Evening star., 1938-10-11
OF STARS,
MEN AND ATOMS
Notebook of Science Prosress
in Field, Laboratory
and Study.
By THOMAS r. HENRY.

BY THOMAS r. HENRY.
Discovery in Yellowstone National
Park Of rocks which have reverted from
a higher to lower form, an apparent
contradiction to current theories of the
origin of rocks. has just been reported to
the Geological Society of America by
DR.. Charles N. Fenner of the Geophysi-
cal Laboratory of the Carnegie Institu-
ton in Washington.
Many geologists maintain that all
igneous rocks, or rocks of molten origin
such as granite, were formed by a
process analogous to evolution among
animals. There are "lower" and higher"
forms. depending on complexty of
structure, and there Is never any re-
tracing of steps to lower level.
This evolution" as it has been pic
tured, lis essentially chemical process
1t Is assumed that al igneous rocks had
as their common ancestor an enormous
mass OF molten material deep within the
earth. Chemically this primordial rock
stuff, called magma, is believed to have
been predominantly basic, rather than
acidic, containing large quantities Of
lime, iron, magnesia and other bases.
Following the rock evolution analogy,
the idea of an acidic rock reverting to q
basic is comparable to that OF members
Of the dog family reverting to lizards.
DR.. Fenners discovery near the Gardiner
River does not necessarily diSprove the
current theories of rock formation, but
shows beyond much doubt that this may
have proceeded In more than one way.
largely upon laboratory experiments in
which pressures such as exist in the
depths of the earth cannot be approx
mated, and which therefore assigns less
active Importance to the gasseS con-
tanned in magmas under such pressures.
The existence OF the great magma
masses in the beginning, however, is in
eScapable.
Columns of this magma occasionally
rose very slowly into higher levels Of
the earth'S crust, where pressure Is less
intense and temperatures are lower.
Some came to rest within the crust and
some issued forth as lava flows at the
surface. AS the magma cooled, some Of
its molten elements reached tempera-
lures which compelled them to unite in
definite molecular combinations, and to
separate from the liquid as solid min
eral crystals. which sank Or rose, de-
pending on their weight relative to that
OF the magma. 1gneous rocks are ag-
gregateS OF such crystals.
The theory further states that this
capitalization followed a definite Sc
quence. analogous to the evolution OF
the animal species. First, the basic ele-
ments crystallized out into minerals
forming such basic rocks as baSalt, while
the last elements to crystalline were
alkaliS and silica, forming such acidic
rocks as granite. Between these two ex-
tremes were intermediate stages, in
which rocks containing varying amounts
of bases and alkalis were formed.
Proponents Of the rock evolution
theory maintain that after the higher
types Of rocks, the GRANTEES, have been
formed they will not hybridize with lower
types, the dark-colored rocks rich in
iron, lime and magneSia. But the Yel-
lowstone National Park rocks studied by
DR.. Fenner convince him that such re-
version to type actually has taken place.
He found that the principal rock I'M
DERIVING the area was fresh, even-
lava erupted by one Of the many VOL
canoes active in this region in past
geological periods. Through this basalt
lower type from the standpoint Of
evolution, pre- historic stream had
carved small gorge, closely parallel
ing the present Gardiner River. Much
later a volcano erupted, discharged a
sheet of acidic lava. Some Of this lava
flowed down the valley carved in the
basalt and eventually cooled and hard
ened to form rhyolite, rock which
would have been granite had it been
formed beneath instead of upon the
earth's surface, and which represents a
higher type
DR.. Fenner carefully examined areas
where this molten acidic lava came into
contact with the older basic rock. or
basalt. and found that the two often
united chemically to produce interme-
diate products-analogous to reverting
to type in biology.
The outstanding characteristic of the
Gardiner River rhyolite," he says, was
it's ability to attack basalt with great
vigor, whereas the outstanding charac-
teristic of rhyolite formulated in the
theory of crystal fractionation is its
inability to attack basalt'
He discovered that in many places the
rhyolite has penetrated deeply into the
basalt in the form Of complex networks
OF veins and disklike masses, which rami-
fly through the basic rock in intricte pat
terms The basalt nearest the rhyolite was
modified in composition, he says. While
retaining its solid structure, it was init
mately permeated by rhyolitic material
in such a manner that basaltic constitu-
ents were carried away and rhyolitic
constituents were substituted.
AS an answer to the problem of how
the heavy and increasing viscuous lava
could penetrate downward into solid
rock DR.. Fenner suggests that lit was
not the liquid rhyolite, but gaseous en-
anations given off from it that were the