THE PARALLEL ROADS OF GLEN ROY. 211 



ner indicated, the single road of Glen Gluoy and the 

 highest and lowest roads of Glen Roy would be ex- 

 plained in a satisfactory manner. 



To account for the second or middle road of Glen 

 Roy, Sir Thomas Dick-Lauder invoked a new agency. 

 He supposed that at a certain point in the breaking 

 down or waste of his dam, a halt occurred, the barrier 

 holding its ground at a particular level sufficiently long 

 to dam a lake rising to the height of, and forming the 

 second road. This point of weakness was at once de- 

 tected by Mr. Darwin, and adduced by him as proving 

 that the levels of the cols did not constitute an essen- 

 tial feature in the phenomena of the parallel roads. 

 Though not destroyed, Sir Thomas Dick-Lauder's the- 

 ory was seriously shaken by this argument, and it be- 

 came a point of capital importance, if the facts per- 

 mitted, to remove such source of weakness. This was 

 done in 1847 by Mr. David Milne, now Mr. Milne- 

 Home. On walking up Glen Roy from Roy Bridge, 

 we pass the mouth of a lateral glen, called Glen Glas- 

 ter, running eastward from Glen Roy. There is noth- 

 ing in this lateral glen to attract attention, or to sug- 

 gest that it could have any conspicuous influence in 

 the production of the parallel roads. Hence, probably, 

 the failure of Sir Thomas Dick-Lauder to notice it. 

 But Mr. Milne-Home entered this glen, on the north- 

 ern side of which the middle and lowest roads are fairly 

 shown. The principal stream running through the 

 glen turns at a certain point northwards and loses itself 

 among hills too high to offer any outlet. But another 

 branch of the glen turns to the south-east; and, fol- 

 lowing up this branch, Mr. Milne-Home reached a col, 

 or water-shed, of the precise level of the second Glen 

 Roy road. When the barrier blocking the glens had 

 been so far removed as to open this col, the water in 



