THE PARALLEL ROADS OF GLEN ROY. 
387 
valleys — that the whole region, as proved by Mr. Jamieson, is 
filled with the traces of their action ; the theory which ascribes 
the parallel roads to lakes dammed by barriers of ice has, in my 
opinion, an amount of probability on its side which amounts to 
a practical demonstration of its truth. 
Into the details of the terrace formation I do not enter. Mr. 
Darwin and Mr. Jamieson on the one side, and Sir John Lubbock 
on the other, deal with true causes. The terraces, no doubt, are 
due in part to the descending drift arrested by the water, and in 
part to the fretting of the wavelets, and the rearrangement of 
the stirred detritus, along the belts of contact of lake and hill. 
The descent of matter must have been frequent when the drift 
was unbound by the rootlets which hold it together now. In 
some cases, it may he remarked, the visibility of the roads is 
materially exalted by differences of vegetation. The grass upon 
the terraces is not always of the same character as that above 
and below them, while on heather-covered hills the absence of 
the dark shrub from the roads greatly enhances their con- 
spicuousness. 
Reviewing our work, we find three considerable steps to have 
marked the solution of the problem of the Parallel Roads of 
Glen Roy. The first of these was taken by Sir Thomas Dick- 
Lauder, the second was the pregnant conception of Agassiz 
regarding glacier action, and the third was the testing and 
verification of this conception by the very thorough researches 
of Mr. Jamieson.* To these may be added the important obser- 
vation of Mr. Milne-Home in Glen Glaster ; with other remarks 
and reflections scattered through the literature of the subject, 
or suggested by the latest visit to the spot. 
Thus ends our rapid survey of this brief episode in the physi- 
cal history of the Scottish hills — brief, that is to say, in com- 
parison with the immeasurable lapses of time through which, to 
produce its varied structure and appearances, our planet must 
have passed. In the survey of such a field two things are specially 
worthy to be taken into account — the widening of the intellec- 
tual horizon and the reaction of expanding knowledge upon the 
* No circumstance, or incident, connected with this discourse gives me 
greater pleasure than the recognition of the value of these researches. They 
are marked throughout by unflagging industry, by novelty and acuteness of 
observation, and by reasoning power of a high and varied kind. These pages 
had been returned “ for press ” when I learned that the relation of Pen 
Nevis and his colleagues to the vapour-laden winds of the Atlantic had not 
escaped Mr. Jamieson. To him obviously the exploration of Lochaber, and 
the development of the theory of the Parallel Roads, has been a labour of 
love. 
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