94 MR DAVID MILNE HOME: MEMOIR ON THE 
the sides of the valleys, indicating that the lakes had subsided from one level 
to another. 
2d, I pointed out that in the Lochaber district, there is even yet an 
enormous accumulation of detritus, consisting of beds of clay, sand, and gravel, 
and that these beds occur at levels far higher than what had been the surface 
of the old lakes; so that ample materials for blockages at the requisite heights 
existed. 
3d, I showed, by reference to the action of the rivers Roy, Spean, Spey, 
and other streams, that extensive masses of detritus had been cut through 
and removed, leaving scaurs or cliffs several hundreds of feet in height, 
so that it was reasonable to presume that, by similar agency, the blockages 
of the Glen Roy lakes might have been from time to time cut through and 
removed. 
4th, I farther submitted, that the size or mass of the required blockages 
should not be estimated, by reference to the width and depth of the valleys 
at present; because, at the period when these lakes existed, the rivers 
now running in them must have occupied channels far above their existing 
channels. 
These being the grounds on which I supported the detrital theory, I now 
proceed to mention the further observations recently made confirmatory of 
these grounds. 
I. Localities, where beds of Sand, Clay, and Gravel, at High Levels occur. 
1. In the district of Stratherrick, which is not far from Lochaber, on the east, 
I followed the course of the River Foyers up to the mountains, among which it 
takes its rise. This river runs into Loch Ness, on the south side. 
In various parts of its course, there are old haughs bounded by cliffs, showing 
the successive levels from which the river subsided, cutting through enormous 
deposits of sand and gravel. 
- About 3 miles above the upper Fall of Foyers, I took a rough sketch of two 
of these haughs. Both were bounded by steep cliffs, which had evidently been 
river banks, the one about 20 feet, and the other about 60 feet above the 
river. 
The following diagram (page 95) exhibits these old river haughs and cliffs :— 
In company with Captain Fraser of Balnain, who has a shooting lodge near 
the source of the river, I followed its course, till we reached a height above the 
sea of about 1774 feet. On each side of the river the hills are covered by 
great hummocks of sand and gravel, and occasionally clay containing pebbles 
and boulders. I did not ascend farther, but with the telescope I observed 
knolls and scaurs of detritus at least 300 feet higher; and learnt from Captain 
