in character for their time. In them the principle of interpenetrating round vaults, the forms of whose arches are necessarily determined by the forms of their surfaces, gives place, in a measure, to that of an independent system of arches which command the forms of the vaults. The diagram (Fig. 68) will explain their character. It will be seen that the pier arch and the transverse arches are all pointed, and that the diagonals are semicircular. It will be seen, too, that the crowns of the diagonals reach to a considerably higher level than those of the transverse and longitudinal ribs, and that consequently the vaults are, like early French vaults, considerably domed, as in the section a, b. The ribs are much less developed in section than the ribs of the vaults of St. Denis—the diagonal rib, c, being so shallow as apparently to add little strength to the groins, and the transverse ribs, d, being plain square-edged arches of little projection.
It is evident that the central aisle was originally designed for vaulting with quadripartite vaults, since a group of three vaulting shafts rises from each pier capital. These shafts clearly belong to the original construction, as may be seen (Fig. 69) by their perfect adjustment with the imposts of the great arcade, and by their being banded by the original triforium string. They emphasise the divisions of the bays and give a continuity to the vaulting system, like that which is characteristic of Gothic design in France. Another feature with a likeness to French design is the wall which shuts off the triforium arcade, screening from view the timber roofs over the aisle vaults. This arrangement was not followed in the subsequent pointed architecture of England, where the timbers of the aisle roofs are generally visible from the pavement of the central aisle. In all other respects the structure is strictly Norman-Romanesque in character. The great arcades are supported by ponderous round columns, the spaces between them being not quite equal in extent to two of their diameters; hence the massiveness of the construction is in striking contrast to the comparative lightness of St. Denis. It may be noticed in passing that the hood-moulding over the pier archivolts is an early instance of a feature that afterwards became practically constant in the pointed architecture of England. But this feature, whose
