40 



GEOLOGY OF THE EUREKA DISTRICT. 



rano-e, both in silica and nia<»-nesia. Two complete analyses were made of 

 this limestone, one from the sunnnit and the other from the base of the 

 epoch, each representing- a well defined and persistent bed, as follows: 



Silica 



Alumina 



Ferric oxide 



Ferrous oxide . . . 



Manganese 



Lime 



Magnesia 



Water 



Carbonic acid . . . 

 Phosphoric acid . 



Chlorine 



Organic matter . , 

 Alkalies 



Total 



Base of 

 Hamburg 

 limestone. 



24 '00 

 ■12 



■12 



41-97 

 ■80 

 •16 



32^62 

 •07 

 ■01 



trace 



trace 



99-87 



Summit of 

 Hamburg 

 limestone. 



3^94 

 ■64 

 ■43 

 •20 

 •61 



51 •96 

 •52 

 •37 



40^71 

 •50 

 •01 

 •03 



trace 



99^92 



An examination made of a dark compact limestone from the base of 

 the Hamburg, collected on the north side of the ravine opposite the dump 

 of the Richmond shaft, g-a.-\-e 



Silica -84 



Carlxmate of magnesia 1-18 



A gray dolomite from the 350-foot crosscut in the Dunderburg mine 

 yielded 



Silica -07 



Carbonate of magnesia 40'04 



111 general, this limestone is sharply contrasted in its lithological habit 

 with the Prospect Mountain body, as it is darker in color, can-ies siliceous 

 material in place of the clayey beds of the latter, and possesses a character- 

 istic rough and ragged surface produced by Aveathering. The thickness of 

 this limestone may be taken at 1,200 feet, and except in the shaly lime- 

 stones at the top and bottom of the series, no planes of bedding are trace- 

 able for any great distance. At Adams Hill, however, where the beds lie 



