530 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



these, so far as observed, have any ore bodies of value been found. The 

 prospects in the Weber Grits are especially barren, and it is difficult to con- 

 ceive what inducement has been offered to the miners to expend the amount 

 of labor they have in this region. In general they seem to have been 

 attracted by the darker beds, containing carbonaceous matter, whether sand- 

 stone or shale, which, in general, have a little pyrites in them and sometimes 

 a trace of gold. Along the Sacramento gulches also, and as far as the ridge 

 which divides them from Horseshoe, the labor of the miner seems to have 

 been ban-en of practical results. This is the intermediate region between 

 the Lincoln Porphyry intrusions around the Mount Lincoln massive and 

 those of White Porphyry along the line of Horseshoe gulch. 



Sacramento mine. In the Blue Limestone of the ridge south of Little 

 Sacramento gu!6h, and east of the London fault, is the Sacramento mine, 

 which has been worked for a number of years and produced a good deal of 

 rich ore. At the mine itself the Blue Limestone forms the surface, the 

 overlying porphyry having been removed by erosion, so that it is impossible 

 to say what proportion of the original ore body may have existed in the 

 upper part of the limestone. The ore, which consists of galena and sand 

 carbonate of high grade in silver, is found generally in irregular masses 

 throughout the limestone beds. Some clayey iron oxide occurs as gangue, 

 and considerable sulphate of baryta is found associated with the mineral. 

 Several hollow caverns have been found by the explorations of the mine, 

 in one of which remarkably beautiful stalactites of white fibrous arrago- 

 nite occur. These caves have evidently been formed since the deposition 

 of the ore and are connected with natural jointing planes in the lime- 

 stone. Some of the caverns are partially filled with a clayey material, 

 which runs four to five ounces per ton in silver, and is evidently an infiltra- 

 tion from the ore bodies, which continue on either side of the cave without 

 bearing any relation in form to it. The limestone above the horizon of the 

 ore is generally darker colored than that below, which is of a light-gray 

 color and more crystalline structure; but the distribution of the ore bodies 

 is too irregular to consider them a definite deposit along the dividing plane 

 between these two varieties of limestone. The lighter limestone has the 



