302 Prof. A. C. Ramsay on the Erosion 



rock or vegetable soil by water arising from the melting of the 

 ice/' the grinding power is so immense, that in unweathered 

 ground comparatively recently covered by a glacier, every foot 

 of surface is often polished and striated. If, indeed, water usually 

 separates ice from the rock so that it does not press upon it, 

 a glacier, whether 30 or 3000 feet thick, would need to be 

 treated in the main as a floating body; and it is well known 

 that with floating ice there is some eight or ten times as much 

 ice below as above the water. 



As for bosses " still standing out in the midst of the valleys " 

 proving that glaciers have no erosive power, the reader unlearned 

 in theories of denudation will easily understand that the same 

 kind of argument might be applied to the pillars of earth left 

 for a time in the midst of a railway-cutting the actual exca- 

 vation of which he had not seen ; or because Goat Island still 

 stands in the middle of the falls, the Niagara has not cut its 

 gorge; or because other low islands lie higher up, the river has 

 not worn out a channel on either side of them and will not 

 destroy them ; or in marine denudation, that the chalk between 

 Old Harry and his Wife and the mainland of Swanage Bay, and 

 that between the Needles and the Isle of Wight, has not been 

 washed away by the sea, because the islets still stand in the 

 midst. If, however, it be said that the glacier-islets are the 

 result of old subaerial denudations before the glacier began to 

 flow, I might perhaps doubt it, but, for evident reasons, for the 

 purpose of this argument, I will not quarrel with it. If they 

 have not been left prominent either by streams or ice, then, 

 according to the hypothesis which accounts for these valleys by 

 disturbance, the bosses in the midst of the glaciers are the result 

 of a process of dislocation of which I should like to see the spe- 

 cial proof. 



The peculiarity and in part the amount of this wearing action 

 of ice is indeed due to that very " plasticity w which enables ice to 

 mould " itself upon the inequalities of the hard rock." And it is 

 just therein that its excavating power differs from that of water. 

 Still water cannot excavate a large basin-shaped hollow, and in 

 the depths of a lake water is still; but glacier- ice, having 

 "moulded itself upon the inequalities of the hard rocks over 

 which it passed," can even move right over a barrier of rock and 

 grind it into roches moutonnees. The very fact that a roche mou- 

 tonnee has, as stated by Sir Roderick, a "Stoss-Seite" is indeed 

 proof that with sufficient pressure behind, a glacier can to some 

 extent pass uphill ; and those who remember the great size and 

 height of many of these barriers in Switzerland, as, for instance, 

 the Kirchet and the hill behind the Grimsel, will be prepared to 

 follow the arguments urged in my original paper — and, for dif- 



