On turning to the south aisle the same impression is received. The circular and stunted form of the piers, with their remarkable bases and the peculiar form of their enriched capitals (see Figs. 989 and 990), strike one at once with the idea that they belong to a late and rather debased epoch. The insertion of the clerestory windows over the piers (an arrangement which is also met with at the nunnery) is bad construction, and led to the adoption of the low and poor flying buttresses (which are evidently an afterthought) as a means of steadying the main structure. [Illustration: FIG. 999.--Iona Cathedral. Window in North Side of Choir, East End of South Aisle, &c.] The north side of the choir is so peculiar in its arrangements that little can be gathered from it with regard to dates. If the pillar and [Illustration: FIG. 1000.--Iona Cathedral. Section of Arch Mouldings.] arches of the high chapel over the sacristy (see Fig. 983) are of thirteenth century work, as their ornamentation would at first sight lead one to suppose, they might possibly have been re-erected in their present position; but they are more likely to have been made in imitation of thirteenth century work, and built here at a late period. The section of the arch mouldings (Fig. 1000) is almost identical with that of the chapter house arches, which (as will be afterwards explained) are almost undoubtedly of very late date. These arches gave a view of the altar from a high chapel, which, as will be pointed out, was perhaps connected with the library or dormitory. The chapel has been added to the church, and the walls are not bonded into the choir. The decoration of the upper portion, with its imitation dog-tooth or nail-head ornament round a straight sided arch (Fig. 1001), shows that it is of very late date. [Illustration: FIG. 1001.--Iona Cathedral. Interior of Sacristy and Chapel above.] This structure appears to occupy the position of the original north aisle, which at one time extended (or was contemplated) the full length from the presbytery to the north transept. The water table over the old aisle roof runs the whole length, and has a sloping water table where the roof abutted against the north transept. The old corbels to receive the timbers of the aisle roof also still exist. The aisle would no doubt block one of the Norman transept windows, but that could not be avoided. The doorway from the choir to the sacristy (see Fig. 987) is a very fine feature, and one would be inclined to consider it somewhat earlier than the other parts of the sacristy and upper chapel. Possibly it may have formed an access to the aisle before the upper chapel was raised to its present position.