DURING THE TERTIARY PERIOD IN THE BRITISH ISLES. 165 



Strath Beg. Judging from the respective areas of the granophyre and agglomerate, we 

 may infer that the former has not risen here exactly in the centre of the old funnel, but 

 rather to the north of it. It is no doubt this fortunate divergence that has spared a 

 segment of the vent from obliteration. It is interesting to observe, however, that the 

 granophyre has likewise risen along the outer or southern margin of the agglomerate, 

 generally between that rock and the limestone, but sometimes entirely within the 

 agglomerate. The distance between the nearest part of this ring of eruptive rock and 

 the edge of the boss of Beinn an Dubhaich is under 400 yards, the intervening space- 

 being occupied by limestone (or marble), much traversed by N.W. basalt-dykes. These 

 dykes do not enter the rocks of the veDt, and are abruptly truncated by the mass of 

 Beinn an Dubhaich. The structure of this locality in shown in fig. 54. Further 

 westward, the group of vents, which as we have seen probably rose out of the plateau 

 basalts, first served for the rise of the masses of gabbro, and the subsequent pro- 

 trusion of the granophyres has destroyed or concealed any relics of it that might have 

 survived. 



Fig. 54. — Section from Beinn Dearg to Beinn an Dubhaich, Skye. aa, Lower Silurian limestone; bb, volcanic agglomerate ; 

 ccc, basalt-dykes older than granophyre; d 1 , granophyre of Beinn Dearg; cP, granophyre in the agglomerate neck; d 3 , 

 granophyre of Beinn an Dubhaich ; e, basalt-dyke younger than granophyre. 



(2) Relation to the Bedded Basalts of the Plateaux. — On the north-west side, the 

 granophyre of Glamaig and Glen Sligachan mounts directly out of the bedded basalts. 

 These latter rocks, which rise into characteristic terraced slopes on the north side of Loch 

 Sligachan, appear on the south side immediately to the west of Sconser, and stretch west- 

 wards round the roots of Glamaig into the Coire na Sgairde. As they approach that hill 

 they assume the usual dull, indurated, splintery, veined character, where they have under- 

 gone contact metamorphism, and weather with a light crust. Some of them are highly 

 amygdaloidal, and between their successive beds thin bands of basalt-breccia, also 

 much hardened, occasionally appear. Veins of granophyre become more numerous 

 as we come nearer the main mass of that rock. The actual line of junction runs 

 into the Coire na Sgairde and slants up the Druim na Euaige, ascending to within a 

 few feet of the top of that ridge. A dark basic rock lies on the granophyre, the latter 

 being here finer grained and greenish in colour, and projecting up into the former. There 

 is so much detritus along the sides and floor of Glen Sligachan that the relations of the 



VOL. XXXV. PART 2. Y 



