DEEP BOREHOLE SURVEYS AND PROBLEMS 



menced vertically and at a distance of 60 m. apart, actually 

 met at a depth of 850 m. 



About 25 years ago interest in the survey of boreholes 

 was quickened by a series of very ingenious contrivances 

 which were invented to cope with borehole deviation. 

 Borings hitherto considered vertical were now subject to 

 doubts. In 1908 Joseph Kitchen presented the results 

 of his surveys of some 22 deep boreholes on the Rand 

 before the Institution of Mining and Metallurgy^ which 

 stimulated a wide discussion and was supported by many 

 other instances of deflection. He surveyed the dip of the 

 holes at intervals of about 500 ft. and averaged his results, 

 which method, though not precise, sufficed as an indication 

 of the great deviation in this area. With an average total 

 borehole depth of 3,370 ft. he found an average horizontal 

 displacement of 1,165 ft. with an average lowest depth of 

 survey points of 3,015 ft. He shows in Table I figures of 

 average angular deviations obtained by instrumental 

 survey in the holes. 



1 After J. Kitchen by permission of the Institution of Mining and Metallurgy. 



These tend to oppose the general rule that inclined strata 

 exaggerate the deviation which, however, may be a local 

 circumstance. The accompanying displacement is shown 

 in Table II. 



1 The Deviation of Rand Boreholes from the Vertical, by Joseph Kitchen, 

 Session 1907-1908. 



