"The second kind of furnace, which is by far the most numerously found and widely distributed, is, in fact, nothing but an improvement of that which preceded it, the edges of the furnace or crucible being considerably raised in height. They vary in depth from 7-1/2 to 8 feet, with a diameter of most irregular dimensions, from 18 inches upwards, and a thickness of 12 inches to 7 feet. They are likewise formed of fire-proof clay, and their average capacity is about 25 gallons. "The constructor, having dug out in the side of the hill an opening circular, or rather semi-circular, at the base, with a diameter nearly three times as wide as the future furnace, arranged in the centre of this hole a kind of furnace-bed made of plastic clay at bottom, and covered with a layer of fire-proof clay on the top of it. The bed of the furnace, which lies on the natural and hardly levelled earth, is, generally speaking, not so thick as the side walls, which are formed of sandy or siliceous clay, always fire-proof on the inside, but sometimes of a more plastic nature on the exterior; the empty space left between the walls of the furnace and the solid ground round it was filled up with earth and other material. In front the furnace was enclosed by a rough wall, sometimes straight and sometimes curving, built, without mortar, of rough limestone, and dressed with earth to fill up the gaps. In front of the furnace an opening was made in this wall, taking its rise a few inches above the bottom of the furnace, and increasing in size in an outward direction, so as to enable the workmen to see into, and work in, the furnace. "The work thus commenced was carried up to the requisite height; and when the excavation in the side of the hill was not lofty enough, the dome of the furnace was raised by placing buttresses against the fire-clay, so as to prevent the earth falling in. When these furnaces were established on almost level ground, as is sometimes the case, they form a truncated cone, with a base varying in size according to the height of the apparatus. "The furnace was not always built upright; it often deviated from the perpendicular, leaning to one side or the other to an extent as considerable as its own diameter, but no constant rule as to this can be recognised. The internal shape was just as irregular, changing from circular to oval, without any apparent motive beyond want of care in the workman. The crucibles or furnaces are sometimes larger at the top than at the bottom, and sometimes these proportions are reversed, but always with extreme irregularity. We have noticed some which at a point 10 or 12 inches above the crucible were perceptibly contracted on three sides, thus representing the first rudiments of the appearance of our modern furnaces. But this, perhaps, was nothing but a caprice on the part of the builder.