242 
THE TERTIARY VOLCANOES 
BOOK VIII 
Its channel was constantly being filled up by fresh streams of basalt or 
deflected by the uprise of new cinder-cones. But, fed by the Atlantic 
rains, it maintained its seaward flow until the general subsidence which 
carried so much of the volcanic plain below the sea. Yet the higher part 
of this ancient water-course is no doubt unsubmerged, still traversing the 
schists of the Western Highlands as it has done since older Tertiary time. 
It may, perhaps, be recognized in one of the glens which carry seaward the 
drainage of the districts of Moral’, Arisaig, or Moidart. 
Let us now turn to the remarkable lava which has sealed up the river- 
cliannel of Eigg, and of which the remaining fragment stands up as the 
great ridge of the Scuir. This rock presents characters that strongly dis- 
tinguish it from the surrounding basalts. It is not one single uniform 
mass, but consists of a number of distinct varieties, some of which are a 
volcanic glass, while others are a grey “ porphyry,” or devitrified pitchstone. 
Fig. 280. — View of the Scuir of Eigg from the South. 
These are arranged in somewhat irregular, but well-marked, and, in a general 
sense, horizontal sheets. On the great eastern terminal gable of the Scuir 
this bedded structure is not clearly displayed, for the cliff seems there to be 
built up of one homogeneous mass, save a markedly columnar band that 
runs obliquely up the base of the precipice (Fig. 278). If, however, the 
ridge is looked at from the south, the truly bedded character of its materials 
becomes a conspicuous feature. Along the cliffs on that side the two 
varieties of rock are strongly distinguished by their contrasting colour and 
mode of weathering, the sombre-hued pitchstone standing up in a huge 
precipice striped with columns, and barred horizontally with bands of the 
pale-grey “ porphyry,” which, from its greater proneness to decay, seems sunk 
into the face of the cliff. At the south-east end of the ridge the bedding 
is especially distinct. West of the precipices, to the south of the Loch a’ 
Bhealaieh, the dark pitchstone which forms the main mass is divided 
by two long parallel intercalations of grey rock, and two other short 
lenticular seams of the same material (see Figs. 280, 281). It is clear 
from these features, which are not seen by most travellers who pass 
