Note 49 — PART II. A GENERAL DESCRIPTION OF THE LINE OF THE WALL.

In some parts of the line, the joints of the Wall are at present filled with earthy matter instead of mortar, and it is the opinion of some authorities, and amongst them, the eminent architect and intelligent antiquary, Mr. Dobson, of Newcastle-upon-Tyne, that in these places, clay has been originally substituted for mortar. Very loath to suppose that the original builders of the Wall would leave any portion of it in so unsatisfactory a state, I have been in the habit of accounting for the apparent absence of mortar in the following way:—The upper part of the structure having been overthrown by a ruthless enemy, and the lower parts covered with the fallen rubbish, the whole heap would speedily become coated with vegetation. Roman mortar, with all its tenacity, would not be able to resist the powers of vitality; and the constant demands of the ferns and the foxgloves would, in the course of time, abstract the whole of the lime. The roots of the plants, by whose agency the work of abstraction had proceeded, yielding in due time to the process of decay, would themselves, in the form of vegetable earth, supply the place of the lime which they had withdrawn.