62 ON THE PARALLEL ROADS 



and of running water, under every modification ; and that per- 

 haps, these could be no where so well established. But this 

 is not all ; — for if, as I am inclined to believe, it shall ulti- 

 mately be decided, that the Glen-mor-na-Albin, not only elu- 

 cidates the mode in which the ancient lakes of Lochaber were 

 evacuated, but that the shelves left by these lakes also, throw 

 a reciprocal light upon the origin of the Glen-mor-na-Albin, 

 then the science of geology will have reaped no inconsiderable 

 advantage, by the attention of its followers having been direc- 

 ted, as I hope it will be, to such a field of inquiry. 



NOTE. 



The descriptive part of this paper, was written from my 

 notes, soon after returning from my last visit to Glen Roy. 

 I have just had (January 1818), an opportunity, of reading 

 for the first time, Dr MacCulloch's learned and ingenious es- 

 say " On the Parallel Roads of Glen Roy" which was read at 

 the Geological Society of London, nearly about the time that 

 the Royal Society of Edinburgh did me the honour of listen- 

 ing to my first remarks on the same subject. I observe, that 

 I have the misfortune to differ very materially from Dr Mac- 

 Culloch, as to the height of Shelf 2d, or the uppermost line 

 of Glen Roy, when considered with reference to Loch Spey. 

 As will be seen by looking at the text, (page 33, of the fore- 

 going), I conceive that this line may be traced to within about 

 200 yards of Loch Spey, and that, from the present level of 

 the ground there, having been increased by the accumulation 

 of a mossy stratum, I believe the level of the shelf to be ac- 

 tually 



