306 MR. E. B. BAILEY ON THE [June 1913, 



Plate XXXII. 



Generalized geological map of the Loch Awe District, based upon Sheets 28, 

 29, 36, 37, & 45 of the 1-inch map of Scotland issued by H.M. G-eological 

 Survey; revised and reduced by the author. Scale: 4 miles = l inch, or 

 1 : 253,440. 



Discussion. 

 The Secretary read the following remarks, received from 

 Mr. J. B. Hill :— 



' In a paper communicated to the Geological Society in 1899 I described 

 the Loch Awe Group, the members of which consist of limestone, black slate, 

 and quartzite, the latter forming the top of the sequence. Black slate and 

 limestone are not, however, confined to those horizons, slate often occurring 

 higher up in the series among the quartzite, and limestone likewise appearing 

 at other horizons. These occurrences beyond the main bands I nevertheless 

 regarded as local and of limited continuity, 



' In the Tayvallich peninsula the Author has described a limestone band 

 above the quartzite ; and the question arises whether that band is local in 

 character, or whether it represents a persistent band marking a definite horizon 

 in its passage across the Highlands. The latter interpretation would imply 

 that not only was there a definite horizon of black slate and limestone below 

 the quartzite, but a corresponding succession above the quartzite. In the 

 Loch Awe area, reduplication by folding is so pronounced a characteristic that 

 the hypothesis of a double sequence must be viewed with suspicion, and needs 

 strong evidence to support it. 



' If, however, the pillow-lavas of the Tayvallich peninsula were represented 

 in tlie Loch Awe basin in association with the limestones of that area, there 

 would be some grounds for placing that limestone above the quartzite, as such 

 lavas have not been detected below the latter at the margin of the Loch Awe 

 Group in the south-east where that group succeeds the Ardrishaig Series. 



' In the Loch Awe basin there is an immense epidiorite-sill of composite 

 type, part of which is vesicular and corresponds petrologically to the pillow- 

 lavas. I was for some time under the impression that the vesicular rock 

 represents a contemporaneous lava ; but the mapping of the area did not 

 support this opinion, and pointed to its intrusive origin. 



' Later, Mr. Kynaston mapped these rocks in tbe neighbourhood of Port 

 Sonachan, and, after starting with a similar opinion, was forced to abandon it 

 and considered that they represented an intrusion at a shallow depth beneath 

 the surface. 



' At a still later period Dr. Peach mapped similar rocks in the Loch Avich 

 district, on the north-west side of Loch Awe, and, although inclined to regard 

 theni as lava-flows, could find no evidence in that direction, noting that no 

 pyroclastic rocks had been found associated with them, and that their thickness 

 and wide extension points rather to their intrusive nature. 



' Rocks of this character have not been observed below the quartzite to the 

 south-east, between the Loch Awe and the Ardrishaig Groups, but their intrusive 

 nature may satisfactorily account for such absence. 



' Not only is there an absence of pyroclastic rocks in the Loch Awe basin, 

 but the peculiar acid rocks associated with the pillow-lavas of Tayvallich are 

 also unrepresented, and it is probable that the Tayvallich rocks occupy a 

 higher horizon than those of the Loch Awe basin.' 



Mr. Barrow congratulated the Author on the able manner in 

 which he had dealt with the additional evidence afforded by the 

 volcanic zone on the question of the succession in the Highland 

 Bocks. He wished that the Author had gone more fully into the 

 history of the question as a whole. The quartzite was believed 

 by the speaker to be the Highland Quartzite, which crossed 

 Scotland from Port Soy to Islay, and, as Harkness had shown, 



