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 reached a
col, or watershed, looking into Glen Spey, and of precisely the same
elevation as the highest road of Glen Roy.

He then dropped down to the lowest of these roads, and followed it
towards the mouth of the glen. Its elevation above the bottom of the
valley gradually increased; not because the shelf rose, but because it
remained level while the valley sloped downwards. 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 eastwards.

PARALLEL ROADS OF GLEN ROY.

After a Sketch by Sir Thomas Dick-Lauder.

The bottom of 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, at Makul, 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 problem. The effort of the mind to form a coherent
image from such facts may be compared with the effort of the eyes to
cause the pictures of a stereoscope to coalesce. For a time we
exercise a certain strain, the object remaining vague and indistinct.
Suddenly its various parts seem to run together, the object starting
forth in clear and definite relief. Such, I take it, was the effect
of his ponderings upon the mind of Sir Thomas Dick-Lauder. His
solution was this: Taking all their features into account, he was
convinced that water only could have produced the terraces. But how
had the water been collected? He saw clearly that, supposing the
mouth of Glen Gluoy to be stopped by a barrier sufficiently high, if
the waters from the mountains flanking the glen were allowed to
collect, they would form behind the barrier a lake, the surface of
which would gradually rise until it reached the level of the col at
the head of the glen. The rising would then cease; the superfluou