428 MINING INDUSTRY. 



tity of ore was already on this surface awaiting the completion of the com- 

 pany's mill, which has since gone into operation. The assessor's returns 

 show that in the quarter ending December 31, 1869, 2,437 tons were worked, 

 yielding on an average $43 59 per ton, in coin. The Aurora Consolidated 

 mine during the same quarter produced 2,672 tons of ore, that yielded 

 $28 50 per ton. In the figures just given there is a decided falling off in the 

 yield of the rocfe; as compared with earlier returns. There would appear, 

 however, to be large quantities of ore of similar grade, which in the future 

 ought to be mined and milled at a fair margin of profit. 



The Flats. — Just west of the Aurora deposits and a little further down the 

 hill are the gently sloping surfaces known as Bromide, Chloride, and Pogonip 

 Flats. The aggregate area included in these locations is about 2,000 feet long by 

 an average width of 600 feet, amounting to about 25 or 30 acres. The deposits 

 of ore present still another type, differing from those already described. The 

 surface consists of limestone, lying in strata that are nearly horizontal, though 

 dipping gently to the westward in most places. The strata are not always 

 well defined, but are somewhat broken and irregular in their bedding; and are 

 cut through by numerous seams and joints that are filled with crystalline min- 

 erals, chiefly calcspar, with some quartz. The ore occurs in channels, or 

 pockets, of irregular form and variable extent. Not all the strata are ore- 

 bearing ; on the contrary the ore-channels appear to be confined to one, or, at 

 most, to few of the limestone beds. The distribution of the ore-deposits over 

 the area is quite irregular, and in accordance with no law or system 

 thus far apparent. The conditions of their occurrence bear but little resem- 

 blance to those that characterize deposits of ore in veins ; they are, rather, a 

 network of seams, channels, or chambers that extend themselves horizontally 

 through the bed of limestone containing them, but with constantly varying 

 directions and dimensions. The pay-ground is sometimes limited or separated 

 from poor ground by seams or joints of calcspar or by "floors" in the lime- 

 stone, but they are as frequently ill-defined, the ore-bearing rock merging into 

 and mingling with the barren rock, without any apparent line of demarkation. 



In their mode of origin these deposits may have a close resemblance to 

 those of regular veins, for the breaks and fissures that traverse the region may 

 have been the channels through which ascended from below the vapors or 



