300 Prof. A. C. Ramsay on the Erosion 



Roderick's opinion seems to have been formed a long time ago ; 

 for, adopting M. Escher's authority, anyone who consults his 

 map of the ancient extension of the Alpine glaciers, will see that 

 he draws an enormous glacier, which issuing from the broad flat 

 valley of the Rhine, tranquilly overspread the country on all sides 

 of the lake, and without the necessity for any plunge, could only 

 have been fed by smaller tributary streams of ice that, if such 

 existed, descended on the northern slopes of the Hohe Sentis*. 



In like manner, Sir Roderick is of opinion that the basin of 

 the Lake of Geneva was not scooped out by ice, because "it 

 trends from east to west," or at right angles to the main flow of 

 the glacier — because ice, per se, neither has nor has had any 

 excavating power" — because (p. 12) "in valleys with a very 

 slight descent, .... no erosion whatever takes place, particularly 

 as the bottom of the glacier is usually separated from the sub- 

 jacent rock or vegetable soil by water arising from the melting 

 of the ice," and because even in gorges " whence the largest gla- 

 ciers have advanced for ages, we meet with islands of solid rock 

 and little bosses still standing out, even in the midst of the val- 

 leys down which the icy stream has swept," and "there is no 

 proof of wide erosion" — and, yet again, because (p. 15) "ice has 

 so much plasticity that it has always moulded itself upon the 

 inequalities of the hard rocks over which it passed," and " has 

 never excavated the lateral valleys, nor even cleared out their 

 old alluvia," and furthermore, in general terms, because ice 

 could not have been propelled up an inclination from the bottom 

 of a lake, let the angle, I presume, be ever so small. 



Now the east and west course of the lake is here treated as if 

 the glacier of the Rhone which overspread it were the only gla- 

 cier which helped to cover the area; but if any one will take the 

 trouble to refer to the map which accompanies my memoir, or, 

 better still, to M. Escher' s, he will see that the mass of ice must 

 have been prodigiously swelled by the great tributary glacier of 

 Chamouni, which, descending from Mont Blanc, filled a valley 

 some fifty miles in length, and joined the Rhone glacier near the 

 lower end of the Lake of Geneva. Neither does it require much 

 reasoning to see that during the cold of the glacial epoch all the 

 higher region south of the lake must have maintained its glaciers 

 and filled the valleys that run north ; for even now some of the 



* I have to apologize to my friend M. Escher von der Linth for not 

 having used his map of the ancient glaciers as my chief authority when my 

 Memoir on the Lakes was read. The first time I saw his map, which was 

 sent me by Principal Forbes of St. Andrews, was after the publication 

 of my memoir. Had I seen it in time, I w r ould certainly have availed my- 

 self, in the construction of my sketch map, of the authority of a geologist so 

 accurate and distinguished as Escher von der Linth. 



