344 



GEOLOGY OF THE COM STOCK LODE. 



given to Point XV., in using it 

 alone as a basis for the cocirdi- 

 nation of tlie results of the sur- 

 ve^ys on the 5C0 and 4()0-foot 

 levels, is to be criticised. It 

 was intended to use several 

 consecutive points for this pur- 

 pose; l)ut in each case local 

 interferences prevented. As a 

 whole, however, the results are 

 ^f sufficiently interesting to jus- 

 ^ tify further and more careful 

 ^- investigation. 



■~ Experimentson the 600-foot level. Results. 



t — This series of measurements 

 i was made with the intention of 

 ^, observing the variation of po- 

 I tential encountered in passing 

 I across the ore bodv, without 

 actually entering it. Care was 

 = also taken to place all the 

 ^ points, so far as practicable, 

 T. in rock of the same variety, 

 i and to remove the ends of the 

 line of survey as far from the 

 ore body as possible. 



The plan of the position 

 of the drifts on the (iOO-foot 

 level, relatively to the ore- 

 chambers, is given in Fig. 29. 

 As before, the points tapped 

 are distinguished by small cir- 

 cles, to which Roman numer- 

 als are annexed. P. C. in this 



