an auger 75 when rotating removes the material 76 from hole 71 a sonic generator or seismic source 77 generates sound along rays 78a 78b and 78c for example to adjacent hole 70 one of the objects of this invention is to maintain the axis 80 substantially parallel to axis 81 in normal use the sonic signal is generated in the preferred embodiment by a source of power such as a signal generator 82 coupled to the seismic source and input 83 of oscilloscope 86 with wires 84 and 85 respectively a suitable isolation means not shown may be employed between wire 85 and wire 87 if necessary auger head 72 which is boring hole 71 must have an axis 80 substantially parallel to axis 81 when cutting head 73 reaches a predetermined depth the parallelism of the two axes 80 and 81 must be checked to accommodate the check cart 10 is moved into hole 70 to a position as nearly opposite ray 78a as possible signal generator 82 generates a signal down wire 84 to seismic source 77 which generates a signal into the ground toward borehole 70 along rays 78a 78b and 78c for example detector 56 the actual.