f 
Geology of the Lake Superior Region. — Jr^ehell. T? i 
lands in the Lake Superior region for the United Stages gov- 
ernment. Tlieir report appeared in 1851* and is accouipaniea!:::^' 
b}' a map whicli, has a classification Avhich, in the light of 
what is known now of the geology of the Lake Superior region, 
appears curious and fantastic. All the rocks are divided in- 
to aqueous, metamorphic and igneous formations, which, for 
a grouping as to origins, is not bad. The aqueous rocks ex- 
tend down to and include the Potsdam sandstone and its un- 
derlying conglomerate the base of the "Silurian." Below that 
is the Azoic systeni, a metamorphic group, comprised in two 
parts, viz., "cr3^stalline schists" and "quartz." The igneous 
rocks are represented as of two sorts, granite and trappean, 
the latter being sometimes associated with the Azoic and 
sometimes with the Silurian. As with Logan, the names and 
the classification of the New York series were employed as 
far as possible, the copper-bearing formation being at the 
base of the Silurian. 
Examining this map more carefully, it is learned that under 
"Azoic" is included, essentially, the rocks of the real Huro- 
nian, viz., the area of the original Huronian and their exten- 
sion on the east shore of lake Superior and the slates of the 
Thunder Bay district. The granitic and trappean rocks asso- 
ciated with these make up the Azoic. In general the Mar- 
quette and Menominee iron distri(rts, and the area north- 
westward on the Brule river as far as Lac Vieux Desert are 
fragmental Azoic. These are surrounded by igneous granite 
and pierced by trappean rock. It will be seen that Logan in 
1863 followed Foster and Whitney in distinguishing the up- 
per copper-bearing series as of Silurian age, but not in put- 
ting the slates of the Animikie in the Azoic. The copper- 
bearing series is placed bodily, as the equivalent of the Pots- 
dam of New York. Ilrseems further that Foster and Whitney 
were not aware of the existence of two series of slates in the 
Thunder Bay district. 
After the foregoing the next contribution to the geology of 
the Lake Superior region which needs to be mentioned here 
was the repf)rt of the Michigan survey, conducted by Brooks, 
Pumpelly and Kominger. Major Brooks adopted the exi>and- 
*Report on tlu' Geology of the Ijake Suporior Land district. J. W. 
FosTKR iiiul ,r. I). WiUTNEY. Part II. 18.")1. Washington. 
