[Enclosure]⁶

The Parallel Roads of Glen Roy in Scotland have been the object of repeated examination, but they have never hitherto been levelled with sufficient accuracy. Sir T. Lauder Dick⁷ 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 & well-defined marks of its action at any considerable height on the land, & more especially considering the remarkable observations by M. Bravais⁸ on the ancient sea-beaches of Scandinavia, shewing that they are not strictly parallel to each other & 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 & 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, & in rendering this line conspicuous.— The heights of the three roads, one above the other & above the level of the sea, ought to be accurately ascertained. M^r Darwin observed one short beach-line North of Glen Roy & 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, yet considering how rarely such evidence is afforded in any quarter of the world, it cannot be doubted that one of the most important problems in geology,—namely the exact manner in which the crust of the earth rises in mass,—would be much elucidated, & a great service done to Geological Science.