The exterior masonry of the Wall consists, on both sides, of carefully squared free-stone blocks[43]; the interior, of rubble of any description firmly imbedded in mortar. The character of the facing-stones is peculiar, yet pretty uniform. They are eight or nine inches thick, and ten or eleven broad; their length, which is perhaps their characteristic feature, not unfrequently amounts to twenty inches. The part of the stone exposed to the weather is cut across ‘the bait,’ so as to avoid its scaling off by the lines of stratification; the stone tapers towards the end which is set into the Wall, and has a form nearly resembling that of a wedge. The cut shews its usual form. Owing to the extent to which the stones are set into the Wall, the necessity of bonding tiles—so characteristic of Roman masonry in the south of England—is altogether superseded. There does not appear to have been a single tile used in any part of the Wall. Stones of the shape and size which have now been described were just those which could be most easily wrought in the quarry, most conveniently carried on the backs of the poor enslaved Britons to the Wall, and most easily fitted into their bed. The uniformity in their appearance is such as to enable us, after a little practice, at once to recognize them in the churches, castles, farm-buildings, and fences of the district through which the Wall runs. [Illustration: Junction of the west wall of Birdoswald with the Wall] [Sidenote: MASONRY OF THE STATIONS.] In Cumberland, the stones are rather larger than in the eastern portion of the line, a thickness of twelve inches not being uncommon, with a corresponding breadth. The blocks in the north face of the Wall, also, are not unfrequently larger than those in the south. The stones of which the walls of the stations are composed are smaller than those of the main Wall. Their average thickness is from five to seven inches, and their breadth from six to eight. The woodcut which is here introduced, depicts the junction of the west wall of the station of AMBOGLANNA with the Wall, and well displays the different character of the stones used in two erections. As already observed, the stations appear to have been built before the Wall, and as the necessity of the case required that they should be run up as quickly as possible, a smaller class of stone was allowed to pass muster here than was used in the Wall. The workmanship also is of inferior quality. [Sidenote: THE TOOLING OF THE STONES.] [Illustration: diamond broaching]