In the north aisle the first three bays and a portion of the fourth are Archbishop Roger's work, with the exception of the windows. The most notable feature, as usual, is the vaulting-shafts, which spring from above the string-course, and are in clusters of three. In each cluster the central shaft is even thicker than the others, and the capitals, which are carved with foliage of Norman character, share a common five-sided abacus, while the bases are circular and rest on radiating brackets smaller than themselves. These brackets, which are said to be unique, have square corners and are moulded, but only on the front, and their receding portion consists of a concave moulding containing a convex block. In the north-west corner there is but a single shaft, which rises from the bench-table, is banded at the string-course, and has a square-topped capital. The vaulting has wall-ribs, cross-springers, and groin-ribs, and is rather high-pitched. Upon the cross-springers the mouldings are a large keeled round having on either side a hollow between fillets, while the groin-ribs are moulded as in the Markenfield Chapel. In the westernmost bay the vault has shown signs of weakness (like so many other parts of the building adjacent to the ill-fated tower) and has been strengthened by a cross-arch with a half-arch abutting against it on the west side, both springing from corbels. The corbels are quite in Archbishop Roger's manner, and indicate that these strengthening arches, and therefore the blocking walls from which they spring, are of his period. Moreover, the abacus moulding of the first choir capital is continued as a string to the shaft (which it encircles) in the north-west corner. This string is interrupted by a rather inexplicable round arch in the west wall, and has also been broken by the obtrusion of the Perpendicular tower-pier, and by the blocked doorway which once opened from the Rood Screen. Below this doorway (adjoining which there is a recess in the obtruding masonry of the tower-pier) the wall shows traces of a gallery or staircase. On the north wall the string-course, which is rather undercut, is original as far as the end of the fourth bay, and marks the level to which the sills of the original windows descended in steps.[102] In the present windows, which descend to the old level, the mouldings of the arch are stopped upon a set-off and the jamb is left plain. [Illustration: TRANSITIONAL VAULTING CORBEL. CHOIR AISLE.]