; 
: 
1884.} The Crystalline Rocks of the Northwest. 997 
Of this series of 18,000 feet goo feet consist of limestone ; 
2000 feet consist of “chloritic and epidotic slates,”:and 17,100 
feet consist of quartzite and conglomerate. Perhaps 5000 feet of 
this thickness may be considered intrusive, consisting of diorite 
and other forms of “ greenstone.” This will leave 12,000 feet, at 
least, for the aggregate thickness of quartzite and conglomerate, 
being nearly double that observed in the same horizon in North- 
ern Minnesota. 
It is plain to see that if there be any parallelism between these 
beds and the various groups made out in the Northwest, the 
whole of these strata must he made the equivalent of Group V, 
or the quartzite and marble group. The 2000 feet of chloritic and 
epidotic slates, represented as near the base of the original Hu- 
ronian, followed as they are by an immense thickness of con- 
glomerate and slate-conglomerate, are anomalous unless there be 
below them other slate-conglomerates. This, indeed, is very prob- 
able, since on the shore of Lake Superior, near the mouth of the 
River Doré, according to the same authority, the lowest part of 
the Huronian is seen to consist of a green slaty conglomerate, 
containing “ boulders ” of granite and gneiss. 
The extension of the term Huronian from the horizon of the 
original Huronian, upward through the overlying groups, may be 
Justified by the expression of the original intent in the application 
of the term, but it certainly seems not warranted by any descrip- 
tion of rocks by the Canadian geologists, nor by any claim that 
has usually been put forth by the authors of the name. 
There is, therefore, a conflict between the Taconic and the 
Huronian, both in respect to the horizon which they are intended 
to cover (both being referred by their authors to the Lower Cam- 
brian) and in the horizon of rocks which they actually compass. 
e Huronian, however, in its original and typical description, 
can be parallelized with only the very lowest of the strata that 
a included in the typical and original Taconic; while the Ta- 
conic stretches upward at least as far as to include the fourth and 
third grand groups made out in the Northwest, that is to say, the 
hydro-mica and magnesian schists, and the carbonaceous and are- 
naceous black slates. 
: This leaves two series of rocks untouched by the scope of 
either the Huronian or the Taconic, as these systems were at first 
defined ; namely the mica schist group, and the granite and gneiss 
