Evening star., 1932-01-26
SAND-CUT STONES
TELL AGE STORY
Science Able to Read Blows
by "Ventifacts" Found
Over Earth.
BY THOMAS r. HENRY.

Winds of a hundred millions years ago
may have left records which will enable
biologists to tell in what direction they
were blowing, and whether they were
strong and steady or light and variable,
In any particular place in past ages.
These records are "ventifacts," or
stones cut by wind-blown sand so that
they have smooth faces. They have
been found all over the earth, dating
from different geological periods. Eff
fort TO interpret them now are engag-
ing the interest of the Committee on
Sedimentation of the National Research
Council. One experiment conducted for
the committee, according to the report
Just issued, consisted of blowing sand
against rocks with an electric blower to
find cut Just how their faces would be
cut. When this is known it may be pos
Slble to reconstruct a picture of the wind
conditions which produced particular
rock patterns found in vcrious geological
formations.
The direction and force of the pre-
vaillng winds, it is pointed out, would
be an important factor in interpreting
the geological story Of the past. but it
is difficult to imagine anything more
1rrecoverable than gusts Of air after
they have passed. But the experiments
indicate that the most ephemeral Of all
things may have left the most per-
manent records. One curious difficulty
has been to distinguish these stones
cut by the wind and stones swallowed
by dinosaurs and used for grinding
stones IN their stomachs or gizzards
II Turkies' Gizzards.
To test this, according to the report
by Kirk Bryan Of the Committee on
Sedimentation, Dr.. David White of the
United States Geological Survey Sc
cured the stones from the gizzards OF
II turkeys The birds had been fat
tened in yard, and the grinding ma
ter1al consisted of pebbles of quartz
and fragments of glass and porcelain
II was believed that the grinding ac-
tion in turkeys gizzard would have a
similar effect to that in the gizzard Of
one Of the prehistoric monsters. These
stones are known as gastroliths.
Close study of these stones, Bryan
reports, shows a clear difference be-
tween glzzard-ground and wind-cut ma
terlal By striking against each other in
the grinding process the stones in the
birds gizzard were given a smooth but
not polished surface. But stones re-
covered from ancient geological forma-
tlons, contemporaneous with the dino
saurs, were highly polished. The polish
was due to scratches too fine to be
seen under a 20-times magnification.
Hence, Bryan holds, the gastroliths
owe their final polish, at least, to wind
action.
Preliminary results of the electric
blower experiment, conducted by DR..
Walter H. Schoewe under Bryans di-
rection, the report says, show that the
form Of stone in the path of a con-
tinuous stream of sand varies accord
ing to the resistance Of the stone in
relation to the size of the sand and the
height and width of the model in pro-
portion to the height and width Of the
stand stream. 1t also appears that the
greatest abrasion takes place on sur
faces steeply inclined to the horizontal |
wind stream.
Ten Types Recognized.
Ten rather clearly differentiated |
types Of the wind-worn stones can be |
recognized from specimens gathered ]
from all over the world. the report says. |
There are the polished, grooved, |
secured. cut, shaped, faceted irregular. |
pyramidal, ridge-shaped and Brazil-nut |
types. These types would have been |
formed in ancient deserts by different |
types and directors of wind blown sand |
in respect to the stone itself Expert |
mentS have indicated that there is an |
essential difference in the pattern cut |
by steady winds from one direction, |
alternating winds from two directions |
and variable winds. This must be
worked out by further tests
Stones of this sort formed all the
time in suitable environments, the re-
port says, and their Importance for
biologists comes when they are found
in association with very ancient de-
posits. Some have been found in
Sweden which presumably were carved
by winds of the Cambrian geological
period nearly a half billion years ago
The earliest found in North America
JuraSSic period which followed the time
when the great coal beds were laid
down. There have also been found
gastrolithS from the same period which
may have been ground in the gizzards
OF the dinosaurs. The great number
of North American ventifactS, the re-
pert states, date from the ice age and
early modern periods covering a span p,
of not more than a million years. They
have been found in Arizona, Maine, |
New Jersey, Massachusetts, Iowa and
California. Many have been found in |
Northern Europe dating from the same
period.
Ventifacts Of very recent origin have !
been reported from practically all the |
great deserts, from Northern Europe |
and from North America. One investi- !
gator found within an area a half |
mile square in the Red Sea desert F.!
about 400 faceted stones, most of which |
were ortented with their faces at right /
angles TO the wind.
CNMThIMC