12.-PRELIMINARY REPORT UPON THE INVERTEBRATE ANIMALS INHABITING 
LAKES GENEVA AND MENDOTA, WISGONSIN, WITH AN ACCOUNT 
OF THE FISH EPIDEMIC IN LAKE MENDOTA IN 1884. 
:! 
I 
BY S. A. FORBES. 
LAKE GENEVA. 
My first visit to Lake Geneva was made in October, 1881, as an incident of work 
in progress on the Illinois Slate Natural History Survey, my purpose at the time 
being to compare the invertebrate fauna and the biological conditions of that lake 
with those of the much smaller and shallower lakes of the same series in northeastern 
Illinois. On this visit I hauled the dredge and beam-trawl and the surface net re- 
peatedly in several parts of the lake, both along shore and in the deepest water, and 
carefully worked the product of the dredge and trawl through a set of assorting 
sieves, saving in alcohol everything collected. In August, 1887, I improved the op- 
portunity of a casual visit to this lake to make much larger collections with the sur- 
face net, ran several lines of soundings across the lake, and collected from deep water, 
for analysis, the peculiar, soft, fine, mud — largely a chemical precipitate — which 
covers the bottom there to a great depth.* 
* This mud has a peculiar, rank, almost offensive, odor, and a soft, greasy feel, and rubs away largely 
between the fingers. It is of a pale slate-blue color when dry, darker when moist, tinder the micro- 
scope it has a semi-crystalline appearance, and contains very little vegetable d 6 bris and not much 
sand. It effervesces freely in sulphuric acid, but does not wholly dissolve. A sample of this mud 
which had been taken from a depth of 20 fathoms was submitted to Prof. William McMurtrie, of 
the chemical department of the University of Illinois, who reported upon it as follows; 
“ The following are the results of analysis of lake mud : 
Per cent. 
Carbon dioxide ( CO 2 ) 25. 00 
Calcium oxide ( CaO ) 27. 13 
Magnesium oxide (MgO ) 3. 65 
Organic matter 4. 80 
Insoluble residue 32.20 
Ferric oxide ( Fcj O 3 ) 1..50 
Aluminic oxide ( Ah O 3 ) 4. 67 
“These are doubtless engaged in combination as follows: 
Calcium carbonate ( CaCos ) 48. 445 
Magnesium carbonate ( MgCOa ) 7. 665 
Ferric oxide ( Fej O 3 ) 1.500 
Aluminic oxide ( Ah O 3 ) 4. 670 
Organic matters 4. wOO 
Insoluble residue 32.200 
“ The insoluble residue consists of clay and sand.” 
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