STRUCTURE OF PROSPECT MOUNTAIN. 15- 



nature. On Ruby Hill there are at least two beds of shale, one of which 

 is intercalated in the Prospect Mountain limestone, and it is certain that at 

 least that number can be found on Prospect Mountain. 



Whether the third and widest belt of shale encountered in this tunnel 

 actually comes to the surface or not cannot be determined at present with 

 absolute certainty, but shale rock is found above the Industry mine, and it 

 is probable that it is a part of the third body of shale encountered in the 

 tunnel. 



This third belt of shale is also somewhat different in character from the 

 first, which seems closely allied to that found on the surface at Ruby Hill. 

 It consists of alternate strata of argillaceous shale and thin bands of stratified- 

 limestone, and, although considerably thicker than the lower shale of Ruby 

 Hill, is lithologically almost identical with it. The width of this shale in 

 the tunnel may be owing to the flatter position which it occupies or to local 

 expansion. The first zone of limestone has the usual appearance of the 

 mineral limestone of the district. It is crushed and broken, and all signs 

 of stratification have been obliterated. It is usually gray in color and 

 sometimes stained yellowish by iron oxide. It contains vuggs and numerous 

 seams. Where not too much crushed, it is crystalline in texture and some- 

 times brecciated, the different fragments being cemented together by calcite, 

 One of its peculiarities is the difference of the varieties which it presents 

 within a few feet. The foregoing will apply to all the metalliferous lime- 

 stones of the district. It is difficult to state what the precise differences 

 are which distinguish the mineral limestone from the other limestones. It 

 is not the difference in geological age which distinguishes it, but rather 

 differences which are due to d}*namical and chemical action. It is never 

 continuously stratified, and it is never found for any considerable distance 

 without a change in its physical characteristics. It always bears strong 

 evidences of metamorphism. The next zone of limestone is the largest, 

 extending 935 feet from the first to the second belt of shale. .It presents 

 the usual characteristics of the mineral limestone, and owing to its great 

 extent offers almost all the varieties of that rock to be seen on any part of 

 the mountain. The narrow belt of mineral limestone found further on is 

 similar to the main mass, from which it is separated by a thin belt of shale.- 



