1868.] ARGYLL ARGYLLSHIRE. 269 



verse valley of Loch Eok as another instance in which two streams, 

 each working backwards towards its own source, have finally de- 

 voured and carried off the ridge which separated them, and thus at 

 last converted two narrow glens into one broad valley. Now the 

 first thing to be noted in regard to the whole district of Cowal, or 

 the mass of mountainous land which separates Loch Fyne from the 

 great depression which is occupied by the Firth of Clyde, is, that 

 whilst the dip of all the strata on Loch Fyne is towards the north- 

 west, on the shores of the Firth of Clyde it is precisely opposite, or 

 south-east. The intervening mass of mountains is therefore the 

 seat of a great anticlinal axis. Sir R. I. Murchison first pointed out 

 to me that a magnificent section across this anticlinal is presented 

 along the banks of Loch Eck. This would not necessarily account, 

 however, for a valley which runs not along the anticlinal, but across 

 it. In an area, however, of great disturbance, where, as in this 

 case, there is every mark of the beds having been subjected to the 

 most violent tension from subterranean movement, transverse cracks 

 and subsidences must be always liable to occur. But in any case it 

 is a district of great disturbance ; and where this is the case it is a 

 gratuitous assumption to attribute a transverse valley to forces which 

 are comparatively inadequate to the work. I have pointed out how 

 entirely Mr. Geikie avoids giving us any description of structural 

 detail when he deals with hills and valleys, when that detail is ad- 

 verse to his theory. But there is one valley in the Highlands in 

 respect to which he does enter into much detail, and gives us a 

 special diagram setting forth its structural peculiarities : it is the 

 valley of Loch Tay. The valley, he says, now runs along the top of 

 an anticlinal axis, so that, as he expresses it, that which geologically 

 is the top of a mountain is geographically the bottom of a glen. 

 The mountain of Ben Lawers, which rises above the lake, is repre- 

 sented as exhibiting beds forming structurally a synclinal trough, 

 and yet, in physical geography, constituting an isolated mountain cut 

 out of the thickness of the rocks which once surrounded it and have 

 all been washed away. 



I^ ow, in regard to this case, on which Mr. Geikie lays great stress, 

 and from which he jumps to the largest and most general conclu- 

 sions, I have several observations to make. In the first place, not 

 believing as Mr. Geikie seems to do, that all the hills and valleys in 

 the Highlands can be accounted for by any one theory as to the phy- 

 sical agencies concerned in their production, I should be quite 

 prepared to admit, upon adequate evidence, that Loch Tay has had a 

 wholly different origin from Loch Awe, and that the processes which 

 formed Ben Lawers have been wholly different from those which 

 formed Ben Cruachan. In the second place, I have to observe that 

 even the facts of this case, as given by Mr. Geikie, are quite capable 

 of a different interpretation from that which he assigns to them. 

 It is not only possible, but in the highest degree probable, that a 

 valley due to fracture should lie along the top of an anticlinal axis. 

 That is precisely the line along which hard crystalline rocks would 

 be exposed to the maximum of tension, and therefore along which 



