314 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
size they run down to mere threads. The brown bands themselves are often 
streaked with lines of the lighter kinds. Under the microscope both light 
and dark kinds are seen to be felsites with a quartz-saturated base precisely 
like that of the rock of the upper layers above described, and to differ from 
each other only in the amount of red, black, and brown ferrite particles con- 
tained. The ferrites are not arranged in lines as in the peculiar rock of the 
upper part of the cliff. 
Beyond this point the felsite continues to be the coast rock through 
section 28, but in the northeastern part of this section, and the southeastern 
of section 21, it becomes involved with a black diabase, the diabase first ap- 
pearing to intersect it, and then to become peculiarly intermingled with it 
in irregular areas. Finally the black prevails, with here and there a vein 
of the red, forming one of the usual rudely columnar flows of moderately 
coarse black diabase. These confused rocks, which were not examined 
thoroughly enough to warrant further description or conclusions, terminate 
at a shingle beach in the bay above the Great Palisades. 
The rock exposures about the Palisades are of the greatest interest, 
because of their bearing on the question of the relation of the acid and 
basic flows of the series. Since we have here a great flow of quartz- 
porphyry unmistakably overlying a succession of plainly-bedded fine- 
grained diabases and amygdaloids, it follows that all idea of the greater 
antiquity of the acid as compared with the basic rocks of the Lake Supe- 
rior region must be abandoned. This is a conclusion clearly indicated in 
all parts of the Keweenaw Series, but the exposures are here so fine and so 
unequivocal that I have described them already in some detail in con- 
nection with the general part of this report. The description need not be 
repeated here, but a few details may be added. All along this part of 
the coast the layers are trending more and more away from the coast line 
towards the north, as a result of which the harder rocks form points pro- 
jecting towards the southwest. Two of these points, both formed of quartz- 
porphyry, are shown on the accompanying sketch-map. They are the Great 
Palisades and the bold point just below the mouth of Baptism River. Each 
has a shorter side trending east and west, and a longer side trending well 
