628 MESSES. CLOTTGH, MATJEE, AND BAILEY ON [NoV. I9O9, 



flows on both sides of Loch Achtriochtan, inside the cauldron, and 

 are brought by the fault into juxtaposition with all three of the 

 lower groups lying outside the fault. 



Group 3, the limestone, is exposed in a small patch at the 

 bottom of Coire Cam, where it lies well in advance of the unfaulted 

 outcrop, although the latter overtops it on the summit of the ridge 

 to the extent of 1000 feet. 



Group 1, the quartzite, is probably represented by the small 

 outcrop at the base of the lavas in Coire nan Lab. 



In Coire Mhorair and Coire Odhar-mhor there is an extensive 

 exposure of the quartzite (1), thin phyllite and black schist (2), and 

 limestone (3). 



Beyond this, to the east, much of the ground between the lavas 

 and the fault is occupied by flaggy, quartzo-micaceous ' Moine 

 Gneisses ' ; the outcrop of the quartzite (1) can, however, be traced 

 along the foot of Stob Dearg ; and in Allt Coire an Easain, farther 

 south-eastwards, all the four zones of Glen Coe seem to reappear. 

 The supposed equivalents of groups 1, 2, & 3 are here much thinner 

 than in Glen Coe, but this thinning is quite in keeping with the 

 behaviour of the various groups in this part of the Highlands. The 

 dip of the Schists in the Allt Coire an Easain section is towards the 

 east, wherefore it appears likely that the greater part of the volcanic 

 rocks of the sunken area rests upon the thick phyllites of group 4. 



At Dalness, however, within the fault, exposures of quartzite 

 jut up sporadically through the lavas. Probably these are portions 

 of a quartzite group, overlying the phyllites of group 4, and 

 represented, outside the fault, by outliers (group 5 on the map) on 

 the summit of Stob Dubh and other prominent hills in the neigh- 

 bourhood. The quartzite between the two branches of the fault in 

 Beinn Ceitlein is also probably referable to group 5. 



The preceding description has been given, in order to enable the 

 reader, with the help of the sketch-map (fig. 2, p. 627), to contrast 

 the general distribution of the Highland Schists within the faulted 

 area with that in the surrounding country. 



The effect of the branch fault, running through the Allt Charnan 

 valley, is also clear. It throws down the thick phyllites of group 4 

 to the east against quartzites, banded phyllitic rocks, and limestone 

 (c ale -silicate hornfels), which are believed to represent groups 1, 2, 

 & 3, respectively, of Glen Coe. 



In two other important sections, one at Stob Mhic Mhartuin and 

 another at Stob Beinn a' Chrulaiste, differences both of strike and of 

 lithological character distinguish the Schists on the two sides of the 

 fault-plane. These sections are described in detail in the sequel, 

 where a fuller discussion of the behaviour of the fault in relation 

 to the Schists south-east of Dalness will also be found. 



(3) The inclination of the boundary-fault. — The incli- 

 nation of the main fault surrounding the cauldron is a point 

 of some interest. Along the northern front the fault generally 

 overhangs the cauldron at angles varying from 70° to 50°, measured 



