662 MESSES. CLOTTGH, MAEFE, AXD BAILEY ON [Xov. 1909, 



the dislocation would meet one another in a perfectly natural 

 manner if continued forward across the gap now occupied by 

 granite. 



(2) The movement of subsidence was of a somewhat unusual, 

 probably very rapid type, as is indicated by the manufacture of a 

 flinty crush-rock at some points, at least, along the line of dislocation. 

 This flinty crush- rock owes its peculiar character to extreme 

 trituration, with the probable accompaniment of incipient fusion, 

 due to heat generated by friction in the plane of the fault. 



(3) The boundar3 r -fault, where it has not been obliterated by the 

 Cruaehan Granite, that is along four-fifths of its original extent, 

 is surrounded by a discontinuous complex known as the fault- 

 intrusion. This includes both granitic rocks and coarse 

 porphyrites. 



The inner boundary of the intrusion-zone is the boundary-fault 

 of the cauldron, and is almost mathematically exact. In several 

 notable instances large independent masses of the intrusion show 

 smooth, clean-cut inner margins against the fault-plane, and ragged 

 transgressive outer margins against the Schists beyond. Moreover, 

 while the minor intrusions scattered through the zone outside the 

 fault are innumerable, but three or four insignificant examples are 

 to be found inside. 



(4) Along its outer irregular margin, the fault-intrusion is some- 

 times obviously chilled and sometimes not ; along its inner smooth 

 margin against the fault-plane, it is invariably chilled. In like 

 manner, the alteration induced by the fault-intrusion is almost 

 entirely restricted to the zone external to the fault. 



(5) There is clear proof that the cauldron-subsidence was not 

 effected in a single stage. The evidence for this is best displayed 

 on the northern margin of the cauldron, where an outer parallel 

 branch of the fault of manifestly early date exists. Like its 

 later companion, this early branch has its own special band of 

 flinty crush-rock and its own special fault-intrusion. The latter, 

 however, during the movements of subsidence connected with the 

 production of the inner branch of the fault, has itself been sheared, 

 and in many cases broken down, with the production of flinty 

 crush-rock. 



Another good example of an early branch of the fault, accom- 

 panied by an early fault- intrusion, presents itself on the east side 

 of the cauldron. Here the older branch occupies the interior 

 position. 



(6) The fault-intrusion surrounding the Glen Coe cauldron is, in 

 all probabilitj r , merely an offshoot from the Cruaehan magma. 

 The latter has penetrated the foundered area from the south, and 

 underlies the lavas of the central district in which it causes 

 contact-alteration. It cuts across lavas 2000 feet thick, without 

 showing any indication of arching or tilting them. This lobe of 

 the Cruaehan Granite is confluent to the south with a much more 

 extensive mass which, with its great core, consisting of the more acid 



