48S The American Geologist. Jane, 1894 • 
Grand Portage island lies in the mouth of a bay of the same name in 
T. 63 6E., Cook county, Minnesota. The rocks of the island have ix<Mi 
described by Prof. N. H. Winchell;* they consist of sheets of sediment- 
;in and igneous rocks dipping southeastwardly at a small angle into the 
lake. The lowest beds exposed are at the northeast corner of the island; 
they c< insist of coarse and fine grained sandstones and arenaceous slates. 
They are cut and overlain by sheets of basic igneous nicks (at least a 
considerable part of which are effusive), which dip in entire conformityf 
with the underlying elastics. The lowest exposed layers of the sand- 
stone are decidedly conglomeratic, the foreign pieces often being several 
inches across. These conglomeratic beds are composed largely of frag- 
ments of quartz, gray and reddish quarteite. siliceous slate, a dark flinty 
rock, red quartz porphyry and red granite. Most of these, more espe- 
cially the quartz pebbles which make up the bulk of the rock, are 
clearly water-worn and well rounded. The quartzite and slate pieces 
are similar to those occurring just to the north and northeast in the 
Animikie strata, and the same can be said of the quartz porphyry and 
granitic pebbles. In fact all the pebbles of the conglomerate can be 
matched in the Animikie strata near by. The red quartz porphyry and 
granite have been shown to be, at least in their present condition, later 
than the Animikie, £ and rocks of this nature, which could have fur- 
nished the pebbles in the conglomerate under discussion, do not seem to 
be known in this region, except in the Animikie and later series. More- 
over, the alteration and recrystallization of the Animikie sandstones. 
pebbles referable to which occur in the conglomerate, date from the 
same time as the quartz porphyry and granite. In addition to the fact 
that the pebbles of the conglomerate can be referred to the Animikie 
rocks close at hand much better than to any others, is the fact that the 
sandstone and conglomerate of Grand Portage island do not show evi- 
dence of having been subjected to metamorphosing forces, as do the 
sandstones of the Animikie in the immediate vicinity. 
It thus seems evident that the elastics of Grand Portage island can 
not be referred to the Animikie. as has been done hitherto, but that thej 
probablj represent one of the lower parts, if not the lowest, of the Ke- 
weenawan in this locality: and that the contact formerly considered as 
here existing between the Animikie elastics and the Keweenawan erup- 
tives is really that between two parts of the Keweenawan itself. For a 
considerable distance to the west of this place the lowest rocks of the 
Keweenawan as far as known are entirely eruptives, but where the 
lower part of l he Keweenawan first occurs to I he east ton t he east side of 
Thunder has | the lower member consists of a considerable thickness of 
sandstones, and it is with these that the elastics of Grand Portage an' 
probably to be correlated. 
The above only serves to emphasize the existence, already agreed 
*Geol. and Nat. Hist. Surv. of Minn., 10th (1881) Ann. Rept., pp. 4.V4H: 1882 
tR. D. Irving; op. cit., p. 367. 
1W. S- Bayley ; The Eruptive and Sedimentary Rocks on Pigeon Point, Minnesota, 
and their Contact Phenomena: U. S. fteol. Survey, Bull. 109; 1893-, 
