32 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
conglomerates of one section from a common source. Thus the Portage 
Lake conglomerates all carry a great predominance of non-quartziferous 
porphyry pebbles, while further northeast a granitic porphyry or augite- 
syenite becomes very abundant, and still further, in the region of the Cal- 
umet mines, a true quartz-porphyry prevails. In the latter case the source 
was a quartz-porphyry mass to the southeast, of which small exposures are 
still to be seen. In the Eagle River conglomerate again a common pebble is 
a quartzless porphyry, much like the massive rock exposed at the old Suffolk 
location to the southeast. The same association is to be noted in the Onto- 
nagon and’ Porcupine Mountains regions. 
These original acid rocks embrace all of the kinds included as pebbles 
in the conglomerates, viz: true quartziferous porphyries, with large doubly 
terminated quartzes and orthoclases as porphyritic ingredients; a non- 
quartziferous porphyry; compact felsite; granitic porphyry and augite- 
syenite; and true granite. Most of these rocks are of some sort of reddish 
hue, running from a pale pink to a bright brick-red; whence in large 
measure the red colors of the conglomerates and sandstones derived from 
them. 
In recapitulation, then, it is to be said that the Keweenaw Series con- 
sists of eruptive flows and beds of detrital rocks interstratified with one 
another, the eruptive rocks occurring also subordinately in dike form. 
The eruptive rocks include basic, intermediate, and acid kinds, as is 
commonly the case with volcanic regions of more modern activity, but 
there is no such chronological relation between these three kinds, as is so 
often found to be the rule in Tertiary and post-Tertiary volcanic regions. 
An extraordinary thing is the complete absence from the series of any- 
thing like volcanic ash; another point of difference between it and the 
rocks of regions of more recent volcanic activity, and one which helps 
to support the view that the eruptive rocks of this region have come through 
open fissures, and not after the manner of the volcanic flows of the present 
day, as the extreme uniformitarians would have us believe. 
The detrital rocks of the series are all composed of water-derived frag- 
ments, broken for the most part from the acid rocks of the series itself. 
