074 
PROFESSOR PRESTWICH ON THE ORIGIN 
Section of Glen Turret detrital terrace mound from tke Turret at tke foot of the pass into 
Glen Gluoy to the River Roy, a distance of 1 mile. 
a'. River gravel. b. Detrital mound. * Ice-worn surface of rock. 
It is true that the top of this terrace corresponds approximately with the level 
of No. 4 “ road,” but the several other similar smaller mounds lower down Glen 
Roy bear no relation to that level. They follow the fall of the valley, and gradually 
increase their depth beneath the road with their distance from the head of the glen. 
The great mound at the west end of Loch Laggan is in the same way considered 
to have been made by the discharge of the Gulban river into the lake which filled 
Glen Spean to the height of the “parallel road” No. 4. I had not the opportunity 
of closely inspecting this mound, but from what little I saw of it, I should refer 
it to the same origin as the one in Glen Turret. Mr. Jamieson says that the front 
of it is about 20 feet above the level of the loch, and that it rises 50 feet, Now 
as the level of the lake is 819 feet, this would make the height of the front of the so- 
called delta say 840 feet, the level of the pass of Makoul being 848 feet; so that, 
although the delta at its lower end would have been about 10 feet below the surface 
of the lake, its upper portion would have been 40 feet, if not more, above the level 
of the lake waters. Mr. Jamieson states also that the delta “ at the mouth of the 
Rough Burn is at a level corresponding with the lowest of the parallel roads; ” but that 
“the top of the delta rises considerably above this hue.” It is, therefore, not easy to 
see how these mounds or terraces could be deltas formed in the old lake, the level 
of which was that of the pass of Makoul. There are also similar terraces, often much 
below the old lake level, where there are no tributary rivers, as hr the case of the 
one on which the village of Inverroy stands, that above Inch, and others in the 
Spean Valley (see fig. 23, p. 716). The fine examples off the entrance to Glen Treig 
are well known ; sketches of them by Captain White are given in Sir Henry 
James’s ‘Notes.’ 
§ 5. The Level of the Snow-line. 
Lastly, there is another, and as it seems to me a fatal, objection to Mr. Jamieson’s 
hypothesis, in the excessive inequality hr the level of the snovMine in closely adjacent 
districts which it would necessitate. 
W.N.W. 
Fig. 4. 
E.S.E. 
