I have often observed, that when a mountain is level at its summit, the strata which compose it are also level; but if the summit is not placed horizontally, the strata inclines also in the same direction. I have heard that, in general, the beds of quarries inclined a little to the east; but having myself observed all the chains of rocks which offered, I discovered this opinion to be erroneous, and that the strata inclines to the same side as the hill, whether it be east, west, north, or south. When we dig stone and marble from the quarry, we take great care to separate them according to their natural position, and we cannot even get them of a large size, if we cut them in any other direction. Where they are made use of for good masonry, the workmen are particular in placing them as they stood in the quarry, for if they were placed in any other direction, they would split, and would not resist the weight with which they are loaded. This perfectly confirms that stones, are found in parallel and horizontal strata, which have been successively heaped one on the other, and that these strata composed masses where resistance is greater in that direction than in any other. Every strata, whether horizontal or inclined, has an equal thickness throughout its whole extent. In the quarries about Paris the bed of good stone is not thick, scarcely more than 18 or 20 feet: in those of Burgundy the stone is much thicker. It is the same with marble; the black and white marble have a thicker bed than the coloured; and I know beds of very hard stone, which the farmers in Burgundy make use of to cover their houses, that are not above an inch thick. The different strata vary much in thickness, but each bed preserves the same thickness throughout its extent. The thickness of strata is so greatly varied, that it is found from less than a line to 1, 10, 20, 30, or 100 feet thick. The ancient and modern quarries, which are horizontally dug, the perpendicular and other divisions of mines, prove that there are extensive strata in all directions. "It is thoroughly proved," says the historian of the academy, "that all stones have formerly been a soft paste, and as there are quarries almost in every part, the surface of the earth has therefore consisted, in all these places, of mud and slime, at least to certain depths. The shells found in most quarries prove that this mud was an earth diluted by the water of the sea, and consequently that the sea covered all these places; and it could not cover them without also covering all that was level with or lower than it: and it is plain that it could not cover every place where there were quarries, without covering the whole face of the terrestrial globe. We do not here consider the mountains which the sea must also at one time have covered, since quarries and shells are often found in them.