APPENDIX A. 157 



approach also to the structure of ordinary sand rock, but the gene- 

 ral character of the rock material has not changed much. 



The sum of the thickness of thtf rock series passed over between 

 the mouth of the river and the stamp mill, which is two miles up, 

 can not be much less than 1500 or 2000 feet. 



Under the more thick-bedded, argillaceo-arenaceous rocks men- 

 tioned, follow thinly laminated, blue, shaly layers, and then a bed, 

 or several beds, of a rather coarse-grained, grayish sand rock, hard- 

 ened by an abundant admixture of calcareous cement, and inter- 

 laminated by thin flexuose seams of a shining black shaly sub- 

 stance. This latter is the silver-bearing rock, varying from about 

 I foot to 4 and 5 feet in thickness. Further up the river the 

 strata retain the same direction, and in descending order, below 

 the silver-bearing sand rock, we find at once a change in both 

 the color and composition of the rock ; we go through a series of 

 brown sandstones and coarse conglomerate beds, of very great thick- 

 ness, which seem to be directly followed by the trappean rock se- 

 ries. The miner has in this brown sand rock an infallible indica- 

 tion that he is below the silver-bearing beds ; thus, when he sees 

 in an outcrop the dark bluish slate-like beds and the brown sand 

 rock coming in close contact, he knows that the silver-bearing rock 

 band must be found between. The silver is contained in the sand 

 rock in thin leaflets and granules, in pure metallic condition ; the 

 black shaly seams covering the surface of the ledges are generally 

 richest in metal. Narrow fissures in the sandstone are also some- 

 times filled out with paper-thin sheets of silver, and the small druse 

 cavities are lined with a film of it. Remarkable is the occurrence of 

 rock oil in some of these druse cavities. In the sand rock contain- 

 ing the silver, thin seams and granular specks of vitreous copper ore 

 are usually found interspersed ; the miners consider them as sul- 

 phuret of silver, but I examined the ore and found it composed 

 of copper alone with no silver. 



By repeated synclinal or anticlinal curves in which the strata are 

 bent, in various localities higher up the river, either higher or 

 lower beds are brought to the surface. The silver-bearing bed is 

 found again a mile south of the stamp mill, on the properties of the 

 Cleveland and Collins Mining Companies, which join each other; 

 also in Little Iron River. At the Scranton mine the ore is found 

 under the same conditions, always resting on a foot wall of brown 



