Now, a dome cut in this manner by four planes is not a very sightly form, and needs some embellishment (Fig. 334); but if a horizontal circle be drawn within it by means of a cornice resting on the crowns of the supporting arches, it assumes at once an agreeable form, and one which has been largely used both in Byzantine and in modern architecture (Fig. 335). My present purpose, however, suggests another mode of giving sightliness to the squared dome. The lines drawn on its surface may lie in vertical as easily as in horizontal planes, and by making such lines pass through the angles of the square, touching the dome throughout their length, and intersecting one another at its apex, we obtain a form not wholly unlike a square groined vault; the great differences being that the intersecting diagonals of a groined vault assume elliptical curves, whereas these are semicircles; that in the one they represent an actual angle, while in the other they are arbitrarily drawn on an unbroken surface; and that the ridges or crowns of the vault in one case are horizontal, while in the other they are raised and circular. This mode of vaulting, though frequent in some parts of France, is seldom found in this country. [Illustration: Fig. 336.--Goring Church, Oxfordshire.] There is, however, an instance of it in the vaulting beneath the tower of Goring Church, Oxfordshire. (Fig. 336). Though this is not really _groining_, but a disguised dome, there is a ready process by which it may be, and continually was, converted into genuine groining.