real cohesion, as the smoked surfaces of the faces of junction proved, that the expansion and contraction of the limestone blocks by change of temperature (when fires had been lighted) had completely severed the mortar union between them and the wall.
The whole fabric stood, therefore, ready to be overthrown by any force competent simply to overset it upon its base, in a southerly direction. The Figs. b, &c., 175 show that the whole mass had canted over to the south, turning upon the front lower arrises, of the side or jamb blocks, the latter carrying the lintel, for a short portion of the arc of descent, upon their upper ends. The brickwork above, owing to the position of its centre of gravity with reference to its base upon the lintel, when freed from the face of the wall, and the small velocity with which the mass must have been overturned, had fallen on the central space of floor, between the three stone blocks. The lintel block, had landed upon the floor, close to the upper ends of the side jambs, and had then, partly by the direction of descent, partly by the effects of its own elasticity, and that of the beton and tile floor, either fallen over, or slided (or both), forward a few inches further south, having been broken in two by the stroke on the floor, at a soft joint in the limestone. The two side jambs, from their peculiar form in horizontal section, and their setting, at an oblique angle to the face of the wall, had canted round the inner angles of the front arrises at their bases; and in their descent, the moment they got free from the lintel, had turned round partially, upon an axis parallel each to its own length, and lay, after thus rotating through about 90° each, with its east face uppermost, both having rotated towards the west; so that when fallen, was re-
