304 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
crystalline character is rather to be regarded as an intersecting mass. This 
rock resembles closely in the hand specimen a moderately coarse flesh- 
colored granite, much more closely than the similar rock at Duluth. Large 
cleavage facets of pale flesh-colored feldspar make up most of the specimen, 
which shows also quite distinctly large quartz areas. There are also indefi- 
nite dark-colored patches of small size. Under the microscope, however, 
the rock is seen to be essentially the same as that at Duluth, from which it 
differs chiefly in its relatively small amount of ferric oxide. The section is 
almost entirely made up of feldspars (orthoclase with a little oligoclase) and 
quartz, which occur both in quite small and quite large areas relatively to 
the feldspars. All of these areas are, however, included within the feldspars, 
never filling corners between them as with true granite; and since many 
areas polarize together within the mass of one or more feldspar crystals, it 
is evident that the quartz is all Jater than the feldspars, i. e., either secondary 
to them, or filling spaces left in them by some solving process. 
From the last point noted in the foregoing section (near south line of 
Sec. 28, T. 55, R. 8 W.), to the red rocks of the south point of Beaver 
Bay (S. E. 4, Sec..12, T. 55, R. 8 W.), a distance of eight and a half miles, 
the only rock noted was a very dark-gray to black diabase or gabbro, now 
olivine-bearing, now not, always very highly augitic, and often showing a 
very coarsely nodular weathered surface, resulting from the resistance to 
weathering of the very large augites. Usually the exposures are low lake- 
ward-dipping surfaces; but in the N. W. 4, Sec. 27 are cliffs of the black rock 
150 feet high. A rude columnar structure is often visible. For a while the 
high dip, 18° to 20°, is continued, but more to the south of east than before, 
and soon it flattens, and the trend becomes more nearly parallel to the 
shore-line. 
At Beaver Bay a red granite-like rock and a quartziferous porphyry 
suddenly appear again among the black rocks. The occurrences are very 
interesting, and much like those described as presenting themselves at the 
close of the above detailed section (N. E. 4, Sec. 33, T. 55, R. 8 W.), but more 
difficult to reduce to order. Fig. 18 is a sketch map of Beaver Bay, show- 
ing the exposures of the different rocks. 
The common black rock of the vicinity, as seen for instance along the 
