§ I. It will be remembered that in the Sixth Chapter we paused (§ X.) at the point where the addition of brackets to the ordinary wall cornice would have converted it into a structure proper for sustaining a roof. Now the wall cornice was treated throughout our enquiry (compare Chapter VII. § V.) as the capital of the wall, and as forming, by its concentration, the capital of the shaft. But we must not reason _back_ from the capital to the cornice, and suppose that an extension of the principles of the capital to the whole length of the wall, will serve for the roof cornice; for all our conclusions respecting the capital were based on the supposition of its being adapted to carry considerable weight condensed on its abacus: but the roof cornice is, in most cases, required rather to project boldly than to carry weight; and arrangements are therefore to be adopted for it which will secure the projection of large surfaces without being calculated to resist extraordinary pressure. This object is obtained by the use of brackets at intervals, which are the peculiar distinction of the roof cornice. § II. Roof cornices are generally to be divided into two great families: the first and simplest, those which are composed merely by the projection of the edge of the roof mask over the wall, sustained by such brackets or spurs as may be necessary; the second, those which provide a walk round the edge of the roof, and which require, therefore, some stronger support, as well as a considerable mass of building above or beside the roof mask, and a parapet. These two families we shall consider in succession.