The silver messenger. (Challis, Idaho) 1890-1912, 1910-09-06

a remarkable degree with
IL the Increase in velocity. so
y that mining engineers can
@DD make accurate calcula-
tons concerning the We
~ locity which is necessary
" 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 nave Increased the transporting
power OF the water 1923 times and II
you quadruple It you have increased
the weight OF the pebble which it
would move 4,096 times. This at first
thought seems incredible, but it 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 mile tn six hours. will carry
along with 1t PARTICLES of fine clay
and keep them in suspension. Water
moving at twice that velocity will lift
and carry along with 1t 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
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. blocEs as big as
~ in,
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 II after a
storm one pauses to listen he will
hear what sounds like distant can
ponading, 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
fne over a rocky bed is determined by
its ability to shove along sand and
nebbles and gravel over its bottom. 1t
&c those PARTICLES of solid matter that
accomplish the erosion. acting as
rasp. or sandpaper, or more properly
q sand blast. to remove the solid rock
beneath and deepen the channel OF
stream. In order to do this, however,
there has to be proper adjustment be-
tween the supply of loose solid matter
N he transported and the volume and
ye,ocitv of the water. If there is more
sond and gravel than the current can
handle this will accumulate upon the
bottom and fill up rather than deepen
the he'd. If there is too little material
the stream will flow over the rocks
without effecting much erosion, while
~ there is lust the right amount o.
eo,ia matter to be showed along 1t vii
I,onsn the channel with great rapid
ity.
There are many striking examples
80 the work which has been accom-
nl,shed by rivers in deepening ant
r.;daning their channels. We lool
,non the rise Of mountain chains Al
sa;,g most majestic illustrations o
,be mower of natural forces, but tn
fact is equally impressive that in man,
cases rivers which run across the I'M
~ mountain elevation are able to wea
,+nwn their channels as fast as tn
mountains rise and thus maintain
their ancient onward course. Tn
Hudson river has thus sawed down
channel through the solid rocks whic'
in ancient geologic times arose acros
IT'S course at West Point and below
all that picturesque valley Of the Hue
son being a valley Of erosion. Tn
delaware river has worn an eve
more striking gorge through the Blu
Ridge at the Delaware Water Gal
where It cuts directly across the yer
hard strata Of Medina sandstone col
stituting Blue Ridge, forming perpei
aicular walls on either side 1000 fee
On height. Similar gorges are foun
In the Susquehanna and Potomac an
many other rivers along the App
,ochian chain just above where the
emerge upon the surrounding lowlan
We often speak Of such rivers
.hursting" through their barrier. 81
,sera was no bursting in the oper
o., These gorges were cut by tt
low process which we have describe
,ha rivers lowering their channe
w as the mountains slowly ro'
across them.
Among the most striking example
r,vers which have by erosion ke
y, With the elevation OF mountain
p"ross their course is that OF the 7
a ,sn'h,a river, in oregon, where for
, ,amn distance It occupies trou'
.un directly through the moun'a
asa,n thousands Of feet In depth "A
e o,Ssr very striking instance is tn
70 he seen IN the Amur rive. .,r ~a'
10 =. uses the Bureya mountains
II uo ,n s,beria For nearly 100 mil