No. 2.] SPENCER— COPPER-BEARING ROCKS. 61 



stone had been permeated by the liquid trap which has since 

 been converted into the mehphyres. 



On the north shore of the Lake the variety of the sedimentary 

 rocks is somewhat greater. As shown by Bell, to the above list 

 may be added d irk m issive argillites, and flaggy black shales, 

 Slaving the miss divided by numerous vertical joints, red shales* 

 red and white dolomitic sandstones, reddish compact limestones, 

 and red and yellowish-gray marls. 



c. — Geological Structure, — The typical series of the copper- 

 bearing rocks on the South Shore has a great development, hav" 

 Ing an average width of six miles. It is more than 150 miles long, 

 and its thickness, as shown by the Geological Survey, is not less 

 than 15,000 feet, or nearly three miles. The greatest thickness 

 Is to the northward. The range of hills, made up of the de- 

 posits of the Nipigon or Copper-bearing Period, has a trend of 

 about N.P].. while the dip is N.W., at angles varying from 

 60 to 25 degrees, flattening out to the north-eastward. The 

 lapse of time occupied for the deposition of so much material 

 must have been very great. During all this time there were 

 long series of submarine volcanic eruptions, which, occasionally 

 ceasing to act, permitted the abrading forces to be forming the 

 pebbles which were deposited in the shallow seas to form 

 what arc now the intercalated beds of conglomerates and sand- 

 stones. A gradual subsidence was going on while the seas were 

 getting filled with so much igneous and sedimentary matter. The 

 deposition of the sandstones was comparatively rapid, and the time 

 was insufficient for the bleaching of the red rocks by decompos- 

 ing organic remains, if they were present, The whole series, 

 made up of alternate layers of igneous and sedimentary rocks, has 

 Its respective b^ds conformable, although the individual mem- 

 bers are not uniformly deposited. Thus the Allouez Conglo- 

 merate can be traced lor thirty miies from Portage Lake north- 

 eastward, having a thickness of 15-20 feet at the Allouez and 

 Central Mines, a distance of 15 miles apart, while at the Phoenix 

 Mine, between the two others, the stratum is represented by a 

 fthin clay seam, a few inches thick. 



Again, the great Diorite Bed, which has a thickness of 1,200 

 feet at the Phoenix Mine, thins out at a distance of about twelve 

 miles to the south westward of this mine, while it extends a long 

 distance to the north-eastward. This large development of 

 diorite consists of various beds having thicknesses varying from 

 10 to 400 feet, and characterized by rocks of various textures. 



