ROCKS NORTH OF BEAVER BAY. 309 
with the coarse gabbros, since they appear to lie in a zone parallel to the 
general trend, and since they form unmistakable flows elsewhere along this 
coast. The fine-grained diabases at the contact of the two zones are then 
to be taken as subsequent intrusions, as those cutting the red rocks of the 
south point of the bay undoubtedly are. But this explanation is not entirely 
satisfactory. Probably a better one is reached by regarding the red erys- 
talline rock at the south point of the bay as the intersecting mass from 
which came the flows of quartziferous porphyry. 
In the country north of Beaver Bay, as far as the north line of T. 56, 
R. 8 W., Messrs. McKinlay and Campbell found numerous exposures of 
coarse-grained gabbro, frequently forming bold ridges trending N. 50 to N. 
60 E., and presenting to the northwest precipitous rocky faces sometimes 
upwards of one hundred feet in height, and to the southeast gradual slopes. 
Commonly these exposures show coarse-grained dark-gray to black olivine- 
gabbros, such as characterize the Beaver Bay Group generally, but among 
the specimens brought back are some of orthoclase-gabbro in all respects 
like those figured on Plate V at Figs. 1 and 2. One orthoclase-gabbro is 
somewhat peculiar, and is interesting as exhibiting in an extreme way some 
of the characteristics of this class of rocks. It is found on the north line 
of Sec. 2, T. 56, R. 8 W., 760 paces west of the northeast corner. Exter- 
nally it is quite coarse, mottled white and green, titaniferous magnetite mak- 
ing up fully one-third of the rock. Under the microscope the twinned augites 
are occasionally fresh, but are commonly wholly altered to greenish uralite. 
Among these ledges of coarse-grajned rocks are much rarer beds of 
fine-grained kinds, while Mr. McKinlay found, in the northeast part of T. 
55, R. 8 W., quite a zone of fine-grained brownish diabases, occasionally 
showing some tendency to an amygdaloidal character, and including beds 
of the typical melaphyr or fine-grained, lustre-mottled olivine-diabase. These 
beds are to be seen well exposed along the north branch of Beaver River 
in Sec. 35, T. 55, R. 8 W., and in Sec. 2, T. 56, R. 8 W. 
On the coast below Beaver Bay, for two miles and a half, coarse black 
gabbro, like that at and above Beaver Bay, is constantly in sight. It also 
forms the rocky island near the east line of Sec 6, T. 55, R. 7 W., where, 
as also frequently along the shore, it exhibits the usual rather flat lakeward 
