MASONRY (from the French word maps eerie), signifies the appli cation of stone to building purposes. It is a most important branch of the arts of construction; because much both of the beauty and durability of an edifice depends upon the excellence of the workman ship, and upon the colour and resistance of the stone. In situations where the geological character of the soil is clayey, or where stone is only to be obtained by means of a long and expensive land carriage, there is so important an economical advantage in the use of bricks, that stone is rarely resorted to, unless it be for the external decoration of important public buildings ; and much of the style and taste of any particular locality may be attributed to the relative abundance of these materials, or rather, to the nature of the materials employed to produce the external effect of a building. Thus we find that in the greater part of England, and in Holland, where stone is only used exceptionally for elevations, and where brickwork is the normal mode of building, there is generally an absence of bold, and what may be called palatial, character in the prevalent style of architecture ; whilst in Edinburgh, I'aris, Genoa, Rome, Madrid, &e., the stone elevations of the houses and public buildings are marked by a breadth of handling our London architects rarely attain. Perhaps the great facilities for internal com munication afforded by the railway system, may bring about a change in the style of construction adopted in London ; but the facts of the co-relation between the habitual use of stone and the state of archi tectural taste, and of the influence which that material exercises on architecture, will remain the same.
Stone is used in walling, either in what is called rubble, or in ashlar masonry ; or sometimes again in the style called brick and stone, or mixed masonry. Rubble masonry, in its turn, may be either random or dressed, according as the separate stones are dressed, or are left in the rough state in which they leave the quarry. Ashlar work is usually, but not necessarily, executed with large stones, which, under all conditions of use at least, are dressed to regular faces on the beds and joints ; whilst the exposed faces may either be left rough, or they may be worked to a smooth surface. In mixed masonry the propor tions of stone and brick vary greatly ; for in some instances the use of stone is confined to the window-dressings, strings, cornices, &c., and in others it is further introduced in bonding courses, or alternate layers. Another technical subclassification of walling masonry is derived from the manner in which the faces of the stones are dressed ; and according to the nature of the material : it is said, if granite be used, to be polished, fine gritted, fine axed, bolstered, or point dressed ; if lime stone be used, it is said to be rubbed, tooled, or hammer-dressed; and the same words apply to sand stones. In some styles of architec ture an attempt is made to secure a certain amount of picturesque effect, by treating the surface of the stone In a bold, but affected, style of rough dressing, known amongst architects by the name of rustica tions, or of vermiculatione. In these remarks upon the use of stone, attention has been only directed to walling purposes ; because its appli cation to window and door cilia, to lintels, copings, staircases landings, paving, &c., is rendered so compulsory by the very nature of the re quirements of the 1)0,1-Udder eases, that the discussion of the conditions of ttiose branches of the mason's art must be left to the particular sub jects themselves.
The qualities to be sought for in a building stone are durability, facility of working, capability of receiving a fine surface, and agreeable colour ; Irut, as in all large towns, the state of the atmosphere is to a greater or less extent able rapidly to modify the original colour of the stone, the conditions of durability, and of the facility of working, in so far as the latter is likely to affect the cost of the work, are the most important. It would appear that there is some hitherto unexplained
law affecting these questions, whereby the stone of any particular locality resists the atmospheric influences of that locality more success fully than it could do those of any other situation ; but whatever may be the explanation of this phenomenon, it is certain that an atmosphere highly charged with carbonic, or with sulphuric, acid gases, is highly dangerous to the building stones usually employed. It is on this account that London and Manchester are so particularly unfavourable for masonry, and require such extraordinary care in the selection of the stones intended to be used in the elevations of public buildings in them, even without reference to the normal conditions of decay. As the atmosphere of every town has its own distinctive peculiarities, it may be as well to illustrate the above remarks by some incidental references to the action of the London atmosphere on the stones hitherto exposed to it ; and to accompany them with some other inci dental remarks on the accidental circumstances likely to modify tho general laws thus arrived at. [ATMOSPHERIC INFLUENCE.] The stone which hitherto has been proved to be the most adapted to resist the action of the London atmosphere is the Portland °elite : fine-grained, sub-crystalline, carbonate of lime, of considerable hardness and density, and without any very distinct traces of bedding in the best varieties. The cost of the labour upon it, and the high price of the stone itself, on account of the limited source of supply, render the use of Portland stone less common than would be desirable, and have led to the introduction into the London stone market of cheaper and inferior materials. There are, however, some outlying patches of the Portland oolite which might be brought to London at the present day, such as the Tisbury, Upway, and Purbeck deposits ; and it really seems that the fault of the high price of this variety of stone lies rather in the want of enterprise on the part of the merchants, than in any scarcity of the raw material. Portland stone, like all regularly stratified bodies, cleaves more easily in one direction than in others ; but in the finer beds (that is to say, in the beds producing the finest stone) the character of the molecular structure becomes so homogeneous that the planes of stratification become imperceptible ; and when this is the case there is less danger in using the stone, for ordinary purposes of masonry, in false bedding, than would be the case if the planes of separation of the beds were more distinctly marked. The best beds of the Portland stone are exposed to the inconveniences of flint nodules, and of vents, as the workmen call the cracks produced in the mass of the stone by the contractions which accompany its solidification. The upper beds, or the roach Portland, are Shelly, more decidedly crystalline in the structure of the cementing material around the fossils, harder and more difficult to work, and totally unfit, on account of the numerous holes of the fossils, to be used in the masonry of ornamental structures ; whilst, for hydraulic works, or other purposes requiring great strength and durability, the roach is of great value.