306 Prof. A. C. Ramsay on the Erosion 



why they are absent. It may be that some of the alluvial flats 

 of the valley are lake-hollows filled up. 



But another statement urged by Sir Roderick against my 

 theory is, that the scooping-out of such hollows by ice is im- 

 possible, because ice cannot flow up an inclined plane. If so, I 

 repeat, what is the meaning of the " Stoss-Seite" or upper side 

 of a roche moutonnee that bars a wide glacier valley, through 

 which barrier perhaps a mere narrow river gorge passes — as, for 

 instance, in the case of the Kirchet so well known to Alpine 

 men, or, on a smaller scale, of the roches moutonnees near the 

 slate-quarries in Nant Francon ? In both cases the barrier re- 

 mained intact till the drainage of the glacier- formed lakes cut 

 gorges through them — or, if Sir Roderick prefer it, till convul- 

 sions made gorges. Its moutonnee form will convince every 

 accomplished glacialist that the ground was once covered by 

 ice. The strike of the rocks will be enough for ordinary geolo- 

 gists ; for no man can suppose who sees the corresponding forms 

 of the roches moutonnees on either side of the narrow gorge of 

 the Aar, that that gorge existed before the period of the great 

 glacier, and that the glacier flowed entirely between the walls of 

 the narrow passage. If I am right in this, then the great old 

 glacier of the Aar flowed right over the hill, from bottom to top, 

 and away into regions far beyond, in the manner I have imper- 

 fectly shown in my little book on the old glaciers of Switzerland 

 and North Wales, and equally so whether the gorge was formed 

 by sudden violence or by water. 



In the existence, therefore, of " Stoss-Seiten" and in their 

 upward striations, both in small and large roches moutonnees, 

 there is proof that the belief that glaciers cannot flow over 

 hillocks, and even hills of considerable size, is a mere assertion 

 founded on prejudice : to me the wonder is, that any one can 

 ever have believed it who has truly observed phenomena in the 

 Alps, or who is familiar even with the ancient glaciation of our 

 own country. And if this be so, I see no difficulty in accepting 

 the hypothesis that the length and inclination of the slope 

 which the bottom of a glacier may ascend depend simply on 

 the thickness of the ice, and on the amount of the propelling 

 power behind, that power being due to the weight and mass of 

 the descending ice, and the average angles of the valley behind 

 the point whence the upward ascent begins*. 



Now, in dealing with this question, most of the geologists 

 who have opposed me have treated the larger lake-hollows much 

 as they do Time. Unconsciously they seem to me to be afraid both 

 of it and of them . " Look," they seem to say, " at these mountains, 



* I think it might be possible to make a very good approximate calcula- 

 tion on this point, and I hope it may yet be done. 



