part 2] THE SOUTH-WEST HIGHLAIS'DS OF SCOTLAND. 97 



Original order of deposition. — Two items of evidence 

 indicate that the column on p. 96, with Loch-Avich Slates at the 

 top and Erins Quartzite at the bottom, represents the original 

 ordei' of deposition of the rocks of the Loch- Awe Nappe. 



(1) In the Tayvallich Peninsula, the Tayvallich Slates, Limestones, and 

 Lavas very clearly overlie the Crinan Quartzite. Where the volcanic escarp- 

 ment reaches the sea, the second lava from the bottom has numerous pipe- 

 amygdales springing from its base, while its upper portion is thoroughly 

 slaggy. I have always agreed with Dr. Peach that this lava is ' right way 

 up,' and growing experience has strengthened my belief. Anyone who has 

 spent much of his life among lavas, must have met with many examples of 

 pipe-amygdales rising from the base of a flow, or from the base of an 

 individual band or lenticle within a flow, but never descending from the top. 



Dr. Peach has already published a horizontal section showing the position 

 and relations of this invaluable Tayvallich Lava (1911, fig. 4, p. 69).^ If this 

 flow is ' right way up ' (and who can doubt it ?), then the field- relations show 

 almost conclusively that the Tayvallich Slates and Limestones are of later 

 date than the Crinan Quartzite.^ 



(2) At Kilmory Bay, J. S. Grant Wilson found the Ardrishaig Phyllites dip- 

 ping steeply beneath a conglomeratic grit forming the base of the Loch-Awe 

 Group (1911, p. 64). The grit has the appearance of being- ' right way up,' 

 for it includes a succession of seams of fine-grained conglomerate, all of them 

 with well-defined bases and ill-defined tops. In this case, perhaps, it is wise 

 to regard the evidence as suggestive rather than conclusive ; but it gives 

 valuable support to the testimony afforded by the pipe-amygdales mentioned 

 in the previous paragraph. 



Structure. — Small-scale isoclinal folding is often an obvious 

 feature of the geology of the Loch-Awe Nappe. The isoclinal 

 folds and the concomitant cleavage are disposed with a marked 

 tendency to fan-arrangement — steep or vertical along an axial 

 belt, and inclined inwards on each side. Despite all this, there is a 

 fine simplicity in the surface-distribution of the rocks. The Loch- 

 Avich Slates have an outcrop in the neighbourhood of Loch Awe, 

 and the other subdivisions follow round about it in the order given 

 in the table. This simplicity betokens a general synclinal or anti- 

 clinal structure for the district as a whole. Mr. Hill, who, as will 

 be remembered, instituted the separation of the Loch-Awe and 

 Ardrishaig Groups as two great stratigraphical units, always 

 referred to the structure of the district as synclinal. I do not 

 know what influenced Mr. Hill in this matter, but there are two 

 very good reasons, which were open to anyone to make use of at the 

 time when he wrote on the subject: the first is the upward structural 

 succession encountered north-westwai-ds from the flat central belt 

 of the Cowal Anticline ; and the second is the obvious emergence 

 of the Ardrishaig Phyllites from beneath the outcrops of the Shii-a 

 Limestone and Crinan Quartzite where these latter terminate 

 northwards across the general strike of the folding. 



My own observations afford additional proofs of the existence of 



^ I am not certain that the photograph (1911, pi. iv) was not taken, by 

 mistake, of an overlying lava. 



^ See also 1922, Report A, par, 3. 



Q. J.G. S. No. 310. H 



