PORPHYRY AND BLACK SHALE OF THE ONTONAGON RIVER. 199 
shale, and conglomerate of the Upper Division, and the Outer Trap and 
Great Conglomerate of the Lower Division are all distinctly recognizable. 
No detailed measurements have ever been made in the Ontonagon country, 
but when there I saw enough to convince me that some satisfactory corre- 
lations could also be reached between the remainder of the Lower Division 
as here developed and as developed on Portage Lake, especially by the 
use of the interleaved sandstone and conglomerate bands, which here, as 
further east, continue down to quite low horizons. 
There are, however, some important differences between the Portage 
Lake series and that of the Ontonagon. One of these is the characteristic 
epidote-quartz alteration of the amygdaloids, the so-called “veins” which 
carry the Ontonagon copper. A more important difference, however, is 
the occurrence in the Ontonagon region of massive quartziferous porphy- 
ries at what appear to be quite high horizons, an occurrence which con- 
tinues to prevail for nearly a hundred miles to the westward, the porphyry 
occurring in irregular belts of greatly varying lateral extent. Large expos- 
ures of a dark reddish-brown porphyry, holding large crystals of orthoclase 
and oligoclase, occur north of the village of Rockland, in the NE. 4 See. 
9, T. 50, R. 39 W., but a very short distance south of a broad conglomerate 
that appears to be the equivalent of the Great Conglomerate of Keweenaw 
Point. 
The black shale and gray sandstone belt of the Upper Division of the 
series, already recognized as occurring near Portage Lake, is strongly 
marked in the vicinity of the Ontonagon River, having been recognized 
as far east as Sec. 14, T. 51, R. 38 W., 10 miles to the northeast, along the 
strike, from the Ontonagon. Near the Ontonagon it has been traced across 
sections 22, 21, 28, 29, 32, and 31 of T. 51, R. 38 W., and sections 4, 5, 
and 7 of T. 50, R. 39 W., to the Ontonagon in Sec. 12, T. 50, R. 40 W. 
The exposure on the SE. 4 Sec. 21, T. 51, R. 38 W., is on the banks and 
in the bed of a small stream just to the west of the Greenland and Ontonagon 
road. There are to be seen here several hundred feet in thickness of alter- 
nating dark-gray sandstone and black shales, overlaid by a considerable 
thickness of red sandstone, and underlaid by a broad porphyry-conglom- 
erate, evidently the equivalent of the Outer Conglomerate of Keweenaw 
