168 FRAGMENTS OF SCIENCE. 



The winds, robbed of their vapor, and charged vvitli the 

 heat set free by its precipitation, pursue their direction 

 obliquely across Ireland; and the effect of the drying proc- 

 ess 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 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 Culloden, 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- 

 cient power upon the tropical ocean, the vapors raised and 

 drifted 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 



