REMARKS ON GLEN EOT. 11 



shed at the head of the Spey became sufficiently open to admit of 

 water passing out, and as soon as the ice melted out of the top of 

 Glen Eoy a lake would take its place, discharging itself over this col. 

 Such a lake at first might he superficial — that is to say, resting on 

 the surface of the decaying glacier. Gradually the ice receded 

 farther and farther down Glen Eoy and became reduced in height, 

 but the surface of the lake being determined by its outlet would 

 stand at the uppermost line until the icy barrier melted back as 

 far as the mouth of Glen Glaster. As soon as the water gained 

 admission to this side glen it would escape over the col at the head 

 of it (if there was no obstruction in the way), and as that col is 

 80 feet below the one at Lochan Spey, the lake would then sink to 

 the level of the middle line which corresponds with the Glen Glaster 

 col. There it stood for a time until the ice which yet occupied 

 the lower end of Glen Roy shrank back still farther — far enough 

 to allow of the water communicating with Glen Spean, which it 

 would probably do first over the hollow between Meal Derry and 

 Craig Dhu, near Bohinia. When this event happened the lake 

 would spread into Glen Spean and, if there was no obstruction to 

 the eastward, would drop to the level of the lowest line which 

 corresponds with the escapement at Makoul. Such I think is the 

 most probable explanation, if it be the fact that the two upper lines 

 finally cease at the places shown on the Ordnance map. Dr. Tyndall 

 also took much the same view of the matter in his lecture at the 

 Eoyal Institution^ in which he likewise enforced with his usual 

 power of illustration the efi'ect due to the position of Ben l!»fevis 

 and the western mountains on the vapour-laden winds of the 

 Atlantic. 



V. The ALLTTvitTM at Bohuntine explained. 



Where these two upper lines cease Glen Eoy is very narrow, and 

 at this part of it there is a remarkable accumulation of detritus, 

 which commences rather suddenly just near the Gap at the hill of 

 Bohuntine. It is thickest near the Gap, the quantity between that 

 and the mouth of Glen Glaster being greater than it is farther 

 down the valley. This stufi" consists of sand, muddy gravel, and 

 silt with a few stones, but there is rather an absence of large 

 boulders. Much of it is well stratified and some of it even finely 

 laminated. Both its nature and the stratified mode of its arrange- 

 ment show that it has been deposited in water. Now, where did 

 aU this stuff come from, and how did it lodge so thickly just here, 

 right opposite the north end of Bohuntine where the two upper 

 lines stop ? There are no streams joining the glen between the 

 Gap and Glen Glaster to have brought it in, and that is just the 

 place where it is thickest. Above the Gap, Glen Eoy is compara- 

 tively empty of detritus until we come to the junction of the 

 Turret. My notion is that this mass of detritus consists of the 

 gravel and mud that fell into the lake from the front of the glacier, 



1 Proc. Roy. Instit. vol. viii. (1876) p. 233. 



