ELECTKICAL ACTIVITY OF ORE BODIES. 



351 



electrical properties altogether (earthy), the field of electric action being 

 confined to certain definite parts of the ore-dei)Osit. (See also page 364.) 



Experiments on the surface. — Encouragcd by tlie rcsnlts on the GOO-foot level, 

 it seemed not impossible that currents might also be observed on the surface 

 itself, insomuch as the ore extends in places to within 100 feet from the sur- 

 face, while vestiges of croppings, etc., still remain 



A line of points lying in general in a north-and-south direction, and at 

 distances of about 100 feet apart, was chosen, the object being to extend 

 the electric survey from shale in the north, free from ore, over Ruby Hill 

 and the large ore bodies in its interior, to quartzite in the south, also more 

 or less free from ore. It was hoped that in this way a passage through a 

 field of electrical activity might actually be made. Unfortunately, the work 

 was interrupted by a heavy snow-storm and accompanying frosts. 



P. C. was placed about half way up the hill in compact limestone. 

 Point I. is the most northerly of the series, and remote from ore; Point IX. 

 approximately over the Richmond ore bodies. The results are contained 

 in the following table, e is the mean of a single triple set. The potential 

 of P. C. (Point VI.) is arbitrarily put equal to zero. 



Table XVIII. 



In the table the unusually high values for the resistances of tlie cir- 

 cuits, P. C. earth T. Q., are a striking feature. This may be due either to 

 the compact and impervious structure of the rock (the drill making very 

 slow progress), or, as the experiments were made in the earli* spring, to 

 the possibility that the moisture in the rock was still frozen. In either 

 ease, however, the supposition that the conductivity of the rocks is princi- 

 pally due to the presence of moisture in their pores receives fresh support. 



