244 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



We may consider this accessory information yielded by 

 this method in the same way as Professor Heiland of the 

 Colorado School of Mines. In Fig. 162 we have a hard 

 limestone overlain by loose sandy clays, the former having 

 a wave velocity of ?^ and the latter of Vi when a charge is 

 fired at S. The shock wave intervals are measured off on 

 the graph, shown where the scales E 

 of the concussion are set off at inter- 

 vals of 200 and 280 m.; the corre- 

 sponding times are the ordinates. 



At El and Eo the course-time and 

 wave velocities are proportionate 

 (straight-line law), the shock being in 



Distance 



Fig. 162. 



Fig. 163.— Diagrams of 

 time-travel curves over 

 different tectonic features. 



one uniform stratum with velocity Vi, but from the latter point 

 onward the waves lengthen, running in the deeper stratum 

 with the higher wave velocity V2. The resulting course- 

 time curve shows a nick at k, such nicks always betraying 

 density, etc., changes in the strata. The position of the 

 nick point gives the surface limit ^ of the hard stratum at 



^ "Electrical Prospecting in Sweden," p. 31. 



