The two central compartments of the nave have circular windows (sixteen feet in diameter) to light the aisle, and round-headed windows in the clerestory; and between the arches of the latter windows are small arched recesses. In the two western bays the clerestory is similar, save that the intermediate recessed arch is omitted. In both the voussoirs are counter-charged, and the wall from the springing up to the eaves is coursed with stone and lava. The transept gables are only noticeable for the courses of inlaid patterns with which they are enriched. All these patterns are formed with white stone and lava. The latter, indeed, forms the whole ground of the walls, and varies in colour from a greenish grey to black; and the patterns are formed with the darkest lava and stone. The cloister is similarly inlaid above the arches, but it has almost all been restored in a most injudicious manner. They have _struck_ and _ruled_ (I believe that is the technical phrase for this most abominable of inventions, is it not?) an enormous red mortar joint between all the stones,[43] and wherever this has been done the diaper appears to be formed with a chequer of black and red; wherever the cloister has not been retouched the diaper is black and white. I have left, almost until the last, that which is after all the crowning wonder of this singular church--the western porch. I have already referred to its position and plan. The majesty, I may say the awfulness, of this entrance, can hardly be exaggerated. It owes little to delicate detail or enrichment of any kind, for, though these have been, they are no longer; but it is the gloom and darkness, the simple, nervous forms of arch and pier, the long flight of steps lost in obscurity and crowded constantly (when I saw them) with a throng of worshippers, which constitute the strange charm of this strangest of entrances. I told you that in the nave the two western bays of the aisle alone had groining ribs; in the porch below it is only in the western bay that they are used, and this affords interesting evidence of the very gradual yet regular development of our art.