398 
THE TERTIARY VOLCANOES 
BOOK VIII 
of the granophyre run through the basic rocks. The contrast of colour 
between the pale reins of the intrusive rock and the dark tint of the basalts 
is well shown in the channel of the water. Similar sections may be seen on 
the flanks of Beinn Fhada, especially in the great corry north of Ben More, 
where the granophyre sends a tongue of finer grain between the beds of 
basalt. On the east side of Loch Ba’ numerous proofs of similar intrusion 
Fig. 353. — Section on south side of Cruach Turr an Lochaiu, Mull. 
u, bedded basalts and dolerites ; b, granophyre ; c, marginal finer-grained band ; d d, veins from the granophyre 
traversing the basic rocks. 
may be observed. Thus at the east end of Loch na Dairidh, where the 
granophyre has been intruded into the basalts, hand-specimens may be 
obtained showing the two rocks welded together. On the slopes of Cruach 
Tbrr an Lochaiu, where the granophyre has a felsitic selvage, the bedded 
basalts are traversed by veins of the latter material (Fig. 353). A little 
further east, at the head of the Allt na Searmoin, the bedded basalts, 
some of which are separated by slaggy seoriaceous surfaces, are intersected 
by another protrusion from the compact felsitic porphyry (Fig. 354). 1 A 
mile lower down the same valley a separate mass of granophyre sends out 
veins into the basalt, which as usual is dark 1 iluish-grey in colour, indurated 
and splintery. 
As the posteriority of the Mull granophyre and felsites to the basalts is 
thus proved, the further question 
remains as to their manner of 
intrusion. Here and there, 
especially on the south-eastern 
side, between the head of the 
Scarrisdale river and Loch Ba’, 
the line of junction between the 
two rocks is nearly vertical, but 
a body of black felsite intervenes 
as a huge wall between the 
Fig. 854. Section at head of Allt na Searmoin, Mull. orc Unary granophyre and the 
«, basalts and dolerites, with slaggy upper surfaces ; 6, felsite. , , ,, _ . , . 
basalt. On Benin Fhada and 
Beinn a’ Chraig the line of separation, as I have above remarked, is inclined 
1 This rock appears to the eye as a black finely crystalline -granular felsite. Under the 
microscope, it was found by Dr. Hatch to “present a markedly granulitic structure, consisting 
mainly of' small rounded grains of dirty brown turbid felspar, with isolated granules of colourless 
quartz. Scattered through the rock, or accumulated in patches, are small spherical or drop-like 
granules of a bright green augite (coccolite). ” 
