Drilling deep into the earth holds a fascination for earth scientists derived in part from the fact that the drill hole is the ultimate test of a hypothesis. When surface exploration methods have been fully uti lized and all the geological inferences drawn about the structure be neath the surface, we must finally drill to sample directly the third dimension of the crust of the earth. The drill is thus the tool of choice of the energy and minerals re sources industry. Because of high cost, drilling has been only sparing ly used for solving fundamental problems in the earth sciences. But now,...