PROSPECTING. 145 



rock is not of a sufficiently homogeneous character to exhibit a uniform 

 increase in value as an ore body is approached. Usually when there is a 

 marked increase in this value there are other indications of the presence of 

 ore bodies, such as stained and broken rock, fissures, and like phenomena, 

 which lead the miner in the proper direction ; and the determination of the 

 direction in which an ore body lies from a point in a drift where good assays 

 have been obtained is a very difficult matter, while prospecting in a wrong 

 direction is always a very expensive affair. At a remote point, where data 

 indicating the direction of an ore body would be of exceeding utility, the 

 relative differences in the assays are so small that no marked advantage can 

 be obtained from them and they would be very liable to mislead the pros- 

 pector. Notwithstanding these drawbacks, it is possible to render the 

 assaying of country rock of practical advantage, especially when the 

 diamond drill is used as a means of prospecting. Subsequent to the elec- 

 trical experiments and to the determination of the values of the country 

 rock on the 600-foot level of the Richmond, a considerable body of ore was 

 discovered just a few feet below this level near the point XV., where the 

 electrical phenomena and the assays indicated the presence of ore. The 

 discovery was made, however, by following a stratum of ferric oxide in a 

 cross-drift a short distance from the main level, and was not due either to 

 Dr. Barus's experiments or the assays of country rock, as before the discovery 

 of this ore body it was supposed that the phenomena observed were referable 

 to the large body of ore which existed above this level. This body of ore, 

 however, was further removed from point XV. than the ore subsequently 

 discovered. 



The correspondence between the assay values of the rock and the 

 values of electrical potentials found by Dr. Barus is clearly not accidental. 

 If it is possible that the phenomena are connected as cause and effect, or 

 that the differences of potential are due to the traces of ore in the rock, 

 then both methods only lead to the detection of local differences in compo- 

 sition, which may indeed be referred with some probability to the presence 

 of ore bodies in the neighborhood, but which might also be due to an acci- 

 dental dissemination of metallic compounds and be independent of the 

 existence of ore in considerable quantities. On the other hand, if the two 

 2654 L 10 



