3 86 
THE TERTIARY VOLCANOES 
BOOK VIII 
position of a group of older volcanic funnels which provided facilities for 
the uprise of the basic and acid magmas. The group of vents which, as 
we have seen, probably rose out of the plateau-basalts, and first served for 
the rise of the masses of gabbro, has by the subsequent protrusion of the 
granophyres been still further destroyed and concealed. 
The granophyre intrusions in the great Strath agglomerate have lately 
been mapped and described by Mr. Harker. As regards their internal 
structure and composition, this observer remarks that compared with the 
normal granophyres of the lied Hills and other bosses of the district, these 
smaller intrusive masses are darker and manifestly richer in the iron-bearing 
minerals, and have a slightly higher specific gravity. But in their general 
characters they agree with the other granophyres. The most interesting- 
feature in them is the evidence they afford that they have enclosed and 
partially dissolved fragments of basic rocks. To this evidence further 
reference will He made on a later page (see p. 392). 
(2) Relation of the Granophyre to the Bedded Basalts of the Plateaux. 
Metamorphism of the Basalts . — 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 westwards round the roots of Glamaig into the Coire 
na Sgairde. As they approach that hill the)' assume the usual dull, 
indurated, splintery, veined character of their contact metamorphism, 
and weather with a pale 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 
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. 1 There is so much detritus along the sides 
and floor of Glen Sligachan that the relations of the two groups of rock 
cannot be well examined there. But the basalts, which present their 
ordinary characters to the north of the Inn, are observed to become more 
and more indurated, close-grained, dull and splintery, as they draw nearer to 
the granophyre of Marsco. This part of the district furnishes the clearest 
evidence of the posteriority of the great cones of Glamaig and its neighbours 
to the plateau-basalts which come up to the very base of these hills. 2 
Bound the eastern group of cones some interesting fragments of the once 
• continuous sheet of plateau-basalts remain, and show the same relation of the 
acid protrusions on that side. One of these lies on the granophyre of the 
flanks of Beinn na Caillich, a little to the west of the loch at the northern 
1 I think it probable that some of the greenish portions of the granophyre along this part of 
the junction-line will be found to have had their structure and composition altered by having 
incorporated into their substance a proportion of the bedded basalts through which they have 
been disrupted. 
2 The dykes of granophyre in these basalts are referred to at p. 444. 
