§ III. But in the decoration of these several parts, certain minor conditions of ornament occur which are of perfectly general application. For instance, whether, in archivolts, jambs, or buttresses, or in square piers, or at the extremity of the entire building, we necessarily have the awkward (moral or architectural) feature, the _corner_. How to turn a corner gracefully becomes, therefore, a perfectly general question; to be examined without reference to any particular part of the edifice. § IV. Again, the furrows and ridges by which bars of parallel light and shade are obtained, whether these are employed in arches, or jambs, or bases, or cornices, must of necessity present one or more of six forms: square projection, _a_ (Fig. LI.), or square recess, _b_, sharp projection, _c_, or sharp recess, _d_, curved projection, _e_, or curved recess, _f_. What odd curves the projection or recess may assume, or how these different conditions may be mixed and run into one another, is not our present business. We note only the six distinct kinds or types. Now, when these ridges or furrows are on a small scale they often themselves constitute all the ornament required for larger features, and are left smooth cut; but on a very large scale they are apt to become insipid, and they require a sub-ornament of their own, the consideration of which is, of course, in great part, general, and irrespective of the place held by the mouldings in the building itself: which consideration I think we had better undertake first of all. § V. But before we come to particular examination of these minor forms, let us see how far we can simplify it. Look back to Fig. LI., above. There are distinguished in it six forms of moulding. Of these, _c_ is nothing but a small corner; but, for convenience sake, it is better to call it an edge, and to consider its decoration together with that of the member _a_, which is called a fillet; while _e_, which I shall call a roll (because I do not choose to assume that it shall be only of the semicircular section here given), is also best considered together with its relative recess, _f_; and because the shape of a recess is of no great consequence, I shall class all the three recesses together, and we shall thus have only three subjects for separate consideration:-- 1. The Angle. 2. The Edge and Fillet. 3. The Roll and Recess.