AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 25 



of sinking. On the upper edge of the paper (Fig. 4), a 

 curve scale can be fixed for the continuous series of borehole 

 depths, which can be diminished to a definite scale by means 

 of suitable transmission bevels i and k. Thus, given 

 favorable conditions, we may obtain the approximate 

 dip of the strata by noting the length of the transition 

 in the curve between two changes in it. Note in Fig, 

 4a, which shows the progress of a diamond-drill borehole, 

 that the curve is uniform to a as the crown is cutting in 

 clay shales; from a onward, where the crown encounters 

 the milder strata (coal) the curve flattens, and from h to 

 c where it is entirely in coal it flattens more, steepening 

 again at c on passing through the softer coal into more hard 

 shale. An enlarged view of the borehole is shown in Fig. 

 4a to assist in elucidating the problems arising. Thus 

 bd is the borehole diameter and ab the depth difference 

 read on the curve scale, hence the strata dip 



tan a = ^ (1) 



from which the actual thickness eg is easily obtained, since 

 thickness of strata = ac cos a. 



To facilitate reading, the depth of each change of strata 

 may be marked on the record. If necessary the recorder 

 can be driven independent of the plant. This method 

 has been well tried with good results at one of the deepest 

 boreholes in Germany, at Czuchow in Upper Silesia. Still 

 it is only an aid to recording strata and is not infallible 

 especially in very varied thin alternations of highly inclined 

 beds. Better results would arise if the paper were made to 

 move corresponding to the strata dips. Jahr's method 

 may, however, be regarded as a valuable adjunct to boring. 



Lapp's Stratigraph. — Here the pen moves by clockwork 

 at a definite rate over the paper which moves corresponding 

 to the deepening of the borehole. The recorder is connected 

 to the rope drum shaft on the pay-out feed from which 

 the rods hang. In Fig, 5 we have a view of Lapp's device 

 in which the worm wheel s transmits its motion through a 



