construction of ground-floors, streets, or highways, in such a manner that they may be conveniently walked upon. In Britain, the pavement of the grand streets, &c. is usually of flint, or rubble-stone; courts, stables, kitchens, halls, churches, &c., are paved with tiles, bricks, flags, or fire-stone; sometimes with a kind of freestone and ragstone.

In some streets, e.g. of Venice, the pavement is of brick; churches sometimes are paved with marble, and sometimes with mosaic work, as the church of St Mark at Venice. In France, the public roads, streets, courts, &c., are all paved with gres or gritt, a kind of freestone.

In Amsterdam and the chief cities of Holland, they call their brick pavement the burgher-maifers pavement, to distinguish it from the stone or flint pavement, which usually takes up the middle of the street, and which serves for carriages; the brick which borders it being destined for the passage of people on foot.

Pavements of freestone, flint, and flags, in streets, &c., are laid dry, i.e. in a bed of sand; those of courts, stables, ground-rooms, &c., are laid in a mortar of lime and sand; or in lime and cement, especially if there be vaults or cellars underneath. Some masons, after laying a floor dry, especially of brick, spread a thin mortar over it; sweeping it backwards and forwards to fill up the joints. The several kinds of pavement are as various as the materials of which they are composed, and whence they derive the name by which they are distinguished; as,

1. Pebble-paving, which is done with stones collected from the sea-beach, mostly brought from the islands of Guernsey and Jersey; they are very durable, indeed the most so of any stone used for this purpose. They are used of various sizes, but those which are from six to nine inches deep, are esteemed the most serviceable. When they are about three inches deep, they are denominated bolders or bowlers; these are used for paving court-yards, and other places not accustomed to receive carriages with heavy weights; when laid in geometrical figures, they have a very pleasing appearance.

2. Rag-paving was much used in London, but is very inferior to the pebbles; it is dug in the vicinity of Maidstone in Kent, from which it has the name of Kentish ragstone; there are squared stones of this material for paving coach tracks and footways.

3. Purbeck pitches; square stones used in footways; they are brought from the island of Purbeck, and also frequently used in court-yards; they are in general from six to ten inches square, and about five inches deep.

4. Squared paving, for distinction by some called Scotch paving, because the first of the kind paved in the manner that has been and continues to be paved, came from Scotland; the first was a clear close stone, called blue whynn, which is now disused, because it has been found inferior to others since introduced in the order they are hereafter placed.

5. Granite, a hard material, brought also from Scotland, of a reddish colour, very superior to the blue whynn quarry, and at present very commonly used in London.

6. Guernsey, which is the best, and very much in use; it is the same stone with the pebble before spoken of, but broken with iron hammers, and squared to any dimensions required of a prismoidal figure, let with its smallest base downwards. The whole of the foregoing paving should be bedded and paved in small gravel.

7. Purbeck paving, for footways, is in general got in large surfaces about two inches and a half thick; the blue fort is the hardest and the best of this kind of paving.

8. Yorkshire paving, is an exceeding good material for the same purpose, and is got of almost any dimensions of the same thickness as the Purbeck. This stone will not admit the wet to pass through it, nor is it affected by the frost.

9. Ragstone or firestone paving, is used for hearths, stoves, ovens, and such places as are liable to great heat, which does not affect the stone if kept dry.

10. Newcastle flags, are stones about two feet square, and one inch and a half or two inches thick; they answer very well for paving out-offices; they are somewhat like the Yorkshire.

11. Portland paving, with stone from the island of Portland; this is sometimes ornamented with black marbled dots.

12. Swedland paving, is a black slate dug in Leicestershire, and looks well for paving halls, or in partly-coloured paving.

13. Marble paving, is mostly variegated with different marbles, sometimes inlaid in mosaic.

14. Flat brick paving, done with brick laid in sand, mortar, or grout, as when liquid lime is poured into the joints.

15. Brick-on-edge paving, done with brick laid edge-wise in the same manner.

16. Bricks are also laid flat or edgewise in herring-bone.

17. Bricks are also sometimes set endwise in sand, mortar, or grout.

18. Paving is also performed with paving bricks.

19. With ten inch tiles.

20. With foot tiles.

21. With clinkers for stables and outer offices.

22. With the bones of animals, for gardens, &c.

And, 23. We have knob paving, with large gravel-stones, for porticoes, garden-feats, &c.

Pavements of churches, &c., frequently consist of stones of several colours; chiefly black and white, and of several forms, but chiefly squares and lozenges, artfully disposed. Indeed, there needs no great variety of colours to make a surprising diversity of figures and arrangements. M. Truchet, in the Memoirs of the French Academy, has shown by the rules of combination, that two square stones, divided diagonally into two colours, may be joined together chequer-wise 64 different ways; which appears surprising enough; since two letters or figures can only be combined two ways.

The reason is, that letters only change their situation with regard to the first and second, the top and bottom remaining the same; but in the arrangement of these stones, each admits of four several situations, in each whereof whereof the other square may be changed 16 times, which gives 64 combinations.

Indeed, from a further examination of these 64 combinations, he found there were only 32 different figures, each figure being repeated twice in the same situation, though in a different combination; so that the two only differed from each other by the transposition of the dark and light parts.