solid
cobbles and boulders by running water after lodgment in the beds of
large streams, at a distance from the mine, is not great. When these
materials are carried further forward by floods or torrents they move
along the bottom until they find permanent lodgment, consequent upon a
decrease in the grade of the bed of the stream or from some other
cause. In water the weight of rocks is materially lessened, and the
friction which would be due to their weight is correspondingly
decreased.
The
constant collision and rubbing of the harder rocks against each other
smooths and polishes them, somewhat changes their form and lessens
their surface, and, to a certain extent, reduces them to fine powder
but not to sand. Experiments made to ascertain the wear due to erosion
of solid materials transported by rivers or streams tend to establish
the fact that no perceptible deposit can be attributed to such cause,
as the sediment from such wear is found to be a very fine powder, which
immediately passes off in suspension.
The
distribution of gravels along the course of any stream will be found to
be in accordance with their size, form and specific gravity, and
distance from the source. Thus the material composing the bed of a
stream, which may at its source consist entirely of large boulders and
cobbles, will become finer and finer through the successive stages of
gravel, pebbles, and sand, until it is finally discharged as muddy
water into the ocean.
Effects of Hydraulic Debris.—The
working of hydraulic mines in California has here and there given rise
to disputes with farmers. These disputes have, unfortunately, been
carried into the domain of local politics, and thereby not only brought
into undue prominence, but also exaggerated, and an equitable
settlement prevented. Meantime manipulators have taken advantage of the
situation to the detriment of both the farming and the mining
interests.
Flickr
Stumbleupon
Scribd
