s then President of the Geological Society,
presented to that Society a memoir, in which the roads were discussed,
and pronounced to be the margins of lakes once embosomed in Glen Roy.
Why there should be three roads, or why the lakes should stand at
these particular levels, was left unexplained.

To Dr. MacCulloch succeeded a man, possibly not so learned as a
geologist, but obviously fitted by nature to grapple with her facts
and to put them in their proper setting. I refer to Sir Thomas
Dick-Lauder, who presented to the Royal Society of Edinburgh, on the
2nd 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 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 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 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 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 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