ridge level of the old one, gaining a floor without raising the walls. The gables never seem, as in the Scottish towers, to have risen above the parapet. Probably one reason why the Norman roofs were lifted and flattened was to allow of military engines being placed upon them, and the use of lead must have come in rather suddenly just before the close of the Norman period. The floors of these keeps are almost always of timber; thick rough planks, resting upon stout balks 12 inches or 14 inches square, placed about 2 feet or 3 feet apart, and resting either on a ledge or in regular joist-holes. Such floors exposed the keep to be burned, and once well on fire it would certainly burn till it was gutted. The basement is now and then vaulted, but the vaulting is very rarely original, and when it is so the keep is late. The vaulting at the Tower and at Dover is modern brickwork; the Ludlow vault seems Early English; that at the lower part of Carlisle, that of Porchester, Brougham, Bowes, and Richmond, Decorated; the vaulting at Middleham, Newcastle, and Mitford may be original. The vaulting at Norham, a late keep, may be original, but was more probably inserted at an early period by Bishop Puisèt. That of Bamburgh is an insertion. The basement of Bowes was vaulted, but what remains of one rib is either Decorated or later. In a few examples where guns have been mounted on a Norman keep, a brick vault has been sprung over the upper chamber, and the roof filled up and paved. At Dover, Carlisle, and Newcastle, where this has been done, the upper openings of the hall are closed, and the interior of the fabric utterly disfigured. There is certainly no original vaulting of a great chamber higher than the basement.