PORTAGE LAKE SECTION. 191 
these augite-syenites, I take these aggregations to be altered augite, of 
which mineral a brightly polarizing core is now and then visible. Magnet- 
ite and apatite also occur in the section. 
The second pebble shows a much lighter red and coarser rock than 
the last, with much rarer black particles. The thin section of this is com- 
posed chiefly of orthoclase, oligoclase—the latter less abundant than in the 
preceding pebble—and secondary quartz. A marked appearance of sphe- 
rulitic strueture runs through the slice, being produced by the radiating 
arrangement of the secondary quartz. Unmistakable augite is seen in this 
section, and is largely replaced by ferrite and magnetite. These aggrega- 
tions are, however, much rarer than in the previous pebble. 
The third pebble is close to the last, but deeper red in color. It shows 
in the section orthoclase and oligoclase predominating, and some secondary 
quartz, but no spherulitic structure. There is much red oxide of iron, 
plentiful needles of brown ferrite arranged in definite directions, and a 
little quite fresh augite. 
The fourth pebble shows an aphanitic, hard, chocolate-brown matrix, 
fusible with difficulty, with a few minute porphyritie feldspar crystals. In 
the section of this pebble the matrix is made up chiefly of a translucent 
substance much stained with red iron oxide, and thickly studded with 
minute black, opaque particles. The porphyritic feldspars are triclinic, and 
there are also a few good-sized augites with the usual ferritic alteration. 
Conglomerate 22 of Pumpelly’s section’ on the south side of Portage 
Lake corresponds either to the base of the main or Great Conglomerate of 
the Eagle River section, or to one of the sandstone layers immediately below 
that horizon. On the north side of Portage Lake, both on the road running 
westward from Houghton, and in the ravine just west of the Mineral Range 
Railroad, in the southern part of Sec. 22, T. 55, R. 34 W., are black shales, 
which are unquestionably the same that are found all the way to Bad 
River, in Wisconsin. These shales belong over the outer conglomerate of 
Keweenaw Point. Between these two horizons is a horizontal width of some 
4,800 feet. In the southeastern part of this space the layers dip at a high 
angle—40° to 50°—northward, but this angle must rapidly decrease to the 
1 Atlas Geological Suryey of Michigan, Plate XIV—XIX. 
