STRUCTURE OF RUBY HILL. 23 



served in a tunnel which is run into the southwest side of Ruby Hill some 

 few hundred feet to the northeast of the Isandula shaft, a shaft sunk in the 

 debris of Spring Valley. In this tunnel the quartzite is cut through, and 

 there are signs of a flat undulation ; the strata dipping to the northeast in 

 the face of the tunnel and to the. southwest at its entrance. There is said 

 to be another locality where this can be observed, but it was not possible 

 to examine it, as the drift in which it occurs was inaccessible. It is in a 

 drift run to the west from the Buckeye shaft, and 30 feet below the first 

 level (Lawton tunnel) of the Eureka mine. The position of the quartzite 

 can be seen on vertical cross-section No. 6, Plate VII. 



The quaruite ana limestone contact. — There is no regularity about the dip of the 

 quartzite and limestone contact, and there are but few places along its sur- 

 face where a cross-section would show that the dip remained constant for 

 any considerable distance. A glance at the various vertical cross-sections 

 and the plan of underground contacts (Plate III.) will show that both the 

 dip and the strike of the quartzite contact are very irregular. In some 

 places, though these are not frequent, this contact pitches back. This can 

 be observed on the plan of contacts (Plate III.), where the quartzite on the 

 fourth level of the Eureka projects out over that found below on the fifth. 

 It also pitches back at the end of a drift from the big cave situated nearly 

 on a level with the little tenth level of the same mine. This cave, which 

 will afterwards be described, lies west of the main incline from the ninth 

 level. Besides smaller irregularities in the quartzite, there are three large 

 protrusions along the course of this contact, which occur, respectively, in 

 the Phoenix, K. K., and Richmond mines. The first of these occurs in the 

 Phcenix and K. K. ground and extends from above the fourth level down to 

 the seventh of the latter mine with a northerly trend. The second begins 

 about 300 feet southwest of the Lawton or Eureka shaft on the third level 

 and extends with a northeasterly trend down to the tenth level. The third 

 begins on the surface near the "compromise line'" 1 and trends in a north- 

 erly direction down to the ninth level of the Richmond, where it disappears. 

 Along the line of dip of this same contact there is a great depression sev- 



"The " compromise line" is the line dividing the respective claims of the Richmond and Eureka 

 companies, and was established during the early litigation between those mines. 



