Yd. 69.] LOCH AWE SYNCLLNE (ARGYLLSHIRE). 307 



reappeared in Ireland. The relative positions of the rocks of the 

 groups had been proved by the speaker more than twenty years ago, 

 and the conclusions reached were published in Sir Archibald 

 Geikie's first Presidential address to the Geological Society (1391). 

 The Blair Atholl Limestone (believed by the speaker to be the 

 Tayvallich Limestone) was shown to be on one side of the Quartzite, 

 and the Caenlochan Schist (Ardrishaig Phyllite) on the other. At 

 the extreme north-eastern end of this outcrop, the quartzite was- 

 very thin, and passed down insensibly into the underlying dark 

 schist, which there intervened between it and the Caenlochan Schist. 

 Proceeding south-westwards, one noticed first the occurrence of 

 small grains of the dark material at the base of the quartzite, later 

 on small pellets, and finally in the area in question the original 

 dark mud was at times completely eroded away ; but now pellets of 

 it. of larger size, occur in the quartzite. The real evidence adduced 

 by the speaker, on which the succession turned, had never been 

 published. 



The Author, in reply, pointed out that Mr. Hill treated the 

 mass of epidiorite in the vicinity of Loch Awe as a unit — either 

 an immense sill or an immense lava. On this hypothesis Mr. 

 Hill had, of necessity, set aside any interpretation involving the 

 occurrence of lava, since parts of the mass showed definitelv 

 intrusive relations. The Author's observations led him to regard 

 the mass as a complex series of lavas and associated sills. 



Replying to Mr. Barrow, the Author drew attention to a paragraph 

 written conjointly by Dr. Peach and himself in the Geological 

 Survey Memoir on Sheet 28 (Scotland). The paragraph followed 

 upon a description of the succession in the Tayvallich peninsula, 

 and ran as follows [18, p. 61]: — 



' It would be unnecessary to go beyond this, were it not that the relations 

 of the Loch Awe Group in Argyllshire have been used in support of the 

 theory of the " unconformable quartzite " in Perthshire and elsewhere. The 

 writers are now of opinion that the change of front in the Tayvallich district 

 strengthens, by analogy, the alternative interpretation of the Perthshire 

 sections, which has for years been identified with the name of Mr. Barrow.' 



Since the above was written the Author had tried to reach greater 

 certainty in the matter, but without success. The district lying 

 between Loch Awe and that part of Perthshire in which Mr. 

 Barrow had worked was very difficult indeed to interpret. Quite 

 apart, however, from the doubtful analogy between Loch Awe and 

 Eastern Perthshire, the Author, speaking without any special 

 knowledge, believed that Mr. Barrow was right in regarding the 

 Perthshire quartzite as an interstratified member of the Perthshire 

 sequence, and not an unconformable later group for ever making 

 its appearance in isoclinal synclines. 



Mr. Barrow had also referred to Islay. Here the Author was 

 on familiar ground ; and, while admitting certain general resem- 

 blances between the Islay-Jura sequence and that of Loch Awe, he 

 found the differences of detail so considerable that he preferred to 

 maintain an agnostic attitude in regard to matters of correlation. 



