CHARACTERISTICS AND DISTRIBUTION OF LAKES 635 
character, and owing to the chmatic conditions the water of the lakes 
never attains a \ ery high temperature. In fact, the lakes are generally 
covered with ice for a period of about five months each year. For 
the winter 1902-03 the maximum thickness of ice on the Lower Lake 
was 34 inches, and on the Upper Lake 28 inches.^ The days are warm 
and pleasant in summer, but the temperature falls rapidly after sun- 
set. The nights are very cool, and hoar-frost may be expected every 
month of the year. Several sets of temperature observations were 
made on the two lakes during the months of July and August in 1902 
and 1903 ; in general the temperature conditions during summer 
w^ere found to be similar to those that have been observed in lakes of 
corresponding size and depth at much lower altitudes. There was an 
upper stratum of water, or superthermocline region, the temperature 
of which increased materially during summer ; a bottom stratum, or 
subthermocline, the temperature of which changed very little during 
summer ; and a more or less distinct transition zone or thermocline 
between these two strata. The thermocline was found to be from 10 
to 13 feet thick in these lakes, and the water in the lower portion of 
it was about 5° C. colder than that in the upper portion. This transi- 
tion zone was not nearly so pronounced, however, in these lakes in late 
summer as was found by Juday in lakes in South-Eastern Wisconsin 
and Northern Indiana, but it agreed very closely with this zone in the 
latter lakes when their upper stratum of water had a corresponding 
temperature early in the summer. During these observations westerly 
winds blew with considerable regularity, beginning usually about 
10 a.m. and lasting till late in the afternoon. As a result of this the 
water of the superthermocline region was kept stirred up, so that 
its temperature was tolerably uniform. This produced a fairly 
distinct thermocline. The superthermocline was considerable thicker 
in the Lower than in the Upper Lake, owing to the fact that the 
wind was much more effective in disturbing the upper water of the 
former, because of its much larger size. On 7th August 1903, 
for instance, this upper stratum was 26 feet thick in the former and 
only 10 feet thick in the latter. During both summers the tempera- 
ture of the Lower Lake was somewhat higher than that of the Upper 
Lake. Most of the afHuents How into the latter, and it was found 
that the water of all except one was colder than the surface water of 
the Upper Lake, so that these affluents would help somewhat in keep- 
ing down the temperature of this lake. 
The transparency of the water varied somewhat. In general a 
Secchi disk just disappeared from view at a depth of about 18 feet 
early in July, and the water gradually became more transparent as 
the season advanced, so that by the middle of August this depth had 
^ See Juday, op. cit, p. 155. 
