STRUCTURE OF RUBY HILL. 43 



material, however, can be found in many places in the mineral belt, and 

 this dark rock exhibits no characteristic features that would distinguish it as 

 coming from the front limestone. 



characteristics of the from limestone. — It has not been possible to find an y charac- 

 teristic features in either of these two limestones which would distinguish 

 them from each other; and although the limestone southwest of the fissure 

 certainly belongs to the lower belt of limestone and that northeast of it to 

 the upper, yet there is nothing in the appearance of either that would indi- 

 cate that they belonged to different masses unless it is that the front lime- 

 stone is less disturbed and that its stratification is more frequently percep- 

 tible. 



The quartzite southeast of the compromise line. The quai'tzite ill the foul' mineS SOlltll- 



east of the Richmond shaft appears to be substantially a solid mass many 

 hundred feet in thickness. Its contact with the limestone is very irregular, 

 and the rock near the surface is often displaced to a greater or less extent 

 by faults, but it is comparatively easy to explain these irregularities and to 

 account for the phenomena exhibited. Not so, however, with the quartzite 

 in the Richmond and Albion ground northwest of the working shaft of the 

 former mine. 



The quartzite in the Richmond and Albion. The explanation of tll6 OCCUlTenCe of 



this quartzite and of the manner in which it was brought into its present 

 position in this part of the hill is a matter of great difficulty, partly owing 

 to the absence of sufficient explorations in the neighborhood of the Rich- 

 mond shaft and partly on account of the complex character of the move- 

 ments which have taken place. The quartzite (see Plate III.) on entering 

 the Richmond ground from the Eureka bends toward • the west, as has 

 already been stated, and forms a promontory which pitches to the north. 

 This rock is first encountered in the Richmond shaft at a point about 30 

 feet above the seventh level and the shaft continues in quartzite down to 

 the deepest point reached, namely, a perpendicular distance from the sur- 

 face of 1,230 feet, which would give the quartzite a vertical thickness of at 

 least 580 feet. A cross-cut on the twelfth level, driven a little east of north, 

 passes through 360 feet of this rock before reaching the limestone. A cross- 

 cut on the 1,050-foot level driven a little west of north strikes the limestone 



