214 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
In attempting to trace the porphyry of the Porcupine Mountains east- 
ward we find that across T. 49, R. 43 W., the region where it would lie is 
mostly drift-covered, but that in the northern part of T. 49, R. 42 W. 
there are large exposures of quartzose porphyry occupying a belt one to 
two miles in width, and trending east-north-east across the township to the 
northeast corner. T. 50, R. 41 W. is next crossed by the belt in its south- 
ern portions, without many exposures. One is reported by Mr. B. N. 
White at the center of Sec. 21, T. 50, R. 41 W. Across the middle sec- 
tions of T. 50, R. 40 W. the government surveyors have written the 
words, “‘red slaty trap,” which are evidently meant for the red porphyry. 
The same words are used in the plat of T. 50, R. 39, for the quartzose 
porphyry already described. Westward from the Presqu’ Isle River to the 
Montreal I have no knowledge of any porphyry exposures. The country 
is mostly low and the rocks covered where the porphyry would be expected 
to appear. Beyond the Montreal it reappears, as subsequently described. 
North and west of the porphyry area of the Porcupine Mountains 
there is everywhere found a belt of basic rocks having a surface width of 
from about one-fourth to one-third mile, and a thickness varying from 
300 to 500 feet. Toward the middle of the thickness a porphyry-con- 
glomerate is included, with a thickness of over 60 feet. The basic rocks of 
the belt are in very regular and rather thick flows, some half dozen beds 
appearing to make up the whole thickness. Among the massive portions 
of the beds a very fine-grained, dark-red, compact and semi-conchoidal ° 
rock is abundant, occurring both above and below the intermediate con- 
glomerate. Under the microscope the slices of this rock, from points far 
apart along the length of the belt, show the characteristic arrangement be- 
longing to Pumpelly’s melaphyrs. Olivine, plagioclase, magnetite and 
augite are the ingredients in order of age. The augite occurs in crystals 
including numbers of the small plagioclases, while the magnetite and the 
olivine are crowded into the spaces between the augites, the latter mineral 
being usually much altered to both red (hematite) and green (serpentine) sub- 
stances. Another rock of this belt—occurring in some places in two layers, 
one above and one below the intermediate conglomerate, and in others only 
above that horizon—is an aphanitie dark-gray to black or reddish-brown rock 
