One or two courses of facing-stones having been placed in their beds and carefully pointed, a mass of mortar in a very fluid state was poured into the interior of the wall, and stones of any kind or shape that were of a convenient size were ‘puddled’ in amongst it. Whin-stones, as being most abundant in the district, are generally used for the filling. Course after course was added, and one mass of concrete imposed upon another, until the Wall reached the required height. When the whole was finished it formed a solid, compact mass, without any holes or crevices in the interior, and in a short time became as firm as the unhewn rock. In some parts of the line the mortar has been ‘hand-laid.’ The rubble of the interior having been first disposed in its place, the mortar has been laid upon it with a trowel. In this case the mortar never penetrates the interstices of the mass, and does not make such solid masonry as the method generally pursued. When, however, this plan is adopted, the rubble stones are often laid upon their edges in a slanting position; and when those of the next layer, as occasionally occurs, are made to lean in the opposite direction, we have the kind of [Illustration: herring-bone work] masonry represented in the adjoining diagram, which is appropriately called herring-bone work. The nearest approach to this that I have seen upon the line of the Wall is at Steel-rig, and Hare-hill. In Hodgson’s Northumberland[48] a section of the Wall on Walltown crag is given, exhibiting herring-bone masonry. In this instance the stones are disposed transversely to the Wall, at Steel-rig and Hare-hill they are disposed longitudinally; the latter method is the easier of the two.[49] On wavy ground the courses of the Wall follow the undulations of the surface, but on steep inclines the stones are laid parallel to the horizon. The Wall, in this case, must have been built up from the bottom of the defile, where also, in order the better to resist the superincumbent mass, it not unfrequently has a greater breadth than usual. As shewing that different sections of the Wall have been erected under distinct superintendents, it may occasionally be observed that, whilst on one slope of a ‘gap’ the stones are laid parallel to the horizon, on the other, differing little perhaps in inclination, they are laid even with the ground. [Sidenote: DURABILITY OF THE STRUCTURE.]