472 - Geological Society. 



2. 'The Bala Country: its Structure and Rock-Succession.' 

 By Miss Gertrude Lilian E lies, M.B.E., D.Sc, F.G.S. 



March 23rd.— Mr. R. D. Oldham, F.R.S., President, 

 in the Chair. 



The following communication was read : — 



'The Structure of the South- West Highlands of Scotland.' 

 By Edward Battersby Bailey, M.C., B.A., F.R.S.E., F.G.S. 



Evidence is given for allotting the South- West Highlands to 

 three great structural divisions in descending order, as follows : — 



Loch Awe Nappe. 

 Iltay Nappe. 

 Ballappel Foundation. 



The two lower of these divisions are themselves structural com- 

 plexes. Thus the Iltay Nappe includes two recumbent folds : the 

 Carrick Castle Fold above, the Ben Lui below. Of these two, the 

 upper closes towards the south-east, the lower towards the north- 

 west. Their common limb is displayed to great advantage in the 

 ' flat ' region of Loch Ta} r . On evidence of original succession 

 derived from Islay, this Loch Tay limb is interpreted as an 

 inversion. Its position with reference to the Loch Awe Nappe 

 suggests that the latter has travelled from the north-west. In 

 fact, all available evidence points consistently to movement from 

 the north-west during the development of the three structural divi- 

 sions named above. 



Later structures include the Cowal Anticline, Loch Awe Syn- 

 cline, and Islay Anticline. The last-named is causally connected 

 with the Loch Skerrols Thrust — the southern continuation, as it is 

 supposed, of the Moine Thrust of the North-West Highlands. 

 During this stage, movement proceeded outwards in both directions 

 from the fan -axis of Loch Awe. 



In a general way, there is a close relationship between depth of 

 cover and degree of metamorphism. No metamorphic inversions 

 have been noted, and it is clear that e^stallization continued until 

 the close of the early nappe-movements. 



In Cowal a peculiar type of metamorphism reigned, alike in 

 pre-anticlinal and in anticlinal times, wherefore it would seem that 

 the early and late movements of the South- West Highlands are 

 but successive chapters of a continuous history of mountain- 

 building. Hence it would appear, among other things, that the 

 north-westward movement manifested in Islay is an example 

 of back-movement of a root-region. 



