THK PA HALLEL ROADS OF GLEN ROT. 15? 



learned as a geologist, but obviously fitted by nature to 

 grapple with her facts and to put them in their proper set- 

 ting. I refer to Sir Thomas Dick-Lauder, who presented 

 to the Royal Society of Edinburgh, on the 2d of March, 

 1818, his'paper on the Parallel Roads of Glen Roy. In 

 looking over the literature of this subject, which is now 

 copious, it is interesting to observe the differentiation 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 anal- 

 ogies, 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 

 involved 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 constructive im- 

 agination 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, 

 farmed 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-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 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 highest shelf, until finally he 



