The San Francisco call., 1903-12-26
The Burden of Glaciers.

The Burden of Glaciers.
BY C. FREDERICK WRIGHT. A. NJ. Ii. d.
rAuthor of The Ice Age in North America,
Man and the Glacial Period" EteI
Copyright. 1903. by Joseph B. Bowles)
In its movement over the uneven sur
face of the land the ice which flowed
southward over so great a part of
North America in the glacial period
ground off the prominences and dragged
the grist along slowly under it. spread
ing it out.over the country invaded and
tending to fill UP the valleys and pro-
duce a general level. 1t is this action
Of the glacier that has largely pro-
duced the level plains of the prairies of
the Mississippi Valley; so to speak, the
glacier has ''ironed" out the rufties in
the continent and left it comparatively
smooth. The whole glaciated area is
covered with ancient river channels
and gorges, which have been complete
" filed up with the grist of the glacier,
while to a great depth it is spread out
over the central and southern portions
to furnish the arabic soils from which
the richness of the country is derived.
The depth of these glacial deposits
south of the great lakes probably aver
ages more than 100 feet, and in some
places where a buried river gorge is
penetrated it is known TO have been
more than 500 feet in depth. Over
Northern Germany and Northwestern
Russia the depth of the glacial deposits
is estimated TO average 125 feet.
These glacial deposits can be easily
recognized and distinguished from
those made by water by their unassort-
ed character. by the angularity of the
imbedded fragments of stone and the
frequent occurrence of scratches upon
them. Deposits made in running water
are uniformly assorted and stratified,
but in the direct glacial deposits the
pebbles and rock fragments are indis-
criminately mixed in the whole mass
like plums in a pudding.
A few facts concerning the glacial
period give new force to the adage,
Truth is stranger than fiction" The
5000 600 square miles covered by the
glacial ice in North America and Eu-
rope to the depth of one mile (probably
an underestimate would furnish 6O0O,-
600 cubic miles of ice, all of which is
formed by water distracted from the
ocean. This would reduce the level of
the ocean the world over 250 feet and
add TO the northern part of the conti-
nents tive or three times the weight of
the entire land surfaces of North Amer
lea and Europe which are above sea
level. This additional weight would be
such a powerful attracting force that
it would lower the general level of the
ocean fifty feet more.
The weight of this ice over every
square mile would be 4,O00,0O0,0G0 tons,
which would have to be multiplied by
5000. 900 TO get the total amount. This
is probably enough 10 cause the crust
Of the earth TO sink under it when the
ice accumulated, and to allow it to
rise again when it had melted off.
This perhaps of itself accounts for the
great changes of level in the northern
hemisphere which have taken place
since the beginning of the glacial
period.
The spring freshets or this glacial
period were of enormous dimensions,
causing, as 1 have recently ascertained,
the Missouri River TO rise annually 200
feet instead of forty, as it sometimes
does now.
The. close of the glacial period was
so recent that it comes down beyond
the advent of man. Glacial man fol-
lowed up the retreating ice border in
New Jersey, Ohio, Kansas and Mime
sofa as he is now doing in Greenland
and Alaska
The glaciers of the world are now
nearly all retreating. The front of the
Muir glacier which / visited in 1886
and have described in my Zee Age in
North America, is now three miles
farther back than il was at that time
and, according to all accounts, it is
thirty miles farther back than it was
when Vancouver discovered It 100 years
ago.
We are not so far separated from the
glacial period as it would seem to the
casual observer. Probably it would re
ouire but a slight increase OF snowfall
combined with slight lowering of the
temperature, to cause glaciers again to
form on the White Mountains and in
Labrador. and the already existing gla-
ciers to begin a readvance. When once
begun it would be difficult to tell when
the advance would stop, for glaciers
of themselves tend to lower the tenn
perature and to increase the snowfall
When we reflect upon the way the heat
of the tropics is distributed by the
gulf stream and the Japanese current
il is not difficult to see how compara-
lively slight changes in land level af-
fecting the course of the oceanic cur
rents might bring on a glacial period
again. But of any tendency in this
direction we have no evidence.
Prospective Customer = What have
you got in the way of fruit, this morn
ing, grocer?