620 MESSRS. CLOT/GH, MAUFE, AND BAILEY ON [NOV. I909, 



further exposure of the base of the group in the stream-bed of 

 Coire nan Lab, but the conglomerate is absent here, and the sedi- 

 mentary beds consist mostly of shale. 



Southward group (1) may be traced in strong development along 

 the slopes of Bideau nam Bian to Dalness, where at several points 

 in the bed of the Etive and in the adjoining slopes, the old schist 

 floor shows through, in a highly irregular manner. These inliers 

 of the Highland Schists are often in a disturbed and brecciated 

 condition for a thickness of a few feet down from the surface. In 

 other cases they are massive throughout, but sprinkled over with a 

 few angular scraps and fragments of rock. 



Reference may again be made to the basic andesite, resting upon 

 conglomerate containing granite boulders, which lies at the base of 

 the volcanic pile in the Cam Ghleann. It is quite probable that 

 this represents an original extension of group (1) in an easterly 

 direction. 



(c) The Uneven Floor upon which the Volcanic 

 Series reposes. 



In the preceding section evidence has been adduced of an un- 

 conformable overlap in the volcanic series of such a character that, 

 in an easterly direction, beds of group (2) and even of group (3) 

 come to rest directly upon the old schist floor. The absence of 

 group (1) may merely indicate that the source of supply in this 

 instance lay to the south-west, but that of group (2) between 

 Cam Ghleann and AUt Coire an Easain can be definitely correlated 

 with the very irregular form of the old floor. 



In ascending the Cam Ghleann from the position of the boundary- 

 fault, we encounter several detached outcrops of rhyolite and ande- 

 site, and also patches of breccia, consisting of angular fragments of 

 schist and rhyolite. The relations of all these rocks to the sur- 

 rounding schists strongly suggest that they accumulated on an 

 extremely irregular surface, but the most striking example of such 

 an irregular pre-existing surface is exposed farther up the glen. 

 In this direction the main mass of the rhyolite lavas is encountered 

 underlain, as already described, by several feet of shale, below which 

 comes a thick dark andesite resting on a conglomerate containing 

 granite boulders. The dip, which is steep in Sron na Creise, on the 

 west, is here very low, and yet the boundary between the volcanic 

 rocks and the schists runs as if it were the trace of a vertical plane, 

 straight up the hill-slope to the east. The exact junction between 

 the two groups of rocks is not clearly seen on this hill-face ; but 

 patches of breccia accompany the schists in proximity to exposures 

 of rhyolite, and, once on the hilltop, it is possible to demonstrate 

 that the boundary is not a faulted one. Here the agglomerate, 

 group (3), overlying the rhyolite, group (2), is reached ; and at one 

 locality a particular bed can be traced some little distance in 

 advance of the main volcanic mass, and can be shown to repose as 



