[Illustration: Plate III. ARCH MASONRY.] The added projections at _x x_, in _d_, are called CUSPS, and they are the very soul and life of the best northern Gothic; yet never thoroughly understood nor found in perfection, except in Italy, the northern builders working often, even in the best times, with the vulgar form at _a_. The form at _b_ is rarely found in the north: its perfection is in the Lombardic Gothic; and branches of it, good and bad according to their use, occur in Saracenic work. § VIII. The true and perfect cusp is single only. But it was probably invented (by the Arabs?) not as a constructive, but a decorative feature, in pure fantasy; and in early northern work it is only the application to the arch of the foliation, so called, of penetrated spaces in stone surfaces, already enough explained in the "Seven Lamps," Chap. III., p. 85 _et seq._ It is degraded in dignity, and loses its usefulness, exactly in proportion to its multiplication on the arch. In later architecture, especially English Tudor, it is sunk into dotage, and becomes a simple excrescence, a bit of stone pinched up out of the arch, as a cook pinches the paste at the edge of a pie. § IX. The depth and place of the cusp, that is to say, its exact application to the shoulder of the curve of the arch, varies with the direction of the weight to be sustained. I have spent more than a month, and that in hard work too, in merely trying to get the forms of cusps into perfect order: whereby the reader may guess that I have not space to go into the subject now; but I shall hereafter give a few of the leading and most perfect examples, with their measures and masonry. § X. The reader now understands all that he need about the shell of the arch, considered as an united piece of stone. He has next to consider the shape of the voussoirs. This, as much as is required, he will be able best to comprehend by a few examples; by which I shall be able also to illustrate, or rather which will force me to illustrate, some of the methods of Mont-Cenisian masonry, which were to be the second part of our subject. § XI. 1 and 2, Plate IV., are two cornices; 1 from St. Antonio, Padua; 2, from the Cathedral of Sens. I want them for cornices; but I have put them in this plate because, though their arches are filled up behind, and are in fact mere blocks of stone with arches cut into their faces, they illustrate the constant masonry of small arches, both in Italian and Northern Romanesque, but especially Italian, each arch being cut out of its own proper block of stone: this is Mont-Cenisian enough, on a small scale. 3 is a window from Carnarvon Castle, and very primitive and interesting in manner,--one of its arches being of one stone, the other of two. And here we have an instance of a form of arch which would be barbarous enough on a large scale, and of many pieces; but quaint and agreeable thus massively built.