THE PAKALLEL ROADS OF GLEN ROY. 207 



occupied themselves with its analogies, adjuncts, and 

 details. There is no man, in my opinion, connected 

 with the history of the subject, who has shown, in 

 relation to it, this spirit of penetration, this force of 

 scientific insight, more conspicuously than Sir Thomas 

 Dick-Lauder. Two distinct mental processes are in- 

 volved in the treatment of such a question. Firstly, 

 the faithful and sufficient observation of the data ; and 

 secondly, that higher mental process in which the con- 

 structive imagination comes into play, connecting the 

 separate facts of observation with their common cause, 

 and weaving them into an organic whole. In neither 

 of these requirements did Sir Thomas Dick-Lauder fail. 



Adjacent to Glen Eoy is a valley called Glen Gluoy, 

 along the sides of which ran a single shelf, or terrace, 

 formed obviously in the same manner as the parallel 

 roads of Glen Roy. The two shelves on the opposing 

 sides of the glen were at precisely the same level, and 

 Dick-Laudor wished to see whether, and how, they 

 became united at the head of the glen. He followed 

 the shelves into the recesses of the mountains. The 

 bottom of the valley, as it rose, came ever nearer to 

 them, until finally, at the head of Glen Gluoy, he 

 reached a col, or watershed, of precisely the same 

 elevation as the road which swept round the glen. 



The correct height of this col is 1170 feet above 

 the sea ; that is to say, 20 feet above the highest road 

 in Glen Roy. 



From this col a lateral branch-valley Glen Turrit 

 led down to Glen Roy. Our explorer descended from 

 the col to the highest road of the latter glen, and 

 pursued it exactly as he had pursued the road in Glen 

 Gluoy. For a time it belted the mountain sides at a 

 considerable height above the bottom of the valley ; but 

 this rose as he proceeded, coming ever nearer to the 



