THE PARALLEL ROADS OF GLEN ROY. 
377 
treatment. Firstly, the faithful and sufficient 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 obvi- 
ously in the same manner as the parallel roads of Glen Roy. 
The two shelves on the opposing sides of the glen were at pre- 
cisely 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 water- 
shed, 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. It 
is therefore 20 feet above the highest road in Glen Roy. 
From this col a lateral branch- valley led towards Glen 
Roy. Our explorer descended from the col to the highest road 
in that 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 reached a col, or watershed, looking into 
Glen Spey, and of precisely the same elevation as the highest 
parallel road of Glen Roy. 
He then dropped down to the lowest of these roads, and fol- 
lowed it towards the mouth of the glen. Its elevation above 
the bottom of the valley gradually increased ; not because it rose, 
but because it remained level while the valley sloped down- 
wards. He found this lowest road doubling round the hills at 
the mouth of Glen Roy, and running along the sides of the 
mountains which flank Glen Spean. He followed it eastward. 
The Spean Valley, like the others, gradually rose, and therefore 
gradually approached the road on the adjacent mountain-side. 
He came to Loch Laggan, the surface of which rose almost to 
the level of the road, and beyond the head of this lake he 
found, as in the other two cases, a col, or watershed, of exactly 
the same level as the single road in Glen Spean, which, it will 
be remembered, is a continuation of the lowest road in Glen 
Roy. 
Here we have a series of facts of obvious significance as 
regards the solution of this question. The effort of the mind 
to form a coherent image from such facts, might be compared 
with the effort of the eyes to cause the pictures of the stereo- 
