involved the alteration of the nave and aisle piers, so that the
slight vaulting shafts of finer stone might be inserted in the older
masonry. The lower part of each of the piers of the nave arcade on the
side towards the centre of the church was re-faced with the same
material, and smaller shafts of Purbeck marble were introduced upon
the piers, replacing probably the heavy ones of an earlier date. These
shafts formed the support to a more delicate moulded member, which was
now substituted for the original and very simple outer order of the
original arch. A string-course of Purbeck marble was inserted as a
line of separation between the nave arcade and the triforium, and also
between the triforium and clerestory. The triforium itself remained as
it had been before 1186; but the clerestory was dressed again, so that
it obtained quite a new character. It was re-faced with the
fine-grained stone, and the slight shafts which supported the
clerestory arcades were provided with Purbeck capitals and bases. This
arcading itself was also changed from its earlier type. The central
arch was still made round in form, but those on either side of it were
each pointed, and all were more finely moulded than before. Above this
point rises the new stone vault, which is carried upon a framework of
strong transverse and diagonal ribs. Between these the shell, or
filling, which formed the surface of the vault, is of chalk, roughly
cut and irregularly laid; above this was placed a thick coat of
concrete.

Some flying-buttresses were built now in order to meet the thrust
exerted by the new arched vault of the nave. These were constructed in
two series, one being concealed under the sloping roof over the
triforium and acting in place of the earlier round-arched abutment.
Its supports were provided at the points where the transverse and
diagonal arches of the nave vault began to spring away from the