake of Geneva, clearly dividing two bodies 

 of ice, the lower of which was, where thickest, nearly 1000 feet, 

 and the upper and sliding stratum must have been nearly 3000 

 feet thick. It is, in fact, a piece of mere elementary knowledge 

 that any heavy body passing steadily across any other body, the 

 parts of which are moveable, will communicate motion to the 

 parts over which it passes, whether one or both of those bodies 

 be viscid or plastic, or of some other compound character; and 

 when I wrote my original paper it never occurred to me that 

 there was any need of mentioning a point so obvious. But in a 

 glacier that fills a lake-basin, this is by no means the only, and 

 perhaps not the principal, cause of motion. A glacier does not 

 throughout all its course move on simply by virtue of gravity. 

 Pressure from behind has a great deal to do with it ; as, for 

 instance, in the case of the Rhone glacier, familiar to so many, 

 and cited by Professor Merian and Dr. Tyndall. There, at the 

 cataract, the ice fractures and slides down comparatively rapidly 

 in masses, but at the base, where it moves slowly, pressure from 

 behind causes the masses to touch and reunite, and the whole 

 slides on, a re-formed mass, into the lower valley, the inclination of 

 which is small. So, in the case of the lakes, the depths of which 

 seem so appalling, but the real angles of the beds of which are so 

 small, there seems to me nothing either impossible or remarkable 

 in the idea that the long and enormous onflowing inclined 

 mass of the glacier of the Rhone pushed before it in the plain 

 (for such it is) its own more sluggish continuation up a slope of 

 25' for a distance of 20 or 25 miles. I believe that the same 

 argument is equally applicable to the Lago Maggiore, where the 

 already vast glacier, swelled by the mighty tributary of the Val 

 d'Ossola, was thus enabled to push along the low average slope 

 of 2° 21' for a distance about half as great. The very islands in 

 many a lake once filled with ice help to prove this; for, as in 

 the case of Loch Lomond, they are mere roches moutonnees, and 

 I for one cannot conceive that the mammillation ceases imme- 

 diately below the surface of the water. 



Having got thus far, I will not repeat my arguments to show 



