Yol. 65.] TIIE CATJEDKON- SUBSIDENCE OF GLEN COE. 647 



belonging to this group is forthcoming along the northern front of the 

 subsidence, where it will be shown in the detailed descriptions that : 



(1) Their surface-distribution bears somewhat the same peripheral relation 



to the sunken area as that of the fault-intrusions (pp. 653-55) ; 



(2) In some cases they aim at the early fault-intrusion of the district, without 



ever cutting it (p. 655) ; 



(3) They have been sheared locally, like the early fault-intrusion (pp. 653, 



656) ; and 



(4) The pink porphyrite of the fault-intrusion proper is, in Meall Dearg, 



clearly chilled against a typical member of the series (p. 659). 



It is believed, however, that while there were several early 

 volcanic felsite dykes, there were also later dykes of the same type 

 belonging to a period later than the fault-intrusion. Thus north 

 'of Garbh Bheinn, felsite dykes are known which sometimes adopt 

 the normal north-north-east direction of the great porphyrite suite ; 

 but they are few in number, and all of them are of earlier date 

 than the porphyrites of the same neighbourhood. 



The majority of the local dykes are of quartz-porphyry or horn- 

 blende-andesite, and are intruded into the lavas within the cauldron- 

 subsidence. They are older than the north-north-east dykes, and 

 they have not been found cutting the fault-intrusion or the Cruachan 

 Granite. It is impossible, therefore, to fix their precise age, but it 

 is clear that they belong to the Glen Coe centre. 



Lastly, we may mention certain early hypabyssal intrusions, 

 occurring in the district, but not obviously connected with the 

 Glen Coe centre. These are horizontal sheets of vogesite, always 

 cut across by the porphyrite dykes, and never found intrusive into 

 the lavas and granites, although in the schists they are widely 

 distributed. In addition to this, numerous blocks, almost certainly 

 derived from one of these sheets, have been found enclosed in an 

 intrusion-breccia with fault-porphyrite matrix, exposed in a stream- 

 bed west of Garbh Bheinn. It appears fairly certain therefore 

 that these vogesite sheets are the earliest manifestation of igneous 

 activity occurring in the Glen Coe district. 



(b) Special Description of Selected Sections. 



A general account has now been given of the marginal pheno- 

 mena of the Glen Coe subsidence. We may next consider a few 

 sections along the line of the boundary-fault, which seem to require 

 further illustration. 



Stob Beinn a' Chriilaiste. — Sufficient has been said already 

 on the direct evidence for the faulting observed on each side of 

 Allt Coire an Easain, and again at Meall a' Bhuiridh and in the 

 Cam Ghleann. Further, it has been pointed out that the fault- 

 intrusion, linking these localities together and uniting them with 

 Stob Beinn a' Chriilaiste on the north, speaks for the continuity of 

 the boundary-fault in this ill-exposed eastern portion of the district. 



