The principal kinds of stone used in building are the LIMESTONES, or _calcareous rocks_ of the geologist; of these it would be useless to describe or enumerate more than a few. In our own country, the _Portland stone_, so called from its principal quarries being in Portland Island, in Dorsetshire, holds the first rank, and is that almost exclusively used in London for building, and for the ornamental parts of edifices. It unites the qualities of being easily sawn and worked, when lately quarried, and of subsequently hardening by exposure to the air; it is close and even in its texture, admitting of being wrought into delicate work, and receiving a very smooth surface, which it will retain for a considerable period, though it is surpassed in durability by many other rocks. It is said that the Banquetting-house, Whitehall, was the first building in London in which this stone was employed. St. Paul’s, Westminster and Blackfriars’ bridges, Newgate, and, indeed, most of the public buildings of the metropolis, are examples of its use. _Bath-stone_, so called from its being entirely used in the neighbourhood of that city, is softer and far less durable than the preceding. When recently quarried, it may be sawn with a toothed saw, like timber, and can be carved with the greatest facility into the richest ornaments; hence it is often employed, and, if sheltered from the weather, is well adapted for such purposes, from its rich, even cream colour; but though it hardens considerably by exposure, it is acted upon, after a time, by the air, so as to render it very perishable. The restoration of Henry the Seventh’s Chapel, Westminster, is, unfortunately, made with this stone. The two preceding, and many others, distinguished by names according to the principal localities, as _Oxford_-stone, _Ketton_-stone, &c., belong to what geologists term the _Oolitic_ formation, from the resemblance of some kinds of the rock to fishes’ roe, which is observable in that we have last mentioned. They all agree in their principal qualities. _Purbeck-stone_, also from Dorsetshire, is used for steps, paving, door-sills, and copings; it is coarser, harder, and less uniform in texture than the foregoing, and not, therefore, calculated for fine buildings, except for the purposes we have specified. _Yorkshire-stone_ resembles the last; it is used for the same purposes, but especially for paving. The greatest part of the foot-paths in the streets of London are laid with this or the preceding. _Rag-stone_ is obtained from quarries on the banks of the Thames, Medway, &c. It was the stone chiefly used for building in ancient London, and a great deal is still used for paving.