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History of York County Pennsylvania From the Earliest Time to the Present online

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classification which seems to require the few-
est hypotheses for its support, and to lend
itself most readily to any new developments
of our knowledge.

The Eozoic (or "early life") in this olassiti-
I cation, comprises those rocks usually crystal-
line in structare, but of very varied and di-
I vergent character, in or below which the very
earliest known or suspected forms of life oc-
cur — and those very sparingly in York Coun-
I ty. This series comprises all the rocks which
j are geologically inferior to the Hellam Town-
ship Quartzite.

The PalsBozoic (or "old life") includes all

j the rocks from and including the Hellam

I quartzite to the new red sandstone, and is

I made up of the quartzite, hydro-mica schists,

and their included iron ores, the great blue

and buff limestone on which the city of York

j is built, together with that of lower Wind-

j sor Township; that near New Holland, in

Manchester Township; around Newmarket,

in northern Fairfax Township; and north of

Dillsburg in northern Carroll Township.

The Mesozoic (or "middle life") rocks are
the reddish brown sandstones and shales (and
perhaps the igneous rocks penetrating them)
which cover almost the entire northwestern
part of the county. If the imagination
might be indulged in likening the area of
the county to the lower part of a horse's leg,



this formation would constitute the fetlock
joint and all that portion immediately above
the hoof proper.

The Cainozoic (or "new life") includes all
these rocks of which the origin is of later
date than the last mentioned, but still before
the date of any evidences of the appearance
of man on the planet. It is not known to
me that there is a representative of this age
present, unless it be that marked "marl" in
the geological map, which has been supposed
to belong there.*

The Quatenary and recent deposits com-
prise those deposits which have been made
from the earliest appearance of man on the
planet down to the present time, including
of course those of origin so late that they
might have been historical. Such are the
marks of the denudation which has shaped
the meadows and hills as they are at present;
the moulding of the ravines and deepening
of the stream beds; the distribution along
the latter of gravels, etc.; and finally (for
the sake of saving one more division of time,
which would otherwise lie wholly within this
one, and at best remain very uncertain as to
exact date) the works of man's hand which
are discoverable in the arrowheads and
sculptures not infrequently observed along
the lower course of the noble river which
forms York's northeastern boundary.

One word more is necessary as to the sub-
division of the rocks of these diiferent geolog-
ical ages before their occurrence in York
County becomes our theme.

If the average thickness of all the strata
which have been yet recognized as distinct in
the state of Pennsylvania were laid one upon
the other, it has been estimated that the height
of the pile would reach something like forty
thousand feet. But this is made up almost
without taking into account other than the
Palaeozoic I'ocks. If the ordinary methods of
calculation were pursued in estimating the
thickness of the Mesozoic or new red sand-
stone and shale alone which crosses York
County, three miles and a half would be
added to this column, j No very great thick-
ness of Tertiary or Cainozoic rocks is to be
found in Pennsylvania, but if instead of

*In volume CC, p. 334, of the publications of the Second Geo-
logical Survey of Pennsylvania, among the specimens collected
during the year 1875 are two, of which the provisional field
numbers are 424 and 425, marked respectively "Mesozoic lime-
stone (marlite?)" and "marl (?) Mesozoic limestone conglomer-
ate," both from Welly's larra, Dillsburg. From the second en-
try, it would appear that there were two distinct specimens
comprised under the same field number. Whether the same be
true of the former number also, or whether I was led at first to
regard this marl as a small remaining patch of Cretaceous marl
like that of New Jersey, I cannot now say. Nor have I at hand
the evidence which induced the belief, subsequently, that this
was of Tertiary (Cainozoic) age. That, however, is my present
impression. P. F.

fThere are, however, good reasons for rejecting such an



counting upward, or from the most recent
of the Eozoic series, we were able to count
downward to its lowest member or to the
earliest existing rocks of the globe, it is
probable that a thickness of this series alone
greater than all of those that we now know
put together would be established. That
the exposure of rock in York County will not
justify the belief that any considerable frac-
I tion of this Eozoic series can be reached by
i boring, the following list of its divisions,
t accepted by many very able geologists, will
sufficiently show. They are given in
descending order, the lowest being the earli-
est known, and the first named the most recent.
*VI. Keweenian.
V. Taconian.
IV. Mont Alban.
III. Huronian.
II. Norian.
I. Laurentian.

THE EOZOIC EOCKS OF ¥0KK COUNTY.

I have not seen in York County any rocks
which I considered to be of Laurentian age.
If there be any, they are to be sought in the
portion of the South Mountain, which is
included in parts of Carroll and Franklin
Townships, but it is very improbable that any
will be found there. The same may be said
of the Norian, which is simply another name
for what was once called "Upper Laurentian. "
There remain, then, only the Huronian, the
Mont Alban and the Taconian, for the
Keweenian is not known in this part of the
1 United States. The lowest member of the
\ Eozoic series, therefore, which has been
recognized in York County is the Huronian,
and if I be not in error in my deductions,
the rocks of this age form the greater part,
if not all of its lower sections. On the
accompanying geological map it is colored
pink, as well as all that previously referred
to in Carroll and Franklin Townships form-
ing the South Mountain.

A broad flat arch of these rocks crossing

I the Susquehanna somewhat obliquely be-

' comes evident in plotting the observations on

section lines along either the right or left

bankf of the river.

The perpendicular thickness of the Huro-
nian rocks which constitute the visible parts of
this arch has been calculated by me to amount
I to 14,400 feet or two and seven -tenths miles
(or four and three-tenths kilometers) meas-
uring from the lowest rocks exposed a short
distance above McCall's Ferry to the base of

*See Vol. E, p. 241, Publication of the Second Geological
Survey of Pennsylvania.
I .fSee these sections in Atlas accompanying Vol. CCC,

, Second Geological Survey of Pennsylvania, by the writer.



466



HISTORY OF YORK C0U:N^TY.






the Peach Bottom slates. This arch for anti ■ '
elinal, as it is technically called) is a very
important feature in the geology of this part
of the State; for, if my conjecture as to its
extent be 'well founded, it is in all proba-
bility the leading element in the structure of
a broad belt of rocks extending from a point
at least north of the Schuylkill Kiver, (and
not improbably even within the New England
States) to and into the State of Alabama.

But whether this carefully considered
hypothesis be true or not, there is not the
slightest reason for doubting that the rocks
of this part of the county form the floor on
which all the others in the county were laid
down. Another fact in relation to this
tiat arch or anticlinal remains to be con-
sidered, viz. the line along its crown (or along
the top of the arch ) appears not to have been
a horizontal line after the last great earth-
crust movements of which we can find evi-
dence in this part of the continent had been
completed.

As architects, geometers, and geologists
would express it, the axis of this arch appears
to have sloped upwards, from the west of
south to the east of north. As the axis lies
along the summit of the bend in the lower
bed over which all the other beds are laid
down, it follows that it lies in the lowest beds
which form the arch: and to say that this
axis rises towards the northeast, is to say
that, judged from our present surface, the
lower ( and consequently older) beds of this
arch rise nearer to that surface the farther
one follows this direction of northeast, and
of course these same rocks sink lower beneath
the surface the farther one follows the direc-
tion of the arch to the southwest. I have
elsewhere given reasons for the hypothesis
that this "anticlinal" joins and continues
the anticlinal of the Buck Ridge * near |
Conshohocken, a few miles northwest of Phila-
delphia on the Schuylkill River, traversing
Lancaster and Chester Counties a little
south of the Chester Valley, But at Con- |
shohocken, the anticlinal is represented by
Laurentian gneiss, while in Lancaster and
York Counties "the Huronian schists, which
have been torn off by atmospheric denuda-
tion at the former locality, still remain; and
still farther to the southwest it is not unlikely
that even more recent sheathings may be
found, unless the axis be broken or bent and
rise also in this direction. The main fact, ,
which it is my pm-pose. to emphasize here, is
that the same structui-e of arch evidently af-



«See "Theses presentees a la Faculte des Sciences de Lille.
University de France, etc., 1882," and "History of Lancaster
County, etc., Philadelphia: Everest & Peck. Published^l883" p. 3.



fects an enormous thickness of beds, and in all
probability is traced in the flexed rock masses
of at least two entirely different geological
periods: indeed it may possibly be discovered
in those of yet others outside of the limits of
the field which it is the purpose of the writer
to describe,

A somewhat arbitrary division has been
made by the writer between the rocks of the
Huronian and those of the next following
age. The line which constitutes this divi-
sion may be seen passing through the south-
ern part of Lower Windsor, the middle of
Windsor, the eastern part of Springfield, in-
cluding Codorus, and reaching the Maryland
line a short distance east of the boundary
dividing Manhoim from West Manheim
Townships, This line does not profess to
be, and in all probability is not, an accurate
line of demarcation between the two forma-
tions, Jt was adopted as an approximate
dividing line between two regions which ex-
hibit lithological characteristics diverging
from each other in a degree proportional to
the distance on either side of it. The same
is true of the line which separates these lower
rocks from the triangular area in the extreme
southeastern corner of the county, in which
are found the justly famous Peach Bottom
roofing slates. These two lines, which are
in the average parallel to each other, are ap-
proximate boundaries only between the two
regions and that filled by the rocks of the Mc-
Call's Ferry, or the Tocquaii Creek anticlinal.
The rocks of the latter belt are strongly
marked crystallized rocks,* i.e., their structure
is coarse and the minerals which compose
them are large and well crystallized, espec-
ially along the central parts of the belt. The
rocks of the two bordering regions just men
tioned are more ci-ystalline, i. e., crys
tallized imperfectly, or in much smaller mass
es, besides having other differences in kind,
For example, the arch-belt (if I may be per
mitted to express it so) contains larger
amounts and larger specimens of Muscovite
and potash micas. The rocks are lighter, and
not infrequently enough feldspar is found to
give them a decidedly gneissic character;
and the more so in general terms the farther
one gets away from the bordering regions.
The rocks in these latter regions, on the
other hand, are more and more magnesian,
darker in color (usually greenish or yellowish-
green) and softer. They contain large quan-
tities of chloritic minerals, and are more re-
markable for the great number of white
quartz dykes which intersect them than those
of any other series in the county; or indeed.



if they be taken in their entirety, in the
United States, than any other rock series rep-
resented here.

These '• arch -rocks" are very generally
destitute of valuable minerals, so far as they
have been exj)lored in York County, except
on the fringe of the South Mountain, where
they are very generally in close proximity
with a series of iron ore deposits similar to
and in fact continuous with those known as
the ores of the "Great," or "Cumberland
Valley." But though this juxtaposition
would tempt one to connect these ores with
the rocks just spoken of, and though it is
conceded that rocks of this age do often carry
iron ores, the strong probability is that the
proximity is "accidental;"' that is to say,
that the ores occur at the foot of the moun-
tain, because having been originally embedded
(as constituents of minerals) in the rocks
which covered these slopes, during the degra-
dation and destruction of these latter, they
have been disintegrated, carried ■ away from
their original place (sometimes not far off),
and segregated in the soft and unctuous clays
to which these loose beds have been reduced.
But it is not improbable that some of these
ores may have owed their origin to the same
kind of alteration taking place within the
mass of the Huronian rocks themselves. So
that wherever the loose debris of higher for-
mations (and notably of the Hellam quartzite
(Potsdam Sandstone) which everywhere
abounds on the slope in boulders and blocks)
will permit the undoubted Huronian to ap-
pear near one of these great iron mines, it is
likely to be found that a part of the wealth
of the latter consists of a somewhat peculiar
ore, unlike the rest, which can be traced to
its first resting place within the bosom of the
Huronian rocks.

The belt of rocks which represents the
Eozoic in York County, lies, as it maybe said
approximately, between two lines, one fol-
lowing Muddy Creek from its mouth in the
Susquehanna to its right angled bend and
thence through Bryantsville to Constitution;
and the other commencing opposite Turkey
Hill (in Lancaster County ) and passing north-
west of Windsor PostofSce, southeast of Dal-
lastown and nearly through Glen Rock Post-
office. The portion of the South Mountain
above referred to as belonging to the same age
is small in area within the county limits, and
occurring at the end of one chain of Eozoic
rocks where they appear to sink beneath the
newer limestones and shales, its slopes are
gentler, it has been subjected to greater
erosion, and is covered for the most part
with the debris of more recent formations.



467



This belt, thus defined, contains no minerals
which are yet mined (if we except the iron
ores from the category), but the soil formed
by the chemical and mechanical action of the
atmosphere on its rocks is next in fertility to
that of the limestone belt itself. The rocks
of the Eozoic belt thus defined are intersected
by but few igneous dykes or trap; and this
fact taken in connection with the remarkable
prevalence of such dykes in the northwestern
part of the county, and their frequency
throughout the middle belt of limestone and
schists, would lead one to conclude either
that the seat of the igneous action resided
within the beds of the newer rocks, or that
the superposition of the latter in some way
favored the development of the Plutonic
forces which may have forced molten rock
for miles through narrow crevices and cracks
in the envelope of the globe. Perhaps the
explanation may be found in the supposition
that the number of such dykes would depend
upon the number of fractures in the earth's
crust, and that this number would increase
with the growing weight due to thickening
sediments deposited by water. However
this may be (and it does not explain all of
the facts connected with the new red sand-
stone), the only points where I have observed
trap penetrating the rocks of this belt are:
First, in a small exposure north of York Fur-
nace on the Susquehanna; and second, a short
distance east of Black Rock Furnace.

THE BELT OF UPPER EOZOIO.

I have preferred to describe this belt under
a separate heading because there are difficul-
ties connected with its assignment either to the
Eozoic rocks, just considered, or to the Pal-
seozoic, which will next be described. These
difficulties arise in great part from the lack of
outcrops of "rock in place" or bedded rocks,
which remain substantially in the position in
which these were deposited and hardened.
The decomposition which has attacked this
intermediate belt has destroyed the indentity
of the individual beds and strewn the sur-
face with its products, which are mingled
with the remains of rocks of much later date.
This is not surprising, if we may assume
that this belt formed the upper and later por-
tions of the' great Eozoic series, for we have
abundant proof that in contrast to the stabil-
ity and repose of the broad flat arch to the
southeast, this new region was the hinge on
which the first of a number of severe plica-
tions of the strata were operated. This
bending and twisting unquestionably crum-
bled the rocks and left loose material, which
was easily moulded by the waters of the



HISTORY OF YORK COUNTY.



ocean which subsequently covered it to forms |
which more or less resembled those which
had originally characterized it. But after
its consolidation with the next succeeding
formation, both were together similarly treat-
ed, so that in the contorted state in which it
was left, it exhibits some features which re-
call the lower Eozoic, and others which remind
one of the lower Palaeozoic of the county.
I1s precise boundaries, being difficult to as-
certain on the ground, cannot be given with
precision in the text. It will suffice to say
that beginning on the Susquehanna River a
short distance south of the southern outcrop
of the Prospect limestone, one part of it oc-
cupies all the region lying between the north-
western boundary of the Eozoic. already
given, and the southern and eastern limits of
the Hellam quartzite shortly to be described.
It is traversed through part of its extent by
two large trap dykes, and contains numerous
deposits of iron ore which I am disposed to
ascribe to segregation from iron minerals in
other formations. Some lime.stone occurs
interbedded with these rocks (as at Glen Eock)
which maybe safely assumed to be of earlier
date than the important York limestone,
whether or not it be ( as seems not improbable)
a part of the regular Huronian series.

The most extensive iron ore banks noted in
or on the border of this intermediate belt are
the Brillhart and Feigley hanks, and marked
Nos. 11 and 1"^ on the map.

The Peach Bottom districts, including the
famous rooting slates lying to the south of
the flat arch, was described by me in Volume
CCC, Second Geological Survey of Pennsyl-
vania in 1877, where I showed that its position
in the series was doubtful and that these rocks
might be interpreted to represent the upper
Eozoic (below the Potsdam) or the schists im-
mediately above the Potsdam, or (by supposing
a fault) a formation still higher — the " Mat-
inal" of Rogers. Since then fossil algae were
furnished to Prof. James Hall from the quar-
ries, but he was unable to determine the age
of rocks from them with greater precision
than to refer them to the second or third of
the^e horizons with a preference to the sec-
ond.* The commercial value of these slates
will doubtless be treated elsewhere. Photo-
graphs of the quarries, and of the manner of
working them, will be found in Volume CCO,
second Geological Survey of Pennsylvania. "f

THE PAL.i:0ZOIC ROOKS. HELLAM QUARTZITE.

(pOTSDAM SANDSTONE).

Prof. H. D. Rogers, in the first geological



survey of Pennsylvania, marked out and
described the members of the diiferent forma-
tions represented in the State. This forma-
tion, which we may consider the base of the
Palaeozoic, in a sketch like the present, which
is intended for the people and not for spec-
ialists, was considered by him to consist of
three parts: a lower series of "talcose"
slates, a middle white sandstone and an
upper series of talcose slates. It will be
easily understood, by what has just been
said, to what extent the view here of-
fered differs from that of our great pi-
oneer geologist. These "lower talcose
slates," in all pl•obabilit}^ are identical with
the intermediate or upper Eozoic beds, just
described, and therefore their position rela-
tively to the beds beneath them and above
them, is the same, whether they be consider-
ed upper Eozoic or lower Palaeozoic. It will
haveoccured to the reader l)efore this to in-
quire what kind of evidence is needed to sep-
arat e the layers of rock of one formation
from those of another. Like most simple but
comprehensive questions, this cannot be an-
swered in a few words, and I will not at-
tempt to do more than hint at the nature of
the answer in this place. The bases for con-
clusions in geology have widened and deepen-
ed by long and patient comparisons of obser-
vations of different kinds of facts; so that at
the present time botany, zoiilog^', mineralogy,
topography, and a thousand other things
are cited as evidences that this or that layer
of rock is older or younger than another. But
in questions of age all other means of investi-
gation are founded upon stratigraphy , which
proceeds to study the chronological order in
which one rock is laid down upon another, on
the assumption that in sedimentary rocks that
which is really on top is the later or newer in
origin, and that which is below is the older.
In rocks where certain minerals or plant and
animal remains, called fossils, occur, they
have been carefully studied, * and where
various kinds of similar remains have
been found, geologists have assumed that
the beds containing them were of the
"same horizon," even when stratigraph-
ical evidence was not at hand to estab-
lish the point. Thus the secondary or indi-
rect evidence has often been successfully used
to correct the apparently direct evidence of
superposition where this has been obscured by
reason of the overturning of a series of beds,
which has caused those first formed to ap-
pear, at the present time, on top of newer
strata. This much premised, it can now be
explained that the one indispensable concom-
itant of a change of formation is a "physical



break," between the two. That is to say,
that as long as the layers of rock appear to
be nearly parallel to each other, the strong
inference is that the beds are all of the same
formation, but where a sudden change of
"dip" (or inclination to the plane of the
horizon or in compass direction) is noted,
especially \f hen accompanied, as it usually is,
by a change of the material of which the beds
are made, the presumption is strong that this
marks the end of the formation to which
the lower bed belongs; and that then suc-
ceeded movements of the crust of the earth
altering their horizontal position ; and
that we have the commencement of a new
formation, of which the bed, showing the
change of dip and material, is the bottom
layer.

The explanation of the exceptions to this
rule would lead me far away from my present
plan, and must be omitted here. It may be
found in any elementary book on geology.
Now, to apply this to the present case:
There are no good exposures of the Hellam
quartzite with the slate below it at any place
in York County which the writer recalls. On
the flank of the South Mountain, the quartz-
ite is very much rent and crushed into frag-
ments, while of the small patch on the map
about two miles west of Case's ore bank
(No. S on the map) no accurate dip
was recorded. The Hellam quartzite, of
which a part composes the "Chikis Moun-
tain,'' exhibits indeed, in its numerous fold-
ings, the rock called by Rogers "talcose
slate" between its two principal beds of
quartzite, but not appreciably lower than the
latter.

We are forced to look to other parts of
the county for a clearer knowledge of the
relation to each other of this quartzite and
the schists on which it rests. We tind abun-
dant instances of this contact in Chester
County, north of the valley of that name,
and in all of them the quartzite lies "uncon-
formably" (i. e. with changed dip) upon the
schists. The latter, it is true, are somewhat
different ip minor characteristics from those
of which if is here the question, but so also



Online LibraryJohn GibsonHistory of York County Pennsylvania From the Earliest Time to the Present → online text (page 96 of 218)