The Tupelo journal., 1910-07-08

OBO and pebbles increases In
a remarkable degree with
the increase in velocity, so
that mining engineers can
~ $ 6: : ; Il: ;:::;; !: =.. ::::: ::
to remove stones of a certain size
from their sideways. The transport
ing power increases GA times with
each doubling of the velocity; so that
II you increase the velocity threefold
you have increased the transporting
power of the water 729 times and IL
you q%uadruple 1t you have increased
the weight of the pebble which 1t
would move 4,096 times. This at first
thought seems incredible, but 1t is
nevertheless true, and prepares us to
appreciate the astonishing results that
are produced by running water.
Water moving three feet in a sec
ond, or a mile in six hours. will carry
along with it particles of fine clay
and keep them In suspension. Water
moving at twice that velocity will lift
and carry along with it fine sand;
while a velocity four times as great
will sweep along fine gravel and water
moving at the rate of two miles an
hour will carry along stones as big as
q hens egg. There is hardly any limit
to the size of a pebble that would be
rolled along by a current of six or
eight miles an hour, blocks as big as
houses being sometimes set in motion
and transported for considerable dis
tances.
In various ways one can obtain pos
tive evidence of this power of water
transportation. If, for instance, he at
tempts to wade across the Platte
river in Nebraska, which is over
loaded with sand and has a gradient
of seven or eight feet to the mile, and
hence a very rapid current, he will
find his bare legs stung by the par
ticles of sand and fine gravel that are
driven against them. Or if after a
storm one pauses to listen he will
hear what sounds like distant can
%nonading, produced by the knocking
of the stones together as they are
rolled along upon the bottom of the
stream.
The erosive power of a stream flow
ing over a rocky bed is determined by
Its ability to shove along sand and
pebbles and gravel over its bottom. 1t
is these particles Of solid matter that
accomplish the erosion, acting as a
rasp, or sandpaper, or more properly
a sand blast, to remove the solid rock
beneath and deepen the channel OF a
stream. In order to do this, however,
there has to be proper adjustment be-
tween the supply Of loose solid matter
to be transported and the volume and
velocity of the water. If there is more
sand and gravel than the current can
handle, this will accumulate upon the
bottom and fill up rather than deepen
the bed. If there is too little material
the stream will flow over the rocks
without effecting much erosion, while
If there is just the right amount of
solid matter to be showed along it will
deepen the channel with great rapid
ity.
There are many striking examples
of the work which has been accom-
plished by rivers in deepening and
widening their channels. We look
upon the rise of mountain chains as
being most majestic illustrations of
the power of natural forces, but the
fact is equally impressive that in many
cases rivers which run across the line
of mountain elevation are able to rel
down their channels as fast as the
mountains rise and thus maintain
their ancient onward course. The
Hudson river has thus sawed down a
channel through the solid rocks which
In ancient geologic times arose across
its course at West Point and below,
all that picturesque valley of the Hud-
son being a valley of erosion. The
Delaware river has worn an even
more striking gorge through the Blue
Ridge at the Delaware Water Gap,
where 1t cuts directly across the very
hard strata of Medina sandstone con-
~stituting Blue Ridge, forming perpen-
dicular walls on either side 1000 feet
in height. Similar gorges are found
in the Susquehanna and Potomac and
many other rivers along the Appa-
lachian chain Just above where they
emerge upon the surrounding lowland.
We often speak of such rivers as
bursting" through their barrier. But
there was no bursting in the opera
ton. These gorges were cut by the
slow process which we have described,
the rivers lowering their channels
gradually as the mountains slowly rose
across them.
Among the most striking examples
of rivers which have by erosion kept
pace with the elevation of mountains
across their course Is that of the CO.
lumbia river, in Oregon, where for a
long distance 1t occupies a trough
running directly through the mountain
chain thousands Of feet in depth. An
other very striking instance is that
to be seen in the Amur river where
it crosses the Bureya mountains in
eastern Siberia. For nearly 100 miles