Mr Milne on (he Parallel Boads of Lochaber. 355 



Olonichan, at the river Roy, where the mica-slate rocks, through 

 which the river now runs, are covered immediately by boulder-clay, 

 — the boulder-clay being here covered by deposits of irregularly 

 stratified beds of gravel and sand, from 150 to 200 feet thick. At 

 this place, I observed among the boulders in the hill, granites (with 

 red and grey varieties), old conglomerate, and red porphyry, — 

 rocks, all of which must have come from a distance. 



From the fact that this boulder-clay occupies alike the highest 

 and lowest parts of the glens ; and, more especially, that in several 

 places it is seen distinctly covered over by laminated clay as well as 

 by stratified gravel and sand, it may be inferred that the boulder- 

 clay, with its imbedded blocks, was deposited, certainly not after the 

 drainage of the lakes, but either before the valleys were occupied 

 with water, or during that period. 



In regard to gravel and sand, I do not remember having, in Glen 

 Boy or its contiguous valleys, observed any considerable beds of it, 

 so high up as the boulder-clay. But at lower levels, there are 

 everywhere enormous cliff's of it to be seen, several of which I mea- 

 sured, and found to exceed 180 feet in height. These cliffs are 

 formed out of the ancient bottom of the lake or estuary which filled 

 the valleys, and are composed of materials washed down from higher 

 levels. The adjoining mountains of the district afford ample evi- 

 dence, that gravel as well as boulder-clay had been, by some cause 

 or other, brought and deposited over all this country, filling the 

 valleys to heights exceeding the highest of the Glen Roy shelves. 

 Thus, on the turnpike road between Tyndrum and Inverournan, 

 near the summit level between the two valleys, which I estimated 

 to be about 1030 feet above the sea, there is great abundance of 

 sand and gravel. On the Black Mount, about 4 miles north of In- 

 verournan, and at a height of 1300 feet above the sea, there is an 

 immense accumulation of gravel and boulders, particularly on the 

 south side of the summit. In the high ground north of Dalwhinnie, 

 which I estimated at 1200 feet above the sea, there are great heaps 

 of gravel, forming mounds and ridges. These facts, taken into con- 

 nection with the undoubted fact, that detrital matter has been spread 

 over the greater part of Scotland, to a height of at least 1500 feet 

 above the sea, pretty clearly indicate, that detrital matter not only 

 may l»ave been, but actually was spread over the Lochaber district, 

 and filled its several valleys, to the height of at least the highest of 

 the Glen Roy shelves, thus affording ample blockage for its lakes. 



I may mention that there are, in this part of the Highlands, 

 several lakes of small size, at very high levels, the existence of 

 which renders the lake theory of the Glen Roy shelves less impro- 

 bable than to some it may appear. Thus, at the well-known pass 

 of Rest-and-be-Thankful, there is a small lake, which is about 800 

 feet above the sea, and there are traces of its having stood formerly 

 from 40 to 50 feet higher. To the south and west of Loch Treig 



