402 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Bell has much more recently examined this region, his explorations 
having extended far into the interior.’ He carries the Huronian far beyond 
the area indicated by Logan, including, however, in the Huronian all the 
schistose rocks met with, and even large areas of gneiss and granite. It seems 
thus evident that there are, in the area outlined by Bell and copied on the 
accompanying general map of the Lake Superior region, true Huronian 
schists and older rocks. 
RELATIONS OF THE KEWEENAW SERIES TO THE HURONIAN. 
Having given thus an outline account of the rocks of the Lake Supe- 
rior region which are to be referred with greater or less confidence to the 
original Huronian of Murray and Logan, I have next to consider the rela- 
tions sustained by the Keweenawan or copper-bearing series to the Huro- 
nian, to which consideration the foregoing discussion was indeed prepara- 
tory. The data at hand upon which I have to. base my conclusions as to 
this disputed question are, in the first place, the lithological similarities 
and dissimilarities of the two systems, and, in the second place, the struct- 
ural relations between the two where they are found in proximity to each 
other. 
If the basic eruptive rocks of the two groups are alone considered, 
the lithological similarity is very close. The vesicular or amygdaloidal 
character so common in the Keweenawan rocks is generally wanting in 
the Huronian, as are also the pseud-amygdaloids, and the peculiar fine- 
grained brownish and purplish diabases that are so common in the upper 
part of the copper series. The more massive rocks are, however, identical 
in the two groups, and the classification of the Keweenawan basic rocks 
given in Chapter III would cover those of the Huronian as well, so far 
as microscopic investigation has gone. The so-called diorites of the 
Huronian being taken as uralitic diabases, all the basic eruptive rocks of 
the two groups fall into the augite-plagioclase class, ranging between the 
orthoclase-bearing more acid kinds, and the more basic kinds holding no 
orthoclase, much olivine, and haying the feldspar anorthite, or near it. 
Even with the very similar basic rocks there are, however, structural 
1 Geological Survey of Canada; Report of Progress for 1870-71, p. 322. 
