45G PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 11, 



atright angles to its strike, the greater number being included between 

 the directions N.W. & S.E., and N. & S. The relation of the rocks is 

 shown in the sketch-section, Fig. 4, from which it will be seen that 

 the trappean series is divided into two parts by the great greenstone 

 bed, the upper portion being known as the northern, and the lower 

 as the southern mineral range. Now although lodes in many cases 

 pass through both ranges, yet, as a rule, up to the present time they 

 have rarely proved to be of value for copper in both, the most im- 

 portant deposits being confined to the southern side, and at no great 

 distance from the greenstone, the principal mines being the Cliff near 

 Eagle Eiver, the Amygdaloid, Delaware, and Pennsylvania near 

 Eas'le Harbour*. 



"&•• 



Eig. 4. — Section from Cojpjper Harbour to Lac la Belle 

 (after Eoster & Whitney). 



Copper 

 Harbour. 



a. Upper sandstones and traps, I c. Lower metalliferous traps. 



b. Upper metalliferous traps. | d. Chlorite rock and sandstone. 



e. Porphyry ? 



The lode worked at the Cliif mine has been traced for about 2| 

 miles, but the main workings are below the greenstone, and extend 

 southward for about 1400 yards. It is a nearly vertical fissure, 

 varying in breadth from a mere line to six feet, filled with broken 

 rock and zeolitic minerals, with native copper, both in fine particles 

 and large masses, the latter being common in the wider portions, 

 which alternate with barren strings made up of laumonite and de- 

 composed trap. The containing rock is a hard trap, with interstra- 

 tified beds or " flows " of amygdaloid, which have been laid down 

 in the plans to the number of 12 or 13. These are occasionally 



^ The total yield of copper from the mines of Lake Superior in 1864 was 

 as follows : — 



From 13 mines in Portage Lake district, 4293 tons of 70 per cent, mineral. 



„ 16 ,, Keweenau „ 2548 „ „ 



„ 19 „ Ontonagon „ 1722 



8563 tons. 



These quantities are in American customary tons of 2000 lbs. The above 

 total is equal to about 5609 statute tons of fine copper. 



The largest individual production was, in dressed mineral (70 per cent) : — 



1485 tons 13 cwts., American weight, from Quincy Mine. 

 1133 ., 19 „ „ „ Cliff Mine. 



932 „ 8 „ „ „ PewabicMine. 



609 „ 3 „ „ „ Central Mine. 



525 „ 10 „ „ „ National Mine. 



