Vol. 65.] THE CATJLDEOJf -SUBSIDENCE OF GLEN COE. 635 



at many points north of Glen Coe, it is important to notice that the 

 later movement along the old fault has had so insignificant an effect 

 that it has not cut out the original chilled edge of the fault-intrusion ; 

 nor, as already remarked, has it shifted the north-north-easterly 

 porphyrite dykes, which cross the fault-line. 



In An t-Sron, and also in Meall Dearg and Sron Garbh, north 

 of Glen Coe, there is of course independent evidence that the 

 boundary-fault, if not actually at the chilled edge of the intrusion, 

 must at all events he very close at hand. The prolongation of the 

 fault-line between Stob Beinn a' Chrulaiste and the Cam Ghleann, 

 and between this glen and the eastern flank of Meall a' Bhuiridh, is, 

 however, on a somewhat different footing. At each of the three 

 places named the fault is clearly defined, and against it the fault- 

 intrusion is distinctly chilled. In the intervening ground, however, 

 exposures are poor, so that it has not been found possible to 

 locate the fault precisely ; and we can only say, in reference to these 

 tracts, that the fault-intrusion stretches in a continuous belt 

 from Stob Beinn a' Chrulaiste through the Cam Ghleann to Meall 

 a' Bhuiridh, and that its inner margin is, as a rule, an even line. 

 An exception to this rule is to be noted in the exposures on the 

 hilltop east of the Cam Ghleann ; for here the fault-intrusion 

 pierces the schists along its inner margin irregularly and without 

 chilling. The schists of this exposure, however, almost certainly 

 lie outside the fault, since their strike is at right angles to that 

 found in neighbouring outcrops on the south-west, which are clearly 

 within the boundary-fault. 



The fault-intrusion continues southwards from Meall a' Bhuiridh ; 

 but before long it loses its main distinguishing character, and ceases 

 to show a chilled interior margin, although prohably still bounded 

 on this side by the fault-plane. A little farther on it joins the 

 Cruachan Granite, at the point where the latter sweeps across the 

 fault into the sunken mass withiu. 



"We are now in a position to discuss the details of the internal 

 constitution of the fault-intrusion, and the relation subsisting 

 between this complex and the contiguous portion of the Cruachan 

 Granite. 



Beginning at the south-eastern corner of the area, a branch of 

 the pink granitite leaves the main Cruachan mass and extends 

 north-north-eastwards, being bounded on the north-west by an 

 even line, presumably the trace of the fault. It is not chilled, 

 however, against the plane which is supposed to represent the fault 

 in this locality. 



About a mile to the north of the point where this pink granitite 

 diverges from the main mass of the Cruachan intrusion, it passes 

 gradually into the grey tonalite. The passage can be followed in 

 the cliff facing the River Ba to the north of Allt Coire an Easain. 

 The change of type is rather sudden, being completed within a space 

 of 20 yards or so ; but within these limits the transition is perfect. 



