128 Reports and Proceedhigs — 



in Scotland, right over the vratersheds, 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 tlie form of the country 

 traversed by the ire. lie was not certain that the present features, resulting from 

 denudation, were riglitly attributed to glacial agency alone, as other causes appear to 

 have been at work. He instanced cases of enormous denudation at early geological 

 periods which it was difficult to trace to any glacial action. lie thought that during 

 the Glacial period the main features of the country were to some extent modified 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 obliterated by 

 glacial action, 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 Henry James observed that, having at one time been in charge of the Geological 

 Survey of Ireland, he could endorse the views of the author as to the glaciation of 

 that country, though he agreed with Prof. Eamsay 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 difference 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 

 astronomical combinations, that the astronomical causes might be neglected. 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, hut 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 although in the British 

 Isles the polar drift might have been pushed out to sea by later glacial action, still it 

 "would only have been transferred a little further on; and had any such drift been 

 deposited generally over the north of Europe, traces of it ought to be found along the 

 south and east margins of the Scandinavian drift. He appealed to the vast scale of 

 the changes of level to which tliis part of the earth's crust had been subjected, and 

 especially to the shell-beds of Moel Tryfaen and Macclesfield, to prove that changes 

 of level of at least 1400 feet had taken place since the Glacial period, and inquired 

 ■whether elevations on even that scale would not recall glacial conditions over a large 

 part of the area under notice. He again proposed to the Society a question which he 

 had asked several years before. What was the maximum pressure which ice would 

 hear without becoming water or being crushed; and whether the consideration of this 

 and the other conditions involved would lead us to assign a limit to the possible 

 lateral extension and vertical thickness of an ice-sheet moving on a plain or uphill 

 which would affect such speculations as that under discussion ? 



Mr. Mallet said that he was to some extent a disbeliever in glacial theories, thougli 

 he had from an early period in his life noticed the scratched condition of much of the 

 surface, and the presence of transported boulders in Ireland. He regarded, however, 

 the main valleys traversing the island as of far earlier date, and due to the original 

 form imparted to the land on its elevation, in consequence of lateral pressure. He 

 thought that some portion, if not the whole of the striation, might be due to the 

 slipping of the coating of detritus upon hard rocks, which would be the natural result 

 of the elevation of a portion of the sea-bed covered with pebbles, sand, and mud. 

 He thought the phenomena resulting from this cause could not be distinguished from 

 those resulting from the operation of glaciers. If so, the effect generally attributed 

 to glacial causes must be accepted with great caution. As to the limits to which ice 

 would be capable of propagating its own motion, it had been found by experiment 

 that a direct push could not be propagated through a mass of ice for any distance sO' 

 great as a mile. He thought that this put an end to the view of valleys being ex- 

 cavated by ice, though, of course, if crushed, ice would stiU propagate its force 

 laterally, and might produce certain effects. He denied that the results often 

 attributed to grounding icebergs could be due to such a cause. 



