454 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [^PI"' Hj 



irregular than is usual in the lower beds, three different belts of 

 metalliferous rock being known. The principal one is 24 feet thick, 

 without any defined walls; and about one-half of it is workable : the 

 drivage is done on the upper or hanging wall, which often presents 

 a laminated appearance from the occurrence of strings of calcspar, 

 testing cross-cuts being driven into the vein below at intervals; the 

 copper mass is chiefly on the lower or foot- wall side, the upper part 

 being a hard compact trap. The yield of the rock sent to the stamps 

 in 1864 was about 272 lbs. per cubic fathom, equal to 15 lbs. per 

 ton, or about | per cent. 



The second or Pewabic group is more important than the preceding, 

 and includes several belts or lodes, whose thicknesses and positions 

 are given in Fig. 2, which represents the section obtained in a cross 

 cut made at the 70 fathom-level of the Pewabic mine. 



The most important members of this series are the highest, or 

 Pewabic lode, and the lowest, or Albany and Boston conglomerate. 

 The former has been systematically mined by the Quincy, Pewabic 

 and Franklin Companies for a length of about 1^ mile in a north- 

 easterly direction from the Hancock shore of the lake. North of 

 the Franklin it has been traced, but not worked, for a further length 

 of about 3| miles, up to the Albany and Boston mine. It is a dark 

 brownish-red amygdaloid, fiUed with small vesicles containing 

 chlorite and native copper ; the thickness varies from 6 to 30 feet, 

 the average being 9 feet in the Pewabic, and 10 feet in the Quincy 

 mine ; the hanging wall is a compact greenstone -like trap ; while 

 ^. ^ ^ . - _, ,. the foot-waU is a dark-coloured amyg- 



Fig-. ^.—Section of PeiuaUc ^^^^.^^ with very smaU kernels of chlo- 

 Lode m the end of tJie 130- ^^^^ ^- 3 ^-^^^^ ^^^ character of 

 fm. level, Pewabic Mine. ^-^^ ^^^^ ^^ ^-^^ 130-fathom level of the 

 _d Pewabic mine. Copper is well sprin- 



kled through the whole mass, with a 

 few small masses near the foot- wall, 

 and with irregular calcspar strings in 

 the upper side. Although not produ- 

 cing any very large masses, the yield is 

 tolerably uniform, the produce being 

 at the rate of 1-5 per cent, in the 

 Pewabic, and 1-6 per cent, in the Quincy mine: the latter is sunk 

 below the 100-fathom level. The concentration of the copper 

 towards the foot-wall is characteristic of the whole of the amyg- 

 daloids. 



The other members of the group, below the Pewabic lode, although 

 not of any great importance as regards produce of copper, are of 

 interest as establishing the regular succession of the amygdaloids 

 over areas of a certain extent, the section being substantially the 

 same in the Pewabic cross cut as it is in the Albany and Boston line 

 about 3^ miles further north. It is not necessary to go further into 

 the characteristics of these belts or lodes ; but it may be incidentally 

 remarked that the epidote lode is fiUed with a purplish rock, contain- 

 ing a great deal of bright-green epidote, and that the Albany and 



