22 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 19, 



they were also much less rounded, indicating our approach to the 

 source from whence they came. This source was soon reached. It 

 is a large mass of granite presenting precisely the same characters 

 as the dark blocks which have proceeded from it. Their principal 

 origin was thus clearly determined. 



Immediately on the W. of the upper parts of Loch Long and of 

 the lower part of the valley above-mentioned, is the mountain well 

 known as the Cobler, and directly to the N. of it, the lofty summit 

 of Ben Nime, which in height rivals Ben Lomond itself. If a spec- 

 tator stand at the upper extremity of the valley and look to the 

 north, Ben Nime will be situated on his left, and immediately in front 

 he will see Ben Voirlich, also a lofty mountain, the base of which 

 extends to the western shore of Loch Lomond. Between him and 

 this latter mountain he will observe a valley descending rapidly east- 

 ward to Loch Lomond, which he will overlook stretched out on his 

 right. This valley in ascending divides into two branches. The 

 principal one runs in a north-westerly direction between Ben Nime 

 and Ben Voirlich, defining the extent of the latter mountain from the 

 lowest point of the valley on the shore of Loch Lomond to its upper 

 extremity at which the small lake. Loch Sloy, is situated, at a great 

 elevation above the larger lakes. The other branch of the valley is 

 much shorter, and takes a more westerly direction into the bosom 

 of the mountains immediately associated with Ben Nime. A consi- 

 derable stream runs from Loch Sloy, and is increased at the junc- 

 tion of the two branches of the valley by water descending along the 

 shorter valley. The rapidity of the fall must frequently render this 

 stream a perfect torrent from Loch Sloy down to Loch Lomond. 



Mr. Montgomery followed the valley on the left towards Ben Nime 

 and found a large mass of granite in situ, similar to the dark-grey 

 granite already mentioned. In pursuing the course of the larger 

 branch to Loch Sloy, I remarked the absence of the blocks of dark 

 grey granite, while the presence of others, although few in number, 

 of lighter colour and containing large crystals of felspar, indicated 

 this valley to have been the course along which the blocks of this 

 character had proceeded from their source down to the head of Loch 

 Long. Time, however, did not allow me to reach their source in this 

 direction. I could only ascertain that it lay to the N. of Loch Sloy ; 

 a conclusion, which, as we shall see, was subsequently verified. 



With the present configuration of the surface, whatever might be 

 the agency of transport, the blocks coming from Loch Sloy would 

 have the greatest tendency to descend directly eastward to Loch Lo- 

 mond, as would also the blocks of grey granite descending the other 

 valley, mentioned above as penetrating into the mountains about Ben 

 Nime. With a little alteration, however, in the present surface, it is 

 sufficiently obvious that a portion of these blocks would descend 

 southward to Loch Long. These are manifestly courses which have 

 been traversed by the blocks which now line the shores of these lakes. 

 They are more numerous about the head of Loch Long than towards 

 its southern part ; and they also exist in considerable numbers on 

 the western shore of Loch Lomond, from its northern limit for many 



