The Washington times. (Washington [D.C.]) 1901-1902, 1901-08-25
SCULPTURED BY GLACIERS
Beautiful Geological Specimens at
the National Museum.
Rock Surfaces DcIicntely Carved and
GrOOved by Prehistoric Convul-
sion Of Nnture-How Facts Are Es
tabIished by the Scientists.

scum devoted to geology are specimens
of rock surfaces curiously and some
times beautifully grooved and carved
The carvings in some cases are 50 per-
feet as to suggest the work of the skill
ed artisan. AS matter of fact, these
| apparent holdings are not holdings al
all, nor arc they the handiwork of man
They represent a CONFUSION of nature
at a period so remote that there is nc
| mode of reckoning it. In other words
they are TIE rock-scorings of the glacla
invasion of the northern part of this
country. Whether the ice came down
| by land or sea. whether by glaciers
creeping over the face of the country
or by icebergs and ice foes sailing over
submergiEg waters. science is unable to
determine Be that as it may, that
the ice came sweeping down over the
face of the earth in huge quantities
and with irresistible force these rocks
| in the Museum attest.
| These scorings are the trails left
| by the invader. To the geologist their
character reveals the nature of the icy
| visitant as tracks reveal the track
maker. The glacialist distinguishes
with as much certainty the traces of a
! glacier or of an iceberg or ice foe as
| hunter the track of a bear or a moose
! or a serpent. \ glacier may be likened
| to a prehistoric monster who leaves
| print of its foot imbedded in the rock.
From such slight tokens of its some
time existence Prof. owen builds the
hi ,,ft Il A mi 81
it, and describes its habits.
For purposes of convenience in geolo-
| sy the common term growing" is used
to describe all the effects of the glacial
invasion on rock surfaces alluded to-.
Respecting their mode of origin glacial
grooves belong to two classes, which it
is of some importance to distinguish.
The one class had an existence as
grooves prior to the incursion of the ice
by it The other class owe their origin
solely to glacial action.
Previous to the sweeping down of the
ice the surface of the rock had been
subjected to various destructive agen-
cies which produce great inequalities
in 1t, among which were surface
grooves Thus the invading ice found
burrows formed already. Where these
lay coincident with its course it's work
was merely to rasp them out and polish
and striate their sides. In their remodel
ed form they sometimes have the aspect
of channels due wholly to glacial &C
ton; but the observation of the expert
often discovers features which, In their
nature. indicate that they could not
have arisen solely from glacial abra-
sion. There must have been a pre-ex-
istent channel to guide and mold to it
self the abrading ice.
A main element in the growing was,
of course. inequality in the hardness of
rock. This finds its simplest expression
where beds of unequal hardness were
slightly upturned so as to present their
beve.ad edges TO the ice, which acted
along them like a beading plane. In
such cases the soft beds We're easily re-
moved. while the harder ones Were left
standing forth as ridges, the whole as
Stunning a fiuted surface. Grooves of this
sort. which are to be seen in several
specimens at the National Museum, are
little more tkan an expression of the
unequal hardness of the rock beds. On
a large scale this is thought to have
been sometimes an important factor in
determining the topography that re-
suited from glaciation.
That streams of water flow beneath
glaciers has been determined by most
abundant observation, but excepting in
the immediate vicinity of the ice Dor
der. where alone observation has pene-
trated. the precise relations of the ice
TO the stream are chiefly matters of
conjecture. Whether the ice continually
tends to press down upon the stream
and to fierce il hither and thither at will
or whether the stream maintains itself
by melting and wearing back the en-
croaching Ice as fast as it presses upon
it, and so retains a constant channel,
is unknown. 1t is quite certain. how
ever. that such subglacial streams have
much abrasive power because they are
loaded with fine. rasping glacial silt.
most effective abrasive agency. That
they cut Cor themselves rock channels
is unquest.nned; that into these the ice
subsequently molds itself and in turn
molds them by its own abrasions
is attested by observation. The
curious form of some of the rock
scorings suggests that they were par
tally worn by a stream of water, while
their engravure points to their occu-
pancy by ice which was nodded to their
toFtuous courses, and which in turn re-
fashioned their walls, reducing them to
those smooth, striated surfaces and
those beautiful curves that attest, to
the eye of the trained observer the
work of a glacier