The Interior of the Earth 



regions to be inferred from the study of more 

 superficial formations. One can follow within 

 the earth's crust the geological strata encased 

 one within the other and determine the sequence 

 and thickness of the strata that a well sunk at 

 any point of the globe would traverse. Every 

 day brings forth new applications of strati- 

 graphy to mining or hydrological research. But 

 all this science stops short at the granite. What 

 is the thickness of this bottom bed? What is 

 there beneath it? Paleontology is silent and 

 petrology has very little to teach. 



The same may be said of the magnetic in- 

 vestigation of the globe, an infant science which 

 gives promise of great things for the future. 



It has hitherto confined itself to the deter- 

 mination of magnetic constants for all points of 

 the earth's surface, and has already been able 

 to reveal faults and internal dislocations, which 

 might have for years escaped the perspicacity of 

 geologists. Some day it will no doubt be pos- 

 sible to separate the share of magnetic action 

 due to electric earth currents from the mag- 

 netism of the rocks themselves. It will then be 



possible to begin usefully the study of sub- 



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