The herald-advance. (Milbank, S.D.) 1890-1922, 1901-12-13
WEAR OF THE EARTH
HOW THE FACE OF OUR GLOBE is
CONTINUALLY CHANGING.

The atmosphere plays it's part in geo.
logical operations. Its c%orroding pow
er, backed by rain and wind. helps to
decay and disintegrate those rocks
which ere exposed to its influence. Rain
completes the work thus begun. Wind
blows dust, sand and volcanic ashes
over large tracts Of earth-in fact.
0ver the whole of it.
1t Is only Of late years that geolo-
giStS have discovered that fine vol
canic dust Is carried over the whole Of
the earth's surface n plays a very
important part In the deep sea depos-
Its. On deserts and nearly rainless re-
gions blown sand will wear away the
hardest rocks by beating against
them. Some sandstone formation. ap-
pear to have been piled up by wil.ds.
Winds cause ocean currents, waves
and storms. The great denuding
power of the sea is largely due to the
atmosphere. Some parts Of the Eng
lish coasts are being rapidly washed
away. Plants and animals have their
distribution considerably affected by
winds and ocean currents. Again,
whether living in water or on land,
animals live on the oxygen supplied
from the atmosphere, and land plants
absorb carbonic acid from the same
source.
Rain acts in two ways: ~ chemic-
ally by d~issolving certain substances,
such as lime, out Of the rocks, and e.
mechanically by wearing down their
surfaces as 1t flows over them. Any
old building-,a ruined castle or cathe-
dral. for instance-shows a "weath-
ered' surface resulting from the ac-
ton of rain and wind. In sandstone
structures the details of carving are
often lost, and on old tombstones the
lettering can hardly be deciphered.
Springs are due to rainwater collecting
In rocks and rising to the surface.
Rivers are fed by rains and springs.
A river is a very powerful geological
agent. In the hardest rocks rivers
gradually carve out a valley or gorge.
This is accomplished partly by chemic-
ally dissolving certain mineral sub
stances, but chiefly by mechanical
erosion, the stones, sand and mud
wearing away the bed of a stream as
they run and tumble over it.
The finest examples of river action
are the famous canyons of Colorado,
which In some places are gorges 5000
or even 5000 feet deep, with vertical
sides. But, as already pointed out,
riVopc h0v0 a o0nc<pvro<{Vyn noki0r c-s<o
as important as their destructive ao-
ton. By bringing down their burden
Of sediment into lakes, estuaries and
seas they build up great piles Of rock
and SOW the dust of continents to
be-"
Glaciers IRE rivers Of ice fed by the
eternal SHOWS" Of high mountain
ranges such as the Alps They wear
out their own valleys as rivers do;
they transport mud, sand and stones to
great distances. in some cases sending
them sealed up in icebergs to float far
out 20 sea and on melting deposit their
burdens on the sea floor. or the coast
Of Newfoundland northern icebergs
are depositing q great mass Of 'gla-
cial drift"
The sea is a great denuding agent;
destructive. It is the workshop where
nearly all the ~stratiied rocks have
been accumulated and ranged in layers
or strata. The rivers and ocean cur
rents continually bring in fresh sup
plies Of debris even for: hundreds Of
miles.
Man, compared with the lower ami
mails. produces but little effect as a ge-
illogical agent. Still the human race
has considerably modified the distribu-
ton OF plants by cutting down forests
and by scultivating certain plants to
supply food. So with animals. Ger
taiE useful species have been cultivat.
ed and enormously increased at the
expense of others which prove useless
or harmful.
But plants and animals have had.
and still have. far more influence geo.
logically. Coal seams are made up of
vegetable remains OF former periods.
Forests have an important influence
on climate and on animal as well as
plant life. In the comparatively un-
known world OF the ocean marine
plants doubtless have important func-
lions.
Marine animals accomplish a vast
amount OF geological constructive
work. Great deposits thousands Of
feet thick owe their existence to small
calcareous creatures living In the sea.
Coral reefs afford tie most familiar
Illustration.
The force known as heat Is OF great
Importance. The earth is hotter below
the surface and probably has a very
high temperature toward its center.
In some places not very far below It's
surface it contains highly heated rock.
which occasionally flows over the sur.
face during volcanic eruptions. In
other places we find hot springs In con-
nectfon with volcanic action.
Heat exercises a powerful influence
on rocks deeply buried below the
earth's surface, chiefly by means OF
heated water and, steam. In this way
rocks have been very much altered
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