256 Canadian Record of Science. 
about thirty-five miles, is a marked depression in the 
floor of the bay of from three to four miles in width, 
flanked on both sides by more or less abrupt, continuous 
cliffs of probably Potsdam age. From a depth varying on 
the top of the cliffs from 30 to 150 feet, the descent is quickly 
made to depths reaching a maximum of 612 feet, and aver- 
aging from 350 feet to 400 feet. Whilst the summits of 
these subaqueous cliffs form, on either side of the depression, 
a relatively level surface of about two to four miles in width 
for the whole thirty-five miles, beyond that width the lake 
bottom once more, but more gradually, slopes in the one 
case to the eastward, in the other to the westward, so as to 
form two other depressions parallel to that above described, 
but of much less depth. Beyond Pancake Point the middle 
depression leads to the general depths of the lake bottom 
outside of the bay, but with a somewhat decreased depth at 
the immediate outlet. In White Fish Bay the lake bottom 
is, like the coast near at hand on the southern side, com- 
posed chiefly of beds of sand, and it is clear that these de- 
pressions are now partially filled up with this material 
and with clay. 
These subaqueous cliffs and depressions lie in a general 
direction parallel to the eastern coast line of the lake, and 
have probably their origin in the same cause, though subse- 
quently more defined by river action. The conspicuous 
subaqueous ridge between Michipicoten Island and the 
higher division of rocks of Caribou Island has apparently 
also the same direction. 
The forces which contributed to the formation of Lake 
Superior appear to have taken three principal directions: 
the first in a line from Michipicoten Island eastward and 
westward, parallel with the extreme northern and general 
line of the southern shores of the lake, and with the north- 
ern coast of Keweenaw Point, where profound depths almost 
skirt the shores; the second, already referred to, operating 
in the line of the western coasts, of the subaqueous depression 
near these coasts, and of the axes of Isle Royale and Kewee- 
naw Point, and of the Keweenaw Bay depression; and the 
