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lake is composed not of mud but of partially decomposed organic 
material in which no higher organisms are able to live. 
I have indicated in diagrams, some of the conditions which 
we find in certain of these other lakes, to show you some of the 
variations which may occur. 
I will speak first of Green Lake, which resembles much more 
nearly the condition found in the Great Lakes than does any 
other inland lake of Wisconsin. This is a lake of some 8 miles 
in length, 2 miles in width, with a depth of 237 feet. It is 100 
feet deeper than any other inland lake in Wisconsin. The lifes 
of the lower water of Green Lake is not very different from that 
of one of the Great Lakes, and when we note the oxygen story, 
we can see some reason for this fact. 
Fig. 9 shows the distribution of temperature and oxygen on 
September 6, therefore comparatively late in the summer season. 
You wll notice that in this diagram each vertical space stands 
for 1) meters instead of 5, as in the case of the other lakes, while 
the horizontal scale is the same as in the other diagrams. The 
lake shows a temperature of about 21.5° C at the surface, fall- 
ing slightly to a depth of 9 meters, and then declining rapidly to 
about 20 meters. From that point to the bottom the decline is 
slow until at a depth of 70 meters a temperature of 5.7° is 
reached. I may say in passing that there are no lakes in Wiscon- 
sin in which the bottom temperature remains at 4° C during the 
summer. Even in this lake, 237 feet in depth, the bottom tem- 
perature is always greater than that of the maximum density of 
water. The action of the wind in the spring is sufficient to cir- 
culate the whole mass of water and to give it an opportunity to 
warm up a degree or two above the temperature which gravity 
alone would give it. ‘The distribution of oxygen is quite differ- 
ent from that shown in any of the preceding diagrams. At the 
surface the amount is about the same as in other lakes and there 
is a marked decline in the oxygen at the upper part of the cool 
water. Then the oxygen begins to increase, becomes greater than 
the amount found at the surface, and at the depth of 40 meters 
is nearly 7 ce. per liter. Irom the depth of 50 meters it declines, 
until at the bottom only a fraction of a cubie centimeter is left. 
This abundant supply of oxygen in the lower water depends on 
the great volume of this water in comparison to the amount of 
