384 
POPULAR SCIENCE REVIEW. 
two roads as far as they were visible. We reached the col dis- 
covered by Mr. Milne-Home, and which stands at the level of 
the middle road of Glen Roy. Thence we crossed southwards 
over the mountain Greag Dhubh , and examined the erratic 
blocks upon its sides, and the ridges and mounds of moraine 
matter which cumber the lower flanks of the mountain. The 
observations of Mr. Jamieson upon this region, including the 
mouth of Glen Trieg, are in the highest degree interesting. 
We entered Glen Spean, and continued a search begun on the 
evening of our arrival at Roy Bridge — the search, namely, for 
glacier polishings and markings. We did not find them copious, 
but they are indubitable. One of the proofs most convenient for 
reference is a great rounded rock by the road side, 1 ,000 yards 
east of the milestone marked three-quarters of a mile from Roy 
Bridge. Farther east other cases occur, and they leave no 
doubt upon the mind that Glen Spean was at one time filled by 
a great glacier. To the disciplined eye the aspect of the 
mountains is perfectly conclusive on this point; and in no 
position can the observer more readily and thoroughly convince 
himself of this than at the head of Glen Glaster. The dominant 
hills here are all intensely glaciated. 
But the great collecting ground of the glaciers which dammed 
the glens and produced the parallel roads were the mountains 
south and west of Glen Spean. The monarch of these is Ben 
Nevis, 4,370 feet high. The position of Ben Nevis and his 
colleagues, in reference to the vapour-laden winds of the 
Atlantic, is a point of the first importance. It is exactly similar 
to that of Carrantual and the Macgillicuddy Reeks in the south- 
west of Ireland. These mountains are, and were, the first to 
encounter the south-western Atlantic winds, and the precipita- 
tion, even at present, in the neighbourhood of Killarney, is 
enormous. The winds, robbed of their vapour, and charged 
with the heat set free by its precipitation, pursue their direction 
obliquely across Ireland ; and the effect of the drying process 
may be understood by comparing the rainfall at Cahirciveen 
with that at Portarlington. As found by Dr. Lloyd, the ratio 
is as 59 to 21 — fifty-nine inches annually at Cahirciveen to 
twenty-one at Portarlington. During the glacial epoch this 
vapour fell as snow, and the consequence was a system of 
glaciers which have left traces and evidences of the most im- 
pressive character in the region of the Killarney Lakes. I have 
referred in other places to the great glacier which, descending 
from the Reeks, moved through the Black Valley, took 
possession of the lake-basins, and left its traces on every rock 
and island emergent from the waters of the upper lake. They 
are all conspicuously glaciated. Not in Switzerland itself do 
we find clearer traces of ancient glacier action. 
