Evening star., 1937-01-26

One Of the major problems Of . con-
tinuing civilization In the future Will be
the assurance of an adequate water
supply.
Some Of the difficulties in the way
were stressed by DR.. Oscar E. Meinzer OF
the Geological Survey in his presidential
address to the washington ACADEMY OF
Sciences last week. The recent droughts,
he said, have brought the matter before
the public in an alarming fashion.
The actual amount Of water on earth,
DR.. Meinzer stressed, probably has
changed very little since life began on
earth. The great residual reservoir OF
water is the ocean which contains al
but q small percentage OF the externA
water Of the globe, the rest being on the
surface Of the land, In the 1nterstlces OF
the soil and rocks, or In the atmosphere.
Probably this water supply Is being IN.
creased very slowly by the release OF
water from the magma which forms the
interior Of the earth-but this has not
been suficient to account for any major
changes during geological time.
But there have been very notable
changes in the distribution Of this almost
changeless water supply. At time vast
quantities have been locked up In ice
enough the lower the sea level the earth
over about 400 feet. Many Of the larger
cities now are located on sites that were
under the ocean since the human race
began to live on earth.
Especially variable Is the "land water"
drawn from the ocean by evaporation,
deposited over the continents in the form
of snow or rain, and tending to how back
to the sea. But only about third OF It
ever reaches the sea again-about one.
half in the eastern part Of the United
States, only q small percentage on the
great plains and virtually none In the
Great Basin. A good deal of it Is held
permanently in the interstices OF the un.
deriving rocks which constitute the
water table, permanent reservoir un-
derneath the whole country. Much H
lost through evaporation from lakes,
streams and vegetation.
But. DR.. Meinzer stressed, precipita-
ton and evaporation differ markedly
from time to time in different localities.
1.-THE variations" he said, may be re.
garded as consisting Of q very irregular
cycles of different magnitudes, superim-
posed upon one another. The geologic
record, covering some hundreds Of mil
lions Of years, seems to show that long
ages Of relatively warm and equable cli-
mate, perhaps with q general tendency
toward aridity, were at several times In
terrupted by shorter periods Of more
variable climate, including some cold.
humid stages. The latest Of these variable
periods began perhaps q million years
ago with the first Of the quaternary
glacial stages and Is apparently still In
progress. The geological record shows
that the quaternary, and perhaps also
older periods Of the same sort, con-
sisted Of several major glacial stages
alternating with distinct interglacial
stages and that the glacial stages, or at
least the last one, consisted Of two or
more substages involving considerable
climatic fluctuations. The greater hui
midity of the glacial stages was In large
part caused by decrease in evaporation.
Prom intensive study Of geologic.
archaeological and historical records 1t Is.
however, evident that recent time has
not consisted of o gradual change from
glacial to interglacial conditions. but
rather Of q complicated huctuation OF
climate, In part regional rather than
vorld.wids. between periods that were