238 Geological Society of London. 



■would accumulate, that theory was the best which accounted for the terraces by the 

 lakes having been formed by the intervention of glaciers blocking the valleys, as, 

 according to this theory, it would not be likely that the levels of the roads in the 

 different valleys would be the same, seeing that the ice-barriers of the different 

 valleys would probably not break at the same moment. The levels were taken at 

 the middle of the slope of the terraces. 



Prof. Eamsay entered into the history of the theories for accounting for the terraces, 

 the first of which, that of Prof. Agassiz (in 1840), accounted for them by a great 

 glacier damming up the valley, and from time to time declining in height. The 

 glacial theory, on which this view rested, had to some extent been doubted, but 

 eventually had been almost universally accepted even by its first opponents. He 

 next cited the works of the late Mr. Robert Chambers as to the existence of old sea- 

 margins, pointing to a gradual sinking of the sea or a rising of the land. There 

 could be little doubt that a great part of Scotland and of the northern part of Eng- 

 land had been at one time covered with glaciers, as had also been the case in other 

 parts of Europe. Unless the whole country had been submerged, and then come up 

 again by a succession of jerks, it seemed impossible that such terraces could have 

 been formed by the sea and still have remained in existence. If, however, there had 

 been great oscillations in temperature, it seemed possible that during the decline of 

 some transverse glacier the varying levels of the lake might have left terraces, traces 

 of which might still be preserved. ^ 



Mr. L. Lyell thought that Prof. Nicol's view, that the different heights of the 

 terraces in Glen Gloy and Glen Eoy were due to a great pressure of water coming 

 from the west, could hardly be sustained. If the sea had stood at that level, Scotland 

 would have been an archipelago, and differences of level, such as the terraces in- 

 dicated, could only have resulted from great tidal action, such as is the case in the 

 Loffoden Islands. He held that there was no evidence to show that such a state of 

 things had existed in the present case. As to the coincidence of the level of the 

 roads with that of the cols, he did not think they were explained on the marine 

 hypothesis. At the base of Prof. Nicol's speculation was an assumption in which he 

 could not agree. It was that the coating of detritus which covered the hills was of 

 marine origin. On the contrary, he held it to be sub-aerial. The fragments of rock 

 were sub-angular, little weathered, and altogether such as might be found in any sub- 

 aerial detritus. At Loch Assynt the beach of the freshwater lake consists of fi-agments 

 of red and white sandstone, unrolled and but partially water-worn. The beach of 

 Loch Maree, a land-locked arm of the sea, was composed of fragments of the same 

 rocks, but these were rolled ; and he believed that this difference was due to the tide, 

 which was absent in Loch Assynt and present in Loch Maree. The materials on the 

 roads of Glen Roy, when he examined them in 1869, much more nearly resembled 

 those on the shores of the freshwater lake than those on the shores of the marine and 

 tidal Loch Maree. He suggested the necessity of the observation of the nearest 

 parallel cases which could be found in cases where no experiments were possible. The 

 phenomena shown in Glen Roy were then compared with similar appearances at the 

 Marjelen See, a small glacier-bound lake in Switzerland, which fulfils in nature all 

 the conditions which the theory of the glacier-lake origin of the Glen Roy terraces 

 required. 



Mr. Gwyn Jeffreys renewed his protest against regarding these beds as marine 

 unless marine remains were found in them. In Prof. Nicol's former paper mention 

 had been made of rolled boulders. These occurred at Glasgow and elsewhere 

 covered with Balani. As, however, no marine remains had been found in Glen Roy, 

 he adopted the freshwater or glacier theory. 



Mr. Daintree, reasoning from observations made in tropical countries, asked 

 whether the terraces might not have been formed during the change of seasons from 

 summer to winter. 



Mr. Evans regretted that no one else was present who would in any degree 

 advocate the author's views. He pointed out that if the surfuce of the rocks below 

 the detritus in Glen Roy was glaciated, the probability was in favour of the super- 

 ficial drift being of marine rather than of sub-aerial origin. He much doubted 

 whether Ben Nevis, or any of the mountains of the district, offered a sufficient 

 gathering-ground for any such glacier as that supposed in the i'roshwuter theory, 

 assuming the climate to have been such as would have admitted of a large lake in 

 Glen Roy. He suggested the possibility of the openings through which the sea 



