

GEOLOGY. 25 



water. These " hills of uptilting," then, were hills not in consequence 

 but in spite of denudation, and would have been many times loftier 

 had it not been for the erosive action. Mr. Jurkes then entered into 

 a discussion as to the relations between the action of internal force 

 and that of external erosive action, and declared his belief that all 

 the striking external features were the result of the direct action of 

 the external forces called the " weather," and were not caused by any 

 direct action of the internal forces, which could only reach the sur- 

 face through the thickness of the crust. He then examined these 

 forces of erosion, and while he attributed to marine action all the 

 greater and more general features, the great plains, the long escarp- 

 ments, and the general outline of the mountains, he believed that the 

 valleys which traversed the plains, the gullies that furrowed the sides 

 of the hills, and the glens and ravines on the flanks of the mountains, 

 were all due to the action of the ice or water which fell on them from 

 the atmosphere. He did not give these views as altogether original, 

 but mentioned M. Charpentier and Mr. Dana as having long ago ap- 

 plied them to the Pyrenees and to the Blue Mountains of New South 

 Wales ; but, having been long skeptical as to their reality, he now 

 wished to record his conviction of their truth. Mr. Prestwich, Prof. 

 Ramsay, and himself, while pursuing different lines of investigation, 

 had all been simultaneously compelled to appeal to subaerial action 

 as the only method of explaining the phenomena they had met with, 

 and Dr. Tyndall had since fallen into the same line of march. 



NEW OBSERVATIONS ON GLACIERS. 



Prof. Tyndall has communicated to the London Times the following 

 interesting statement : 



Many years ago, Mr. William Hopkins pointed to the state of the 

 rocks over which glaciers had passed as conclusive evidence that these 

 vast masses of ice move bodily along their beds. Those rocks are 

 known to have their angles rasped off, and to be fluted and scarred 

 by the ice which has passed over them. Such appearances, indeed, 

 constitute the entire evidence of the former existence of glaciers in 

 this and other countries, discussed in the writings of Charpentier, 

 Agassiz, Buckland, Darwin, and other eminent men. 



I have now to offer a proof of the sliding of the ice exactly com- 

 plementary to the above. Suppose a glacier to be a plastic mass, 

 which did not slide, and suppose such a glacier to be turned upside 

 down, so as to expose its under surface ; that surface would bear the 

 impression of its bed, exactly as melted wax bears the impression of 

 a seal. The protuberant rocks would make hollows of their own 

 shape in the ice, and the depressions of the bed would be matched by 

 protuberances of their own shape on the under surface of the glacier. 

 But suppose the mass to slide over its bed, these exact impressions 

 would no longer exist ; the protuberances of the bed would then form 

 longitudinal furrows, while the depressions of the bed would produce 

 longitudinal ridges. From the former state of things we might infer 

 that the bottom of the glacier is stationary, while from the latter we 

 should certainly infer that the whole mass slides over its bed. 



In descending from the summit of the Weigshorn, in August last, I 

 22* 



