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



mountains tolerably well defined by Loch Lomond on the east, Glen- 

 croe on the south, Glen Fyne on the west, and on the north by the 

 valley which runs eastward from the head of Loch Awe by Dalmally 

 towards Tyndrum (see Map) , The area, thus bounded, includes the 

 Cobler on the south, Ben Voirlich on the east, Ben Loy on the north, 

 and Ben Nime which is more centrally situated. The mass of granite 

 I have described forms the central nucleus of this group, and it is 

 probably to its protrusion that the formation of these mountains is in 

 a great measure due. Its existence entirely removes all difficulty as 

 to the origin of the blocks on the shores of Loch Fyne, Loch Long, 

 and Loch Lomond, and on the banks of the Clyde. I have entered 

 into minuter details than I should otherwise have thought necessary, 

 on account of the great inaccuracy with which the physical features 

 of this tract are generally represented on maps, and the want of any 

 distinct recognition by former geologists of the existence of this 

 granitic nucleus. 



2. Distribution of Blocks around Ben C?machan. (See Map.) 



To the N.W. of the group of mountains above described is another 

 group, of which Ben Cruachan is the highest point ; and which 

 possesses also its own central granitic nucleus. It is bounded on the 

 east by the valley of Glenorchy, on the north by Glencoe, on the 

 south by the upper part of Loch Awe, the Pass of Awe, and the 

 western portion of Loch Etive ; on the west it extends nearly to the 

 sea-coast of Appin. The granitic nucleus is situated somewhat to the 

 south of the centre of the group. It forms both banks of the whole 

 of that part of Loch Etive which runs N.E. from Tyanuilt, and ap- 

 pears to form the base of the northern part of Ben Cruachan. It is 

 penetrated also on the S.E. by the valley of Glenray, of which the 

 southern extremity is at the head of Loch Awe ; and also on the 

 western side by the valley in which Loch Creran is situated. Nume- 

 rous blocks have been transported down all these valleys. The 

 greatest number is found on the shores of Loch Etive, as might be 

 expected, in consequence of that loch penetrating so far into the 

 granitic mass. From the mouth of the loch they extend along the 

 coast to Oban and for several miles south of that place. Many have 

 been driven on the northern point of the small island of Kerrara, just 

 opposite Oban. They are found also on the highest point of the 

 island, and are scattered over the hills which intervene between Oban 

 and Loch Etive, at heights, in some cases, of several hundred feet. 

 Very few appear to have passed from the mouth of Loch Etive in the 

 northern direction. In like manner, blocks, but smaller and less 

 numerous, are scattered on the shores of Loch Creran. A continued 

 series of these blocks also exists aloug Glenray down to the head of 

 Loch Awe, about which they occur in numbers, extending from thence 

 also eastward along the valley a little beyond Dalmally, to a distance 

 of four or five miles. They extend in the opposite direction along 

 the shore of the loch to the entrance of the Pass of Awe, but I could 



