Vol. 6-5.] 



THE CAULDRON-SUBSIDENCE OE GLEN COE. 



659 



This dyke is about 50 yards wide, and runs nearly east and west. 

 As a rule, it is flanked on each side by a thin strip of phyllite, 

 but a foot or two broad * ; and it is, of course, only where the fault- 

 porphyrite has broken through this border of phyllite, and has 

 reached the felsite within, that it exhibits a chilled margin against 

 the latter. This curious relationship appears incomprehensible, 

 unless we suppose that the Meall Dearg intrusion bas a flat base : 

 on such a supposition the interpretation is not difficult. It seems 



cnr'lv felsi.te 

 fTvhe 



[F=Fault, accompanied by fault-intrusion.] 



probable that the fault-intrusion spread outwards in the form of a 

 more or less horizontal sheet, and that the felsite dyke, with an 

 adherent coat of hardened phyllite, fractured, so as to give room 

 for this sheet, at a slightly higher level than the country-rock on 

 each side. Hence the dyke now projects as a low bar above the 

 general level of the floor of the later intrusion (fig. 12). 



Dalness and Beinn Ceitlein. — The features of the fault 

 between Glen Coe and Glen Etive have been so frequently referred 

 to in the foregoing pages that they require no further illustration. 

 There are two branches : the inner one, in Gleann Fhaolain, serves 

 as the boundary-fault of the volcanic rocks : the outer one, in 

 Gleann Charnan, is equally clearly revealed by its effect upon the 

 outcrops of the Schists. In both cases the fault-intrusion extends 

 along the outer margin of the dislocation. The inner fault can be 

 shown, in more than one place along its course, to have a normal 

 inclination of about 70° towards the area of subsidence. 



On the south side of the Etive the inner fault is well seen on 

 the hillside, about 1100 yards south-east of Dalness. It inclines 



1 For some distance there is also a flanking porphyrite dyke, older than the 



felsite. 



