222 proceedings of the geological sociExr. [Jan. 22, 



Discussion. 



Prof. Ramsay agreed in the main with the views of the author, 

 and with the opinion of Agassiz as to the great extension of cold at 

 a certain period both in the northern and southern hemispheres, 

 though he could not carry the theory quite so far as to leave merely 

 a narrow equatorial belt unaffected by ice. He had, however, 

 never seen any mountain-region in the northern hemisphere on 

 which there were no traces of glacial action. As to Ireland, he 

 knew of no portion of its surface which had not been glaciated, and 

 the great striations actually extended, as they do in Scotland, right 

 over the watersheds, and were evidently unconnected with any 

 merely local features. At the same time, even where the general 

 current of the upper portion of the ice was constant, yet there might 

 have been and probably were, undercurrents, the course of which 

 was determined by the form of the country traversed by the ice. 

 He was not certain that the present features, resulting from denu- 

 dation, were rightly attributed to glacial agency alone, as other 

 causes appear to have been at work. He instanced cases of enor- 

 mous denudation at early geological periods which it was difficult 

 to trace to any glacial action. He thought that during the Glacial 

 period the main features of the country were to a great extent modi- 

 fied by the great ice-sheet which capped it, without its having had 

 so extensive an effect as that sometimes attributed to it. Still 

 sufficient changes had been made on the surface to cause the rivers 

 which were resuscitated after the close of the Glacial period to take 

 new courses. The existence of old river-valleys, partially oblite- 

 rated by glacial debris, proved to his mind that hills and valleys, 

 and a diversified surface, existed previously to the Glacial period to 

 almost as marked an extent as they do at the present day. 



Sir Henby James observed that, having at one time been in charge 

 of the Geological Survey of Ireland, he could indorse the views of 

 the author as to the glaciation of that country, though he agreed 

 with Prof. Ramsay as to the probability of valleys in Ireland and 

 in Scotland having existed before the Glacial period and guided the 

 flow of the ice. These no doubt were intimately connected with 

 the varying hardness of the rocks. 



Mr. T. M'K. Hughes remarked that there was no necessity for a 

 polar ice-cap from any secularly recurring cold — seeing that the dif- 

 ference of temperature, known as a matter of observation to be due 

 to geographical causes, was so very much greater than any variation 

 of temperature which had been shown to be possible owing to astro- 

 nomical combinations, that the astronomical causes might be neg- 

 lected. He showed that the glaciation which was relied on as a 

 proof of the passage of large masses of ice from the north, did not 

 appear to come from the north pole, but from local centres, such as 

 Scandinavia, Scotland, and the mountains of Wales and the N.W. 

 of England, from which the ice moved in all directions. He pointed 

 out that the contents of the drift appeared to be ignored ; for al- 

 though in the British sles the polar drift might have been pushed 



