418 MIKING INDUSTRY. 



exclusively confined to the Devonian limestone. The highest stratigraphical 

 position of any mineral deposit yet found occurs along the line of contact be- 

 tween the limestone and the overlying calcareous shale. 



The mode of occurrence of the silver deposits upon Treasure Hill is ex- 

 ceedingly varied ; these may, however, all be classed under four heads : 



First. In fissures, dipping at a highly-inclined angle, and striking approx- 

 imately east and west; that is, across the strike of the limestone of the hill. 



Second. In contact deposits, between the limestone and calcareous shale. 



Third. In beds or chambers in the limestone, parallel to the line strati- 

 fication of the rock. 



Fourth. In irregular, vertical, and oblique seams, or joints, across the 

 bedding of the rock, and having most frequently a north and south course. 



The Eberhardt mine affords the finest and most marked example of a fis- 

 sure, if, indeed, it is not the only one occurring upon Treasure Hill which ex- 

 tends to any great depth below the surface. The width of the claim between 

 the walls is 200 feet. The strike is nearly east and west. The north wall pre- 

 sents a smooth, clean surface, dipping 78° to 80° to the south. 



The material inclosed between the walls is by no means all ore; a large 

 part of it is composed of masses of barren limestone, surrounding which is 

 the quartz and ore-bearing material. The gangue of the ore is made up of 

 pieces of broken limestone of irregular shape and size ; some of it presents 

 the appearance of hard, compact grit; much of it is very fine and completely 

 impregnated with silica, the entire mass being held together by fine granu- 

 lar quartz, which fills up the intervening space. The silver, as cerargyrite, 

 or chloride of silver, occurs finely disseminated through the gangue. In the 

 richer bodies of ore the chloride is found coating and incrusting in their layers 

 the more solid pieces of quartz ; sometime it occurs filling up or lining the 

 cavities and druses. 



The contact deposits are found 9,t the north end of Treasure Hill, 

 wherever the calcareous shales are found in place. All along the line of con- 

 tact of the two formations may be traced the characteristic minerals that 

 accompany the silver deposits ; quartz, calcite, ferruginous matter, all more or 

 less impregnated with chloride of silver and traces of the base metals. 



