220 FRAGMENTS OF SCIENCE 



tion of minds, and to single out those who went by a 

 kind of instinct to the core of the question, from those 

 who erred in it, or who learnedly 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 conspicu- 

 ously than Sir Thomas Dick-Lauder. Two distinct men- 

 tal processes are involved in the treatment of such a ques- 

 tion. First, the faithful and sufiicient observation of the 

 data; and secondly, that higher mental process in which 

 the constructive 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 Roy 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 Eoy. The two shelves on the opposing sides of 

 the glen were at precisely the same level, and Dick-Lauder 

 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 1,170 feet above the 

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

 Ecy. 



From this col a lateral branch-valley— Glen Turrit — 

 iod down to Glen Roy. Our explorer descended from 



