Thomas Cramer Hopkins.

Elements of physical geography online

. (page 1 of 27)
Online LibraryThomas Cramer HopkinsElements of physical geography → online text (page 1 of 27)
Font size
QR-code for this ebook



University of California.







Grand Canyon of the North Platte River, Central Wyoming. (U. G. Cornell.)

Elements of Physical


Professor of Geology in Syracuse University

ov TToAA' oAXa TToXv







^ Copyright, 1908




There are good text-books on physical geography, but
there are many teachers and school departments not satis-
fied with any of them. The author has endeavored to meet
the requirements of these teachers as far as such needs could
be ascertained. With a subject as broad as physical geog-
raphy there will always be lack of uniformity in the man-
ner of presentation, as well as in the subject matter. The
subject is one which is undergoing many changes, and it is
possible that both the teachers and the subject may be
ahead of present text-books in many particulars.

This book is not an experiment. To accommodate the
many students who were going out to teach in the schools
of the State, the author, several years ago, attempted to
bring his courses in physical geography in Syracuse Uni-
versity into harmony with the requirements of the Educa-
tional Department of the State. It was then that he
realized the force of the complaints of many teachers that
none of the text-books met these requirements. After try-
ing two of the leading text-books, he abandoned both and
prepared a text which has been used successfully, in manu-
script form, for two years in his own classes. Before
putting it in book form he studied the conditions in the
public schools of New York and in other states and has
attempted to prepare a book to meet the needs of teachers
and the Educational Departments in this country, not with
the expectation of pleasing all, but with the confident hope
of meeting the needs of many of those who are dissatisfied
with the present books.

It is not important that any class should pursue the



subject in the order in which it is presented in this text.
The author's custom is to begin with Chapter II, because
his classes commence in September. This season is f avora-.
ble for field work, which has to do more with the contents
of Chapters II, III and IV than with Chapter I. If the
work should begin in midwinter, or there should be no field
work, then the order given might well be followed. It is
expected, however, that each teacher will follow his own
plan,— the subject matter is divided into chapters for that
purpose. Each teacher will naturally expand that part of
the subject best illustrated by the geographic conditions in
the proximity of the school. Those in the glaciated area,
by use of the references can devote more time to the study
of glacial phenomena. Those on the shore of the ocean, or
a 'large lake, can give more time to shore features. Those
in the interior can dwell more on the work of streams and
ground water. Intensify the portion which the pupil can
best study from Nature.

Every class in physical geography should have more or
less laboratory and field work associated with the text-book.
One of the functions of the text-book— not the only one, by
any means— is to serve as a handbook, which the pupil
studies as an aid in the interpretation of what he sees in
the laboratory.

To aid the teacher in his work, the author has prepared
a small laboratory manual to accompany this text. The
manual must, of necessity, be a book of suggestions rather
than directions. The work, to be successful, depends on
the skill and tact of the teacher in getting the pupils to
study and work with real things rather than words about
them. Yet the author believes that a good book is as much
needed and fully as important in the work of the laboratory
as in that of the class-room. Many teachers have not had


the opportunity to develop a systematic course of labora-
tory work, consequently much time has been wasted by the
pupils in routine work. The laboratory manual aims to
help the teacher and pupil, by suggestions and questions,
to a knowledge of the earth features and relations.

The text and manual together aim to assist both teacher
and pupil into the spirit of one of the most inspiring sub-
jects in our schools; to bring the pupil into contact with
Nature in such a way that he may see and realize his own
position in this w^orld of complex activities, so that by
observing more closely the familiar phenomena surround-
ing him in his daily life he may extend his observations
and knowledge through the less known into the unknown,
and thus be an intelligent part of the great world in which
he lives.

The author is indebted to many teachers of, physical
geography in different states in the preparation of this
text. After the manuscript was written it was submitted
to a number of prominent teachers in high schools, acad-
emies and colleges for criticism, and the valuable sug-
gestions made by them are incorporated as far as possible.
Especially does he desire to express his indebtedness to the
following eminent teachers for valuable aid : Professor C.
E. Peet, Lewis Institute, Chicago; Miss Mary G. Sullivan,
Buffalo High School; Dr. C. H. Richardson, the author's
colleague in Syracuse University; Miss Jennie T. Martin,
City Schools, Washington, D. C. ; Professor James H.
Smith, Chicago High School; Dr. F. H. H. Calhoun,
Clemson College, S. C. ; Sarah Emerson Green, formerly
the author's assistant at Syracuse University; and P. F.
Schneider of Syracuse. The first three above named read
both the manuscript and the proof with painstaking care,
and the others gave valuable aid in reading either the


proof or the manuscript. Dr. H. A. Peck, Professor of
Astronomy, gave many valuable suggestions on Chapter I,
and Morgan R. Sanford, local forecaster for the U. S.
Weather Bureau, did the same in Chapter X.

For the photographs illustrating the text the author is
deeply indebted to many friends and colleagues who are
credited elsewhere. Special thanks are due to the U. S. Geo-
logical Survey, the U. S. Fish Commission, the Maryland
and Vermont State Geological Surveys, and the American
Museum of Natural History. Where not otherwise credited
the photographs are by the author, except a very few
where the photographer is not known. The illustrations
and explanations of the same form a very important part
of the text and should be studied as carefully as the
words. In some instances the picture illustrates the text,
in others the text is an explanation of a principle best
learned from the picture.

T. C. H.

Syracuse University,
May, 1908,




I. The Earth as a Planet 1

II. Groundwater and Rivers ................. 40

III. Lakes, Swamps and Waterfalls. 100

IV. Glaciers / 138

V. The Ocean 169

VI. Shore Lines 197

VII. The Land— Minerals, Rocks and Soils. ..... 235

VIII. Physiographic Agencies 274

IX. Physiographic Features .................< 309

X. The Atmosphere 348

XL Geography of Plants, Animals and Man .... 400

XII. Physiographic Regions of the United States 449

Appendix 473



Introductory.— Physical geography literally means a
description of the natural features of the earth. The de-
velopment of the subject during recent years has led to the
subdivision as follows :

1. The earth as a globe or planet, its origin and rela-
tion to the other heavenly bodies.

2. The atmosphere or the surrounding gaseous portion.

3. The hydrosphere or the water, including the fresh
water and the salt water of the ocean.

4. The lithosphere or the soli.d land portions, the
causes producing the various topographic forms and the
effects of these on climate and life.

5. Life geography or the effect of physical environ-
ment upon life and its effect on the earth features.

Physical geography includes a study of these subjects with
reference to their influence upon man, his industries, civiliza-
tion and relation to his surroundings. With this aim in view
it leads one within the doorway of each of the natural sciences.

To the ancient philosopher's maxim, "Know thyself," the
modern scientist adds "in relation to Nature." This is the foun-
dation of modern physical geography. In gaining this knowl-
edge man is better able to adapt himself to his surroundings, to
utilize the various forces and products of Nature, to realize not
only his dependence upon his fellow man and the lower forms of
life, but his duty towards them as well, and consciously or un-
consciously, he must gain respect if not love for the Omnipotent
Power that rules over all.

Physical Geography is the science which treats of the



natural features of the earth in their relation to man and
the lower forms of life.

1. The Earth a Part of the Solar System.— The earth
is a nearly round ball consisting of a large rock mass partly
covered with oceanic waters, and entirely surrounded by
the gaseous atmosphere. The whole mass solid, liquid and
gaseous, rotates on its axis as it revolves in space around
the sun. It is but one of a number of similar bodies called
planets and is in no wise conspicuous among them. It is
neither the largest nor the smallest; neither the farthest
from nor the nearest to the sun. Because we live on the
earth, it is most important to us, but if we could look on it
from some distant point in the heavens we should not see
anything to distinguish it particularly from the other

2. What the Solar System Comprises.— The earth is
an important member of the solar system which includes
the sun at the center,' the planets and their satellites, the
planetoids or asteroids, and some comets. Besides the earth
there are revolving around the sun seven other planets
which are named in order beginning with the one nearest
the sun, — Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus and Neptune. Four of these, Venus, Mars, Jupiter
and Saturn, are plainly visible at certain periods. Two of
them, Venus and Jupiter, are at times the brightest bodies
in the heavens except the sun and moon. Part of the time
they are morning stars ; at other times evening stars. The
planets may be distinguished from the true stars by their
steady light. The stars twinkle. Each of the planets, ex-
cept Mercury and Venus, has one or more satellites or
moons revolving around it. Saturn has besides the satel-
lites several concentric bright rings surrounding it. The
relative sizes, distances and other data concerning the
planets are given in Appendix I.


The asteroids or planetoids, about 600 in number, are solid
bodies much smaller than the planets, and revolve in orbits be-
tween Mars and Jupiter. One of the planetoids, Eros, about 20
miles in diameter, discovered in 1898, has a very eccentric orbit
that sometimes brings it within izy2 million miles of the earth.
The student should learn to recognize the larger planets and ob-
serve their movements among the stars from season to season.


Fig. 1. The solar system, showing the order of the planets, satellites,
asteroids, and the orbits of a few comets.

3. Relation of the Solar System to the Universe.—

The Solar System, large and complex as it appears, is but


one of a number of similar systems in the universe. Most
of the bright stars in the heavens are suns similar to ours.
They appear to be much smaller than our sun, but that is
because they are so much farther away. In reality many
of them are much larger. They probably have planets,
satellites, comets, etc., like our own system, but they are so
far away that these bodies, if they exist, are not visible
from the earth. It is not known how many of these sys-
tems there are, nor how far out in space they extend, but
certainly a great distance beyond our comprehension. It
is estimated that with a large telescope one can see between
100 and 200 millions of stars, a large per cent of which lie
in the Milky AYay. With few exceptions all of these stars
are so far away that it takes the light from them travelling
at the rate of 186,000 miles a second many years to reach
the earth. The moon is about 240,000 miles away or about
ten times the distance around the earth; the sun is nearly
400 times farther than the moon ; and the nearest fixed
star or neighboring sun system is several thousand times
farther than the sun. The light of the sun takes about
8 minutes to reach the earth. The light of the nearest star
takes 31/2 years to cross the space separating it from the
earth. Truly the earth is a very small part of the solar
system and an exceedingly minute portion of the universe.
4. The Moon.— The earth has one satellite, the moon,
which revolves around it once a month (27.32 days) and
accompanies it through space in its journey around the sun.
The moon is 2,163 miles in diameter and at an average
distance of 238,840 miles from the earth, but it varies from
221,600 to 252,970 miles. It is because of its nearness to
the earth that it is held in its orbit around the earth in-
stead of pursuing an independent course around the sun.
(The synodic month or the time from full moon to full
moon is 29.53 days, but the sidereal month is 27.32 days.)


5. The Phases of the Moon.— The moon emits no light of its
own. All the light that comes from it to the earth is reflected
sunlight. When the moon is in that part of its orbit nearest the
sun, it is nearly between the earth and the sun, and we see but
a mere fringe of illumination; it is then the new moon. The
sunlight reflected from the earth faintly illuminates its dark side
giving what is called the earth shine. When it has completed a
fourth of its circuit after new moon, it is at right angles to a
line connecting the sun and the earth, and we see one-half of the
illuminated face, that is, a fourth of the whole surface, and the
phase is called the first quarter. When it has completed half a
circuit and is on the opposite side of the earth from the sun, it

Fig. 2. The phases of the moon.

is full moon. At the third quarter the moon has completed three-
fourths of its circuit and one-fourth of the whole surface is again
reflecting light to the earth. The line separating the illuminated
portion from the dark portion is called the terminator. Draw
from observation a figure of the moon showing the light and dark
portion every second night from one new moon to the next;
arrange them in order around an ellipse and compare them.

6. The Sun. — The sun is the center of the solar sys-
tem. All the planets of the system revolve about it and
receive heat and light from it. It is much larger than all


the planets combined, havino^ a diameter of 866,000 miles,
which would make it a million times the bulk of the earth ;
but since its density is less, it has only 332,000 times the
mass of the earth. Imagine the earth at the center of the
sun and the moon revolving around it in an orbit the same
size as the present one ; the moon would then be about half
way from the center to the circumference of the sun.
7. The Sun's Energy.— Nearly all the heat, light, and
other forms of energy on the surface of the earth come
directly or indirectly from the sun. The radiant energy

from the sun, known as
ijisolation, is thought to
pass from the sun to the
earth unaffected by in-
tervening space until it
reaches the earth where
part of it, the part that
we recognize, is percep-
tible as heat and light.
The part of the sun's
insolation received by
the earth is an exceed-
ingly small part of the
whole, and when one
realizes that- nearly all
forms of heat and light come from the sun, the total
quantity radiated into space is something beyond compre-
hension. AU the energy used by man in heating and light-
ing, all that is used in running machinery everywhere, -11
that is used in lifting the waters of the sea to the clouds to
fall as rain, all that wonderful vital energy manifested in
animals and plants,— all of these and probably other forms
of energy as yet unrecognized are flashed like wireless tele-
grams across the vast space that separates us from the sun.

Pig. 3. Showing the relative size of the
sun and the moon's orbit. What is
the scale of the diagram?


8. Eclipses.— Since the sun is the source of the light
received by the earth and the moon, when either of these

Annular Eclipse

Pig. 4. Solar and lunar eclipses.

latter bodies comes between the other and the sun, the
light of the sun will be cut off. The shadow thrown by


the intervening body on the other is known as an eclipse.
The shadow of the moon on the earth produces an eclipse
of the sun, and the shadow of the earth on the moon causes
an eclipse of the moon. If the moon passes entirely into
the earth's shadow, there is a total eclipse of the moon, if
only part of it passes into the shadow, a partial eclipse is
the result. There may be three kinds of solar eclipses : ( 1 )
a total eclipse when the moon passes centrally over the disc
of the sun and so near the earth that the shadow reaches
the earth; (2) an annular eclipse, produced when the moon
passes centrally over the disc of the sun but is so far from
the earth that the end of the shadow does not reach the
earth; then the moon appears as a black spot in the center
of the sun surrounded by a ring of light which gives the
name annular or ring eclipse ; ( 3 ) a partial eclipse of the
sun produced when the moon passes a little to one side of
the line joining the earth and the center of the sun.

If the moon revolved about the earth in the plane of the
earth's orbit, there would be a total eclipse of the moon and sun
once each month, but since the plane of the moon's orbit is in-
clined at an angle of five degrees to that of the earth's
orbit, there is an eclipse only when the moon passes one of the
nodes, that is, the points of intersection of the two orbits, at or
near new moon or full moon. There may be an eclipse of the sun
when there is none of the moon, and there must be at least two
solar eclipses each year. Consult the almanac for several years
and see how many eclipses of each kind there have been.

In 1907 there were four eclipses, two of the sun, one total
and one annular, and two of the moon.

9. Comets.— Comets belong in part to the solar sys-
tem. Several hundred of these bodies have been seen from
the earth at different times. Some of them travel in ellip-
tical orbits which extend millions of miles out into space
beyond the outermost planet in our system, hence the period
of revolution is one of many years. Many comets travel in


a parabola or a hyperbola and become visible once as they
pass around the sun and away again, never to return.
Whence they come and whither they go is not known.
Prom fig. 5 it can be seen that parabolas and hyperbolas
are curved lines, the ends of which never meet.

The comets differ in size and shape as widely as they do
in their orbits. They are characterized by a nucleus or
denser portion surrounded by a nebulous mass called the
coma which streams out from the nucleus and forms the
tail. The tail is single or double and of widely diverse

Fig. 5. Ellipse, parabola and hyperbola. The last two are diverging curves
which never meet.

shapes and differs in length from that of the diameter of
the nucleus to a length of 100,000,000 miles or more. As
a comet approaches the sun, the tail streams out behind it,
as it passes perihelion (the nearest point to the sun), the
tail streams out ahead of it, that is, the tail keeps on the
opposite side of the nucleus from the sun. Celestial pho-
tography has shown recently that the tails of several com-
ets have been suddenly broken into two or more parts.

10. Historical Comets.— The comet ot 1680 is an important
one because it was the first whose orbit was determined by the


principles of gravitation. The computation was made by Sir
Isaac Newton who found that it passed within 140,000 miles of
the sun travelling at the rate of 1,332,000 miles an hour. It had
a tail 100,000,000 miles long.

Ealley's comet (1682) is so called because Halley, a friend of
Newton, computed its orbit and thus identified it with previous
comets that had appeared at intervals of 75 years. He predicted
that it would make its next appearance March 13, 1759. It passed
perihelion within a month of that time. It appeared in 1835 and
is due again in 1910. Watch for it.

Biela's comet (1826) was observed in the latter part of Decem-
ber, 1846, to elongate and divide into two parts which travelled
in parallel orbits 160,000 miles apart. When they next appeared
in 1852 the two portions were 1,500,000 miles apart. They have
not been seen since.

The Comet of 1882 was the most conspicuous one in recent
years. It approached the sun in perihelion close enough to pass
through part of its gaseous envelope. Daniel's comet attracted
attention in the summer of 1907.

11. Meteors and Shooting Stars.— Meteors and shoot-
ing stars are luminous bodies which are frequently observed
in our upper atmosphere and are sometimes seen to strike
the earth. The luminosity of these bodies is thought to be
due to friction against the atmosphere and that before
entering the atmosphere they are cold and non-luminous.
Many of them are dissipated in the upper atmosphere, but
probably the fragments in the form of invisible dust reach
the earth in the course of time. Ten to twenty millions of
meteors strike the earth's atmosphere every day. It is
thought by some that the earth has been formed by the
aggregation of such particles, which would mean that un-
less the earth is losing matter in some way it is still increas-
ing in weight.

12. Meteorites.— Meteors which fall to the earth are
called meteorites. They vary in size from very minute
fragments to bodies of many tons in weight. The great



Tent meteorite in New York City which Peary brought
from Cape York, Greenland, weighs 36.5 tons. The
Bacubirito meteorite in Mexico weighs about 27.5 tons.
The Willamette meteorite, shown in fig. 6, weighs 15.6 tons.
Some are composed of stone, some of metals and some of
both. About four out of every hundred are nearly pure
iron with a little nickel. The source of meteors and
meteorites is not definitely known.

Fig. 6. Willamette meteorite, the third largest known, found
near Oregon City, Oregon. Length 10 ft., height 6 ft. 6 in.,
weight 15.6 tons. (American Museum of Natural History.)


All material things so far as we know have a beginning,
a period of growth, decline, and death. This is not true
of matter itself but of the forms which it takes. The fact
is commonly recognized in regard to plants and animals
but is probably no less true of many inanimate objects, ex-
cept that the changes" go on so much more slowly that they
are frequently not recognized. It is now known that the


hills are not "everlasting." They may be *' rock-ribbed "
but they are not as ''ancient as the sun." The mountains
have a beginning, and a period of growth, after which they
begin to dwindle and gradually disappear. So it is with
the earth, the sun, and the solar system ; they did not al-
ways exist as such. When and how were they formed f

13. The Nebular Hypothesis.— Of the many attempts
to explain the origin of the solar system none has met with
more favor than that known as the nebular hypothesis,
which assumes that at one time all the material in the solar
system existed in the form of a rotating mass of nebulous
gas that occupied all the space from the center of the
present sun out to and beyond the limits of the orbit of the
outermost planet— Neptune. Under the universal law of
gravitation, by which every particle of matter in the uni-
verse attracts every other particle, these gas particles were
attracted towards a common center. In the course of time
a portion of the mass was separated in the form of a ring,
or, as some say, as an irregular mass, which in time, by its
rotation on its own axis, formed a spheroidal body revolv-
ing around the central mass. This was the planet Neptune,

Online LibraryThomas Cramer HopkinsElements of physical geography → online text (page 1 of 27)