HAiN.] GENESIS OF THE ORES. 61 



sandstone. There are a few small crystals of galena. Calcite seems 

 to be entirely absent. In the second shaft a limestone is present and 

 small amounts of galena and fluorspar show. In the third, located 

 farther south, near a contact of limestone and sandstone, small 

 itmounts of galena, pyrite, and fluorspar occur in cracks in the lime- 

 stone. 



Big Four mine. — On the Miller land, section 32, a shaft has been 

 sunk 30 feet in Chester limestone. This rock is apparently in place 

 and undisturbed, though near it pieces of brecciated limestone 

 cemented by calcite were picked up, and in the same vicinity there 

 are small pieces of blende and evidences of faulting. In general it 

 ma}^ be said that in the vicinity small quantities of the sulphides and 

 of fluorspar are widely disseminated and the rocks are faulted and 

 broken in a manner favorable to ore deposition. At the time the 

 area was visited, how^ever, no considerable bodies of ore had been 

 located. Later prospecting is said to have given more encouraging 

 results. 



GENESIS OF THE ORES. 



It is impossible in the present condition of knowledge to make an 

 exact and final statement as to the origin of the ores of this district. 

 Tlie best that can be done is to indicate certain alternative hypotheses 

 and to discuss their possible conflicts and agreements. In view of 

 the unusual character of the ores and the interest attaching to them, 

 it is believed worth while to do this, even though it be admitted at 

 the outset that the explanation offered is founded on hypothesis, 

 though in accord with the facts as known. 



ORIGINAL SOURCE OF MATERIAL. 



The ore bodies represent concentrations of material normally pres- 

 ent in rocks in a disseminated form. The minerals entering into 

 their composition must have come either from the sedimentary rocks 

 exposed at the surface and continuing for some depth below, or from 

 deeper lying igneous rocks of which the dikes present at the surface 

 represent offshoots. Neglecting calcite, pyrite, and other minerals 

 widely distributed, attention may be concentrated on the rarer 

 metallic sulphides — galena, blende, and stibnite — and on the fluorite. 

 The discussion of their possible origin will be taken up in order. 



ORE MINERALS. 



The common ore minerals of this district, neglecting secondary 

 and derived forms, are galena and blende. These sulphides of lead 

 and zinc occur in both igneous and sedimentary rocks and are widely 



