;;.' 



MUSEUM OF COMPARATIVE ZOOLOGY. 



125 



mines have their deposits distributed iu a very irrcgnlar manner, requir- 

 ing much dead work as a neccessary concomitant of the way in which 

 the copper was deposited. 



Another variety of the bed mining is that known as ash-hed mining. 

 As stated before, the ash-bed is a more scoriaceous flow than the iiener- 

 ahty of the mehaphyrs to which it belongs, and has the copper deposited 

 throughout its mass, not rich, but quite uniform, or subject to certain 

 wclbmarked hiws of variation. So far as could be ascertained, the ash- 

 bed shows no sign of hot-water action at Copper Falls, but rather 

 evidence that the copper was deposited from a cold, or, at most, only 

 a warm solution. The rock is but little changed, and retains part of 

 the signs of its fluid state, almost as well marked as they are in some 

 comparatively recent lavas. Iu other mines iu which a transverse fissure 

 vein and a melaphyr (amygdaloid) is mined, the impregnation of the 

 melaphyr with copper seems to be dependent upon its proximity to the 

 vein, being rich near the vein, but growing poorer as it recedes from 

 it. Here the conditions are reversed : the ashd)ed is apt to be poorer 

 near tlio veins than at a distance from them. Where the overlying 

 trap sent down tongues into the ash-bed, the latter became indurated, 

 and consu(piently but little copper was deposited in it at these places. 



The Atlantic mine at Portage Lake is supposed to bo on the ash-bod, 

 or a similar formation. This mine was visited, and the rock found to 

 be similar to that of the ash-bed, except much harder. This rock has, 

 like the rock in the other mines at Portage Lake, been subjected to 

 much more intense metamorphic action than the ash-bed at Copper Falls. 

 The copper here, however, is quite evenly distributed, and all of tlie bed 

 is stoped out and sent to the stamp-mill. So far as could be told by 

 lithological evidence, the Atlantic mine is on tlie same bed as the Cop- 

 per Falls mine, or on a bed having the same origin. The action of 



thermal waters on the former accounts for its present diflxirence from 

 the latter. 



The induration of any rock does not apparently depend upon the 

 question of the heat of the water which acts upon it, but upon the depo- 

 sition of mineral matter in the rock by the water, and on the hardness 

 of the deposited minerals. No mineral matter need be brought in; the 

 induration requires only that the chemical constituents should rcimitc 

 into minerals of greater hardness. These alterations arc always a pas- 

 sage from unstable to more stable compounds, in tlie conditions to which 

 the rocks are subjected. Glass is the most unstable form in which any 

 of the rock constituents can be; but the uielaphyrs, from their origin 



