346 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
One specimen? in the collection, from a bed near the middle of the 
series, is called by Macfarlane porphyritic melaphyr. It turns out, how- 
ever, to be a quartzless porphyry, and is of interest as presenting a 
gradation phase between the wholly crystalline augite-syenites and the 
typical quartzless porphyries. Macroscopically it presents an aphanitic 
light-brownish base, with very abundant minute pink porphyritic feldspars. 
In the thin section the base proves to be chiefly made up of isotropic material 
and small, but not excessively minute, feldspars, which are in large measure 
orthoclase. Minute quartz particles and clusters, some plainly secondary, 
dot this background, which is also affected by a general red stain. The 
quartz also occurs in excessively fine radiating and parallel lines. This 
radial arrangement is also brought out by lines of brown ferrite. Small 
augite points are here and there recognizable. The porphyritic feldspars 
are orthoclase and oligoclase. A single rather large-sized apatite-crystal 
is contained in the section. There are splotches of green chloritic substance, 
which shows also macroscopically, but it is not evident which mineral has, 
by its alteration, given rise to them. 
The red porphyry which Macfarlane describes as making so confused 
an appearance on the east shore of the island is represented in the col- 
lection. It is a quartziferous porphyry,” with a dark purplish-red, aphanitic 
matrix, in which the porphyritic quartzes and feldspars are extraordinarily 
abundant and large. It is near to the rock seen on the Torch Lake Railroad, 
south of the Calumet mine, on Keweenaw Point, to that of which many 
of the pebbles of the Keweenaw Point conglomerates are composed, and to 
that which makes large exposures on Bead Island, at the mouth of Nipigon 
Straits. In the thin section the ground-mass of this rock appears faintly 
pinkish-tinted and cloudy, and contains abundant and very minute ferrite 
particles, which in the vicinity of the porphyritic ingredients show crowding 
and a tendency to linear directions. In the polarized light the matrix shows 
a dark background, strewn with particles and flocks of particles, of feebly 
double-refracting substances, but only rarely showing any networked 
secondary quartz. The porphyritic quartzes are in the usval dihexahedral 
forms, which are generally much eaten into by the matrix. The feldspars 
are both orthoclase and oligoclase, and are much altered. 
1Macfarlane’s No. 15. 3Macfarlane’s No. 11. 
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