416 THE CRYSTALLINE SCHISTS 



fault and traversing that region in a northeast and southwest direction, are 

 described. The existence of the anticline first noticed by Macculloch and 

 Murchison and then in detail by Jamieson, as an anticline of the bedding, 

 is recognised, with this important difference, that it is looked upon as a 

 great arch of foliation, and not of bedding as maintained by the earlier 

 geologists. From a comparison of the different schist-zones on each side of 

 the anticline of foliation the conclusion is arrived at that it cannot be also an 

 anticline of the bedding, but that probably it is an original syncline of 

 bedding traversed by an anticline of foliation ; a reversion to the view 

 originally maintained by Sharpe that the folds of the foliation in the 

 Scottish Highlands were entirely independent of the bedding. 



In 1897 the writer 1 further developed the views he had already published 

 in the Geological Magazine. The Argillaceous zone along the Highland 

 frontier is the oldest of the schist-zones, and is in its normal position in 

 Perthshire. Westwards, however, towards the Clyde its position becomes 

 steeper and steeper, till in the area of the Firth it becomes reversed, having 

 been pushed backwards and inwards upon the main mass of the Central 

 Highlands. In a series of papers lately contributed to the Geological Society 

 of Glasgow, 2 the writer has again more fully expressed his views regarding 

 the structure and succession of the schists of the Southern Highlands as 

 summarized in the following pages. 



It has long been recognised that the metamorphic rocks of the Highlands 

 traverse that area in bands or zones having a general N.E. and S.W. trend 

 roughly parallel with the great boundary fault. The Lower Argillaceous 

 zone abuts against the younger Old Red Sandstone rocks to the south, but 

 separated from it by the boundary fault. Outcropping at the base of the schist- 

 series of the southern Highlands it stretches across the frontier Highlands 

 from sea to sea. In Perthshire it may be seen at Birnam, Logiealmond, 

 Comrie, Callander, and Aberfoyle ; in Dumbartonshire at Luss, Row, and 

 Cove ; and in Argyllshire at Kirn and Dunoon, crossing the Toward 

 peninsula to Loch Striven, whence it can be traced through Bute from 

 Kames Bay to Ettrick Bay. 



The principal rocks of this zone are variously coloured phyllites, including 

 black, blue, purple, grey, green, and buff, with intercalated bands of grit, 

 greywacke, and thin limestones, and they frequently show a finely banded 

 structure referable to their original bedding. Differences of texture may 

 also be observed, more or less gritty bands being often inter-laminated with 

 bands of extremely fine material. Some of these grit bands attain a con- 

 siderable thickness, such as the Leny and Aberfoyle grits, and the Bull Rock 

 greywacke. Towards the east, as at Birnam, Logiealmond, Comrie, and 

 Callander, this zone of argillaceous rocks is not so highly metamorphosed as 

 on the Firth of Clyde, having more the appearance of a clay-slate. In many 

 instances, as in the quarries at Logiealmond, Aberuchill, and the foot of Loch 

 Lubnaig, the bedding is distinctly folded, the folds being crossed by planes 

 of cleavage. Rarely, however, can any folding or crumpling in the cleavage- 

 planes themselves be detected so that the rocks might here be more fitly 

 called clay-slates than phyllites. Towards the Firth of Clyde there is an 

 increasing development of mica along the cleavage-planes, and at Dunoon 

 there is evidence of more intense metamorphism, secondary foliation-planes 

 being developed, while the cleavage is often violently twisted or folded and 

 the folds crossed by ausweichung or strain-slip. 



One of the most interesting features in the Lower Argillaceous zone is the 

 evidence it affords of the behaviour of these beds during the process of plication 

 and crushing. An examination of the arenaceous beds with which these 



1 Trans. Perth. Soc. Nat. Science, vol. ii., 1897, p. 166. 



2 Trans. Geol. Soc. of Glasgow, vol. xi., part 2, 1900, p. 273. 



