Juday—Studies on Some Mountain Lakes. 783 
the R umm er were found to be similar to those that have been 
observed in lakes of corresponding size and depth at much low¬ 
er altitudes, that is, the same three regions were noticeable. 
There was an upper stratum of water, or superthermocline re¬ 
gion, whose temperature increased materially during the sum¬ 
mer, a bottom stratum, or subthermoeline, whose temperature 
changed very little during the summer, and a more or less dis¬ 
tinct transition zone or thermocline between these two strata. 
The thermocline region is always characterized by a consider¬ 
able change in the temperature of the water within a compara¬ 
tively thin stratum. This stratum was found to be from three 
to four meters thick in these lakes, and the water in the lower 
portion of it was about 5°C. colder than that in the upper por¬ 
tion. The decrease in temperature with increasing depth both 
above and below this region was much more gradual. This 
transition zone was not nearly so pronounced, however, in these 
lakes in late summer as has been found by the writer in lakes 
in southeastern Wisconsin and northern Indiana, but it agrees 
very closely with this zone in the latter lakes when their upper 
stratum of water has 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 pretty thorough¬ 
ly stirred up so that its temperature was tolerably uniform. 
This produced a fairly distinct thermocline. The su¬ 
perthermocline was considerably thicker in Lower than 
in Upper lake. This was due to the fact that the wind was 
more effective in disturbing the upper water of the former be¬ 
cause of its much larger size. On August 7, 1903, for in¬ 
stance, this upper stratum was eight meters thick in the former 
and only three meters in the latter lake. Plates XLVIII and 
XLIX show the results of three sets of temperature observa¬ 
tions on each lake. 
During both summers the temperature of Lower lake was 
somewhat higher than that of Upper. Most of the affluents 
flow into the latter lake, and it was found that the water of all 
except one was colder than the surface water of Upper lake, so 
