THE 
AMERICAN GEOLOGIST. 
Vol. XVL OCTOBER, 1895. No. 4. 
[Crucial poixts ix the geology of the Lake Superior regiox. No. 8.1 
THE SYNCHRONISM OF THE LAKE SUPERIOR 
REGION WITH OTHER PORTIONS OF THE 
NORTH AMERICAN CONTINENT. 
By X. H. WixcHELL, Minneapolis^, Minn. 
(Plate XI.) 
After this glimpse of the succession of events in the Lake 
Siii)erior region it will be well to institute another comparison 
with eastern localities, showing a general synchronism of tlie 
geolog}^ of lake Superior with the Adirondack and Taconic 
areas. Reference has already been made to the occurrence of 
eruptive rocks in the Canadian territory which is immediately 
adjacent to these rocks in Minnesota, considered Lower Cam- 
brian by Dr. Selwyn, and to others further north which Dr. 
G. M. Dawson has mapped as Lower Cambrian and places at 
about the same age as the copper-bearing rocks of lake Supe- 
rior. The succession of geological changes, as now made out, 
in the Lake Superior region, appears to be expressed as follows. 
This leaves out of the account the latest of the volcanic con- 
vulsions, viz., that which caused the intrusion of the traps 
that cover the light colored and marly sandstones at Black 
bay and which produced, according to Dr. A. C. Lawson, the 
Lo<i<in sills of the Aniinikie* at a considerably later date than 
the Keweenawan epoch, and which will be considered later. 
It embraces only the essential steps that are covered by the 
*Bulletin VIII, Minnesota Geological Survey, p. 47. 
