306 



IRVING. 



portion of calcite, and partly by the strength and volume of the 

 siliceous solutions. The width of the shoots is dependent on 

 the latter condition, the length, upon the length of the supply- 

 ing fissures. Fig. 19 illustrates the general type of siliceous 

 ore -body in the Cambrian. 







A\30TiKra 



Gtoss S,u\-ic,, c]. Che eL+*. 



PldvNoVl^eCWv 



Fig. 19. Generalized plan and section of a siliceous ore shoot in the Cambrian 

 shale. The plan of the shoot is broken at the center, to illustrate the general paral- 

 lelism of the vertical to the longer diameter of the ore-body. 



Horizons. — The. horizons of the ore bodies are first, that of 

 the sandy limestone immediately overlying the basal Cambrian 

 quartzite and, second, other horizons near the top of the same 

 series, but not definitely determined. The larger number of 

 mines have been opened upon the lower horizon, and as com- 

 pared with the upper, it has so far proved to be superior both in 

 the frequency and size of the shoots, and in the grade of the 



