It is true, that among different nations, and at different times, we may find examples of every sort and degree of incrustation, from the mere setting of the larger and more compact stones by preference at the outside of the wall, to the miserable construction of that modern brick cornice, with its coating of cement, which, but the other day, in London, killed its unhappy workmen in its fall. [Footnote: Vide "Builder," for October, 1851.] But just as it is perfectly possible to have a clear idea of the opposing characteristics of two different species of plants or animals, though between the two there are varieties which it is difficult to assign either to the one or the other, so the reader may fix decisively in his mind the legitimate characteristics of the incrusted and the massive styles, though between the two there are varieties which confessedly unite the attributes of both. For instance, in many Roman remains, built of blocks of tufa and incrusted with marble, we have a style, which, though truly solid, possesses some of the attributes of incrustation; and in the Cathedral of Florence, built of brick and coated with marble, the marble facing is so firmly and exquisitely set, that the building, though in reality incrusted, assumes the attributes of solidity. But these intermediate examples need not in the least confuse our generally distinct ideas of the two families of buildings: the one in which the substance is alike throughout, and the forms and conditions of the ornament assume or prove that it is so, as in the best Greek buildings, and for the most part in our early Norman and Gothic; and the other, in which the substance is of two kinds, one internal, the other external, and the system of decoration is founded on this duplicity, as pre-eminently in St. Mark's. SECTION XXV. I have used the word duplicity in no depreciatory sense. In chapter ii. of the "Seven Lamps," Section 18, I especially guarded this incrusted school from the imputation of insincerity, and I must do so now at greater length. It appears insincere at first to a Northern builder, because, accustomed to build with solid blocks of freestone, he is in the habit of supposing the external superficies of a piece of masonry to be some criterion of its thickness. But, as soon as he gets acquainted with the incrusted style, he will find that the Southern builders had no intention to deceive him. He will see that every slab of facial marble is fastened to the next by a confessed _rivet_, and that the joints of the armor are so visibly and openly accommodated to the contours of the substance within, that he has no more right to complain of treachery than a savage would have, who, for the first time in his life seeing a man in armor, had supposed him to be made of solid steel. Acquaint him with the customs of chivalry, and with the uses of the coat of mail, and he ceases to accuse of dishonesty either the panoply or the knight.