Abstract: There is disclosed an impact applying mechanism, particularly as applied in a subterranean drilling apparatus, and comprising a cylinder (13) arranged with its axis substantially vertical and connected to the member to which impact is to be applied, a piston (5) slidably mounted within the cylinder (13), means to admit pressure fluid to the cylinder (13) below the piston (5), at least one valve tube (24), slidably mounted in the base of the cylinder (13), coil springs (30) to bias the upper end of the valve tubes (24) into sealing engagement with the underside of the piston (5) when the piston is in its lowest position, a flange (26) on the upper end of the valve tubes (24) upon which fluid pressure in the cylinder (13) acts to produce a force urging the end of the valve tubes (24) into contact with the underside of the piston (5), and further coil springs (32) to provide a force to said valve tubes (24) of a magnitude which increases as the piston (5) moves upwardly relative to the cylinder (13) to subsequen

Abstract: The invention is a novel method and apparatus for subterranean drilling and mining, particularly suited to alluvial deposits. The method uses water jets from the lower end of the apparatus to loosen and remove soil. Part of the water is bled off to raise a piston and associated weight, the water being evacuated from the cylinder in which the piston operates from time to time to give periodic impulses to the outer casing. Air may be admitted to the system during the mining mode to increase its efficiency.