Vol. 65.] THE CAULDRON-SUBSIDENCE OP GLEN COE. 621 



a more or less flat cake upon the quartzose schists. Elsewhere 

 patches of rhyolite lava occur near the margin of the group, and 

 here and there the base of one or other of these flows can be seen 

 filling numerous minor inequalities of the old surface of the High- 

 land Schists. It is evident, therefore, that group (3) has, in this 

 case, overlapped on to a steep slope, perhaps even a cliff, of the 

 original topography of Old Red Sandstone time (PI. XXXIII, 

 Section I). 



In Allt Coire an Easain the base of the same group (3), consisting 

 here mainly of breccia derived from the Schists, is again exposed 

 in a manner which brings vividly to mind the extreme unevenness 

 of the old eroded floor. The breccia is frequently absent from slopes 

 precisely where it might be expected to occur, while it crops up 

 in many an odd situation where its presence could never have been 

 anticipated. It is even found tucked away beneath projecting 

 ledges, or packed into holes which represent ancient caves. The 

 picture of a rough land-surface smothered beneath accumulating 

 debris is in fact complete. 



An insight into the irregularities of the old topography is also 

 furnished in Glen Etive, a little above Dalness. On the south side 

 of the river several exposures of siliceous schist are found not much 

 above the level of the stream ; while, some 400 yards away to the 

 north, a small patch of similar schist is again seen about 300 feet 

 higher. Close by this patch is a band of breccia, shown upon the 

 map. This bed consists of fragments of siliceous schist, and can be 

 traced for some distance at a level a little below the lowest of 

 the rhyolite lavas of group (2). 



In contrast with the sections described above, the old floor upon 

 which the volcanic rocks rest at the western end of Glen Coe is 

 relatively smooth and regular (PI. XXXIII), a circumstance which 

 is doubtless due to the fact that it is composed of uniform and 

 relatively soft phyllites, in contradistinction to the harder quartzose 

 schists or mixed quartzites and phyllites forming the ancient surface 

 in the Cam Ghleann and again around Dalness. 



Reference may now be made to some small patches of breccia, 

 which have been observed lying on an uneven surface of the High- 

 land Schists, outside the fault bounding the volcanic rocks. The 

 largest of these patches rests against a steep slope of quartzite, at a 

 height of 2,500 to 3,000 feet on Sgor nam Fiannaidh, and consists 

 of quartzite fragments, together with small pieces of red felsite and 

 porphyritic andesite, set in a siliceous matrix. Another smaller 

 accumulation is preserved in a deep hollow of the phyllites at the 

 head of Gleann Charnan, and is made up of large subangular blocks 

 of phyllite, mixed with a few small fragments of quartzite. Both 

 these breccias are pierced by the ' fault-intrusion,' or by an 

 apophysis from it, and are also cut by later porphyrite dykes. They 

 are, therefore, similar in constitution and in geological relations to 

 the basement breccias already described ; and accordingly they may 

 be regarded as outlying portions of the same, gathered upon the 

 highly uneven land-surface of the period. 



