[Illustration: FIG. 989.--Iona Cathedral. Caps of Piers of Choir and Crossing.] (Fig. 997). The lintels are composed of straight arches, supported by a remarkable shaft on the inside, which recalls the turned shafts of pre-Norman work. The access to the tower is by a small wheel staircase at the south-west angle of the crossing. The original doorway of the staircase entered from the nave, but, after the Reformation, the adjoining [Illustration: FIG. 990.--Iona Cathedral. Caps of Crossing, &c.] west arch of the crossing was built up, and a new door, with a small enclosing wall, was formed from the crossing into the wheel stair (as shown in the Plan). In the upper part of the tower are built recesses, as if meant for pigeons’ nests; and the upper floor in the roof of the [Illustration: FIG. 991.--Iona Cathedral. Carved Slab in St. Oran’s.] [Illustration: FIG. 992.--Iona Cathedral. Macfingone’s Slab in St. Oran’s.] tower is lighted with slits in the wall near the corners, except on the south side, where a larger opening is introduced and filled with tracery (see Fig. 984). The whole of the church has been roofed with timber, but is now quite open to the weather. The stone corbels intended to carry the principals of the roof still remain where the walls are complete (see Fig. 983). Externally, the most prominent features are the buttresses and base course (see Figs. 984 and 995). These exist round most of the south wall of the nave, part of the south transept, and the east end of the choir. The angle buttresses have the general form, with bead on angle and sloping table on top, of thirteenth century work, and the broad, sloping base has also a similar character. Several small intermediate buttresses are introduced, which are in many cases awkwardly situated as regards the windows, being kept below the window sills. The base course on the south side of the nave is set at a level several feet above that of the south transept (see Fig. 995). It is stopped suddenly before reaching the eastmost bay of the nave. The base also stops equally suddenly on the west wall of the south transept, a few feet from the south-west angle buttress. The base course and buttresses would thus seem, where they exist, to indicate a rebuilding of those portions of the walls, the portions left without a base course being possibly older. Although the forms of the base course and buttresses are of early design, there is no doubt but that they are late erections, and that the forms and design are revivals or imitations of older features. Their association with the late doorway of the nave and the late traceries of the choir and south transept sufficiently proves their comparatively recent construction. [Illustration: FIG. 993.--Iona Cathedral. Dog-tooth Ornaments on Slab.]