CHAPTER II 



AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 



Previous to discussing the various instrumental methods 

 of surveying deep boreholes some of the more important 

 ancillary records kept on modern plants will be described. 

 These additional memoranda aid very materially in check- 

 ing the accumulated borehole data in that they frequently 

 save much time and guesswork as to causes of various 

 curious features incident to deep boring. 



PROGRESS RECORDS 



These are continuous automatic checks or descriptive 

 graphs of the progress of the borehole in respect to length 

 and time. They provide a check on the difficult and 

 often unreliable observations of the boring personnel. 

 They yield conclusions as to the successive hardnesses 

 of the strata pierced and assist in their determination, 

 since each stratum corresponds to a definite boring pace. 



The simplest device is a scale fixed on the rods and read 

 every 5 min. and booked, but it is more exact to have a 

 record depending on the length of hole and revolutions per 

 minute, since the rapidity of boring through strata depends 

 on the r.p.m. of the rods in the rotary or the number 

 of strokes per minute in the percussive system. They are 

 known as stratigraphs or strata-progress recorders. 



Jahr's stratigraph^ (Fig. 3) consists of a pen recording 

 on a graph drum the latter revolving at the same rate as 

 the rods and its motion round being at right angles to that 

 of the pen. Thus the increase of depth of the crown bit 

 will appear as abscissae and the corresponding revolutions 

 as ordinates. The recorded line is thus the steeper the 



^ E. Jahr, Chief Mine Survej'or, Breslau. 



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