SUMMARY. 177 



THE STRUCTURE OF PROSPECT MOUNTAIN. 



Manner of upheaval. — Prospect Mountain and its adjacent spurs form an anti- 

 clinal fold, of which the axial plane is somewhat west of the crest of the 

 principal ridge. The course of this plane is nearly due north and south 

 ' except at Ruby Hill, where it turns towards the west. Evidences of bed- 

 ding are so rare that it is often impossible to form an accurate idea of the 

 prevailing angle of dip. When the formations which at present compose 

 the mountain were folded and uplifted, an enormous crushing and grinding 

 force was exerted upon the different members of the series. Those rocks, 

 such as the shales, which were flexible were much twisted and distorted, 

 but retained their original character. The limestones, on the other hand, 

 were much crushed and fissured, and faulted in many directions. Most of 

 the fissures were found parallel to the axis of fold, and as the uplifting and 

 crushing continued great zones of limestone were ground almost to powder. 



influence of eruptive rocks. — Subsequently to the primal folding the various 

 eruptions, especially that of rhyolite, had a further disturbing effect upon 

 the structure of the country. Many fissures and faults have unquestionably 

 been caused by the eruption of the rhyolite, and, as will appear later, it 

 had a direct influence upon the deposition of ore. 



The only known occurrence of granite in the district is on Mineral 

 Hill at the north end of Prospect Mountain. It is probable that this mass 

 formed a submarine hill upon which the quartzite, limestone, etc., were laid 

 down, and that its exposure in its present position is due to erosion after 

 upheaval had taken place. 



Bowlders resembling this granite have been taken from the quartzite 

 in the Richmond shaft. The strata of the formations which compose Pros- 

 pect Mountain usually dip away from the axial plane of the fold, though 

 there are notable exceptions to this rule. 



Section of Prospect Mountain through Eureka tunnel. The best Opportunity for Studying 



the formations on the eastern slope of Prospect Mountain is given by the 

 Eureka tunnel, which has been driven from a point near the head of the 

 west branch of Goodwin Canon in a nearly due west direction into the 

 heart of the mountain. 

 2654 L 12 



