88 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



before the formation of the ore bodies. Had segregation taken place at all, 

 it must have taken place throughout the mass of limestone; and it is very 

 difficult to conceive of metal-bearing solutions or ore in any other form 

 traversing hundreds of feet of limestone, offering every opportunity for the 

 deposition of ore, and passing across fissures in such a manner as to leave 

 no trace of their passage in many of the openings which must necessarily 

 have been in their course, if they were derived from the country rock; yet 

 this is what must have occurred, if the theory of segregation were applicable. 

 Had the ore been segregated, it is probable, too, that there would have been 

 no well-defined boundary between the country rock and the ore. Such is 

 not the case, however. The ore is as definitely cut off when it comes in 

 contact with the limestone as if it had been shoveled or rammed into the 

 caves and openings. The limestone is often impregnated with ferric oxide 

 in the neighborhood of ore chambers, but the dividing-line between the fer- 

 ruginous limestone and the ore is very plain. The limestone at a distance 

 of 6 inches from very rich ore often shows no signs of iron or of anything 

 else that would indicate the proximity of ore. 



segregation from the shaie. — The shale nowhere carries more than a trace of 

 silver and gold, and what has been said in regard to a segregation from the 

 limestone applies also to the shale. Indeed, it is still more improbable that 

 metal-bearing solutions should have been uninterrupted in their passage 

 through the clay of the Ruby Hill fault and should not have been concen- 

 trated on its hanging-wall side. A derivation of the ore from the shale is, 

 therefore, inadmissible. 



segregation from the quartzite. — Silver, gold, lead, and some other minerals have 

 been found in small quantities in the quartzite, but ores were never obtained 

 from the latter rock in paying- quantities, and occurred chiefly in small 

 seams and fissures. It has been explained that there has been considerable 

 motion of the quartzite upward against the limestone along a fissure, and 

 that this fissure contains a great deal of clay and was of prior origin to the 

 ore bodies. What has been said in regard to mineral solutions traversing 

 the clay of the main fissure is equally true in this case. A segregation of 

 ore from the quartzite is, therefore, hardly among the possibilities. Neither 

 is it possible to suppose that the ore was introduced from above, for none 



