296 mr. e. b. bailet on the [June 1913, 



If so, it follows that the Loch Awe Group is a later formation than 

 the underlying Ardrishaig Phyllites, unless it has heen thrust into 

 its present position, which is a most unlikely alternative. 



{7 b) Evidence pointing in the same direction had previously 

 been obtained by Dr. Peach. It has already been noticed that 

 the Tayvallich lavas cross the peninsula with an escarpment facing 

 north. At the foot of the escarpment are limestones and slates 

 belonging to the Tayvallich Division, and from beneath these 

 emerges a passage-zone, followed eventually by the main mass of 

 the Crinan Quartzite. If it can be definitely determined whether 

 the lavas in the escarpment are ' right way up ' or no, then the 

 original order of superposition of the various divisions of the Loch 

 Awe Group follows as a corollary. This is exactly what Dr. Peach 

 has succeeded in doing, with very fair certainty. Fig. 4, taken from 

 Dr. Peach's description, shows the nature of the escarpment where 

 it reaches the sea. The important point for our present purpose 

 is the marked difference which exists between the tops and bottoms 

 of the two lowest lavas. 



Fig. 4. — Volcanic section south of Port an Sgadain, western coast of 

 Tayvallich Peninsula ; after B. N. Peach. 



[Reproduced, by permission of the Controller of H.M. Stationery Office, 

 from Mem. G-eol. Surv. Scot. 1911 : ' Geology of Knapdale, &c.' p. 69.] 



Of these, the lowest of all (a, fig. 4) is about 20 feet thick, with 

 an irregularly-jointed lower portion, containing few gas-cavities, 

 and a remarkably rugged portion, 8 feet thick, consisting entirely 

 of vesicular pillow-shaped masses. The second lava (c, fig. 4) is a 

 highly vesicular rock, 15 to 20 feet thick, with numerous ' pipe- 

 ainygdales' in its lower portion set approximately at right angles 

 to the base, and a porous upper surface. I agree with Dr. Peach 

 in his opinion that this volcanic section has entirely the appearance 

 of being 'right way up' ; and from this it follows that the structural 

 sequence in the Loch Awe Syncline, in all probability, agrees with 

 the original order of superposition. 



V. The Structure and the Metamorphism. 



I have already alluded to Macculloch's early recognition of 

 the fan-structure which roughly marks the central line of the 

 Loch Awe Syncline. This structure seems to become vague in 

 the northern part of the Loch Awe district ; but Mr. P. Macnair is 

 probably justified in regarding it as the equivalent of the Ben- 

 Lawers fan farther north-east in the Central Highlands [11, p. 207 



