20 proceedings of the geological society. [nov. 19, 



November 19, 1851. 



Stirling Benson, Esq., and Dr. John Percy were elected Fellows. 



The following communication was read : — 



On the Granitic Blocks of the South Highlands of Scotland. 

 By W. Hopkins, Esq., M.A., F.R.S., President Geol. Soc. Lond., 

 and President Cambridge Phil. Soc. 



On a visit to the Highlands of Scotland in the summer of 1849, my 

 attention was directed by my friend Mr. Smith, of Jordan Hill, to the 

 blocks of granite which are scattered along the banks of the Clyde. 

 Proceeding thence to Oban, I found on the shores about that place, 

 and on the neighbouring shores of Loch Etive (see Map), similar 

 blocks, but larger and more numerous. These were easily traceable 

 to their source, the mass of granite immediately on the north and 

 north-west of Ben Cruachan, and extending across the upper branch 

 of Loch Etive. In like manner I observed numerous blocks about 

 the head of Loch Awe, on the south-east of Ben Cruachan (see Map) ; 

 and these also were easily traced to the above-mentioned mass of 

 granite up the valley of Glenray, which runs in a north-easterly 

 direction from the head of Loch Awe on the eastern side of Ben 

 Cruachan. Proceeding afterwards to Loch Lomond, I found granite 

 blocks scattered along its western shore ; and I observed them in 

 great numbers also round the head of Loch Long and of Loch Fyne. 

 The source of these blocks presented a great apparent difficulty. The 

 granite of Ben Cruachan was well known *, but no granitic mass, so 

 far as I could ascertain, had been recognized by geologists, or indicated 

 on any geological map, as standing in the same relation to the last- 

 mentioned blocks, as that which the granite of Ben Cruachan bears 

 to the blocks of Loch Etive and Loch Awe. In fact Ben Cruachan 

 was the nearest known source to which the blocks of Loch Lomond, 

 Loch Long, and Loch Fyne could be referred, if we except the red 

 granite near Inverary ; and the character of that granite is entirely 

 distinct from that of the grey and whitish granite of which the blocks 

 are composed. At the same time the nature of the country inter- 

 vening between these localities and Ben Cruachan is such as pre- 

 sented the greatest difficulty in any explanation of the dispersion of 

 these blocks which should refer their origin to that mountain. It 

 was with the view of solving this difficulty that I devoted several 

 weeks of the summer of 1850 to a more detailed investigation of the 

 subject. 



1 . Distribution of Blocks about Loch Lomond, Loch Long, and Loch 

 Fyne. (See Map.) 



I commenced the investigation at the head of Loch Long, ac- 

 companied by Mr. Montgomery of Ayr. Of the blocks in that 

 locality the greater part consist either of a dark-grey granite ; or of 



* See Macculloch's " Observations on the Mountain Cruachan," Trans. Geol. 

 Soc. vol. iv. p. 117. 



