The Baltimore County union. [volume] (Towsontown, Md.) 1865-1909, 1903-02-21
THE MOTIONS OF UNDERGROUND WATERS.

of the U. S. Geological Survey, gives
the Ametfcan Fa,me1 an advance re-
port from the department touching
the motions of underground waters.
1t is exceptionally interesting. The
report says:
The amount of water within the
crust of the earth, says Prof. Charles
S. Slichter, in paper entitled "The
Motion of Underground Waters, re-
Gently published by the United States
Geological Survey, lis enormous,
amounting to SOS, million cubic
yards. F" His estimation is based
upon the supposition that the aver
age depth which waters can pene-
trate beneath the surface is six miles
below land, and FIVE miles below the
ocean floor. This vast accumula-
ton, if placed upon the earth, would
cover its entire surface to uniform
depth of from 5000 to $500 feet.
Under the influence of gravitation the
water is generally in motion, and the
object of Professor Slithter's paper is
to describe the rate and manner of its
overflow and the laws governing the
same. Experiments have shown that
not only do sands and gravels possess
porosity, but rocks presumably solid
and compact may be traversed by
water. Even so hard a rock as Mon
tello granite, selected for the sarcoph-
agus for the tomb of General Grant,
on account fits great strength, shows
aporosity of o.23 per cent. The most
productive water bearing rocks, how
ever, are found to be the porous sand
stones, and in some cases limestones,
whose inner texture has been chemi-
cally dissolved.
The popular idea of underground
waters is derived from the rivers of
copious discharge found in the Nam
moth and other caves. But this idea
is erroneous, as such streams, though
of great local importance, are COM
paratively rare. The great mass of
ground water slowly percolates
through sand and gravel deposits,
sandstone, and other porous material
under wide extent of territory.
Though its motion carries it but
fraction of mile in a year, this
ground water is so widespread and
often so accessible as to be of the
greatest economic importance.
The rate of movement of the un-
derhow has been the subject of long
and careful investigation. To deter
mine this interesting question meas
urements have been made in the river
gravels of streams whose surface
flows have ceased, and from such
measurements more or less trust
worthy results have been obtained.
One of the most accurate and inter
esting of these is a series of expert
ments conducted by Professor Slich-
ter along the valley of the Arkansas
river in western Kansas. The meth
% is an electrical one. A double
row of inch and quarter drive wells
is sunk across the channel of the river
whose underhow is to be tested. The
upstream wells are then charged with
a strong electrolyte, which dissolves
and passes down the stream with the
moving water. The passage of the
electrolyte toward the lower we'll is
shown by the gradual movement Of
the needle of an electrical instrument,
and the final arrival at the we'll is
shown by a sudden and strong de-
Election of the needle. It is exceed
ingly interesting to watch the gradual
movement of the water, which can
be traced from the beginning of the
experiment in this indirect way. By
this method the rate of flow ten feet
below the bed of the Arkansas river
was found to be 2H feet per day.
Other experiments in the beds of the
Hondo and San Gabriel rivers in
southern California, gave rates of az,
a, 5H and 7 feet per day.
The knowledge of the underhow
that exists beneath the gravel of all
great valleys has been taken advan-
tage of in arid sections of the West,
where the running dry Of streams de-
prives irrigators of their water sup
ply. By excavating to bed rock in
river gravel and building an imper-
vious barrier across the channel, these
underground waters are saved in suf-
fcient quantities to be of great value
to the farmer. A notable subsurface
dam Of this kind has been constructed
on the Pacoima creek, California, to
furnish water for irrigation and do
mestic use.
Deep zones of flow are most i'm
portant feature of the movements of
underground waters, and open up an
interesting field of investigation. The
wonderful artesian basin of North
Dakota and South Dakota, which
has proved such an important factor
in the economic development of these
States, forms one of the illustrations
used by Professor Slichter in the ex-
planation of deep-seated underhows.
A cross section of this part Of the
country clearly shows the interesting
fact that the water which comes to
the SURFACE in the gushing wells of
the Dakotas travels underground all
the way from the Black Hills and
Rocky Mountain slopes, in the water
bearing strata known as the Dakota
sandstones. Another illustration of
extensive basins due to deep under
ground flows is found in Wisconsin,
where an extensive area of water
bearing rocks, nearly 900 feet thick,
conducts water of singular purity
under large areas of the State.
1t must be borne in mind that there
is limit to the amount of which
can be drawn from an artisan basin,
and that there is no such thing
as an inexhaustible supply. The
Gradual failure of the Vue11c which