AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 37 



latter by two rollers h, c, carried by a frame e. The bearing 

 pressure on a is regulated by the screw h adjusting the com- 

 pression of the spring g. The base plate p is notched at 

 r, and the end piece i of the frame / is detachable, so that 

 the apparatus can be put into position round the rope. 

 The frame / is mounted on a beam I carried by the springs 

 and bars m, n. The castors q, mounted on vertical pivots, 

 ride on the platform on which the inspector stands. The 

 spindle of the wheel a is coupled directly to the recording 

 train k, which indicates directly the length of rope that has 

 passed a at any particular moment. The complete 

 apparatus, which has proved quite satisfactory in practice, 

 weighs about 57 lb. 



Construction of Borehole Sections or Profiles. — Obvi- 

 ously it is only possible to portray the course of a borehole 

 with any degree of accuracy by referring the observed 

 data all to one plane. Having the depth and inclination 

 data at hand, there are three methods of plotting these in 

 any arbitrary vertical plane ^ viz.: 



1. Plotting the angle from the point where recorded 

 down to the next recorded point. 



2. Reversing 1 by plotting upward to the preceding 

 recorded point on the chart. 



3. Averaging 1 and 2 by plotting at the point on the 

 chart either way, downward and upward, halfway to meet 

 subjacent and superjacent plotted points obtained in the 

 same way. 



Since methods 1 {A Fig. 17) and 2 {B Fig. 17) assume no 

 gradual change of dip as usually obtaining in practice, 

 but imply sudden regular dip changes, they are not now 

 employed or recommended. Method 3 (C Fig. 17) will 

 enable us to average subjacent data and plot this mean. 

 The three hues A, B and C (Fig. 17) are plotted on the 

 assumption that the hole deviates in one plane, say the WE 

 plane of the paper. If a hole has been assumed to bear in 



^ These methods are also discussed by Prof. F. H. Lahee, Bull. Amer. 

 Assoc. Petroleum Geol., Vol. 13, No. 9, p. 198, to which we are indebted for 

 Fig. 17. 



