364 C. CALLAWAY OUT THE NEWER ONEISSIC 



aggregate of felspar and quartz, without foliation ; and, not suspect- 

 ing any thing wrong, I took it to be " porphyry," though there was 

 something about it which suggested the granitoidite with which I 

 was familiar in Wales and Shropshire. Soon after I found distinct 

 foliation, dark crystalline bands striking to the north-west. This 

 was puzzling ; but as, at a short distance ofT, the rock was seen clearly 

 to overlie the dolomite, I clung to the " igneous " theory. Coming 

 down to the present section new light began to dawn. 



This formation occupies the shore of the loch for about a quarter 

 of a mile, filling in the entire break between the sandstone and the 

 Caledonian, no trace of quartzite or dolomite being visible, though 

 bare rock is exposed almost the whole distance. The Caledonian 

 crops up on the flat beach in contorted beds, dipping on the whole 

 easterly, and ending abruptly on the west. Fifty yards from it we 

 come to a green felspathic rock, without definite structure, but 

 looking like partially decomposed gneiss. This passes towards the 

 north-west into a true gneiss (No. 74, p. 416), composed mainly of 

 reddish felspar, quartz, and a greenish mineral, the folia either dip- 

 ping E.N.E. at a low angle, or rising nearly to the vertical, and stri- 

 king to N.N.E. The resemblance of this gneiss to some of the Mal- 

 vern and Wrekin types was very marked. Its appearance is widely 

 contrasted with that of the Caledonian. The foliation is more mas- 

 sive ; the crystallization is much coarser ; the rock is quite destitute 

 of that fissile structure which causes ordinary Caledonian to split up 

 into flaggy pieces, and it is much tougher under the hammer. Its 

 structure and behaviour was altogether that of the Hebridean, to 

 which I referred it ; and the opinion then formed has been confirmed 

 by a long study of the rock in more northerly localities during two 

 successive summers, as will hereafter appear. 



Continuing along the shore to the N.N.W., we pass abruptly from 

 the gneiss to the conglomerate. By Murchison and Geikie it is 

 stated that there is a gradual transition from the one into the other ; 

 and hence it is inferred that the gneissic rock is a " metamorphosed 

 band of felspathic grit." The section described by these authors is 

 undoubtedly the one studied by me ; but, after careful examination, 

 I could not detect the slightest evidence of a gradation. The line 

 of junction is perfectly sharp. The gneiss (No. 63, p. 416), which 

 mainly consists of felspar and a little quartz, and is coloured green 

 (apparently by chloritic products of decomposition, as is commonly 

 the case at faulted junctions), is in actual 'contact with conglomerate 

 and grit. The gneiss and the conglomerate are plastered together 

 by the chloritic mineral, but are readily separable by a slight blow 

 of the hammer. The plane of junction, which displays slicken- 

 sides, is nearly vertical, the gneiss slightly overhanging the conglo- 

 merate. The bedding in both rocks is very obscure. 



In the same locality, a little way up the slope, the gneiss rests on 

 quartzite ; and close by the conglomerate rests on quartzite. My 

 interpretation of these facts is, that by faulting, supplemented by 

 lateral squeeze, older deposits, Hebridean and Torridon, are brought 

 up and thrown over onto the quartzite. 



