220 FEAGMENTS OF SCIENCE. 



descending from the Beeks, 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 Eeeks 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 Koy 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 ob- 

 servations at the two ends of the Caledonian Canal. 

 Fort William at the south-western end has, as just 

 stated, 86 inches, while Culloden, at its north-eastern 

 end, has only 24. To the researches of that able and 

 accomplished meteorologist, Mr. Buchan, w r e are in- 

 debted for these and other data of the most interesting 

 and valuable kind. 



Adhering to the facts now presented to us, it is not 

 difficult 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 sufficient power upon the tropical 

 ocean, the vapours raised and drifted on to these north- 

 ern mountains were more and more converted into 

 snow. This slid down the slopes, and from every val- 

 ley, strath, and corry, south of Glen Spean, glaciers 

 were poured into that glen. The two great factors 

 here brought into play are the nutrition of the glaciers 



