XLI. Pure architectural decoration, then, may be considered as limited to the four kinds above specified; of which each glides almost imperceptibly into the other. Thus, the Elgin frieze is a monochrome in a state of transition to sculpture, retaining, as I think, the half-cast skin too long. Of pure monochrome, I have given an example in Plate VI., from the noble front of St. Michele of Lucca. It contains forty such arches, all covered with equally elaborate ornaments, entirely drawn by cutting out their ground to about the depth of an inch in the flat white marble, and filling the spaces with pieces of green serpentine; a most elaborate mode of sculpture, requiring excessive care and precision in the fitting of the edges, and of course double work, the same line needing to be cut both in the marble and serpentine. The excessive simplicity of the forms will be at once perceived; the eyes of the figures of animals, for instance, being indicated only by a round dot, formed by a little inlet circle of serpentine, about half an inch over: but, though simple, they admit often much grace of curvature, as in the neck of the bird seen above the right hand pillar.[14] The pieces of serpentine have fallen out in many places, giving the black shadows, as seen under the horseman's arm and bird's neck, and in the semi-circular line round the arch, once filled with some pattern. It would have illustrated my point better to have restored the lost portions, but I always draw a thing exactly as it is, hating restoration of any kind; and I would especially direct the reader's attention to the completion of the forms in the _sculptured_ ornament of the marble cornices, as opposed to the abstraction of the monochrome figures, of the ball and cross patterns between the arches, and of the triangular ornament round the arch on the left.