163 FKAGMKNTS OP SCIENCE. 
The winds, robbed of their vapor, and charged with the 
heat set free by its precipitation, pursue their direction 
obliquely across Ireland; and the effect of the drying proc- 
ess rnav 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 vapor fell as snow, and the conse- 
quence was a system of glaciers which have left traces and 
evidences of the most impressive 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. 
What the Macgillicuddy Reeks did in Ireland, Ben Nevis 
and the adjacent mountains did, and continue to do, in 
Scotland. We had an example of this on the morning we 
quitted Roy Bridge. From the bridge westward rain fell 
copiously, and the roads were wet; but the precipitation 
ceased near Loch Laggan, whence eastward the roads were 
dry. Measured by the gauge, the rainfall at Fort William 
is 86 inches, while at Laggan it is only 46 inches annually. 
The difference between west and east is forcibly brought 
out by observations at the two ends of the Caledonian 
canal. Fort William at the southwestern end has, as just 
stated, 86 inches, while Ctilloden, at its northeastern end, 
has only 24. To the researches of that able and accom- 
plished meteorologist, Mr. Buchan, we are indebted for 
these and other data of the most interesting and valuable 
kind. 
Adhering to the facts now presented to us, it is not dif- 
ficult to restore in idea the process by which the glaciers of 
Lochaber were produced and the glens dammed by ice. 
When the cold of the glacial epoch began to invade the 
Scottish hills, the sun at the same time acting with suffi- 
ient power upon the tropical ocean, the vapors raised and 
i rifted on to these northern mountains were more and more 
converted into snow. This slid down the slopes, and from 
every valley, strath, and corry, south of Glen Spean, glaciers 
were poured into" that glen. The two great factors here 
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