622 MESSES. CXOTJGH, MAT7EE, AND BAILEY ON [Nov. 1909, 



The examples so far chosen to illustrate the irregular nature of 

 the old land-surface do not demand any special explanation. There 

 are other cases, however, where it is exceedingly difficult to recon- 

 cile the observed facts with the simple conception of a normal 

 erosion-topography. At the same time it must not be forgotten 

 that landslip-cracks are a prominent feature in the topography of 

 some parts of the Highlands of to-day. More especially is this true 

 of districts formed of phyllitic rocks, or of phyllites and quartzites 

 folded together, such as constituted the buried topography of Glen 

 Coe. Landslip-cracks filled with debris and lava are well calculated 

 to present difficulties of interpretation when brought to light in so 

 involved a district as the one under consideration. But, from what 

 is known of active modern volcanoes, it is unnecessary, and even 

 unwise, to assume that all the irregularities which can be detected 

 are the work of erosion aided and abetted by gravitation alone. 

 We cannot suppose that Glen Coe was exempt from the shaking and 

 shattering by earthquake-violence which constitute such disastrous 

 accompaniments of recent volcanic activity. Possibly, therefore, 

 some of the deposits of the district were accumulated in open fissures 

 or gjas, produced during the period of vulcanicity. Such gjas are 

 well known at the present time in the desert regions of Iceland. 



An example which is considered suggestive in this connexion will 

 now be described. The north-eastern margin of the volcanic rocks, 

 as may be seen from the map, descends the northern slopes of the 

 valley of Glen Coe and, crossing the Coupall River, mounts some 

 little way up Stob Dearg without perceptibly altering its course. 

 The straightness of the boundary is in this case due to the steep 

 south-westerly inclination of the rocks, which dip at angles often 

 amounting to 50° and more towards the south-west, as has already 

 been described. This structural feature may be especially well 

 discerned on the western face of Stob Dearg, where the Lochan na 

 Pola agglomerate with its associated shale bands is inclined at very 

 high angles, and is sometimes even vertical. One would scarcely 

 expect, under the circumstances, to see anything more of the 

 volcanic rocks between this tilted margin and the great boundary- 

 fault to the north, which is held responsible for the disturbance. 

 But, as a matter of fact, there is a belt, extending from the 

 Devil's Staircase to Glen Etive (perhaps even including some of 

 the isolated outcrops iu the Cam Ghleann) along which exposures 

 of rhyolite and breccia are constantly making their appearance. 

 The belt along much of its course passes through ground which 

 is obscured by superficial deposits, so that often its existence can 

 only be recognized in isolated stream-sections. It lies between 

 half and three-quarters of a mile in front of the main volcanic 

 outcrop, and it runs for the most part through lower ground than 

 is traversed by the base of the latter. Careful examination of that 

 part which crosses the face of Stob Beinn a' Chrulaiste, above 

 Altnafeadh (fig. 6, p. 648), shows that the rhyolite outcrops, which 

 it includes, consist of irregular patches, often separated from the 



