152 Proceedings of the Royal Society 
must have been confined to their own valleys. Though Mr 
James Geikie, in his valuable Memoir on the Glaciation of the 
Hebrides, assumes that there were such glaciers, he not only 
admits but maintains, that “the ice, with which the mountain 
valleys of Harris and the south were filled, had no share whatever 
in the glaciation of the northern part of the island , extending from 
the base of the mountains to the Butt, a distance of not less than 
35 or 40 miles. Where, then, did the ice come from which over- 
flowed this by far the largest part of the island % There is only 
one place whence it could have come, — the mainland .” Mr Geikie 
“contends that it was amongst” the “mountains of Wester Boss, 
fringing the borders of the Minch, that the glaciers which over- 
flowed the Lewis were nourished” (“Lond. Geol. Soc. Journal” for 
1873, p. 544). In his second Memoir, read in April 1878, Mr 
Geikie extends this theory to all the Outer Hebrides, maintaining 
“that the ivhole of the Long Island, from the Butt of Lewis to 
Barra Head , has been overflowed from the Minch by ice that moved 
outwards from the inner islands and the mainland ” (p. 861.) If 
this had been the case, one would have expected to find boulders 
chiefly on the east coasts of the Hebrides, and few on the west 
coasts. But the facts are entirely the other way. Not only is it 
on the hills of the west coasts that boulders most abound, and are 
largest in size ; but it is also on the slopes of the hills facing the 
Atlantic that these boulders are mostly seated. On the hills of the 
east coast next the Minch, the boulders are few and small, and they 
are chiefly on the west flanks of these hills, and therefore unlikely 
to have come across the Minch. 
XI. — OBAN AND ITS NEIGHBOURHOOD. 
In the immediate neighbourhood of this town, there are some 
facts of interest. 
(1.) There, as among the Hebrides, the smoothed rocks on the 
hills above Oban face the N.W. 
A little above the Craig- Ard Hotel, there is a fissure in the hills 
from 12 to 20 yards wide, and running due north and south for 200 
yards, at an elevation above the sea of about 180 feet. The fissure 
has apparently been occupied by a trap dyke, which, from the sea or 
other natural agencies, has decayed and disappeared. The walls of 
