The Cambria freeman. [volume] (Ebensburg, Pa.) 1867-1938, 1876-02-11
THE POWER OF WATER.
HOW SOME MOUNTAIN GAPS HAVE BEEN
FORMED-AN INTERESTING ARTICLE.

HOW SOME MOUNTAIN GAPS HAVE BEEN
FORMED-AN INTERESTING ARTICLE.
Every one who has visited the Della,
ware water gap, or assembled the Sus-
quehanna from Harrisburg, or passed
through the cut where the Potomac has
pierced the Blue Ridge at Uarper's
Ferry, or has seen indeed any one of
the numerous gaps made by seaward
flowing rivers through the long noun
tain ridges which flank the Alleghenies,
must have been struck by the question
how a comparatively small stream
could overcome so formidable an OBJ
struction.
Evidently the river could not have
taken advantage of q natural cleft or
fissure through the mountain dam, for
the strata correspond on the opposing
sides ofthe gap,and the river flows over
an unbroken stratumunder-rUHnl
the broken strata of the banks. The
gap as plainly denotes section out of
the mountain as a notch in a stick
does the removal of the wood. The
disconnected edges of the strata tell
precisely the same story as the several
lines of annual growth on the sides Of
a wood choppers cut; the connecting
portions of wood and stone have been
removed The question is, How
The irst and most natural suupOsi-
ton would he that the valley, back of
the dam, had originally been filed,
forming a lake whose outlet was over
the ridge above the present river chan
mel and that, as the outlet was lowered
! Il.
the lake was drained until the entire
valley was laid bare. The supposition
is negatived by the plain fact that it
would be impossible TO fill the valley
10 the height Of the ridge at the point
of the gap. Before the water could
reach that level il would find an outlet
elsewhere, where the natural elevation
of the dam was less. An excellent IL
Iustration occurs a few miles above
Harrisburg, where the Susquehanna
crosses fexture of the mountain
ridge cutting twice through the noun
taIn5 within few miles, when appar-
emily it might easily have avoided the
obstruction by going few miles
around.
Another supposition is that original
" the river ran ut level corresponding
with the top of the ridge, and that the
present valley through which itruus is
the result of erosion; while the river
was slowly wearing through the hard
mountain strata, the softer earth of the
surrounding country was washed away
through its sinking channel, leaving
the more unyielding rocks III mountain
ridges From this point of view, the
river is to be regarded not merely as
the cleaver OF the mountain barrier but
as the creator of it, by reducing the
level of the adjacent land.
Hitherto this supposition has been
the most plausible and the most genes-
ally accepted. But another and, per-
haps, truer explanation is suggested by
PggT Pgg2fT ol PoEeIs VI He "GEi85RE2ration GGi5Rlg Of the
As our Atlantic rivers cut through
the Allegheny ridges, so the Green
river, the chief head stream of the Col
orado, pierces the Uinta mountains,
flowing through a series Of canyons
compared with which our eastern water
gaps are insignificant. As in the case
of the Susquehanna, above noted, the
rivel bursts through the opposing
ihOttAiSstiA4' HAiSAi Dl'stIClALAN IL III
have found an easier passage by going
round them. Why did it choose the
harder course
Prof. Powcll's answer is that it had
the right Of way. twas running there
before the mountains were formed and
simply removed the obstruction as fast
as it rose in the way.
The contraction of the earth causes
the strata near the surface to wrinkle
or fold, and such fold was started
athwart the course Of the stream now
known as Green river. Had the fold
been suddenly formed it would have
been an obstruction sufficient to turn
the water into a new course, to the
east, beyond the extension Of the wrin-
kle; but the emergency of the fold
above the general surface of the country
was little If any faster than the pro
gress of the corrosion of the channel.
We may say, then, that the river did
not cut its way down through the
mountains, from height of many
thousand feet above its present site :
but having an elevation, differing but
little perhaps from what it now has, as
the fold was lifted. it cleared away the
obstruction by cutting a canyon, and
the walls were thus elevated on either
side. The river preserved its level. but
the mountains were lifted up as the
saw reyoives on fixed point as the
log through which it cuts is moved
along. The river was the saw which
cut the mountains in two"
The gigantic nature Of the aqueous
the circumstance that lhc mountain log
or fold had diameter ot fifty miles.
while the depth of the cut, that is, the
elevation Of the fold above the present
level of the river, was over twcnty-four
thousand feet. But a fraction OF this
enormous uplift Of rock remains. As