One more point is worthy of remark--the treatment, namely, of the angles of buildings. These were almost always marked either by a roll-moulding or by a succession of nook-shafts, sometimes extravagantly chevroned or otherwise ornamented. This, when done simply, was always satisfactory, but, in its later and more elaborate form, was, I think, as unsatisfactory. The delicate rounding off of the angles of walls was a point not unthought of in England. In the thirteenth century a nook-shaft was the common contrivance; in the fourteenth, a chamfer; and in the fifteenth men reverted entirely to the square form. Here, however, there is a great and very interesting variety in this apparently simple feature. The most satisfactory plan of all is where a quarter-circle forms the angle, and is finished with a small incision in the form of a V on either side, as it unites simplicity with strength of construction and softness of contour, and does not force itself too prominently upon our observation; and, next to this, the most satisfactory form is where, instead of the moulding being round, it is pointed at the angle. The twisted shafts of the upper stage of the Ducal Palace, and the triple and chevroned shafts of the Ca’ d’Oro, are not improvements upon the refinement of the earlier mode. I have already spoken of the exquisite beauty of the inlaid marbles in S. Mark’s; nothing can be better than their effect, and nothing seems more wonderful than that they should not have been used more frequently in later buildings. I was, perhaps, a little disappointed in not finding, as I had expected, the marble arranged generally in geometrical patterns; but this is quite the exception; and one sees only, in a medallion here and there, the exquisite beauty which their arrangement in this way may produce. As a rule the walls are faced with thin slabs of marble, each of the size in which it came to hand, sawn into as many slices as its substance would allow, and then riveted to the walls and held in place securely by projecting thin lines of stonework built into the wall, and cut with indented or billet ornaments along their edges. There is, however, a degree of real as well as apparent weakness which is not at all satisfactory in this system of incrustation, and I thought how much more noble such work might well become, were it to be inlaid only where no strong work was required to be done--as, e.g., in spandrels of arches,[57] or within arches--and not as here to the concealment of every one of the necessary constructional features. It is to be observed, however, that the slabs of marble are generally higher than they are wide, so as at once to destroy any thought of their being really constructional.