CHAPTER VIII 

 PHOTOGRAPHIC METHODS 



Introductory Note. — In this group we include most of 

 the accepted methods wherein a photographic record is 

 provided of 



a. The actual walls of the borehole or the core outside 

 the apparatus. 



b. The positions of various mechanical or electrical 

 devices inside the apparatus. 



A vast amount of the world's boring is done by churn 

 drills and other percussive drills yielding just the sludge 

 of the percussion for examination at the surface. Even 

 core drilling, which is about three times as expensive, does 

 not always yield complete cores, owing to cavities and fri- 

 able strata. Again the computation of dip, thickness, etc., 

 obtained from the material produced by the drill tool suffers 

 in direct ratio to the discrepancies due to the above geo- 

 logical causes. 



An actual photograph of the borehole walls will remedy 

 this defect and also supplement any faulty evidence. When 

 the deposit is crystalline, as in certain copper, zinc, and 

 salt deposits, little experience is needed to translate the 

 photographic evidence and the same applies to marked 

 geological changes shown in the photograph. In amor- 

 phous deposits and those of massive regular texture more 

 experience must be acquired in order that one may (if 

 possible) decipher the data presented by the film. 



Photographic records of mechanically or electrically 

 controlled devices, or those depending on gravitational 

 action will be easily comprehended by any intelligent 

 person. All photographic records are well suited to con- 

 tinuous recording in and out of the hole. They are coming 

 more and more into favor for very deep holes, the multiple 



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