360 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
stone seen here is the usual saccharoidal quartzose kind, often perfectly 
white, and at times mingled and streaked with more or less brownish material. 
It carries frequent pebbles of white quartz, but none of the Keweenawan 
diabase against which it rests. One mile south, in section 27, the sandstone 
was observed in a horizontal attitude, and in the S. W. 4, Sec. 28 was seen 
in large exposures at the falls of the Ontonagon River. Here it dips south- 
ward at an angle of 15°, but as it is followed northward some 200 yards, 
this dip changes to 18° and 20°. A short distance farther north is a bold 
south-facing bluff of Keweenawan diabase. It should be said that these 
south dips are not wavering and uncertain like those observed on the Douglas 
Houghton River, but are persistent and pronounced, affecting many hun- 
dred feet in thickness, while the exposures are to be likened in extent and 
inclination to those seen on Béte Grise Bay. 
Farther west again, as far as Lake Agogebic, the west branch of the 
Ontonagon River has its course just under an overhanging bluff of diabase, 
following closely the junction line of the two formations. Here and there 
it exposes the sandstone under conditions like those just described. Ex- 
posures of horizontal sandstone are also often met with in the country 
south of this line. 
Along the north face of the South Range eastward from Lake Ago- 
gebic, the sandstone is not unfrequently met with in exposures. The 
principal point of interest in this connection is the way in which it com- 
pletely overlaps the Keweenawan rocks, which, as previowsly shown, con- 
stitute this range. This overlapping is not merely an inference from the 
supposed continuation of the South Range Keweenawan beds beneath the 
sandstone—as for instance in the fifty miles southwest from the head of 
Keweenaw Bay—but may be directly demonstrated by closely approxi- 
mated exposures of the formations concerned. This was first shown by 
Pumpelly’ from exposures examined by him on the west branch of the 
Ontonagon in the northeast part of T. 46, R. 41 W. ‘This place was sub- 
sequently visited under my direction by Mr. Robert McKinlay, who found 
the occurrences as shown in Fig. 3. The sandstone is horizontally bed- 
‘Geological Survey of Mich., Vol. II, Part II, p. 4. It will be seen that Mr. McKinlay found 
large exposures of the Keweenawan rocks much nearer the sandstone than indicated by Professor 
Pumpelly 
