In quarrying sandstone, and those rocks which consist of regular layers, the pick, the wedge, the hammer, and the pinch, or lever, are the chief tools. But for many kinds of limestone, and for greenstone and basalt, recourse is had to the more violent and irregular effects of gunpowder. Indeed, some of the primitive rocks, such as granite, gneiss, and sienite, could scarcely be torn asunder by any other means. The great objection to blasting by gunpowder is, that the blocks are broken irregularly, and much of the stone is wasted; but it has the advantage of being simple in its application, and powerful in its effects. The grains of powder are suddenly converted into a permanently elastic air, occupying about four hundred and seventy-two times more space than their own bulk. The elastic fluid expands with a velocity calculated at the rate of about ten thousand feet per second; and its pressure or force, when thus expanding, has been estimated as equal to one thousand atmospheres, that is, one thousand times greater than the atmospheric pressure upon a base of the same extent. By applying this product to a square inch, upon which the atmosphere exerts a pressure of about fifteen pounds, the elastic fluid of the gunpowder will be found, at the moment of the explosion, to exert a force equivalent to six tons and a half upon the square inch of surface exposed to it; and that with a velocity which the imagination can hardly follow. [Illustration] In boring a rock preparatory to blasting, it is necessary to consider the nature of the stone, and the inclination or dip of the strata, in order to decide upon the diameter, the depth, and direction of the hole for the gunpowder. The diameter of the hole may vary according to the nature of the rock, from half an inch to two and a half inches; and the depth from a few inches to as many feet; the direction may vary to all the angles from the perpendicular to the horizontal. The tools used in this operation are very simple. The chisel, or _jumper_, as it is called, varies in size according to the work to be performed, and its edge is more or less pointed to suit the hardness of the rock to be bored. If the hole is to be small and not deep, it may be bored by a single person; with one hand he manages the chisel, which he turns at every blow so as to cross the previous cut, and with the other hand he strikes it with a hammer of six or eight pounds’ weight, occasionally clearing out the hole by means of a _scraper_. But when the hole is large and deep, one man in a sitting posture directs the jumper, pours water into the hole, and occasionally cleans it out, while two or three men, with hammers of ten or twelve pounds’ weight, strike successive blows upon the jumper, until the rock is perforated to the required depth. To prevent annoyance to the workmen, a small rope of straw or hemp is twisted round the jumper, and made to rest in the orifice of the hole.