THE PARALLEL ROADS OF GLEN ROY. 271 



One of the proofs most convenient for reference, is a 

 great rounded rock by the roadside, 1,000 yards east of 

 the milestone marked three-quarters of a mile from 

 Eoy Bridge. Farther east other cases occur, and they 

 leave no doubt upon the mind that Glen Spean was at 

 one time rilled 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. 



4 But the great collecting ground of the glaciers 

 which dammed the glens and produced the parallel 

 d 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 Eeeks in the 

 south-west of Ireland. These mountains are, and were, 

 the first to encounter the south-western Atlantic winds, 

 and the precipitation, even at present, in the neighbour- 

 hood 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 con- 

 sequence 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 



