WEST END WORKINGS. 185 



The West End shaft when last visited by the writer was 780 feet deep. 

 The soft Fraction dacite, which forms the block on the southwest side of the 

 fault, is first encountered in the shaft, but at a depth of about 20 feet the Oddie 

 rhyolite comes in. The contact of dacite and rhyolite strikes N. 35 to 55 e W., 

 or roughly parallel with the West End fault, and the dip is southwest at an 

 angle of aboijt 65, suggesting that the fault also dips in this direction and is 

 therefore normal. The contact is partly tight and partly separated by several 

 feet of breccia, containing fragments of rhyolite and of later andesite, with the 

 soft materials of the more fragile dacite. The rhyolite contact conies in on 

 the north side of the shaft and continues straight down to a depth of about 

 62 feet, where it passes out on the south side. The general dip of the rhyolite 

 dike is therefore to the south. At one or two places the rhyolite is evidently 

 intrusive into the dacite. The shaft passes downward through the upper contact 

 of the rhyolite with the breccia and traverses solid rhyolite for a short distance, 

 showing that here the thickness of the dike or neck is about 20 feet. On the 

 under contact of the rhyolite, at a depth of 84 feet, is green altered andesite, 

 which has been referred to the later andesite. At this contact also there is a 

 slight breccia. 



The above phenomena are interpreted as indicating that the rhyolite ascended 

 along a fault plane, which in the upper part of the shaft separates the Fraction 

 dacite from the later andesite. The intrusion of this rhyolite caused some brec- 

 ciation of the rigid intruded rocks near the contact, and it is possible that some 

 subsequent slipping along the fault may have slightly brecciated the rhyolite itself. 

 As a rule, however, it has been ascertained that rhyolite of this sort is younger 

 than the faults and is little or not at all affected by them. 



At a depth of 116 feet there is a zone of great movement and probable 

 faulting, in which the chief slips strike N. 10 W. and dip west at an angle of 25. 

 This suggests a northwesterly faulting. 



CHARACTER OF ANDESITE ABOVE 220-FOOT LEVEL. 



Below the lower rhyolite contact, at a depth of 84 feet, the shaft is in 

 andesite for some distance. All this andesite is extremely decomposed in conse- 

 quence of the proximity of faulting, and is therefore difficult to study. Below a 

 distance of perhaps 100 feet from the surface the character of the andesite has 

 occasioned much perplexity in the mind of the writer. The earlier and the later 

 andesites are so closely related that many times they have almost identical char- 

 acteristics, and it is difficult or impossible to discriminate them in the hand 

 specimen or under the microscope. A specimen taken in the shaft, at a depth of 

 116 feet, was judged to have the characteristics of the later andesite rather than 

 of the earlier andesite. Another specimen taken in the shaft, at a depth of 19t> 



