176 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
points the whole rock becomes a nearly uniform, decided brownish-red color. [In 
looseness of texture, and consequent rough and uneven fracture, these rocks some- 
what resemble the typical kinds of the group immediately above the greenstone group 
(Marvine’s ‘‘a”)], but in colors they are decidedly dissimilar. [The lower layers of 
this group] become finer-grained and more compactly built, harder, more brittle, and 
elastic, and with more even and conchoidal fracture, while the color darkens, a dark- 
green predominating, indefinitely mottled with dark dull purple.’ 
In the upper part of the Phcenix Mine Group the amygdaloids are 
poorly developed, and appear to be mere modifications of the pseud-amyg- 
daloids, ‘‘the matrix not being compact, but fine-grained and of a dull 
brownish-red color, and with but little calcite or prehnite” accompanying 
the chloritic pseud-amygdules. Further south the amygdaloids are better 
developed, “‘calcite predominating in some, prehnite in others.” 
Southward from the Phcenix mine the rocks are but poorly exposed in 
the valley between the Bohemian and Greenstone ranges, a few ledges of 
the typical fine-grained diabase appearing here and there above the surface. 
At a point 500 paces south of the center of Sec. 37, T. 57, R. 31 W., 4,650 
feet southeastward from the lowest rocks of the Phoenix mine, the Kingston 
conglomerate is exposed,” with a thickness of 45 feet, and containing pebbles 
of an unusually compact brown-red quartziferous porphyry. ‘The covered 
space between the conglomerate and the Phcenix mine corresponds to a 
thickness of 2,325 feet. 
Southeast from the Kingston conglomerate, the line of section passes 
through a country for the most part drift-covered, though showing a few 
scattering ledges. One of these, in the south part of Sec. 4, T. 56, R. 31 
W., shows a typical luster-mottled melaphyr, with nodular brown weather- 
ings, closely resembling the rocks of the Greenstone. Another exposure, 
on the north slope of the Bohemian Range, near its summit, in the middle 
part of Sec. 9, T. 56, R. 31 W., is a typical brown and green pseud-amyg- 
daloidal diabase, with abundant pseud-amygdules. 
Still further southeast, near the southwest corner of section 10, on the 
old Suffolk mining location, one of the head streams of Tobacco River 
shows in its bed large structureless exposures of a brown quartzless por- 
phyry, which shows, in an aphanitic, dark reddish-brown to purple, easily 
1Geol. Survey Mich., Vol. I, Part II, pp. 103, 104. 
2?Marvine, Atlas Geol. Sur. Mich., Plate XXII. 
