In the clerestory walls of the choir (Fig. 230) great changes are observable. The lower part of the wall, which contains the windows, is built with dark red freestone, while the upper part is of whitish freestone, clearly showing that the clerestory has been raised, together with the parapet. The old line of the eaves is further apparent from the row of Norman corbels which marks the original level before the wall was raised. These corbels are specially visible on the north side of the choir clerestory, but a few also remain on the south side. The new corbel table under the parapet consists of corbels of well-known first pointed form. Turning to the nave, it will be observed (see Fig. 228) that the whole of the clerestory wall (except the two westmost bays) is built with whitish freestone, while the windows are of small size and are pointed. The clerestory of the nave thus corresponds with the raised part of that of the choir in the stone used, but differs from it in the windows, which are narrow. The parapet and corbel table of this part of the building, and indeed throughout nearly the whole structure, are similar to those of the choir, and in the later work have evidently been copied from the earlier ones. In the transept the alterations are plainly seen in the heightened portions of the north and south gables (see Figs. 229 and 230), which are carried out with red freestone ashlar, and in the details of the upper window of the north transept and the rose window of the south transept, which are all of a later character than the Norman work of the lower parts of the transept. In the south transept there may also be noticed a pointed doorway (Fig. 231) built with party-coloured stones, which has been inserted by cutting into the old Norman arcade of the interior. This is distinctly seen in the elevation of the interior (Fig. 232). Probably, when this was done, the older doorway which existed at the east end of the nave south aisle, in the usual position for access to the cloister, was built up, the intention of having a cloister being abandoned. Some traces of the impost of the arch of the original doorway, carved with Norman enrichments, may still be seen. [Illustration: FIG. 226.--Kirkwall Cathedral. Longitudinal Section from West to East.] The two westmost bays of the nave (see Fig. 228) are built almost entirely from top to bottom with red freestone, having a slight admixture of white stone. This indicates a considerable alteration, and it will be found that these two bays were rebuilt at a late period, when a new west [Illustration: FIG. 227.--Kirkwall Cathedral. Section through Transept from North to South.] [Illustration: FIG. 228.--Kirkwall Cathedral. North Elevation.]