106 ME. E. B. BAILEY OX THE STEUCTUEE OF [vol. Ixxviii, 



lower limbs of the Ballachulish and Appin Folds respectively. 

 I venture, therefore, to class these two slides as thrusts, which 

 means, of course, that the Ballachulish and Appin Folds are anti- 

 clines, and that their south-eastward close is an indication of 

 south-eastward movement. 



The identification of the Ballachulish and Fort-AVilliam Slides 

 as thrusts opens the Avay for the entrance of ' nappe terminology.' 

 That portion of the Ballappel Foundation which occurs above the 

 Ballachulish Thrust may be assigned to the Ballachulish 

 Nappe, and is coloured accordingly in PL I; the next great 

 mass, bounded above and below by the Ballachulish and Fort- 

 William Thrusts respectively, may be spoken of as the Appin 

 Nappe. 



A glance at PI. I shoAvs that the Ballachulish Nappe extends 

 as a recognizable entity eastwards from Ballachulish to the limit 

 of the district under consideration. Westwards between Loch 

 Leven and Loch Creran it has been locally removed bv trans- 

 gression of the Iltay Nappe, which there rests directly upon the 

 Appin Nappe. This latter is a very well-defined structural mass 

 in the western part of the area, where it overlies a foundation 

 consisting mainly of Eilde Flags (p. 94). South of the point 

 where the Fort- William (Meal-a'-Bhuirich) Thrust is shown in 

 PL I as losing itself in the F]ilde Flags, the definiteness of the 

 Appin Nappe fails. In this part of the district, the outcrops of 

 the Sub-Eilde Complex serve as a valuable index to the general 

 structure of the ground. 



Suggested Stratigraphical Correlations. 



My many years' experience of the rocks of the three great 

 structural subdivisions of the South- West Highlands has impressed 

 m.e as much with their contrasts as with their resemblances ; the 

 Eilde-Flag and Grien-Coe Quartzite facies belong to the Ballappel 

 Foundation ; the Ben-Ledi Grit facies to the Iltay Nappe ; lavas 

 and volcanic breccias are confined to the Loch-Awe Nappe. 



The most marked resemblance is the recurrence in each district 

 of a thick series of sediments in which the sequence is black slate, 

 transition series, pebbly quartzite, limestone. The agreement, so 

 far as black slates ^ are concerned, is closest between the Ballachu- 

 lish Slates of the Ballappel Foundation and the Easdale Slates 

 of the Iltay Nappe, both of them the seats of an important 

 roofing-slate industry. The comparison of the transition zone is, 

 on the other hand, more tellino- in the case of the Iltay and Loch- 

 Awe Nappes, where a conglomeratic tendency very commonly 

 shows itself in this position as characteristic of a mixed assem- 

 blage of black slate, black limestone, and quartzite. Some of the 

 slate- and limestone-bands, as well as the quartzite, are charged 



^ It is an arguable point whether the Loch-Avich and TayYallich Slates 

 are not wholly included in the transition zone. 



