vaults have been destroyed. But the same arrangement may be seen in the nave of the Cathedral of Durham where the original vaults remain. Their duration, however, is owing to the enormous massiveness of the construction rather than to the form of the support, which of itself is inadequate. Hence, though an important improvement was attempted in these instances, a satisfactory solution of the problem of the
FIG. 8.
buttress was not yet reached. The abutting arches of the Abbaye-aux-Dames and of Durham are indeed true flying buttresses, but they have not the character of such members in Gothic architecture, inasmuch as they are ill adjusted and are not externally apparent.
An advance of no less importance than this buttress development and an integral part of the growing system was the employment of independent arches, or ribs along the lines of the groins, projecting below the vault surfaces and in a measure sustaining them. Here, as in the case of
