The lower church was formerly well lighted with numerous lancet windows, but, unfortunately, these have been filled, within the last thirty years, with dark-coloured glass, so that, without the aid of lamps, this almost unrivalled specimen of mediæval architecture is obscured from view. Only those whose memory goes back to before the above time can form a proper idea of the beauty and purity of its details. [Illustration: FIG. 586.--St. Mungo’s Cathedral. Eastern Aisle and Chapels, looking North.] There is a well about 18 feet deep, built with ashlar, at the east end of the south wall, and near it an altar tomb to one of the family of the Colquhouns of Luss, whose arms it bears. The well may have contributed to the weakness of this part of the edifice; but although the upper part of the building is as much as 18 inches off the plumb, there is no appearance of any settlement at the base. The wall seems to have suffered from a thrust outwards while in course of erection, as the upper story is set back from the lower portion, which is off the plumb. The south doorway of the lower church (Fig. 585) is a very simple and beautiful design, and forms a porch projecting as far as the buttresses. It has a groined ceiling covered with a sloping stone roof. Immediately opposite the south doorway there is a north entrance to the lower church, which has a moulded pointed arch head, but no porch. [Illustration: FIG. 587.--St. Mungo’s Cathedral. Section of Piers.] The interior of the choir is a noble specimen of first pointed design. A striking and unusual feature of the plan is the ambulatory aisle which runs round the east end (see Fig. 570), having four chapels beyond it to the east, as above mentioned. These chapels are not divided, like those in the lower church, by walls, but are quite open, and the pillars stand free. The view (Fig. 586) shows that the pillars are slender and clustered, with dog-tooth mouldings in the hollows. Their section is shown in Fig. 587. The caps are rounded and moulded, while those of the wall shafts are carved with foliage. Fig. 588 shows the south-east bay of the east end. The piscina seen in the south-east angle has the drain carried direct to the outside, and is not carried down to the ground, as usual. The vaulting here is of later date than the rest of the work, as is apparent from the [Illustration: FIG. 588.--St. Mungo’s Cathedral. South Chapel at East End.] [Illustration: FIG. 589.--St. Mungo’s Cathedral. North-East Angle of Choir.] sections of the ribs. As the vaulting was, doubtless, much dislocated by the disturbance which has taken place at the south-east corner, it may have been rebuilt; or, as Mr. Watson points out, it may have been delayed till after the vaulting of the lower church was completed. [Illustration: FIG. 590.--St. Mungo’s Cathedral. South Doorway of Nave.] The main arcade is carried round the east end of the choir (Fig. 589).