“Not exactly. Earth compressed,—settled down in the natural soil,—occupies a smaller volume than that which, having been moved, leaves many interspaces between the materials of the embankment. Soil when removed is said to increase, more or less. Sea-sand does not increase, while pebbly earth, mixed with vegetable detritus, increases greatly. In your memoranda, therefore, you must take account of the looseness caused by excavating, to get the solid content of the soil removed; and take the solid content of the mounds when we make use of them, to know the mass of earth we shall have to transport elsewhere.”
“You will now draw this plan of the cellars to a scale of a quarter of an inch to a foot, so that you may figure the dimensions very legibly where required; then I shall indicate to you on this plan the points where bedded stone must be placed.”
“What are bedded stones?”
“Dressed stone laid as a foundation is thus designated, and which is only dressed on its beds,—that is to say, which presents no visible faces. Dressed stone has always two beds, which are its horizontal surfaces, one or more faces, which are its exposed surfaces, and its joints, which are its separating surfaces. Thus, let us suppose a corner stone, bearing a pilaster, and having the form indicated here (Fig. [23]), the surface a b c d e f, g h i j k l are the upper and lower beds. The surfaces a l b g, b g c h, c d h i, d e i j are the exposed faces, and the surfaces c f j k, a f k l are the joints, as the adjacent stones touch these surfaces. You will easily see that when stones are placed below the surface, as a foundation, it is not necessary to dress the faces which would be visible only to the moles. This cutting therefore is saved; the stone is left in the rough on its vertical faces, and only those on which it rests are cut. For these bedded stones solid blocks are chosen, which sustain pressure, but which may be very coarse in grain, and even sensible to frost (i.e., liable to be cracked by frost), and which could not be employed in the open air without danger; under ground these stones are preserved from the action of frost. But care must be taken with regard to these stones even more than for those above ground, to place them according to their quarry-bed, and their natural stratified position; otherwise they might be broken or crushed beneath the weight of the masonry above.
Fig. 23.
“When our plan is drawn, we shall indicate by a particular colour the parts where we wish bedded stones to be placed. These will be the angles and the junctions of the walls which sustain the heaviest pressure relatively to the rest. Between these bedded stones the masonry will be carried up simply in rubble-work.
“The ground being good, we shall content ourselves with foundations only half a yard below the area of the cellars. But as soon as we have reached this level, the dressed stones will necessarily have faces visible in the cellars; these stones will therefore not merely be bedded, but faced and jointed. We will not take the best and finest grained, but those that resist pressure best, and which in this district are the coarsest in appearance. We shall put dressed stones in our cellars at the angles, the jambs of the doors and air-holes, and in the newels of the stairs.
“But you have enough work for to-day and to-morrow morning.... Ah! I was forgetting! If Branchu meets springs, or drippings, that trouble him, inform me, because we must immediately make drains to collect the water. That will determine us as to the level to be given to the bed of our sewer.”
“What do you mean by the bed?”