SECTION XXIX. If, therefore, the reader does not care for color, I must protest against his endeavor to form any judgment whatever of this church of St. Mark's. But, if he both cares for and loves it, let him remember that the school of incrusted architecture is _the only one in which perfect and permanent chromatic decoration is possible_; and let him look upon every piece of jasper and alabaster given to the architect as a cake of very hard color, of which a certain portion is to be ground down or cut off, to paint the walls with. Once understand this thoroughly, and accept the condition that the body and availing strength of the edifice are to be in brick, and that this under muscular power of brickwork is to be clothed with the defence and the brightness of the marble, as the body of an animal is protected and adorned by its scales or its skin, and all the consequent fitnesses and laws of the structure will be easily discernible. These I shall state in their natural order. SECTION XXX. LAW I. _That the plinths and cornices used for binding the armor are to be light and delicate._ A certain thickness, at least two or three inches, must be required in the covering pieces (even when composed of the strongest stone, and set on the least exposed parts), in order to prevent the chance of fracture, and to allow for the wear of time. And the weight of this armor must not be trusted to cement; the pieces must not be merely glued to the rough brick surface, but connected with the mass which they protect by binding cornices and string courses; and with each other, so as to secure mutual support, aided by the rivetings, but by no means dependent upon them. And, for the full honesty and straightforwardness of the work, it is necessary that these string courses and binding plinths should not be of such proportions as would fit them for taking any important part in the hard work of the inner structure, or render them liable to be mistaken for the great cornices and plinths already explained as essential parts of the best solid building. They must be delicate, slight, and visibly incapable of severer work than that assigned to them.