Whatever may be the misgivings entertained by many engineers respecting the future use of cast iron for structures of certain kinds, it is clear that for architectural purposes this material is likely to be employed to an extent hardly contemplated by many who have looked upon it with disfavor. At the present moment many buildings may be seen in London, in which cast iron has been introduced instead of stone for architectural features, and the substitution of cast iron for façades in many warehouses and commercial buildings seems to show that, notwithstanding the prejudices of the English architect against the importation of the iron architecture of our transatlantic brethren, there is a prospect of its being largely employed for frontages in which ample lighting and strength are needed. The extensive window space necessary in narrow city thoroughfares, and the difficulty of employing brick in large masses, such as pilasters and lintels, have chiefly led to the adoption of material having less of the uncertain durability and strength of either stone or terra-cotta in its favor. Architects would gladly resort to the last-named material if it could be procured in sufficient size and mass without the difficulties attendant upon shrinkage in the burning, and the winding and unevenness of the lines thereby caused. They have also an even more tractable material in concrete ready to their hand, if they would seriously bring themselves to the task of stamping an expressive art upon it, instead of going on designing concrete houses as if they were stone ones. Cast iron has the advantage of being a tried material; it is well adapted for structures not liable to sudden weights or to vibration, and so it has come to be used for features of an architectural kind, by a sort of tacit acknowledgment in its favor. Those who are desirous of seeing examples of its employment in fronts of warehouses will find instances in Queen Victoria Street, Southwark Street, and Bridge Road, and Theobalds Road, where the whole or portions of fronts have been constructed of cast iron. At some corner premises in Southwark, the piers as well as the windows are formed of cast iron, the former being made to assume the appearance of projecting pilasters. There is nothing to which the most captious critic could object in the treatment adopted here; the pilasters and other features have plain moulded members, and there is no principle of design in cast work which has been violated--the only question being the purely aesthetic one--is it justifiable to copy features in cast iron which have generally been constructed in stone or marble? The answer is obvious: Certainly not, when those features suggest the mass and proportions or treatment proper only for stone or marble; but when they do not so represent the material, it is quite optional for the architect to build up his front with castings, if by so doing he can obtain greater rigidity of bearing, strength, and durability. He ought, of course, to vary the proportions of his pilasters and horizontal lintels, and make them more in accord with the material. It is the wholesale reproduction of the more costly and ornamental features, such as we see in many buildings of New York and Philadelphia, where whole fronts are manufactured of cast iron and sheet-metal, which has shocked the minds of architects of culture and sensitive feeling. Such imitations and cheap displays outrage the artist by the attempt to produce in cast or rolled metal what properly belongs to a stone front.