80 DEEP BOREHOLE SURVEYS AND PROBLEMS 



First a trepan is sent down to mark the core head with a 

 blow and then raised to allow the apparatus to enter. 

 The lead plate d on the base outside takes an impress 

 of the core face with its mark. At the same time the lever 

 coming into contact with the core uncovers the objective. 

 After a few seconds the needle is at rest and overexposure 

 of 20 to 30 min. allowed. The image of the needle and the 

 guide points is thus fixed on the sensitive plate. The device 

 is now raised, an interior spring closing the shutter. At 

 the surface the lead plate shows the core-face impress with 

 trepan mark on the lower side and the impression of the four 

 holes on the other. The film, when developed, shows the 

 position of the needle and the guiding marks on the phos- 

 phorescent disc. Thus the core is orientated and later 

 coring is completed and the core compared. 



The instrument is robust, the lenses of the objective being 

 completely isolated in the middle of it and being of great 

 thickness are strong enough for the job. It is only nec- 

 essary to clean the device carefully after use, the whole 

 of the parts, except the needle, being of copper alloy. 



If the borehole water is too hot for normal gelatine the 

 film should be plunged into a bath of 5 per cent formalde- 

 hyde solution; this makes the gelatine insoluble and capable 

 of resisting decay without impairing the sensitiveness 

 of the film or the development of the image, which is done 

 by a slow process. The phosphorescent plate is designed 

 to do away with electric lamps with accumulators which 

 are not suitable for shocks. 



The factors operating against the device are the great 

 consumption of time in letting in the trepan to mark the core 

 and its extraction, etc. Cavings also affect the marking 

 and friable strata prevent its employment. If there is no 

 orientating coupling it suffers all the defects of any other 

 apparatus, giving directions aligned on its own markings. 



Goodman's Core Orientation and Borehole Deflection 

 Apparatus. — This device was invented by Professor Good- 

 man of Leeds University in 1908 and can be employed 

 both for orientating cores and surveying borehole devia- 



