In the first place, the great general rule of treatment of stone in the North and in the South is to be mentioned. In the Northern countries, France, Germany, and England, the stone which was employed for buildings and their decorations was obtainable in large blocks and masses; it was what, for our purposes, we will call ordinary stone, and could be used in the solid; therefore it was possible for carving in the North to be rendered as deeply and as roundly as the sculptor desired. In Southern countries, however, and chiefly in Italy, the stone used for building was not ordinary, but semi-precious stone. Marble, porphyry, and alabaster were available; and the use of such material led to a different ideal in architecture and decoration,--that of incrustation instead of solid piling. These valuable stones of Italy could not be used, generally speaking, in vast blocks, into which the chisel was at liberty to plough as it pleased; when a mass of marble or alabaster was obtained, the aesthetic soul of the Italian craftsman revolted against shutting up all that beauty of veining and texture in the confines of a solid square, of which only the two sides should ever be visible, and often only one. So he cut his precious block into slices: made slabs and shallow surfaces of it, and these he laid, as an outward adornment to his building, upon a substructure of brick or rubble. It is easy to perceive, then, the difference of the problem of the sculptors of the North and the South. The plain, solid Northern building was capable of unlimited enrichment by carving; this carving, when deeply cut, with forcible projection, acted as a noble embellishment in which the principal feature was a varied play of light and shade; the stone having little charm of colour or texture in itself, depended for its beauty entirely upon its bold relief, its rounded statuary, and its well shaped chiselled ornament. The shallow surface, already beautiful, both in colour and texture, in the Southern building material, called only for enrichment in low relief: ornament only slightly raised from the level or simply perforating the thin slab of glowing stone on which it was used was the more usual choice of the Italian craftsman. This statement applies, of course, only to general principles of the art of sculpture; there is some flat bas-relief in the North, and some rounded sculpture in the South; but as a rule the tendencies are as they have just been outlined.