The south-western spire of the west front is also of this period, probably a little earlier in date than the lantern. This is of very remarkable beauty, and very much more elegant than the corresponding spire to the north. The triangular section of the pinnacles at the base of the spire, the crockets with which they are enriched, and the open canopies around, combine to produce a most graceful feature. To the latter years of this century may be assigned the central porch, with room above, inserted between the two middle piers of the west front. Some regard this as a blemish; others as a distinct improvement. One party maintains[13] that it is "an unsightly encumbrance, in its present position, seeing that it violates the uniformity of design displayed in the west front"; the other party contends[14] that it is "an extremely judicious insertion, and that it really does, just as if it was intended for that purpose only, restore its proper dignity to the central arch of the facade." It was most likely built as a matter of structural necessity, to secure the stability of the front. From a settlement of the foundations, or from a failure of the two central piers, or from the great weight of masonry above, for there are no western buttresses, the whole must have been in danger of falling. Mr Paley points out that the "construction of this elegant little edifice is extremely scientific, especially in the manner in which the thrust is distributed through the medium of the side turrets so as to fall upon the buttresses in front. These turrets being erected against one side of the triangular columns, on the right and the left hand, support them in two directions at once, viz., from collapsing towards each other, and from falling forward. The latter pressure is thrown wholly upon the buttresses in front, which project seven feet beyond the base of the great pillars." The room above is called by Browne Willis the Consistory Court. It is now used for the Minster Library. [Illustration: Map, 1610.] The alterations and additions during the Perpendicular period can be detected at a glance. All the Norman windows which had remained unaltered were now filled with tracery, not of particularly good design; the great west window and the others in the west wall were similarly treated; the conical tops to the transeptal corner turrets were altered into battlements; the screens in the transepts were made, and, probably, the groined wooden ceiling in the choir. The most important addition was the New Building at the east end of the choir. This is often erroneously called the Lady Chapel; but when this edifice was erected the Lady Chapel to the east of the north transept, and for more than 150 years afterwards, was still standing. The new building was begun by Abbot Ashton (1438-1471), and finished by Abbot Kirton (1496-1528). The rebus of each of these abbots can be seen in its decorations: an ash growing out of a tun or barrel, and a church or kirk with a tun.