CORE ORIENTATION 87 



S. Collar U keeps switch s' closed until the hoisting 

 apparatus allows the drill to drop again. The drill shank 

 is not packed to keep out pressure water; the chamber B 

 is flooded with water unless previously filled with petroleum, 

 glycerine or other non-corrosive fluid. The switch box is 

 usually oil filled. Figure 2 is a modification of Fig. 1 

 wherein corresponding members are the same and are 

 lettered alike with unit indexes, except that the sheet 

 marker M' is here a stylus mounted on a carriage moved on 

 a track M^ by chain M^ from drum Af^ of clockwork Z 

 for timing M'. This clock also closes switch Z^ by arm Z' 

 of the motor circuit; otherwise a surface switch is used. 

 The track M^ is parallel to the radius of the index sheet S' 

 part of the way, and while the stylus carriage is traveling 

 on this part of the track the stylus marks the sheet. 



Before lowering from the surface the clockwork is wound 

 up and set to close nlotor switch Z' at a known time and 

 then rotate drum M^ for moving the stylus. On gaining 

 the bottom of the hole the motor starts and the tool 

 indents the rock and the mark position will depend on the 

 twisting of the device on lowering. After this the sheet- 

 marking device operates and marks the index sheet. 

 The position of the marking device depends on that 

 of the tool, but the position of the sheet is governed by the 

 compass. After marking the sheet and rock the whole 

 is raised to bank, a coring apparatus is lowered and a core 

 extracted with the said indentation on it. This mark is 

 correlated with the index sheet mark and the direction of 

 dip ascertained. The objections to the device are the addi- 

 tional coring operations, dangers of cavings spoiling mark- 

 ings, the great consumption of time and therefore money 

 and the diameter limitations for all such devices as pre- 

 viously noted. 



Hanna's Apparatus. — This device which is essentially 

 a compass and plumb-bob apparatus has been fairly exten- 

 sively employed in the California oil fields, the inventor 

 having been formerly assignor to the Associated Oil 

 Company of San Francisco. The compass and plumb bob 



