130 
BULLETIN OF THE LABORATORIES 
crystals of biotite (?) are broken up and greatly altered. The unal- 
tered granite (No. 1042) is very coarsely granular and is perforated by 
many diabase dykes having the same general strike as in the schist. 
The granite continues to Little Bear river and thence to Dore^ river, 
to the east of which a chloritic slate appears. The strike is S. 50° E. 
with a dip toward the southwest of about 45°, though the strata are 
very tortuous and embrace included masses. The contact with the 
granite is here as elsewhere evidence of the eruptive nature of the 
granite. Irving’s map does not correctly represent the distribution of 
the granite in this bay. Gros Cap is the promontory west of Michi- 
picoten harbor and is said to bear hematite veins. Bell says it is 
composed of slaty diorite, though the only rock seen by us was a 
tough silicious chlorite schist. At Michipicoten river the rocks are 
said to be dark hornblendic mica schist. 
Leaving Gros Cap we crossed the entrance to Michipicoten har- 
bor and encamped upon a narrow beach nearly directly south of the 
point. The rock here is strongly tortuous and confused. Much of 
the rock is porphyritic in a grayish-green base, while other portions 
are of dense close texture and uniformly micro-crystalline. In one 
place beneath the water the porphyritic rock could be seen to contain 
large rounded masses of a different color, often a foot or more in di- 
ameter. These were supposed to be similar to' the conglomerate peb- 
bles of the west side. As typical of much of the un porphyritic rock 
of this shore we select No. 1068, which appears to the eye like a mod- 
erately fine-grained diorite. The thin section shows it to have under- 
gone great alteration. The greater part of the field is made up of 
elongated unterminated fibrous crystals, lying at all angles and frayed 
out at the ends. These are of a pale green color and scarcely pleo- 
chroic. The polarization colors are very brilliant, like those of tremo- 
lite. In cross section two sets of cleavage lines, with an apparent 
angle of 120-130° appear, while the longitudinal cleavage lines are 
frequently wavy. The twins are numerous and in the plane i-i, and 
the extinction angle c : c = nearly exactly 15°. This combination of 
characters is hard to understand. The absence of pleochroism and 
brilliant polarization indicate a monoclinic augite, but the extinction 
angle, cleavage, and habit are like hornblende. This is, therefore, a 
decomposing hornblende like uralite in general appearance and like 
actinolite in characters. The iron has nearly disappeared from the 
whole rock, a few scales of hematite being found in the hornblende. 
