SUMMARY. 191 



dry assay, while even if the degree of accuracy reached in determining the 

 absolute contents in precious metals of the Eureka rocks has been over- 

 estimated, the value of the results would scarcely be impaired, for it will 

 hardly be denied that the results form a sufficient basis for a comparison of 

 different samples of the same rock, all containing very small quantities of 

 silver and gold. For the purposes of this report it makes little difference 

 whether a certain mass of limestone really contains 10 cents or 20 cents, if 

 it can be proved that a second body of limestone contains twice as much, 

 or, it may be, half as much. In other words, the main purpose was to 

 ascertain the relative contents, not the absolute contents, of the samples 

 assayed. Even if the methods employed were ideally exact, it would be 

 impossible to calculate the metallic contents of large blocks of ground with 

 precision, since it would be impossible to obtain samples which should cor- 

 rectly represent the average of the mass. 



PROSPECTING. 



Methods of prospecting. — There is nothing remarkable about the methods of 

 prospecting in the Eureka District. On Prospect Mountain it consists in 

 following seams or fissures in the limestone which show indications of ore, 

 or in sinking shafts and driving levels in different directions in that rock. 

 At present Prospect Mountain is being explored by a system of tunnels, 

 which method, owing to the nature of the ground and the relation of the 

 claims to each other, offers some advantages. On Ruby Hill the shafts are 

 sunk in the zone of mineral limestone between the quartzite and shale, and 

 prospecting is carried on by cross-cutting between the two last formations, 

 particular attention being paid to the following of fissures and broken 

 ground. Caves, as well as stained limestone, are usually considered an 

 indication of ore. 



Earth currents and assays in relation to prospecting. It Cannot be Said that the eleCtri- 



cal experiments made by Dr. Barus in the Eureka mines have as yet led to 

 any decisive results as regards the indication of the presence of ore bodies. 

 There is, however, a remarkable coincidence in the results obtained by Dr. 

 Barus with those obtained from assays of country rock along a line leading 

 up to an ore body. In both cases the presence of the same body was indi- 



