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that varies to yellowish or blackish tints with silt of clay or 
loam origin. When diatoms are abundant a brownish tinge is 
very evident, and with Oscil/aria rising in quantity, as it does 
in some semi-stagnant waters in late summer, a blackish tint 
becomes pronounced. In midsummer and early fall, when 
water-blooms rise, we find varying tints of green according to 
the kind and quantity of chlorophyll-bearing organisms present. 
The turbidity, as above suggested, is due to a great 
variety of factors, one of the most important of which is the 
plankton itself. Indeed, under some conditions turbidity be- 
comes a token by which the relative abundance of the plank- 
ton may be estimated. The presence in our plankton of vast 
numbers of the most minute planktonts, such as the flagel- 
lates, renders this relation of plankton and turbidity more 
prominent in our waters than it is in waters where such organ- 
isms are less abundant. 
The turbidity otherwise is due to non-living solid matter 
in suspension. This is brought in by tributary streams, and is 
torn loose from the shores and bottom by the current of the 
river, the movements of fish, the wash from steamboats, and 
the constant sweeping of the river channel by fishermen’s 
seines during the open season at stages when seining is possible 
in this place. The dust from prairies and forests brought by 
winds; the waste from factories, distilleries, glucose-works, and 
cattle-yards; and the sewage ofa score of cities along the banks, 
—all make additions to the burden of the water. 
Microscopical examination of the plankton has revealed 
the diverse character and origin of the silt which accompanies 
it. Fine fragments of quartz, bits of mollusk shells, small 
pieces of coal or ashes, minute particles of loam or clay, and 
the fecal pellets of aquatic organisms—especially of mollusks 
and of insect larve—constitute the heavier element of the silt. 
To this is added a variable but ever considerable quantity of 
exceedingly fine sediment of earthy or clayey origin, some of 
which remains long in suspension. The coarser and lghter 
silt consists largely of comminuted vegetation, both terrestrial 
