AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 39 



are unaltered except for the distortion due to projection.) 

 Join ab^ and draw h^Ci parallel to be. The hole is now 65 

 deg. out of the WE plane; slew b^Ci this amount to b^c' 

 and project to b^c^ getting c^ on the c depth line as previ- 

 ously. Join b^c^. In the same way get the due north part 

 of the hole cd to show a vertical dd^ only, since it can have 

 no lateral trend in the WE plane of the paper; and so on 

 to e^, the last length being an extraneous addition to C 

 (Fig. 17). It would be well to smooth a curve through 

 these constructed points, and the same applies to the plan 

 view of Fig. 175. 



Borehole Models. — These are very useful and instruc- 

 tive adjuncts to any scheme of deep boring or precision 

 boring, as in freezing shafts. Thurmann of Halle, Saxony, 

 constructed the interesting and helpful model shown in 

 Fig. 18 in 1909 to assist in visualizing the relative trends 

 and positions of boreholes in a freezing shaft frost wall. 

 It will be seen that he merely erected discs of sheeting or 

 millboard at depths on the central rod scaled from the prog- 

 ress chart, the said rod representing the shaft center. 

 Thus, in the figure, the dots on the discs represent the posi- 

 tions of the boreholes at the various levels or depths. The 

 dotted line shows the position of a supplementary borehole 

 to deal with the wide space in the frost wall between bore- 

 holes 2 and 3. 



Figure 19 shows a glass model of the Chanslor-Canfield 

 Midway Oil Co.'s No. 96 Olinda oil well in California, one of 

 the deepest wells in the world. It is thought that some facts 

 relating to the true shape of the course taken by the lower 

 part of the well, obtained from a study of the model, 

 would have remained unknown without its aid. 



The model is seen to be easily constructed from depth 

 planes scaled from the boring logs and the positions of 

 the instruments on each plane surveyed as shown. The 

 bottom plane surveyed is 6,948 ft. deep. It is conceiva- 

 ble that valuable results may be had from models outlining 

 the course of well or boreholes and these would be more 

 exact than sketched-in hypothetical underground contours. 



