TJic KeiveoiawcDi in Ahnncsota. — Elft/nan. 177 
varying from a foot to many feet in thickness. The Keweena- 
wan rests imconformably upon the Saint Louis river slates 
and is older than the lake Superior red sandstone. 
Winchell (N. H.)/' in 1881, gives many details observed 
along the lake Superior coast from Duluth to Pigeon point. 
The same author/" in 1881, in a discussion of the rocks of 
northeastern Minnesota, considers the acid red rocks forming 
the Palisades, and occurring extensively in the vicinity of 
Grand Marais and in numerous other places, to be meta- 
morphosed sandstone, red shales and conglomerates. "On 
])assing inland from the lake shore back of Grand Alarais, and 
up the Devil's Track and I^rule rivers, the red semi-meta- 
morphic slates of the shore can be followed over a wide ex- 
tent of territory, gradually becoming mere changed and 
crystalline in receding from the lake shore." The same au- , 
thor," in 1882, adds numerous details concerning the geo- 
graphical distribution of the Cupriferous. The gal^l^ro, which 
is found to have wide extent, and its associated red granites, 
are considered as a part of this series. 
Irving," in 1883. gives a systematic account of the cop- 
per-bearing rocks of lake Superior, and the petrographical 
characters of the different members of the series are given in 
detail. The Keweenawan beds in Minnesota are referred to 
the lower division of that series. The following six subor- 
dinate groups, having a total thickness of upwards of 20,000 
feet, represent this series. 
1. The Saint Louis River gab1)ro and associated red 
porphyries. This group comprises the basal gabbro. and con- 
sists of orthoclase-gabbro, orthoclase-free gabbro, fine grained 
diabase, augite syenite, granitic porphyry and felsitic por- 
phyry. The thickness was estimated at about 6,000 feet. 
2. The Duluth group. This group was recognized at 
l)oth ends of the Minnesota coast, and has a maxinunu thick- 
ness of 5,000 feet. It consists largely of a succession of heavy 
but sharply defined beds of fine grained rocks belonging to 
the ashbed diabases and diabase porphyrytes. Coarse grained 
orthoclase-free gabbro, thin amygdaloids and a little inter- 
leaved detrital matter are also present. 
3. The Lester River group. This group was recognized 
at both ends of the coast, and has a thickness of 2,600 feet. 
