th map and plates), by Sir Thomas Lauder Dick, "Trans.
R. Soc. Edinb." Volume IX., page 1, 1823.) procured the assistance of an
engineer for this purpose, but owing to the want of a true ground-plan
it was impossible to ascertain their exact curvature, which, as far as
could be estimated, appeared equal to that of the surface of the sea.
Considering how very rarely the sea has left narrow and well-defined
marks of its action at any considerable height on the land, and more
especially considering the remarkable observations by M. Bravais (518/5.
"On the Lines of Ancient Level of the Sea in Finmark," by M. A. Bravais,
translated from "Voyages de la Commission Scientifique du Nord, etc.";
"Quart. Journ. Geol. Soc." Volume I., page 534, 1845.) on the ancient
sea-beaches of Scandinavia, showing the they are not strictly parallel
to each other, and that the movement has been greater nearer the
mountains than on the coast, it appears highly desirable that the roads
of Glen Roy should be examined with the utmost care during the execution
of the Ordnance Survey of Scotland. The best instruments and the most
accurate measurements being necessary for this end almost precludes the
hope of its being ever undertaken by private individuals; but by the
means at the disposal of the Ordnance, measurements would be easily made
even more accurate than those of M. Bravais. It would be desirable to
take two lines of the greatest possible length in the district, and at
nearly right angles to each other, and to level from the beach at one
extremity to that at the other, so that it might be ascertained whether
the curvature does exactly correspond with that of the globe, or, if
not, what is the direction of the line of greatest elevation. Much
attention would be requisite in fixing on either the upper or lower edge
of the ancient beaches as the standard of measurement, and in rendering
this line conspicuous. The heights of the three roads, one above
the other and above the level of the sea, ought to be accurately
ascertained. Mr. Darwin observed one short beach-line north of Glen Roy,
and he has indicated, on the authority of Sir David Brewster, others
in the valley of the Spey. If these could be accurately connected, by
careful measurements of their absolute heights or by levelling, with
those of Glen Roy, it would make a most valuable addition to our
knowledge on this subject. Although the observations here specified
would probably be laborious