in the Middle Region of Scotland. 167 



it had previously occupied, and would exert an immense 

 lateral pressure on the walls of the valley confining it. Hence 

 it is in situations like this that deep groovings, and especially 

 on vertical surfaces, should be looked for. 



Something of the same kind is seen at Gareloch, which has 

 a form resembling the figure annexed. 

 Striae and grooves abound in the circular 

 valley x, where the ice must have collected ; 

 those in the bottom are few and large ; 

 those on the sides numerous, but generally 

 small. At y, where the valley is contracted 

 to a gorge half a mile in breadth, the bot- 

 tom, being covered with salt water, can no 

 longer be seen ; but great numbers of strii3e are found on the 

 sides, and of various sizes, up to 6 or 8 inches in breadth. 

 At z, where the loch widens out to a mile in breadth, and 

 where the latei'al pressure would, of course,' be greatly re- 

 laxed, the strias disappear, and are no more seen till we come 

 to Row, five miles southward, where the breadth of the loch 

 is again contracted by the point of land at Roseneath. At 

 this place a few are visible (one 16 inches broad) scooped 

 out across the laminae of the clay-slate, which here succeeds 

 to the mica and chlorite slate. 



The cavity x would serve as a reservoir for the ice, or mer 

 de glace, when the glacier occupying the valley was small ; 

 but the grooves found on the top of the ridge dividing 

 Gareloch from Loch Long (on a surface wonderfully smoothed 

 and levelled; point to glacial phenomena on a grander scale. 

 They can only be accounted for, in my opinion, by assuming 

 that one vast mass of ice filled Gareloch and Loch Long, 

 covering the ridge which divides them, and that the whole 

 moved simultaneously in a SSE. direction, constituting a gla- 

 cier four miles broad, and probably 1000 feet in depth.* 



The smooth sides, and even or gently-undulating outlines 

 of the hills between Gareloch and Loch Lomond, which 

 contrast so remarkably with the rough surface and serrated 



* See my paper in IvUnburgh New Philosophical .Inurnil, No. Ixxxiii., [1.35. 



