CAVES AND CREVICES. 3<)7 



outside these limits have failed to discover any accumulations of ore. The 

 limestone on the north side of the Ruby Hill fault presents a fairly com- 

 pact uniform appearance occasionally well stratified. Between the two 

 fissures the limestone is crushed and broken, everywhere showing the effect 

 of great pressure accompanied by movement. Much of this rock indicates 

 alteration by chemical process since the fracturing and displacement. The 

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

 siliceous in composition, and in distinction to the limestone between the 

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

 belts and resembles the lower strata of limestone on Prospect Ridge. By 

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

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

 crashed or mineral limestone, while the beds overlying the main fissure are 

 referred to usually as the front limestone. 



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

 which the main fissure has been formed, to the secondary fissure as shown 

 by a vertical cross-section in the Phoenix mine. It will be seen that the 

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

 rhyolite dike follows the Ruby Hill fault, and nowhere deviates to the 

 southward in its upward course. 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 the 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 1)6611 Stated that the fissure which 



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 secondary 

 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 

 approximately parallel with the Ruby Hill fault, and due to forces acting at 



