220 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
The beds of which this belt is composed are very sharply defined 
and regular, with strongly marked vesicular or amygdaloidal portions, and — 
massive, often semi-columnar, lower portions. The massive rock is very 
fine-grained and commonly of a chocolate-brown to reddish-brown hue. 
Very often it carries mottlings, or pseud-amygdules, of dark-green chlorite, 
epidote and calcite. Nearly all appears to carry olivine in a much altered 
condition, and many of the sections show the characteristic arrangement of 
relatively large augites free from magnetite or olivine, but including num- 
bers of plagioclases, while the interspaces are thickly studded with mag- 
netite and altered olivine. One of these is figured on Plate X, at Fig. 
1. The amygdaloids do not present any peculiar points. Dark-green 
chlorite, epidote, calcite, laumontite and prehnite appear to be the com- 
mon fillings. At several points these amygdaloids have been worked for 
their copper, but unsuccessfully. 
Next in order in the Porcupine section comes a thickness of over 3,000 
feet of red sandstone with imbedded conglomerates. The sandstone, which 
is of the usual porphyry detritus, very greatly predominates over the con- 
glomerate, the latter being disposed in the sandstone in very thin and ir- 
regular bands. The pebbles are, as usual, of porphyry and felsite, but 
pebbles of the basic rocks are not excluded. The exposures of this sand- 
stone in the Porcupine country are too numerous for description. It is the 
best exposed belt of rock in the region, being seen in its entire width. It 
evidently includes no belts of crystalline rocks. Iron River exposes it 
largely, especially in the east half of Sec. 24, T. 51, R. 42 W. Little Iron 
River and Union River make large exposures in the same township. The 
whole thickness may be seen by following the coast line in T. 51, R. 42 
W., and T. 51, R. 43 W.; and again from Lone Rock to the Presqu’ Isle 
River. Numerous exposures are met with in the woods north of the Carp 
River Valley cliffs, while Carp and Little Carp Rivers, in T. 50, R. 45 W., 
and the Presqw’ Isle, in Sec. 9, T. 49, R. 45 W., expose the entire width. 
The same sandstone is seen at a number of points in the eastern part of 
T. 50, R. 44 W., east of the north-and south porphyry ridges of the cen- 
tral and western parts of that township. 
Next in order comes the belt of dark-colored sandstone and shale 
