CAVES AX1> CREVICES, :^(17 



outsidt' these liniiTs Imve tailed to discitver aiiv jicciiinulatioiis of ore. The 

 Hmestoue on tlie north side of the Rub\' Hill fault [)reseiits a fairly com- 

 pact uniform appearaiu'C occasionally \vell .stratified. Between the two 

 fissures the limestone is crushed and l)roken, everywhere showing the effect 

 of g-reat pressure accompanied liy movement. .Much of this rock indicates 

 alteration hy chemical process since the fracturing- an<l displacement. 'I'he 

 limestone south of the secondary fissure is for the most part black in color, 

 siliceous in composition, and in distinction to the limestone lietw(;en the 

 fissures uniform in structure. It is more easily recognized than the other 

 belts and resembles the lower strata of limestone on Prospect Ridg-e. B\' 

 the miners the limestone beneath the secondary fissure is known as the 

 back limestone ; that found between the two fissures is called either the 

 crushed or mineral limestone, while the beds overhing the main fissure are 

 refeiTed to usually as the front limestone. 



Figure 6 represents the relative position of the Ruby Hill fault, along- 

 which the main fissure has lieen formed, to the secondar\' fissure as shown 

 by a vertical cross-section in the Ph(X'nix mine. It will be seen that the 

 two fissures come together just below the .sixth level of the mine. The 

 rli\-olite dike follows the Rub\' Hill fault, and nowhere deviates to the 

 soutlnvard in its upward com-se. In the ground shown by the section the 

 secondary fissure adheres closely to the line of contact between the quartzite 

 and limestone. The ore body is cut by the shaft extending from tlie surface 

 nearly down to the point of contact between the formations. Near the 

 third level the shaft enters the underlying quartzite and has been sunk only 

 a short distance below the fifth level, the sixth being reached by an incline. 



Preexisting Caves and Crevices.— It has been Stated that the fisSUre whicll 



accompanies the main fault on Ruby Hill has been the principal channel 

 through which the intrusive rhyolites have been forced upward to within a 

 short distance of the surface, if, indeed, they have not accumulated on top and 

 subsequently been removed by erosion. On the other hand, the secondar\' 

 fissure carries no rhyolite, but, accompanying it, especially along the contact 

 of rhyolite and limestone, are large and valuable bodies of ore. Between 

 these two fissures the crushed limestone shows the evidence of faulting 

 approxiniateh" parallel witli the l\ul)\- Hill fault, and due 1o forces acting at 



