49 
the mud had nearly uniformly a quite wholesome earthy odor in midsum- 
mer, and except locally along shore immediately below fish markets or 
large drains no more bubbling was noted when the bottom was disturbed 
than was normal at the same time at points fifty to a hundred miles 
farther south. In early July and early September, 1919, and in Septem- 
ber, 1920, the muds taken both in and outside the deeper channel at Liver- 
pool, at Hogfat Bend, three miles above Havana, and just above Havana 
were distinctly foul-smelling and hundreds of large gas bubbles rose to 
the surface each time the sampler hit bottom. In calm hot weather in 
late August, 1919, spontaneous bubbling was observed at Hogfat Bend 
and just above Liverpool; and at Liverpool in early September, 1920 the 
mud samples from the channel were of the same spongy texture previous- 
ly noted in the samples from Rome and Chillicothe. 
Both the shrunken volumes and altered composition of the collec- 
tions of small bottom-animals taken at the fourteen stations worked in 
this section in 1920 add their clear testimony to the advance of pollution 
this far southward since 1915. While the average weight of the channel 
haul here was over 5,000 pounds per acre in 1915, in 1920 it was less 
than 250 pounds—a net loss of 95.3 per cent. In the 4—1-ft. zone for 
the same five-year period the average haul showed a shrinkage of 95.9 
per cent., or from 2,122 pounds to only 87 pounds per acre. The change 
in the composition of the small bottom-fauna, in turn, includes the disap- 
pearance since 1915 of five out of seven families of snails; of more than 
half a dozen species of bottom-dwelling larval midges; and of twelve out 
of thirteen or fourteen families of “other insects,’ worms, small 
Crustacea, and other small bottom-invertebrates. 
By far the greatest destruction, as measured by bulk and weight 
as well as in numbers, appears to have been accomplished among the 
snails in the five-year period, the percentage declines in average snail- 
poundage in the channel and in the 4—7-ft. zone since 1915 (98.7 and 
98.0 per cent.) being greater than the percentage decreases in poundage 
of total hauls (95.3 and 95.9 per cent.), and much greater than the per- 
centage declines in snail yields in some important sections of river be- 
tween Chillicothe and Peoria. While in Peoria Lake, as already pointed 
out, the decrease in snails in the five-year period was largely or alto- 
- gether compensated by increase in the weight of the midge larvae and 
sludge-worms (principally the former), it is clear that under the circum- 
stance in this section of a decline in snails from several thousand pounds 
to less than a hundred pounds per acre, an increase in Chironomidae 
from a trace to as much as 150 pounds per acre could go but a little way 
toward making up the snail deficiency. The following tabulation of 
changes in the snail fauna is substantially the same as the one previously 
given for the Peoria—Chillicothe section, showing the same three species 
—one each of Viviparidae, Pleuroceridae, and Sphaeriidae—still surviv- 
ing, and principally the same list of about seventeen species that disap- 
peared from the section in the five-year period under discussion. 
