THE COMSTOOK MINES. HI 



separately and sent to the surface, the poor being dumped into the old stopes 

 that remain to be filled up. This is sometimes important, because the neces- 

 sity of filling up the exhausted stopes is so great, on account of the unsettled 

 character of the ground inclosing the ore-bodies, that when the necessary 

 dead-work of the mine does not supply sufficient material, waste rock must 

 be mined especially for that purpose. This may cost from $1 to $2 per ton, 

 and, consequently, quartz that will not yield a profit exceeding the cost of 

 obtaining waste-rock for filling is usually employed for that purpose. In the 

 Savage mine, where this was observed, the intended minimum value of quartz 

 sent to the surface at date of visit was stated at $23 per ton. By some 

 others, howler, ore of much lower grade, and too poor to pay under existing 

 conditions, is taken out to surface and held in reserve, awaiting the time when 

 it may be made available by cheaper methods or reduced prices. 



The material inclosing the ore-bodies, or "bonanzas," is of a very unstable 

 character and involves an immense cost in timbering. The great mass of 

 vein-matter is composed of "horses" of country-rock, chiefly propylite, associ- 

 ated with immense sheets of clay. The ore-bodies frequently have selvages 

 of clay of considerable thickness. The whole is soft, yielding, and, owing to 

 its clayey nature, swells on exposure to the air, exerting an enormous pressure. ^ 

 The extraction of such immense bodies of ore, and the opening of such exten- 

 sive chambers with insufficient support of the country-rock or vein-matter, 

 induces large movements of the surrounding masses. In early days, the 

 immense stopes, though timbered at an extravagant cost of material and 

 labor, were not filled with waste-rock but allowed to remain open. Great 

 caves of ground were, of course, the consequence, extending, in some cases, 

 from the surface to a great depth. It is now the custom to fill up exhausted 

 stopes as soon as possible after the extraction of the quartz, but the necessary 

 outlay for maintaining the mine in proper condition for work is still very large. 

 The means of obtaining waste-rock, as observed in the Savage, where the 

 supply from ^he dead-work of the mine is insufficient, affords some indication 

 of the character of the ground to be dealt with. For this purpose drifts, 30 

 or 40 feet long, are driven at convenient points into the country-rock, or, more 

 properly speaking, the barren vein-matter. These drifts are securely timbered. 

 At the end of any such drift a chamber is excavated, about 10 or 12 feet high 



