50 TRANSACTIONS OF THE CANADIAN INSTITUTE, [Vor VI. 
The central subsidence which has been referred to, ceased before the 
deposition of the Cambro-Silurian strata of the south shore, such as the 
red and grey sandstones about Grand Island, the Pictured Rocks and 
Sault Ste. Marie, as well as the small remaining patch of fossiliferous 
beds of Limestone Mountain on Keeweenaw Point, lying west of 
L’Anse, all of which retain the horizontal attitude of their original 
deposition. 
It is to be noted that around Lake Superior, red sandstones of two 
formations come together, or nearly so, in different localities; and at 
one time they were confounded with one another and both supposed to 
be of the same age. The one set is associated with the Nipigon or 
Keeweenian formation while the other is newer. In the region of 
Keeweenaw Point their contact is not clearly seen, and there has been 
some discussion as to their relative ages. But here, as in other parts of 
the lake, the tilting of the one and the undisturbed condition of the 
other serve to distinguish them. 
From what I have said, it would appear that in the earlier ages of 
the earth, or until the Cambro-Silurian period, the Lake Superior region 
was always one of volcanic activity. If we except the unaltered 
fossiliferous strata in the southeastern part, we shall see that in 
approaching Lake Superior as a centre from any point on the ancient 
crystalline rocks which everywhere else surround it, we have furthest out 
a great area of fundamental gneiss, followed by successive zones of 
igneous origin. The Huronian rocks, mainly of volcanic character, 
occupy large areas all around. Then come many masses of intrusive 
granite of various kinds. These are followed by greenstones of the 
Animikie formation and finally, inside of all the others, come the more 
recent amygdaloids, etc, of the Nipigon or Keeweenian formation. 
These zones are not complete or regular, but the above is the general 
order of their occurrence. This rude, concentric arrangement of different 
igneous rocks which become newer and newer as we approach the inner 
part, would indicate that there was here a deep-seated volcanic centre, 
dating back to very ancient geological times. The area of volcanic 
action had thus a great width in the early condition of the earth’s crust, 
but it became more and more contracted as the world grew older and 
at length the active condition ceased altogether. 
I have thus presented some of the fundamental geological reasons 
why the present site of Lake Superior was prepared to become a lake- 
basin, but between the stage in its history at which we have arrived and 
the next actual evidence as to how the basin was formed, there was a 
