144 SILVER-LEAD DEPOSITS OP EUREKA, NEVADA. 



time after Dr. Barus's electrical experiments, but before his results were 

 known to me. Fig. 2, page 82, represents the position of the points I., II., 

 III., etc., as well as the relations of the ore bodies to the formations. Mr. 

 Becker, in his summary, states that the question of the practical value of 

 lode currents to the prospector has not yet been settled. 



The same may be said to be true of the value of the assays of country 

 rock as a means of determining the positions of ore bodies. Nevertheless 

 the coincidence of the two curves just mentioned, although by no means com- 

 plete, is yet too remarkable to be overlooked. The assays taken at points 



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Fig. 6. — Assay curve. 



XIII. and XIV. are abnormal. Although other assays were taken after- 

 wards at these two points, no assays as low as XIII. nor anything as high 

 as XIV. were obtained. If, therefore, the assays XIII. and XIV. were left 

 out, and the points XII. and XV. joined by a straight line, a curve almost 

 identical with that of Dr. Barus would result. 



Practical use of assaying in prospecting for ore. — There are many things that render it 

 a very difficult matter to make practical use of the assay value of the 

 country rock in prospecting for ore bodies. The maximum differences be- 

 tween the various specimens are in any case small; ordinarily the country 



