RUBY HILL FAULT. 



few degrees west of north, passing just west of the Jackson shaft. From 

 this point westward it is difficult to follow the Ruby Hill fault on the 

 surface, as it lies wholly in limestone more or less concealed by soil and 

 de"bris, and the rhyolite which to the southeast of the Jackson fault 

 materially aids in tracing the displacement nowhere comes to the surface 

 after crossing the latter fault. At the time the accompanying map was 

 printed the line of the Ruby Hill fault had not been followed west of the 

 Jackson mine, but since then Mr. Curtis has traced it through the under- 

 ground workings of all the mines as far as the extreme limit of exploration 

 in the Albion. 



According to the investigations of Mr. Curtis the fault after leaving the 

 Phoenix mine runs in a nearly northwest direction, agreeing closely with its 

 course on the east side of the Jackson fault. It passes just to the north- 

 east of the KK shaft and southwest of the Richmond office. It persistently 

 cuts all formations, quartzites, limestones, and shales alike, scarcely devia- 

 ting from a straight line and apparently uninfluenced by the physical 

 conditions of the rock. In like manner the fractures and displacements 

 produced by the earlier orographic changes whicli elevated the region have 

 exerted but little influence on the course of the Ruby Hill fault. A study 

 of the disturbances and dislocations of the strata point to the conclusion 

 that this fault, with its accompanying fissure, was the last dynamic move- 

 ment in the history of Ruby Hill. Wherever underground explorations 

 admitted of observation the average dip of the fissure plane was found to 

 be about 70 to the northeast. Southeast of the Jackson fault the width of 

 the fissure and the dip of its plane are unknown. 



Subsequent to the formation of the fissure and probably nearly coinci- 

 dent with it was the filling of the wider portions with intrusions of rhyolite, 

 notwithstanding the fact that they nowhere quite reach the surface on 

 Ruby Hill. 



Evidence goes to show that the volcanic energy displayed along the 

 fault line expended the greatest activity near its junction with the great 

 Hoosac fault, the powerful extravasations of rhyolite gradually dving out 

 toward the northwest, and beyond the intersection with the Jackson fault 

 failed to overflow the top of the fissure walls. The rhyolites exposed in 



