2 THE CANADIAN NATURALIST. [Feb. 



Portage Lake are worked almost exclusively upon beds, tbe strike 

 and dip of which are parallel with that of the enclosing rocks. 

 Such beds are not, however, altogether absent in other districts of 

 the copper region, where they have been called ' ash beds,' but 

 it is in the Portage Lake district that they occur most frequently, 

 and are mined most successfully. The rocks with which they are 

 interstratified are principally what are called traps and greenstones, 

 together with conglomerates and sandstones. They maintain a 

 general strike of N. 20° to N. 40° E., and have a dip of 50° to 60° 

 north-westward. 



In attempting to describe these rocks more minutely, I shall 

 begin with those lying immediately west of the great cupriferous 

 bed on which the Quincy, Pewabic and Franklin mines are situated, 

 and proceed then to notice those lying to the eastward, which are, 

 geologically, lower lying rocks. 



The rock which is observed at the side of the road leading past 

 the Quincy mine to the Pewabic, and which lies several hundred 

 feet west of the cupriferous bed, is distinctly of a compound 

 nature, but all its constituent minerals are not large enough to be 

 accurately determined. Conspicuous among them is a dark green 

 chloritic mineral, the grains of which vary from the smallest size 

 to one fourth of an inch in diameter. In the latter case they are 

 irregularly shaped, with rounded angles, but they are never quite 

 round or amygdaloidal. They frequently consist in the centre of 

 dark green laminae. The mineral is very soft and has a light 

 greenish-grey streak. It fuses readily before the blow-pipe to a 

 black magnetic glass, and it would seem to be the preponderating 

 mineral in the rock. The other constituents are in very fine grains, 

 and consist of a reddish-grey feldspathic mineral, with distinct 

 cleavage planes, and closely resembling it, light greenish-grey par- 

 ticles but whether of a feldspathic, pyroxenic or hornblendic 

 nature could not be determined. The prevailing colour of the 

 rock is dark greyish-green. Hydrochloric acid produces no effer- 

 vescense with it, even when in a state of fine powder. Its specific 

 gravity is 2 . 83, and the magnet attracts a very small quantity of 

 magnetite from its powder. The colour of the powder when very 

 fine is light greenish-grey. When ignited it loses 3 . 09 per cent, of 

 its weight and changes to a light brown colour. When digested 

 with nitric acid, and then afterwards with a weak solution of 

 caustic potash (to remove free silica) it experiences, including the 

 lo&s by ignition, a loss of 46.36 per cent. This consists of 



