240 PEOCEEDIITGS OF THE GEOLOGICAL SOCIETY.' [March 6, 



opening by wide mouths to the west, and drained by broad straits 

 liable to be suddenly shut during the rise of the land, are not of 

 freqiient occurrence, and of course are quite unknown on the east 

 side of the island. On the other hand, no sufficient reason appears 

 in the lake theory why such detritus or glacier-formed lakes should 

 have occurred here, and this at four successive levels, and in no 

 other part of Scotland. Further, this view is in harmony with the 

 most approved theory of geological change, appealing only to exist- 

 ing causes, and demanding no sudden or violent revolutions, but 

 simply the slow, continuous regular rise of the laud. 



Since the above was written, Colonel Sir Henry James has kindly 

 furnished me with a note of the elevation above the sea-level of the 

 roads and cols. This shows that the Glen-Gloy road (No. 1 in 

 Chambers's ' Ancient Sea Margins '), 1168 feet, exactly corresponds 

 with the col to Glen Eoy. The upper Glen-Koy road (No. 2 of 

 Chambers), 1149 feet, is one foot below the col to Loch Spey, 1150 

 feet. The middle Glen-Eoy road (No. 3, Chambers), 1065 feet, 

 agrees with the col to Loch Laggan. But the lower road (No. 4, 

 Chambers), 856 feet, is six feet above the col to the Spey, 850 feet. 



DiSCXTSSIOiN-. 



Sir Henky James stated that he had given particular instructions 

 to the officers in charge of the survey as to the accurate levelling of 

 the roads. Captain White had informed him that there was some 

 question as to the existence of more than one road in Glen Gloy. 

 There could, however, be no doubt as to the general correspondence 

 of the levels of the terraces at different points. With regard to local 

 variations in the level of the sea, he stated that the mean sea-level 

 was found to be remarkably constant. He considered the question 

 as rather physical than geological. In that district was a country 

 every feature of which had been modified by glaciers ; and there 

 was therefore no difficulty in conceding the existence of glacier 

 lakes. There was, moreover, every probability of a country so cut 

 up by such deep valleys having in places enormous accumulations 

 of ice, and especially in Glen More. The difference in level between 

 the beds in Glen Gloy and Eoy was 20 feet, which could hardly be 

 accounted for on the marine, theory. Nor are there any similar 

 terraces in neighbouring glens, such as ought to be there on that 

 theory. In so exceptional a district, with Ben Nevis acting as a 

 buttress at the east end of Glen More, against which and upon which 

 ice 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 diiferent valleys 

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

 vaUeys 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 account- 



