450 Wisconsin Academy of Sciences, Arts, and Letters. 
Decaying plants, and mineral matter tend to form an organic 
sediment of varying thickness. In places this sediment may 
constitute a layer of considerable thickness; it will be a false 
bottom, for while it may bear a fair amount of stress, any con¬ 
siderable pressure will pierce this layer. This sedimental layer 
is quite impervious to heat, absorbing little and permitting 
none to penetrate, so that the wet soil beneath will be found 
quite chilly by comparison with the warm water above. De¬ 
composition and acidification are important factors in swamp 
physiology and probably of great importance in determining 
the faunal complex; yet too little is known of this phase of the 
subject to permit any detailed analysis. 
Whatever the factors be, given a slight current, the fauna 
immediately changes certain of its aspects, perhaps because of 
the removal of the chemical deterrents. This can be observed 
admirably in the swamps of the Yahara to the north of Lake 
Mendota and south of Lakes Monona and Waubesa. Where 
the water is stagnant the fauna lacks Trichoptera, Zygoptera, 
and Hyalellae; but in presence of a fair current these groups 
are well represented. 
Streams .—As just stated, a stream differs from a swamp in 
that it flows, while the swamp is stagnant. The degree of flow 
is, of course, relative. Much also depends on the composition 
of the bottom. Given a sandy bottom and another of mud it is 
probable that the muddy stream will support little plant life 
while the sandy stream will be choked with vegetation. 
The composition of the substratum is of the highest import¬ 
ance to the biota of the stream. No better examples of this 
exist than Pheasant Branch Creek at the western end of the 
lake and Six Mile Creek flowing in at the north. Pheasant 
Branch Creek is a narrow, rapid stream, about 6 meters wide, 
a little over a meter deep, with a bed of mud covered with silt. 
The water is clear. The creek contains a luxuriant vegetation 
of Lemna, Myriophyllum, Ceratophyllum, and Elodea, in which 
a very rich fauna maintains itself. 
Six-Mile Creek is a slower stream, with a very tortuous chan¬ 
nel, varying in width from 8-12 meters, with a depth of 1-2 
meters. Its bottom is mud and clay. Its water is murky and 
no vegetation exists in the bed of the stream, except for an oc¬ 
casional Nymphaea and Castalia; hence the animal life is essen- 
