EAGLE RIVER SECTION. 175 
The specific gravities of these coarse rocks range from 2.89 to 3.03. 
They include kinds belonging both to the coarse orthoclase-free diabases 
and gabbros, and to the orthoclase-bearing gabbros. Bed 94 is of the latter 
kind. It is made of a coarsely crystalline rock, whose most prominent con- 
stituent is a feldspar in narrow tabular crystals. Magnetite, a green and 
black substance, and apatite are also macroscopically visible. The thin 
section shows, as original ingredients, apatite, orthoclase, oligoclase, mag- 
netite and augite, with secondary quartz, ferrite, chlorite and magnetite.* 
The basal bed (108) is the type of the luster-mottled melaphyrs, and has 
been fully described in Chapter III. 
These massive dark-colored rocks occur again and again about the Lake 
Superior basin in just such relations as here, always in a considerable aggre- 
gate thickness of relatively heavy beds, always without amygdaloids, and 
always, in any given district, less abundant than the finer-grained and more 
easily softened diabases and amygdaloids. To these last-named rocks they 
always offer a marked contrast, not only on account of their dark color and 
massive structure, but because of the bold ridges they always form by virtue 
of their greater resistant power. 
Beneath the Greenstone (bed 108), and separated from it by a red clay 
seam, which is known locally as ‘‘The Slide,” and is a thin conglomerate 
bed further east and west, a few hundred feet of rock are exposed to view 
in the Phcenix mine, which is one of the numerous workings just beneath the 
Greenstone on north and south, or crossing veins. The total thickness of 
these beds, which I may appropriately call the Phoenix Mine Group, is 685 
feet, in beds ranging from 9 to 160 feet. In the upper part of this group, 
whose beds are all inclined through their entire thickness to the pseud- 
amygdaloidal alteration, the rock is— 
of a rather coarse-grained, inclined to loose texture, being rather soft and tough, and 
having a very uneven fracture. The feldspar is greenish-white, and occurs in elon- 
gated crystals, * * * and in the coarser varieties appears spread like a net- 
work upon a background of dark green [and pink, the greenish ingredient a chloritic 
alteration-product which is] separated into frequent and rather well-defined spots, 
while magnetic and specular iron are present in large quantities. In the finer-grained 
beds brownish-red largely prevails, with dirty white in the base, the colors, though 
dull as in nearly all rocks, being well marked and in strong contrasts. At one or two 
1R. Pumpelly, op. cit., pp. 275-230. 
