422 KECENT WOEK OF THE GEOLOGICAL SXJEVEI 



the 2500 feet contour-line, the strata exposed in the stream-section 

 consist wholly of the lower zone of quartzites with their dykes, 

 repeated by inverted folds and minor thrusts. Indeed, from the 

 various arches exposed, it is clear that the basal quartzites only 

 form a tbin veneer over the concealed Archaean rocks. "Were the 

 slope denuded further back, there can be no doubt that the latter 

 would be revealed. About the 2500 feet contour-line the basal 

 quartzites are followed in regular order by the various subdivisions of 

 the "pipe-rock," with their intrusive sheets, and the " Eucoid-beds," 

 until they are abruptly truncated by the great Ben-More Thrust- 

 plane. At the point where this line of section is drawn the effect 

 of this maximum thrust is to bring the basal quartzites to overlie the 

 highest zone of the "pipe-rock" and " Fucoid-beds." When the false- 

 bedded quartzites (Zone 1) are traced along the crest of the moun- 

 tain they are found to overlie unconformably both the Cambrian 

 sandstones and the Archsean rocks. The false-bedded quartzites 

 are succeeded by the lowest subdivision of the " pipe-rock," ex- 

 posed on the mountain top. Descending the north-eastern slope of 

 Coinne-mheall (fig. 15), the observer crosses (1) the unconformable 

 junction of the basal quartzites and the Cambrian sandstones, and 

 (2) the boundary line between the latter and the Archaean gneiss. 



Owing to the high inclination of the Ben-More Thrust-plane at 

 this point, the outcrop descends from the crest of the mountain to 

 the Bealloch, where it is well seen on the great cliff in dip- 

 section. As a result of the friction along the unyielding " sole " of 

 the thrust, causing the upper layers to move more rapidly than the 

 lower, we find that the Cambrian sandstones fold over the western 

 face of the disrupted gneiss, as shown in the foregoing section (fig. 15). 

 By means of the local conglomerate (" the Button-stone ") at the 

 base, the line of junction with the old Archaean platform is easily 

 traced, and the proof of inversion is beyond all doubt. The basal 

 conglomerate and the overlying grits, sandstones, and shales can be 

 followed continuously from the Bealloch, round the south-eastern 

 spur of Coinne-mheall, to the southern shoulder of Ben More, where 

 they are unconformably overlain by a cake of the basal quartzites. 

 That these grits and sandstones are reaUy a portion of the Cambrian 

 sandstones to the west, as originally maintained by Prof. Mcol, is 

 apparent from the fact that the double unconformability is 

 admirably seen along the ridge between Coinne-mheall and Ben 

 More, and further from the presence of the various intrusive dykes 

 on their proper horizons. The area occupied by the Cambrian strata 

 is about half a square mile, about half of which is buried under 

 the basal quartzites. In the corrie on the north-east side of the 

 mountain they reappear with the conglomerate at the base, resting 

 on the old platform. The general inclination of the Cambrian strata 

 is towards the W.N.W., at an average angle of 20° ; the greatest 

 thickness is about 1500 feet. 



In the Bealloch of Coinne-mheall (fig. 16), the hade of the Ben- 

 More thrust-plane becomes almost flat, and hence the outcrop can 

 be followed for two and a half miles down the river Oykel. Along 

 the line of outcrop, the Cambrian sandstones reappear above the 



