250 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21, 



at the level of the lowest Glen Roy line. But I ascertained that the 

 terraces close by the end of Loch Treig do not correspond in height ; 

 they do not, in fact, form part of this Parallel Road, but are about 

 30 feet above it. This seems difficult to account for except by sup- 

 posing these heaps of debris to have been piled up by the glacier to 

 such a height as to dam Loch Treig, after the ice withdrew, to a level 

 exceeding the height of this line. The outpour of the lake would 

 then wear through them ; but it has not even yet cut its way to the 

 very bottom, for the lake is still partly retained by these banks of 

 gravel. 



On tracing the gravelly accumulations up the Laire Glen, I found 

 that they became terraced or flattened at the level of the lowest 

 Parallel Road (which is the only one seen in Glen Spean), but ex- 

 tended up the glen continuously above the level of this line, assum- 

 ing an irregular hillocky outline, and becoming gradually coarser 

 and of a less water-worn character — assuming, in short, the natural 

 aspect of old moraines. It is interesting to note that none of the 

 syenitic boulders occur here. At a deep section of one of these banks 

 at the mouth of Corry Laire, below the level of the line, I noticed 

 that the stuff was heaped together in a highly inclined sloping 

 manner; the mass consisted of coarse water-worn gravel, very 

 pebbly, and the pebbles indicated a considerable amount of water- 

 rolling. This want of horizontal stratification, and the somewhat 

 earthy character of much of the sand, were the chief differences I 

 could perceive between it and ordinary water-bedded gravel. 



The melting of the ice from time to time, aided by heavy rains, 

 would send floods of water over the old moraines, and might thus 

 produce great quantities of rolled gravel in the neighbourhood. 



The meeting of the moraines with the lowest Parallel Road at the 

 mouth of the Larig Leachach is also well worth studying. The ice of 

 this short glen seems to have protruded in much the same way, for 

 the outer mounds are fringed with the gravelly terrace of the Road. 

 Something of the same kind is also seen at the next corry to the west, 

 called Corry Yaddie. But at the time of the two uppermost lines, 

 which mark a period of severer cold, all these glaciers must have 

 advanced far out, and perhaps filled the whole of the lower part of 

 Glen Spean, and hence the absence of the two upper lines there. 

 Glen Gluoy, even, and the basin of Loch Laggan may have been then 

 filled with snow and ice, and some of the higher side ravines of Glen 

 Roy may have had their sheets of ice, or glaciers of the second order. 

 This, it seemed to me, might have been the case with a corry on the 

 west side of Glen Collarig, near which the two upper lines cease, one 

 of them quite suddenly ; the terrace of which it consists bulging out 

 at its termination as if it had there met the ice. The watershed at 

 the head of Glen Collarig seems also to be formed partly by old 

 moraines from an adjoining corry, but these belong probably to a 

 period antecedent to any of the Glen Roy lines. 



Seeing the many fine deltas along the lowest of the Glen Roy lines, 

 I was struck with the remarkable absence of these accumulations 

 along the two upper ones. I do not think the shorter course of the 



