30 THE CANADIAN NATURALIST. [Feb. 



But if rivers which are not torrential, and do not descend from 

 heights, cannot possibly have produced, nor even have deepened, 

 the natural hollows or chasms in which they flow, still it might 

 be contended that, what water has not effected, may have been 

 done by a river, when, in the compacter form of ice, it descended 

 and advanced across the lower country. Unluckily for the sup- 

 porters of the ice-excavating theory, the data which existing nature 

 presents to us, as before said, are decisively opposed to their view. 

 The examination of those tracts over which glaciers have advanced, 

 and from which they have retreated, shows, in the most convincing 

 manner, that ice has so much plasticity that it has always moulded 

 itself upon the inequalities of hard rocks over which it passed, and, 

 merely pushing on the loose detritus which it meets with, or car- 

 ries along with it from the sides of the upper mountains, has. never 

 excavated the lateral valleys, nor even cleared out their old alluvia. 

 This fact was well noticed by the Swiss naturalists, as evidenced 

 by present operations, at their last meeting in the Upper Engadine, 

 and has been well recorded by that experienced and sagacious 

 observer of glacial phenomena, M. Martins.* 



Since that time the able French geologist, M. Collomb, who was 

 associated with Agassiz in his earliest researches on glaciers, and 

 has been the companion, in Spain, of my colleague, M. de Yer- 

 neuil, has recently put into my hands the results of his own obser- 

 vation upon the present and former agency of the glaciers of the 

 Alps, which decisively show that ice, per se, neither has nor has 

 had any excavating power.f None of the glaciers of the Alps 

 cited by M. Collomb, viz., those of the Rhone, the Aar, the Valley 

 of Chamounix, the Allee Blanche, and the valley of Zermatt, pro- 

 duce any excavation in the lower grounds over which they pass. 

 That of Goerner, which, among others, is advancing, affects very 

 slightly the surface of the meadows on which it proceeds, and does 

 not penetrate into the soil. Again, where the glacier of the lower 

 Aar pushes, on its front, upon accumulations of the debris of old 

 moraines and gravel, it scarcely deranges these materials, but slides 

 over them, leaving them covered with mud and sand, but not 



* See ' Revue des Deux Mondes,' March, 1864. The former observations 

 of M. Martins on Norway and on the Alps are of the highest importance, 



f I may add that M. Collomb expresses that which I believe to be the 

 opinion of Eiie de Beaumont, d'Archiac, De Verneuil, Daubr^e, and of 

 all the leading French geologists. 



