BORING, applied to the earth and to rocks, has two chief uses. 1. For some districts, owing to the existence, near the surface, of a bed of clay impervious to water, the surface water is retained in hollows, of greater or less extent. The expense of deep draining has been so great as to induce proprietors to neg lect such land, but this expense has lately been avoided by leading drains to the lowest portion of the hollow, and then opening a bore through the clay to the pervious strata of sand or gravel beneath. This is done by a simple instrument, an auger of 21 or 3f inches in diameter, wrought by means of a cross-bar by one or two men, 2. For artesian, veils and for the discorery of the mineral contents of the the borings for these purposes are performed in the same manner, it is unnecessary to give them separate notices. The object of B. for artesian wells is to open a passage for the escape of water from water-logged strata. See ARTESIAN WEtts. In the search for minerals, B. is had recourse to as a cheap method of discovering the mineral wealth of II district, and whether the quantity and quality of the contained minerals are such as to make the working remunerative. It should, however, never be undertaken without a previous geological survey of the locality; the neglect of this has caused an immense loss of time and money in futile searches for minerals, as in the innumerable cases of bores driven into Silurian and old red sandstone strata, in search for coal. B. is also of use even after the presence of coal has been ascertained, to determine the most advan tageous position for sinking the shaft by which the coal is to he drawn up. The general method of operating is as follows: The boring-instrument consists of an iron shank, having a cross-bar at the top and a hollow screw at the bottom; to this all the successive boring-instruments are fastened. A simple chisel is at first attached to the screw, and one or two men press upon the cross-bar, anti at the same time force it round like an auger, while another workman, by means of a lever erected overhead, with is chain descending from it to the cross-bar, gives an up and down motion to the instrument. When the chisel becomes clogged, from the accumulation of material which it has loosened, it is exchanged for a cylindricaL augc,r, provided with a valve, which scoops out the separated material; and thus by alternate chopping and scooping the work is carried on. The nature of the strata is determined with considerable facility and cer
tainty by examining the fragments brought up by the auger. As the work advances, successive lengths of rod are screwed or. at the upper end. Three poles are erected over the well, for the -purpose of elevating the rods, to permit the change of the tools.
The cost of B. varies with the material through which the operation is carried on. In strata of moderate hardness, the cost is-about 108. a fathom for the first 10 fathoms, and an additional 6s. for each 5 fathoms beyond.
A simple method of B. has been long in use among the Chinese, by which the great loss of time, arising from the screwing and unscrewing the rods, at each elevation of the chisel or auger, is saved. The chisel and scooping instrument are fastened to a rope, which is alternately elevated and allowed to descend by the simple force of gravity; the instrument thus forces its way through the ground. In the softer rocks of the newer formations this method has been successfully employed in B. for artesian wells.
A still greater saving in time and money has been obtained by a process invented by Fauvelle, and described by him before the British association in 1846. His apparatus consists of a hollow boring-rod, formed of wrought-iron tubes screwed end to end, armed at the lower end with a hollow tool. The upper end of the hollow rod is connected with a force-pump by a flexible tube. By means of the force-pump a current of water is sent down the rod into the bore-hole as it is sunk, and the water corning up again brings with it all the drilled particles, so that, except for the renewal of the perforating tool, the rods do not require to be elevated. M. Fauvelle found, by experience, that when he was passing through rravel, or required to bring up consider able masses of broken-of: rock, it was better to inject the water by the bore-hole and let it rise through the hollow tube. In this way he has succeeded in raising stones in. long by 1+ in. thick. For B. in tunnels, see TUNNEL.