Geological Society of London. 375 



broad, and no less than 18 fathoms deep. At the top of its southern 

 bank, which consists of granite, there is another lake (Loch-na- 

 Craig), about 200 yards broad and 9 fathoms deep. The surround- 

 ing hills are low, and there appeared to be no source which could 

 furnish ice to excavate a lake of such depth as Loch Leckan ; and 

 further, the author contended that if one of these two basins were 

 excavated by ice, the other could hardly have been preserved intact. 

 Two other lakes, excavated on the summits of granite ridges, were 

 mentioned ; and the author could not conceive how either a glacier 

 or an ice-cap could have produced such basins. The Dhu Loch, 

 separated from Loch Fyne by a bank of gravel about a mile broad, 

 is entirely in detrital matter, which the author thought might have 

 been accumulated in its present form by the sea beating against the 

 end of a glacier. From its position and level, the Dhu Loch rises 

 and falls with the tide ; and it would appear that it formerly ex- 

 tended some miles further up the valley, where the author had 

 found clays containing a mixture of marine and freshwater Dia- 

 tomaceas. Li five of these cases the author thought it was impossible 

 that the basins were due to glacial action. 



Discussion. — Prof. Ramsay dissented from the concluding parts of His Grace's 

 remarks, which might lead his hearers to suppose that he had attributed all lake- 

 basins, without exception, to glacial action. On the contrary, he had in all cases 

 maintained that they were due in many instances to certain original valleys, due to 

 various agencies, both of superficial denudation and of internal disturbance, and 

 acting at all periods of the earth's existence. These earlier inequalities had 

 indeed received their final configuration from the action of ice ; and it was only 

 certain of the more shallow basins to which he assigned a purely glacial origin. 

 He disclaimed any such ideas, which he regarded as utterly irreconcilable with the 

 phenomena of nature. As to the sides of the basins, he had had great experience, 

 and nowhere had he seen a case in which he could regard the existence of a lake 

 as merely due to a fracture of the rocks. In Scotland it was well known that 

 most of the contortions of the rocks had taken place before the deposition of the 

 Old Red Sandstone. He wished to know whether during the ages that had 

 passed since that time all atmospheric agencies had been suspended. On the 

 contrary, their operation had been such that thousands and thousands of feet of 

 strata had by their means been removed. Nowhere was this more evident than in 

 considering the structure of the Carboniferous areas, where enormous denudation 

 had taken place long before even the coal had been deposited. How then could 

 we ignore this operation in other parts of the country ? As to faults, he submitted 

 that their existence must be proved rather than assumed. Did they exist, they 

 were not gaping faults, but closed ; and he regarded it as physically impossible 

 for such hollows as those in which the lakes were found to be due to such causes. 

 Even if fractures existed, they would not remove tlie matter of which the rocks 

 were composed. They might however, constitute lines of weakness, along which 

 denuding agents might more readily work. As to the lakes on the summits of 

 ridges, he would not pretend to account for what he had not seen ; but he cited 

 similar lakes in the Grimsel, which presented similar phenomena, and which he 

 regarded as undoubtedly due to glacier action. Even on the top of roches inou- 

 tonnees such basins were found ; and though he might not know the exact circum- 

 stances under which they were found, they were undoubtedly due to ice-action. 

 If in Switzerland and other glaciated countries of the present day we found the 

 configuration of the country presenting similar phenomena to those of Scotland, 

 he considered that there was ample ground for attributing both to the same cause, 

 and there was no need of invoking other causes. It was moreover to be borne in 

 mind that though similar contorted gneissose rocks to those of Scotland occurred 

 in several other countries, it was only in those which had been glaciated that such 

 numerous lake-basins were to be seen. 



