To this property of charred wood Sir C. Wren does not seem to have attended, when about to build St Paul's. It is said, he thought piles were not to he depended on for a foundation, excepting when always wet; and there fore dug to a great depth through a dry soil, in order to come at a solid foundation for part of that cathedral. Sec Wren's Parentalia.
Charcoal has also been found useful as a defence to the surface of wood when used as a paint. We lately had a good instance of the effect of sand used for this purpose. At Studly Royal we saw a temple to appear ance of stone, but which on examination we found to be wood covered with paint, and dusted over with sand. We were informed it had stood about 50 years; and the deception was still so complete, that the spectators sup posed the pillars to be stone, till minutely examined.
From marble being plentiful in Italy and France, these countries have been able to make a considerable use of it, even in the main walls of their edifices ; but being sel dom found in sufficient quantities, and of proper quality, in the more northern parts of Europe, it has been here chiefly confined to interior columns, pavements, chimney pieces, and sometimes stairs.
The kinds of stone are as various, as the countries in which the buildings are constructed. Sandstone being very generally found stratified, even in thin lamina, be ing readily cut into different forms, and being, if pro perly selected and used, sufficiently durable, it has, in northern countries, been in most frequent use. It is a general accompaniment of coal strata, and is also often found where the latter does not occur. It varies in its component parts, being at different places argillaceous. siliceous, and calcareous. Its position, in the earth, as sumes all directions, from the horizontal to a vertical plane. The proportional thickness of its strata, lamina:, or beds, varies from that of thin slate to many feet each. The upper beds arc usually very thin or soft, or both; if sufficiently hard, they are employed in floor pavements and covering roofs. Under these the beds, generally, in useful quarries, increase in thickness, hardness, and te nacity. The position of the lamina always require strict attention, that the worked stone may, if possible, be laid in the building upon its natural bed; for although some instances occur, as in the Isle of Portland and at Grins hill, in Shropshire, where the difference is not apparent ly great, yet in all stone (even granite) it is sufficiently well known to workmen. Some stone, as that of Bath, is
so soft when taken out of the quarry, as to be very con veniently worked with tools resembling those used by carpenters; yet when exposed for some time to the at mosphere, it becomes hard and durable. This last, in deed, cannot be deemed sandstone, being nearly altoge ther calcareous.
Besides the before mentioned, there is a very beauti ful stone, dug in the hills near Dunstable, in the parish of Tottenhoc, from whence the stone receives its name. It has the appearance of indurated chalk. It is easily worked, and hardens by exposure to the weather. It should, however, be placed upon a plinth of some other stone, or kept by other means from contact with the ground, otherwise it is, in this situation, liable to be in jured by the frosts. The house of the Duke of Bedford, at Woburn Abbey, is built chiefly with this stone, and various other large houses in the neighbourhood of the quarries. Proofs of its durability may be seen in many old churches. From the closeness of its texture, the beauty of its colour, and the facility with which it is work ed into mouldings, Sec. it is peculiarly fit for house building, both externally and internally. It may now readily be conveyed to London, by means of the Grand Junction Canal.
The very perfect preservation of many beautiful churches in the counties of Lincoln, Rutland, and North ampton, arc evidence of the excellence of the stone of which they are built.
In the central parts of Scotland, different varieties of sandstone, which accompany coal, are used extensively in building houses, &c.; and this circumstance has not a little contributed to the fine appearance of the new streets, squares, and public buildings in the cities of Edinburgh and Glasgow.
Flints, where they abound, and where other stone is scarce, are sometimes used in walls of considerable height ; and notwithstanding their small size, and irregu larity of shape, are broken so as to compose a face of considerable smoothness. The church and steeple of Rickmansworth, in Hertfordshire, affords a fine speci men of this kind of building. But bricks or squared stones are generally used as quoins for this sort of work.