1866.] MACFARLANE ON CUPRIFEROUS BEDS. 5 



sustaining at the same time a loss of 1 .32 p. c. No effervescence 

 is produced by hydrochloric acid, which dissolves out from the 

 rock 32.44 per cent, of bases, consisting of 



Alumina 7.52 



Peroxide of iron 15.04 



Lime 4.34 



M agnesi a 5.54 



which, doubtless, principally belong to the chloritic mineral. The 

 residue contains a very small quantity of the heavier and darker 

 constituent which was found in the rock first described. The 

 residue is not decomposed by concentrated sulphuric acid. 



Next, in downward succession, comes the cupriferous bed gene- 

 rally known as the ' Pewabic Lode,' although it possesses none 

 of the characters of a vein. It has a thickness of about 12 feet, 

 and in places resembles the rock which constitutes the foot-wall of 

 the mine, into which it seems to graduate. In its characteristic 

 varieties it differs, however, completely from that rock. It is a 

 reddish-brown or chocolate coloured uncrystalline rock with amyg- 

 daloidal structure and uneven, almost earthy fracture. The 

 matrix sometimes contains some small amygdules, which are not 

 always completely filled, and thus render the rock porous. The 

 matrix is fusible to a black, slightly magnetic glass. It is in 

 places impregnated with grains of metallic copper, from the 

 minutest size to those having a diameter of a tenth of an inch. 

 Those of a still larger size very generally project from the 

 matrix into the amygdules, or form rounded particles lying entirely 

 within these cavities, and filling them. The copper is here accom- 

 panied by a mineral of a light green colour, very soft, and sepa- 

 rable from the rock as a green powder. It fuses before the blow- 

 pipe to a black slightly magnetic glass. On ignition it changes to 

 a light yellow colour losing 0.4 p. C. of its weight. It is decomposed 

 by hydrochloric acid and the resulting solution contains protoxide 

 as well as peroxide of iron. On analysis, it gave the following- 

 results, in which all the iron is calculated as protoxide, and the 

 difference between it and peroxide put down as water 



Silica 46.48 



Alumina 17.71 



Protoxide of iron 21.17 



Lime 9.89 



Magnesia trace 



