298 MR. E. B. BAILEY 05T THE j~J\ine I9I3,. 



Nicol in a paper read before this Society in 1862 : for, as Gunn 

 lias pointed out, Mcol seems to attribute the high metamorphism 

 of the rocks exposed along the axis of the Cowal Anticline to their 

 having been 



' taken down into those interior regions of the earth's crust where the chief 

 laboratories of lnetamorpliic action are situated' [3, p. 199]. 



But to Mr. Clough belongs the particular credit of a new conception 

 in Highland geology. For, according to his reading of the structure, 

 the depth of the cover, under which the highly metamorphic rocks 

 of Cowal crystallized, was not directly determined by the position 

 of these rocks in an original stratigraphical sequence, but by the 

 degree to which they had been buried beneath superincumbent folds. 

 This conception is likely to prove of wide application, and I may 

 conclude by suggesting that it may render more intelligible the pro- 

 gressive metamorphism noted by Mr. Hill north-east of Loch Awe. 

 It has already been mentioned that near Halmally there are black 

 schists, limestones, and pebbly quartzites which Mr. Hill refers to 

 the Loch Awe Group. They are, as the same author correctly 

 ' points out, much more metamorphic than their supposed equivalents 

 round about Loch Awe. Now, it so happens that a consideration 

 of the relation of these rocks to the Glen Orchy Anticline and 

 the Loch Awe Syncline renders it quite certain that, whatever their 

 stratigraphical position, they structurally underlie the Ardrishaig 

 Phyllites : that is, they are on a definitely lower rung of the 

 tectonic ladder than the Loch Awe Group at Loch Awe. 



It is to be hoped, however, that the ' depth principle ' will not be 

 pushed' too far. There are already difficulties foreshadowed in its 

 application, even in the West Highlands : for the metamorphism 

 continues of low grade on the north-west side of the Loch Awe 

 Syncline, as, for instance, in Islay, across the Sound of Jura. 

 There are probably many factors at work, and one must always 

 remember that great earth-movements may be accompanied by little 

 metamorphism, when the tendency is, as in the Korth-West High- 

 lands, to superpose metamorphic rocks upon non-metamorphic. 

 The evidence which Mr. G. Barrow has adduced to connect the 

 regional metamorphism of the Highland schists with certain wide- 

 spread granitic intrusions must also be borne in mind [4 & 21]. 



YI. BlBLIOGEAPHT. 



(1) J. Macculloch. — ' Western Islands of Scotland ' vol. ii, 1819. 



(2) T. F. Jamiesox. — 'On the Structure of the South-West Highlands of Scot- 



land ' Q. J. G. S. vol. xvii (1861) p. 133. 



(3) J. Nicol. — ' On the Geological Structure of the Southern Grampians ' Q. J. 



G. S. vol. xix (1863) p. 180. 



(4) G. Baeeow. — 'On an Intrusion of Muscovite-Biotite Gneiss in the South- 



Eastern Highlands of Scotland, & its accompanying Metamorphism ' Q. J. 

 G. S. vol. xlix (1893) p. 330. 



(5) 'The Geologv of Cowal' Mem. Geol. Surv. Scot. 1897. 



(6) ' Summary of Progress for 1897 ' Mem. Geol. Surv. 1898. 



(7) J. B. Hill. — ' On the Progressive Metamorphism of some Dalradian Sediments. 



in theBegion of Loch Awe' Q.J. G. S. vol. lv (1899) p. 470. 



(8) ' Summary of Prosress for 1899 ' Mem. Geol. Surv. 1900. 



(9) ' Summary of Progress for 1900 ' Mem. Geol. Surv. 1901. 



