The clerestory windows appear to have been built before the vaulting was arranged, seeing that they are placed very low in the red part of the wall. But when the vaulting was designed, it was found desirable to raise the walls so as to get proper height for the arches. This was done in whitish stone, and shows distinctly on the exterior, as above stated. A row of Norman corbels on the north side marks the original height of the clerestory wall. These corbels appear to have been moved from the Norman part of the choir, and inserted in their present position when the choir [Illustration: FIG. 240.--Kirkwall Cathedral. East End of South Aisle of Choir.] was lengthened. A few corbels remain in their original position on the south side of the choir. The vaulting of the old part of the choir was also altered at the time when the new vaulting was built. The design of the extended choir aisles corresponds with that of the choir, and is very beautiful, though somewhat foreign in character. (See Fig. 240.) The ribs of the choir and aisle vaults have all bold sections of first pointed form. The east end of the cathedral is of this period. The great east window (see Fig. 234) fills the whole space available. This window, including its mouldings, measures (according to Sir H. Dryden) 37 feet 2½ inches by 16 feet 7½ inches. It is well designed, and has side shafts of first pointed form, while the tracery is perhaps a little more advanced. The great rose in the arch, which expands over the whole of the mullions and arches of the tracery, is (as pointed out by Sir H. Dryden) quite peculiar and unique. The three-arched recesses under the east window indicate that the altar stood free from the wall. On the exterior, the junction of the new buttresses with the old Norman ones is distinctly seen. (See Fig. 230.) The former are of red freestone, and project with water tables in stages, while the latter are flat and shallow. The side windows have plain splays in the jambs, and have no caps, one round-headed window on the south side has two lights, and a doorway is formed beneath it. A large base course goes round the choir and marks the new work. It is also continued round the transept chapels at a lower level. Besides the raising of the clerestory walls, above referred to, the aisle walls of the choir have also been raised. On the north side (see Fig. 229) this is effected by leaving the old parapet and building a second parapet above it, while on the south side (see Fig. 230) the old parapet has been removed and the wall heightened with red ashlar, and a new parapet placed at the higher level. Several square windows have been cut in the lower part of the north choir wall. These are modern, and are not shown in the sketch. Their object is to admit light under a gallery which has been inserted in the north aisle. The floor of the choir has been raised, and is now reached by several steps from the