Great Lake Basins of the St. Lawrence. 255 
somewhat parallel with and close to the coast, great sub- 
aqueous cliffs, some probably like Thunder Cape, and of 
irregular outline and at different levels, and which give 
rise to the sudden increase in the depths of the lake here. 
There is, however, the possibility that a great downthrow, 
or dislocation, of the upper division of the Keewenaw 
Series, exists here, the hinge, as it were, of the depression 
being towards the south shore of the lake, and the rocks 
gradually sloping from this hinge to the line of deepest de- 
pression near the western shores. These cliffs lie in a gen- 
eral way parallel with the axis of the western end of the 
lake. Is it not suggestive that here we have the effects 
which gave rise in time to certainly the westerly half of 
this greatest of the inland seas? And may not the forces 
which resulted in these cliffs, or in this great dislocation, 
if such it be, have been simultaneous with some of those 
voleanic forces which at different periods produced the ab- 
rupt overflows, or great dikes, or interstrata, of the main- 
land in the Huronian or Keweenawan rocks, and gave 
direction to the heights which at its south-western end form 
there the rim, as it were, of Lake Superior. The Western 
sandstones of the south-west shore give further clue to their 
period of operation. 
Parallel with these cliffs is another sub-aqueous escarp- 
mentin Keweenaw Bay, about twenty-five miles long, lying 
near the south-east shore and facing in the opposite direction. 
Here there is an abrupt descent from depths of 100 and 150 
feet to depths varying from 300 feet to 552 feet. In the 
large outer bay the maximum depth is only 366 feet, and 
the average does not probably exceed 270 feet. 
At the upper end of White Fish Bay the waters of Lake 
Superior converge, and flowing over the rocky rim of the 
lake here, result in the rapids of the Sault Ste. Marie, as 
they descend to the level of Lake Huron. The lake bottom 
in the bay has points of great interest. Running about due 
northward from near Pt. Lroquois, on the Michigan shore, 
past Parisian Island, on its western side, to opposite Pan- 
cake Point, on the Ontario side of the lake, a distance of 
