196 HIS GRACE THE DUKE OF ARGYLL, K.G., K.T., ON 



reference to such forces as we know to have worked, and to be still working in its interior. 

 A movement of elevation or of depression in any part of our terrestrial surface, to 

 the extent of 2000 feet, would be quite invisible to a spectator standing at the distance 

 of a few hundred miles, and might easily be produced by the operation of such causes as 

 we see must have been concerned in a thousand cases of geological change. In this, as 

 in all other cases of reasoning on physical phenomena of this class, what we have to look 

 for, above all things, is not merely simple effects, which may plausibly be accounted for 

 by invoking some one supposed cause ; but for those complicated and complementary 

 effects which, in great variety and number, are sure to accompany the operation of such 

 great physical forces as those which we may invoke. The evidence which we should seek 

 is essentially cumulative — full of incidental and subsidiary testimony arising out of a 

 thousand facts, which, at first sight, may not seem to have any bearing upon each other, 

 or upon any common explanation. And this is precisely the kind of evidence which only 

 comes to us gradually — as the result of long and continuous observation illuminated by 

 equally continuous thought. Suggestions, indeed, may arise in our minds quite suddenly, 

 and may be of such a character as to be of the highest value, throwing a flood of light on 

 conclusions which had before seemed to rest on a basis hardly adequate to support them, 

 but which now seem very largely confirmed if not actually established. 



A suggestion of this kind has lately occurred to me in respect to the agent of glaciation 

 in the Inveraray district, from certain facts with which I had, indeed, been long familiar, 

 but which I had never before put together in connection with this particular problem. 

 This suggestion it is my object in the present paper to explain. 



The parish of Inveraray occupies some ten or eleven miles of the north-western shore 

 of Locli Fyne, and reaches to within three or four miles of the extreme end or head 

 of that long and very deep arm of the sea. The large fresh-water lake of Loch Awe lies 

 in another deep depression, which, roughly speaking, lies parallel to this upper reach of 

 Loch Fyne ; and the two sheets of water are separated from each other by a range of hills 

 from six to seven miles across from shore to shore " as the crow flies." The trend of Loch 

 Fyne is in that general direction of N.E. and S.W. which is so conspicuous a feature 

 in the physical geography of the West Highlands. The parish is deeply trenched by two 

 great leading glens which join the main valley of Loch Fyne at an acute angle — running 

 pretty nearly north and south, but with some deviation towards the prevalent N.E. and 

 S.W. These two glens, named respectively Glenaray and Glenshira, are nearly parallel, 

 separated by a range of hills and moors hardly exceeding two miles in breadth. This 

 range terminates abruptly in the curious conical hill of Duniquoich, which rises immedi- 

 ately above the town and castle of Inveraray. As the whole country is occupied by one 

 great geological formation, these two glens, which traverse it in such close proximity to 

 each other, might well be expected to present a close resemblance. It is true, indeed, 

 I hat the rucks of the district have a certain variety, which is quite competent to produce 

 in close proximity considerable varieties of aspect. They consist of the whole series 

 comprehended in the general name of the Mica Schists, together with great masses of 



