Schermerhorn—Northern and Northwestern Lakes. 281 
Huron has a mean depth of about 250 and a maximum depth of 
702 feet. Lake Michigan has a mean depth of 325 feet and a 
maximum depth of 870 feet. Lake Hrie is comparatively 
shallow, having an average depth of less than 70 feet and a 
maximum of 210 feet. Lake Ontario has a mean depth of 
about 300 feet and a maximum of 738, or nearly 500 feet be- 
low the level of the sea. The channels of the rivers connecting 
the lakes seldom exceed the depth of 50 feet. If the lakes 
could be drained to the level of the sea,. Lake Hrie would dis- 
appear, Lake Huron reduced to quite insignificant dimensions, 
Lake Michigan to a length of about 100 miles with a width 
of 25 or 30 miles, Lake Ontario and Superior, although with 
diminished areas, would still preserve the dignity of their pres- 
ent titles as Greut Lakes. 
C) > 5 
40000 35000" 30000" 25000" 20000 45000" 70000" $000" a) 
A chemical analysis of water taken from the deepest part of 
Lake Superior failed under the application of delicate tests to 
indicate the presence of salt. 
The beds of the lakes away from thé vicinity of the shore- 
lines, and at depths exceeding 100 feet, are almost invariably 
covered with clay. Specimens from the deep soundings of Lake 
Superior were invariably soft clay varying in color from red, 
yellow to blue. In the deepest parts the drabs and bluish 
tints predominate. 
The temperature at the deepest points varies little from 
the mean annual temperature of the surrounding air. The tem- 
perature of Lake Superior at depths exceeding 200 feet 
varies but slightly from 39° F. In Lake Huron, at depths of 
about 300 feet the temperature in tle months of June and 
August was 52° F., while at a depth of 624 feet the temperature 
was 42° F., the surface temperature being 52° F. and the air 
64° FB. 
The mean annual rain and melted snow-fall of the several 
lake basins is as follows: Lake Superior, 29 inches, Lake 
Huron, 30 inches, Lake Michigan, 32 inches, Lakes Erie and 
