. The Quarterly journal of the Geological Society of London. ed severalweeks of the summer of 1850 to a more detailed investigation of thesubject. 1. Distribution of Blocks about Loch Lomond, Loch Long, and LochFyne. (See Map.) I commenced the investigation at the head of Loch Long, ac-companied by Mr. Montgomery of Ayr. Of the blocks in thatlocality the greater part consist either of a dark-grey granite ; or of * See Maccullochs Observations on the Mountain Cruachan, Trans. vol. iv. p. 117. 1851.] HOPKINS—ERRATIC BLOCKS OF THE S. HIGHLANDS. 21 a very light-coloured granite, containi
. The Quarterly journal of the Geological Society of London. ed severalweeks of the summer of 1850 to a more detailed investigation of thesubject. 1. Distribution of Blocks about Loch Lomond, Loch Long, and LochFyne. (See Map.) I commenced the investigation at the head of Loch Long, ac-companied by Mr. Montgomery of Ayr. Of the blocks in thatlocality the greater part consist either of a dark-grey granite ; or of * See Maccullochs Observations on the Mountain Cruachan, Trans. vol. iv. p. 117. 1851.] HOPKINS—ERRATIC BLOCKS OF THE S. HIGHLANDS. 21 a very light-coloured granite, containing comparatively large crystalsof felspar. These characters I found so distinctly marked as to in-dicate the great probability of these two classes of blocks beingderived from different sources. They appeared to have come downthe valley which forms the prolongation of that in which Loch Long Map of a part of the South Highlands, showing the granitic nucleiof Ben Cruachan andBenNime, and the dispersion of the ErraticBlocks from these Centres Scale of English Miles. Granite districts. ??yCo^y^i--: Erratic granite blocks. is situated, running for three or four miles N. and S. parallel to thewest shore of Loch Lomond, from which it is distant about two orthree miles. It then turns towards the , and rises rapidly tonearly the elevation of the ridge which separates its southern partfrom Loch Lomond. As we approached this upper extremity of thevalley, the dark-grey blocks increased in number and magnitude; 22 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 19, they were also much less rounded, indicating our approach to thesource from whence they came. This source was soon reached. Itis a large mass of granite presenting precisely the same charactersas the dark blocks which have proceeded from it. Their principalorigin was thus clearly determined. Immediately on the W. of the upper parts of Loch Long and ofthe lower part of the valley above-mentioned, is the mountain
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