676 THE CAULDRON-SUBSIDENCE OE GLEN COE. [XoV. 1909, 



more restored, the Etive centre resumed its independent history of 

 subsidence and intrusion, as exemplified by the uprise of the 

 Starav mass. 



In this way an analogy may be detected between the Glen Coe 

 cauldron of Old Red Sandstone times, with its girdle of fault- 

 intrusion, and the Pacific Ocean of to-day, with its fringe of 

 marginal volcanoes. The difference in size of the two is so 

 important that comparison in detail is not admissible. It is possible, 

 however, that the reversal of hade, which can be recognized as a 

 local feature of the Glen Coe boundary-fault, may indicate the 

 beginnings of a peripheral folding, analogous to that which is so 

 conspicuous a feature of the Pacific borders. 



Of cauldron-subsidences of the moderate dimensions characteristic 

 of Glen Coe but few modern examples are known. One cause for 

 this may be sought in the explosive activity of steam, which is so 

 important a factor in volcanic phenomena. When igneous magma 

 has been brought within striking distance of the surface, it can 

 often blast a passage for itself. Sir Archibald Geikie and other 

 workers have established the frequency of this type of ' inde- 

 pendent ' outburst, where volcanoes have arisen without any 

 reference to the existence of fissures at the surface. In such, 

 instances subsidence still occurs to compensate for the outpouring 

 of the magma, but a widely distributed sagging without fracture 

 often meets the requirements of the case. In depth, beneath the 

 limit at which the operation of steam as an explosive agent has 

 been traced, it is not unlikely that the phenomena of subsidence 

 and intrusion more frequently approximate to the ideal simplicity 

 which is so closely approached in the cauldron-subsidence of 

 Glen Coe. 



EXPLANATION OF PLATES XXXII-XXXIV. 



Plate XXXTI. 



Photograph of Coire nam Beith, Glen Coe, showing the volcanic rocks, 

 which rest upon the Highland Schists, turned up against the boundary-fault. 

 On the other side of the fault, the fault-intrusion, consisting of granite, is 

 chilled against the fault-plane. [Photograph No. 619, Coll. Geol. Surv. Scotl.] 



Plate XXXIII. 



Horizontal sections through the cauldron-subsidence of Glen Coe, on the 

 scale of 1 inch to the mile (horizontal and vertical). All dykes are omitted. 



Plate XXXIV. 



Contoured geological map of Glen Coe, on the scale of 1 inch to the mile 

 All dykes are omitted. 



