SECTIONAL TRANSACTIONS.— C. 551 



'ndex minerals of the different belts are, therefore, essentially stress minerals produced 

 by changes in the pressure and temperature at different depths. Thus there is an 

 outermost belt or zone characterised by the production of ( U Chlorite, and at successive 

 depths (2) Brown Biotite, (3) Almandine Garnet, (4) Staiirolite, (5) Kj'anite, and 

 (fi) Sillimanite m.ay be found, though the last appears to be produced most extensively 

 in the permeation area. 



This regional metamorphism appears to be intimately connected with the structure 

 of the Central Highlands, and since it has been shown that these belts or zone.s can 

 in many cases be mapped across Scotland from sea tc sea (Tilley), it is held that any 

 account of structures that fails to take into account the metamorphic condition of the 

 beds must be regarded as incomplete. This intimate connection can be well illustrated 

 by reference to the Corval-Loch Fyne area, and the Loch Tay area, where any 

 departure from the normal succession of the metamorphic belts is found to have an 

 explanation in structure. 



In regard to the age of the different movements, the earlier, which is held to be 

 Pre-Cambrian, is accompanied by features indicating formation at a considerable 

 depth, whilst the later shows features suggestive of formation under relatively 

 superficial conditions, such as those accompanying the big fault-lines that cross the 

 C. Highlands, e.g. Loch Tay Fault, the Bridge of Balgie Fault, the Tyndrum Fault 

 and the Glen Stru Fault. These are essentially overthrust faults, in some cases 

 accompanied by true mylonites with a movement towards the N.W. It is suggested 

 that these may be the result of the Caledonian Movement upon the earlier folding ; 

 marked torsion of the rocks as a whole may also result as in the case of the Schiehallion 

 torsion and the Beinn Douran torsion. Other evidences of the age of later move- 

 ments might be found along the Highland Border. 



Dr. H. H. Read. — Each advance in our knowledge of the Dalradian of the North- 

 east Highlands appears to force us into a closer comparison of that region with the 

 South-west. Several j'ears ago attention was directed to certain leading features in 

 the Dalradian geology of Lower Banffshire and North-west Aberdeenshire, namely : — 



(1) The occurrence in the Banff Division of somewhat peculiar rock-types, and 

 possibly of lavas, recalling types well-known in the Loch Awe Group of the South-west 

 Highlands. 



(2) The correlation of the Keith Division with certain Perthshire Dalradian 

 groups. 



(3) The differing tj'pes of metamorphism in the Banff Division and in the underlying 

 Keith Division. 



(4) The separation of the Banff and Keith Divisions by a line of discontinuity 

 (the ' Boyne Line '). 



(5) The synclinal structure of the Banff Division. 



From these features it was suggested that the Banff Division .ind the Loch Awe 

 Group were comparable in local structure. 



Recently two investigations have been completed that have a bearing on this 

 suggestion. It has been shown that the Deeside Limestone is probably the equivalent 

 of the Loch Tay Limestone, and that this limestone disappears in Deeside owing to 

 the northwardly-pitching Cromar Anticline. The Banff Syncline thus appears to 

 be definitely asymmetrical, having on its west side the equivalents of the Ben Lawers 

 Schist-Blair Atholl Limestone portion of the Perthshire sequence and on its south-east 

 side the Ben Lawers Sehist-Pitlochry Schist portion of that sequence. This asymmetry 

 recalk the asymmetry of the Loch Awe Syncline, which E. B. Bailey has explained 

 on the nappe hypothesis. A possible explanation of the asymmetrical Banff Syncline 

 may be, therefore, that it is a structure affecting a nappe, the Banff Nappe. 



Further, the recognition by E. B. Bailey of the Perthshire Culmination may 

 supply, as it were, a plane of symmetry for the whole Dalradian structures. It may 

 be suggested that to the north-east of this culmination the north-easterly pitch brings 

 on the Banff Nappe, whilst to the south-west the south-westerly pitch brings on the 

 Loch Awe Nappe. To establish the existence of the Banff Nappe and to demonstrate 

 its equivalence to the Loch Awe Nappe may be the reward of further work. 



Dr. E. Greenly. — Evidence available in Anglesey seems to throw light on 

 Highland problems. 



Recent work fully confirms the view that the Mona Complex is of pre-Cambrian 

 age, which seems to throw the burden of proof upon those who would deny that the 

 fiame is the case in the Scottish Highlands. Confirmation has also been obtained 



