1872.] jriCOL PARALLEL EOADS OF GLEN KOY. 241 



iug for the terraces ; the first of which, that of Prof. Agassiz (in 

 1840), accoTinted for them by a great gL^cier 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 donbted, but even- 

 tually had been almost universalljf accepted even by its first oppo- 

 nents. He next cited the Avorks of the late Mr. Eobert 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 England 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 sub- 

 merged, and then came 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 temjjerature, 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 difiereut 

 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 bave 

 been an archipelago, and difl^erences of level, siich as the terraces 

 indicated, could only have resulted from great tidal action, such as 

 is the case in the Lolfoden 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 assump- 

 tion in which he could not agree. It was that the coating of detritus 

 which covered the hills was of marine origin. On the contrary, ho 

 held it to be subaerial. The fragments of rock were subangular, 

 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 fragments 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 tidi', 

 which was absent in Loch Assynt and present in Loch Maree. The 

 materials on the roads of Glen Poy, when he examined them in 

 1869, much more nearly resembled those on the shores of the fresh- 

 water 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 Eoy were then 

 compared with similar appearances at the Marjelen See, a small 

 glacier-bound lake in Switzerland, Avhich fulfils in nature all the 

 conditions which the theory of the glacier-lake origin of the Glcn- 

 Eoy terraces required. 



Mr. GwYisr Jepekeys renewed his protest against regarding these 

 beds as marine unless marine remains were found in them. In 



