Figure 25-14. Stereogram of determination of dip in two non-parallel boreholes. 



in the plane of the stereogram. A' is revolved to the N point, and the pro- 

 jection of the bases of the double cone are traced on the 30-degree small circles. 

 B' is then oriented to N and the 40-degree arcs traced. It is seen that these 

 arcs cross at points F and G, fixing two possible positions of the bedding plane 

 normal common to both boreholes. To find the true position of these normals, 

 we reverse the rotation carried out with points A and B. F now travels 68 

 degrees to F y , indicating a dip of 14 degrees on azimuth 56 degrees, while G 

 moves to G', showing a dip of 44 degrees on azimuth 356 degrees. 



Although there are two possible values of true dip in this example, Figure 

 25-15a illustrates the possibility of only one answer, while 25-156, c, and d 



548 



