RIVER AND LAKE DEPOSITS 
187 
DISPOSAL OF THE RIVER LOAD 
MECHANICAL. 
CHEMICAL. 
In THE RIVER. 
Deposits clay, sand, or 
pebbles in its bed, some- 
times as a sheet, on the 
bottom, but more com- 
monly as bars. These 
Deposits of carbonate 
of lime or other substance 
sometimes precipitated in 
river bed when the water 
On THE LAND. 
may remain for long | is evaporated. 
periods of time. 
Sometimes, in arid 
Where the slope is : 
rapidly decreased, alluvial 
fans are built. Along 
the margins of many 
streams the sediment is 
made into floodplains. 
regions, streams carrying 
much alkali, on spreading 
out over neighboring low- 
lands leaves a thin film 
of these substances on the 
surface. 
In LAKEs. 
Builds deltas. Fur- 
nishes sediment that is 
strewn over the lake bot- 
Supplies various sub- 
stances to lakes. These 
become noticeable in lakes 
without outlets. Then, 
In THE SEA. 
tom. Ultimately these | after awhile, the water 
accumulations fill the |.may become so impure 
lakes (see p. 188). that some of the sub- 
stances must be deposited. 
Builds deltas. Fur-| Carries to the ocean the 
nishes sediment that is 
distributed over the bot- 
tom by waves and cur- 
rents. 
carbonate of lime needed 
by animals, and adds 
other substances to the 
ocean water. 
