each side and concentric with longitudinal axis a a 39 for passage of hydraulic drilling fluid therethrough such drilling fluid may comprise water gases such as n 2 and co 2 drilling mud sand air and the like as well as a combination of these substances the particular drilling fluid used will primarily depend upon the rock encountered and the desired rate of drilling nozzle arms 16 are pivotably connected to drill head 12 by hinges 18 hinges 18 are provided with shear pins 19 of malleable easily fatigued metal such as babbitt metal copper tin and the like thus in the event of jamming blocking or stoppage of the drilling operation arms 16 are readily separated from drill head 12 thereby permitting extrication and retraction of drill head 12 from the drill hole pins 19 should normally be able to withstand hydrostatic pressures of approximately 7 000 psi prior to shearing however hollow arms 16 further comprise nozzles at the ends thereof any suitable configuration for example convergent divergent nozzles is permissible the main criterion for nozzle configuration is efficient conversion of high pressure fluid to high velocity fluid arms 16 are of half cylindrical or spoonlike configuration at 17 above hinges 18 drill head 12 also comprises flow diverters 20 diverters 20 are of any suitable configuration such that vertical downward fluid flow through channel 14 is diverted to radial flow against arms 16 thereby extending arms 16 radially and horizontally outward the preferred configuration of diverter 20 is an annulus surrounding drill head 12 fig4 illustrates the preferred embodiment of.