A GENERAL REPORT ON THE
 PHYSIOGRAPHY OF
MARYLAND ee

A DISSERTATION i

PRESENTED TO THE PRESIDENT AND FACULTY OF THE JOHNS HOPKINS

UNIVERSITY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

BY

CLEVELAND ABBE, Jr.

BALTIMORE, MD.
MAY, 1808.

 
UTH. BY A HO EH A CO BALTO
MARYLAND WEATHER SERVICE.	VOLUME 1, PLATE IIIA GENERAL REPORT ON THE
PHYSIOGRAPHY OF
MARYLAND

A DISSERTATION

PRESENTED TO THE PRESIDENT AND FACULTY OF THE JOHNS HOPKINS

UNIVERSITY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

BY

CLEVELAND ABBE, Jr.

BALTIMORE, MD.
MAY, 1898.

oy
 

PRINTED BY

The Friedenwafd Company

BALTIMORE, MD., vu. >. a.

REPRINTED FROM
REPORT OF MARYLAND STATE WEATHER SERVICE, Vol. 1, 1899, pp. 41-216.
A GENERAL REPORT

ON THE

PHYSIOGRAPHY OF MARYLAND

Puystocraruic Processes.

INTRODUCTION.

From the earliest times men have observed more or less closely the
various phenomena which nature presents, and have sought to find
an explanation for them. Among the most interesting of these phe-
nomena have been those which bear on the development of the sur-
face features of the earth or its topography. Impressed by the size
and grandeur of the mountains, their jagged crests and scarred sides,
early students of geographical features were prone to ascribe their
origin to great convulsions of the earth’s crust, earthquakes and vol-
canic eruptions.

One generation after another comes and goes, yet the mountains
continue to rear their heads to the same heights, the rivers to run
down the mountain sides in the same courses and follow the same
valleys to the sea. So men came to look upon the mountains as per-
manent after they were upheaved, and adopted them as symbols of
eternity and unchangeableness. How often to-day, even, do we hear
expressions such as “the everlasting hills,” and “firm as a rock.”
With such conceptions concerning the origin of mountains and their
duration went the related ideas that the rivers found valleys ready
made for them in the shape of cracks and chasms in the earth,
formed during the birth of the mountain ranges. Those who held
these views thus saw no relations whatever between the mountains
and the rains which fell upon them, between the rivers and the shap-
ing of the valleys which held them. They believed the mountains
42 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

existed first and that the rains, snows, glaciers and rivers came after-
wards.

Other men recognized in the waters flowing through the valleys a
powerful agent by means of which the gorges, canyons, and broader
valleys had been carved out. This carving, however, they believed
to have been done in some long past period, when a great volume of
water swept down the river courses, tearing away rocks and trees and
fashioning the valley; or they held that all the lands of the earth
were at one time submerged by the ocean, and that great currents,
flowing in the seas of that period, carved out the river valleys which
we see to-day. Those who held such views are now called the Catas-
trophists, because they appealed to great convulsions, catastrophes
and cataclysms to explain the various geological and geographical
phenomena which they saw about them.

Upholders of the cataclysmic theories concerning the origin of the
earth’s features were numerous and even in the majority as late as
the beginning of the present century, yet a few individual thinkers
had centuries before held different and what are now believed to be
truer ideas concerning geological phenomena. Among the early
forerunners of the present school were Aristotle and Strabo. Aris-
totle opposed the catastrophic teachings, saying that “ the changes of
the earth are so slow in comparison to the duration of our lives, that
they are overlooked.” * Strabo also maintained that the features of
the land and sea were to be explained by the operation of natural
processes during past ages.

Thus early were foreshadowed the conclusions which Hutton pro-
nounced as the result of his studies in the fields and on the shores
of Great Britain. These conclusions are briefly summarized in the
following statement given by Playfair:* “ Amid all the revolutions
of the globe the economy of Nature has been uniform, and her laws
are the only things that have resisted the general movement. The
rivers and the rocks, the seas and the continents, have been changed
in all their parts; but the laws which direct those changes, and the
rules to which they are subject, have remained invariably the same.”

*See Lyell, “ Principles,” 1873. p. 21, quoted from “ De Die Natura.”
* Playfair, “Illustrations of the Huttonian Theory.” p. 374.
MARYLAND WEATHER SERVICE 43

In this passage is the key to the principles which have guided the
modern study of geology and geography. Since the year 1785, in
which Hutton published his “ Preliminary Sketch of the Theory of
the Earth,” the student of the Earth Sciences has been guided more
and more by the principle that the Past is to be interpreted in the
light of the Present.

To-day we recognize that the greater number of the valleys have
been carved in the landmasses by the everlasting and continuous
action of the weather in breaking up the rocks and of the rivers in
carrying these broken rocks away. We do not regard the earth’s
features as the products of convulsions or catastrophes such as deluges
or holocausts, but as resulting from the interaction of two sets of
agencies, slow in performance but powerful and all-pervading. One
set of agents continually strive to build up the land above the seas,
and these we call agents of construction; the other set of agents as
constantly and persistently strive to tear down or destroy the work
performed by the first class, and to this set we give the name of
destructional agents or agents of denudation. We have, then, to
consider two great classes, the agents and processes of construction
and the agents and processes of destruction or denudation.

PROCESSES OF DENUDATION.

The agents of denudation are all the time actively carrying on
their work about us. Indeed, most of them are perfectly familiar
to us and frequently attract our attention, but we rarely or never
stop to think what they mean, what relation they bear to the surface
forms of the earth, or even what influences they exert upon us. It
will be profitable then to consider briefly these agents and their
methods of work.

For convenience of treatment, the different agents and their proper
processes may be grouped into three general classes, viz. Atmospheric,
or those agents and processes which are peculiar to the atmosphere
as we commonly regard it; Aqueous or hydrous, or the action of

1The main facts and principles of rock-weathering as explained in the
sequel, are taken from G. P. Merrill’s “ Rocks, Rock-Weathering and Soils.”
1897. pp. 172, et seq.
44 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

moisture and water after it has left the atmosphere; Organic agents
and processes, whose effectiveness is due to the direct or indirect inter-
vention of members of the Animal or Vegetable kingdoms.

Atmospheric Processes.

The direct chemical activity of the atmosphere in breaking down
the rocks is not very great. The atmosphere contains, in addition to
its essential constituents nitrogen (4/5) and oxygen (1/5), very
‘appreciable quantities of a number of gases such as carbonic acid gas,
nitric acid gas, and ammonia, which, when in combination or aided by
moisture, are very effective agents of rock disintegration and decay,
but when in the dry state as parts of the atmosphere, possess but little
chemical power. It is therefore the water vapor in the atmosphere
which plays the most important part in the atmospheric processes.
This will be treated of separately and need not be further noticed
here since it becomes most effective after collecting as rain.

The mechanical processes of the atmosphere are of more direct
influence. Districts which are subject to an extreme daily range in
temperature, as the peaks of high mountain ranges, most tropical
countries and many continental interiors, present many striking illus-
trations of the way in which rapid alternations of expansion and con-
traction cause rocks to break up. After a long day, during which
the sun pours down its heat upon the exposed ledges and raises them
at times to temperatures far exceeding 100° F., there succeeds a
clear night during which rapid radiation and cooling takes place.
Thus the rocks may undergo variations in temperature amounting
oftentimes to a range of more than 75° F. within twenty-four hours.
Such rapid and considerable expansion and contraction as this change
in temperature involves cause the exposed rocks to crack or “ scale.”
In this way large fragments of slight thickness may be broken off.
Livingstone reports that in parts of Africa angular masses of rocks
weighing 200 pounds and more are thus split from the parent ledge.
Many instances of this method of rock breaking are reported from
the high mountains of western America, and throughout the northern
tier of states where the conditions are favorable.
MARYLAND WEATHER SERVICE 45

Another mode of rock disintegration results from the different
amounts of expansion exhibited by the various mineralogical con-
stituents of a rock. When a piece of granite, for example, is raised
to a moderate temperature, say summer heat or 78° F., the feldspar,
hornblende, mica and other minerals composing it expand. The
amount of expansion differs so greatly in different minerals that an
uneven distribution of strains is produced throughout the mass which
tends to loosen the interlocking grains. The continued annual and
daily expansion and contraction of the rocks may cause them in time
to break down into sand and gravel.

An effective agent of denudation at certain points in Maryland is
found in the atmosphere in motion or the wind. As the wind blows
over the surface of the ground or across bare exposed mountain peaks
it catches up the lighter particles of soil and rock debris and whirling
them up into the air, may project them with considerable force
against opposing cliffs or other immovable objects. The effect upon
both the rock particles and the objects hit is similar to that of a sand
blast. Various cliffs in California, Arizona and other portions of the
West have been carved into fantastic shapes by this natural sand
blast. In South America the upper portions of certain cliffs have
been so undercut that the remnants appear as huge boulders perched
upon the ledges by some mighty transporting agent. On sandy shores,
such as Cape Cod, or, in the wastes of the Sahara, the flying sands
have been found to polish and plane down pebbles too large to be
moved by the wind. Sometimes, as in the deserts of South Africa,
the pebbles show longitudinal scratches and grooves worn in them by
the flying sands.

Besides thus aiding in wearing down the resistant rocks, the wind.
also modifies the earth’s surface by transporting sand and soil from one
point to another. In this respect the destructional and the construc-
tional effects of the wind merge into each other. The destructional
process was illustrated in an interesting manner last year when the
Loch Raven reservoir was being cleaned out. The cleaning neces-
sitated the drawing off of a considerable portion of the water, as the
result of which a broad shoal of mud and sand which had collected
46 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

near the upper end of the Loch Raven gorge was laid bare. This
flat being exposed to the hot September sun and brisk winds became
thoroughly dried, until the grains of sand no longer cohered. The
prevailing west wind “drawing” into the narrow chasm caught up
the dry sand, and, driving it out of the channel, drifted it upon the
road at the curve, covering it to a depth of nearly a foot. In a
somewhat similar manner great quantities of sand are annually car-
ried from the long sandy beaches of our Atlantic coast line and either
driven out to the sea or into the lagoons between the beaches and
the mainland. In arid regions the wind may become a very impor-
tant agent in the removal of rock debris.

Thus the atmosphere is seen to furnish chemical agents for rock
solution and decay, to aid in the mechanical disintegration of the
rocks through its changes in temperature and to carve or transport
the finely ground products of their disintegration.

Aqueous Processes.

Pure water falling upon the bare rocks of mountains or wind-swept
ledges on the lowlands would have but slight effect chemically in
breaking down the rocks into rock debris and into the finer particles
which make up the soils of the earth’s surface.

Atmospheric water commonly contains in solution in small quan-
tities nitric acid, ammonia, and carbonic acid as well as other less
important substances, so that the rain upon reaching the earth is a
powerful chemical agent, which can produce important changes in
the rocks of the earth’s crust. Rocks containing iron-bearing min-
erals, such as iron-pyrites, the amphiboles, pyroxenes, etc., also suffer
considerable disintegration as a result of oxidation or rusting out of
those minerals. The oxidation also involves at times an increased
size or swelling of the altered mineral, so that physical strains and
dissociations may also be effected.

Of great importance is the process of hydration or the chemical
combination of water in certain minerals. This change generally
accompanies the oxidation of the rocks and causes even greater in-
erease in volume than does the latter process. Some of the hills
of Brazil are believed to have been increased in height by this means,
MARYLAND WEATHER SERVICE AT

which may be readily understood when it is learned that the trans-
forming of granitic rocks into soil by hydration entails an increase
in volume of 88 per cent.’ The rocks of the Piedmont Plateau
region of the eastern United States have been deeply affected by this
alteration in their physical condition. For many feet below the
surface there extends a zone of rock which has suffered hydration
and consequent swelling of the altered minerals. When a block of
this hydrated rock is brought to the surface it keeps its shape and
compactness only a short time; soon it crumbles away like a piece of
air-slaked lime.

Besides the chemical agents which the rain washes and absorbs
from the atmosphere there are powerful organic acids which the
decaying vegetable and animal remains lying on and in the soil fur-
nish to the waters percolating through it. These substances added
to the water make the moisture which pervades all rocks and soils
a very powerful and active agent in their disintegration. Clearly a
district whose rock foundations are thus weakened by chemical and
physical changes will offer but slight resistance to the attacks of rain,
rivers and waves.

The rich soil and the even-floored valleys which characterize lime-
stone and marble areas have resulted from the rapid and uniform
removal of the carbonate of lime in solution in the soil-water and by
the streams. It has been estimated that 275 tons of lime or calcium
carbonate are annually dissolved from every square mile of the Cal-
ciferous limestone of the Appalachian region, and this limestone is
but one of several different beds which occur in that region. But
these solvent waters attack not alone the yielding limestones. Granite,
gneiss, sandstones, shales, quartzites, all yield more or less readily
to its attacks, and none escape without some loss.

Striking illustrations of the great solvent power of the waters of
the earth’s surface are furnished by the corroded surfaces of quartzites,
metamorphosed siliceous conglomerates and other siliceous rocks. One
need but to go on an excursion to the rocks of Deer creek in Har-
ford county, and, climbing to the summit of the ridge, stand on the
projecting ledge which overlooks the gorge from the south in order

‘Merrill, op. cit. p. 188.
48 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

to have under his very feet a striking illustration of the inability
of the resistant silica or quartz to withstand the great solvent. The
rocks at this point are a fine-grained siliceous sandstone and a quartz
conglomerate which have been much metamorphosed or mineralogi-
cally altered under great pressure, and have, in consequence,
been thoroughly impregnated with a secondary deposit of silica.
Such rocks form one of the most resistant combinations which the
earth presents to the elements, yet the surface of this ledge is pitted
with shallow basins from three inches to one and a half feet in
diameter and one to three inches in depth, which have been gradually
dissolved out by the standing rain water. Little runways or channels
generally connect one basin with another or lead out to the edge of
the cliff. No lichens of corresponding sizes grow on these rocks, and
the slight undercutting of the walls of the basins at a line corre-
sponding to the average level of the water indicate that they are
the product of aqueous solution. Similar basins and channels may
also be seen developed on the exposed crests and ledges of quartzitic
sandstones which form Dan’s mountain, Backbone mountain and a
number of other localities in this state and elsewhere. With exam-
ples of such intensity of action it is less surprising to learn that T.
Mellard Reade * finds data according to which he estimates that Eng-
land and Wales annually lose through solution an average of 143.5
tons of material per square mile, and this does not apply only in
limestone areas but is an average for all the different rocks.

Powerful and important as are the chemical ways in which water
aids in denuding the land, the mechanjcal action of this agent is of
equal importance and generally much more striking. One of the
important processes of denudation is the splitting of rocks by frost
action. All rocks are more or less porous and contain water, while
most rock masses are traversed by numerous sets of cracks called
joints, and by finer partings, rifts, seams or the like, all of which
permit water to penetrate below the surface of the ledges. The
elevated and exposed peaks of all zones and the ordinary ledges of
the Temperate and Arctic zones are all subject to frosts and thaws
intermittently during the winter months. These sharp, sudden frosts

‘Merrill, op. cit. p. 194.
MARYLAND WEATHER SERVICE 49

Seize on the water imprisoned in the pores, joints and cracks of the
tocks and by the expansion, which results in the formation of ice,
cause a tremendous pressure to be exerted against the sides of the
confining crevices. The great power exerted by this expansion of
freezing water may be Judged from the calculation that the walls of
a crevice which thus confines frozen water are subject to a pressure
per square foot equal to the weight of a column of ice one mile high
or about 150 tons. Successive frosts and thaws are thus able to split
off innumerable small chips and to gradually work out huge blocks
which later are by the same process reduced to sand. Pike’s Peak in
Colorado, a granitic mass, has large talus slopes wholly composed of
angular fragments which have been thus split from its crest and
sides. All the mountains and ridges of western or Appalachian
Maryland show the results of the same action. Along the roadway
to High Rock and Mt. Quirauk in the Blue Ridge may be seen fine
examples of talus slopes composed of huge frost-riven fragments of
the enduring quartzite which makes the ridge. Steep slopes of such
fragments line either side of “The Narrows,” as the gorge of Will’s
creek at Cumberland is called, and there furnish, already quarried,
inexhaustible materials for constructive purposes and for railroad
ballast.

Frost action does not stop with the breaking down of lofty moun-
tains or scarred precipices, but continues to work over the coarse
material thus furnished, converting it finally, with the help of the
agents already noticed, into the rich soils which support the crops
of the country; thus, although frequently damaging to a few crops,
it is of the greatest help to the farmer, since it readily reduces
almost to powder the stones of his fields and continually enriches the
soil by bringing to it new material from the original sources. A
striking illustration of the splitting action of freezing waters is found
ready at hand in the unsightly sealing which disfigures houses and
trimmings of sandstone. The sandstone commonly used in Mary-
land is very porous and readily absorbs water during a rain or snow-
storm. If a frost comes while the stone is thus soaked the freezing

of the imprisoned water causes it to split or scale off, particularly in
4
50 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

a direction parallel with the original bedding. Grace Episcopal
Church, Baltimore, gives the best illustration possible of this pro-
cess and its results.

Most of the processes which have been discussed so far have
resulted in the disintegration or solution of the rocks of the earth’s
crust, thus preparing them for transportation. We have also to
consider water as an agent of denudation and transportation com-
bined. There are two forms of water which act in this double
capacity, namely, ice in the shape of glaciers and floating ice and
liquid water in the rills, brooks, rivers, lakes and oceans.

A portion of the water which falls as rain sinks into the soil and
rocks as has been shown; a very fair proportion is evaporated and
goes back into the air again; and a comparatively small proportion
runs off on the surface. The latter portion is familiar to most of us,
as the formation and growth of rills during a shower is easily ob-
served. No rill, however small, runs down even a sodded slope with-
out catching up at some point a fragment or two of soil. Soon the
rills unite to form a small run which rushes downward still faster,
carrying the fragments which loaded the rills and acquiring more
soil and pebbles by its own strength. In this way the stream carves
for itself a gully or channel. The waters gather into brooks and
creeks and rivers, each increase in size and volume being accom-
panied by an increase in the amount of soil and rock debris which the
streams bear onward. As has been shown, the streams thus trans-
port and carry away from the surface of the land not only what has
been broken off mechanically by frost, wind, temperature-changes,
ete., but also what the waters succeed in dissolving away by chem-
ical means. The streams not only carry away the soils and dislodged
fragments of rock, but also do some breaking themselves. The small
rill or rivulet carries fine grains of sand which it knocks and pushes
against the soil and rocks over which it flows; the brook, with the
larger volume, rolls pebbles along its course; and the mountain tor-
rent transports large boulders. These rock-fragments the streams
use as tools which they continually hurl against the bottom and sides
of their channels, thus wearing away the rocks and cutting their
MARYLAND WEATHER SERVICE 51

valleys deeper and deeper. In the course of down-cutting untold
numbers of boulders are reduced to powder, but eventually the chan-
nel is cut almost to the level of the sea.

Thus the rains are working to wear away the general surface of
the land by washing down the soils and to deepen the streams by
giving means of transportation and movement to their tools.

The snow collects on lofty mountain tops, and gradually sliding
down under the force of gravity, begins to solidify into the ice of
glaciers. The glaciers moving slowly, perhaps not more than one
inch in a day, push on irresistibly until they melt away. Rocks roll
down the slopes of mountains, and lodging on the glacier gradually
melt their way down to the bottom of the ice-river, and there, with
other fragments which the moving ice has plucked from its bed,
serve as cutting tools whereby the glacier deepens and widens its
channel. When glaciers combine and grow to such a size that they
cover the half of a continent, as was recently the case in North
America and Europe, they scrape off the loose rock and soil and
grind and polish the rocky ledges below until they gradually wear
away the surface.

On the seashore the waves of the ocean are continually beating
against the land. The great breakers of storms hurl many tons of
water against the projecting rocks of the coast, and the water pene-
trating every crack and crevice subjects these rocks to enormous hy-
drostatic pressure. In this way great and small blocks are gradually
split from the cliffs and reefs and fall to the foot of the beach. Here
the waves seize the fragments which they have broken off above,
and hurl them against the rocks below. Thus the ramparts of the
land are gradually battered down and undermined, and broad sub-
marine shelves appear. On sandy coasts the weak cliffs give way
rapidly before the waves and are driven back until the sands which
they have furnished form a broad shallow shelf on which the waves
must break until they have removed it and can again reach the cliffs.

Organic Processes.

Organisms aid the general reduction of the land in various ways
which, although often of small moment individually, are very pow-
52 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

erful taken as a whole. The fine frost- or heat-riven fragments of
the rock suffice to support at first a few simple plants and lichens.
These send out their roots in search of food and penetrate
the fine crevices of the rocks. The roots, continuing to grow,
split the rock-pieces apart as they increase in size and thus furnish
more material for the soil in which they grow. When the trees
strike root in the soil collected in rock-crevices their roots often
exert power enough during their growth to split off large boulders.
Every plant clinging to the face of a cliff, every clump of moss or
lichen fastened to a rock, is aiding in the breaking down of the rock
by its growing roots and -by the various acids which it produces.
Even the minute organisms known as bacteria, by reason of the
nitric acid which they liberate in the course of their growth and their
presence in countless myriads throughout the cracks of the rocks,
exert a not inconsiderable disintegrating influence upon the rocks in
which they lodge. Merrill says (p. 203), “ The organisms act even
upon the most minute fragments, reducing them continually to
smaller and smaller sizes.”

To the accumulated soil are added, in the course of time, the
remains of plants and animals, which yield in the process of decay
various acids, that are taken up by percolating waters and further
distributed through the rocks, where they aid in their chemical and
mechanical disintegration. The evacuations of various animals, such
as ants, also afford supplies of disintegrating acids.

Burrowing animals, such as rabbits, squirrels, prairie-dogs, earth-
worms and the like give important aid to the denuding and trans-
porting agents by keeping the soil loosened and pervious to rain and
moisture. Darwin found that earthworms, by continually trans-
porting earth to the surface from their burrows beneath the large
stones in the pastures, have been largely instrumental in the gradual
burial of these rocks, thus materially aiding in the disintegration of
such masses. Considerable quantities of decaying organic matter,
such as litters of dead leaves, scraps of food, excrement and so on
are also generally to be found in animal burrows and thus another
very fruitful source of organic acids is afforded.
MARYLAND WEATHER SERVICE 53

Summary.

From the foregoing it appears that a multitude of agents and
processes are incessantly at work all about us, tending to break
down the rocks and to wash the debris thus produced into the
valleys and thence to the sea. The gases of the air, the wind, the
temperature changes accompanying the days and seasons, combined
with the chemical and mechanical actions of the waters on the earth’s
surface and the organisms which live thereon, are all striving to
reduce the lands that stand above the sea. Clearly, if these forces,
unmodified and undiminished, continued to act indefinitely, the con-
tinents and islands would not long remain above sea-level. Since
the subaérial agencies would work much more rapidly than the
waves they would first be reduced to smooth, featureless tracts, whose
inclination seaward would be just sufficient to carry off the water
which falls as rain. Then they would gradually yield to the attacks
of the waves, and in the end would be planed off to more or less
even surfaces some feet below low tide, forming wave-cut submarine
benches and platforms. Geikie* estimates that the continent of
Europe would be reduced to sea-level in about four million years
if exposed for that length of time to the attack of atmosphere, rain,
and rivers, and supposing these to work at the same rate that they do
to-day. In the same period of time the sea-waves would cut away
a strip of land along the shore less than one hundred miles wide,
considering them to advance at the rapid rate of ten feet per cen-
tury. Another authority’ estimates that the waves remove annually
one cubic kilometer of material from the land, while the subaérial
agencies are carrying away not less than fifteen times as much.

When all the above considerations are kept in view, together with
the fact that the surface of the land is well supplied not only with
high hills and minor elevations, but also with many lofty mountain
chains and plateaus, it is patent that there must be constructional
processes at work counteracting the destructional ones which have
been described. They will be discussed in the following pages.

1Geikie, A. ‘“ Textbook,” 3rd ed. p. 467.
+de Lapparent, quoted in Scott, W. B. “An introduction to Geology.”

pp. 303-4.
54 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

PROCESSES OF CONSTRUCTION.

Crustal Movements.

The most important of the processes which are at work counteract-
ing the destructive effects of denudation are those movements of the
earth’s crust which are tending to elevate it above the level of the sea.

These movements are of two general kinds or classes. One class
includes those movements of the earth’s crust which extend over areas
of continental extent and do not result in the appreciable dislocation
of the strata through folding or tilting. ‘These movements are some-
times called epeirogente.

The second class of movements and dislocations affect restricted
portions of the continental plateau and are expressed as foldings, tilt-
ings and faultings of the different crustal elements. They are the
fundamental movements whereby mountains attain their elevation
above sea-level. Such movements are therefore called orogenic or
mountain-making. Many familiar examples of such movements and
dislocations might be cited. The best known to Marylanders are the
long ridges and mountains of the Appalachian province of the state
formed by the folding and faulting of the Paleozoic strata of that
district. The Blue Ridge also is the result of the pushing of a big
block of hard sandstone and volcanic rocks over the easily eroded
limestone of the Cumberland or Hagerstown valley. In the west
the Sierra Nevada and the Great Basin ranges are formed of huge
blocks which have been broken or faulted and then tipped up so
that one edge of the block forms the crest of the mountain range.
All such mountains have had their present physiognomies carved out
during and since their elevation by the various denuding agencies
above described.

Volcanic Eruptions.

The ejection of lava, voleanic ashes, scoriae and the like from
volcanic vents are very effective and important agents of construction
in some localities, but they have not recently affected the surface con-
figuration of Maryland. The sheets of diabase which characterize the
sandstones of the Newark formation, and the acid and basic voleanies
of the Blue Ridge district show, however, that volcanic activities were
present in Maryland in past geological ages.
MARYLAND WEATHER SERVICE 55

Subaérial Processes of Construction.

In discussing the denudation of the land, several references were
made that indicate the constructional activities of agents and processes
mainly and ultimately destructive.

Thus the wind-whirled sand which carves out the standing rocks
of the shores is spread over the surface or formed into dunes so com-
mon and characteristic of the whole Atlantic coast of America. The
sand blown from the beaches is also often dropped in great quanti-
ties into the lagoons behind them and thus becomes an important
factor in bringing about their conversion into dry land.

Aqueous agents are also active builders. Deposits from evapor-
ating waters about mineral hot springs often build important topo-
graphic features such as the great terraces. and basins of the Yellow-
stone National Park. The mechanical deposits from running or
standing waters are the most numerous and important of the con-
structional forms built by water. Among these are the talus-cones
and flood-plains and deltas of rivers, and the beaches, spits and bars
produced by wave action in lakes and seas. The great ice-sheet of the
Glacial Period, and the smaller glaciers of lofty mountain areas have
left very striking constructional topography in the form of terminal
moraines, eskers, drumlins and kames. From these examples it may
be seen that water in its various forms has constructive as well as

destructive effects.

Organic Processes.

Small plants living in the waters of various thermal springs are
now known to be very effective in promoting chemical deposits. On
the slopes of dunes and on other sandy areas are coarse grasses and
shrubs and sometimes even trees that, on account of the binding
power of their roots, protect the sands from further removal. Sim-
ilarly, the grasses and sedges of the mud-flats and marshes, by
retarding the currents flowing over them, cause the deposition of silt,
while their long roots, matting together, convert the mud thus de-

posited into a more or less resistant mass.
56 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Summary.

Constructional processes thus fall into two great divisions: first,
those which originate in movements of the earth’s crust resulting in
uplift, and second, those which accompany the progressive denudation
of the land. The essential process which must precede all degrada-
tion is uplift, and this may either be continental (epeirogenic) or
mountain-forming (orogenic). These movements, gradually pro-
gressing, permit the agents of denudation to become effective, and
thus minor constructional features, such as dunes, flood-plains, deltas
and the like are produced by agents which are on the whole destruc-
tional in their results. These minor features, however, are not as
permanent as the hills and mountains which are carved out of the
uplifted areas.

It is apparent, then, that there are upward movements which coun-
terbalance the wearing away of the land’s surface, and that these
uplifts are at present somewhat in excess of the downward tendency.
This is more clearly seen by the study of geographical boundaries as
they existed in former geological periods. In the course of ages
America has grown to its present size from being comparatively small
in area and confined to islands over what is now Canada, northern cen-
tral New York and the Piedmont Plateau of the Atlantic Slope. The
very last emergence added a strip of land one hundred to two hundred
miles wide to the eastern coast of North America from Long Island
south to Mexico and Yucatan.

Although the study of ancient geographical boundaries or paleo-
geography is very interesting, and there is much material within the
state of Maryland for such investigations, this will be left for a
future paper. At present the development of certain typical river
systems and the topography which they have carved out are to be
considered.

DRAINAGE DEVELOPMENT.

A Topographic Cycle.
It seems possible in the light of the more recent investigations in
physiography to deduce certain general laws concerning the develop-
MARYLAND WEATHER SERVICE 57

ment of the relief of the earth’s features. Those districts which can
be shown by geological evidence to have been long above sea-level are
generally found to have mild forms of relief, while the recent eleva-
tions commonly have strongly marked topographic characters. Such
regions, for example, as the Piedmont Plateau of the Atlantic Slope of
North America, the Scandinavian peninsula, portions of central Ger-
many and northern France, have stood at relatively the same elevation
above sea-level for long periods and are found to have a mild and
rounded topography, while the Alps, the Himalayas, the Coast
Ranges and the Grand Canyon of the Colorado have been carved
out during geologically recent times and are regions of strong relief.

Among the various cases just cited different grades or degrees of
topographic relief may be shown to exist. Thus, for example, the
geological date of uplift of the Himalayas is known to be earlier
than that of the Coast Range, and an examination of the drainage
reveals the fact that the streams of the former district are somewhat
more intricate on account of the longer time which they have had
to extend their branches. Again, in the recent Red River basin of
the North, the streams are still less minutely branched than are those
of the Coast Range.

If now the drainage of a newly emerged or recently elevated dis-
trict be followed through the several periods of its development, it is
possible to find all these various types of drainage occurring in a
natural and appropriate sequence. As the rains fall upon the slightly
uneven surface of the old sea-floor the waters gather in the inequali-
ties of the surface, forming lakes or, combining as streams, run down
the steepest slopes they can find to the sea. The directions taken by
these newly-formed streams are wholly consequent upon the original
inequalities of the surface and its slope. It will appear later that
such streams whose courses are determined by, or coincident with,
courses which would result from, original configurations of the sur-
face are common enough to be classed together as a type. They
are, for convenience, called consequent streams.

At first these consequent streams are small in volume, but repeated
rains gradually increase the size of the streams and they begin to
58 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

carry away the debris which the elements and their own powers loosen
from the surface. Thus efficient tools are provided, and the streams
begin to sink their channels rapidly, since along those lines are con-
centrated the greatest activities of the running waters. The first
result is the excavation of a deep canyon or gorge, this work begin-
ning at the mouths of the streams and progressing rapidly headwards.
While the narrow canyon is being pushed towards the head of the
stream, along the lower course the gorge is beginning to widen as
the result of the action of frost and rains. Widening is greatest at
the top of the canyon, which is the portion first and longest exposed
to the weather, and, except at the extreme upper end, where the
gorge is youngest, its cross-section will reveal a flaring top.

The stream will continue to cut down its channel until it has pro-
duced a slope whose inclination seaward is the minimum required to
carry down the water. When such a slope is reached, then the
stream begins to lose its downward cutting powers and works more
and more against the sides of the canyon, and we thus have a second
reason for finding the canyon wider at the mouth of the stream. The
deepening of the main channel goes on faster than does that of the
side streams, but as the accomplished grade progresses up stream the
tributaries, heretofore unable to keep up with the rapid down-cutting,
now begin to adjust their slopes also. Until the lower portions of
main and side streams are thus adjusted, however, the as yet unaf-
fected headwaters do not feel the effect of the uplift and can accom-
plish but little in the way of erosion. There is not, then, at this
stage in development, a large number of side streams, and the divides
are broad, flat, poorly drained, and sometimes even marshy. The
whole district has an appearance somewhat like that shown in
Fig. 1.

As this general stage in the drainage development is the one
passed through immediately succeeding the birth of the new land
it may be appropriately termed Infancy. It is by no means an
imaginary topographic phase. Many illustrations of ‘such topogra-
phy could be brought forward. The drainage and topography of the
Coastal Plain, particularly that portion lying in Maryland, still car-
MARYLAND WEATHER SERVICE 59

ries the ear-marks of this period in its development. The wandering
courses of the Chester, the Choptank, the Patuxent, the lower Po-
tomac, etc.; the deep gorges now half filled by the waters of the sea
and the bay, which have been cut by the streams of southern Mary-
land; and the level remnants of the original Lafayette surface, which
are still to be found at points remote from the attacks of the largest

      

x -—Copyright. 1894, b: From Harper’s Weekly.—Copyright, 1894, b:
ee eee Pe Harper é Brothers
Fig. 1.—View of model illustrating Fie. 2.—View of model illustrating
topographic youth. revived topography.

streams, all indicate that the Coastal Plain is not long past its in-
fancy. The classic example of infantile drainage and topography is
that great gorge already referred to, the Grand Canyon of the Colo-
rado, but it is not wholly typical on account of the desert conditions.

The rapidly increasing number of small streams along the sides
of the canyons, the continued beating of the rains and the winds,
in fact, all the active processes of denudation, since they never cease
in their activity, do not permit the newly started streams to retain
60 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

such infantile characters long. The steep walls are gradually worn
back, and the few original consequent tributary streams, having cut
down their lower channels to the grade of the main stream, begin to
push back their headwaters. New side streams spring up along the
walls and slopes of the gorge, cutting deep scars and seams in them,
and thus hasten their recession. As the number of tributaries in-
creases the broad flat divides are narrowed and even begin to lose
their flatness. The lakes which formed at first have their outlets
cut down and are drained, while the channels of the older streams,
which were rough and broken by falls and rapids, gradually lose
their inequalities. The volume of the main stream is somewhat
increased by the growing number of side branches, but as each one
of these comes down laden with the debris which its active little
headwaters and its steep banks furnish, a great load is soon added to
it. All of this load the larger stream cannot manage to trans-
port, and so some portion is dropped at the mouths of the several
tributaries, forming cone-like alluvial deposits that project into the
main valley, while part is taken by the master stream and is used by
it to steepen its slope, thus enabling it to carry off a greater load.
Many streams in this stage may be found among the high lands of the
Sierras, the Himalayas and other regions of plentiful rainfall and
recent elevation. Excellent examples may be found in certain por-
tions of Southern Maryland. In St. Mary’s county numbers of the
southwestward flowing streams show these adolescent features, with
the over-loading of the main stream and consequent flood-plain
building.

The constant increase of the catchment area by reason of the ever
growing number of streams and the pushing back of the headwaters,
continues until the divides between opposing streams, whether of the
same or of different drainage systems, are sharp and steep. The rami-
fying branches have sought out every square mile of territory, so
that the whole region is completely drained. The small headstreams
thus having no new territory to conquer by linear development begin
to reduce the steepness of their own slopes, to soften their valley
sides, and to reduce and round off a little the tops of the hills. Thus
MARYLAND WEATHER SERVICE 61

the amount of mechanical sediment brought to the larger streams
decreases while the volume of water still remains about the same.
The main channels smoothed out still more are so far reduced that
they describe smooth regular curves from source to mouth. Up to
this time the slope of the river channels has been slowly changing,
but it now reaches a period of comparative stability, since the changes
in load and in volume, which are the factors determining the curve,
are very much slower hereafter. The channel slopes are now more per-
manently suited to the needs of the streams and the latter may be said
to “have established graded channels. The accompanying figure
shows the slope to be steepest at the source, but to rapidly decrease
to a midway point whence it is of constantly but very gently de-
creasing fall to the mouth. As all the streams gradually approach
such a graded condition, the inter-stream areas forming the divides
also gradually wear down. Such an area is included within the

me

 

1" a ashm

Fic. 8.—A normal stream profile (after Penck).

boundaries of the Piedmont Plateau on Plate ITI. Similar top-
ography characterizes most of Northern Virginia and large portions
of Eastern New England. The country and its drainage may be
said to have reached its Maturity.

The gradual change in topography and in drainage which have
just been briefly sketched presupposes, first of all, that the land and
sea have remained constant to each other long enough to permit such
development to occur. This supposition is not always justifiable,
since multitudes of cases can be cited to show that after a period of
rest long enough to permit of the topography developing to some
stage earlier even than Maturity, earth movements have closed what
may be called the current cycle and have inaugurated a new one.
In order to make the series of topographic forms complete, however,
some students have carried the scheme beyond the stage of Maturity
and described yet another and final stage which has been likened to

Old Age.
62 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Suppose that after Maturity is reached, the same conditions endure
for an indefinite period. The streams would still continue to deepen
their channels although at an ever decreasing rate. The hills and
mountains would gradually sink lower and yet lower, yielding now
more to the solvent action of the waters charged as they would be
with acids from the mantle of soil and vegetation which covers every-
thing. Finally all slopes would be reduced to the lowest possible
angles and the divides also would be very insignificant, except at
points far from the mouths of the streams. The lowest zone would
be along the sea-coast, where the land would be reduced quite to sea-
level. From here inland there would be the slightest possible rise
in order to permit the rains to really drain away and not gather into
stagnant pools. The whole district would be nearly featureless and
so closely approach a plain in appearance and contour that it might
appropriately be called an almost-plain or peneplain, just as an
almost-island is a peninsula.

It is obvious that the lowest level to which a land can be worn
down by stream action is sea-level, and even this can never be
reached except at the very shores, since some slope is needed to
carry off the water. Therefore the ocean is called the great base-
level, or the base down to whose level all the forces of Erosion or
Denudation are working to reduce the land. Local base-levels may
exist for a time, such as the level of a lake, which is the base-level
for streams entering it, or the level of a stream where it crosses an
unusually resistant stratum, which may be the base-level for its tribu-
taries above this point. But eventually all the streams are con-
trolled by the level of the sea. Such an enormous duration of time,
throughout which the position of the land would have to remain
fixed with reference to the sea-level, would be required, however, to
permit of the production of such a complete peneplain, that there is
scarcely any warrant for supposing that such a condition has often
existed. Nowhere to-day can an example of such a topographic fea-
ture be found.

On the contrary, everywhere there is evidence to show that the
land and sea do not long continue constant to each other. Young as
MARYLAND WEATHER SERVICE 63

are the Coast Ranges of California, they had, since their elevation,
attained very nearly to ripe Maturity, when great subsidences took
place, drowning part of them. ‘These accidents again were recently
followed by successive lesser re-elevations. The eastern coast of
North America has suffered repeated elevations and subsidences since
the period of the last great elevations of the Sierra Nevada, and is
still undergoing slight oscillatory movements. Other instances might
be cited to show that the chances are probably small for a locality
to reach even to the perfection of well-matured topography.°
Although the topographic cycle has perhaps never had an oppor-
tunity to run its full course, yet it is convenient for the purposes of
understanding and explaining topographic forms to retain the con-
ception of a complete cycle, which might be renewed, if, after attain-
ing to the stage of a peneplain, the land were again elevated and
the streams commenced their tasks anew. As we have seen, how-
ever, the rule is that at some stage in the ideal cycle the march of
development will be interrupted. Such interruption may result from
one or several causes. The most common interruptions come from
re-elevation of the land, whereby the streams receive increased
energy, or from depression, which allows the sea to invade a portion of
what was dry land and reduce the energy of the streams by decreas-
ing the height from which they have to fall to reach sea-level.
When by reason of the rise of the land the streams renew the vigor
of their own cutting, and begin to cut canyons below the general
surface which they have before produced, they are said to be revived.
The same phenomenon would be produced if, after long delay, the
master stream of some system should succeed in cutting through a
stubborn ledge and begin to work rapidly down through a more
yielding understratum. It will appear farther on that most of Mary-
land’s streams show the reviving effects of re-elevation. The illus-
tration forming Fig. 2 shows a district of revived drainage. De-
pression whereby the lower courses of most of the rivers are sub-
merged beneath the sea hastens the reduction of what is left above
sea-level, and by decreasing the slope of the lower courses often

1See R. S. Tarr, “ The Peneplain.” Amer. Geol., vol. xxi, 1898. pp. 351,
et seq.
64 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

causes the building of flood-plains at these points. The coasts of
Maine, of Norway, and of Maryland afford excellent examples of
such topography, which is called drowned.

Migration of Dwides.

The progressive development of a piece of country through the
stages of a Topographic Cycle is accompanied by many interesting
processes, some of which will be considered in this and the following
section.

When the broad flat divide which characterizes the infancy of
stream growth is converted to the sharp serrated crests and ridges of
earliest maturity, the streams, which before were battling against a
common enemy, viz. the unreduced land mass lying between them,
are then brought into closer rivalry. Each stream heading against a
divide is endeavoring to wear it away and to gain more drainage area.
If the streams are pretty evenly matched, then the divide must grad-
ually sink down, until it becomes a low ridge almost exactly beneath
the line along which the headwaters of the opposing streams first
met on the surface of the plateau. Should it happen, however, that
the streams on one side of the crest had an advantage over the
opposing set then the rocks would be worn away unevenly on the
two slopes; the stronger streams would wear away their side faster
and the divide would move towards the weaker set of streams.

There are many ways in which one set of streams may come to
have more power than an opposing set. The favored streams may
have a shorter course to the sea, thus giving them a steeper slope, or
what may amount to the same thing, the course may lie on softer rocks
which, being more nearly reduced to the sea-level or base-level along
the lower course, concentrate the greatest possible amount of steep
slope at the headwaters. This is excellently illustrated in Maryland
by the contrast in slope which exists between the tributaries of the
Monocacy, a stream situated on easily eroded slates, sandstones and
limestones, and the main streams of the Patapsco, the Patuxent and
other rivers which have to cross the resistant gneisses and other
crystalline rocks of central Maryland. Again, greater rainfall will
give to one side larger volume and greater cutting powers. Excel-
MARYLAND WEATHER SERVICE 65

lent illustrations of the advantage gained in the latter way are fur-
nished by the streams on the western slopes of the Cascade, and the
Sierra Nevada, and on eastern slopes of the Andes in equatorial
America. Also a tilting of the land in the direction of the favored
stream, by increasing the slope of the one and decreasing that of the
other, may give advantage sufficient to cause a shifting of the divide.
This particular method has been appealed to farther on in explaining
certain anomalies in the drainage of the Maryland Coastal Plain.
Another way by which divides are caused to shift or change their
positions arises from the attitude of the rocks. In districts underlain

 

Level

or

  
 

Base Level

 

 

 

Fic. 4.—Diagram illustrating a simple shifting of divides.

by layers of alternating hard and soft rocks, which are inclined at an
angle to the horizontal, the divides first tend to become located upon
the hard rocks. For example if, as may easily be the case at birth,
certain streams, such as a in Fig. 4, are so located that they cross
the hard layers, then, because of the hindrance which they thus
meet with, they can reduce their channels but slowly. This gives
an advantage to streams located like b, which, being on yielding rocks,
can cut down more rapidly. Therefore a must slowly retreat and b
advance step by step until the divide d-d is located upon the hard

band H-H. Once thus located, the divide will not tend to move one
5
66 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

side or the other, unless the hard layer be inclined, as represented in
Fig. 5. In such an event it is evident that, as the land is denuded,
the divide will follow down the dip of the strata, assuming the posi-
tions D, D’, D’ successively. The tendency in all cases is to main-
tain divides upon the most resistant strata. Many instances of such
a cataclinal or down-the-dip shifting of divides are furnished by the

 

 

 

 

 

 

 

Fie. 6.—Diagram illustrating shifting of divides through stream capture.

Appalachian Province of Maryland. Shriver’s Ridge, Big Savage
mountain, Winding Ridge, Catoctin mountain and many smaller
mountains are examples of such divides.

The manner in which divides or watersheds migrate has been
brought about generally by a slow, gradual shifting. Divides be:
tween two river systems or two parts of the same system may at
MARYLAND WEATHER SERVICE 67

times shift suddenly. Thus, as shown in Fig. 6, one stream J,
perhaps the larger, has to cross a very refractory band R on its way
to the sea, while the other stream JJ traverses yielding rocks along
its whole course. In the course of time the second stream II, by
reason of its easier path, will reduce its channel to a much lower
level than it is possible for the first stream I to do along that
portion of its course above . Thus more power is gained for the
side streams of JJ, and they are enabled to push back the divides
until I has been intercepted at c. Owing to the low level of the
channel of IJ and its tributary 2, J is turned into the valley of 2,
leaving its lower course to flow on as a shriveled, beheaded stream.
This change in river courses shifts the divide gradually at first, then
with a bound from d-d to R, again illustrating the law that hard
rocks tend to form divides, soft rocks to form valleys. When the
arrangement of the streams is not in accord with this the conditions
may be regarded as anomalous and disturbing, or modifying factors
may be looked for.

Many illustrations of such cases of river piracy and capture can
be found in the Appalachian region of eastern North America. A
single example found in the neighborhood of Harper’s Ferry may be
cited here. Others will be considered when the Appalachian Prov-
ince of Maryland is described. In Fig. 7 is represented a bit of
drainage along what is now the Shenandoah Valley and the Blue
Ridge. At the period represented the whole Atlantic slope probably
appeared as a broad, gently rolling plain. This plain was but slightly
interrupted by the low crest of the Blue Ridge which the Potomac
river and Beaver Dam creek crossed through low shallow water-gaps.
Beyond the eastern limits of the figure Beaver Dam creek joined the
Potomac. The young Shenandoah had begun to develop along the
broad band of limestones which lie just west of the hard quartzites
and voleanic rocks forming the Blue Ridge.

Shortly after the time represented in Fig. 7 the whole eastern
slope of North America was tilted and raised. This elevation revived
the streams and they began first to deepen their channels and then
to push back their headwaters and sidestreams. The Potomac, with
68 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

its large volume, rapidly sank its channel through both the limestone
and the hard rocks of the Blue Ridge. Thus the mouth of the Shen-
andoah was lowered and this stream began to push back its drainage
basin. Beaver Dam creek also felt the effects of the revival, and
would have done battle with the growing Shenandoah for the mastery
of the area west of the Blue Ridge; but the creek was seriously handi-
capped, for it could not work back faster than its small volume could
cut down its gap in the Blue Ridge while the Shenandoah had the

 

©
8

   

THE.
KITTATINNY

     

SHENANDOAH

 

 

 

 

 

From National Geographic Monographs, American Book Co.
Fie. 7. Fie, 8.

Examples of river piracy (after Willis).!

aid of the powerful Potomac. So it resulted that the Shenandoah
worked faster than Beaver Dam creek was able to do, and finally cap-
turing the headwaters of the latter stream led them off to the north-
east, leaving the beheaded stream to continue with the Blue Ridge
for its future western boundary. As the Shenandoah grew in vol-

The Kittatinny Plain is referred to elsewhere in the text under the
name of the Schooley Peneplain, a term earlier employed by Davis.
MARYLAND WEATHER SERVICE 69

ume, by further captures of a like character, its valley deepened and
widened up to the foot of the mountains; the’ gap in the Blue Ridge
where Beaver Dam creek formerly crossed was left high and dry as
a wind-gap, forming a deep notch in the crest of the Blue Ridge; and
a small stream flowed westward from the edge of the gap down into
the Shenandoah, taking a slope and direction exactly the reverse of

the one formerly held by the creek. Thus was developed the later
drainage shown in Fig. 8.

Relations of Streams to Structure.

In studying the location and migration of divides, it has been seen
how much the streams are influenced by the relative positions of the
yielding and the resistant rocks; how divides may change their posi-

“tions and finally come to coincide with the bands of resistant rocks or
with those rocks most favorably situated for resisting erosion. In the
processes of divide-shifting, the streams which have the most favor-
able locations either as regards rocks or in relation to base level or
both, have been found to be the most successful in extending and
developing their courses. From these considerations it is to be ex-
pected that wherever the various strata are of varying degrees of
resistance and are arranged in an orderly manner, as is the case in
the Appalachian districts, there the streams are to be found express-
ing the arrangement of the strata as they come to the surface. The
valleys would be located on the more yielding rocks, while the inter-
stream areas and divides would be formed by the resistant strata.

The manner in which such arrangements are perfected is simple.
As the newly exposed land rises higher and higher and the youthful
streams born upon it cut deeper and deeper, they discover the vari-
ous strata which form it. If the beds are horizontal and undis-
turbed, as is the case in the Coastal Plain, and approximately so in
the Alleghany Plateau, then the surface of the land does not pre-
sent long belts of various rocks but is largely covered by one stratum.
In such a case a peculiarly irregular branching of streams which is
uncontrolled by variations in rock character is developed. This class
of streams, called autogenous, is specially described in the chapter on
the Coastal Plain. It is also characteristic of West Virginia plateau
districts.
70 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

When the new land emerges from the sea and is folded into long
troughs and ridges, as was the case in the Appalachian district, the
streams find very different conditions of development. They at first
take courses consequent upon the folds of the strata and thus collect
in the lowest troughs, passing from one trough to the next by the
lowest sags in the dividing, arched ridges. As the streams cut deeper,
the small consequent streams flowing down the sides of the long
ridges, and the larger streams, where they flow through sags in the
crests of the ridges, saw through the various strata and reveal the
hard and soft, the resistant and the yielding layers. After these
first cuts are made streams rapidly develop along the yielding bands,
and, by the shifting of divides through capture, the rivers one by one
come to be located on these strata. At various points the larger,
streams, able to cut down rapidly, maintain the consequent positions
which they assumed at birth and cross from one belt of soft rocks to
another in spite of the hard intervening ridge. The valleys on the
soft rocks which are opened up after the birth of the streams are
called subsequent valleys, and their streams subsequent streams, be-
cause their origin is subsequent to that of the consequent streams.
As the streams progress towards Maturity, further adjustments serve
to bring nearly all of the earlier subsequent streams and each of the
younger ones into close accord with the arrangement and structure of
the strata. The resulting stream-pattern will thus clearly show the
direction of the underlying rocks. In the Appalachians, where the
strata lie in long parallel folds, the streams have developed into a
peculiar pattern like that made by the branches of a grapevine on a
trellis, which is sometimes spoken of as a trellis or grapevine system.
Its characteristics are shown in the arrangement of Bluestone river
in Fig. 9. The same illustration also shows, in its upper left-hand
corner, the irregularly arranged drainage which has developed on
the horizontal beds of the Cumberland Plateau lying northwest of
Alleghany Front and beyond the Bluestone river.

Where the rocks are faulted and tilted instead of being regularly
arched and folded, the streams also arrange themselves along subse-
quent courses, but as the relations of the various beds are not as reg-
MARYLAND WEATHER SERVICE 71

ular as in the case of simply folded strata, the stream pattern is not
usually as regular in its development.

In areas of crystalline and metamorphosed rocks which have lost
all traces of stratigraphic relations but still retain their relative powers

 

 

 

 

 

Fic, 9, Streams adjusted to Appalachian structure (after Willis).

of resistance and some sort of banded arrangement, it is to be ex-
pected that the streams would still show certain adjustments to the
rocks which they encounter. The particular features of such ad-
justed drainage will be treated of further on, but, in general, it may
be said that the smaller streams and many of the larger ones would
72 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

normally be found arranged in accordance with the directions of least
resistance.

Although streams are normally affected by the rocks with which
they come in contact in accordance with their degrees of resistance,
these laws are not always operative. For example, the Potomac river
' cuts across the hard ledges of the Appalachian district fully as often
as it turns and flows parallel with the direction of these ridges, in the
valleys located on yielding strata. The points where this river
cuts through the high ridges of hard conglomerate or sandstone are
rarely points where it would have located if it had developed its posi-
tion normally as many of its small tributaries have done. Various
other features of the Potomac are anomalous, and to explain them it is
necessary to go back to a time when, as will be explained in another
place, the river was a large stream meandering from its source across
a broad peneplain to the Atlantic. It has already been remarked
above that when a land is reduced to a peneplain its streams are bor-
dered by broad flood-plains in which they wander almost at random.
Tt is not to be wondered at then that the Potomac, when it reached
this stage, wandered from the well-adjusted course it had secured to
itself during its maturity. A subsequent uplift set all the streams to
cutting down and again caused the river to trench itself in its random,
unadjusted course, thus preserving its senile wanderings for us to
study. One way in which lack of harmony between streams and
structure may be brought about is thus seen to be the wandering of
streams during Old Age or under peneplain conditions.

When an area is wholly buried beneath a blanket of younger rocks
or sediments, the streams which arise upon the new series of deposits
take their courses quite independently of the structure of the rocks
buried beneath them. Continued erosion may carry these streams
down through the overlying strata upon the lower series and the
stream courses will then be at variance with the arrangement of the
latter rocks until sufficient time has elapsed to permit of a readjust-
ment of the courses to the newly discovered conditions. Such a state
of affairs will result when the streams at present draining the Coastal
Plain blanket of sediments described in the next chapter, shall have
MARYLAND WEATHER SERVICE 73

cut through these and reached the underlying Piedmont rocks. This
will be more quickly understood by referring to Figs. 11 and 12.

Another type of superposition is seen when a stream cuts down
through a yielding stratum and comes in contact with a hard bed
which it would have avoided had not the overlying softer bed tempted
it. Tllustrations of this are not infrequent in the Appalachians. It
appears that Braddock’s Run, near Cumberland, was for a short time
thus superposed across Wills Mountain.

There are other ways in which a region formerly characterized by
well-adjusted drainage may have its streams thrown out of adjust-
ment. The country may be buried beneath extensive flows of lava,
such as characterize the Deccan plateau of southwestern India or the
great lava plains of the Snake river in Idaho. A great ice sheet,
with its attendant deposits of till, sands, gravels and boulder clay,
may so alter the face of the country, as has been the case in northern
North America and Europe, that scarcely a single mile of any
stream’s course can now be pointed to with certainty as having been
established before the advent of the ice. To this disturbing agency
New England owes all its picturesque lakes and ponds and the many
waterfalls along the altered courses of its rivers, which by their
great resources of power for driving mills have made the Northern
States the leading ones in manufacturing. Maryland can furnish,
however, no examples of stream discordances resulting from either
volcanic or glacial agencies. Several other causes of poorly adjusted
streams might be mentioned, such as volcanic ash blankets, extensive
loess and other alluvial deposits.

Having thus briefly reviewed the processes which control the topo-
graphic development of any area, we will now proceed to take up in
particular the development of Maryland topography. The state, as
remarked in a previous volume, may be divided into three general
physiographic provinces, namely, the Coastal Plain, the Piedmont
Plateau and the Appalachian Region. The boundaries of these prov-
inces are represented on the map forming Plate III. To the con-
sideration of each of these with their subdivisions separate chapters
will be devoted, followed by a chapter in which specia] attention will
be given to the Piedmont Plateau.
74 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Tue Coastat Piain Province.

INTRODUCTION.

General Structure.

The eastern portion of the Atlantic Slope of North America, from
Cape Cod to Florida and around the shores of the Gulf of Mexico,
is bordered by a broad fringe of horizontally bedded deposits, extend-
ing from the Fall Line to the edge of the continental shelf, whose
topographic characters and geological origin have won for it the name
of the Coastal Plain. The researches of the stratigrapher and the
paleontologist have unraveled the intricacies of the numerous beds
which compose the Maryland area, and an account of their results is
found in another place.” Here will be given only a brief sketch of
those events in the history of the Coastal Plain which are most impor-
tant from the geographical standpoint.

The Coastal Plain series begins with a group of formations, the
Potomac Group, whose lithologic characters clearly indicate the con-
ditions of the lands which they bordered. The lowest strata, Pa-
tuxent formation, composed of arkosic sands and clays, clearly show
that the materials were derived from a deep mantle of disintegrated
gneissic and phyllitic rocks such as that which now characterizes the
surface of the Piedmont Plateau from Maryland southward. These
beds everywhere rest upon the uneven surface of crystalline rocks
which belong to the same series as those which constitute the Pied-
mont. This surface may, in fact, be traced as it passes out from
beneath the sedimentary deposits and, bared of that covering, forms
the rolling surface of the Piedmont Plateau of to-day. Detached
portions of the sedimentary beds, as well as their general lithologic
characters, indicate that they formerly extended farther westward
than they do to-day. Their presence shows that hills now three or
four hundred feet above sea-level once formed the ocean floor and
were swept by waves, tides and currents.

Above the clays and arkose follow beds of clean white sands, and
these again are overlain by lenses of iron-ore-bearing clays, Arundel
formation, which were deposited in bogs that formed in depressions

1 Maryland Geol. Survey, 1897, vol. i, p. 188 et seq.
MARYLAND WEATHER SERVICE 75

of the older deposits. These depressions have the characters of old
water-courses, and are interpreted as indicating a period of elevation
above sea-level when the rains had opportunity to erode the surface
of the earlier deposits. Interesting fossils in the shape of Dino-
saurian skeletons found in these deposits show that great lizard-like
creatures frequented the shores of the period.

Higher members of the Potomac group consist of variegated clays
and coarse, irregularly bedded sands, Patapseco and Raritan forma-
tions. They are succeeded by sands and clays in alternating sequence,
with slight variations in characters and progressing towards deposits
of an argillaceous and finally glauconitie and marly character,
Matawan, Monmouth, Rancocas and Pamunkey formations, which
show that for some time true marine conditions prevailed in place
of the shore conditions which produced the earliest formations.
The transition from shore to deep-water conditions was preceded by
a period of elevation during which a very considerable amount of
erosion and valley-making went on. Smaller variations of level also
took place from time to time and are recorded rather by the physical
breaks and interruptions to deposition than by the lithological changes
in the deposits.

Following the last period, the Pamunkey, which was characterized
by deposits formed in moderately deep and quiet seas, came a period
when the seas abounded in the microscopic plants called diatoms,
and the deposits of this time are characterized by heavy accumulations
of the siliceous skeletons of these small organisms. Following these
came extensive deposits of clays and sands, crowded with infra-littoral
organic remains, in which molluscan shells largely predominated.
All of these deposits, representing several more or less clearly defined
formations, are embraced in what is known as the Chesapeake Group.
With the close of this period the deep-water history of this portion of
the Coastal Plain ends. Elevation with landward depression suc-
ceeded the Chesapeake, during which the rocks of Maryland were
subjected to a period of decay. These land conditions again gave way
to littoral conditions. As the coastal border gradually sank, the
transgressing line of ocean breakers rapidly worked over the materials
76 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

already at hand in the older deposits and the decayed crystallines of
the present eastern Piedmont belt. Thus was produced a sheet of
gravels, sands and clays which spread out over the whole of the
Coastal Plain province from Maryland southward to the Gulf.

The constituents of this formation, the Lafayette, change in char-
acter from one locality to another, and in many ways indicate that
they were arranged by the restless waters of an ocean beach, thus
distinguishing them from most of the earlier members of the series
which, as already shown, have deep-water or estuarine characters.

Lafayette deposition was closed by an elevation which gradually
elevated the Coastal Plain above the ocean, and enabled the Pied-
mont streams, not only to extend their courses eastward across the
slowly emerging land surface, but also to cut deep gorges in the un-
derlying strata. Besides the topographic record of the post-Lafayette
emergence, evidence of the weathering influences of the atmosphere
is not lacking in the general state of disintegration of the materials
composing the formation.

Following the elevation and dissection of the Lafayette formation
came a succession of depressions and elevations, accompanied in turn
by deposition and denudation, that has produced a complicated history
down to the present time. The deposits of this period have been
described hitherto, so far as they have been recognized, as the Colum-
bia formation, and appear at various elevations along the rivers, estua-
ries and inter-fluviatile districts of the Coastal Plain.

Professor R. D. Salisbury has published many interesting facts
regarding the Coastal Plain gravels of New Jersey, and the investiga-
tions of the Maryland Geological Survey now in progress point to an
early solution of the problems connected with the later history of the
Coastal Plain in this state.

It appears, therefore, from what has been stated that the Coastal
Plain is built up of a series of strata, for the most part composed of
still unconsolidated materials arranged almost horizontally. Each
successive sheet bears a portion of the geological and topographic
record of the province, the whole showing that the land in this
region has undergone many variations in altitude. Careful detailed
MARYLAND WEATHER SERVICE 7

study and mapping of the individual earlier members of this series
will in the future yield interesting results and give many additional
facts concerning the past topographic history of the old land area
lying beneath and west of the province, but at present no attempt
will be made to consider more than the comparatively recent history
and topographic changes which have taken place within the area.
Therefore, confining ourselves to that portion of the Coastal Plain
which lies within the boundaries of Maryland, the next section will
set forth the limits and subdivisions of the province.

Boundaries and Subdivisions.

Before the post-Lafayette emergence, the Coastal Shelf or Coastal
submarine Plain stretched from the unknown shore of those times
eastward almost if not quite as far as the present edge of the con-
tinental shelf. We need not go back farther, however, for our
present needs than to the middle of the Neocene, when the last exten-
sive submergence took place. The exact extent of this submergence,
during which the Lafayette formation was accumulated, is at present
somewhat in doubt. Mr. A. Keith* has reported that remnants of
this formation occur along the eastern foot of Catoctin mountain in
Maryland and Virginia; but as the determination of the age of the
deposit in those districts is based partly on lithologic characters and
partly on the possibility of correlating certain topographic features
of the western Piedmont Plateau with post-Lafayette formations in
the Coastal Plain series, the date cannot be regarded as being defi-
nitely determined. Outliers of the Lafayette situated nearer the
western boundary of the continuous strata, and of whose age there
is no doubt, clearly show, however, that the submergence was very
considerable in amount and in extent, and that it was terminated by
an uplift which raised the western portion of the coastal shelf higher
above the sea-level than it stands to-day.

After the emergence, and as the result of it, the heretofore wholly

1A, Keith, “Geology of the Catoctin Belt,” U. S. Geol, Surv., Fourteenth
Ann. Rept., 1892-3, ii, p. 285.

?McGee, W J, ‘The Lafayette Formation,” U. S. Geol. Surv., Twelfth
Ann. Rept., 1890-1, i, pp. 508-511.
78 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

submerged Coastal Plain became divided into two great sections,
which continue to the present time. These two sections were an
eastern submerged portion, which will be referred to as the sub-
merged or submarine section, and a western emergent portion, here-
after designated the emerged or subaérial section. The common
boundary between these was the new shore line.

The term Coastal Plain as heretofore used by students of Ameri-
can geology has generally referred to that portion of the Coastal
Plain which is called in this paper the subaérial section. Since the
subaérial plain admits of comparatively easy investigation, because
of the deep dissection it has undergone, and because it is habitable
by Man, while the eastern submerged portion is wholly beyond our
reach save through the revelations of the sections obtained from arte-
sian well borings, very naturally our conception of the Coastal Plain
has been bounded on the east by the Atlantic shore line. It is
believed, however, that the proposed extension in the scope of the
term Coastal Plain and its subdivision into a submarine and a sub-
aérial portion is fully justified by the stratigraphy of the province
and by the fundamental topographic form of the two divisions. To
these two divisions of the Coastal Plain J. W. Powell’ has added a
third one, which is designated the marsh portion, recognizing as a

“which is covered more

separate subprovince that part of the plain
or less intermittently with water by tides and storms.”

The limits of the Coastal Plain, as thus newly defined, are on the
east, the boundary of the coastal shelf, and on the west the intri-
eately crenulate line which marks the boundary between the uncon-
solidated sands and clays of the Mesozoic and Cenozoic and the erys-
talline rocks of the Piedmont Plateau. West of this continuous
boundary are scattered small detached areas, whose lithologic and
stratigraphic characters show that they belong genetically to the
Coastal Plain series, but have been separated from the main body
by the activity of denuding processes since the province was raised
above the sea-level.

7“ The Physiography of the United States,” 1896, p. 75.
MARYLAND WEATHER SERVICE 79

SUBMARINE DIVISION.

Boundaries.

The submarine portion of the Coastal Plain may be considered
as extending from the western shores of Sinepuxent and Chinco-
teague Bays eastward to the one hundred fathom line, which is very
closely coincident with the eastern boundary of the continental shelf,
and lies on the average about one hundred miles off shore.

The Sea Floor.

Viewed as a whole, the surface of the submarine division of the
coastal plain is a broad, even surface, gently sloping seaward and
swarming with animal life. It is the feeding ground of most of our
valuable sea fish and, therefore, the chief cruising ground for fisher-
men. Upon closer examination the shelf is seen to be very mildly
and irregularly undulating, the swells and troughs becoming fewer

LAGOON SEA LEVEL

 

 

Fie. 10.—Section across off-shore beach and lagoon.

and milder seaward. These features are admirably shown on the
U. S. Coast and Geodetic Survey charts.

Off-shore Beaches.

Shoreward the even surface of the submarine plain is broken by
the narrow bank of sands, which forms the long barren stretch of
Sinepuxent Beach. This beach, and the long shallow bay behind it,
see Fig. 10, are of particular interest, because they furnish excellent
home examples of a type of coast line which characterizes North
America from Long Island to Southern Mexico. This type is found
wherever there is strong on-shore wave action across a shallow coastal
shelf. As the great swells come in from the Atlantic the depth to
which their vibrations disturb the ocean waters approaches more and
more closely the actual depth of the water over the shelf. Ulti-
mately, the disturbances begin to act on the bottom. The waves
thus meet with considerable resistance in their lower sections, due to
80 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

friction between the water particles and the sea floor, The result
is that sand and mud are stirred up by the onward moving waves,
and are carried shoreward with them until they break upon the
beach. The breakers stir up still more sand by the impact of the
mass of falling water. Many an unhappy bather who has had his
mouth filled with the gritty water, as a wave, thus ladened, broke
over him, will testify to its truth.

The sand stirred up by the waves and breakers is disposed of in
several ways. Some of the material is carried along the shore by
currents, much of it is thrown into a long heap or windrow landward,
where the surf is breaking, and a portion is carried back to the deeper
water by the undertow. The greatest advance in building beaches
by such wave action is made by storm waves, whose greater power
enables them to accomplish much in a short time. The great
changes produced by storms are well recorded, because of their sud-
den appearance and often disastrous consequences to human interests,
but although they are among the prime factors in producing coastal
changes, they do not so strongly overbalance the less striking but
long-continued activity of other agents. Important among the latter
is the wind, which heaps the dry sands of the beach into dunes, thus
insuring the stability of the beach as such above the water. A very
considerable amount of sand is also blown into the lagoons which lie
behind the off-shore beaches, thus materially aiding in the slow pro-
cess of filling up those water bodies.

Outside the beaches and along the coast various marine currents
are constantly at work distributing the sands which the waves and
the undertow bring out from the beach or stir up from the bottom.
These currents may be of tidal origin, set in motion by the daily ebb
and flow of the great tidal wave, and would have their directions deter-
mined by the obliquity which the crest of the tidal wave’ makes
with the general direction of the coast line. Other tidal currents

1 By tidal wave is here meant the broad wave of water which the attrac-
tion of the moon and other forces maintains upon the open ocean and
draws after it as the earth turns upon its axis. The term should not be
confused with the phenomenon popularly called a “tidal wave” which
results from some voleanic explosion or seismic disturbance beneath the
ocean and has nothing whatever to do with ordinary tidal phenomena.
MARYLAND WEATHER SERVICE 81

with general off- and on-shore directions occur at the tidal inlets to
the lagoons and sounds behind the beaches, where the inflowing and
outflowing waters of the sounds have built bars and extensive shoals
or tidal deltas.

The waves themselves, aided by the winds which drive them, set
up the most important currents. As the waves run obliquely against
a coast they set up a steady drifting of the water in the direction
resultant from the direction of the coast and the direction in which
the surges are moving. Tor example, if, as is the case on Maryland
coasts, the heavy surges set up by a storm come rolling in from the
east or northeast against a shore line whose general direction is south-
west, the energy of those waves is partly expended in beating directly
against the beaches, although a very considerable component turns
along the shore in a southwesterly direction. In this way a south-
west drift along shore is set up. Again, storms from the southeast,
in a similar manner, set up a northeasterly drift or coast current.

These currents are well known to the fishermen and members of
the Life Saving Service along our coasts. Their direction of flow
may be detected by the drifting of wreckage during and after storms,
and the average direction of drift during series of months and years
is expressed in the general configurations of the beaches, capes, inlets
and shoals. Along the Maryland and Virginia coast there seems to
be an almost even balance between the two sets of currents. To the
north, i. e. on the Maryland shores, the smooth beach shows but
little by which to judge. The closing of an inlet into Sinepuxent
Bay (see below, p. 83), and the recent opening of a shallow one to
the south, across the beach into Chincoteague Bay, are in favor of
a southerly current. So also is the general configuration of Assa-
teague Island and its apex at Fishing Point, while the general direc-
tion of the shoals and bars off Cape Charles indicate that a decided
current from the north brings down the sands which are drifting
around the Cape into the mouth of Chesapeake Bay.

On the other hand, the position and direction of the banks and
bars of the Chincoteague, Black Fish, Winter Quarter, Isle of Wight

and Fenwick Shoals and the forms of the beaches on the east side
6
82 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

of the Eastern Shore of Virginia point very decidedly towards the
presence of a current setting from the south or the southwest.

Coastal Lagoons.

Behind the low sandy beaches along the Atlantic coast of Mary-
land are imprisoned shallow lagoons somewhat similar to those of the
New Jersey coast. These bays, though having different names in
different parts, Sinepuxent, Isle of Wight and Chincoteague Bays,
are nevertheless all one body of water. The width is very variable,
ranging between half a mile at Ocean City to four or five miles at
the wider portions. The shores of the lagoon are formed on the east
by shallow marshes along the western edges of the outside sandy
beaches, and on the west by the low, half-submerged topography of
the mainland, somewhat modified by the salt marshes, which have
attained considerable size at some points.

The floor of the lagoon is very shallow and flat, and largely com-
posed of sand, which blows over from the dunes along the beaches,
of mud and, near the western shore, of matted roots, which really
form the foundation for the overlying sands.

The deepest portions of the bays are found along the western side,
next to the mainland, and even in these spots the depth does not
exceed seven or eight feet. Over most of the bay the depth is from
one to three feet, so that the waters can be navigated only by boats
of very shallow draught. The reason that the channel, as the zone
of deepest water is called, is uniformly located so far towards one
side, and that the western one, is, that the easterly storms, and indeed
every brisk wind, blow quantities of sand from the dry dunes of
the beach across into the bay. Thus a sandy shoal, now only one
or two feet below the level of high water, has been built just in the
lee of the barrier beach. Tight or ten rods in the width of this shoal
have been so far built up, that it is now a brackish marsh overgrown
with coarse salt grass, and much of it is firm enough to tread on with-
out sinking. Beyond this naturally reclaimed portion the shallow
sandy bottom is steadily encroaching year by year wpon the formerly
deeper waters of the bay. At the same time the marshy western
shores of the lagoon are being slowly consumed by the attacks a
MARYLAND WEATHER SERVICE 83

the waves which arise in the shoal waters of the bay, although no
accurate estimate of the rate of recession can be given.

The currents and the position of the water level in Sinepuxent and
Isle of Wight bays are not influenced at all by the tides, and very
little, if at all, in Chincoteague Bay, except in the immediate
vicinity of Chincoteague Inlet. All the important currents are con-
trolled entirely, both as to their directions and force, by the winds
and configuration of the bay shores. When a brisk north or north-
east breeze is blowing the waters are driven southward, thus setting
up a current in that direction and tending to cause low water in the
upper end of the bay, while a southerly wind may at another hour
of the same day wholly change matters and heap up the waters at the
north end of the bay.

The waters of these shallow lagoons do not communicate with the
ocean except through Chincoteague Inlet and a small break in the
long cordon of sandy beach that was recently made a few miles
south of Ocean City during a severe storm. Up and down the whole
length of the Maryland shore there are but these two inlets to the
land-bound waters, one being very small and unimportant. This
condition is not typical for such bays or lagoons as are found on the
coasts of New Jersey and the Carolinas. It is more usual to find
inlets interrupting the even stretches of sandy beach at several
points, forming gates to the sounds similar to Barnegat Inlet of the
New Jersey coast or Topsail Inlet of the Carolina coast. Such inlets,
however, are of uncertain duration, and several along the Carolina
shores are known to have been closed completely, as the result of
the washing in of sand during great storms. Other inlets, formerly
deep enough to admit sea-going vessels at low tide, are now so shallow
that entrance is completely barred. It appears that one or two such
inlets at one time cut across the long sandy reaches of Sinepuxent
beach.

J. T. Ducatel * states in his Annual Report for 1835, that: ‘ It is an
interesting fact connected with the past and present condition of
Sinepuxent sound that, since the closing up of some inlets admitting

1 Ducatel, J. T., and Alexander, J. H., Rept. on the New Map of Maryland,
1835, p. 52.
84 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

the ocean into it, its waters having thus become comparatively fresh,
the oysters and clams, by which they were formerly thickly inhab-
ited, have died, leaving extensive beds of their exuvie.” The former
abundance of these shell-fish in the sound is also evidenced by the
Indian shell heaps found on Sinepuxent neck, proving that the
Indians of the vicinity resorted to the sound for their supply of
oysters. This change in the saltness of the water of the sound is an
interesting illustration of the control exerted by geological condi-
tions in changing the lives and habits of men. Prior to the
storm, or series of storms, which closed the inlets, the thriving oyster
beds attracted the aborigines and furnished them with a much prized
article of food; now the nearly fresh waters of the same sound no
longer support the finer grade of salt water oysters, and to obtain
them we must search farther south in the vicinity of Chincoteague
Island where the ocean waters still reach.

SUBAERIAL DIVISION.
Boundaries.

The subaérial division of the Maryland Coastal Plain extends from
the western shores of Chincoteague and Sinepuxent Bays to the
western boundary of the province. It will be regarded as embracing
the so-called “ tidewater ” section of the state with its many navigable
streams and that old river valley, the Chesapeake Bay, which, from
earliest times, has been the leading highway of traffic in Maryland.

General Topography.

Passing from the submarine to the subaérial division of the Coastal
Plain, there is no sudden change in general topographic features.
The surface of an area newly arisen above the sea, where it had long
been the seat of deposition, would naturally possess the predominant
characteristics of the sea floor. One prominent feature is the broad,
even plain, once the smooth or gently undulating sea bottom. The
relatively new land surface of this division possesses this character
in a very marked degree, and is typically illustrated by Plate VII,
Fig. 2. Many portions of the Eastern Shore of Maryland are char-
acterized by long interstream stretches of considerable breadth that
MARYLAND WEATHER SERVICE 85

are almost plane surfaces, and the same is true of several areas on
the Western Shore in the peninsula of Southern Maryland. Taken
as a whole, the Subaérial Division is quite as flat as the Submarine
Division, although considerable depressions, particularly in its west-

ern portions, due to stream erosion, cause many interruptions in the
continuity of the plain.

   

oN
present EON

    

Fig. 11.—Piedmont Plateau partially submerged.

Another feature generally belonging to emerged marine plains, and
characteristic of that portion of Maryland’s Coastal Plain which falls
under this class of land forms, is the gentle and uniform seaward
inclination of the general surface. This is admirably shown by the
hypsometric map forming Plate VI of Volume I, 1897, of the
reports of the State Geological Survey. As may be seen from this
map, the general slope of the Eastern and Western Shores of Mary-
land is towards the southeast, the rate of decline being about three
86 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

feet per mile for the counties of Southern Maryland and rarely more
than one and a half feet per mile over the eastern counties of Kent,
Queen Anne’s, Caroline and Talbot.

Drainage Pattern.

Besides the general features of the province and the gentle sea-
ward slope of its surface, the drainage pattern, which is the direct
product of these two factors combined with the general homogeneity
of the strata, is characteristic and typical for the area. This stream
pattern is irregularly branching or dendritic. The smaller streams
in most cases make approximately a right angle with the general
course of the larger streams, where they join the latter, but the
larger waterways do not obey the laws which govern drainage devel-
opment under the simple conditions of a Coastal Plain, although
the courses of the main stream, it is true, are approximately parallel
with one another and enter the bay or ocean at right angles to the
shore line which they intersect. Most of the streams, however, de-
part from the type in that they do not traverse the width of the
Coastal Plain’s subaérial portion from the old land to the Atlantic,
but generally flow from either side down into Chesapeake Bay. This
abnormality of the streams will perhaps be more easily understood if
the stages in the development of drainage on an emerging Coastal
Plain are briefly reviewed.

General Drainage Development.

Starting with the epoch when the western portion of the Coastal
Plain began to appear above the sea, it is evident that, as the land
rose and the waters receded eastward from their old bounds, the rivers
flowing from the older land area or the Piedmont Plateau would
gradually extend their courses across the new land, keeping their
mouths at the new shore line. This advance of the lower courses of
the old streams would keep pace with the retreat of the coast line,
and the direction of the new lower courses would be determined both
by the slope and the inequalities of the new surface over which they
passed. In the normal course of events, therefore, these extended
streams should enter the ocean by courses approximately at right
MARYLAND WEATHER SERVICE 87

angles to the general direction of the coast line, as shown in Fig. 12.
This is to be more confidently looked for in the case of those streams
whose volume and size would enable them to easily overcome the
slight obstacles which the generally smooth surface of an emerged
marine plain might offer to such a course. Such is the case with the
Chattahoochee, the Tombigbee, the Savannah, the Santee, and num-

 

Fig. 12.—Piedmont Plateau and Coastal Plain elevated.

bers of others which cross the southern Coastal Plain from the old
land to the sea. It is therefore surprising to find that large, pow-
erful rivers, such as the Potomac, the Susquehanna and the Dela-
ware, which have successfully crossed many resistant strata in the
Appalachian district, turn aside on reaching the incoherent beds of
the Coastal Plain and pursue such roundabout routes before they
finally reach the Atlantic.
88 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

While the streams of the old land are thus actively extending
their courses and reducing their channels to a suitable grade, another
class of streams have come into existence. The rain which falls upon
the surface of the newly-born land is partly drained into the extended
lower courses of the preéxisting rivers, but it also happens that a
large share of the drainage is effected by streams which originate
upon the Coastal Plain itself independently of the extended rivers.
These streams, which arise independently of former drainage lines
of any sort, are guided in their development only by the character
of the strata and the initial inequalities, large or small, which they
find on the surface of the new land. As the general inclination of
the surface is seaward, and they are acting almost wholly under the
influence of gravity, their courses are taken as nearly as possible
along the lines of steepest slope, generally at right angles to the coast
line.

If the land continues to rise these new streams also will extend
their lower courses to keep pace with the receding shore line. At
the same time their headwaters are being extended by the gnawing
back of the ravines which characterize stream heads and by the
development of new ravines. These new ravines start upon the side
slopes of the old ones, and as there is no important variation in the
amount of resistance offered by the various strata, whereby any
control could be exerted upon the direction of growth of the new
ravines from which they start, all have equal chances for develop-
ment. A ravine once started tends to keep on in the same direction,
as may be observed in the case of the small ravines and gullies devel-
oping along bare hillsides. The result of this mode of development
is the growth of a more or less intricately and irregularly but syste-
matically ramified drainage system of dendritic pattern, which has
come to be recognized as typical for the drainage developed upon newly
exposed plains of subaqueous origin. Smaller streams of the same
type may also develop in regions whose main drainage lines are under
control of other factors, such as tilting or folding. In these cases the
subordinate or tributary streams only will belong to the type under
consideration. This is an important fact, as it will appear that to
MARYLAND WEATHER SERVICE 89

this second category belong the majority of the streams of the Coastal
Plain in Maryland. This general stream pattern has been designated
by McGee * as autogenous.

During the earliest stages in the drainage development of an
emergent coastal plain, small lakes and swamps may dot the surface
of the new land in greater or lesser numbers. They would arise from
the accumulation of rain-water in the original inequalities of the
surface. Such inequalities on the sea bottom are produced by the
actions of waves and currents which do not always distribute sedi-
ments in a perfectly even manner. This is very well shown by the
character of the sea floor along the present Maryland coast. The
lakes or swamps, due to accumulation of water in such hollows,
should disappear early in the course of drainage development. Their
outlets generally admit of rapid cutting down, so that the waters are
soon drained off. Thus lakes of this origin, characterizing only the
earliest or Infantile to Adolescent stages in topographic development,
when present, give a clue to the topographic age of the area.

The ideal scheme of Coastal Plain drainage as outlined above is
interrupted by the southwestward prolongation of the Susquehanna
river in the expanse of Chesapeake Bay, which divides the Subaérial
Section into the Eastern Shore and the Western Shore of Southern
Maryland.

THE EASTERN SHORE,

The Eastern Shore of Maryland occupies a large part of the penin-
sular Coastal Plain between Delaware Bay, the Atlantic Ocean and
Chesapeake Bay. This topographic subprovince also includes most
of Delaware and the Eastern Shore of Virginia.

Relief.

The peninsula has but slight altitude, rarely reaching a maxi-
mum elevation of one hundred feet even in the higher northern
counties, and declining gradually southwards to a mean elevation of
about twenty-five feet in Somerset and Worcester counties. Besides
the broad open valleys of the larger streams and the flat interstream

1MeGee, W J, U. S. Geol. Surv., Eighth Ann. Rept., 1885-86, pp. 561 et seq.
90 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

areas, the only topographic feature of prime importance is the broad
height of land which forms the divide between the eastward and west-
ward flowing streams. At this point it is enough to indicate that its dis-
tance from the Atlantic or from Delaware Bay rarely exceeds fifteen
or twenty miles, while it generally lies from thirty to forty miles
east of the eastern shore of Chesapeake Bay and just north of Berlin,
Maryland, is sixty miles distant. The high land extends south-south-
east from Elk river, keeping approximately parallel to the eastern
shore of the peninsula as far as the headwaters of the Pocomoke river.
Tt then turns to the south-southwest, following the Atlantic coast
line in a sympathetic curve down the lower portion of the Eastern
Shore of Virginia, gradually decreasing in elevation until it merges
into the low-lying lands north of Cape Charles.

Stream Characteristics.

The Eastern Shore is on the average fairly well supplied with
streams, the majority of which drain southwestward into the Chesa-
peake. All the large streams, following more or less tortuous courses,
flow into the Bay, and most of the smaller streams have courses
roughly parallel to the larger ones. Only small streams, generally
insignificant in size and comparatively few in number, drain east-
ward into the lagoons lying behind the off-shore beaches and bars of
the Atlantic coast.

All the streams fall into one or the other of two classes. They
either lie wholly upon the general surface of the country, are small
in volume, not navigable, except where dammed, and do not reach
directly to tidewater, or they reach tidewater and the larger ones
are navigable at least by small boats for some portion of their length.
The streams belonging to the first class are characterized by broad,
shallow valleys, with very gentle side slopes, which are not seamed
by rill-channels, but present smooth, rounded or even plane contours.
Generally there is some alluvium collected along the stream chan-
nels, but as a topographic feature these flood-plains are usually diffi-
cult to distinguish from the mild side slopes of the valleys. In the
northern portion of the Eastern Shore peninsula, where the general
altitude is highest, the streams have more sharply defined valleys,
MARYLAND WEATHER SERVICE 91

and are, in general, more actively engaged in working over the ma-
terials of their flood-plains. Contrasted with this section, are the ~
streams of the inter-estuarine areas in the southern counties. There
one may travel for miles and never cross a well-marked channel.
Where the forests have been allowed to remain, they have so far pre-
vented evaporation that the swamps which formed in original surface
inequalities retain a considerable amount of moisture, even through
the hot summer months, and sometimes little rivulets may be found
in close proximity to these forested areas. As a rule, however, the
configuration of the surface betrays no sign of stream sculpture, but
seems to have received its outlines wholly from the waves and cur-
rents of the ocean during its last period of submergence. It is in
the middle counties—Talbot, Caroline and Dorchester—that the
streams approach more nearly the typical inland drainage of a
recently emerged marine plain. In these counties the stream charac-
ters correspond closely to the general description given above.

The streams whose lower courses merge into tidal estuaries belong
to the second class of Eastern Shore Coastal Plain streams. The
headwaters of nearly all the members of this class belong to the first
class of streams, and present the characters which have been de-
scribed. The transition in these streams from the shallow alluvium-
lined valleys of the above-tide district to the free and open estuarine
division is not a sudden one. Between the two extremes lies a
stretch of river whose waters ebb and flow with the tide, but whose
steep banks are deeply fringed by reed-covered marshes. This tran-
sition is most clearly and beautifully illustrated by the Choptank
river, which may be taken as the type. The same features are shown
almost equally well by the Nanticoke, the Wicomico, and the Chester
rivers.

The lower course of the Choptank is an open bay about six miles
wide in its broadest part, so that in spite of the comparatively shallow
waters (off Cook’s Point there is a maximum depth of ten and one-
quarter fathoms) strong winds or sudden storms in summer always set
a heavy sea running. The shores are low, rarely rising twenty feet
above tide, and intricately dissected by small tidewater creeks, par-
92 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

ticularly along the peninsular area between the Choptank and Eastern
Bay. The banks facing the channel do not slope down gently to the
shore, except in those cases where the land stands lowest and is in a
protected bay. Usually they form sharply-cut cliffs of varying
height. These cliffs, fashioned by the waves which often arise on
the river, are best developed along the exposed stretches of shore,
and are in every instance accompanied by some form of spit or bar
stretching to leeward, and built of the waste cut away by the waves.
Already in this lower course of the river, the small creeks emptying
into it are found to be shoaling and silting up their channels, as a
result of the sand-bars and beaches which obstruct their mouths.
Proceeding up the river, however, the marshlands, which have been
confined to creeks and lagoons below, begin to encroach on the open
waters of the channel. The sharp points, unlike their congeners
downstream, do not have off-shore extensions in the shape of sandy
shoals or spits, but have developed marshy accumulations of sand
and alluvium firmly woven together and held by a mass of matted
grass roots. For a short distance these marshes are confined to the
stream mouths, and the points, while having intermediate stretches
along the shore, are undercut, forming cliffs. These cliffs can often
be traced along behind the marsh-formed outlines of the points and
bays. Above Secretary creek the marshes increase in area so greatly
that the bounds of the channel are formed almost wholly of those
accumulations. The tortuous stream grows narrower as the marshes
widen, and swings in broad meanders, sometimes cutting directly
against the steep banks of the stream, when a strong bend carries
the current sharply to one side or the other.

Back of the marshy ground the banks of the river appear as steep
cliffs, which are now well wooded, and thus protect the banks from
the attacks of the rain and the wind. These steep wooded banks pre-
sent a decided contrast to the generally less precipitous slopes which
border the small tidewater confluents of the Choptank, and they
clearly form sudden interruptions in the broad, gently rolling surface
of the interstream areas. The boundaries between the firm land of
the Coastal Plain and the tidal marshes, as expressed topographically
MARYLAND WEATHER SERVICE 93

by these low bluffs, are clearly designated on the U. S. Coast and Geo-
detic Survey Chart No. 135. This chart conveniently sums up for
general study the tidewater details of the river system, and shows
even better than one can see the facts on the ground, the gradual
encroachment of the marshes and the line of low bluffs behind them.
It is very clear from this map that the original banks of the river,
up to the head of navigation and beyond, are represented by these
marsh-bound cliffs. Apparently the earlier channel, which the river
followed before it had built the marshy flood-plains, was much more
direct than it is to-day. Some allowance, however, must be made for
the straightening of the banks under the action of the waves in earlier
times, such as is now going on farther down-stream. At the present
time, also, there is some straightening done by the cutting of the
stream where its channel is turned against the higher bluffs at the
apex of some meander.

Above tidewater a marked change comes over the valley. Instead
of strong tidal currents, which by their scour keep open a narrow
pathway, the channel is occupied by a small stream, which is unable
to carry away all the waste washed into it from the valley slopes.
These slopes, also, while maintaining their steep faces for a short
distance, rapidly give way to the milder slopes and open valleys of
the interior. The flood-plain, which characterizes the stream in its
non-tidal portion, is clearly continuous with the growing marshes of
the tidewater district.

On comparing the other large streams of the Eastern Shore with
the Choptank, they are found to depart but slightly from the charac-
teristics of that stream. What variations occur, relate chiefly to
the shores of the estuarine portion, and are discussed below under the
head of Shore Features.

The streams flowing eastward into the coastal lagoons of the Atlan-
tic shore have already been briefly touched upon. They are, in Mary-
land, small and insignificant runs, flowing over marshy bottomlands.
The largest is St. Martin’s river, emptying into Isle of Wight Bay,
and next in size is Trappe creek, which flows southeastward from
Trappe, near Berlin. Although so insignificant in Maryland, this At-
94 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

lantic drainage attains a somewhat greater, although still very mod-
erate, development in Delaware, where it numbers among its principal
streams Indian river, Broad Kill, Mispillion creek, Motherkill or
Murderkill creek, Appoquinimink creek and Christiania creek. The
topography along the lagoons of Maryland and behind the off-shore
beaches on Delaware Bay clearly shows that these creeks, even the
smaller ones, belong to the class of streams known as “ drowned.”
That is to say, after having established themselves upon’ the new land
surface, and cut out characteristic valleys, a slight subsidence has
allowed the sea waters to penetrate inland, overflowing and drowning
the lowest portions of their valleys. The larger streams of St. Mar-
tin’s river and Indian river have, with the Pocomoke and Nanticoke
rivers, common sources in the Great Cypress Swamp which covers
such a large area in Sussex county, Delaware and Wicomico county,
Maryland.

This swamp is particularly interesting because of its position on
the great Atlantic-Chesapeake divide discussed below. It has been
pointed out that one of the characteristic features of the ideal drain-
age of a newly emerged Coastal Plain is the formation of lakes,
swamps, morasses, etc., in the original inequalities of the new surface.
There are along the Atlantic seaboard several examples of such
swamps, and particularly are they found in Florida, Virginia, Mary-
land and New Jersey, including the Everglades, the Great Dismal
Swamp of Carolina-Virginia, the Great Cypress Swamp of Maryland-
Delaware, and numerous small swampy districts along the Atlantic-
Delaware river divide of the Coastal Plain in New Jersey. In all
these cases there are two reasons why the swampy districts have not
been drained. First, they are formed in inequalities produced by a
submergence which took place in very recent geologic time, namely,
the Pleistocene epoch. These districts seem to have been the last
to come above the sea, even at that late date, so that there has been
but little time for streams to do much active cutting. Moreover, it
is to be noted that these swamps are located chiefly along main divides,
suggesting that the streams which sprang up during the first period
of post-Pleistocene emergence were able to drain swamps which were
MARYLAND WEATHER SERVICE 95

located nearer the shore line, but have not as yet found time or
strength to draw off the waters confined by the inequalities of the
main divides.

Allantic-Chesapeake Divide.

The peculiarly swampy character of this divide and its unsym-
metrical location on the peninsula between the Atlantic and Chesa-
peake Bay are facts which distinguish it, when compared with the
more usual characters of stream divides, and the laws which control
their development.

It has been pointed out, in discussing the origin of the Coastal
Plain province, that streams whose courses were extended across its
subaérial portion or originated thereon would normally flow eastward
and southeastward into the Atlantic. Thus the divides crossing the
Coastal Plain would have been parallel to the streams and approxi-
mately at right angles to the shore line. How then can the present
arrangement of drainage lines on the Eastern Shore be accounted for?
In studying the development of stream divides it has been found to be
a general rule that when the streams on one side of a watershed have
a greater development than their opponents on the other side, their
superiority may be traced to one of two causes. Either some original
characters of the country gave to one system long courses and to the
other short ones, or some features in the district subsequently revealed
in the course of continued development have combined to aid one
set of streams, while not offering equal advantages to the others.

There is no apparent reason for the unsymmetrical location of the
divide in question, when the normal development of the Coastal
Plain is examined for an original cause. The whole history of the
Coastal Plain, so far as it is recorded in its earlier sedimentary de-
posits, would go to show that the streams ought not to be abnormal
in any particular. Neither can there be found any traces of factors
which, appearing after the streams had begun to develop, would be
able to influence them in such a marked manner. A common factor
of this latter class which in many parts of the country has played an
important réle is a heavy or very resistant stratum of rock. Such
a stratum, by retarding the development of the streams compelled to
96 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

flow over it, gives the other streams, not so hindered, an opportunity
to advance their headwaters and to reduce their channels more rap-
idly to a gentle slope. But no stratum of sufficiently contrasted
resistance to produce such an effect can be found in the series of
Coastal Plain strata within the boundaries of Maryland. If the indu-
rated clays and sands of the Lafayette Formation be appealed to as
sufficiently resistant to have such an effect on the streams the results
produced would be just the opposite of those observed. The west-
ward-flowing streams would first have encountered the opposition of
the eastward dipping beds of the Lafayette, while the eastward-flowing
streams of the Atlantic, having their courses down the dip, would
have been last influenced by such opposition. The result then would
have been that the Atlantic drainage would have developed at the
expense of the Chesapeake streams, and the divide would now stand
nearer the bay than the ocean.

Again, in a district of comparatively uniform and homogeneous
lithologic structure such as the Coastal Plain, it might easily happen
that one portion, receiving a heavier average rainfall, should there-
fore develop a stronger drainage system. The maps of average An-
nual Precipitation in Maryland and Delaware, published in the report
of the Maryland State Weather Service for 1892-3, show the heavier
rainfall to have occurred within the catchment basins of the Choptank
streams, while the maps for 1894-5 show a slightly greater fall for the
Atlantic streams in the same latitude. There are no strongly marked
topographic features of the Eastern Shore which exert any control
over the distribution of rain, and it is probably fair to conclude that
the average of a number of years would show that there is a pretty
even and equable distribution of rain to either district.

Shore Lines.

The most striking feature of the Eastern Shore, next to its ex-
treme flatness, is the very intricate character of its western shore line.
At first sight the meandering outlines appear to be a maze of creeks
and coves without plan or system, and certainly the stranger, who
tries to find his way about the multitude of creeks along Kent Island
and Eastern Bay at the mouth of St. Michael’s river or in Bay Hun-
MARYLAND WEATHER SERVICE 97

dred at the entrance to the Choptank, would soon become confused
by the great number of closely similar creeks and minor estuaries
which are found there. These intricacies all work out very simply,
however, by tracing out certain lines which may be found more or
less clearly marked in nearly every cove and bay.

If, on one of the U. S. Coast and Geodetic Survey Charts of Ches-
apeake Bay, lines be drawn along the channels of the principal
streamways, a pattern will be produced resembling so many bare
trees, very crooked as to their trunks, and stripped of all except the
largest limbs. The roots of these river trees lie in Chesapeake Bay,
and their tops, merging into the surface streams of the province, lie
against the great divide." Tracing out the channels of all the little
tide-creeks and bays, it will be found that many of the channel lines
join or branch from the main stem and major branches, thus forming
the subordinate branches and twigs of the “trees.” Several smaller
independent systems, such as the Little Choptank, Eastern Bay and
St. Michael’s rivers, which spring directly from Chesapeake Bay, will
also develop.

If now these “trees”? be compared with the branching patterns of
most streams, for example, of such a river as the Patapsco of the
Piedmont Plateau or the Patuxent of the Piedmont and western
Coastal Plain, a striking similarity in the systematic irregularity of
the branching at once appears. From such a comparison it is but a
step to the conclusion that running streams of fresh water once
carved out the channels which are now filled with the brackish
waters of Chesapeake or Isle of Wight Bays. An elevation of one
hundred feet would be sufficient to convert all these irregularities of
coast line into a corresponding multitude of larger and smaller creeks
which would empty into a great tidal river along the main channel
of Chesapeake Bay. A depression of less than half this amount
would convert all the rivers of Dorchester, Somerset, Wicomico and
Worcester counties into such tidal creeks as are now found along their
shores, and to a less extent would affect in a similar way the present
streams of the more northern counties. Chesapeake Bay and its

1See Russell, I. C., ‘‘ Rivers of North America,” Fig. 22, p. 219.
7
\

j
{

L
98 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

tributary bays and rivers thus belong to that great class of streams
called drowned rivers, and the coastal topography of the whole
Coastal Plain of Maryland is for a similar reason to be classed as
drowned topography.

Drowned topography and drowned rivers are not peculiar to Mary-
land, however, nor even to the Coastal Plain, although they are
excellently illustrated in these districts. The numerous islands and
deeply land-locked harbors along the New England coast, particu-
larly in the state of Maine, afford beautiful examples of the same kind
of coastal features, while the beautiful friths of Scotland and the
famous fjords of Scandinavia and Finland are world-renowned exam-
ples of this class of land forms.

Since the drowning of the streams, the resultant expansion of the
water areas in the valleys thus affected, and the introduction of tidal
currents, have brought new forces into action which influence the
development of shore topography along the streams. In describing
the lower course of the Choptank, mention has been made of the
wave-cut cliffs and wave- and tide-built bars and spits, which now
distinguish the estuarine portions of that stream.

«All these features are developed to a greater or lesser extent in
the other rivers. The best development of wave-cut cliffs is found
along the Sassafras and Chester rivers, where wide expanse of water
is combined with high banks. The waves generated by the severe
southeast and southwest storms, although raised in comparatively
shallow waters, are forceful enough to undereut and bring down great
masses of the indurated fossiliferous sands and marls. These blocks
he quietly on the shoal beaches during the numerous small storms of
summer, but in winter are rapidly broken up and distributed along
the shores. As a result of this continual supply of new material
from neighboring cliffs, waves are building sand bars across the
mouths of the smaller creeks, and as a result of this damming they
are gradually filling up.

The tide flowing in and out of the rivers twice a day is also a
factor and an important one in fashioning the outline of the river’s
shores. Several shore forms in the Choptank have been described
MARYLAND WEATHER SERVICE 99

and attributed mainly to wave work. The side-currents or eddies
set up between the shore and the main tidal current in the channel
generally play an important and sometimes a controlling part in the
building of the spits and bars which characterize the shores. The
manner in which these tidal eddies work has been recently worked out
by Dr. F. P. Gulliver’ for a much larger estuary on the coast of the
state of Washington, and Fig. 13 is designed to illustrate the arrange-
ment of such eddies during flood tide. No special studies have vet
been made of the many admirable shore features which the rivers of
the Coastal Plain exhibit, but while working on the areal geology of
the Eastern Shore I was able to note that in at least one case eddies

 

 

 

 

Fic. 13.—Scheme of Flood-tide Eddies in an Estuary (after Gulliver).

set up by the tide had influenced the growth of a cusp on the Sassa-
fras, and it is very probable that tidal currents have also been influ-
ential in determining the growth of two sandy points on the Chop-
tank.

The example in the Sassafras river is found at a point on the
south bank of the river a short distance below Ordinary Point, which
is itself probably, in part at least, the result of similar eddies. One
day while endeavoring to tack down stream my companion and I
found that we could make very little headway as we approached
the south shore at this point, although when out in midchannel the
strong ebb tide helped us along very nicely. On looking over the

1 Gulliver, F. P., Bull. Geol. Soc. Amer., vol. vii, pp. 411-41, Fig. 7.
100 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

side of the boat I saw that the waving eel-grass which grew in the
shallow water near the shore was turned up-stream by a steady cur-
rent of some strength. Evidently here there was a back-set eddy
given off by the channel current, and conforming in its course to
the smooth curve of the sand and gravel beach whose outline it had
been instrumental in determining.

On the same river the long sandy spit known as Ordinary Point
has been built up by the combined forces of tidal currents and the
southwest winds, which set up strong waves, particularly in the
broader portions of the lower river. The waves beating against the
sandy cliffs on the northern bank of the river have washed out great
quantities of sand, which the shore currents have carried up-stream,
until, being deflected out towards the channel by a low point of land,
they were there opposed by the tidal currents and forced to drop
the sand which they carried. The tide acting regularly twice a day
overbalances the less regular action. of the strong waves, and has
now stopped the further growth of the bar across the channel, by
turning the tip down-stream, so that its further growth is opposed by
the very waves which serve to build the bar outwards.

Besides these constructive and destructive changes which-are tak-
ing place within the smaller estuaries, the islands at the mouths of
the rivers seem to be gradually wearing away. The low swampy
islands which characterize the Chesapeake border of the Eastern
Shore are reported to have been firm, dry lands twenty-five years ago.
Certainly now many fine trees which once flourished on them are
being killed by the salt water penetrating to their roots. In many
places, for example along the exposed portion of Kent Island, it is
found that marshes formerly protected by and formed behind sandy
beaches are now exposed directly to the beat of the waves and are
being rapidly cut away, leaving a bench of soggy and matted roots
about two feet below the mean tide level. Many years ago Ducatel ’
reported that the mouth of the estuarine portion of Pocomoke river
and sound were filling so steadily with detritus and fine mud that it
was not practicable to keep a ship-channe! open there as an approach

1Dueatel, J. T., and Alexander, J. H., Report on the New Map of Mary-
land, 1835, p. 49.
MARYLAND WEATHER SERVICE.
VOLUME 1, PLATE V.
MAP SHOWING COASTAL PLAIN TOPOGRAPHY OF ANNE ARUNDEL COUNTY.
FROM RELAY SHEET, U. S. G. S.MARYLAND WEATHER SERVICE 101

to a ship canal. It is also significant that the upper portion of the
Wicomico river must be annually dredged out and the banks held
back by posts and planking for the distance of a mile or so below
Salisbury in order that the ship-channel may be kept free from the
considerable amount of sand and mud which washes down from the
surrounding banks.

These phenomena of washing away in certain portions seem to be
contradictory, for the filling up of the streams does not occur at
points where it can be related to the washing and wasting of the
banks and cliffs before the attack of the waves. The washing away
of the cliffs is chiefly confined to the districts in the vicinity and
along the shores of Chesapeake Bay, except for the great flats which
are growing in Pocomoke sound, while the filling is going on near
the heads of navigation of the tidal streams. The rapid cutting
which is going on along the western shore of the Chesapeake is inter-
preted by McGee’ as an indication that the Coastal Plain is now
subsiding, since only by steady subsidence can such continued wast-
ing of the cliffs without contemporaneous shoaling of the adjacent
shallow waters be accounted for. The steady filling in of the Eastern
Shore streams of the tidewater province must either indicate a tilting,
whereby the eastern portion of the Coastal Plain is being slowly
raised and the bay portion depressed, or else the phenomenon directly
contradicts the above conclusion, and the fact that Chesapeake Bay
does not shallow more rapidly is to be explained by supposing that
the original depth of the bay was greater than has heretofore been
considered as probable. A ‘consideration of the estuaries on the
peninsula of Southern Maryland may offer a solution to this problem.

THE WESTERN SHORE.

The streams of that portion of the subaérial Coastal Plain which
forms the peninsula of Southern Maryland or the Western Shore all
belong to Chesapeake Bay drainage. There are but two or three
large rivers which can be properly regarded as coming within the
boundaries of this section, namely, the Potomac, the Patuxent and

*McGee, W. J., U. S. Geol. Survey, Seventh Ann. Rept., p. 618.
102 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

possibly the Susquehanna. All three of these streams have very con-
siderable portions of their courses located upon the crystalline and
the non-metamorphiec formations of Western and Central Maryland or
Pennsylvania, while only the lower portions of their courses cross
the western portion of the Coastal Plain. All the other streams of
the area rise within the boundaries of the Coastal Plain, so that their
courses lie wholly within the province, and their origin upon the sur-
face of the plain is obvious. The history of the three streams first
mentioned is less evident. The Potomac and the Susquehanna which
head far back in the Alleghanies and assumed the upper portion of
their courses long before the Lafayette (Pliocene) submergence, un-
doubtedly belong to that class of streams already described which
extended their lower courses seaward from the old land across the
emerging plain. The Patuxent, judging from the present geological
map of Maryland, would also seem to belong to this class of ex-
tended rivers. It is believed, however, from studies of the neighbor-
ing and related streams of the Piedmont Plateau, as well the fea-
tures of its headwaters, that this stream, together with the Gun-
powder and several others, originated on a former western extension
of the Coastal Plain, all sedimentary records of which have been
removed by subsequent erosion.

The streams of the Western Shore when compared with those of
the Eastern Shore present considerable similarity in general features
such as the drainage pattern, drowning and terracing. In several
respects these features are more sharply accentuated than in the
Eastern Shore streams. The reason for this seems to be the greater
amount of elevation which this section underwent at the time of the
post-Lafayette emergence whereby the streams were able to cut
deeper valleys which now give high-banked estuaries with more
marked terraces.

Stream Characters.

As soon as the “extended” streams of the Western Shore cross

the western boundary of the Coastal Plain, i. e. the Fall Line, their
valleys undergo a sudden change in character. From the narrow,
steep-sided gorges which characterize the streams of the Piedmont,
MARYLAND WEATHER SERVICE 103

the valleys change to open meadows bounded first by one or two
broad terraces thirty or forty feet above the meandering channel and
farther off by low, mild hill-slopes. These terraces can sometimes
be traced up the streams westward from the Fall Line and are then
found to merge into probably contemporaneous terraces, described
later, which characterize a number of the Piedmont streams. Of the
streams which present good illustrations of these confluent terraces
may be particularly mentioned the extended Potomac, Anacostia
river or the Eastern Branch and the Patuxent.

Proceeding down-stream from the vicinity of the Fall Line the
stream banks become higher and slightly steeper, the flood-plains do
not increase much in size, and the terraces appear to stand higher
above the streams. At the same time the small side-streams trench
somewhat into the terraces and their own upper courses cut deep
narrow ravine-like valleys whose lower portions are somewhat leveled
by an extension into them of a terrace plain. The characters of the
down-stream terraces and side ravines are very well illustrated along
the Patuxent to the east of Upper Marlboro’ and near Princess Anne
in Prince George’s county. At these points, however, the river
already begins to be influenced by the tides and thus comes almost
within the estuarine zone.

Along this lower fluviatile portion the terraces stand generally in
two series, as they do in the upper portions. The lower series has
an average elevation of five feet above the present flood-plain, and its
width varies from one hundred yards to half a mile. It is composed
of fine gravels, quartz sands and a small amount of clay and loam.
The upper series stands forty or fifty feet above the lower and is
built of coarser gravels and cobbles. Near Princess Anne a gully in
this upper terrace clearly shows that it is in part the result of cutting,
in part formed by the deposition of gravels.

Both sets of terraces have been trenched by the small side-streams
as they cut their way down to the present channel-grade of the main
drainage. These streams pursue direct courses across the upper
terrace, however, while their steep-sided trenches meander through
the lower terrace in a manner which indicates that previous to cutting
104 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

of the present trenches they flowed for a time under flood-plain con-
ditions. Such facts aid in picturing the conditions under which the
streams have worked and give a clue to the relative variations in the
rapidity of rise of the land after its Pleistocene depression, for these
terraces represent stages in the fluviatile phase of Pleistocene depo-
sition. The somewhat direct courses of the side-streams across
the upper terrace indicate a rapid rise to some height which did not
permit flood-plain conditions to arise. Having thus obtained an ele-
vation of perhaps forty feet, the land remained quiet while the lower
and broader terraces slowly formed. Finally, the land again rose,
very slowly at first, so that the streams for a short time crossed ex-
tensive sand-flats just above the level of the water; then more rapidly,
so that the runs trenched the meandering courses which they had
been forced to assume during the short delay just preceding.

Drainage Plan.

On comparing the drainage patterns of the Eastern Shore and the
Western Shore no fundamental differences are to be observed. The
streams of the Western are generally shorter than those of the Fast-
ern Shore and are of steeper slope, but the method of branching is
the same and the streams belong to the same class, that is, thev are
autogenous. Indeed, these streams, though smaller, have, on account
of their sharper cutting into the higher land of the Western Shore,
developed even more typical autogenetic drainage than the low-lying
and weaker streams of the east. Thus the branching of the head-
waters of the Wicomico river in Charles county or of the Piscataway
creek in Prince George’s county present admirable examples of auto-
genous development. This type of drainage is also represented in
Fig. 14.

Divides.

The most striking feature of the drainage of Southern Maryland is
the location of the second-order stream divides. The Hypsometric Map
of Maryland* expresses very well the unsymmetrical location of these
divides, which always stand nearer the northern than the southern
member of any two of the larger streams. Thus the streams of St.

1Md. Geol. Survey Reports, vol. i, plate vi, p. 142.
MARYLAND WEATHER SERVICE 105—

Nv EZ
LZ YY
LZ Yi; f=

 

Fic. 14.—Unsymmetrical Divide between Potomac and Patuxent Drainage, near Leonard-
town, St. Mary’s County. (From Nomini Sheet, U.S. G. 8.)
106 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Mary’s county, which flow southward into the Potomac are about
three times as long as those which empty into the Patuxent. Simi-
larly it is to be observed of the Calvert county streams that those
flowing southwestward to the Patuxent predominate over those which
drain eastward into the bay. This characteristic has already been
recognized as a typical feature of the location of the divides of the
eastern division of the subaérial Coastal Plain. It is a very interest-
ing and remarkable coincidence that here in a region of more strongly
marked relief and of more active streams is found a drainage system
possessing the same unsymmetrically located divides which mark the
sluggish drainage of the Eastern Shore. What makes the coincidence
even more striking is the fact that the short steep streams lie to the
east of the divides in both cases, while the longer, flatter streams are
on the west slopes. These facts suggest very strongly that there may
be some intimate and causal relation between the location of the
divides on the Eastern and Western Shores.

If the divides and streams are studied on the small-scale Hypso-
metric map of Maryland a number of instances may be found which
seem to suggest a simple explanation for the locations of the divides
of Southern Maryland. In one case, that of Lyon’s creek in Calvert
county, the headwaters of the stream start with a southeastward
course, but after flowing for two or three miles in this direction, make
a sharp turn at right angles and flow off southwestward to the Pa-
tuxent. At the point where the creek makes the sharp bend a small
stream heads and flows eastward into Herring Bay on the Chesapeake.
Again in Charles county, southeast of Bryantown, the headwaters of
a stream which empties into the Wicomico river start with a north-
eastward course, after a mile, sharply turn southeastward and again
soon turn sharply southwestward. Near where this stream bends
heads a small stream which joins the Patuxent just above Benedict,
having taken a northeast course seemingly in direct continuation of
the upper part of the preceding stream. These cases suggest that
there has been some capturing by southeastward flowing streams and
corresponding decapitation of westward and northeastward flowing
streams. The large scale maps of the U. 8. Geological Survey (see
MARYLAND WEATHER SERVICE. VOLUME I, PLATE VI.

 

 

 

Fic. 1—TRIBUTARY OF THE CHOPTANK,. NEAR QUEENSTOWN.

 

 

 

Fic. 2.—SEVERN RIVER, NEAR ROUND BAY.
MARYLAND WEATHER SERVICE 107

Fig. 14) do not support this conclusion by detailed evidence. They
do show, however, that the intricately branching headwaters of the
southwestward flowing streams have pushed their weaker opponents
very far to the northeast and have developed more intricate and ex-
tensive drainage systems than the latter.

Another factor which must be considered in any attempt to ex-
plain the unsymmetrical divides in Calvert county is the retreat of
the cliffs along the western shore of the Bay. On comparing Plate
VI, Fig. 2, with Plate VI, Fig. 1, there is seen to bc a marked
difference between the relief of the eastern and the western shores of
Chesapeake Bay. The eastern shores are low and flat, while the west-
ern banks present picturesque cliffs such as those near Cove Point,
shown in Plate IJ. This decided contrast is due chiefly to the fact
that the Western Shore was originally elevated to a greater height
than was the Eastern Shore. This initial difference, however, has
been accentuated by more recent developments. The great storm
winds on the Bay come from the northeast or the southeast, while the
storms from the west are less severe and of shorter duration. Con-
sequently the western shores are exposed to the severer storms and
must withstand long-continued attacks of the larger storm waves. The
result is that the bay shore of Calvert county, which from the con-
figuration of the Bay is the coast exposed to the longest sweep of
easterly winds, has been steadily undercut and worn back by the
waves until the cliffs thus produced occupy a position several hun-
dred yards west of the shore line which bounded the Bay in earlier
times. The rate at which this recession has been going on is not
known at present, but the members of the Coastal Plain Division of
the Maryland Geological Survey have instituted a series of observa-
tions and measurements which in the future will yield some inter-
esting results on this subject.

The fact of the recession of the cliffs is well established. In the
course of the retreat the plane of the cliff face cuts across the
topography of districts which formerly lay some distance back from
the shore. The lower courses of many streams have been entirely
removed, and their valleys which once descended to the bay level
108 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

in the usual fashion now appear as notches in the crest line of the
cliff. These notches are very beautifully shown in the view repre-
sented by Plate II. Again, a shallow bench of clay is found to
extend out under the water from the present foot of the cliffs to a
distance of one-third or half of a mile beyond which the water rap-
idly deepens. This bench is undoubtedly the planed-off stump left
ly the waves as they cut their way landward, pushing the cliffs before
them. The result of this westward migration of the Cove Point
cliffs has been to shorten very materially the length of the streams
flowing down the present eastern slope of the Calvert county divide,
and the appearance is thus produced of an encroachment upon the
headwaters of these curtailed streams by the longer streams of the
western slope. The unsymmetrical location of the divide in Cal-
vert county is, therefore, in part at least, only apparent. Even if
shore recession were an adequate explanation for the lack of sym-
metry of the Calvert county streams the same would not apply to the
streams lying between the Potomac and the Patuxent. In this case
the shorter streams which flow into the Patuxent have not lost as
much of their lower courses by wave erosion as have the Calvert
county streams, yet the lack of symmetry is just as marked as in the
latter case.

Estuaries.

As the streams come more and more under the influence of the
tides their banks gradually recede and the waves are found to have
destroyed considerable portions of the Columbia terraces... Thus pass-
ing to the estuarine portion proper, high, steep wave-cut cliffs replace
the sloping banks, and sandy beaches or wave-fashioned contours ap-
pear in the stead of sandy terraces. The broader valleys which the
streams of this subdivision carved out, produced broader estuaries
than those of the Eastern Shore when the subsidence took place
whereby the streams were drowned. Hence the shore features along
the Potomac and the Patuxent are those of stronger waves and tides
and the variety of forms is greater.

Besides spits and barrier-bars or beaches, such as have been de-
seribed from the Eastern Shore streams, there have also been formed
MARYLAND WEATHER SERVICE 109

along these shores V-bars, cusps, hooks, ete., which in many cases are
worth studying because of the economic importance which they bear.
For example, on the Potomac a lighthouse has been erected on the
apex of the sawtooth-shaped V-bar which forms Piney Point. The
sharper, shorter curve of the tooth is formed by the wide beach on
the southeast or down-stream side, while the gentler back slope of
the tooth consists of a long, gently curving, narrow beach which
appears to be sometimes breached by the greater storm waves. The
down-stream curve of the point, as well as the greater thickness of
the down-stream beach, suggests that the growth of the point has
been chiefly directed down-stream. For some miles above Piney
Point there are long, smoothly curving beaches which bridge over
the mouths of Flood and Herring creeks by means of low sandy bars,
and thus give continuous and even sweeps of shore contours. These
features are indicative of moderate and steady currents which sweep
along the foot of the low cliffs and the barrier bars carrying sands
southeastward to drop them off the point of the cusp. The shorter and
more sharply-curving beach forming the southeast side of the point
has been built by a weaker or less constant current which, flowing at
right angles to the course of the first current, has carried the ma-
terial brought by the latter around the point and down the short
beach. These currents are the joint products of winds and tides, but
the latter being regular and periodic in their action, are the con-
trolling factors and have given the major characters to the estu-
arine shores. .

Of a different type from the Piney Point bar is the formation of
Point Lookout at the mouth of the Potomac. Piney Point was built
by tidal currents which, for some reason perhaps resulting from in-
itial inequalities in the shore line, set up ~ddies in whose triangle of
confluence deadwater permitted bar-building. At Point Lookout the
southerly drift along the bay shore set up by the prevailing northeast
storm winds of the Chesapeake has built sand bars and beaches across
Deep Creek into its neighbor, Tanner creek, and continued to grow

southeastward until opposed by a current which sets along the curved
beach and bar of Cornfield Harbor. This Cornfield Harbor current
110 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

has built bars and beaches across Point Lookout and Potter creeks,
and the growth of these northwestward indicates that the current
here runs in the same direction for the longer period, although it is
possible that reversals in its direction sometimes occur. A very brief
examination of the eastern beach of Point Lookout reveals the fact
that its method of growth has been at times gradual and again more
rapid. During most of the time the minor sterms and waves
bring sands along the shore to be deposited as a long, evenly-sloping
beach such as is forming to-day. Sometimes, however, great storms
have arisen and their strong winds have raised waves so large that
they broke some distance out from the beach then existing. Thus a
second beach was built up by the waves although several rods out
from shore, and when the storm subsided the every-day waves in-
creased the newly built beach. A record of these changes is left in
the abandoned beaches and the marshy stretches between them which
now lie within the present beach line.

Many examples of similar shore features can be found along the
Patuxent and the Potomac. The Magothy and the Severn, in the
sandy and clayey cliffs along their shores, also furnish favorable op-
portunities for such features; but the estuaries of the Patapsco, Gun-
powder and Bush rivers generally have such low and marshy banks
that there is no ready source for the sand necessary for the construc-
tion of beach topography.

Recent Stream Changes.

Mention has already been made in the appropriate place of the
changes which have taken place in the streams and coast lines of the
Eastern Shore during historic times. The same may be found on
the Western Shore. When the country about Baltimore was first
settled the many small creeks and the larger rivers offered, in their
drowned lower courses, convenient harbors and landing places which
were more or less accessible from the interior. At that time schooners
of good size and moderate draft could lie alongside the wharf at Elk-
ridge Landing loading with the iron obtained from the neighboring
deposits in the Potomac group of formations. To-day the river is so
choked with the sands, mud and gravels which wash down from the
MARYLAND WEATHER SERVICE 111

Patapsco gorge and from neighboring hills, that large vessels can no
longer sail so far up the river. Every year the floods and freshets
bring down more waste from the land and add it to what has already
been deposited, so that the channel grows steadily shallower and the
landing grows less and less accessible.

The Anacostia river has had a similar history. Down to the early
days of the city of Washington this stream was navigable for several
miles from its mouth. To-day the channel and valley are so choked
by the silt which the stream brings down that during high tide there
is scarcely a foot of water on the broad flats which fill the stream-
way, and at low tide acres of marsh are laid bare. Thus within a
hundred years this stream is seen to have effected great changes in
its channel by deep accumulations of detritus derived from the sur-
rounding hills.

One other instance of similar filling-in of a stream channel during
historic times may be cited. Somewhere about 1785 Piscataway
creek in Prince George’s county was a navigable stream as far up as
the town of Piscataway, which is now about two miles from tide
water of any depth. ‘At that date,” says Alexander, “it certainly
afforded a channel for vessels of good draft up to and a little beyond
the Tobacco Warehouse.” In 1835, however, the tortuous channel
had so far filled up with mud and alluvium that the depth of water
“at quarter ebb” was only 1 foot 104 inches, and at high tide was
only three feet. Moreover, at that time the processes of shoaling
seem to have been active. J. H. Alexander says: “The progressive
changes attributable to these causes [%. e. those causing deposition of
sediment by checking the flow of the current], if they are to be
judged from the effects of the last two years, are going on with con-
siderable rapidity. Shoals of soft mud and shells, which were passed
over at that period [1785 circ. ], are now islands, covered with marine
grasses and aquatic plants, and submerged only at high tide; and the
public landing, once at the warehouse and afterwards nearly half a
mile below it, is now difficult of access and appears to be fast receding
down the river.” Since 1835 no record is found of further changes

+J. T. Ducatel and Alexander, J. H., Report on the New Map, etc, 1835,
pp. 11 and 12.
112 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

in this region, but there is no apparent reason for doubting that the
filling-in then in progress has continued to the present time.

These instances could be multiplied, but they leave no room for
doubt that the strong tendency of all the smaller and most of the
larger tidewater streams of Southern Maryland, as well as those of
the Eastern Shore, is to fill up their channels with the detritus which
they carry.

ECONOMIC PHYSIOGRAPHY OF THE COASTAL PLAIN.

Soils.

The various geological stages through which the Coastal Plain has
passed have had considerable influence upon the soils, and through
them upon the crops of the province. The early strata, those of
Cretaceous and Eocene age, which are best developed in parallel belts
along the northwestern boundary of the Coastal Plain, are sandy
loams which yield good returns of fruit and garden truck. In this
belt the most prosperous peach- and other fruit-farms have been
located, and large quantities of fine peaches are still shipped from the .
northern counties of the Eastern Shore. The same belt extends
northeastwards into Delaware and New Jersey where similar erops
are raised. These strata carry with them a natural storehouse of
valuable fertilizer in the form of greensand or glauconitic shell marl.
In the early days of Eastern Shore farming this marl was much used
as a fertilizer, particularly in Cecil, Kent and Queen Anne’s counties.

In the central and southern counties the clayey loams which
come from the Miocene or Chesapeake deposits afford extensive areas
of good wheat, grass and tobacco lands, which formerly were of great
importance to the state. Since the rapid development of the wheat
fields of the West, however, the yield of these lands has grown com-
paratively insignificant, so that at present the farmers are not able to
make wheat crops pay even by the aid of expensive fertilizers. Among
the best-paying crops of the Coastal Plain are the products of the
lighter sandy loams of the Pliocene (Lafayette) and Pleistocene de-
posits. These soils cover the whole Eastern Shore south of the Chop-
tank and are also of importance on the more dissected Western Shore.
Large and early crops of berries and melons are annually shipped
MARYLAND WEATHER SERVICE. VOLUME |, PLATE VII.

 

 

 

 

 

Fic, 2.—FARM-LANDS OF THE COASTAL PLAIN, IN TALBOT COUNTY.
MARYLAND WEATHER SERVICE 113

from the cultivated areas of these soils, and the canning of tomatoes,
corn and other products constitutes one of the important industries of
the province.

Waterways.

The post-Lafayette and the post-Pleistocene submergences of the
Coastal Plain have been of immense benefit to the inhabitants of
Maryland. As a result of the drowning of the Chesapeake river
ocean-going vessels are admitted as far inland as Georgetown, D. C.,
Baltimore, Havre-de-Grace and Chesapeake City. Valuable harbors
also are provided, so that a large share of commerce has been attracted
to Maryland shores. Besides interstate and international trade which
is thus favored by the configuration of Chesapeake Bay with its deep
exit to the high seas, trade within the state is greatly benefited by
these waterways. That geologically recent submergence whereby the
river valleys carved in post-Pleistocene times were drowned for more
than half their length gave to the inhabitants of the Coastal Plain
the most favorable facilities for easy and cheap transportation of their
crops. The estuaries then formed are the entrances to tidal streams
that penetrate into the very heart of the rich lands. They are gen-
erally of sufficient depth to admit the light-draught steamers plying
on the waters of Chesapeake Bay and the numerous wharves which
are encountered on ascending any one of the navigable creeks testify
to the readiness with which the people have availed themselves of
their natural opportunities. In the proper seasons these wharves may
be seen piled high with the crates of fruit and other products which
are being sent to Baltimore for distribution among the neighboring
states.

Besides thus affording easy paths of intercourse with other impor-
tant sections of the state the estuaries yield peculiar and characteristic
products of their own. The same streams which, during the sum-
mer, are the arteries and highways of a commerce based on the pro-
ducts of the soil, become in winter the fields of one of Maryland’s
greatest industries—the oyster fisheries. Great quantities of these
oysters are annually sent to Baltimore, and their gathering has given
rise to a race of hardy fishermen and expert sailors only excelled by

8
114 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

the codfishers who sail every year to the Great Banks of Newfound-
land. The oyster-canning industry, whereby the interior of the
continent is supplied with canned oysters, has also arisen as an indi-
rect result of the post-Pleistocene drowning. The diamond-backed
terrapin, the duck and the other wild fowl of the littoral marshes also
deserve a place among the list of resources which the geographic his-
tory of the province has bestowed upon this state.

Railroads.

While the many waterways which intersect the Coastal Plain have
given boat traffic the best start among transportation facilities, rail-
roads have been built to a number of points, thus connecting them
more directly with the vigor and energy of the great commercial cen-
ters of Philadelphia and New York. Generally the railroad, seeking
as it does that course which requires the least modifications from the
natural topography in order to make an easy grade, has to pursue a
more or less tortuous route. On the Eastern Shore the low and
almost insignificant character of the divides and the shallow stream
valleys permit the roads to run in very direct routes from one objec-
tive point to the next. A glance at the map of the state shows these
routes and the indifference which they display towards the divides.
It is also noteworthy that, although touching at several waterside
towns, the railroads are confined on the whole to those wider portions
of the small peninsulas where the hauling distance to the boat lines
becomes something of a factor in the cost of transportation. By
reaching these remoter points they are thus able to maintain a foot-
hold in spite of the lower rates offered by the boat lines. On the
peninsula of Southern Maryland the one railroad and its branch are
compelled to hold pretty closely to the divide, as a short distance on
either side the country becomes so cut up that it would be wholly
impracticable to build a line. This is particularly true of the south-
eastern portion of the peninsula in Calvert and St. Mary’s counties.

Liffect of Topography upon the Inhabitants.

When the early settlers came to Maryland they found the tracts
of the Coastal Plain oceupied by peaceful tribes of Indians who lived
MARYLAND WEATHER SERVICE 115

by fishing in the deeply indented rivers and hunting through the pine
and hard wood forests which covered the interstream areas. The
settlers themselves took to farming, encouraged by the rich soils, and
also obtained plenty of fresh fish and oysters from the neighboring
waters. Soon large and prosperous plantations grew up, which
afforded by their products good incomes to their owners. The earlier
inhabitants were thus mainly agriculturists. As the value of the
oyster beds increased and the demands for the oyster grew the race of
oystermen sprang up. These men naturally settled along the shores
near their work. At present the two classes, which originally must
have been somewhat mixed, can be clearly distinguished, the regular
farmer keeping to the higher interfluviatile areas, while along the
shores and in the vicinity of the large towns are the houses of the
oystermen. On the Western Shore the dissection of the interior
lands near the Bay has handicapped the farmer very decidedly, while
the deep rivers and estuaries give good opportunity for the fishermen
to ply their trade.

Thus the geological and physical features of the Coastal Plain,
which are the direct results of its geological history, are seen to have
almost wholly determined the pursuits and the habits of its settlers
and inhabitants.

Tue Pizpmonr Pratreau Province.

BOUNDARIES.

The Piedmont Plateau province is so called from its position along
the eastern foot of the Appalachian ranges. It includes the broadly
rolling upland of moderate elevation which extends from the eastern
slope of the Blue Ridge and Catoctin mountain eastward to a line
which runs approximately parallel to the coast, and marks the west-
ern limits of tidewater. This line extends from New York past
Philadelphia, Baltimore, Washington, Richmond, Raleigh, and Au-
gusta to Macon, Georgia, ‘and along a comparatively narrow zone, is
characterized by turbulent channels with waterfalls, cascades and
rapids. To the west the streams may have long quiet stretches, while
eastward all the streams open out into placid tidal estuaries. This
116 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

eastern boundary of the Piedmont Plateau is so noticeable a feature
that it was early recognized and named the Fall Line from the man-
ner in which it affects the streams. The Fall Line is really a zone
several miles in width and probably marks a simple monoclinal
flexure or a series of slight faults whose downthrows are towards the
east. The western boundary of the province, formed by the eastern
base of Catoctin mountain, is a clearly defined topographic feature,
the cause of which will be later explained.

As would be expected when topographic boundaries are so well
defined, the geologic and structural boundaries are almost equally dis-
tinct. On the east along a crenulate line which often coincides with
the zone of falls or the Fall Line, lie the extreme western limits of
the Coastal Plain sediments. These horizontally bedded and poorly
consolidated deposits lie across the bevelled edges of the folded and
crumpled crystalline rocks of the Piedmont Plateau, and present such
a marked stratigraphic and lithologic contrast to them that the geo-
logic boundary between the two provinces is sharply defined. The
lack of completely consolidated layers in the Coastal Plain deposits
has prevented the development of marked escarpments which, by
their steep inland-facing front-slopes and long, gentle seaward-dipping
back-slopes, would more clearly define the limits between the two
provinces. On the west the transition from the highly altered crun-
pled schists of the eastern part of the province to the usually unal-
tered and less severely folded and faulted strata of the Appalachian
region is not as sudden and well marked as the change from the
Coastal Plain. From the crumpled gneiss of the eastern portion
the Plateau extends across the highly plicated, but less profoundly
metamorphosed, phyllites which form most of Parr’s Ridge and its
western slope. Farther west, along Catoctin mountain, in the up-
arching and great overthrust faultings of the limestone and quartzite
upon the igneous rocks of the Blue Ridge, the structure approaches
that of the Appalachians. Although the change in structure is thus
gradual, yet the topographic change is more marked. The reason for
this is that the great overthrust faults along the flanks of the moun-
tains have elevated the hard quartzite which forms the crest; and sub-
MARYLAND WEATHER SERVICE 117

sequent denudation has worn away the softer rocks on either side.
A similar explanation applies to Sugar Loaf mountain, south of Fred-
erick.

The Piedmont Plateau, as it has thus been bounded on the east
and west, extends from Alabama to New York, and an homologous
district can be traced farther northward, where it embraces Rhode
Island, Connecticut, Eastern Massachusetts and the coastal portions
of Maine and New Hampshire. Maryland, therefore, embraces only
the small trapezoidal-shaped portion which is included by the Fall
Line and Catoctin mountain, the Potomac and the southern boun-
dary of Pennsylvania.

TOPOGRAPHIC ELEMENTS OF THE PROVINCE.

Viewed from any of the higher points of the Piedmont, such as
the granite knoll just east of Cockeysville or, better, the divide
between the Big and the Little Gunpowder Falls northeast of Glencoe,
the topography resolves itself into three different classes of features.
The first in importance is the broad rolling surface which extends
in every direction as far as the eye can reach. Over this general
surface are low knobs and ridges which seem to rise a little above
the general level of the plateau. Finally, below the general level,
numerous streams have sunk channels and valleys which at first
escape notice, since all except the nearer valleys are masked by the
rolling hills of the plateau upland. The following discussion is
divided into three corresponding sections, namely, the Upland, the
Valleys in the Upland, and the Residual Masses above the Upland.

The Upland.

As has been remarked, the most striking feature in the topography
of the Piedmont Plateau is the very even sky-line given by its many
hills, whose rounded tops rise very nearly to the same plane. Could
the valleys which have been cut out in the plateau be filled again,
it is easy to see what the surface thus restored would look like.

Between the present streams, and at the points farthest from the
channels, the divides have low, flat, convex curves, but as the present
streams are approached the gentle arches of the divides change to
118 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

equally gentle concavities, which are sharply interrupted by gorges.
The restored surface then, would not be a perfectly even one, but
would reveal a country of low, well-defined divides whose streams
flowed through broad, open valleys bounded by gently sloping hills.
This former surface, now a dissected upland, may be easily traced
across Cecil, Harford, Baltimore, Howard and Montgomery counties,
and through portions of Carroll and Frederick. Extensive areas of
the earlier surface that have escaped dissection may sometimes be
found where the land is drained only by very small streams at some
distance from the larger and more active rivers. Such remnants are
especially well preserved in the district along Parr’s Ridge, on the
two circumscribed patches of granite and gneiss, one of which lies
north of Green Spring Valley and the other across the marble belt
to the northwest of Towson, and on the upland between Big and
Little Gunpowder Falls.

This old surface, which seems to approach very closely to the con-
ception of a peneplain, is shown by the Hypsometrie Map of Mary-
land not to be perfectly horizontal but to rise gently westward.
Starting with an average elevation of about four hundred and fifty
feet in the vicinity of the Fall Line, a steady rise of about twenty
feet to the mile brings it to an average elevation of eight hundred and
fifty or nine hundred feet along Parr’s Ridge. This ridge forms
the divide between the streams flowing eastward across the Piedmont
Plateau into the Chesapeake Bay direct, and those which flow first
westward to the Monocacy and thence through the Potomac to the
Bay. Beyond Parr’s Ridge the general surface of the Plateau at first
descends somewhat rapidly, and then, after reaching the Triassic
(Newark) deposits, very gently to the Monocacy. From the valley
of this river the general surface ascends by stages to a bench along
Catoctin mountain, on which Mt. St. Mary’s College and Thurmont
are located, at an elevation of about six hundred feet. The Upland
may thus be considered as divided into two portions by Parr’s Ridge,
and each part will be found to have its own peculiar characters.

It appears, then, that the Piedmont region is much like a gently
rolling plateau, whose surface, traversed from southwest to north-
MARYLAND WEATHER SERVICE.
VOLUME 1, PLATE VIII.
MAP SHOWING PIEDMONT TOPOGRAPHY OF CARROLL COUNTY.
FROM ELLICOTT SHEET, U. S. G. S.MARYLAND WEATHER SERVICE 119

east by the dividing line of Parr’s Ridge, slopes gently eastward and
somewhat more sharply westward. ‘This plateau surface differs from
that of the most widely recognized types of plateaus, since it does
not appear to be in any way dependent upon or the result of the
structural features of the land-mass which it characterizes. In this
respect it stands in strong contrast with the high plateaus of Arizona
which owe their level, even surfaces to the horizontal position of the
strata. Nor can it belong to the class of almost featureless plains,
which appear where seas or lakes have left heavy deposits of sedi-
ments, as is the case of our own Coastal Plain. On the contrary, the
highly inclined and folded ervstalline rocks which compose the eastern
portion of the plateau, as well as the more yielding faulted blocks
of the Monocacy valley, are indifferently bevelled off, and the folds
truncated by the surface of the upland.

The intricate foldings, as well as the great chemical and miner-
alogical changes which the rocks of the Piedmont Plateau have
undergone, indicate that they once formed the deep-seated roots of
more loftv mountain ranges. The sediments of the Appalachian
Province also point to the same conclusion. In order to reach the
surface of the land where they are now exposed to view, these rocks
must have been subjected to long-continued and active erosion. The
reduction of that lofty range could have been accomplished either
slowly by the waves of the ocean, or more rapidly by the steady at-
tacks of the elements. The probabilities are largely in favor of the
second explanation.

As one traces the level of the Piedmont upland beyond the bounds
of the province itself, several interesting facts are learned, which
are important to one who would know the complete history of the
Plateau. Within the Piedmont Province this general surface is
found to cut across the tilted and now deeply dissected beds of the
Newark formation; where these have been removed, the Silurian lime-
stone beneath is seen to be below the general level of the upland. Trac-
ing this surface farther westward the even crests of the Blue Ridge,
North mountain, Warrior’s Ridge, Dan’s mountain, Savage mountain,
and many others seem to properly form elements of this almost plane
120 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

surface. Northward and southward similar elements may be found
such as the crests of Kittatinny and Schooley’s mountaine in New
Jersey, and Massanutten mountain in Virginia. In fact, the Pied-
mont Plateau upland is generally regarded as being but the seaward
remnant of a broad, gently rolling surface, which once extended
westward beyond Alleghany Front, northward along the Appa-
lachians into New York and New England and southward across the
Cumberland Plateau of Tennessee to an unknown distance. This
broad plain was cut indifferently across crystallines and folded sedi-
mentary strata and was produced during the final stages of that long-
continued denudation which has resulted in exposing the roots of the
Piedmont mountain chain. Since the days of its formation, the
surface of this old lowland has been elevated and much dissected by
erosion, but there is every reason to believe that the high mountain
crests are remnants of the once extensive peneplain. This peneplain
was first described and studied in Pennsylvania and New Jersey, and
was named by Professor William M. Davis of Harvard University
the Schooley Peneplain,’ after the mountain of that name whose
crest line is one of the striking remnants of its surface.

The geological periods during which the peneplain was produced
may be determined quite definitely by at least two lines of evidence.
First its surface is found to bevel strata of all ages from the Archean
to the Triassic. This fact fixes its maximum age; it cannot be older
than the youngest rocks upon which it has been carved. The pene-
plain, therefore, must be younger than the Triassic or Newark beds
which it traverses in the valley of the Monocacy, in the New Jersey
area and in the broad valley of the Connecticut. In the second place,
any strata found deposited upon the peneplain must be younger than
that surface, and vice versa the peneplain must be older than those
deposits. Now it is possible to trace the general surface of the
Schooley peneplain to the very edge of the continuous boundary of
the oldest Coastal Plain sediments, and, outside this boundary, scat-
tered outliers of those strata are found resting upon the uneven sur-

* Davis, W. M., “The Rivers of Northern New Jersey,” Nat. Geog. Mag.,
1890, vol. ii, pp. 81-110.
MARYLAND WEATHER SERVICE 121

face of the plain. The geological map of Maryland shows very
clearly how the Maryland portion of the peneplain passes beneath the
Coastal Plain strata, and, indeed, everywhere along the boundary
between the two provinces this relation may be clearly made out.
The diagrammatic sketches forming Figs. 11 and 12 give some idea
of the relations which the topographic features of the two provinces
bear to each other. The new geologic map of Alabama also shows
very clearly how the folded, faulted and planed-off paleozoic rocks
of the southern Appalachians gradually pass beneath the nearly hori-
zontal strata of the Gulf Series of the Coastal Plain. When Davis’
recognized the significance of this burial of the peneplain surface
beneath the Coastal Plain sediments it was believed that the Potomac
group, the oldest and the lowest strata found there, was of Lower
Cretaceous age. As these strata were found to be made up, in their
lowest beds, of materials scarcely removed from their parent ledges,
the surface of erosion on which they rested, 7. ¢. the surface of the
Schooley peneplain, was regarded as the topographic product of
erosion during early Cretaceous times. The peneplain has been often
called the Cretaceous Peneplain for this reason, and consequently the
Piedmont upland was understood to have been produced during Cre-
taceous times. More extended stratigraphic work in the lower hori-
zons of the Coastal Plain, together with careful studies of the verte-
brate fauna and the flora of the Potomac Group, have finally led
Clark, Marsh and others to refer the lower beds of this series to the
Jurassic. A corresponding change must therefore be made concern-
ing the age of the Schooley peneplain and of the Piedmont upland.
Since on the one hand it must be younger than the Triassic beds across
which it is cut, and on the other is at least as old as the late Jurassic
formations which overlie it, the period of denudation during which it
was produced would seem to embrace late Triassic and early Jurassic
times.

Valleys in the Upland.
The valleys which have been incised in the plateau are character-
istic of the province, but they are not all of the same type. One

1 Davis, W. M., ‘“ The Geological Dates of Origin of certain Topographic
Features, etc.,” Geol. Soc. Am. Bull., ii, 1891, pp. 545-548.
122 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

set of valleys is distinguished by their steep sides and narrow chan-
nels, another class has broader valleys with milder bounding slopes
and is not as extensive as the first class. Yet a third class has but
one representative, namely, the Monocacy with its tributaries, which
is distinguished by broad benches at several levels, wandering stream-
courses with steep but low side slopes, and channels in which long
stretches of smooth water alternate with zones of low rapids and
rougher water.

All three classes of valleys are of considerable importance to the
inhabitants of the province. By sinking their channels below the
general surface of the plateau the streams have cut up or dissected
that surface to such an extent that it has become rough and hilly,
making the travelling across country quite arduous. This discom-
fort, however, the streams have themselves partly remedied by mak-
ing their gorge-like valleys just the least bit wider than was needed
for their own use, so that the early settlers found room for wagon-
roads by the sides of the channels, and later comers have taken advan-
tage of the same features in building their steel road-ways. Further-
more, the steep channels, full of little falls and cascades, which are
confined by narrow gorges, offer many sites favorable for the build-
ing of mills and dams. <A brief consideration of the characteristics
and origin of these different types of streams and valleys will there-
fore be of interest.

The lower portion of the valley of Deer creek in Harford county
has almost exactly the characters which distinguished the stream
valleys of the old upland before it was dissected. The rounded hills
slope gently towards the stream, and pass beneath a rather broad
valley floor and flood-plain which accompany the stream for the
greater part of its length. ‘The channel itself has, along its lower
portion, come slightly under the influence of recent uplifts, so that
it is sometimes in a very shallow trench, but most of the time it
wanders through the flood-plain unrestrained by walls. The general
impression gained from a view of the valley is that of a gently rolling
country with broad vallevs and gently flowing streams, just such a
landscape as is presented to the eve of one, who, standing on one of
MARYLAND WEATHER SERVICE 123

the upland remnants, by the aid of the imagination restores the old
surface of the country. In Cecil county two-thirds of the course of
each stream generally flows in such a valley, while the lower third
occupies a more rugged channel.

Those streams which empty into Chesapeake Bay, however, south
of the Little Gunpowder do not present such characters except in the
immediate vicinity of their headwaters. Such streams as the Little
Gunpowder, the Big Gunpowder, the Patapsco and the Patuxent, for
the greater portions of their courses flow through narrow gorges of
gradually increasing depth and width. Although the map shows that
the courses of the streams are often somewhat winding, the topo-
graphic map, or better still an examination of the streams themselves,
reveals the fact that this indirectness in course is not the result of
wanderings over modern flood-plains, but that the gorges themselves
follow more or less closely the swings and turns of the channel.
Along the largest streams, such as the Big Gunpowder and the Pa-
tapsco, there is barely room to admit the railroad tracks and an occa-
sional wagon-road. Among the streams belonging to this class the
channel course is not affected to an important degree by the different
rocks through which it cuts and in this respect differs from certain
other streams to be noticed below.

These streams are also characterized by channels whose varying
grades reveal how recent an event, relatively speaking, was the eleva-
tion which caused the streams to thus entrench themselves below the
plateau. Beginning at the mouth of any one of these streams, as the
channel is followed up-stream, its grade is found to be very steep
for several miles. The distance to which this steep grade extends
depends upon the size of the stream and to some extent upon
the character of the rocks flooring the channel. Plate XIX shows
that the Big Gunpowder has this steepened grade as far as Loch
Raven, or for a distance of something over eighteen miles up-stream
from its mouth. Above this point the Gunpowder runs in a lime-
stone valley for eight miles until reaching Warren Mills, bevond
which the channel is continuously on gneiss, phyllite or serpentine to
its source in Pennsylvania. The easily reducible marble above Loch
124 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Raven has not maintained the steeper abnormal, convex grade main-
tained below that point, and when the gneiss is again reached the
grade has changed to the normal concave character.

Gwynn’s Falls and Jones’ Falls (Plate XIX), streams of about
equal size, have both pushed their steep grades about eight miles
up-stream, reaching Powhatan and the Lake Roland dam respectively.
These are smaller streams than the Gunpowder, and therefore have
not had the volume and the power needed to reduce their grades to
as low a slope, or to push the steep grades back as far as the latter
stream has done. The zone of falls, approximately eight miles wide,
which is here described, marks the position of the zone of displace-
ment, which has been denominated the “ Fall Line.” All these
streams with their gorges and troubled rock-ribbed channels show that
they have not yet succeeded in reducing their courses to even and
matured grades. These immature characters do not generally ex-
tend, however, quite up to the heads of the streams. For several
miles from their sources streams like the Gunpowder, Gwynn’s Falls
and the Patapsco have the broader, open valleys and quiet currents
which characterize mature drainage and, like the lower course of
Deer Creek, reproduce the old upland surface.

Certain tributaries of the streams above referred to occupy valleys
which depart from the normal type of side-valleys of youthful
streams. Instead of being confined between the steep walls of nar-
row, ravine-like gorges, as is usual for the tributaries of large streams
in areas recently elevated, these favored brooks flow through rela-
tively broad valleys with fertile floors, but steep sides. Western Run
and a small tributary of Beaver Dam creek, Dulaney’s creek and Mine
Bank run are a few of the streams belonging to this class. Jones’
Falls is an independent stream which also belongs in this class. Most
of these broad valleys have been opened out on areas of soluble
marble, leaving the surrounding gneiss and granite areas standing
prominently above the lowlands. In the case of the headwaters of
Little Deer creek, however, a broad lowland bordering the stream has
been opened out on the band of yielding and crumbling phyllites,
which runs northeast and southwest across Harford and Baltimore
MARYLAND WEATHER SERVICE 125

counties. The same is true where some of the tributaries of Western
Run cross the phyllite, although in the latter case the stream is flowing
not parallel with but across the strike of the foliation. Besides their
breadth and their arrangement parallel to the general direction of
the structure of the country, these broader valleys are in some cases
also distinguished by containing remnants of the earliest strata of
the Coastal Plain series. These remnants are of two horizons. One
consists of the variegated clays and washed gravels, which form a
portion of the Potomac Formation, and it is found chiefly as small
patches in the Green Spring Valley, in the vicinity of Lutherville and
about Oregon. The other horizon is that of the Pleistocene, whose
deposits consist of gravels and sand brought in by the larger streams.
These deposits are much more extensive than are those of the
Potomac, remnants being widespread over the valleys about Cock-
eysville, Dulaney’s Valley, Green Spring, Mine Bank run, and the
valley of Western Run. The Pleistocene may also be traced along
the narrow gorges of several of the streams which, for portions of
their courses, flow through the open valleys.

The presence of remnants of the Potomac and Pleistocene forma-
tions in these valleys gives some clue to the geological period during
which they were etched out. Since they were sunk below the general
level of the upland they must have been one of the sets of valleys
carved out by streams acting under the revivifying influences of an
elevation just succeeding the period in which the upland was formed.
In the preceding section it has been shown that the upland surface,
whether a peneplain or a surface of advanced maturity, was pro-
duced in the interval between the elevation of the Newark and the
early portion of Potomac time. These valleys are, therefore, younger
than earliest Potomac time. At the same time, since they contain
Potomac deposits, they cannot be younger than late Potomac time.
As these deposits are of later Potomac (Patapsco) age the valleys con-
taining them must be of middle Potomac date. Recent studies in
the Potomac group have led to its being referred in part to the
Jurassic and in part to the Cretaceous, and from the data given above
the date of formation of these valleys is probably very late Jurassic
or early Cretaceous.
126 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

In the western half of the Piedmont Plateau, within the drainage
of the Monocacy river, small level-floored valleys, eaten out along
limestone lenses, are also frequently met with. The limestone of
these valleys is regarded by many as identical with the Cambro-
Silurian limestone of the Great Valley and of Frederick, but a study
of the stratigraphic relations in the Monocacy valley makes it appear
very probable that these lenses were completely buried by the estu-
arine deposits of the Newark (Triassic) formation. No remnants of
this formation were found within these limestone valleys so that it
cannot be definitely asserted that they are of pre-Newark age. On
the other hand the fact that they are invariably occupied by small
streams, which have there developed subsequent courses, rather indi-
cates that these valleys have been developed during more recent
times than have their counterparts in the east.

West of Parr’s Ridge the upland declines rather gradually while
on the phyllites and disappears entirely when the eastern boundary
of the Newark formation is passed. On these yielding rocks a ter-
raced and dissected lowland has been carved out. Its highest level
is an extensive but dissected plain maintaining an almost uniform
height of five hundred feet above tide from the Potomac along
Catoctin mountain to Emmitsburg. This elevation increases slightly
northward in Pennsylvania, but is remarkably constant through Mary-
land and Virginia. Although it was formerly a continuous lowland
extending across the valley of the Monocacy, subsequent elevations
have caused large portions of the surface to be removed by erosion.
The extent of the remnants is variable; large areas may still be seen
about Frederick and to the south, but northward towards Emmits-
burg the surface is represented by areas only a mile or two in width.

Below this higher level the Monocacy has at different periods in
the past cut lower and less extensive valley floors or valley lowlands,
which now appear as broad benches of varying width, overlooking the
present stream channel. At a level of four hundred and fifty feet
or fifty feet below the uppermost surface is the first of these subse-
quent terraces. This is the most persistent and uniform of the lower
terraces and often attains a width of three to five miles. It is best
seen over the district between Thurmont and Emmitsburg.
MARYLAND WEATHER SERVICE 127

Following the present channel of the Monocacy, and sometimes
traceable for short distances up the larger side-streams, is a third ter-
race, the lowest of the old valley floors. It has an elevation of about
three hundred and fifty feet in the vicinity of Frederick and south-
ward, rising very gradually northward where it is more widely dis-
sected and removed. The width is variable, but rarely exceeds a
mile. A’steep slope leads down from the second terrace. Below
this lowest bench the present channels have entrenched themselves
to a depth of one hundred feet or less.

The channel of the Monocacy, though of gentle slope and graded
for considerable stretches, is often interrupted by low unreduced
ledges. It generally lies five or six feet below an extensive flood-
plain which is submerged for more or less protracted periods, several
times a year. Side-streams joining the Monocacy have trenched
the flood-plain during its unflooded periods, and have along their
lower courses developed smaller flood-plains of their own. The chan-
nels of these tributaries are not as perfectly graded as is that of the
main stream, and frequent low falls interrupt them.

The lowlands eroded on the yielding rocks of the Newark forma-
tion are one of the striking features of the Piedmont Plateau through-
out its extent from Massachusetts to Virginia. The lowland of the
valley of the Connecticut river is the most extensive and best known
of these valleys. As the Plateau has there suffered greater elevation
the valley is cut to a greater depth below it than in the case of the
Monocacy, and is therefore a more pronounced depression in the gen-
eral topography of the upland. The valley of the Connecticut, how-
ever, was within the limits of the area covered by the great Ice Sheet
of the last Glacial Epoch, and as a result of modifications imposed
upon it by the ice and the glacial rivers its minor topography is dif-
ferent from that of the corresponding valley in Maryland which did
not come under these influences.

There are then, as has been shown, three types of valleys sunk
below the Piedmont upland: the narrow circuitous gorges with steep
sides and rapid currents and closely fitted by the streams which made
them; the broader, level-floored valleys developed along yielding lime-
128 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

stone or phyllite and occupied by slightly meandering streams which
may later on enter narrow gorges, and the broad even-topped, ter-
raced lowland of the Monocacy and its tributaries.

Residual Masses above the Upland.

As the general surface of the Piedmont Plateau is traced north-
ward into New England it is found that there are several prominent
elevations which rise sharply above the general level of the plateau.
Mount Monadnock, Mount- Ascutney, and Mount Wachusett are
prominent examples of these features. Going southward into the
Carolinas similar prominences may be observed, but more striking
than these is the manner in which the surface may be traced in and
out among the high peaks of the Black mountains, particularly in the
vicinity of Asheville. These various mountains and peaks are evi-
dently portions of the old land area which for some reason was not
reduced during the period of base-leveling that produced the even
surface of the upland. They may owe their present prominence to
one of two causes, either they are composed of rocks of superior resist-
ance to those surrounding them or they were situated so far from the
seacoast that sufficient time did not offer in which the streams could
work back to and reduce them. Mount Monadnock was first de-
scribed as being such a remnant, and its name has been adopted as a
designation for all more or less isolated residual masses left standing
above the general level of the peneplain.

Maryland presents only a few low examples of such monadnocks
above the general upland of the Piedmont. Rocky Ridge and its
fellow, Slate Ridge, both in Harford county, are the best-marked
illustrations of this class of topographic forms. Both ridges have but
a slight elevation, not more than one hundred feet above the plateau
surface, and owe their prominence to the fact that they are com-
posed of unusually resistant rocks. Rocky Ridge marks a band of
quartzite and conglomerate, and Slate Ridge, as its name implies, is
the outcrop of a band of roofing slates which is pinched into the
phyllite. Plate I shows something of the character of the crest of
Rocky Ridge, and a general view of the west side of Rocky Ridge is
given in Plate XVII. The same quartzite which forms Rocky Ridge
occurs along the south side of Green Spring Valley and forms Set-
MARYLAND WEATHER SERVICE 129

ters Ridge at the west end of that depression, but this ridge is less
marked in elevation and not easily distinguished from the other
inequalities of the general surface. In the valley of the Monocacy,
and rising above its floor to an elevation of twelve hundred feet,
stands Sugar Loaf mountain, clearly a monadnock with respect to
the broad, even five hundred foot level of the valley. The moun-
tain is also a monadnock with respect to the Piedmont upland which,
crossing Parr’s Ridge at eight hundred and fifty or nine hundred
feet, was found to decline to six hundred feet along the base of
Catoctin mountain at Mount St. Mary’s College, Emmitsburg.

Summary.

The general topographic features of the Maryland Piedmont
Plateau have been found to be similar to those of the same topo-
graphic province along other portions of the Atlantic Slope. The
most important topographic feature is the rolling surface which forms
the upland of the Plateau. This surface was brought to its former
slight relief by the action of rivers and streams, and was bevelled
down across hard and soft rock indifferently. It has a general gentle
rise westward from an elevation of four hundred feet at the Fall Line
to a maximum of nine hundred feet at Parr’s Ridge, whence farther
west it declines to an average elevation of six hundred feet along the
base of Catoctin mountain. Above this general level rise low resid-
ual masses or unreduced monadnocks, such as Sugar Loaf Mountain
and Slate Ridge, while below the upland narrow gorges have been
cut out, limestone lowlands have been etched, and on the Newark for-
mation broad, terraced valleys have been carved.

THE ROCKS AND THE STRUCTURE OF THE PIEDMONT.

In order to understand the systematic development of the Pied-
mont drainage, the various rocks, their relative resistances and their
arrangement with reference to each other must be considered.

The Rock Types.

The rocks of the Piedmont province may be conveniently considered

in two divisions, an eastern and a western one, as was the topography.
9
130 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

The eastern portion of the Piedmont, eastward from a line joining
Seneca on the Potomac and Manchester, Carroll county, is largely
composed of rocks which are now completely crystalline and show
little evidence of ever having been deposited as sediments. Only a
few scattered areas of the eastern division are composed of semi-
crystalline rocks which have been altered from former sediments to
their present state by the action of great, long-continued heat and
pressure.

The crystalline rocks are probably older than the semi-crystalline
metamorphosed rocks, possibly representing the lower members of
the Paleozoic series to the west, and are generally referred to the
Archaean or the oldest of the geological eras. They include granites,
diorites, peridotites, pyroxenites, gabbros, marbles, quartz schists, and
gneisses. For the present purposes these rocks need not be spécially
discussed. The granites and the closely related diorites differ slightly
in color and in the characters of their dark-colored constituents. They
are both quarried extensively. Both yield to erosion at about the
same rate. The darker, heavier rocks, called gabbro, cover an area
about equal to that of the granites and diorites but are concentrated
about Baltimore, Havre-de-Grace and Rising Sun and in a belt through
central Harford county. On weathering the gabbro usually yields
a characteristic heavy reddish soil due to the large percentage of
original ferro-magnesian constituents. On the accompanying map
(Plate XVI), the gabbro, granite and diorite have all been given the
same symbol with the gneiss which covers the larger portion of the
eastern Piedmont slope. The latter is a normal gneiss of a white, a
dark gray, or blue color, which has been very completely metamor-
phosed by repeated squeezings. It has a complicated structure, shown
by its large and fine crumplings and plications, and is composed of
bands of varying width which often show marked differences in re-
sistance to erosion.

The marbles are completely crystallized saccharoidal masses which
often show dolomitic bands with impurities in the shape of irregular
zones of accessory minerals, such as brown mica, white hornblende,
tourmaline, ete., resulting from a recrystallization of the original
MARYLAND WEATHER SERVICE. VOLUME |, PLATE IX.

 

 

 

 

 

Fic. 2.-HERRING RUN, BALTIMORE COUNTY.
MARYLAND WEATHER SERVICE 131

impurities. Bands of quartz schist, composed chiefly of secondary
quartz and divided into numerous planes by layers of flaky mica often
accompany the marbles from which they are sharply defined, while
they change gradually into the gneisses which may be present on
the other side. The quartz schist is closely allied mineralogically to the
metamorphosed sandstone and conglomerate now appearing as the
Cambrian quartzite of Rocky Ridge in Harford county. Next in
importance to the quartzites and schists are the peridotites and
pyroxenites. These are dark, medium fine-grained rocks of consid-
erable specific gravity which occur, not over large areas, but in
restricted patches. One long, narrow, irregular band is located in
northern Harford county running northeast and southwest, another
is about fifteen miles long and runs northeast-southwest midway be-
tween Sykesville and Woodstock. Just north of this band is a large
circular area at Soldier’s Delight and an irregular one lies between
the latter point and Catonsville. Both varieties of these basic rocks
are subject to a constructive alteration or chemical change which pro-
duces serpentine or steatite according as the original rock was perido-
tite or pyroxenite. The Bare Hills is composed of a small patch of
the altered rock serpentine.

A narrow interrupted diabase dike extends from a point west of
Guilford, northward and eastward through Worthington Valley past
Parkton, and so through the northwest course of Harford county out
of the state. This rock weathers very easily into a red soil, leaving
irregular fragments scattered over the surface or in the loam. Since
in this portion of the state it does not show any characteristic topo-
graphic form it has been colored like the gabbros with which it 1s
closely related.

The evidently clastic rocks of the eastern Piedmont are the
quartzite already mentioned in connection with the quartz schist
and detached areas of the same phyllites which chiefly underlie the
western division. Beginning in a small point north of Reisterstown,
the phyllites extend northward, then turn northeastward, gradually
widening near Parkton and pass out into Pennsylvania. These rocks
are finely laminated sericite and chlorite schists, which are much
132 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

contorted and finely puckered in the eastern division. They yield
very readily to erosion. In their midst about Cardiff they have
pinched in a deep lens of fine-grained blue-black roofing slate, on
either side of which is a band of the quartzite conglomerate. The
slates, the quartzite and the conglomerate, and the phyllite are dis-
tinguished by separate symbols on the map.

On the west the rocks of the Piedmont Province are semi-crystal-
line, crystalline and clastic in nature. The semi-crystalline rocks
are the phyllites and their associated crystalline fine-grained lime-
stones. The phyllites, which are much faulted and puckered, often
hard to separate from the gneiss of the eastern division along the
eastern slope of Parr’s Ridge, become less and less disturbed west-
ward. The crystalline limestones, or fine-grained marbles, occur
particularly in the vicinity of Westminster and Union Bridge. The
eruptive rocks of a basic character found in the phyllites have been
so highly altered by pressure that they now appear as chloritic and
epidotic schists. These once wholly crystalline rocks are probably of
Archaean age; but other basic eruptives in the form of diabase dikes
and sheets were pushed up through the Newark strata during Meso-
zoic time. These dikes are but little altered, but the baking to which
they subjected the adjacent sandstones and shales has hardened the
latter and changed the prevalent red color to a bluish-black or a
deep brown.

Among the remaining sedimentary rocks in the western portion
of the Piedmont are the soft red shales and sandstones of the Newark,
the Shenandoah limestones of the Frederick valley and the Cam-
brian quartzites.

Topographic Valences of the Rocks.

The various rocks enumerated above, by reason of the different
degrees of resistance which they offer to weathering and erosion,
control in great measure the topographic features of the province.
Although the facts at hand are insufficient for a detailed discussion
of the topographic characteristics of each rock type, they may be dis-
cussed under the following heads:

The gneiss, granites and gabbro all offer about the same resistance.
MARYLAND WEATHER SERVICE 133

They form by far the greater portion of the general surface of the
plateau, and are characterized by rounded hills and gentle slopes on
the old upland surface. The steep walls of the recent gorges and
the slopes of the hills leading down to the broad valleys are also
characteristic of these rocks. With them have been grouped the
diorite and the diabase because of their small areal extent and essen-
tially similar topography. ‘There are bands of varying resistance dis:
tributed throughout the rocks of this group, particularly the gneiss,
which is by nature of variable lithologic character. These zones are,
however, so irregular in size and position that for the present one
cannot say more than that they follow the general direction of the
gneiss foliation. They are expressed in the topography by occa-
sional expansions or contractions in the gorge-floors and by softening
or intensification of the steep contours of the valley walls.

Next in areal importance come the phyllites of the western and the
northern central portion of the Piedmont. In the tongue-shaped area
of the latter section the phyllites produce more rounded hills and
gentler slopes than are general on the gneiss. Where streams cross
the band, as Black Rock run does, for example, the valleys are much
broader and have milder channel slopes than those which charac-
terize the same streams in the gneiss. Deer Creek has developed a
fair-sized subsequent tributary on the phyllites, and other streams
crossing it sometimes send out little feeders along the strike of the
formation. The large area of phyllites forming Parr’s Ridge and
part of the western slope present very similar topography but on a
more extensive scale. The small headstreams of the Monocacy drain-
age carve deep narrow valleys, but they have more rounded slopes
and wider floodplains near their headwaters than do corresponding
small streams on the eastern slope. The prominence of Parr’s Ridge
itself is due to its location at the headwaters of the two opposing
drainage systems and not to any marked resistance of the phyllitic
rocks forming it.

Folded in with the phyllites of the western division are lenses of
limestone and marble, whose high degree of solubility has permitted
the hollowing out of broad flat-bottomed valleys. These valleys find
134 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

their counterparts on the eastern slope of the plateau in long narrow
valleys which have been opened out on curving bands of marble.
Green Spring valley, Worthington’s valley and the related meadow-
lands along Western run are typical illustrations. Long Green valley
on the Baltimore and Lehigh Railroad is more nearly like the level-
bottomed, lens-shaped valleys of the western portion. About Luther-
ville several smaller areas of marble coalesce and form a broad, open
lowland, now slightly dissected. Not all the marble bands of the
eastern division, however, have been etched so completely. The
two parallel bands of marble lying southwest of Ellicott City are
crossed by headwater streams of the Little Patuxent, which are now
just beginning to work out valleys little lower than the general upland
level. These limestone and marble bands are the weakest topographic
factors in the Piedmont complex.

Next to the limestones and marbles in weakness come the various
members of the Newark formation. These shales, sandstones and
limestones form the benches and terraces along the Monocacy river
and are wearing away only less rapidly than the limestones and mar-
bles. Where surfaces of erosion are preserved in this formation, as
on the benches and terraces, the topography is almost featureless.
The slopes from one level to a lower one are usually seamed by small
ravines of slight depth and moderate inclination. When streams have
cut down to the present level of the Monocacy they have compara-
tively broad bottomlands along their lower courses and have already
advanced beyond Infancy even for some distance up-stream. All
these characters obtain in spite of the comparatively recent periods
of uplift which the Triassic district has undergone. The diabase
dikes which cut the other rocks of the Piedmont and are in the
western portion at least of Triassic age, weather so readily that they
are of no topographic value when they occur in the gneiss and lime-
stones of the eastern portion. Where they have baked the Triassic
shales and sandstones west of Parr’s Ridge, however, their presence
is revealed by low swells upon the otherwise gently undulating plain.
When a stream crosses the diabase dikes the valley slopes of the
stream are steepened and numerous fragments occur in the slightly
roughened channel.
MARYLAND WEATHER SERVICE 185

The most resistant rocks, those forming the most prominent topo-
graphic features, are the serpentines, the slates, the quartz schists
and the quartzites. The most extensive of these rocks are the ser-
pentines and steatites which, as has been mentioned, are alteration
products from peridotites and pyroxenites. As these rocks are the
results of changes near the surface they offer much fewer opportuni-
ties for chemical and physico-chemical processes of disintegration than
do rocks of a different nature. They therefore now stand out as low
ridges or rounded knolls above the surrounding gneiss. The serpen-
tine is most striking topographically where it is crossed by streams,
for then its resistance to weathering and to the wear of running water
cause it to form steep, boulder-strewn, rocky gorges with steep,
rough channels. The best illustrations of these characters are. found
where the North Branch of the Patapsco crosses a broad band of ser-
pentine several miles north of Marriottsville; where Winter’s run
crosses the same band, and farther north, in Harford county, where
a tributary to Deer creek crosses a band of similar rocks. The
rounded but barren slopes of the Bare Hills, and the elevated, irreg-
ular interstream area of Soldiers’ Delight, rising to one hundred feet
or more above the surrounding surface, are each caused by the pres-
ence of large masses of this rock.

The serpentines are only slightly less prominent than the slates,
the quartzites and the schists. These three types form the most
prominent eminences above the upland. The quartz schist, or Set-
ters Ridge quartzite, as it is sometimes called, forms a distinct ridge
overlooking the marble-floored Green Spring and Mine Bank run val-
leys. . In Harford county the prominent elevation of Rocky Ridge is
maintained by a heavy band of quartzite and metamorphosed quartz
conglomerate whose unyielding qualities are also responsible for the
rock towers and turbulent channel where Deer creek crosses the ridge
at “The Rocks.” A near view of the water gap and the ridge is
shown in Plate I. Slate Ridge is a somewhat broader and less marked
ridge situated north of “ The Rocks,” and is caused by the presence
of the band of slates between Cambria, Md., and Peachbottom, Pa.
Although the slates of Slate Ridge are probably stratigraphically re-
136 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

lated to the quartzites of Rocky Ridge, they have been separately col-
ored on the map because of their lithological difference, while for a
like reason the Setters Ridge quartzite which is probably a product of
fumarole action* has been classed with the Rocky Ridge quartzites
because of their lithologic similarity.

In conclusion, it may be said that the Piedmont Plateau rocks pre-
sent different types whose topographic expressions are sufficiently
dissimilar to permit of the divisions which have been discussed.
These divisions have been represented on the map forming Plate
XVI, and the symbols have been arranged, not in a chronological,
but in a topographical order. Those rocks which are the most
resistant and form the most prominent features stand first at the head
of the column. They are succeeded by weaker and weaker rocks
until the soluble limestones and the incoherent Coastal Plain deposits
are reached.

Structure of the Predmont.

Whatever may have been the original structure and the strati-
graphical relations between the various semi-crystalline and crystalline
rocks of the Piedmont Plateau, all traces of these features have been
destroyed by the profound dynamical metamorphism to which they
have been subjected since their formation. This metamorphism has
induced in the rocks a secondary foliation by arranging the min-
eral constituents in long parallel lines and planes, but this folia-
tion bears no close relation to the possible original bedding planes of
the rocks. A cross-section of the plateau shows that the foliation
planes dip steeply east and west down towards an axial line which
crossing the Potomac near Great Falls proceeds northward past
Gaithersburg and Westminster into Pennsylvania. On the western
side of the axis of this fan-like structure the strike of the foliation of
the phyllites with their infolded lenses of marble is parallel to the
axis. On the east the gneiss, with its infolded phyllites and marbles,
keep a northeastward course to the latitude of Westminster, then
make a sudden turn to the eastward and, following this new direction

1See Md. Geol. Survey, vol. i, 1897, p. 163.
*Thus it appears that the structural axis is not related to the boun-
dary between crystalline gneiss and semi-crystalline phyllites.
MARYLAND WEATHER SERVICE 137

for some miles, the bands of marble, quartz schist and gneiss again
turn northeastward. The arrangement of the marble in long parallel
bands which make a sudden eastward curve with most of the Paleo-
zoic strata of Pennsylvania is suggestive of an original Appa-
lachian structure. No reliance, however, may be put upon these
appearances as indicating the original relations to the gneiss.

The western half of the fan shows a decreasing amount of defor-
mation, although the blue and white Paleozoic limestone about Fred-
erick shows a very considerable crumpling of its bedding planes.
Upon the eroded surface of the phyllites and the blue limestone rest
the beds of the Triassic sandstones and their intercalated diabase dikes
and sheets. The latter are deeply and thoroughly broken up into
angular blocks by a great number of fault planes produced prior to
the formation of the upland. ‘any of the fault blocks have been
greatly changed from their originally horizontal attitudes, while some
may still retain their early positions.

RELATIONS OF STREAMS TO STRUCTURE.

The structure of the Piedmont Plateau is so different from that
of most portions of the earth’s surface that the problems connected
with the relations between it and the drainage lines found thereon
are much simplified. Although the true structure of the Piedmont
is probably very much more complex than that of the Appalachian
province, the land surface has undergone so many partial or complete
repetitions of the topographic cycle that all the influences which
original foldings and faultings may have exerted are now unimpor-
tant. For this reason it is impracticable, in the study of the Piedmont
drainage, to apply the more detailed refinements which Davis, Hayes,
Campbell’ and others have used so successfully in studying the
Appalachian streams.

Present Discordant Locations of Streams.

Any map giving the drainage of the state will show that the
streams flowing down the eastern slope of Parr’s Ridge to the

*Davis, W. M., “The Rivers and Valleys of Pennsylvania,” Nat’l Geog.
Mag. i, 1889, p. 183. Hayes and Campbell, “‘ Geomorphology of the Southern
Appalachians,” Nat’l Geog. Mag. vi, 1894, p. 63.
188 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Chesapeake follow approximately parallel courses which have a gen-
eral southeastward trend.

The general trend of the stream courses is almost exactly at right
angles to the slightly eastward curving, southwest-northeast strike of
the foliated crystalline rocks which make up the complex series of
the Piedmont. As pointed out above, these crystallines embrace
numerous bands of resistant rocks alternating with zones of more
yielding character. Although resembling the Appalachian mountain
district in this respect, even the main stream courses of the Piedmont
do not pass from one yielding band to the next as they do in the
Appalachians, see Fig. 9, but appear quite indifferent to such varia-
tions. For example, the Big Gunpowder pursues a course wholly
independent of the numerous broad marble bands which it crosses,
while its tributaries—West Branch, Western Run and Piney Run—
also traverse indifferently gneiss, phyllite or limestone. The head-
waters of the Patuxent south of Marriottsville, the streams of Worth-
ington’s valley and Gwynn’s Falls near Pikesville are further in-
stances of the Jack of co-ordination between the Piedmont rocks and
the streams flowing across them. Evidently the streams of the eastern
portion of the Piedmont have not long been located in the rocks
now exposed or else the law of divides on hard rocks, valleys on soft
or yielding ones here finds many exceptions to the rule.

Among the streams of the western section of the Piedmont occur
many similar cases of unadjusted or discordant streams. The small
portion of the western section shown on the map, Plate XVI, reveals
several such cases even among the smaller streams where adjustments
are usually most marked. The larger geological map of the state
shows a number of westward flowing streams whose courses appear
to be quite unaffected by the presence of limestone lenses. The
Monocacy itself pursues a course which is at present rather indepen-
dent of the rocks it crosses. From Emmitsburg southward for thirty
miles the main stream and its tributaries flow back and forth across
soft shales or sandstones and several times cross the harder diabase
dikes. When opposite Lewistown the stream leaves the Newark
formation and for twenty miles follows the great band of Shen-
MARYLAND WEATHER SERVICE 139

andoah limestone forming Frederick valley. Not content with this
selection the Monocacy again changes, this time from limestone to
phyllite, and after meandering back and forth across limestone and
phyllite, finally cuts across a corner of the Seneca creek Triassic sand-
stone to join the Potomac. So imperfectly adjusted a course as this
could hardly have been developed upon the rocks of the Monocacy
valley as now exposed. The long lenticular area of limestone would
surely have exerted control enough to confine the growing stream
within in its boundaries.

To sum up it is clear that, as a whole, the streams of the Pied-
mont Plateau follow courses which have not been strongly influenced
by the arrangement of the rocks now exposed to view. Many cases
of marked discordance can be found not only among the larger, more
powerful streams, but also among the smaller, younger streams where
adjustments are most common.

Normal Arrangement 1s Accordant.

If one attempts to construct in imagination the general drainage
plan of the Piedmont, as it would appear after having developed
through a normal topographic cycle, the present unadjusted drainage
stands out quite sharply through contrast. Following on Plate
JII the general trend of the structure, and supposing that both
the Susquehanna and the Potomac through their size were able to
maintain their present courses, the general features of the smaller
drainage lines may be outlined as follows. The side streams starting
from the Potomac and the Susquehanna would be working along the
strike of the gneiss, phyllite, limestone, ete., and thus be able to cut
out their valleys easily and rapidly. The north and south drainage
would thus have distinct advantages over the streams flowing east-
ward to the ocean, as the latter streams would have to cross the
resistant as well as the yielding strata. While one of these eastward
flowing streams was attempting to reduce the harder bands a stream
working its headwaters from the north or from the south along one of
the yielding bands weuld easily be able to intercept the less favored
stream and carry its headwaters off along a course parallel with the

strike. The least resistant bands, such as the phvllite extending
140 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

southwest from the Susquehanna or the limestones running north-
ward from near Point of Rocks, would determine the location of the
principal valleys; areas of marble, such as those forming the Texas,
Dulaney and the Green Spring valleys, would be obtained by one
stream system, while resistant bands, such as the serpentine strip east
of Sykesville, would form marked ridges and divides. Such unad-
justed courses as that of the lower Big Gunpowder which flows indif-
ferently through granite-bound gorges or broad, marble valleys, or
that of Gwynn’s Falls which, flowing out of the gneiss, crosses the
end of the long tongue of the Green Spring valley marble and turns
back into the gneiss again without developing even a fair-sized sub-
sequent along the marble, would not develop under the conditions of
a normal cycle.

In general, normally adjusted and accordant drainage lines from
the Potomac to the Susquehanna would have located the main divide
of the Piedmont along a line running northwest from Baltimore.
Secondary divides running northeast and southwest at either end of
the main divides would be demanded by the streams flowing into the
Monocacy and the ocean. This arrangement with its numerous trel-
lised streams, Fig. 9, would be very different from the present plan
in which the main divide runs northeast and southwest and the prin-
cipal drainage lines are southeastward, while the stream patterns,
instead of showing the results of adjustments, pursue random courses
which branch in tree-like patterns across hard and soft rocks alike.
The question naturally arises, Why do the streams show so little
regard for the structure of the province?

Causes of Present Discordances.

It appears impossible to explain this discordant drainage by appeal-
ing to any of those ordinary phenomena which accompany uninter-
rupted stream development. The streams under discussion are en-
trenched to a depth of from one to three hundred feet below the
general upland surface of the plateau. If they originated upon this
upland, and are now sunk below it simply as the result of uplift,
then they should now exhibit the trenched but well adjusted courses
of streams which have attained to Maturity, for that was the stage
MARYLAND WEATHER SERVICE 141

in the topographic cycle reached by the upland before it was given
its present elevation. Since it is inconceivable that they could have
developed such courses upon the Piedmont rocks under normal con-
ditions, it is necessary to conclude that the present drainage lines
were developed upon some other surface under other conditions and
that the pattern thus independently produced has been impressed upon
the Piedmont in spite of its lack of accord with the structure of the
latter area.

The development of drainage along lines independent of the struc-
ture of the deeper rocks beneath it is not an unknown phenomenon,
although it is not often reported. Those portions of the earth’s sur-
face which were the seat of widespread glaciation during the Glacial
Period, namely, northern North America and Europe, had their
pre-glacial topography more or less completely marked by the de-
posits which the retreating ice sheets left. Upon this new, con-
structional, glacial topography new streams of a peculiar kind have
originated, and pre-existent rivers have either been blotted out or
been materially modified in courses and directions. As the new or
modified streams cut down through the glacial drift they have en-
countered the underlying rocks and have established their courses
upon them. These courses, however, having been assumed on the
glacial cover are independent of the subjacent structures and their
newness is evidenced by the unreduced ledges which cause the many
falls and rapids of the streams within the glaciated districts.

The famous cataracts of the Nile are due to the fact that the river,
cutting down along a course taken on the surface of Cenozoic de
posits, has reached a completely buried, irregular surface of granitic
rocks. The Nile first took its course along the slopes of the upper-
most rocks. Later, when revived by a geologically recent uplift, it
deepened its channel until the granitic ledges became barriers to
further downward cutting at those points. A very similar case is
that of the rapids in the Grand Canyon of the Colorado. The
Paleozoic and younger strata forming most of the canyon walls
buried beneath them the Archaean gneisses and granites which the
Colorado has now uncovered after cutting down through the softer

mantle.
142 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

In all of these cases the streams are more or less closely following
the courses which they established upon a cover of overlying rocks.
After sufficient time has elapsed the covering strata were removed
and the streams remain following discordant courses across the older
and once buried rocks. There is good evidence in the outliers
remaining to show that the eastern portion of the Piedmont Plateau
was formerly partly buried beneath a mass of sediments belonging
to the Coastal Plain. Similarly, in the western division, the strati-
graphic conditions of the main body of the Newark formation and the
scattered positions of remnants and gravels of the same indicate
that these deposits once stretched over considerable areas of the
limestones and phyllites now exposed to view. The thicknesses of both
series of rocks were sufficient to quite mask the buried topography
and give surfaces entirely independent of the former ones. It is
apparent, then, that the conditions necessary for the development of
drainage along lines independent of the structure of the Piedmont
Province have existed in Maryland. These conditions obtained im-
mediately antecedent to the present, and there is every reason to
suppose that they were the controlling factors in the development of
the present discordant drainage. On the east the irregular branching
of the eastward flowing streams closely resembles the general pattern
of the streams of the Coastal Plain province, compare Plates V and
VII, while the general southeastward direction of their chan-
nels is in accordance with the general dip of the Coastal Plain sur-
face and strata. On the west the same wandering courses charac-
terize the Monocacy and its tributaries, where they cross the meta-
morphosed or semi-metamorphosed rocks, as are to be found upon
the yielding masses of the Newark beds. Moreover, if the Triassic
rocks be restored over the areas whence they have been removed it
appears that the Monocacy occupies a longitudinal position just
where it would naturally develop if the elevation of the land was
not sufficient to reveal the underlying rocks.

More detailed evidence of the origin of the Piedmont streams will
be found in a special study of that problem given below. This shows
that the streams, after developing courses which were characteristic
MARYLAND WEATHER SERVICE. VOLUME |, PLATE xX.

 

 

Fic. 1.-PATAPSCO VALLEY AT THE MOUTH OF BRICE’S RUN, BALTIMORE COUNTY.

 

 

Fic. 2.-PATAPSCO VALLEY AT ILCHESTER, ON BALTIMORE AND OHIO RAILROAD.
MARYLAND WEATHER SERVICE 143

of Coastal Plain streams, cut down through the Coastal Plain and
Newark covers and impressed themselves upon the underlying struc-
tures. They thus belong to the class of superimposed rivers. Ex-
amples of such drainage from other portions of the world have been
cited above, but they are not lacking from districts nearer home. In
Texas’ streams and topography have been found which show signs
of similar superposition from the blanket of the Coastal Plain sedi-
ments. In Connecticut’ the lower course of the river of the same
name departs at Middletown from an easy course along the Triassic
sandstones, and turning to the southeast enters a deep gorge in the
gneiss, which it follows to Long Island Sound at Saybrook. This
aberrant position is attributed to superposition from the surface of a
former northern extension of the Coastal Plain whose nearest repre-
sentatives are now found on Long Island.

GENERAL TOPOGRAPHIC HISTORY OF THE PIEDMONT PLATEAU.

Reviewing the topographic features of the Piedmont Plateau, the
succession of events and the stages in the topographic evolution of
the province may be briefly summarized as follows: After the cessa-
tion of those movements which folded the sediments of the western
interior seas into the Appalachian mountain system and raised them
higher than the eastern crystalline land areas whence the sediments
had been derived, the Piedmont district was slightly depressed and
long shallow bays were formed in which the muds and sands of the
Newark formation were deposited. How much time this required
cannot be ascertained; but long before the end of Jurassic time these
sediments had been consolidated, the bays drained of their waters,
and the strata uplifted and broken into a multitude of blocks. Vol-
canic action also had forced in between the strata sheets of heavy
dark-colored lavas. Then came a long period of terrestial quiescence
during which the broad, even expanse of the Schooley peneplain was
stretched across the variously arranged rocks of the Piedmont and

Tarr, R. S., “Origin of some Topographic Features of Central Texas,”
Amer. Jour. Sci. (3), 1890, xxxix, 306-310. ‘‘ Superimposition of the Drainage
in Central Texas,” ibid., x], 359-361.

*Kummel, H. B., “Some Rivers of Connecticut,” Jour. of Geol., 1893, i,
371-393.
144 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

the Appalachian regions. This peneplain probably extended fifty
to one hundred miles beyond its present eastern boundary. This
period of quiet ceased in late Jurassic time, being brought to a close
by a slight elevation which permitted the fashioning of small hme-
stone valleys below the general surface of the eastern Piedmont por-
tion. This elevation was of short duration and gave place to the
strong eastward tilting which permitted the westward transgression
of the upper Potomac formations and later groups.

After this the land oscillated up and down causing the series of
submergences and elevations which are recorded in the various strata
and unconformities of the Coastal Plain series. During most of these
oscillations of the eastern portion, the plain beyond Parr’s Ridge stood
continuously above sea-level, and the rivers, steadily working on their
valleys, reduced many of them very nearly to base-level, leaving the
ridges and mountains between to indicate the former higher altitude
of the country as a whole. As these base-leveled valleys were pro-
duced during Tertiary time the general plain to which they were
reduced, now 500 feet above tide, is called the Tertiary peneplain.
At the close of Tertiary time a movement of the lands bordering the
west permitted the sea to rapidly transgress upon the Piedmont
Plateau almost to its western limits.’

The blanket of soil, which had been produced by long exposure to
the atmosphere, was rapidly and incompletely worked over into the
Lafayette formation and spread out as a thin mantle of irregularly
stratified gravels, sands and clays. Again a period of elevation and
erosion came on, during which deep gorges were cut in the Piedmont
Plateau by the streams which originated on the Lafayette surface.
Large areas of Lafayette materials were stripped from the surface of
the crystalline rocks and carried down into the stream valleys. Along
the Monocacy valley this elevation initiated the cutting out of the
second terrace, which lies below the upper floor or Tertiary peneplain
level.

The post-Lafayette elevation and period of erosion was followed by
a number of oscillations which are recorded in the various deposits

1Concerning the extent of this transgression, see chapter on the Coastal
Plain, p. 77.
MARYLAND WEATHER SERVICE 145

of Pleistocene age. Pleistocene time closed with a decided elevation
of the Maryland Piedmont Plateau causing the streams to trench
their valleys, and to cut narrow gorges in the underlying gneisses
and other foundation rocks. Although the streams west of the Fall
Line are still at work reducing their channels, the portions of their
valleys which are east of this line have, after this elevation, in common
with the Coastal Plain, been depressed and converted into estuaries.

ECONOMIC PHYSIOGRAPHY.

In studying the Coastal Plain the physical features of that province

were found to exert considerable control over the industries and

habits of the people. The topography of the Piedmont Plateau has

likewise influenced the settlements and the occupations of those who
chose this region for their home.

Soils.

The early settlers, having to raise all their food, naturally sought
out the best locations for their broad farms and beautiful estates. On
their arrival they found two general classes of farmlands.

The first class embraced the somewhat rolling but extensive tracts
of the interstream upland areas. The soils were found to be good
producers of corn, wheat and grass, and the surface not so rough as
to make its cultivation forbiddingly difficult. The long continuous
tracts of these interstream areas also made traveling easy as long as
one stayed on the upland, while the stream valleys were shut in and
narrow. For these reasons, probably, the various stately manor lands
were laid out where the upland expanses were greatest; and the man-
sions surrounded by fine groves and broad fields were located on the
most promising of the small plateaus. In the earlier days the crops
from these broad upland farms were among the richest in the state
and rivaled those of the Eastern Shore.

The second class of farmlands comprised the alluvial loams and
sandy flood-plains along the streams. These lands are generally
restricted in area, since the valley bottoms are usually narrow and
limited in extent. Where streams have opened out lowlands on the
marble and limestone lenses rich lands of considerable extent offer

most favorable farm sites. The lands along the streams have the
10
146 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

advantages of running water and good springs from the hillsides,
they are not as well drained, however, as are the lands of the
upland, and they are subject to damaging floods. Comparatively few
settlers chose the valley lands at first.

A marked exception to the above rule is found in the Monocacy
vallev, where the farmlands are all located on the several benches
and terraces leading down to the river or on the low bottomlands
belonging to it. So little of the old upland is left that the condi-
tions of occupation are quite different from those farther east.

Streams.

While the farming class were searching for good soils and favorable
homestead sites, the manufacturers and millwrights were seeking
favorable locations for mills, dams and flames. The streams of the
Piedmont Plateau yielded a great abundance of water-power, and
soon mills dotted the vallevs. Each section early came to be sup-
pled with its grist mill, and in due time cotton mills were also built.
These industries in time became of great importance. The
flour mills are now generally abandoned, however, only a few of the
most favorably situated ones having been able to maintain them-
selves against western competition. The cotton mills have held out
much better, because it has not been until recent years that southern
cotton has been spun and woven at home.

The water-power which the Piedmont streams furnish is not
the only wealth which they bring to the state. The land movements
during late geological time have caused the streams to trench their
courses considerably, and in so doing have rendered accessible the
building stones which were previously hidden beneath the surface.
The granite now extensively quarried at Port Deposit would not be
so easily obtained and shipped had not the Susquehanna river cut its
deep gorge. The locations of the serpentine quarries of Harford
county are determined to a greater or lesser extent by the streams
which intersect the rock. A formerly important soapstone quarry on
Winter run in the southeast corner of Carroll county was made pos-
sible only through the fact that the stream had there cut a deep gorge
in a long band of steatitic serpentine. Along the Patapsco and Jones’
MARYLAND WEATHER SERVICE 147

Falls many quarries of granite and gneiss have been located, because
the stream gorges offered favorable openings or transportation
facilities. :

It is interesting, by way of contrast, to compare the different con-
ditions under which the Cardiff-Delta slates are quarried. As no
stream cuts across Slate Ridge in the vicinity of those two settle-
ments, the quarries have been located along the summit and are
worked entirely from above. This is the most difficult way to attack
the slates, and as there is no natural drainage for the quarries, the
water which is constantly accumulating in the pits greatly increases
the cost of working.

Lines of Communication.

The valleys and ridges of the Piedmont Plateau furnish excellent
examples of the way in which topographic features influence com-
merce and human activities.

One of the first acts of the early settlers of the Piedmont region
was to lay out highways. These early roads were not always located
advantageously with reference to the topography, but both the divides
and the valleys were extensively employed. When the better turn-
pikes came to be built, however, they were almost without exception
built along the divides. The reason for this was that fills and
bridges were thereby avoided and better drained roadbeds, not sub-
ject to floods, were obtained. Radiating in all directions from Bal-
timore, these old pikes may be followed into almost every corner of
the state, and their location on the more elevated ridges enables the
traveler to obtain beautiful views of the richly wooded, rolling upland
and tree-filled valleys.

With the advent of the canals and railroads more even grades
were demanded and sought for. They were found by following the
larger valleys.

The canals were built to overcome the obstructions to navigation
which the Fall Line rapids occasioned, even in the larger streams
such as the Susquehanna and the Potomac.

One of the early canals was the Susquehanna Canal, built along
the east shore of the Susquehanna river in order to transport mer-
148 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

chandise from the limits of navigation at Port Deposit northward
along that stream to the Pennsylvania line. This canal has now
wholly fallen into disuse.

Another early and successful canal was constructed around the
Great Falls by the Potomac Company. To obtain the necessary
water and the most favorable grades this channel, now part of the
Chesapeake and Ohio Canal, was laid out along the north bank of
the Potomac, taking advantage of the natural trenches cut by that
river. This canal was long the cheapest and best means of trans-
portation between the coal and wheat lands of Allegany county and
tidewater.

Since the era of railway construction began every advantage has
been taken of the topographic features of the country. The Balti-
more and Ohio Railroad crossing the Piedmont Plateau from tide-
water found an easy exit from the depression about Baltimore and a
gentle though crooked grade to the crest of the divide by following
up the South Branch of the Patapsco river to Mount Airy and then
along the Monocacy drainage to Point of Rocks.

The Western Maryland Railroad striking north and then west-
ward could not utilize the lower course of the North Branch of the
Patapseco on account of its narrow valley and very crooked channel.
By following the broad, well-graded valley of Gwynn’s Falls (see
Plate XIX, fig. 2), as far as Emory Grove, however, an easy de-
scent was found into the more favorable upper course of the North
Branch of the Patapsco and thence an easy grade led to the sag in
the divide at Westminster. A branch of the Western Maryland road
running north from Emory Grove follows the Gunpowder-Monocacy
divide as far as Manchester.

The Northern Central Railway enters the state from the north by
following down the main branch of the Big Gunpowder and does not
leave this stream until at Phoenix Mills the broad marble lowlands
about Cockeysville open out and offer an easy crossing to the valley
and gorge of Jones’ Falls, which it follows down to Baltimore from
Lake Roland.

A striking example is afforded by the Baltimore and Lehigh Rail-
MARYLAND WEATHER SERVICE 149

way which takes advantage of the gorge of Deer creek to penetrate
Rocky Ridge. Were it not for the aid thus rendered by the creek
the engineers of the road would have been obliged to tunnel through
the obstruction or else have gone a number of miles out of a direct
course. Deer creek would not have been located across the quartzite
and so could not have cut the gorge had it not accidentally taken
this position while flowing on the Coastal Plain covering from which
it was superimposed upon the quartzite. Besides the railway a
county road also utilizes this gap and there are reasons to suppose
that before the advent of the white man the Indians also used it as a
thoroughfare.

In conclusion it appears that the topography has very materially
controlled the settlement and economic development of the Pied-
mont Plateau by determining the location of the farms, the mills,
and the railroads.

Tue APPALACHIAN PRovINcE.

BOUNDARIES OF THE PROVINCE.

The Appalachian Province of Maryland embraces what is com-
monly known as Western Maryland. The eastern boundary of the
province is formed by Catoctin mountain, while the western limits
are artificially confined by the western boundary of the state, although
topographically and structurally the province continues westward
until it merges gradually into the lowlands of the Ohio drainage.
To the north and south the topographic features of the province reach
far beyond the limits of our state. The broad lowland of the Great
Valley and the many parallel even-crested ridges with intervening
valleys, which are so characteristic of the province, extend from
central Alabama and Georgia northward through Maryland and
then across Pennsylvania until they disappear in the plateau country
of southern New York.

General Topographic Features.

The topography of the Appalachian Province is more varied, more
picturesque and grander than that of either of the other two prov-
inces. In its eastern part the broad and somewhat serrated crests
of the Blue Ridge and Catoctin mountains overlook the broad, gently
150 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

rolling floor of the Cumberland or Hagerstown valley, which is
watered by Antietam and Conococheague creeks, streams of some
size that have sunk meandering trenches to depths of seventy-five or
eighty feet below the general level of the valley floor.

Beyond the Great Valley may be seen: the long, even crest of
North Mountain. This strongly marked topographic feature is the
most easterly of a series of long, parallel mountains running north-
east-southwest and alternating with long, narrow valleys. These
ridges and valleys are the chief topographic features of the district
between the Great Valley and Dan’s Mountain west of Cumberland.
They are termed the Appalachian Ridges and have been classed
under that name as one of the sub-provinces of the Appalachian
Province on the Outline Map, Plate III. Beyond these ridges,
which gradually increase in height westward, the general surface
spreads out as an extensive upland or plateau with an average eleva-
tion of 2500 feet, from which low parallel ranges of mountains rise.

THE STRUCTURE OF THE PROVINCE.

Present Structure.

In describing the Piedmont Plateau it was pointed out that the
topography was so closely related to the geology that a map could be
made showing the amount of topographic influence which the various
formations had exerted, although strongly influenced by the covering
of Coastal Plain sediments. The Appalachian Province still more
strikingly shows this relationship, since the winds, rains and rivers
have been at work for ages etching out the mountains and vallevs
along the lines determined by the structure of the country. The
hills and the mountains all indicate by their parallel arrangement and
N.E.-S.W. trend that the resistant rocks cross the state in the same
direction, while the valleys tell the same story about the location of
the less resistant formations. Such an arrangement of ridges and
valleys as characterizes the Appalachian Province might indicate
a structure similar to that shown in Tig. 5, but an examination of
the attitudes of the various strata shows that the actual structure is
as reproduced elsewhere.” This cut shows that the strata have been

*Md. Geol. Surv. Rept., vol. ii, 1898, p. 59, fig. 6.
MARYLAND WEATHER SERVICE.
VOLUME 1, PLATE XI.
MAP SHOWING APPALACHIAN TOPOGRAPHY OF ALLEGANY COUNTY.
FROM FROSTBURG SHEET, U. S. G. S.MARYLAND WEATHER SERVICE 151

thrown into folds whereby at certain points hard resistant conglom-
erates and sandstones have been brought to the surface, while at other
points they have been thrust deep down and only the more yielding
rocks above them appear. Many of the smaller ridges and even
elevations such as Wills Mountain, mark lines along which some
hard, resistant stratum has been arched up. Such ridges have their
general cross profile determined by the arched strata which maintain
them. Other prominent ranges, such as the Blue Ridge, owe the
elevated positions of their resistant rocks to great dislocations along
which the rocks have been thrust up above their earlier positions.
Between the ridge-forming folds or anticlines there were orig-
inally valley-forming troughs or synclines, in which it is probable
that the rains gathered and formed streams which would be classed
as consequent. To-day a number of small streams occupy similar
positions among the ridges and mountains of Washington county. It
is not at all likely, however, that these present streams have inherited
their courses from consequent ancestors. On the contrary, since the
synclinal troughs are occupied by yielding shales, it is much more
likely that the streams took courses immediately above their present
locations during the time when this whole district was being reduced
to the general surface of the Schooley or Cretaceous peneplain. Dur-
ing that period of erosion the summits of the present hard ridges
appear to have acted as guides directing the streams to develop along
the more easily eroded strata of the synclines. In many cases the
arches of hard rock originally rose so high above sea-level that they
were truncated by the broad, gentle surface of the peneplain, as it
was gradually extended across the folds. The domes of rock were
thus completely unroofed and their cores of softer rocks became
exposed to the attacks of the elements. Guided by these easier paths,
certain rivers extended their courses, not along constructional troughs
or synclines, but along the axial lines of the arches or anticlines.
Along the axis of a comparatively broad flat anticline in Garrett
county the two branches of the Savage river have opened the broad
depression lying between Savage and Meadow mountains.
152 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Original Structure.

The gradual change from the much disturbed strata of Washington
and Allegany counties to the almost horizontal arrangement of the
same strata in the plateau districts of Garrett county and of West
Virginia, serves to remind the observer of the original positions of
these beds. The successive layers of finer and coarser materials, the
remains of animals and plants, and the close resemblance between
many members of the series and various deposits which may be
seen forming to-day, all point to the conclusion that these strata were
deposited in succession over the floor of some very ancient sea. These
strata, now so crumpled and folded, must have originally been almost
horizontally disposed, just as any series of layers of mud and sand at
the bottom of a pond may be seen to have arranged themselves when,
the pond being drained, a ditch is cut across its old bed. All the
present dislocations of those ancient strata are the products of folding
and faulting under compression, which came after the rocks were
laid down as horizontal beds of clays, sands and calcareous muds at
the bottom of the interior Paleozoic sea.

The Appalachian and the Coastal Plain Structures Compared.

The strata now forming the Appalachians were deposited in more
or less close proximity to a shore or coast which lay along the eastern
limits of that ancient sea. The general location of this ancient land
area, as indicated by the sediments derived from it, seems to have
been in the district now occupied by the eastern Piedmont Plateau
and western Coastal Plain provinces. In the period during which
the Paleozoic strata were deposited this province was a more or less
lofty land area, whose rivers, flowing westward, carried down large
quantities of detritus to the sea. As the amount of materials thus
transferred from land to sea floor increased, the sea itself would have
been largely filled up had not the lands beneath the sea gradually
subsided. In this way there was accumulated the great series of
Paleozoic strata which stretched far westward from the coast of that
time.

If now the strata deposited in this Paleozoic sea are compared prior
to their dislocation, with the present Coastal Plain series, several points
MARYLAND WEATHER SERVICE 153

of resemblance, particularly as regards origins and relations to the
mainland, may be pointed out. Both the Paleozoic and the Meso-
zoic-Cenozoic sediments were deposited in seas often comparatively
shallow, but which, although constantly filling with new materials,
were also for a while gradually deepening, thus continuing the period
of deposition. Both series of sediments were derived not only from
areas immediately bordering the respective basins of deposition, but
also in part from precisely the same region, namely, the Piedmont
district. These comparisons show that during long periods in geo-
logical history the Piedmont region has been supplied with a Coastal
Plain.
TOPOGRAPHIC SUBPROVINCES.

It is clear from the general description of the Appalachian Prov-
ince given above that a four-fold subdivision is possible on the basis of
the topographic types represented. These subdivisions from east to
west may be designated as The Blue Ridge, The Great Valley, The
Alleghany Ridges and The Alleghany Plateau.

The Blue Ridge.’

The physiographic subprovince here designated by the name of
the Blue Ridge includes the Blue Ridge proper, the Catoctin moun-
tain and the district lying between them. Blue Ridge proper, which
forms the western boundary of the subprovince, is a long, straight
ridge with slightly uneven and knobby crest maintaining an average
elevation of 2000 feet above tide level. It starts in Pennsylvania as
a portion of South Mountain, passes southward through Maryland
and, after declining somewhat on each side of the Potomac gorge at
Harpers Ferry, rises again in Virginia to a somewhat lesser elevation.
That portion which lies within the limits of Maryland owes its crest-
line altitudes to the superior resistance of the Lower Cambrian or
Weverton sandstone which reached its present elevation partly as
the result of a great overthrust fault, partly through more recent
elevations of the whole of the Appalachian district.

+The names applied to this topographic unit vary in the different states
traversed. In Pennsylvania the entire range is called South Mountain, in
Maryland, South Mountain or the Blue Ridge, and south of the Potomac
the Blue Ridge. Keith has applied the general term Catoctin Belt.
154 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Although subsequent denudation has carved numerous scars and
slight sags in the crest of the Blue Ridge, except for the narrow
defile of a small branch of the Antietam creek debouching at Leiters-
burg, the Ridge presents an unbroken crest from Gettysburg Gap on
the north to the deep gorge of the Potomac at Harpers Ferry. The
western slope of the Blue Ridge Divide has the greater relief since
its summit rises about 1500 feet from the level of the Cumberland
or Hagerstown valley. The contours of this slope are generally pre-
cipitous along its upper zones. Over the lower portion they become
much softened, however, and grade into low, rounded foot-hills which
mark the outcrop of a band of fissile shales, Harper’s shale, lying
between the quartzite and the limestone, Shenandoah. The eastern
slope of the South Mountain, since this is the direction in which the
capping sandstone dips, is much milder than the western face. It
also presents Jess boldness of relief because the contrast between the
sandstone and the voleanic rocks lying against it on the east is much
less pronounced than is that between the sandstone and the limestone
or the shales of the Hagerstown valley.

East of the Blue Ridge proper, and almost parallel with it, runs
the straight and slightly undulating ridge called Catoctin mountain,
which forms the eastern boundary of the Blue Ridge subprovince.
Its prominence is due to the greater resistance of the heavy Cambrian
quartzite, which has withstood the attacks of the elements more suc-
cessfully than the rocks on either flank. Again it is with the Catoc-
tin, as with the Blue mountain, that that slope, which descends to
the yielding rocks of the broad valley lowland, is the longer and the
more precipitous, while the opposite slope is the milder and the
shorter. Here, however, the valley lowland is that of the Frederick
or Monocacy valley carved out on the Frederick limestone and the
Newark formation. This lies to the east of the ridge, while the
shorter and milder decline forms the western slope.

The continuity of the ridge is interrupted only twice within Mary-
land. Both gaps are in the northern portion of the crest -and are
cut by the two tributaries of the Monocacy between which is situated
the town of Thurmont. The more northern of these streams is the
MARYLAND WEATHER SERVICE 155

larger and has cut such a deep gap through the crest that it serves
for the passage of the Western Maryland railroad on its way across
the range.

Turning now to the valley included between the two crests just
described it is found that this portion of the Blue Ridge subprovince
has a number of peculiar and interesting features. It attains its
best marked and most characteristic development in the southern
portion of the district, in the drainage basin of the Catoctin creek,
and is less characteristically a valley in the northern half of the
area which is drained by the Monocacy and Antietam tributaries.
In spite of the fact that nearly half of the drainage basin of Catoctin
creek is underlain by igneous rocks, like granite and quartz porphyry,
and the remainder by the still more resistant Catoctin schist, the
stream has reduced a considerable portion of its basin almost to a
base-levelled state during a geologically recent period. Starting with
an average elevation of about 500 feet over that portion of the valley
lying along the Potomac the old valley floor, now appearing as even-
topped remnants between the streams, may be traced northward a little
beyond Myersville, where it has reached an elevation of about 750
feet. A considerable part of this rise is accomplished within the last
ten miles, where it is accompanied by a decreasing degree of regu-
larity in the character of the old valley surface. This gradual change
in perfection of modelling is what would naturally be found to exist
over the up-stream portion of an old valley, since the lower portions
of a stream’s course are always found to be reduced more perfectly
and uniformly than are its up-stream limits. Beyond \.yersville the
traces of this old valley floor are quite lost if the feature ever existed
there. Below the more or less even surface of what may be called
the 500 feet level, the Catoctin and its tributaries have incised their
channels to depths up to a hundred feet, according as they are farther
from or nearer to the present local base level, the channel of the
Potomac river. The cross-sections of the gorges, as well as their
depth below the old level, are indicative of their relative locations.
Beginning with the narrow V-shaped ravines of the most distant and
youngest branches, the gorges gradually assume a cross-section shaped
156 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

like a U. This form is characteristic of the lower course of the main
stream and of the larger branches. It indicates that the streams
have progressed beyond the stage in which vertical down-cutting 1s
predominant, and have reached a point where the weathering of the
canyon walls furnishes material somewhat in excess of the stream’s
ability to transport it. Above the general 500 feet level there
remain a few areas not wholly reduced. These are more numerous
along the sides and particularly at the head of the basin where they
gradually merge with that portion of the area which never was reduced
to the 500 feet plain.

The northern portion of this district, lving between the crests of
South Mountain and Catoctin, seems never to have been reduced to
such a valley lowland as formerly existed along Catoctin creek. The
reason for this is evident. This portion of the area is drained chiefly
by four or five streams already mentioned, all of which have to cut
their way out across the refractory and practically insoluble quartzite
before they can begin to work on the almost equally resistant epidote-
schist. In contrast to these difficulties stand the conditions governing
the Catoctin creek drainage. This system is largely employed in
draining the areas of granitic rocks and the quartz porphyries, both
of which, on account of the considerable percentages of feldspar in
them, yield more readily to the solvent action’ of the ground water.
Owing to this peculiarity of the various rocks, Catoctin creek which
flows directly into the Potomac after traversing the granitic rocks
has been able, both in the past and the present, to reduce the lower
portion of its channel with comparative ease, and so retain a decided
advantage over its opponents on the north. The combined action of
the resistant rocks to the north, and the superior powers thus pos-
sessed by the headwaters of Catoctin creek working up from the
south has, so far, resulted in confining the drainage of the northern
streams within comparatively narrow bounds. Although the vol-
umes of the latter streams have thus been limited to such meagre
proportions, small subsequent streams and valleys along the com-
paratively yielding quartz-porphyries have been developed, and
to-day there may be seen green, level-floored, narrow vallevs winq-

‘Keith, A., U. S. Geol. Surv., 14th Ann. Report, pp. 310, 378.
MARYLAND WEATHER SERVICE. VOLUME |, PLATE XIll.

 

 

 

 

Fic. 1.—THE POTOMAC AT WILLIAMSPORT, ON WESTERN MARYLAND RAILROAD.

 

 

tw

.-VIEW FROM MARYLAND HEIGHTS, SHOWING “THE GREAT VALLEY”
IN THE DISTANCE.

Fic.
MARYLAND WEATHER SERVICE 157

ing in and out among numerous bluntly conical hills or long ridges.
Below these valleys, particularly near the mountain fronts, the tor-
rent-like streams have often cut steep, wild gorges.

The Greater Appalachian Valley.

The Greater Appalachian Valley,’ or as it is sometimes called, the
Greater Valley, embraces all the country lying between the Blue
Ridge on the east and Dan’s Mountain or Alleghany Front on the
west, and thus has a width of about 73 miles. As has been noticed
above, the Greater Valley admits of a two-fold division into the
Great or Cumberland Valley on the east and the zone of Alleghany
ridges on the west.

The Great or Cumberland Valley is the rather broad, even depres-
sion lying between the Blue Ridge on the east and North Mountain
on the west. This broad, fertile valley, sometimes known as the
Hagerstown Valley where it passes through Maryland, is a marked,
topographic feature throughout the whole extent of the Appalachian
province. The sharp contrast which it makes with the surrounding
ridges is well shown by the model which was constructed for the
Cumberland Valley Railroad and is here reproduced as Plate XIV.

The principal topographic feature of the Great Valley is its broad,
gently rolling floor. Although this floor is now much cut up by
minor drainage lines, its formerly almost level surface has given the
present hills very strikingly accordant elevations. So nearly coinci-
dent are the various heights that, if a flat board floor could be laid
across the valley it would be supported by almost every hill and would
have an altitude of about six hundred feet above sea-level. Long
divides with broad tops maintain this average elevation over con-

siderable distances, and are generally occupied by highways. There
is a slight descent from the northern boundary of the state to an

elevation of from 500 to 550 feet along the Potomac, which brings
this former plain into relation with the plain along the Catoctin creek
and the Monocacy river. Southward from the Potomac, however,
this plain rises as it follows up the Shenandoah valley, finally reaching
a maximum elevation of 1700 feet in southern Virginia. The pho-

1B. Willis, The Physiography of the United States, 1896, p. 169.
158 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

tograph forming Plate XIII, fig. 2, illustrates the general character
of this valley floor in the vicinity of the Potomac.

The principal streams draining the Maryland section of the Great
Valley are Antietam and Conococheague creeks, both of which rise
in Pennsylvania and flow southward through Maryland to the Po-
tomac. The valleys of these streams are deep, narrow and steep-
sided, that of Conococheague creek being particularly gorge-like in
character. The streams themselves are rather rapid and have not
yet reduced their channels to even grades, as is shown by the low
ledges of shale or even limestone which sometimes interrupt their
flow. The courses of the channels are tortuous, often quite mean-
dering, and the turns and twists of the channels are always followed
by the gorge walls. This fact indicates that the streams originated
their meanderings on the flood-plains which accompanied them when
the present dissected valley floor stood at a lower elevation and these
streams flowed upon its continuous surface. As the area was ele-
vated the streams began to cut down along their courses, always keep-
ing a little behind the Potomac as it deepened its channel. Thus
the winding courses which the streams followed on their earlier flood-
plains became impressed upon the limestone and shale beneath, and
these more resistant rocks still retain the streams in their old courses
which are described as inherited or superimposed.

The general characteristics of the Alleghany Ridges have already
been briefly sketched. Several of these ridges are due to the up-
arching of resistant sandstones which have withstood the attacks of
the elements, while the yielding rocks which covered them have given
way. The best examples of such prominences are found in Wills
Mountain, Martin’s Ridge, Warrior’s Ridge and North Mountain.
The dome of the arch in the latter case has been partly removed,
however, and the yielding shales beneath which were formerly pro-
tected are now rapidly giving way. There is thus forming a shallow
and elevated valley along the axis of the uplift. All of these moun-
tains rise very nearly if not quite to the 2000 foot level.

Other crests, such as those of Town Hill, Sideling Hill and
Tonoloway Hill, fail to reach this height by about five hundred feet.
MARYLAND WEATHER SERVICE 159

They owe their elevation to the fact that, in a number of cases, the
Carboniferous conglomerate or sandstone was depressed below the
general level of the Schooley peneplain, and thus escaped being worn
away during the production of that feature. Subsequent elevation and
erosion have removed the softer rocks, which are then exposed by
the unroofing of the arches or anticlines and these small synclinal
remnants of the hard sandstones now stand out in relief as protecting
caps to the yielding strata just beneath them. Thus what was orig-
inally a series of constructional synclinal valleys has been converted
into a set of parallel, even-crested ridges with synclinal summits.
Between these mountains and ridges comparatively broad, even-
floored valleys were at one time carved out by the streams which
had breached the anticlinal arches during the Mesozoic era. For so
long a time did the land stay at rest after the elevation of the
Schooley peneplain that these streams reduced their valleys to very
gentle slopes, even far back in among the ridges. Sufficient time,
however, was not allowed for their reduction of the ridges, also, as
was the case during the preceding cycle. It was at this time that
the level floor of the Great Valley was produced, the general sur-
face of which can be followed in and out among these western
ridges. This generally even and accordant surface is often referred
to as the Shenandoah Plain, because it is so typically developed over
the yielding rocks of the Shenandoah valley. Having been devel-
oped only in the vicinity of the streams, the Shenandoah Plain is
found to rise gradually as it extends towards the headwaters of the
various mountain streams of the central district. The general eleva-
tion, however, is found to be somewhat greater and the inclination of
the surface steeper than would be the case if due simply to the nor-
mal stream slope of the region. These features are believed to be
due to a general and unequal elevation of the land after the Shen-
andoah Plain had been developed. This elevation, or more strictly
speaking, warping, was greatest along a northeast-southwest axis
located near the eastern boundary of the Alleghany Plateau, and
also along a minor axis running southwestward from southern Vir-
ginia and West Virginia, the influence of which was extended as far
160 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

northward as Maryland and eastward to the Atlantic coast line,
affecting to some extent the district of the Alleghany ridges.”

This warping of the Shenandoah Plain exerted a marked influence
upon the development of the well-adjusted streams of the Appa-
lachian district which, at the close of the period of denudation, were
meandering over comparatively broad flood-plains. The elevation
which succeeded the period of denudation revived the activities of the
streams, and they rapidly deepened their channels, cutting narrow
winding courses, taken from their former directions on the Shenan-
doah Plain. Continued denudation has now worn away consider-
able portions of the inter-montane region, so that its general sur-
face can be traced only in the long, flat inter-stream areas and the
rounded crests of those hills which rise to the general level of the
plain.

Among the most characteristic remnants of this formerly extensive
surface may be mentioned Shriver’s Ridge, with an elevation of
1071 feet, the northern spur of Knobbly Mountain across the Po-
tomac river with an elevation of 1115 feet, the heights northeast of
Cumberland with an average elevation of something over 1000 feet,
and the broad, dissected district extending northward from Old Town,
which is drained by Big Spring run and Town Creek, with an average
elevation of about 900 feet. The character of the gorges which
the streams have cut below the uplifted Shenandoah Plain clearly
shows that the rate of elevation was not uniform. At least three
distinct terraces can be made out along the banks of the Potomac
in the vicinity of Cumberland. Each terrace indicates a period of
temporary quiescence for the land, during which the stream was
able to expend some of its energy in the horizontal cutting and
widening of its channel; while each slope from a higher to a lower
terrace indicates renewed activity in vertical down-cutting. The two
upper terraces belong to the class of stream-cut terraces, as is shown
by the fact that their almost horizontal tops are bevelled across the
upturned shales. Only a very thin layer of scattered cobbles and
gravels is found on either terrace. The lower terrace is so heavily

* Hayes, C. W., and Campbell, M. R., Nat’l Geog. Magazine, vol. vi, 1994
plate 6.
VOLUME I, PLATE XIV.

MARYLAND WEATHER SERVICE.

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MARYLAND WEATHER SERVICE 161

covered with river deposits of sand, gravel and boulders that it is
difficult to say whether it is a cut or a built terrace or a combination
of both. These terraces, particularly the two lower ones, may be
followed down the Potomac beyond Harpers Ferry running in and
out of the stream valleys which join that river from either side and
gradually declining in elevation. Up-stream they have been traced
as far as Keyser and undoubtedly extend a considerable distance
further. Attempts have been made’ to correlate these terraces with
contemporaneous epochs of deposition contained within the Coastal
Plain series, but very recent work in that group of deposits by the
New Jersey and Maryland surveys has so altered former conceptions
of stratigraphic sequences and conditions of deposition that it seems
best for the present at least not to attempt a statement regarding the
stratigraphic equivalents of these features.

The Alleghany Plateau.

The Alleghany Plateau extends from northern central Alabama,
where it is known as the Cumberland Plateau or tableland, north-
ward and eastward through Tennessee, Kentucky, Virginia, West
Virginia, Maryland and Pennsylvania into New York, where it
forms the high lands covering the southern half of the state from the
Catskills to Lake Erie. This plateau, which preserves, in its general
level, the largest continuous areas of the Jura-cretaceous, or Schooley
peneplain, is not characterized by a broad, unbroken expanse, but
has been so deeply dissected that only the even crests of isolated
ridges remain to indicate the former extent of the plateau. Standing
on some lofty central point, such as the crest of Keyser’s Ridge in
Garrett county, one sees all about these long level-topped crests which
seem to rise very nearly to the same general height, although there
is a gradual decrease in elevation northward and eastward from the
district between Savage Mountain and Keyser’s Ridge. The long
ridges are arranged in almost parallel ranks and follow the broad
curves of the Appalachian svstem, while their even crests are the

1McGee, W J, “The Terraces of the Potomac Valley,” The Eveniny Star,
‘Washington, June 20th, 1885.
Keith, A., U. S. Geological Survey, 14th Ann. Report, 1892-93, pp. 285
et seq.
11
162 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

present representatives of that broad peneplain which has already
been so often referred to in dealing with the eastern portions of
Maryland. The most representative elevations of this peneplain are
found in Savage Mountain, which has an altitude of about 3000 feet
in Keyser’s Ridge and Negro Mountain, with elevations of 3000 feet,
in Winding Ridge 3000 feet, and Hoop Pole Ridge 2800 feet.
These elevations are the culmination of the westward rise of the
Schooley peneplain in the latitude of Maryland. Farther westward
the general surface gradually declines to the Ohio and the Mississippi
rivers. Within the Maryland portion of the plateau the strata are
still gently folded, so that the extension across them of the old pene-
plain surface here also resulted in the removal of several rock domes.
Thus, while the land was being reduced to very mild topographic
forms, the way was being prepared for the easy carving out of lofty
mountain ranges during a subsequent time. As a result of the ele-
vations which have taken place since the Schooley peneplain was pro-
duced, the streams which had developed on that surface, and whose
courses were adjusted to its underlying structure, have deepened their
valleys very considerably. There were other streams, however, which,
although they oceupied courses located on vielding rocks, had carved
their valleys out along synclinal axes and have not, since their eleva-
tion, materially deepened their valleys.

There are thus seen to be two classes of valleys and streams within
the boundaries of the Maryland portion of the Plateau, one class has
synclinal or consequent streams and valleys, the other class embraces
the subsequent or anticlinal streams. The characters of the valleys
of these two classes are quite as distinct as their relations to the
structure. The subsequent streams have developed their courses gen-
erally along Jennings and Hampshire shales, which formed the cores
of anticlines whose domes were the resistant Pocono sandstone. The
elevation which interrupted further development of the Schooley
peneplain gave all these streams increased activity and they began
to actively reduce their valleys to the new base-level.

To-day the new valley-floors thus produced may still be seen as flat-
topped hills of Hampshire and Jennings shales bounded by steep and
MARYLAND WEATHER SERVICE 1638

often precipitous cliffs which are capped by rocky crags of Pocono
sandstone. Perhaps the largest area covered by this surface of denu-
dation is to be found in the vicinity of Accident. This town is
located near the center of a broad amphitheater, whose boundaries
are the curving Pocono-capped crests of Winding and Keyser’s ridges,
and whose floor is a very gently rolling surface, large portions of
which remain over the inter-stream areas. This is the old floor pro-
duced just after the elevation of the Schooley peneplain. Numerous
disconnected areas along the northwestern flanks of the Savage river
valley also preserve this surface. Turning to those streams which
pursued consequent or synclinal courses, it appears that instead of
occupying deep valleys with steep bounding slopes, their valleys are
comparatively shallow and stand at higher levels than do the sub-
sequent valleys. These consequent vallevs are now lifted high above
the other streams and present very slight contrasts in relief as com-
pared with the other streams of the Plateau. The best example of
this class of streams and valleys is found in the valley of the Castle-
man river. This stream is located on the portion of the Fairfax
formation, or Barren Measures, which reposes in the synclinal basin
between Meadow and Negro mountains. The valley is very broad
and comparatively shallow, especially at the southwestern end of the
eyncline, and there is no sudden break in the slope from the crests
of the two limiting mountains to the axis of the valley. The reason
why the streams draining such valleys as that of the Castleman river
have never been able to reduce those valleys successfully is due to
the fact that the whole valley is floored with a resistant conglom-
erate or sandstone, which must all be removed before the mountain
can be lowered. Thev are hemined about by the same hard stratum,
and the streams which have to cross it in order to leave the valley
cannot remove the core of the anticline below the level to which they
have cut down their outlet. It is, however, a much easier task to
cut a gorge through a narrow ridge of the sandstone than it is to
remove a broad, almost flat sheet of the same rock. Therefore,
streams like the Savage have carved deeper and more sharply bounded
valleys than have such rivers as the Castleman.
164 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Just here it may not be amiss to refer to those broad, wholly en-
closed valleys whose meandering streams are often bordered by rather
marshy ground. Such valleys are known in Garrett county as Glades,
while any valley which has steep bounding slopes and slightly marshy
flood-plain is called * glady country.” These poorly drained areas
are calculated to attract attention in a district where the sharp relief
of the country in general insures unusually well-drained soils. To
one familiar with the poor drainage of the glaciated districts of the
United States, glaciation ’ at once offers itself as an explanation of this
topography. here are, however, none of the other signs of glacia-
tion, such as transported boulders, striated ledges or morainic mate-
rial. Moreover, it is possible to adequately explain the Glade
Country by appealing to processes acting there at present and during
the past. The following explanation, based on recent geological
studies in the Glade districts, is offered by Mr. A. C. McLaughlin of
the Maryland Geological Survey.

The typical Glades of Maryland are located on the strip of Jen-
nings and Hampshire shales which lies between Backbone mountain
and Hoop Pole Ridge in the vicinity of Oakland and Deer Park.
This broad, gently rolling valley is drained by two rather slug-
gish streams known as North Glade run and Green Glade run, both
of which unite beyond Hoop Pole Ridge to form Deer creek, a tribu-
tary of the Youghiogheny. Hoop Pole Ridge is a monoclinical ridge
of Pocono sandstone which offers considerable resistance to erosion
and has retarded both of the streams crossing it. While thus retarded
at the edge of the Glades by this sandstone ledge, the headwaters of
these streams have been working on the yielding shales until they
have been reduced very considerably, in fact, quite to the level of
the stream crossing on the sandstone. The stream grades are now so
flat here that they cannot carry away the debris washed by the
rains from the low shale hills. The result is that immediately along
the streams the accumulation of alluvium has been so rapid that the
stream is slightly choked and has thus become marshy. The Glades
therefore are simply a well-reduced local base-level plain determined
by the marked contrast between the yielding shale and the investing

1 Gibbes, Geo., The Glades of Maryland, Amer. Nat., vii, 1873, p. 636.
MARYLAND WEATHER SERVICE 165

barrier of resistant sandstone. It might be added that possibly the
inability of the two streams to remove the alluvium may be due to
decreased volumes, resulting from recent captures by the headwaters
of the Savage or the Youghiogheny rivers, both of which have tribu-
taries on the shales in the immediate vicinity of the Glades.

So far the Marvland streams of the Alleghany Plateau have been
considered from their purely local relations. It is interesting to con-
sider briefly their general relations to the broad structural features of
the region. From this point of view also there are two classes of
streams here; first, those which flow westward down the general dip
of the strata to the Ohio, and second, those which flow eastward
against the general dip to the Atlantic. The Youghiogheny and
Castleman rivers take out all the Ohio drainage, while the Savage
and the North Branch of the Potomac lead off the waters which flow
into the Atlantic. It has already been pointed out that the whole
Appalachian district formerly bore the relation of a coastal plain to
a land area lying somewhere to the east. In view of this fact the
rivers should naturally all flow westward down the inclination of the
strata towards the old sea. As a matter of fact, only the Yough-
iogheny and the Castleman approach to this arrangement, while the
Potomac and its tributary, the Savage, go in directly the opposite
direction. They even do more, for they cut across what we can see
of that old land area and empty into the Atlantic at a point where
formerly there may have been high hills. To explain this anomalous
course of the Potomac is one of the larger and more difficult prob-
lems for the physiographers of the Atlantic slope to solve.

GENERAL TOPOGRAPHIC HISTORY OF THE PROVINCE.

The topographic history of the Appalachian Province may be
briefly summed up as follows. The Province originated as a coastal
plain along the western shores of some ancient land area, part of
which may be represented in the ancient ecrystallines of the Pied-
mont Plateau. Probably shortly before the close of the Paleozoic
this coastal plain was elevated and deeply folded in its eastern por-
tion by powerful compression. This elevated and corrugated coastal
plain then suffered a partial reversal of its westward flowing drain-
166 A. REPORT ON THE PHYSIOGRAPHY OF MARYLAND

age, and remaining for a great length of time in a quiescent state, was
so far reduced by erosion as to present the features of advanced topo-
graphic maturity and perhaps even become a peneplain. This period
of repose was closed by a decided warping of the new surface that
raised it to an elevation of about 2000 feet in Western Maryland, but
only to about 300 feet in the central portion of the state. Then fol-
lowed another period of repose during which the Shenandoah Plain
was carved out. Finally a series of elevations at irregular intervals
has warped the two plains, still further bringing the Schooley pene-
plain level to altitudes of 3000 feet in the western and 500 to 800 in
the central section of the state, while the Shenandoah Plain stands at
1000 feet to 1500 feet in the west and 500 feet in the east. The
latest elevations have caused the streams to cut below the level of the
Shenandoah Plain a series of steep, terraced gorges that they are still
deepening.

ECONOMIC PHYSIOGRAPHY OF THE PROVINCE.

Lines of Communication.

The obstacles offered by the successive parallel ridges of the Appa-
lachian province delayed the westward movement of the population
in colonial days and restricted the east and west lines of travel to the
valleys of the Potomac, the Susquehanna, and the James. The
earliest inhabitants found these natural highways already selected as
the lines of communication between the distant parts of the great
Indian Confederacy, and accepted the experience of the aborigines by
building their roads along the same lines.

As the population of the western portions of the state increased the
demand for more perfect highways became urgent, so that before the
end of the eighteenth century several well-defined lines of travel had
been established between the tidewater regions along the Atlantic and
the Ohio drainage. The Cumberland road extended from Washing-
ton to Cumberland via Hagerstown and Hancock, and thus followed
the line of easiest travel along the valleys and across the divides at
their lowest points. Beyond Cumberland the road was exteuded
across Big Savage mountain and the Alleghany Plateau, keeping on
the divide between the Potomac and Youghioghenv until it entered
MARYLAND WEATHER SERVICE. VOLUME |, PLATE XV.

 

 

Fic. 1.-THE YOUGHIOGHENY NEAR OAKLAND.

 

 

Fic. 2.-THE YOUGHIOGHENY AT FRIENDSVILLE.
MARYLAND WEATHER SERVICE 167

the valley of the latter, which it followed to the Monongahela, and
thence down stream to Pittsburg.

Later the promoters of the Chesapeake and Ohio Canal gained the
right of way up the Potomac valley, which is followed to Cumber-
land. The course of the Potomac at Harpers Ferry and Point of
Rocks offered the easiest means of communication across the Blue
Ridge district, and when once occupied the Chesapeake and Ohio
Canal effectually stopped the westward progress of the Baltimore
and Ohio Railroad along the same route until a compromise was
effected in 1832. West of Cumberland the railroads crossing the
state follow the valleys of the rivers, utilizing the courses of the
Potomac river, Wills creek, Georges creek, Jennings run, the Savage
river, and the Youghiogheny river.

Natural Resources.

The resources of the Appalachians are varied and valuable. The
early settlers found the mountains clothed with dense forests of pine
and hard wood, but they lacked the means for transporting the lumber
to a ready market. Even now with a canal and several railroads the
cost of hauling from the forest to the point of shipment is so great
as seriously to reduce the profits of the lumbering trade.

The many varieties of soils in the Appalachians are closely related
to the geological formations, and their distribution is clearly influenced
by the geological structure. Since most of the higher hills and sharp
ridges are due to the presence of sheavy beds of siliceous sandstone,
the soils of the upper slopes are generally sandy and poor. Beneath
these strata come beds of shales which are sometimes calcareous, so
that the lower slopes, hills and subsequent valleys contain soils which,
while somewhat stony, give fair yields in wheat, corn, ete.

The Great Valley, with its rich limestone soil and easy means of
access from the north and south, forms a broad band of the most fertile
lands in the state. If it had not been for the re-elevation of the
Shenandoah plain this district would be most favorable to farming.
As it is, the rolling surface and steep valley slopes are somewhat
difficult to till with ease. The land is so rich, however, that the whole
stretch of the valley is or might }e under cultivation.
168 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

The chief sources of mineral wealth in the province are the de-
posits of coal, iron and cement rock. The coal beds are the remnants
of larger areas preserved by their depression below the limits of erosion
during the formation of the Schooley peneplain. They have proved
of inestimable value to citizens of the state. The Clinton iron ores
were formerly very valuable, but in the present state of the iron
market they are of relatively little importance. The cement rock is
obtained from certain portions of the Silurian limestones and is the
basis of a growing industry. The exposures are favorably situated
along the lines of travel, so that the mills have every advantage for
the shipment of their product.

Inhabitants.

The physiography, industries and resources of the Appalachian
province have strongly influenced the character and occupation of the
inhabitants, who may be grouped into several well-marked classes.
In the higher more rugged and less populated portions of the area
are the mountaineers, who gain their livelihood by lumbering and
desultory farming. Gathered about the rich deposits of coal, iron
ore and cement are miners, who are occupied almost exclusively in
the extraction of wealth from the underlying rocks. They present a
class of marked characteristics in education, training, religion and
nationality. The valleys between the mountains, especially the Great
Valley, and the larger more level areas of the glades, furnish incentive
and opportunity for farming communities, which are reasonably well
recompensed for their efforts in the tilling of the soil. In the cities
and larger towns are concentrated those who serve as distributing
agents for the products of the land and the necessities of the inhabi-
iants.

Tur DEVELOPMENT OF THE STREAMS OF THE PrepmMont PLatreav.

INTRODUCTORY REMARKS.

In 1888 Mr. W J McGee published a series of papers’ on the
earlier members of the Coastal Plain series, in which he interpreted

‘McGee, W J, Three Formations of the Middle Atlantic Slope, Amer. Jour.
Sci. (3), vol. xxxv, 1888, pp. 120, 328, 367, 448.
MARYLAND WEATHER SERVICE 169

the geographic and topographic history of the regions by means of
the sedimentary records. In this series he makes the statement * that
“the former westward extension of the [Potomac] formation can be
reliably inferred from the topographic configuration of the Piedmont
region, the western part of which has a drainage evidently determined
by lateral heterogeneity of the vertically bedded terrane and a char-
acteristic topography resulting therefrom, while the eastern part has
a drainage independent of the varying obduracy of the terrane and
therefore evidently superimposed by a formation (which could only
have been the Potomac) now generally removed by erosion.” This
statement is based on some work done several years previously upon
the geology about the mouth of the Susquehanna river.” In this
paper an epigenetic or superimposed origin for the streams of the
eastern portion of the Piedmont Plateau was first proposed. As
AlcGee did not give much detailed evidence in favor of this view, the
writer undertook in 1895-96 the collection of details which are essen-
tial to the determination of its correctness. The purpose of this
chapter is to set forth the results of the study thus inaugurated.

In 1889 W. M. Davis,’ in his study of the Pennsylvania drainage,
suggested that the discordant position of the lower course of the Sus-
quehanna might be explained by supposing superimposition from a
flood-plain contemporary and coextensive with the Potomac forma-
tion. Later in studying the rivers of New Jersey‘ he came to the
conclusion that the locations of several small streams across the trap
ridges of First and Second mountains were due to superimposition
from a westward extension of the Coastal Plain sediments.

Only one other investigation of this nature has been conducted on
the streams near Maryland. Miss Bascom’ in 1897 published a short
account of some discordant drainage near Philadelphia which is ex-

1Op. cit., pp. 133-134.

2>McGee, W J, The Geology of the Head of Chesapeake Bay, U. S. Geol.
Surv., VII Ann. Rept., 1885-86, pp. 545-644.

* Davis, W. M., The Rivers and Valleys of Pennsylvania, Natl. Geog. Mag.,
vol. i, 1889, pp. 241-242. |

*Davis, W. M., The Rivers of Northern New Jersey, Natl. Geog. Mag., vol.
ii, 1890, p. 99. :

> Bascom, F., The Relations of the Streams in the Neighborhood of Phila-
delphia to the Bryn Mawr Gravel, Amer. Geol., vol. xix, 1897, pp. 50-57.
170 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

plained by superimposition from the cover of Potomac clays and
gravels,

Beyond the limits of the Middle Atlantic Slope one or two im
portant river studies have been executed which have some bearing on
the Maryland problems. In 1890 R. 8S. Tarr* reported cases of
streams in Texas which were superimposed from Cretaceous upon
Paleozoic rocks; and H. B. Kummel,’ a year later, suggested that
the eastward deflection of the Connecticut at Middletown, where it
leaves the yielding Triassic rocks and cuts a gorge in the crystallines,
might be due to superimposition from the extended Cretaceous cover.

THE PROBLEM PRESENTED.

The observations of A. Keith, W J McGee, and others have shown
that the gently rolling upland surface of the Piedmont Plateau is a
continuation of the Schooley peneplain of New Jersey and Penn-
sylvania. The conditions of formation of a peneplain, or even of a
district well advanced in topographic maturity, carry with them the
expectation of finding the streams well adjusted to the underlying
structure. Since the streams of the Maryland Piedmont region are
found to be unconformable to such conditions, the question arises, as
to what is the cause of this discordance.

The proximity of the partially removed Coastal Plain sediments
and the number of isolated patches of the Coastal Plain formations
found lying beyond the general boundary of the latter province, seem
to offer a ready answer to the question. This is the one suggested
by McGee, viz. that the streams have inherited their present courses
in large part from a previous cycle when they were located on the
surface of the then more extensive Coastal Plain.

DETAILED STUDY OF TYPICAL STREAMS.

The succeeding detailed descriptions and studies of certain streams
have been made with the threefold purpose of examining the evidence

‘Tarr, R.S., Origin of some Topographic Features of Central Texas, Amer.
Jour. Sci. (3), vol. xxxix, 1890, pp. 206, ete., and Superimposition of the Drain-
age in Central Texas, ibid., vol. xl, pp. 359-361.

>Kummel, H. B., Some Rivers of Connecticut, Jour. of Geol., vol. i, 1893,
pp. 371-393.
MARYLAND WEATHER SERVICE.

 

 

 

 

 

Raver) )

 

 

 

 

 

 

 

 

 
VOLUME 1, PLATE XVI.

 

 

 

 

LEGEND.

ORDER OF

     
  

~ RESISTANCE
i TO EROSION

Quartzite

Magnolia

 

 

 

 

 

 

 
   

 

 

 

 

 

A MAP
h lati Gneisses r
| we the relations 5 s
\ = ft \ Showin’ THE “Ween
\ \ é \ 1 | Phyllites
| | Drainage and Underlying Rocks
| OF THE Newark
| EASTERN PIEDMONT PLATEAU
SSS SS = ad A ) | | SeAl6 Marbles |
ee ‘i = , /] > Sy 5 Smiles=linch
‘ Rela I | 5 } | a a ee Coastal Plain
: BZ f | -
Jima | MARYLAND GEOLOGICAL SURVEY = Gyanite, Ete. |
= 4 | | WM. ts. CLARK, STATE GEOLOGIST |
Pay, | | 1898 as'|
—~ eam é See erat, | ae Se a a ras sar i = = SSS Srey Se 107]
7640" ; / Sp) 7620 _ 7620 7610 : |

 

 

 

 

 

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MARYLAND WEATHER SERVICE 171

for and against the theory of superimposition; of finding, if possible,
the topographic evidences which will indicate a former westward
extension of the Coastal Plain blanket; and of determining the date
or dates at which the streams may have been superimposed.

The systems of drainage described in the following pages are con-
fined to the Eastern Piedmont Plateau and are represented upon
Plate XVI. The area included in this plate is indicated by shading
on the Index Map, fig. 15.

 

 

 

  
 

 

INDEX MAP

 

SHOWING

 

THE AREA INCLUDED IN

PLATE XVI.

 

 

 

 

 

 

Fic. 15.—Index map showing location of Plate XVI.

Deer Creek.

Deer Creek rises in the gneissic areas of the northwestern corner of
Harford county, Maryland, and southern York county, Pennsylvania,
and drains the whole northwestern portion of Baltimore county. The
general direction of the drainage system is southeast as far as The
Rocks, where after passing through the gorge at this point the stream
changes to an easterly direction and empties into the Susquehanna
about eight miles above Havre de Grace. Across its path lie bands of
gneiss, phyllite, slates and quartzites, pyroxenite, gabbro, and granite,
each having its own characteristic topography.

From its headwaters down to The Rocks, Deer Creek and its tribu-
172 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

taries may be regarded as a physiographic unit. This portion of its
course lies partly in the gneiss and partly in the phyllite. The folia-
tion and lines of structural weakness of these rocks strike northeast
and southwest, while the general trend of the main stream is at right
angles to this direction. The stream thus shows disregard for the
relatively greater resistance of the silicious bands that are mingled
with the much less resistant micaceous facies of the phyllites. All
the stream courses are sunk below the general level of a peneplain,
whose surface is well preserved in the accordant crests of many hills
on either side of Rocky Ridge. The peneplain stands fifty or seventy-
five feet below the long even crests of Rocky Ridge and Slate Ridge.
It is particularly well developed in the vicinity of Belair, along the
course of Deer Creek both above and below The Rocks and along
Winter run. The appearance of the peneplain above The Rocks
is shown by Plate XVII.

The hill-slopes bounding the valleys of Deer Creek and Little Deer
Creek fall rapidly from the gently undulating surface of the Belair
peneplain down to the broad flood-plains that characterize even the
smaller streams of this system. They are frequently roughened by
small ledges whose ragged faces, half-buried by the present flood-
plains, show that they once bounded more rugged gorges and valleys.

Froop-piaiss.—The bottom-lands that characterize these streams
are clearlv shown by two lines of evidence to be flood-plains. Wher-
ever fences cross the bottom-lands they are built in the form of swing
gates, such as are used to fence across a stream. This indicates that
floods in these valleys are frequently high enough to destroy fragile
structures built across them. Again, the structure of the bottom-
lands or meadows as exhibited in the banks of the streams during
low water points to a constructive rather than a destructive origin.
For example, a vertical section of the flood-plain on Little Deer Creek
exposed but a few hundred feet above its junction with Big Deer
Creek shows at the top one and one-half feet of rich black loam over-
lving three feet of gravel. The constituents of the gravels have a
diameter of about one and one-half inches near the top and increase
to boulders of a foot or more at the base. These pebbles and boulders
MARYLAND WEATHER SERVICE.

 

 

 

VOLUME |,

 

PLATE XVII.

ROCKY RIDGE AND THE VALLEY OF DEER GREER.
MARYLAND WEATHER SERVICE 173

are water-worn, rounded or subangular fragments of phyllite, quartz-
ite and vein quartz, and have evidently been derived from points near
at hand. The width of the meadowland, which continues down
stream as far as The Rocks, varies somewhat. It is broadest across the
less resistant bands of the phyllite and narrowest in the siliceous and
quartzitic areas where it reaches a minimum width of fifty feet. In
spite of the fact that the valleys broaden very markedly when on the
phyllites and by their narrowing indicate that the quartzites are harder
to reduce, yet there is no apparent tendency on the part of the main
stream to seek out a more convenient course along the more yielding
rocks or to follow the strike of the foliation and jointing planes of
either. This applies more particularly to Big Deer Creek, as Little
Deer Creek appears to have developed its course more nearly along
these lines of least resistance.

Broad Creek.

The headwaters of Broad Creek, that is those west of Pylesville,
have developed mild contours over their drainage basin. Standing
on the refuse piles of the first slate quarry south of Cambria station
one looks westward across fertile, gently rolling fields well watered
by streams with broad bottom-lands, all converging towards Pylesville
to form the main stream. At Pylesville it has cut its way through
the slates, quartzites, and conglomerates of Slate Ridge, thus opening
a passage for itself, the railroad and the highway. The creek itself
is about six feet wide and as many deep at Pylesville, but after cross-
ing the ridge of slates it opens out in a broad meadow, along one side
of which it flows for five or six rods until it enters the gorge through
the quartzite. This gorge has a flood-plain forty to eighty feet in
width which is strewn with boulders two feet and less in diameter
and is evidently submerged during moderate floods, since its present
dry portions are much tangled by driftwood. The sides of the gorge
rise rapidly, in the lower portion even precipitously, to a height of
one hundred feet above the channel and are densely wooded. The
stream flows rapidly over gravel shoals and across sharp ledges of
micaceous quartzite and conglomerate at the lower end and in no
part of the gorge is there even a low cascade. These facts indicate
that the stream has nearly established a graded channel.
174 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

After flowing for a quarter of a mile through this narrow gorge
Broad Creek emerges upon a broad meadow whose even surface
stands at a level which is four or five feet above the ordinary level
of the stream. This meadow-land, stretching out sometimes to a
width of a quarter of a mile, runs squarely against the foot of the
steep slopes of rocky cliffs descending to it from the even upland
surface. The rocks underlying this meadow are chloritic phyllites that
are especially subject to decay and removal wherever they are found
in the Piedmont, while the more resistant bands of quartzite and con-
glomerate serve to retain the prominent benches and form the bare
ledges which sometimes bound the meadow-land.

Viewing the topography thus far described it may be briefly
summed up as follows: The primary feature of the district is the
broad extent of the peneplain extending in all directions as a gently
rolling surface. Running northeast and southwest and rising above
the general upland are the even-crested elevations of Rocky Ridge
and Slate Ridge. Besides these higher elevations there are less
prominent inequalities of the surface caused by the resistant bands of
the quartzitic gneiss and the serpentine which intersect the general
areas of gneiss and granite. The streams pursue general eastward
eourses whose directions are only very slightly influenced by the
variations in the rocks across which they flow. “The valleys are sunk
below the general upland as relatively wide trenches, except where
they cross an unusually resistant band. When within two or three
miles of the Susquehanna these streams lose their broad-bottomed
valleys and descend to the level of the larger river through steep
narrow defiles with their channels frequently broken by low caseades.

James’ and Bynum’s Runs.

These two short streams have the same general characters and one
description will serve for both. Both streams head on the mildly
undulating surface of the Piedmont Plateau just south of Deer Creek.
The characters of their headwaters are those of a stream on a well
reduced land surface. The upper valleys are shallow and broad with
very mild slopes from divide to stream channel, and the streams flow
quietly through alluvial meadows with very moderate stream grades.
MARYLAND WEATHER SERVICE 175

On either side of the turnpike from Belair to Churchville the topo-
graphy is mild and is easily distinguishable from the rolling slopes
descending on the north toward the channel of Deer creek. On the
south the topography and character of the streams change rapidly
and the broad divide merges into the more cut-up surface of the middle
portion of the drainage system. The stream valleys become steeper
sided and the washed-in detritus from the slopes forms small alluvial
bottoms over which the streams meander during the summer. Where
the streams pass the “ Fall Line” they become more troubled and
flow more rapidly over low cascades which alternate with short
stretches of quiet water.

Inttle Gunpowder Falls.

The Little Gunpowder Falls, which forms the lower portion of the
boundary between Harford and Baltimore counties, rises on the phyl-
lites and gneisses between Monkton and Blackhorse and flows in a
southeasterly course as far as the estuary of the Gunpowder river,
where it enters the waters of Chesapeake Bay. In its course it
traverses phyllites, marbles, gneisses, gabbros, and granites without
any appreciable conformation to the differences in resistance to erosion
which these various rocks present.

The headwaters show that the stream is now increasing its drainage
basin, but at a lower rate than the Big Gunpowder. The rocks un-
derlying its upper course are gneisses ranging in character from the
weak muscovite gneiss to the less yielding fine-grained hornblende
gneisses. Where the stream passes over bands of the latter type the
valleys become somewhat contracted and the scenery a little more
rugged. Lower down on its course, as near Taylorville, the Little
Gunpowder crosses narrow lenses of marble which are more easily
corroded than the less calcareous gneisses and schists. Wherever the
stream encounters the marble it is customary to find it meandering
through broad and fertile meadow-lands which are often flooded after
heavy rains. The lower course of the Falls adjacent to the trestle
of the Baltimore and Lehigh Railway is in a narrow gorge eighty
to one hundred feet below the ordinary level of the upland. The
stream channel is filled with angular fragments of gneiss, quartz and
176 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

schist, and frequently has low ledges of gneiss cutting across it. The
flow is rapid and the stream seems to be working steadily even when
the low waters of summer enable it to handle only the coarse sand
and finer gravels.

The last phase of the stream’s inter-Piedmont course is entered
just below the mills at Reckford, where the channel becomes of less
uniform grade and is characterized by short stretches which are prac-
tically level in times of flood. The alluvial meadows built up of the
sands, gravels and alluvium brought down by the floods at high water
become broader and the stream flows in a more irregular course with
a rapid current.

Big Gunpowder Falls.

The Big Gunpowder rises on the phyllites in the northeast corner
of Carroll county, and flows in a general southeasterly direction across
the phyllite, gneiss and marble belts of central Baltimore county to
the head of the Gunpowder estuary, where both the Big and the Little
Gunpowder empty into Chesapeake Bay. The waters forming the
lower courses of this river are the combined product of the confluence
of three main branches forming the chief drainage lines of northern
and central Baltimore county. The more northerly branches unite
near Monkton and are known, respectively, as the North, or Main
Gunpowder, and the West Branch of the Gunpowder. The usage of
these terms is somewhat unfortunate since the more prominent and
larger stream is known as the West Branch while the smaller and less
important is known as the Big Gunpowder.

Tus Norra or Main Brancu.—The latter rises just across the
Pennsylvania line in south-central York county. As it enters the
state it is relatively small, having a width of only six feet, and is only
about fifteen feet wide a short distance above its junction with the
West Branch near Monkton. Its valley is conformable to the size
of the stream and, as far as Monkton, has a rather open character.
Near the state boundary the stream flows rather rapidly through a
narrow alluvial plain bounded by hills inclined at an angle of about
30° to the flood-plain. The rounded contours indicate only a moder-
ate rate of denudation. The slopes meet the flood-plain in a sharp
line and change their inclination to a much flatter angle as the crests
MARYLAND WEATHER SERVICE 177

of the hills are approached. Following down the stream the banks
continue steep, but the increasing volume of water makes the lateral
cutting on the outside of the curves more active, so that the banks
are often precipitous on one side and relatively mild on the other.
(Illustrations of these stream-cut cliffs are frequent between Bentley
Springs and Monkton.) The flood-plain feature continues for some
distance and the plain increases in width somewhat out of proportion
to the size of the stream, with the result that the channel is now
frequently on the opposite side of the valley from the vertical cliffs
which the stream cut at an earlier stage of its development. The
shallow, open, yet steep-sided, valley, with its alluvium-lined’ floor,
characterizes the stream as far as its junction with the West Branch.
The channel is from forty-five to fifty feet below the hilltops and
from fifteen to fifty feet wide, according to the varying resistance of
the gneiss. The bed of the stream is made of angular boulders with
frequent ledges in the lower part of its course except where covered
with sand, gravel and loam.

The side streams flowing into this portion of the Big Gunpowder
Falls have their lower courses more or less flood-plained, while in their
upper portions, particularly about their incipience, they are marked
by steep-sided valleys that sink sharply below the general upland.
Generally these streams, after flowing for a longer or shorter dis-
tance across broad, flat meadows, enter the Falls without any marked
change in their grade. Such is the manner in which Owl Branch, a
tributary at Turner’s Crossing, and several other streams join the
Falls. At Parkton, however, Fourth Mine Run is interrupted by a
series of low rapids after leaving its meadow-land. These rapids are
due in part to gravel-bars, and in part to ledges of the gneiss that
enable Fourth Mine Run to descend about six feet in the course of
the hundred yards between its flood-plain and the channel of the Falls.
This seems to be an exceptional manner of junction and is probably
due to the local development of a more resistant band in the gneiss
at this point.

Tue West Brancu.—The larger, more interesting, and more im-

portant branch of the Gunpowder, termed the West Branch, results
12
178 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

from the confluence of two streams near the paper-mills southwest
of Lineboro, on the Western Maryland Railroad, in the northeastern
corner of Carroll county. While local opinion regards the northern
branch as more important and as the head of the Gunpowder, near
Melrose postoftice, there are just as good reasons for regarding the
southern branch, heading north of Manchester, as of equal import-
ance. Both of these streams flow northeast for two or three miles in
narrow valleys, then unite and pursue a general southeasterly course
for fifteen miles or more across the gneiss and phyllite to a point
between Monkton and Whitehall, where the West Branch joins the
main stream just described. In this distance it receives the waters
of several large tributaries, especially Big Grave Run and Georges
Run. The valleys of the two head-streams are characteristic. The
northernmost, after emerging from the hills as several small rivulets,
flows for some distance through a broad and open limestone valley un-
til just before its union with the Southern Branch when it cuts directly
across a band of gneiss forming a steep-sided gorge. This gorge is
now filled with an artificial flood-plain, due to the construction of a
mill-dam at its lower end. Since the difference in elevation between
the northern and southern streams is fully twelve feet, the waters of
the stream must have flowed very rapidly through the gorge before
they were artificially restricted. The Southern Branch flows in steeper-
sloped valleys whose cross-sections approach more closely to the shape
of a V. The channels are always marked by narrow flood-plains,
which vary in their width according to the character of the under-
lying rocks. The floor of the valley seems in many instances to be
due to the solvent action of the stream and the slowly moving ground-
water of the adjacent hills. The stream itself meanders over this
plain in a trench, four or five feet below the surface of the valley-
floor, exposing a section through alluvium, loam and stream gravels.
The presence of angular blocks of gneiss, one or two feet in diameter,
in the bed of the stream indicate its efficiency during floods.

Below the confluence of the two tributaries the waters flow through
broad, level meadows, averaging seventy-five to one hundred feet in
width, that make a sharp line at the base of the steeply inclined sides
MARYLAND WEATHER SERVICE 179

of the deepening gorge which widens into more gently rounded valleys
where the course of the stream is over the less resistant marbles and
phyllites. For example, just below Rockdale the West Branch leaves
its steep, narrow gorge for half a mile or more and wanders across
level meadows a quarter of a mile in width.

At the confluence of the West Branch and its tributaries the valleys
usually open out somewhat, and the flood-plain extends up the valleys
of its tributaries for a distance of several hundred yards. Above
this flood-plain the side streams, such as Georges Run, emerge from
small gorges of steep grade which they have cut through the under-
lying gneiss. Above these smaller gorges the streams are usually in
long, broad meadows, extending back to the hills that rise to the
general level of the upland.

Tur Bie Gunrpowprer.—After the West Branch joins the so-called
Falls of the Gunpowder the volume of the Falls is considerably in-
creased and consequently the gorge becomes wider. The increased
power resulting from increased volume is indicated bv the larger rock
fragments now found in its channel and also by the occasional evi-
dences of lateral swing and corrasion found in the flood-plain. Gneiss
boulders, two feet in diameter, are found in the channel of the West
Branch, while in the flood-plain deposits and in the present channel of
the Falls, just below Monkton, a few sub-angular fragments, two to
three feet square, occur. A well-marked instance of lateral corra-
sion, due to increased power, is between Monkton and Pleasant Valley
Station. At this point a low level-topped ridge of gneiss rises five
feet above the swampy flood-plain. The ridge is almost wholly sur-
rounded by water, even when the Falls are at a low stage, but a low
neck of gneiss, about three feet above water level, joins it to the high
projecting bank around whose base the Northern Central Railway
passes by a cutting and an embankment.

The general characters of the gorge of the Big Gunpowder below
Monkton are but slightly modified from those of the gorge above
the junction with the West Branch. The flood-plain is on the whole
but little wider, averaging sixty or seventy feet, and often narrows to
less than fifty feet. It is always a collection of sand and fine gravel,
180 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

sometimes with a foot of brown loam on its surface. It abuts sharply
against the sides of the gorge, and these are either rocky cliffs or steep
grass-grown slopes in which the rocky ledges are but thinly buried.
These steep slopes and low cliffs rise sharply for one hundred and
fifty or two hundred feet and then round off, grading somewhat less
rapidly into the gentle streamward slopes of the general upland.
These general features characterize the Big Gunpowder as long as its
course lies within an area of gneiss or granite. The bands of marble
which it crosses, however, sometimes modify the stream topography in
minor details.

After receiving the waters of its largest tributary, Western Run,
the Gunpowder passes through one of the most interesting portions of
its course, in the vicinity of Cockeysville. While running on the mar-
ble, which extends from Ashland to Lutherville and thence eastward
to Loch Raven, the stream turns sharply to the east and enters a deep,
narrow gorge cut through a boss of granite, which rises three hundred
and sixty feet above the level of the marble valley. The stream has
scarcely any flood-plain, and at times the gorge becomes so constricted
that there has not been room enough to make a road along the edge of
the flood-plain without considerable blasting. ‘The bottom-land in
this portion of its course, unlike that farther up-stream, has been
formed by the abrasive action of the stream on the hard underlying
rocks instead of being built up by deposition. Although marble
bands are encountered in the passage through this granitic area the
level of the marble slopes is little below the general level of the
upland surface. There is, however, a bench three hundred and fifty
or four hundred feet above the course of the Gunpowder which con-
forms in altitude to the level of the residual portions of a pre-Potomac
valley-floor that has been partially preserved in the Potomac-capped
levels at Lutherville, Timonium, and points in the Green Spring
Valley.

The lower portion of this gorge, which debouches at Loch Raven,
has been modified by the artificial restrictions which have been con-
structed at the latter point, as a portion of the Baltimore water-supply
system. Below the dam the stream enters the continuation of the
MARYLAND WEATHER SERVICE 181

marble belt which it left at Ashland, and continues in it until it
enters the gneiss once more near Summerfield. Below this point the
river flows in a gorge of increased depth and steeper sides, and the
rocky channel of the river occupies a narrow trench two hundred and
fifty feet below the upland, with a floor varying in width from
seventy-five to one hundred feet. The narrow flood-plain extends
about twenty-five feet back to the foot of the canyon walls on either
side of the stream. Through it project numerous ledges, showing
that there is but a thin veneer of alluvium covering the solid gneiss
beneath.

The grade of the channel steepens more rapidly from the point
two miles above the crossing of the Belair Turnpike to the mouth of
the river, and is frequently broken by ledges and small cascades
(Plate XIX). As the channel steepens the slopes of the gorge begin
to retreat and to lose a little of their steepness, until after a rapid fall
and several sharper cascades and rapids the river debouches into its
estuary between Loreley and Bradshaw.

Western Run.

Western Run, which is the most important branch of the Gun-
powder below Monkton, heads on the limestones and gneisses of
Worthington’s Valley, just north and east of Glyndon. After flow-
ing across a small tongue of gneiss it runs eastward for about five
miles, following the southern boundary between the gneiss and the
marble band extending from Glyndon to Glencoe. Two miles west
of Belfast P. O. the Run turns sharply southward, deserting the band
of marble, and flows for four miles in a winding gorge through the
gneiss until it emerges on the marble near Cockeysville, only to re-
enter the granite at Ashland Furnace on its way to join the Big Gun-
powder Falls, one mile above the Warren cotton-mills. The principal
tributaries of this trunk stream from west to east are Gladman’s Run
on the south, Piney Run and Black Rock Run on the north, and
Beaver Dam Creek which enters it from the southwest.

Much of the territory drained by these streams is characterized by
broad, open, slightly rolling valleys of very moderate depth, bounded
by rather steep slopes. The trend and boundaries of these valleys are
182 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

intimately related, in most instances, to the direction and extent of
the marble areas that occur as a number of narrow, approximately
parallel bands, separated by narrow strips of gneiss. The drainage
lines, as shown by the large scale map (Plate XVI), run directly
across the general trend of the bands, and with the exception of the
northern branch of Beaver Dam Creek, only small streams have
courses along the marble. The general level of the area formed of
these interwoven bands of marble and gneiss, is slightly below that
of the surrounding rocks. The gneiss bands usually form the minor
divides within the basin, but not infrequently the divides run as
easily across the marble as across the gneiss. The two broader areas
of marble occurring at Belfast P. O. and Mantua Mills, where the
narrow bands unite, are lower than the general level of the area be-
cause of the greater solution to which they have been subjected,
owing to the fact that both of them are crossed by moderate-sized runs.

gv ¥

& é a...
Qneiss a T “ie iu pelle. S Sneiss

Fic. 16.—Profile across Western Run Valley.

The vicinity of Belfast P. O. and Priceville now appears as a plain,
whose trenched and slightly dissected surface is indicated by the
summits of gently rolling hills bounded by comparatively steep slopes
of gneiss. The summits representing the former valley-floor are now
covered with a thin deposit of coarse gravel and cobbles of vein
quartz that have been brought from some distance and depesited by
a stream larger than the Piney Run of to-day.

Piysy Run.—Piney Run and its tributary, MeGill’s Run, rise on
the gneiss of Baltimore county near the Carroll county line, due
east of Westminster. The two streams follow parallel courses across
gneiss, phyllite, and marble down to Dover, where they unite and
flow by a common channel to Western Run. These streams have
sharply incised and steeply bounded courses on the gneiss, with fresh
flood-plains of moderate width, and channels which are largely com-
posed of gneiss fragments and, rarely, quartz pebbles.

Grapman’s Ruy.—Just at Mantua Mills, half a mile below the
MARYLAND WEATHER SERVICE 183

mouth of Piney Run, Gladman’s Run joins Western Run. This tribu-
tary rises on the large gneiss area west of Cockeysville and flows north-
ward across the narrow marble and gneiss belts to the main stream.
The hills gather closely about its headwaters on the gneiss and rise
steeply from the stream-bed, but in the marble they become lower
and more rounded towards the stream, while a flood-plain thirty feet
wide is developed and continues with the stream until it emerges into
the flood-plain of Western Run. Small subsequent valleys are being
developed on the narrow marble band, but they are clearly in very
youthful stages of development. Gladman’s Run, in crossing the
narrow band of gneiss south of Western Run Valley, does not seem
to suffer any contraction in the width of its channel. The Run is
here about six feet wide and flows in a meandering course on a flood-
plain fifty feet wide. Its channel is chiefly of gravels and sand.
The gneiss hills are generally more or less under cultivation and
slope down sharply for about thirty-five feet to the level flood-plain
of the Run.

Brack Rocx Ruy.—Black Rock Run, like Piney Run, rises on the
gneiss and phyllite areas northwest of the marble bands and flows
southeast across the marble bands and gneiss to join Western Run near
the crossing of the Falls Turnpike. In its upper course it is a small
and rapid stream, three to six feet wide, flowing through a broad,
level meadow-land. The flood-plain has a width of about two hun-
dred feet on the main branch and is bounded by steep, smoothly
rounded slopes of chloritie schist. A smaller tributary, flowing
parallel to this portion of the main stream and lying west of it, has
a very similar valley though on a smaller scale. The steep side-slopes,
however, are in this latter instance less rounded and more rugged and
along the lower portion of the stream course they are sometimes even
precipitous.

About seven miles from its headwaters Black Rock Run crosses a
narrow band of marble, at the same time turning southwest and fol-
lowing the southern edge of the marble for about a mile before it
bends southward and again cuts into the gneiss. Just where it makes
the first bend after entering its valley on the marble, a small subse-
184 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

quent, also located on the marble, joins the Run from the east. This
small stream is bounded by steep slopes of the marble, and its head-
divide on the latter is still almost as high as the general level of
the gneiss-supported upland. As the junction with the larger stream
is approached this narrow valley widens, the contours become milder
and the general characters of a valley developed upon a marble or
limestone band appear.

In this small subsequent valley, known as Stringtown Valley, better
than at any other locality in the Piedmont province, is seen the influ-
ence exerted by structure on the marble valleys of the district. The
foliation-planes of the gneiss and phyllite and the associated beds of
marble and quartzite all have a general southeast dip with an ineli-
nation of about 30°. The planes of weakness and fracture of the
marble are parallel to the planes of foliation. Therefore, a stream
working out its channel on the marble would have a tendency to
shift its channel laterally down the dip, because solution would be
easier and more rapid on that side of the stream. This shifting would
also be aided by the ease with which undermining of the opposite
bank by lateral corrasion could be carried on (see Fig. 5). Now,
the right or northwest valley-slope of Black Rock Run has a very
mild and even descent to the flood-plain of the stream, while the left
hand or southeast slope is steep and rough with the stream flowing at
or near the base. The right hand slope is largely on the marble,
while the left hand slope is about two-thirds on the gneiss. Thus the
configuration of the valley is not symmetrical with respect to the
location of the stream as is the usual case, but has a cross-section
resembling 2~- with the stream at the lowest point. These unequal
slopes pass down into the even levels of the flood-plain and meadow-
lands through which Black Rock Run meanders for half a mile to its
confluence with the smaller western branch.

At the junction of the two streams the course turns southward into
the gneiss and enters a wild, narrow gorge just above Butler P. O.
This gorge is half a mile long, scarcely two hundred feet wide, and
its steep, rugged slopes are often bare, rocky ledges which stand out
as ribs of gneiss or quartzite. The cliffs slope abruptly down two
MARYLAND WEATHER SERVICE 185

hundred feet to the rocky channel of the stream. About a quarter of
a mile from the head of the gorge there is a band of resistant quartzite
which has withstood the wearing of the stream so well that a waterfall
thirty feet in height still bears witness to the hardness of the ledge,
although the channel has now cut down one hundred or one hundred
and fifty feet below the top of the gorge. This ledge has been util-
ized as the foundation of a mill-dam which still ponds the stream above
the falls, though the mill which it once supplied with water-power
has now fallen to pieces. Above the falls the stream is quiet and
inactive, but below the dam there is a rapid current in a channel of
steeper grade. It should be observed that the level, down to which
Black Rock Run has and can reduce the upper portions of its channel
and valley, is determined by the depth to which it can cut this re-
sistant quartzite band in the gneiss. In other words, the level flood-
plains and the floor of Stringtown Valley are incipient local peneplains
controlled by the quartzite sill. The lower portion of the channel is
filled with large and small fragments of quartzitie rocks which bear
witness to the great transporting power of the stream at high water.
Leaving this narrow course on the broader band of gneiss, the Run
occupies a steep-sided but more open course on the narrow marble
band just above Butler P. O. There the stream begins to develop a
small flood-plain which continues across the gneiss at Butler and
widens perceptibly where it joins the meadows along Western Run.

Braver Dau Creex.—The headwaters of Beaver Dam Creek have
their beginning about in the centre of the large gneissic area lying
west of the Cockeysville marble quarries and north of the Green
Spring Valley. The stream occupies a rather shallow, open valley
on the gneiss uplands and descends through a steep, narrow, wooded
ravine with very steep grades to emerge from this shut-in portion of
its course near the marble quarries at Cockeysville. Thence it fol-
lows a northeasterly course across a broad rolling valley of marble,
two miles in width, until at Ashland a sudden turn to the east car-
ries the Creek against the gneiss hills overlooking Cockeysville on the
east. Through these high hills it has cut a gorge a mile in length,
three hundred feet deep and fifty feet in width in its course to the
Gunpowder.
186 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

A large branch of Beaver Dam Creek drains the eastern half of a
narrow marble band and valley lying north of the gneiss on which
Beaver Dam Creek heads, and joins the Creek on the north, midway
between Cockeysville and the quarries. Thus its whole course lies
on the marble. The headwaters of this branch have worked back
westward along the marble about as far as the headwaters of Beaver
Dam Creek, but the side branching of the latter stream is much
more intricate than that of the former. Small side-streams of this
northern branch have cnt relatively short steep-sided ravines in the
gneiss slope on either side the marble, but they are very limited in
their extent and are as yet mere tendrils reaching out only a short
distance from the main stem. This branch of Beaver Dam Creek
(incorrectly designated as Western Run on the Baltimore sheet of
the U. S. Geological Survey) has its narrow valley partially filled
with iron-ore bearing sands and clays, which are similar to and
evidently of the same age as those found in the Green Spring Valley
and in the vicinity of Lutherville. These deposits are mainly con-
fined to the southern flank of the valley and extend half way up to
the top of the gneiss hills. Besides these terrace-like deposits about
Oregon the smooth floor and gentle, even slopes of this valley are
sparsely strewn with gravel and small cobbles of not more than five
inches diameter. The valley thus simulates in every way, except in
size, the even-floored, gravel-strewn Green Spring Valley, and the
same kind of evidence points to its having had the same origin and
history.

Jones’ Falls.

Jones’ Falls, like Western Run, drains a valley located along a
marble band, the Green Spring Valley, and so far appears to have
taken advantage of the opportunities offered by calcareous rocks for
developing a drainage basin with the smallest possible expenditure
of energy. It also takes an anomalous course across a point of com-
paratively unyielding gneiss when it might have followed an easier
course around the point, by keeping to the marble. These two con-
tradictory performances by the stream, as well as the considerable
amount of interest that many of the inhabitants of Baltimore are
forced to take in the stream, are sufficient to draw attention to it.
MARYLAND WEATHER SERVICE 187

Jones’ Falls may be said to originate on the gneiss northwest of the
small oval marble area called ‘“ The Caves.” Three quite minutely
branching streamlets flow from the gneiss into the basin-like depres-
sion of “The Caves,” and there uniting in one stream, pass out
through a deep, rugged defile leading from its southeastern corner.
The stream continues in a steeply bounded course until it reaches
the Green Spring Valley, west of Chattolanee and opposite the station
of Stevenson on the Green Spring Valley branch of the Northern
Central Railway. Here it is joined by the somewhat smaller stream
that has pushed its head along the Green Spring marble out to
Reisterstown Turnpike. The principal fork of this small tributary
heads on the gneiss northeast of Chattolanee Hotel and flows south,
while a small run flowing north from the same point drains the
southwest corner of “ The Caves.” The crest of the divide between
these two small runs is relatively wide and below the general eleva-
tion of neighboring stream-divides. The crest of this low, saddle-
shaped divide stands at five hundred and forty feet above the level
of the sea, while the altitude of divides between much larger streams
in the immediate neighborhood averages at least six hundred feet,
and the general altitude of the rolling upland plateau is six hundred
and fifty feet.

It is a noteworthy fact that all the streams joining Jones’ Falls
from the south are small and insignificant in volume, though two
branches of good size unite with the main stream on the west of
Rockland and the large West Branch at Mt. Washington brings a
considerable volume of water to swell the stream. This characteristic
of shortened affluents from the south may also be observed in the
case of Mine Bank Run and its fellow of the Gunpowder drainage
west of Loch Raven station, and to an equally marked degree in the
case of Western Run. Such unsymmetrical drainage patterns, de-
parting so widely from the normal plan, which is beautifully ex-
hibited over neighboring portions of the Piedmont Plateau, indicates
that some disturbing factor is, or has been, acting to cause these
variations. It is true that along the south side of the Green Spring
and Mine Bank Run valleys there is developed a heavy quartzitic
188 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

phase of the general gneisses which is lacking on the north boundary,
and it is natural at first to conclude that the stunted growth of the
streams entering from the south is the result of the superior resist-
ance offered by this quartzite band. This is undoubtedly an im-
portant factor and it must be conceded that, in part at least, the slight
development of these streams may thus be accounted for. When,
however, the tavo sets of tributaries which supply Westerv Run are
compared in a similar way it appears that here also there exists a
greater development of the northern tributaries. The lithologic
conditions in the two cases are often precisely the reverse. No re-
sistant band of quartzite runs along the southern boundary of the
main valley. On the contrary, the quartzite, which is frequently
associated with the Piedmont marble bands, has been found chiefly,
if not solely developed along the northern boundaries of Western
Run Valley. Indeed, it is a significant fact that in the cases of
Black Rock Run and others, the streams have cut gorges through
beds of quartzites and yet exhibit a greater headwater development
than the smaller tributaries of Jones’ Falls.

These facts make it impossible to explain the development of the
streams by regarding them as merely the products of the usual shift-
ing of divides controlled by the lithological variations in the territory
drained.

Two explanations for this unsymmetrical development of tributaries
may be offered. The first is that a general tilting of the land toward
the south has increased the activity of the southward-flowing streams,
while it has put the northward-flowing streams at a disadvantage.
The second explanation assumes that originally the general trend of
the whole drainage was continuously southeastward, but that certain
streams, favored by being originally located on the less resistant
marble, have subsequently developed rapidly along these lines of
least resistance, have intercepted and diverted the southeastward
drainage lines and, deepening their valleys, have developed short,
young side-streams from the south while keeping the long, old trib-
utaries from the north.

Proceeding according to the first hypothesis, suppose that Fig. 17
MARYLAND WEATHER SERVICE 189

represents the cross-section or cross-profile of a valley and its side
slopes, drawn to natural scale. The main stream at ordinary stage
wanders somewhat from side to side of its valley V building a nar-
row flood-plain. It is supplied by side-streams which drain the general
surface of the upland & — P, and may be assumed to be equally de-
veloped on either side. As long as the land remains in this attitude
erosion and stream development will proceed evenly and no peculiar
features will be developed which cannot be referred to the usual
processes of stream evolution upon a terrane of varying lithologic
character. There will be a rapid development by the streams of a
grade that will represent a balance between the volume, the load
and the declivity of grade of the stream. The grade thus established
will be maintained as long as the factors which have determined it
remain constant. If from any cause this condition of affairs is
altered by a tilting to the left the balance of forces before obtaining

 

Fig. 17.

will be disturbed and changes in stream activities must result. The
immediate effect of such a tilt is to alter the slopes of the beds of
those streams whose directions were more or less at right angles to
the axis of tilting. A little study of the figure will make it plain
that such a change in the general attitude of the land will decrease
the steepness of the slope from & to V, while the valley-slope from
P to V will have increased declivity. Moreover, since the valley-
bottom 1 has an appreciable breadth it also will undergo tilting
towards R, and the effect will be a shifting of the stream towards
the latter point. The streams whose courses lie from P to J,
having their beds steepened, would experience an increase in the
velocity of their currents, a corresponding increase in cutting power,
and a consequently increased rate in the deepening of the chan-
nels and in the extension of the headwaters. On the other hand,
the streams flowing from R to V would experience a decrease in
their slope and a consequent loss in their velocity and cutting power.
190 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

They would accordingly not be able to extend their drainage areas as
rapidly as before, or to deepen their channels. If sufficient time
elapses it must come to pass that streams on the slope P— V will
extend their headwaters at the expense of streams on the slope
F — V, thus shortening the latter streams.

In an area which has been tilted, therefore, the streams flowing
in the direction of the tilting will have deeper valleys, more rapid cur-
rents, and an increased branching among their headwaters. The
streams flowing against the tilt, on the other hand, may be of the same
depth as before the tilting, or possibly even less, since the decreased
velocity of the streams may cause them to deposit some of their load of
debris. They may not extend their drainage basins by headwater
erosion and may even suffer some shrinkage in volume as the result of
the encroachment of the other more favored streams.

A comparison of the conditions demanded by the preceding ex-
planation with those obtaining in the main streams and tributaries of
Jones’ Falls and Western Run shows that while there are many points
in common the degree of coincidence is not marked. Although the
streams flowing southward uniformly have greater development and
are more aggressive and powerful than those flowing northward, and
although the streams flowing eastward follow the south side of their
valleys more or less closely, yet those flowing northward are rarely
one-half as long or one-third as well supplied with smaller side-streams
as those from the north. The former, moreover, do not show any
sign of decreasing in volume or lessening of grade, but, on the con-
trary, present the steeply bounded, narrow valleys with high-grade
channels that characterize side-streams in their earlier stages of
development. It is, therefore, evident that the preceding hypothesis
of a general tilting does not fully explain the unsymmetrical distri-
bution of the tributaries.

The second hypothesis, based upon a partial rearrangement of the
drainage lines of the two streams from a former, more southerly
course, requires at the outset some competent means of placing the
large and small streams in their initial positions across the marble and
quartzite beds. This may be accomplished by supposing the whole
MARYLAND WEATHER SERVICE 191

network of drainage lines newly located upon the face of the country
across gneiss, quartzite, marble, or serpentine without reference to
any differences in resistance.

Starting with an initial arrangement of the drainage somewhat as
shown by the accompanying diagram, Fig. 18, the history of the
stream may be inferred as follows: As the various streams cut their
channels deeper and gradually pushed out their headwater and side-
streams, the branches already located on the marble and the new
tributaries there originating were able to grow in size and power
more rapidly than the streams located on the resistant gneiss and

 

oR Marble

      

y

whe itena

t 4 4 Gneiss

 

 

Fic. 18.—Former unadjusted course of Jones’ Falls.

quartzite. These favorably located streams thus outstripping in their
growth the others and guided in their development by the course of
the marble bands would soon cause some readjustment of the smaller
streams. For example, a small side-stream beginning near Rockland
may have worked northward past the quartzite ridge and acquired

headwaters from the north and side-streams on the marble.’ Starting

1 This is a very probable change, for a stream flowing across the point of
gneiss with its hard, resistant quartzite facing, would need a very long time
to reduce its channel, while a much smaller stream starting on the soluble
marble would wear down its course very rapidly.
192 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

from the same point, Rockland, the smaller stream would then reduce
its channel to a lower grade than the slightly larger stream on the
gneiss could possibly do in the same time. Soon a critical stage in
the position of the divide between the two streams would be reached.
The smaller stream, from its lower grade, could push its divide
nearer and nearer to the main channel of the larger and higher stream,
until at last the latter would be intersected and all the waters of its
upper course be diverted into the channel of the small invading

 

 

 

 

 

Fic. 19.—Present partially adjusted course of Jones’ Falls.

diverter. The lower course of the beheaded stream would continue
in its former channel but much shrunken in volume and unable to
push its headwaters against the opposition of the more powerful and
favored pirate stream that cut off its headwaters. The same or
closely similar changes would be going on between the other streams
where they cross the marble belt. Various interstream adjustments
probably would occur until, finally, Jones’ Falls, as at present, favored
by the long stretch of marble down to Lake Roland and Rockland,
had captured the heads of all the streams crossing the eastern portion
MARYLAND WEATHER SERVICE 193

of the marble, and led out the drainage by one common channel
around the gneiss and down to Rockland.

While these changes in the stream courses were slowly being
accomplished the streams must have been gradually deepening their
channels in the gneiss until one by one they were diverted to courses
on the marble. If this is the manner in which the Jones’ Falls and
Western Run systems were developed, there should be some traces of
the valleys carved by the streams before their diversion. Since no
such abandoned channels have been found, it must be inferred either
that the diversion of the earlier stream courses proceeded so rapidly
that the courses on the gneiss were not deepened sufficiently to permit
of their being distinguished amidst the various inequalities now ex-
isting, or that the early streams were not originally placed as sup-
posed but were gathered into common channels along Green Spring
Valley and Western Run.

A third hypothesis assumes that the sediments-of the Coastal Plain
were formerly thick enough in this area to completely mask the former
Piedmont topography, and that the streams were located independ-
ently of earlier valleys and divides and were controlled only by the
surface configurations of the Coastal Plain.

No one of these various hypotheses is entirely satisfactory and the
facts at hand seem to indicate that this unsymmetrical distribution of
the tributaries is not due to a simple cause but is the result of the
combined action of two or more such sets of conditions as have been
implied in the foregoing hypotheses.

AcE or Jonzs’ Farrs.—At several points along the lower course
of Jones’ Falls, especially within the corporate limits of Baltimore
city, are beds of coarse gravel, sands, and clays, resting on the beveled
edges of the gabbro and gneiss. The line of contact between these
two formations is well shown near the eastern end of North avenue
bridge and at the Jones’ Falls gneiss quarries some distance up-stream.
At both exposures the contact appears as a sharply drawn horizontal
line separating the even, flat surface of the eroded erystallines from the
heavy deposits of gravel which have been determined by Darton * as of

*See “ Geological Map of Baltimore and Vicinity,” Geo. H. Williams, Ed.;
pub. by Johns Hopkins University, 1892. N. H. Darton on Sedimentary
Formations.

13
194 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Pleistocene age. Similar gravels are found scattered over the limestone
floor of the Green Spring Valley. At a point opposite Stevenson
fifty or sixty feet above the present stream channel are located some
old abandoned iron mines. The exposures in the open pit show the
following section of sedimentary deposit. At the bottom are about
fifteen feet of stratified mottled red and white clays with several beds
of fine, white quartz sand and clayey pellets. Above the sand and
clay pellet bed come two or three feet of gravel in which the diameter
of the pebbles does not average above three or four inches. The
pebbles are of quartz and well rounded, and may therefore be set
down either as of marine littoral or of fluviatile origin. These char-
acteristics ally the deposits with those of the Potomac* group, and
this correlation is corroborated by the fact that neighboring portions
of this same marble tract are overlaid by Potomac beds. It is there-
fore evident that the depression now called Green Spring Valley and
occupied by the headwaters of Jones’ Falls was in existence as a
depression in Potomac time, and that it was submerged during the
same period and received the deposits above mentioned. Later, the
Pleistocene gravels were spread over the eroded surface of these
earlier formations and through these clays, gravels and crystallines
the present Falls has cut and is still cutting its lower gorge. The
stream at this point must, therefore, be vounger than the Pleistocene
deposits below which it has trenched its channel.

Discussion or Prorite.—The accompanying line drawing, Plate
XIX, represents in some detail the varving slope or grade of Jones’
Falls channel, and a study of this profile brings out several interesting
facts concerning the development of the stream. The first obvious
fact is that the bed of the stream, where located on rocks, approxi-
mately uniform in lithologic character, has well-defined and widely
recognized features. Starting from the divide the grade is at first
very steep but rapidly loses its declivity, and for two-thirds of its length .
approaches the horizontal by constantly decreasing amounts. The
normal grade is shown by the dotted line below the solid one repre-
senting the profile of Jones’ Falls. While the upper half of the
Jones’ Falls curve is substantially in accord with the normal profile,

‘Report of Maryland Geological Survey, vol. i, 1897, p. 190.
MARYLAND WEATHER SERVICE 195

the lower half of its course deviates very markedly from the latter
curve. Instead of being slightly concave and very nearly horizontal
the channel descends by a decidedly convex curve. Thus the upper
half of the stream is characterized by a matured and perfected grade
profile, while its lower course has a very youthful character.

Besides this marked change in the general form of the stream’s
grade between Green Spring Vallev and Baltimore, there are several
smaller cases of sudden change of grade extending over shorter
stretches. The best-defined localities, where these breaks in the even
continuity of the grade occur, as shown by the drawing, are at and
just below the dam at Lake Roland, at Woodberry and Hampden,
opposite Druid Hill Park, and in Baltimore between Eager and Pres-
ton streets. At each of these points the stream drops from ten to
twenty feet by low falls or cascades within stretches of fifty yards or
less. An exception is found at Woodberry where, in the course of
half a mile, the stream falls forty feet. These several interruptions
in the evenly descending profile of the stream might be due to one
of two causes, both of which are to be found within the Piedmont
Plateau province. A band of rock more resistant than adjacent rocks
down-stream will produce such falls, because it will persist as more or
less of an obstruction to the stream after the more easily removed
bands down-stream have been worn down to a lower level and a
milder slope. Falls due to such obstructions are especially common
in the Appalachian region where the mountains and ridges are com-
posed of strata of different degrees of resistance. A more closely
allied illustration is found at the rocks of Deer Creek where quart-
zite and conglomerate produce a cascade in Deer Creek because they
are more resistant than the foliated micaceous gneiss farther down-
stream.

The second cause for such cascades is dislocation. If a plane of
dislocation or faulting with the up-throw on the up-stream side, or
the down-throw on the down-stream side, cross the channel of a
stream, then, supposing any considerable dislocation to have taken
place along that plane since the stream began to cut its channel, it is
plain that there must be some cascade or fall in the stream from
196 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

the uplifted side to the down-thrown side of the plane. | McGee‘ has
explained the cascades on the eastward-flowing Piedmont streams by
assuming both causes. In the particular case of Jones’ Falls, and
also on one or two other streams, it is found that most of the cascades
and falls occur where dikes of medium-grained pegmatite have been
intruded in the gneiss. This pegmatite is less easily corraded than
the foliated, micaceous gneiss, and therefore stands out in slight relief
on the steam-bed as the sill of the falls. There are no evidences of
special faulting in the immediate vicinity of the cascades except in
the drop just below Lake Roland; but as there are undoubtedly
numerous small faults throughout the Piedmont, it is possible, per-
haps probable, that these fall-points are located by such dislocations
as well as by the more resistant pegmatite.

The recent elevation of the stream basin, inferred from the trench-
ing of the Jones’ Falls channel below the Pleistocene gravels, is
verified by the character of the stream’s profile. The concave profile
of the up-stream area contrasted with the convex profile lower down
clearly indicates that, after once having reduced its channel to a
normal profile (Fig. 3) and having had the Pleistocene gravels and
clays spread along it, a subsequent uplift has incited the stream to
renewed activity in cutting its channel to the new and lower base-
level. When a stream thus begins to reduce its channel to a new
level the start is made at the lowest point, or the mouth of the stream,
and thence the work of reduction proceeds backwards up-stream. The
profile suggests that the Falls is already approaching its new grade
along that portion of its course between North avenue and the harbor,
but the convexity of the profile between Baltimore and Lake Roland
indicates that along that portion of its course the down-cutting of the
stream is still insufficient to counteract the upward tendency of the
land. The profile of the Falls in Pleistocene times, as evidenced by-

the levels of the remaining gravels, is represented by the dot and dash
line of the drawing.

*W J McGee, U. S. Geol. Surv. Sth Ann, Rept., 1885-6, p. 620, ete., and
plate 1xviii.
MARYLAND WEATHER SERVICE 197

Patapsco River.

The drainage basin of the Patapsco may be divided into two sub-
divisions of unequal size and power, corresponding to the two main
branches of the river. The larger stream, or the North Branch,
which has its headwaters on the eastern slope of Parr’s Ridge in the
vicinity of Westminster, flows southeastward about ten miles to the
Baltimore county line, near Glen Falls, and then turns southward
following a somewhat tortuous course to its junction with the South
Branch between Marriottsville and Woodstock. The smaller, South
Branch, also rises on Parr’s Ridge, about sixteen miles south of West-
minster, in the immediate vicinity of Mount Airv, and pursues a
winding course whose general direction is due east for about sixteen
miles before it unites with the North Branch to form the main stem
of the Patapseo. From this confluence the Patapsco pursues a
broadly curving course, turning finally southeastward and eastward
to enter the head of the Patapsco estuary, twenty miles from Mar-
riottsville.

South Brancu.—The South Branch occupies a shallow, meander-
ing gorge depressed about two hundred feet below the general level
of the Piedmont upland. The valley of the stream in its upper
portion has few canyon-like characters, but is comparatively broad
and shallow on account of the somewhat less resistant nature of
the rocks in this district. Small lenses or bands of rock of greater
resistance cross the valley, for example, at Woodbine Station or on
the railroad between Hood’s Mills and Morgan, causing the bound-
ing slopes to increase in declivity and the valley to become slightly
narrower. A short distance above Sykesville the valley begins to
lose the more open character of its upper portion and gradually
narrows and steepens, its side-slopes assuming the more gorge-like
characters which it retains with minor variations down to its junction
with the North Branch.

The particular bands of resistant gneiss mentioned above have
special interest because of the marked influence which they have
exerted on the development of the flood-plains of the stream and on
the past industries of the locality. By reason of the resistance which
198 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

these bands offer to the down-cutting of the channel, small side-streams
flowing into the South Branch above them have, with the aid of the
larger stream, developed marked expansions of the valley and the
flood-plain. The resistant ledges produce low falls in the main
channel and have furnished favorable sites for two mill-dams. The
quiet, waters of the ponds produced by these dams were favorable to
the deposition of considerable quantities of mud which have partly
obscured the surface of the eroded expansions of the valley. Now
that the dams are broken the ponds are drained and their old bottoms
have become green swamp- and bog-lands, resembling the poorly
drained surface of a glaciated district, or the former channel of a
beheaded stream.

The flood-plain, which is so extensive in the upper portion of the
stream, gradually contracts down-stream until it reaches the more
confined gorge portion, where it attains a fairly uniform width of
two hundred feet. The channel itself is often located on ledges of
the metamorphic rocks only thinly covered by beds of gravel and
sand, and is sometimes broken in its descent by bare ledges of the
rocks appearing through the flood-plain deposits.

All of the more important side-streams of the South Branch, such
as Gillis Falls, Piney Run, Piney Branch, and Winter Run, are
situated on the northern side of the main stream. As they differ in
many respects from the larger stream they deserve especial mention.
Their courses may be divided into three portions. The lower parts
of the streams are generally occupied for two hundred yards or more
by extensions of the flood-plain which bounds the channel of the
main stream. For this distance the small valleys are more open than
they are higher up-stream and the side-slopes are no steeper than
those facing the South Branch itself. In the second portion of their
courses the broad flood-plains become more constricted, the steepness
of the side-slopes increases, and the stream channel becomes rocky or
filled by boulders whose size often indicates that they have rolled from
the neighboring slopes, since they are too large to be moved even
at flood stage by the stream whose channel they obstruct. Above
this zone of rapids the streams are again characterized by flat, alluvial
MARYLAND WEATHER SERVICE 199

plains, bounded by steep, rounded hills, which rise sharply from the
surface of the latter to heights of one hundred or one hundred and
fifty feet above the meandering channels.

The bottom-lands themselves are composed mainly of black loam
with sand, gravel, and irregular fragments. They are well exposed
in sections made by the shallow gravel-floored trenches, from one to
three feet deep, which the meandering streams have incised in them.
These valley floors in the upper courses of the side-streams are due
to washing-down from the hills of such quantities of soil and rock
debris that the small streams fed by perennial springs in these valleys
are unable to keep their courses free.

The South Branch and its tributaries as a whole do not exhibit any
striking degree of adjustment to the general structural features of
the area of that portion of the Piedmont Plateau which they drain.
The foliation and various lithologic bands have a general northeast
and southwest strike, across which all the streams except the smaller
tributaries flow indifferently eastward and southeastward. Definite
examples of minor adjustment are not recognized except in the case
of a small stream entering from the south at Marriottsville, but the
most probable cases are all located on the south side of the Branch.
These streams are all of small size, the longest being hardly more
than five miles in length, and have their lower courses in general
accord with the strike of the foliation of the rocks.

At Marriottsville a small stream about three miles long has devel-
oped along the narrow band of marble which extends south from
the town for about ten miles. The stream follows the marble closely
and has developed a level-floored valley much like the smaller tribu-
taries described below. Although a subsequent stream, it has not
as yet captured all the territory covered by this belt of yielding
marble, nor are the remaining six miles or so to the south occupied
by subsequent streams, as might be expected. Small branches of
the Little Patuxent headwaters cross it in obviously fortuitous paths
and a branch from the Middle Patuxent, somewhat larger than the
stream at Marriottsville, also sends out branches which cross and re-
cross the lithologic boundaries without regard to the character of
the rocks.
200 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

A striking instance of non-adjustment is found in the case of
Winter Run, which rises in the area between the South and North
Branches and pursues a general east-southeast direction to Marriotts-
ville, where it joins the South Branch. The upper two-thirds of the
valley are broadly open, rather shallow, and characterized by a flood-
plain of moderate width which is sometimes rather boggy. The
course of the stream and of its small tributaries is everywhere at
variance with the general strike and structure of the gneiss. This
discordance becomes more marked where the stream is observed to
have chosen and persisted in what proved to be a difficult path across
a broad band of steatitic serpentine, through which it has had to cut
a narrow gorge. If the stream had been free to choose it could have
found much easier paths on either side of the band.

The difficulty with which the Winter Run gorge is being cut
down shows very clearly that the extensive headwaters of the Run
were not developed after the stream had cut its way back across the
gneiss and the serpentine, for had such a process been necessary some
stream starting on the marble would have developed faster and would
now be the main stream instead of the present Run.

Norra Brancu.—The North Branch of the Patapsco, which rises
in the vicinity of Westminster, occupies in its upper course a rela-
tively broad, shallow valley, bounded by steeply sloping, rounded hills
that rise one hundred feet above the small run at the river’s source.
Opposite the source is a low sag in the usually even crest of Parr’s
Ridge, which forms the divide.

The North Branch is characterized throughout by a flood-plain of
very moderate width, whose general characters vary but little from
one portion to another. For several miles down-stream from the
source, and to a considerable extent along the headwaters themselves,
there is a relatively broad plain of decidedly marshy character that
has not been developed as the result of retarded down-cutting in the
channel as was the case on the headwaters of the South Branch.
This is more probably due to the dams which have been built both
at Tannery Station and higher up at Westminster.

As the valley begins to expand, forming the broader reach between
MARYLAND WEATHER SERVICE 201

Patapsco and Glen Falls, the flood-plain widens into rich, fertile
meadows two or three feet above the level of the winding stream at
the usual stage of the water. Where the gorge makes a decided curve
the meadows become broadly developed on the convex side and some-
times a terrace ten to fifteen feet above the flood-plain is preserved
there also. The broad, flat meadows accompany the North Branch
as far as Glen Falls Station where, at the confluence with Glen
Falls and a small stream from the north, they unite with the flood-
plains of the latter streams and form a broad, triangular plot of moist
meadow-land.

Before passing on to a consideration of the lower course of the
North Branch mention may be made of the sets of river terraces which
have been developed along the portion of the stream just described.
Two well-marked terrace levels stand above the broad meadow-lands
and occasionally three may be distinguished. The lowest terrace,
which is not always found, stands four or five feet above the meadows
and is most often seen where the stream has cut an ox-bow channel
behind a higher portion of the meadow-land, leaving an isolated rem-
nant of a former flood-plain, which is not now submerged even during
the heaviest floods. Examples of this terrace, which is largely com-
posed of loam and fine gravel mixed with sand, may be seen along
the Western Maryland Railroad between Finksburg and Patapsco
Station.

The second terrace stands about ten feet above the meadows and
five or six feet above the first one, and is built of coarser quartz
gravel, sand and loam. This terrace is from thirty to fifty feet in
width, and a very persistent feature as far as Glen Falls where it
merges with certain terrace gravels belonging to the Glen Falls
terrace.

On the steep hillside eighty or ninety feet above the stream channel
is the third terrace represented by limited areas of water-worn gravels
and rounded or sub-angular pebbles. The quartz, gneiss, and quart-
zitic rocks which contributed the materials of these thinly spread
deposits, as well as the materials of the lower terraces, occur in the
immediate vicinity. As there are no traces of water-worn deposits
202 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

upon neighboring hilltops it is probable that the gravels of this high-
est level were supplied from fragments obtained in the immediate
vicinity of the stream. The absence of any traces, upon the hilltops,
of the Lafayette does not, however, prove that these gravels do not
represent the worked-over remnants of such a deposit. On the con-
trary it is quite possible that they are the only remaining evidence
of the former presence of that formation in this district.

Below Glen Falls the terraces decrease in importance, usually
being absent or developed only where some broad swing in the course
of the stream has left the old flood-plain on the convex side of the
curve. Asa rule, only a single terrace is found, corresponding in
elevation to the second one in the series of the upper portion of the
stream. At the mouth of Beaver Run, two miles south of Finks-
burg, the broad flood-plain of the Run joins the relatively narrower
one along the North Branch and lies about twenty feet below a broad,
flat, sandy terrace, forming the point between the Run and the North
Branch. Again, two miles north of North Branch Postoffice a mill
has been built on a flat terrace, twenty feet above the channel, which
passes around it in a broad swing. The section which the stream
makes where it cuts through the terrace shows that the latter is
composed of water-worn cobbles, gravel and pebbles, generally iron-
stained and overlaid by two feet of angular fragments of the black
hornblendic schist which forms the neighboring hills. The last locality
where the terrace gravels were seen before reaching the confluence with
the South Branch was half way between the latter point and North
Branch Postoffice. At this place a stream of moderate size, which
rises on the land between Hernwood and Harrisonville, empties into
the North Branch just east of a low knoll of marble. On the crest
of this marble knoll and extending down its slopes for ten or fifteen
feet is a thin veneer of gravels and pebbles closely resembling in
lithologic characters the materials of the second terrace found along
the upper course of the North Branch. At the southern foot of the
knoll the North Branch makes a smooth swing to the northeast and

east in a muddy and sandy flood-plain, which the small side-stream
has helped to build.
MARYLAND WEATHER SERVICE 203

The small tributary streams which combine as the headwaters of
the North Branch and others near Patapsco Station flow at the bottom
of relatively deep ravines. Their channels are usually somewhat
winding as they occupy narrow flood-plains strewn with angular frag-
ments which have rolled from the surrounding slopes. Sometimes a
stream crosses a band of quartzite or a quartz vein and then the little
valley grows narrower and the channel steeper. Generally the head-
waters of these small side-streams are characterized by open, shallow
catchment basins which form but slight depressions and belong to the
rolling surface of the Piedmont upland. Those larger streams which
join the North Branch along its lower course generally correspond
more closely to the types illustrated by Glen Falls and Winter Run,
while the sides of the gorge, particularly along its lower course, are
serrated by small brooks of uniformly steep grade confined between
high, steep banks. These latter streams do not take their rise any
considerable distance back upon the plateau.

Glen Falls, which is a stream about four miles in length, heads in
the vicinity of Glen Morris and Emory Grove. It begins as a small
rapid rivulet, flowing in a narrow wooded ravine, but within a mile
it is joined by several side-streams which swell its volume to a run of
some size. Simultaneously with this increase in volume of the stream
the valley widens and the flood-plain develops, gradually increasing
in width until it merges into the broad meadows at the confluence
with the North Branch. The side slopes of the stream are steep and
rounded, and descend sharply to the surface of the flood-plain.

One of the interesting tributaries of the North Branch is the small
stream already referred to as rising between Hernwood and Harrison-
ville and joining the North Branch between North Branch Postoffice
and the confluence. This stream, though having its headwaters
situated on the gneiss of the Piedmont, follows throughout most of
its length a subsequent course located on an S-shaped band of marble.
This marble band appears to be a detached portion of the long
strip of marble which stretches southward from Marriottsville and,
like the latter, has a band of quartzite along its eastern edge. On
the marble the stream has developed, by the solvent action of its
204 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

own waters and the ground-waters which gradually drain into it, a
wide, level-floored valley of rich alluvial soil. Below this meadow-
land the Run has sunk its channel from two to ten feet, the amount
increasing down-stream. At the highest floods it does not appear
that the meadow-land is extensively submerged, although the trench
is evidently filled. Twenty or thirty feet above the meadows a narrow
level bench runs along the valley-slopes, coinciding approximately
with the line between the marble and the gneiss. This bench is
somewhat better marked on the northwest side of the valley. On
the southwest side the band of quartzite causes the whole southwestern
slope to rise more steeply than does the oppesite one.

At the mouth of the stream a marble knoll, rising thirty-five feet
above the channel, embraces nearly all of the area occupied by the
marble. On the west of this eminence is a small side-stream, while
on the east the main stream cuts its course across a resistant band of

 

 

 

 

 

Fig. 20.—A minor adjustment in a side stream of the North Branch of the Patapsco.

quartzite and the gneiss beyond, which lie on the eastern border of
the marble. Behind the knoll between these two valleys is a low
saddle which is not covered with stream gravels. Through it now
passes the road from Hernwood to Marviottsville. An explanation
for the relations existing between the gravels capping the marble
hill, the location of the run on the quartzite, and the saddle in the
marble behind the knoll, is shown in Fig. 20.

The low marble knoll at K standing thirty feet above the present
level of the stream, is capped by a thin veneer of Pleistocene gravels,
while at the same elevation, along the sides of the marble valley of
MARYLAND WEATHER SERVICE 205

stream HH, are benches in the marble and sometimes even slight cuts
in the gneiss. Moreover, the elevation of these gravels and terraces
coincides with the better-defined and more-widely distributed terrace
found along the North Branch of the Patapsco. It is, therefore,
probable that in Pleistocene time the stream valleys stood near he
three hundred-foot contour within the territory included in the figure.
At.that time the heavily loaded streams brought down quantities of
sand and gravels, some of which was deposited on the triangular area
about K. Over the flood-plain thus formed the streams G and H
entered the Patapsco by some common channel perhaps between the
points 1 and 2. While building this flood-plain and the level expan-
sion of the three confluent valleys the combined forces of the streams
had reduced the marble, the gneiss and the quartzite to an approxi-
mately even surface, so that at the close of the gravel-depositing period
the three varieties of rocks were buried beneath the gravels and
sands of the streams.

When the elevation and tilting occurred, which closed the Pleisto-
cene deposition and revivified the overloaded and sluggish streams,
H and G were incised below the flood-plain while they held a position
vertically above that which they now occupy, except that G instead of
entering the Patapsco at 1 turned eastward and joined Hf by the
dotted course, a, and thence flowed with the latter stream to 2. The
streams cut rapidly through the old flood-plain which served to guide
them for a time in their down-cutting. When the foundation of
marble and quartzite was reached the deepening of the channels
went forward more slowly but continued until they also were reduced
to a grade about ten feet above the present channel. When this posi-
tion had been reached vertical corrasion seems to have ceased for a
while and the streams gave more attention to the widening of their
valleys, as recorded in the broad lower portion of the valley.

In spite of the retarding influence of the quartzite, Q, on the
downward-cutting of H and the opportunity which was thus given for
a stream to start on the marble at 1 and work back to the elbow of G
just above a, it would seem that G persisted in its course at a almost
up to the time when H began to broaden its vallev, because the floor
206 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

of the notch at a stands at almost as low a level as does the floor of
the valley about H. While this deepening of H and G was being
accomplished a small stream at J was slowly working away the gravels
of the Pleistocene flood-plain and the marble flooring beneath them,
eradually extending its head back towards G. The rate at which it
could develop and deepen its course was not as rapid at first as was
that of G and H, because these two streams were already established
and of great volume, while 7 was small and had heavy loads of giavels
to remove. Both the large and the small streams flow into the same
master stream, the Patapsco, whose large volume and great power
enabled it to maintain its channel at a very low slope, so that there was
no essential advantage, due to differences in the relative height of local
base level, possessed by the stream which emptied into the river lower
down. Thus the controlling factor in the rate of development of the
two streams came to be a lithologic one, and the speed of down-
cutting was determined by the relative resistances of the marble and
the quartzite. In this respect the small stream starting at 7 had an
advantage over H — G, since the former stream was located on the
easily degraded marble , while the latter stream had to reduce both
gneiss and quartzite before the marble could be brought to as low a
level as the channel of the Patapsco.

With the advantage of being located on the marble from mouth
to source 1 was able to work back and cut down so rapidly that it
tapped the channel of G before G and H combined could quite reduce
the resistant bands across their common mouth. Thus G was diverted
from its course at a and led out by an easier path, while its old
channel remained as a dry pathway and a low wind gap behind the
knob &. <A second uplift of lesser degree caused both the streams to
trench the valley-floors which they formed after the first post-Columbia
tilt, so that at present H is cutting a steep, rough gorge, now ten feet
deep, through the quartzite and gneiss, while G, on its marble floor,
has rapidly widened the new trench it cut until there are very slight
traces of the old valley level left along its course. -

Mat Srem or Pataprsco.—From the confluence of the North and
the South Branches to the head of the estuary of the Patapsco, the
MARYLAND WEATHER SERVICE 207

river occupies a well-marked gorge, which is sunk three or four
hundred feet below the general level of the plateau. ‘The steep sides,
narrow flood-plain and rocky channel of this portion of the stream’s
path are well illustrated by the accompanying views, Plate X,
which show the gorge in the vicinity of Ilchester and also at the
mouth of Brice’s Run. The features above enumerated continue
without material change to the bridge at Relay, where they give
place to the corresponding features developed by the stream on the
less resistant sediments of the Coastal Plain. Throughout the Pied-
mont stretch the channel is characterized by numerous low rapids,
particularly between Ellicott City and Relay, where the channel is
frequently crossed by pegmatite dikes, of greater or lesser width,
whose superior resistances, when contrasted with the foliated gneiss,
ete., cause them to stand out as low sills across the channel. Between
the sharper pitches of the channel often come stretches of rapidly flow-
ing but unruffled waters, whose smooth surface reflects the luxuriant
vegetation of the banks and adds greatly to the beauty of the stream.
These quiet stretches grow longer and more frequent in the gorge
above Hollofields and there accompany a slight decrease in the grade
of the channel. Just at Relay the gorge widens suddenly and rapidly
like the flaring mouth of a trumpet, sending the stream out into the
broader valley which it has carved on the Coastal Plain. Here the
stream ends its troubled course and occupies a broad, level-floored val-
ley, bounded by lower and more gently sloping hills with terraced
slopes.

There are very few examples of terraces along the rock-walled
gorge of the main stream. Where the river crosses a T-shaped marble
band at Alberton is the best and, perhaps, the only occurrence of a
terrace which this portion of the Patapsco valley can show. A few
hundred yards above the village the gorge suddenly broadens to a
width of a quarter of a mile between its higher banks. At the same
time the channel suffers a slight change in its position, so that the
stream running against its south bank is there bounded by steep
slopes of the gneiss rising one hundred and fifty to two hundred feet
above it, while on the north it is seen to lie not more than twenty-
208 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

five or thirty feet below a gravel-strewn bench, whose former even
surface is now somewhat dissected by the numerous gullies and small
waterways which are eating into it. This bench completely occupies
the widened gorge except for the narrow trench whose floor is formed
by the present channel and flood-plain. The overlying gravels are
thinly strewn over it and mixed with the rich soil produced by the
decomposing limestone. The pebbles are not of large size, as a rule,
and usually consist of sub-angular or partly rounded fragments of
vein quartz. At the down-stream corner of this terrace a slight emi-
nence rising from it suggests a second and higher level.

The other terraces along the lower course of the Patapsco are found
only after the river has left the narrow gorge and has entered the
broader valley by which it crosses the edge of the Coastal Plain.
Below Relay the river emerges into a broad amphitheater-like space
which is bounded by low hills of the Potomac formation and the Pleis-
tocene. The stream loses its troubled features and becomes a gently
flowing current which swings in broad curves over an alluvium and
gravel-covered flood-plain. The present channel and flood-plain is
immediately overlooked by two terraces built of Pleistocene gravels
and sands. The lower terrace has an elevation above stream channel
of about fifteen feet, and is perhaps a quarter of a mile wide where
best developed, e. g. in the vicinity of Elk Ridge Landing. The
broader and more strongly marked terrace stands about forty feet
above the present channel and attains a width of half a mile just below
the Baltimore and Potomac Railroad.

Both these terraces may be traced from their beginning at Relay
down to the shores of the harbor where they form topographic feat-
ures for a short distance along the water-front. The higher terrace
may also be traced for some distance up the valleys of Deep Run and
the other small streams which join the Patapsco between Relay and
Elk Ridge.

The type of the tributaries which flow into the lower course of
the Patapsco is represented by Brice Run. This is a stream about fire
miles in length which flows southward from Randallstown and the Lib-
erty Turnpike to join the Patapsco about half a mile above Alberton.
MARYLAND WEATHER SERVICE.

 

 

PROPILES

OF THE

DRAINAGE LINES

OF THE

EASTERN PIEDMONT PLATEAU.

 

 
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Warren Malls

VOLUME |, PLATE XIX.

 

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Lower Course of Brg Gunpowder. —t
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Jones Falle F :
i mile
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Patahseo River and Tributaries

 

 
MARYLAND WEATHER SERVICE 209

The fan-shaped area which is drained by this stream is characterized
by an intricately developed drainage scheme whose broad, shallow
valleys are bounded by gently sloping hills and floored by medium-
sized flood-plains. The valley increases gradually in depth until
about a mile from its mouth, when it begins to deepen and narrow
rapidly. The stream channel itself in this lower gorge is filled with
fragments from the sides of the valley and is comparatively steep,
averaging forty-five feet to the mile. There is a narrow flood-plain
even in this portion of the course, but its deposits of loam and allu-
vium are very thin, and it is largely formed of angular fragments of
the gneiss, as is the channel.

The broad, open heads of the valleys, combined with the deep,
narrow lower courses, are clear indications that relatively recent
uplift has taken place along the zone covered by streams thus char-
acterized. The Patapsco has since this uplift been able to cut its
channel down almost to grade again, and this in a comparatively short
time, because of its relatively greater volume. The sidestreams hav-
ing less volume and consequently less power have not been able to
work as rapidly as the large stream, so that their upper courses still
remain unaffected by the uplift, while their lower courses show the
trenching which resulted from the change in level.

CuayneL Prorirr.—The accompanying drawing, Plate XIX,
shows the vertical elevation above mean tide of the Patapsco, of its
two branches and of the streams which head against them on the
western slope of the divide of Parr’s Ridge. The drawing includes
the whole of the South Branch, the course of the main stream, and a
part of the North Branch with its main tributary, Morgan’s Run.
As the data for completing the grades of Linganore Creek and Bush
Creek were lacking they were carried only to the Monocacy.

The drawing shows that the Patapsco and its branches agree in
general with the other streams of the eastern Piedmont district.
The channel grade is on the whole very mild as compared with that
of the western Piedmont streams. The South Branch, which is of
less volume than the North Branch, is shown to have the steeper

grade of the two. This is in accord with the general law that, other
14
210 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

things being equal, the stream having the largest volume of water
will reduce its channel to the lowest grade. In comparing the grades
of these two streams it is well, however, to bear in mind that the
North Branch has a considerable portion of its lower course arranged
parallel with the strike of the foliation of the gneiss. The relation
of volume to grade is brought out very clearly on comparing the
grade of the Patapsco with those of the smaller Piedmont streams.
Streams like Jones’ Falls and Gwynn’s Falls show a decided convexity
upwards along that portion of their grades which just precedes their
passage out into the Coastal Plain province. This feature is by no
means so pronounced in the profile of the Patapsco, although the
vertical exaggeration of the latter is twice as great as that of the two
former streams. The milder grade of the Patapsco is due to the
fact that with its larger volume it has been able to reduce its channel
to a much lower level and a smoother course than it was possible for
the smaller streams to do in the same length of time. That a per-
fectly graded course has not been attained, as yet, even by the large
streams, is shown by the low falls which still characterize their chan-
nels and by the slight upward convexity of the profile.

GENERAL CHARACTERISTICS OF THE PIEDMONT SfREAMS.
Stream Patterns.

The general system of division and subdivision followed by the
streams of the Piedmont Plateau has been likened to the manner in
which the trunk of a tree divides and subdivides. From this resem-
blance the system is known as dendritic. In the particular case of
the streams which have been considered in the preceding sections the
general alignment of the main streams, or the trunks of the trees,
is southeastward towards Chesapeake Bay. The streams flowing into
the Monocacy follow a general westward direction. Since the drain-
age of any district normally tends, from the very first, to arrange
itself along lines determined by the distribution of the rocks encoun-
tered, it is evident that the history of many of the streams of the Pied-
mont are somewhat abnormal, as they very rarely follow courses which
are in accord with the structure. The most striking cases of divergence
are furnished by the larger streams, such as the Big Gunpowder, the
MARYLAND WEATHER SERVICE 211

Patapsco and the Monocacy. Equally significant examples, however,
are found among some of the tributary and smaller streams. For
example, the dendritic headwaters of Western Run are strikingly out
of adjustment with the long, narrow bands cf gneiss and marble lying
across their paths. The whole course of Deer Creek is at variance
with the relative resistances of the quartzite, the gneiss and the
serpentine bands across which it flows. About the small head-streams
of the Patuxent there are ample opportunities for adjustment in the
presence of several bands of soluble marble, but only the very
smallest rivulets have assumed subsequent courses.

The small streams at the very head of the West Branch of the Gun-
powder, the corresponding streams of the North Branch of the
Patapseo, Little Deer Creek, and several small streams on various
marble areas include most of the noteworthy instances. There is,
however, a rather numerous class of streams, like Jones’ Falls, West-
ern Run, and the westward flowing tributaries of the Monocacy, which
show a partial adjustment to the rocks of their drainage basins.

Valleys.

From the facts just given it follows that the vallevs of the streams
naturally fall into two main groups, viz.: (1) valleys which are entirely
at variance with the general structure and, (2) valleys which conform
more or less completely to the variations in the rocks. The two
sets of valleys have rather different characters in certain portions of
their courses.

All those streams whose headwaters do not lie in subsequent valleys
are characterized in this portion of their course by comparatively
broad, open and shallow basins lying comparatively close to, if not
actually on, the upland surface. As these streams descend their
valley-walls gradually close in, their side-slopes steepen and within
eight or nine miles of their mouth they enter narrow, steep-sided
gorges which continue until the streams reach sea-level.

Those valleys which are determined in their location by the pres-
ence of yielding rocks, and therefore belong to the class of subsequent
valleys, may be again subdivided into two classes. One class includes
the valleys made by the streams which now oceupy them. These are
212 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

represented by Little Deer Creek, and Broad Creek above Pylesville,
and Long Green Valley. They are peculiarly distinguished by the
very commonplace fact that the streams traverse them from end to
end, longitudinally. The second class consists of those valleys which
apparently were not fashioned by the streams now traversing them.
These are peculiarly distinguished by containing the remnants of an
earlier filling and by the fact that the streams draining them usually
cross them transversely. The class is represented almost solely by
the irregularly outlined depression embracing Green Spring, Dula-
ney’s, Mine Bank Run and Cockeysville valleys.

Channel Profiles.

Comparative studies of the channel profiles show that the Piedmont
streams possess several peculiarities. In the first place, their channels
do not possess the normal profile curve throughout as this is typically
represented in Fig. 3; secondly, the divergences from the normal
profile occur altogether along the lower courses of the streams; and,
finally, the profiles of the westward flowing streams are found to be
both steeper and more nearly normal than those flowing eastward.

The fact that these stream profiles do not show the normal channel
curve throughout their extent is a clear indication that there has been
at least one interruption in the uniform development of the streams,
and this interruption has been of the nature of a general uplift, or series
of uplifts, since only that could cause the lower courses of the numer-
ous eastern streams to show the convex-upward profile which is char-
acteristic of immature streams, while the upper courses of the streams
retain the mature concave profiles developed before the uplift. More-
over, there is an obvious and close connection between the steep,
narrow gorges, which belong to the lower courses of all the Chesa-
peake streams of the Piedmont, and this convexity of the lower por-
tions of their channel-grades.

Even more interesting, however, is the comparison of the profiles
of the streams on either side of Parr’s Ridge. It has already been
remarked that the Monocacy tributaries have much steeper grades
just at the divides. They also are of much milder grade in the
middle and lower sections of their courses, and reach a lower elevation
MARYLAND WEATHER SERVICE 213

more rapidly than their eastern opponents. This marked contrast in
the grades of the two sets of streams is evidently due to a common
cause. The Monocacy flows, throughout most of its course, either
on limestone or on the yielding Newark formation, while the eastern
Piedmont streams have by no means such an easy path. Thus the
Monocacy and its tributaries have always kept their lower courses
close to the mild, low grade of the powerful Potomac, and have been
able to push back their headwaters vigorously against those of the
other streams.

These present conditions suggest a new explanation for the forma-
tion of Parr’s Ridge involving the relations between the rocks of
the eastern and the western Piedmont during the production of the
Schooley peneplain. Then, as now, the Potomac river was the great
master stream of the whole Province and was able to maintain a
comparatively low grade. The present distribution of the Newark
and of its remnants, taken in connection with various discordant drain-
age features among the eastern tributaries of the Monocacv, indicate
that the Newark formation formerly extended farther east towards
what is now Parr’s Ridge.

Granting that the Newark formation had an even greater extent in
Jurassic time than it has to-day, and understanding from present
profiles what advantages the Potomac tributaries possess, it must be
conceded that the Monocacy river, or a closely similar stream, occu-
pied a subsequent valley on the Newark. Such being the case, the
eastern tributaries of that stream must have had advantages over the
eastern Piedmont streams in those times just as they do to-day. It
therefore seems probable that Parr’s Ridge remained as a low divide
during the formation of the Schooley peneplain.

HISTORY OF THE PIEDMONT STREAMS.
Origin.

Any account of the origin of the streams of the Piedmont Plateau
must, in order to be satisfactory, explain the several seemingly anom-
alous characteristics which they present. The chief of these anoma-
lies is the fact that although the streams are well developed yet they
show an almost total disregard for the underlying rock structure.
214 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Lesser peculiarities are the minor discordances and adjustments, and
the peculiar location of a number of streams against the southern or
southeastern limit of their valleys.

The discordance between the streams and the structure of the
Plateau is so widespread that some wide-spread cause is necessarily
required to explain it. Such wide-spread discordances can only re-
sult from the streams cutting down through a broad blanket of some
sort which hid, at the time of the origin of the streams or early in their
history, the structure and topography later discovered. Thus the
broad loess deposits of China and of the central United States serve
as such covers through which the streams of to-day have already cut
or are cutting their way down to the underlying rocks. The broad
sheets of glacial till of the north, or the less extensive lacustrine clays
of Lake Agassiz or Lake Bonneville, serve the same purpose for their
respective regions. The deep mantle of disintegrated material which
forms the soil and subsoil in more southern districts might also serve
as an agent of superposition. It is of a comparatively uniform degree
of resistance, thus resembling the glacial and lacustrine deposits and
producing similar drainage patterns for the streams which originate
on it.

In the partially removed cover of Coastal Plain sediments there is
ample evidence of a past ability to produce such a phenomenon,
provided there is enough evidence to warrant the conclusion that the
Coastal Plain has thus served the drainage of the Plateau. To prove
this it must be shown—

1. That the Coastal Plain has covered those portions of the Plateau
which now show discordant drainage.

2. That the superimposed drainage, if it came from the Coastal
Plain, ought to have its general direction in accord with the drainage
lines of the latter and its general pattern of the same type.

There is some evidence favoring the first condition in the oceur-
rence of several outlying remnants of the Coastal Plain deposits.
To this may be added the just conclusions, based on considerations
of the lithological characters of these sediments that they once ex-
tended farther west, and that they do not now occupy exactly their
MARYLAND WEATHER SERVICE 915

old shore-lines. Both of the features required by the second condi-
tion have already been shown to be characteristic of the major portion
of the drainage under consideration. It therefore seems a true con-
clusion that the streams of the eastern portion of the Piedmont Plateau
originally took their courses on the surface of the Coastal Plain; that
the streams cut down through this cover and laid bare the old surface
of the Piedmont region, at the same time establishing themselves
thereon in courses out of harmony with the varying lithologic char-
acter of the region.

Minor Discordances.

The Pleistocene subsidence of the lower courses of the streams per-
mitted the contemporaneous accumulation of broad, gravelly and
sandy flood-plains, occupying the valleys of Western Run, Dulaney’s
Creek, Mine Bank Run and Beaver Dam Creek, as well as Green
Spring Valley. It is a well-understood fact that when a river has
reached the flood-plain building stage, it is in a state of delicate
balance, so that a very slight disturbing element can cause the stream
to shift its course very decidedly. With this in mind, the unsymme-
trical location of the streams in the valleys mentioned, and the some-
times discordant positions which they have taken, may be explained
as follows. The Pleistocene period of flood-plain building was brought
to an end by a general elevation which was of the nature of a tilting
towards the southeast. This tilt caused all the east-and-west and north-
east-southwest streams to slide over their flood-plains southward or
southeastward. Thus Dulaney’s Creek and its companion became
located upon the ledge of gneiss which they had reduced; the streams
in the northeastern portion of ' ine Bank Run valley shifted over
upon the pegmatite dike; and Western Run, Piney Run and J ones’
Falls took their present positions along the southern limits of their
valleys. The elevation which accompanied the tilt revived the streams
and caused them to trench their channels below the Pleistocene flood-
plains, thus initiating the period of active erosion which caused the
convexity of all the eastern stream profiles.
216 A REPORT ON THE PHYSIOGRAPHY OF MARYLAND

Recent Changes.

Since the Pleistocene deposition and post-Pleistocene elevation,
further adjustments have probably gone on, the streams have incised
themselves more deeply in the positions which they inherited from
the tilted flood-plains, and there is a general tendency to reduce the
stream-grades as rapidly as possible.

CONCLUSION.

The results of the study of the Piedmont Plateau drainage may be
summarized as follows:

1. The streams of the eastern division of the Piedmont Plateau
have been superimposed from the formerly more extensive Coastal
Plain cover.

2. The date of this superimposition is probably post-Lafayette,
although there are some facts that point to its initiation in post-
Potomac time.

3. Secondary superimposition from Pleistocene flood-plain deposits
in subsequent valleys show that recent elevation has been accompanied
by a tilting toward the southeast.

4. The westward extension of the Coastal Plain, as evidenced by
the discordant drainage which it produced and by sedimentary records,
cannot be traced with certainty west of Parr’s Ridge.

5. The minor cases of discordance which occur in the drainage
of the Monoeacy are the result of superimposition from the Newark
formation.

6. Parr’s Ridge has been, as it is now, the divide between Monocacy
and Chesapeake Bay streams since late Jura-Trias times; it is being
gradually shifted eastward because of the greater activity of the
Monocacy drainage; and it represents, not a part of the plain-surface,
but a low, minor divide on the Schooley peneplain.
VITA.

Cleveland Abbe, Jr., was born in Washington, D. C., March 25,
1872. He is the son of Cleveland Abbe, of New York City, and
Frances M. Neal, of Cincinnati, Ohio. His early education was
received at home and later from the public schools of Washington.
After graduating from the High School of that city in 1890, he en-
tered Harvard College in September of the same year, becoming a
member of the Class of 1894. While pursuing a general course, in
college, he became particularly interested in the study of Geology
and Physical Geography under Professors N. 8. Shaler and W. M.
Davis. On graduating in June, 1894, he returned to spend another
year under Prof. Davis and others, devoting his time to Physical
Geography, Glacial Geology and Pedagogy. During this year, 1894-
95, he held a University Scholarship.

In the fall of 1895 the candidate came to Baltimore and entered the
Geological Department of Johns Hopkins University as a graduate
student. Here he pursued a special course in Geology for three years,
accompanied by three summers of active field-work in the employ
of the Maryland Geological Survey. In 1896 he was awarded one of
the University Scholarships in Johns Hopkins University, and in 1897
was appointed Fellow in Geology in the same university. The degree
of Master of Arts was conferred upon him in 1896 by Harvard Uni-
versity, as the result of the work done there in 1894-95 and of special
work done about Baltimore in 1896.

In conclusion, the candidate wishes to express his regard for and
obligations to Prof. Wm. B. Clark of this University, whose continued
kindly encouragement has brought him through many difficult places
and without whose very material assistance the field-work required
for the present study would not have been so thoroughly carried out.
To Prof. E. B. Mathews of Johns Hopkins University, Prof. R. E.
Dodge of Teachers’ College, Columbia University, and to many
friends in the U. 8. Geological Survey are due thanks for helpful
comments, suggestions and discussion. From Prof. W. M. Davis of
Harvard University has come the initial and enduring enthusiasm for
the work presented.