CHAPTER III. 



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 usually 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 toward the west. At those places on 

 the western side of the mountain where the strata have been laid bare by 

 mining explorations, the traces of bedding are so rare that it is impossible 

 to form an accurate idea of the prevailing angle of dip. 



When the alternating beds of shale and limestone, which at present 

 form 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 and would give, stood the 

 test of this great pressure with the least injury to their physical structure, 

 and, although they were much disturbed and flattened out, retained their 

 original character. With the limestones it was otherwise. Their hard and 

 compact nature and their tendency to break instead of bend when subjected 

 to great pressure caused the formation of numerous fissures and faults. 

 Most of these fissures were formed parallel to the axis of fold, though many 

 faults also occurred in every direction. As this uplifting and crushing con- 

 tinued great zones in the fold were ground almost to powder. Where the 

 limestone was the weakest or the pressure the greatest the first shattering 

 began, and as these breaks weakened the mass of the rock where they took 

 place, the grinding went on indefinitely until the uplifting force had spent 

 itself. 



influence of eruptive rocks. — Subsequently to the primal folding by which Pros- 

 pect Mountain was formed eruptions of rhyolite occurred, which had a fur- 



