1863.] JAMIESON PARALLEL ROADS OF GLEN ROY. 253 



glacier-lakes belonging to this later period, some beds of marine 

 drift with sea-shells may yet be discovered underneath the lacustrine 

 silt and gravel of Glen Roy. 



A considerable amount of glacier-action after the chief submergence 

 of the drift-period would also explain a circumstance that has always 

 seemed to me remarkable, namely, the absence of any clear trace of 

 the upper limit of this submergence. One would think that, however 

 indistinct the intermediate halting-places might be, yet the upper- 

 most shore-line ought to be more clearly marked. But if we suppose 

 the ice to have made a decided advance after the emergence of the 

 land, it is clear that it would blot out all trace of the old shores, so 

 far as it extended. I believe we owe the first suggestion of this 

 explanation to the fertile mind of Mr. Darwin. 



This re-extension of the glaciers would also enable us to account 

 for much of the valley-gravel without the aid of marine action. I 

 have pointed out in a former paper some features of this upjDer rolled 

 gravel that mere river-action, however prolonged, does not account 

 for. But if we can call in the agency of glaciers for these features, 

 we might explain the superficial accumulations of our Highland 

 valleys (I am not now speaking of our lower grounds) simply by 

 glaciers followed by a very long period of river-action. Extensive 

 effects might have arisen from the occasional bursting of glacier- 

 lakes, and also from the melting of the ice, if it thawed rapidly. 

 Pools and lakes would be formed by the moraine- mounds left along 

 the valleys on the shrinking of the ice, and these would obstruct the 

 drainage to some extent, but would be afterwards modified by the 

 rivers gradually cutting through them. 



Might not some of those curious accumulations known as eskers, 

 osar, and bairns have been formed by this re-extension of the ice 

 ploughing into the old marine beds, and forcing them up into long 

 narrow mounds ? In some regions these may have arisen from the 

 glaciers terminating in the sea, forming a kind of marine moraine ; 

 and, if the end of the glacier floated, fine mud and sea-shells might 

 gather beneath it. 



b. Relation to the 40 -feet beach of the West Coast. — Another ques- 

 tion presented itself. It is well known that a fine old coast-line 

 occurs along the border of Argyleshire, about 40 feet above the 

 present beach, marking a long pause of the sea at that level. What, 

 then, is the relation of this old beach to the time of the Parallel 

 Roads, and the glaciers connected therewith ? 



I observed that this 40 -feet beach fringes the head of Loch Eil 

 distinctly on both sides up to Fort William, and can be traced on to 

 the entrance of Glen Nevis. It is well marked close beside the 

 bridge at the mouth of the Glen, and appears to extend quite across 

 it on towards Bannavie, forming a broad shingly margin along the 

 base of the moraine hillocks. These, however, above that level, 

 preserve their original irregular surface dotted with boulders. 



This 40-feet beach is therefore later than the Glen Roy lakes, and 

 later than those large glaciers whose moraines I have described as so 

 remarkable in Glen Spean. 



