of Edinburgh, Session 1866 - 67 . 73 
that the tertiary coal of the Western Islands will ever come to be 
of commercial importance. 
Proofs of the long continuance of volcanic action among these 
islands are afforded by the great thickness of the successive sheets 
of igneous matter, which in one mountain alone — Ben More — reach 
a depth of 3185 feet without revealing either the actual bottom or 
top of the series. Another and striking piece of evidence on this 
subject is given by the well-known Scuir of Eigg. That island 
consists of nearly horizontal sheets of dolerite, like those of Mull, 
resting unconformably upon oolitic rocks. After their eruption, 
they must have been long exposed to the wasting agencies of the 
atmosphere. A valley was cut out of them, and its bottom was 
watered by a river, which brought down coarse shingle and sand 
from the distant Cambrian mountains of the north-west. These 
changes must have demanded a lengthened lapse of time, yet 
they took place during an interval in the volcanic history of the 
island. The igneous forces which had been long dormant broke 
out anew, and poured several successive coulees of vitreous lava 
down the river-bed. In this way the channel of the stream came 
to be sealed up. But the same powers of waste which had scooped 
out that channel continued their operation. The hills which had 
bounded the valley crumbled away, and the lava-currents that 
filled the river-bed being much harder than the surrounding rocks, 
were enabled in great measure to resist the degradation. Hence 
the singular result now appears that the former hills have been 
levelled d<?wn into slopes and valleys, while the ancient valley 
occupies the highest ground in the neighbourhood, and its lava- 
current stands up as the well-known precipitous ridge of the Scuir 
of Eigg. The gravel and drift-wood of the old river are still to be 
seen under the rock of the Scuir. 
The author then proceeded to point out the possible connection 
between these tertiary volcanic rocks and the metamorphism of 
different parts of the West Highlands. He showed that in 
Mull, under Ben More, the volcanic rocks themselves give signs of 
having been subjected to a process of metamorphism, and that they 
are associated there with masses of syenite, like those of Raasay 
and Skye. Maceulloch pointed out that the syenite of the two 
latter islands was later than the secondary rocks of that district ; 
VOL. VI. 
K 
