part 2] THE SOUTH-WEST HI&HLANDS OP SCOTLAND. 125 



The age-relations of the black slates and quartzites found above 

 and below the Ardrishaig Phyllites no longer present a difficulty. 

 From Dalmally westwards the large-scale movement has been 

 accommodated by thrusting without inversion. The movement 

 has been interpreted as having come from the north-west, because 

 the Ben-Lui Fold, to judge from these same age-relationships, is a 

 syncline closing in that direction. 



lY. COJN^CLTISIOIS^. 



Perhaps I may be pardoned for returning once again to two 

 elements of Highland tectonics which should never be lost sight 

 of. The first is the comparison of two sides of large-scale non- 

 recumbent folds Avherever these are recognizable ; the second is 

 the critical enquiry into any case where what seems to be a single 

 rock-group has three — or more — distinctive margins. The first 

 will always be connected in my mind with Clough and the Cowal 

 Anticline ; the second with Mr. H. B. Maufe, who, in the days 

 before the recognition of slides in the Southern Highlands, was 

 wont to insist that one of our main problems was the three-sided 

 limestone of Ballachulish. 



The beacon which has lighted the way in the development of 

 the views expressed in the present paper has been the asymmetry 

 of the Loch-AAve Syncline — on the one side the rocks of the Islay 

 Archipelago, on the other those of Cowal. Is it credible that 

 this asymmetry is due to change of facies ? N^o, — the Islay rocks 

 can be traced right under the Loch-Awe Sjaicline and away 

 through Perthshire, not transformed into Cowal rocks, but in 

 contact side by side.^ As for the Cowal rocks, they too can also 

 be followed for some distance beneath the Loch- Awe Syncline, but 

 presently they are found to double back upon themselves, and thus 

 to return whence they came.^ 



While it was easy to see this much, at any rate in a vague and 

 general manner, still there was a difficulty in obtaining anything 

 approaching to clear vision. The long-accepted correlation of the 

 Ardrishaig and Ben-Lawers Schists blocked the way. But this 

 correlation involved a three-sided formation (p. 121). It had, 

 therefore, to be considered very critically. It was found unstable, 

 and with its fall light gained access. 



Appendix I — Bibliocieapht. 



1819. J. Macculloch. — ' A Description of the Western Islands of Scotland & 



the Isle of Man, &c.' 

 1840. J. Macculloch. — Geological Map of Scotland, with Memoir (posthumous). 

 1852. D. Sharp. — ' The Arrangement of the Foliation & Cleavage of the Rocks 



of the North of Scotland ' Phil. Trans. Roy. Soc. vol. cxlii, p. 445. 



1858. J. NicoL. — Geological Map of Scotland and Explanatory Note. 



1859. R. I. MuECHisoN. — 'Fii-st Sketch of a New Geological Map of the North 



of Scotland ' Q. J. G. S. vol. xv, p. 419. 



^ See also 1922, Report A, par. 8. 

 ^ Ibid. Report A, par. 6. 



