ELECTKICAL ACTIVITY OF ORE BODIES. 343 



is mei'ely to represent iu a systematic way the potential of consecutive 

 points, a curve may be constructed by representing the hnear distance of 

 ;inv point from 1. as abscissa, the corresponding' [)0tential as ordinate. In 

 tliis way Fig. 28 was obtained. From an inspection of the curve it ap])ears 

 that the ore body is in general at a lower potential than the points remote 

 from it. 



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Fli;. 28. — Earth potential and distauce. Hichmoud mine, 4(1(1 and .'lOd-foot levels. 



Here it must be remarked that only the extreme points on the 400-foot 

 level (XXVII., XXVI., etc.,) can, so far as known, be considered actually 

 distant from ore. In the vicinity of Points I., II., etc., 500-foot level, there 

 are not only the streaks of ore, n and j) (Fig- -7), but also chambers 7 and 10, 

 and still further east the large ore bodies of the Eureka Consolidated Mining 

 Company. This has been indicated by the dotted line in Fig. 28. 



The variation of potential is irregular, however — even more so than, 

 with the rough method of delineation, would have been anticipated — and its 

 amount is small. In fact, it will be seen that certain unavoidable errors 

 might conspire to produce an almost equivalent change. From results of 

 such a magnitude, in short, no prediction as to the occurrence of ore or 

 electroactive material would be justified. Not to mention minor matters, 

 the survey described suffers from a serious objection, due to the fact that 

 the temporary contact in progressing from I. to XXVII. passed through a 

 great number of varieties of rock, and therefore also, probably through a 

 great variety of absorbed liquids, holding more or less saline matter in solu- 

 tion. In such a case the electromotive force due to the contact of these 

 liquids would seem to come into play. As the matter will again be dis- 

 cussed (see page 356) I will add here only that electi'ic effects thus produced 

 cannot, a priori, be regarded as negligible. Furthermore, the preference 



