Abstract: A rock head for use with an auger borer to bore a passageway through a body of soil and rock and simultaneously laying a pipe in that bored passageway. The rock head has a base connectable to the leading end of the auger. A plurality of movable mounts are provided on the base and a roller cone is secured to each movable mount. A spring is disposed between the movable mount and the base. The spring is compressed as the movable mount pivots the roller cones inwardly toward a central region of the base. This reduces the diameter of the rock head so that it can travel through the bore. Each movable mount is provided with at least one wheel so that it can ride smoothly through the bore. When the rock head exits the pipe, the springs automatically pivots each roller cone outwardly so that at least a portion thereof is disposed beyond the outermost edge of the base. In this second position, the rock head has a greater diameter than the pipe bore and therefore it cannot travel therethrough.