I02 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



"blende scliists, as at Ben Pin to the north. In Glen Finnilee is a* 

 series which the author regards as newer, and probably Pebidian. 

 At Passfern are qnartz rocks which the author identifies with those 

 beneath the limestone in Glen Laggan, near Loch Maree, and pro- 

 bably of Silurian age. At Bannavie is a granite which the anthor 

 considers to be Pre-Cambrian. 



(2) Fort William and Glen Nevis. — In this district chloritic 

 schists and gneiss occur, which the author regards as Pebidian. 

 These are overlain towards the sonth by Silurian rocks. 



(3) BaTlacliulisli, Glen Coe^ and Blade Mount. — Chloritic schists 

 and qnartzites occur here, followed along Loch Leven unconformably 

 by Silurian rocks. On the east of the Ardsheal peninsula there is 

 granitewhichtheauthorbelievestobe Pre-Cambrian. Going eastward 

 from Ballachulish are black slates, probably of Silurian age. In Glen- 

 coe are granite-banded felsite, gneiss, and breccias, resembling as a 

 whole the rocks of the Welsh Arvonian group. Between the Black 

 Mount and Loch Sullich are traces of a great Pre-Cambrian axis,, 

 bringing up the gneissic series ; this is traceable also towards Glen 

 Spean and Loch Laggan to the N.E. Silurian quartzites are also 

 found along broken lines, resting on the gneiss rocks. 



(4) Tyndrum to Callander. — South and east of the former are' 

 gneisses and silvery mica-schists. Crystalline limestones and ser- 

 pentines are associated near Loch Tay, resembling those in the 

 Pebidian series of Eorth Wales. 



The author states that the Silurian (and Cambrian) rocks flank 

 the Pre-Cambrian in lines from N.E. to S.W.. Thus here, as else- 

 where, subsequent denudation has removed enormous masses of the 

 more recent rocks, only here and there leaving patches of these in 

 folds along depressions in the old Pre-Cambrian floor. 



Discussion-. 



Professor Judd said that the time was too short, and there was a 

 difficulty in finding a common ground for discussion. Dr. Hicks 

 seemed to think that the age of rocks could be fixed by their 

 mineral characters. As to the age of these altered rocks, he thought 

 most geologists held their viewvS in suspense ; he, however, thought 

 Dr. Hicks's section ofiered as great difficulties as any other. Where, 

 for example, were the fossils, if these Silurian beds were not altered^ 

 as asserted by Dr. Hicks ? He thought the Callander limestones 

 much altered. 



Prof. Hughes thought that the specimens exhibited by Dr. Hicks 

 proved that he had at any rate one group of gneissic rocks, and 

 another group of rocks hardly at all altered ; and if the unaltered 

 rocks rested on the metamorphic series in the manner described by 

 Dr. Hicks, he must accept Dr. Hicks's reading of the district as- 

 regards those two divisions. In reply to Prof. Judd, he maintained 

 that Dr. Hicks's section was quite clear and natural, whether its- 

 general accuracy would be confirmed by subsequent observers or 

 not. 



