272 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
enough a felsitic porphyry, with various products of devitrification in the 
base. 
These three varieties of red rock, thus described as occurring at Duluth, 
are evidently but different phases of the same rock, and without much 
doubt are connected with each other in the mass, though this was not 
proved in the field. 
The exposures of gabbro on the Cloquet River regarded as belonging 
to this belt are on Sec. 10, T. 54, R. 13 W. (270 N., 1,500 W.); on See. 5, 
T. 53, R. 13 W. (1,700 N., 2,000 W.); at the falls on the N. E. 4, See. 18, 
T. 53, R. 13 W. (1,650 N., 700 W.); at a number of points through See. 
36, T. 53, R. 14 W,; in the S. E. 4, Sec. 35, T. 53, R. 14 W. (75 N., 600 W.); 
and about the falls in the S. E. 4, See. 34, T. 53, R. 14 W., where the show- 
ing is a very large one. The rock seen at these points is pretty uniform in 
character, and is a very fresh olivine-gabbro. It is light-gray in color, very 
coarse-grained, and composed chiefly of very fresh plagioclase (anorthite). 
Quite fresh diallage fills in the spaces between the feldspars. A few large, 
fresh olivines occur here and there in the section. 'Titaniferous magnetite 
is abundant and large-sized, and biotite occurs in a few small scales. 
From the last exposure examined on the Cloquet, in Sec. 10, T. 54, R. 
13 W., it is some eighty miles in a N. 50° E. direction to the vicinity of 
Brulé Lake, where Mr. Chauvenet found again a large development of 
coarse gabbros and red granitic porphyries. ‘The intermediate country has 
not yet been surveyed, and is well-nigh unknown, save to the Indians. 
There can be little doubt, however, that the same belt runs through. I am 
informed by Professor N. H. Winchell that he found such rocks on what would 
be the line of this belt in making a northwesterly traverse from the mouth 
of Poplar River. Some sixteen miles back from the mouth of Baptism 
River in a northwesterly direction, Messrs. Campbell and McKinlay found 
a granitic porphyry, which may belong to the same belt, but the country 
was low and swampy, and no other exposures were in sight. 
The exposures about Brulé Lake, and the headwaters of Brulé and 
Cascade rivers are on a grand scale, and of great interest. To reach them 
my assistants, Messrs. Chauvenet and McKinlay, started from the lake shore 
at Grand Marais, Sec. 21, T. 61, R. 1 E.; went thence northwest to Devil’s 
