Evening star., 1915-10-10

Dtmcult run, which lies De-
tween Little Falls and Great
Falls, and considerably nearer
the upper than the lower falls, has
been the subject and the territory Of
several rambles during the spring.
summer and autumn of this year. The
Rambler has found that neighborhood
productive Of many stories which
seem.. at least to him, Of interest. Be
cause Of its remoteness and the hard
ship of travel through that wild, rough
country. only a few Washingtonians
and those of an adventurous turn Of
mind and stoutness Of foot and leg, ex-
plore It, Desiring to tell his patient
followers something about the geologic
history of this region. the Rambler ad-
dressed formal communication to
Guy E. Mitchell. one of the officials Of
the geological SURVEY.
Mr. Mitchell, inclosing the Rambler's
letter. addressed request to E. w.
Shaw. geologist of the survey.
~
Throuph the courtesy, good nature
and learning of Mr.. Shaw the Rambler
is prepared to present a nature story
of this region near Washington, a. re-
gion which has not been made the sub
ject of a regular geological survey re-
port. Mr.. Shaw has written for the
Rambler two accounts of the country.
The first of these follows:
The things of principal geologic in
terest concerning Difficult run and
Black pond are about as follows:
Difficult run occupies valley Of Its
own carving. the valley having been
produced by the gradual removal OF
earth and rock particle by particle and
pebble by pebble during the thousands
of years while the run has been run
Ring. The narrowness Of the gorge is
due 20 a comparatively recent uplift
Of the region. which has rejuvenated
all Of the minor tributaries of the Po-
tomac and caused them to cut gullies
and wash out most of the fine and me-
dunn m-coarse PARTICLES in their beds,
leaving only huge powders. which
themselves are sometimes moved in
time OF flood. The smaller the tribu-
tary the less powerful it is as an erod-
ing agent. and hence the gorgelike
features are best developed on streams
which are neither so small as to be
unable to cut down rapidly or so large
as to be able to keep up with the mas
ter stream. the Potomac, and to widen
out their valleys somewhat, as Rock
creek and other larger tributaries
have done.
There is some indication that the
country around Great Falls has been
affected more profoundly by the uplift
referred to than any of the surround
ing region. Probably all of the move
ments which took place were connect
ed with a general uplift of the Appa-
lachian province. and along line run
ming northeast and southwest through
Great Falls the uplift was more pro-
nounced than elsewhere.
In any case Difficult run. once
quiet little stream flowing on a sur
face high above its present bed, and
having a general appearance similar
to the headwaters Of Difficult run near
Ash Grove. Then, perhaps 100000 years
ago. or one one-thousandth of the way
back In the history OF the earth with
which the geologist Is more or less
familiar, came the uplift in the form
Of a gradual bowling up Of the Appa-
1achian region. perhaps accompanied
by earthquakes, but not volcanoes, and
on account of the upheaval the Po-
tomac flowed more rapidly and became
a moro powerful eroding agent As II
deepened its valley the tributaries were
constrained to do likewise, for they
were also rejuvenated, and unless they
deepened their valleys to correspond
with the master stream they would be
left hanging high in the air.
The rocks in the vicinity Of Difficult
run were formed millions of years ago;
one hundred million Is perhaps as good
q guess as any. at the beginning of the
clearly recorded part of the earths his
tory. They are of igneous and meta
morphic varieties; that is to say. some
were formed by the solidification of a
molten mass of lava and others by the
modification through pressure and tenn
perature of some other varieties of
rocks. In any case, they have no doubt
been subjected to pressure and temper
ature far beyond anything which man
makes use of, and almost beyond the
power Of the human mind to realize.
The rock is made up mainly of quartz,
feldspar and mica, but in places con-
tains numerous small crystals or gar
net. None of these minerals Is sufi-
ciently clean and free from flaws to
work UP into gems. but most of them
where better formed have been used
in jewelry. Under the influence of
weather. the rock is gradually broken
up by rain and frost. and becomes a
light bun earthly mass such as may be
seen in many railroad cuts in this re-
gion.
BLACK pond lies in an abandoned
channel of the Potomac river. Appar-
entity the river, or at least large part
of il, once flowed through the depres-
sion IN which Black pond Is situated,
and II is a general characteristic of the
stream channel that 1t is in places deep