The Press., 1901-11-28
LEAR OF THE RTH
HOW THE FACE or OUR GLOBE is
CONTINUALLY CHANGING.

HOW THE FACE or OUR GLOBE is
CONTINUALLY CHANGING.
Geological Agents That Are Always
Busy In Nnture's Great Workshop.
Where Man Has Comparatively LIT
tie Influence.
The atmosphere plays its part In gedJ
logical operations. It's corroding pow
er, backed by rain and wind, helps to
decay and disintegrate those rocks
which are exposed to its influence. Rain
completes the work thus begun. Wind
blows dust, sand and volcanic ashes
over large tracts of earth-in fact,
over 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 anu 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 formations ap-
pear to have been piled up by Winds
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 py
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 dissolving certain substances,
such as lime. out of the rocks, and (2)
mechanically by wearing down their
surfaces as 1t flows over them. Any
old bullding-a ruined castle or cathe-
dral, for instance-shows a wealth
cred" 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 very powerful geological
agent. In the hardest rocks rivers
gradually carve out valley or gorge.
This is accomplished partly by chemic-
ally dissolving certain mineral SUBJ
stances, but chiefly by mechanical
erosion, the stones, sand and mud
wearing away the bed of 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,
rivers have constructive action quite
as important as their destructive ac-
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 are 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 to sea and on melting deposit their
burdens on the sea floor. Off the coast
of Newfoundland northern icebergs
are depositing great mass of "gla-
cial drift"
The sea is a great denuding agent;
but its work is more constructive than
destructive. 1t is the workshop where
nearly all the stratified 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 ge-
illogical agent. Still the human race
has considerably modified the distribu-
ton OF plants by cutting down forests
and by cultivating certain plants to
supply food. So with animals. Ger
tain 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,
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 I'M
known world of the ocean marine
| plants doubtless have important func-
| tons.
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 the 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 it's 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-
| nection 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
or "metamorphosed." The crystalline
schists have thus been brought to their
present state by series of chemical
| changes due to heat. and there is nc
doubt that they were once ordinary
deposits OF clay, sand, etc.-Hutchin.
| SONS "AutohiograDhy of the Earth -