AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 23 



faster the boring progresses and the flatter the slower the 

 crown penetrates the measures; therefore a horizontal 

 portion of the line shows that the tool is not piercing the 

 rocks even though the rods are rotating; that is to say, 

 that the rod feed is not paying out. When the plant is 



S^^m%^ Y/////?///^/y//////i^/^^///'//^, 



Fig. 3. — Jahr's stratigraph — the derrick drive. 



idle, and therefore the driving shaft of the recorder, the 

 registration ceases. The most important inferences from 

 the record are provided by changes of direction in the pen 

 line because they show that different strata have been 

 struck and thus provide valuable clues as to the conditions 

 arising in this new ground. Such a change in the line only 

 occurs in the flatter measures ; in inchned deposits the change 

 is more gradual because the crown only then penetrates 

 the new stratum gradually. In Fig. 3 note that the motion 



