Hole C is plotted on the stereogram with holes A and B (fig. 25-16). If 

 the bedding plane were perpendicular to the bore hole, the axis of the hole would 

 be the normal. The angle through which this normal must be tilted to coincide 

 with the true normal to the bedding plane should equal the measured dip in 

 hole C. By rotating the stereogram to place C successively on the same great 

 circle with each of the previously determined normals F' and G', the angular 

 differences may be measured. In this example, C is 16 degrees from G', 

 indicating that 44 degrees on azimuth 356 degrees is the correct answer. This 

 may be verified by applying stereographic procedure for nonparallel drillholes 

 to holes C and A, and again to holes C and B. 



Figure 25-16. Use of third borehole to select true strike and dip in non-parallel boreholes. 



550 



