Elements of Physical Geography; together with a treatise on the physical phenomena of the United States. Illustrated, etc

Front matter

MITCHELL'S SCHOOL & E O GTt A I»H IE S. FIFTH BOOK OF THE SERIES. ELEMENTS OF PHYSICAL GEOGRAPHY, TOGETHER WITH A TREATISE ON THE PHYSICAL PHENOMENA OF THE UNITED STATES. ILLUSTRATED BY ONE HUNDRED AND FIFTY ENGRAVINGS AND THIRTEEN COPPER-PLATE MAPS EXECUTED IN THE FIRST STYLE OF THE ART. By JOHN BROCKLESBY, A.M PROFESSOR OF MATHEMATICS AND NATURAL PHILOSOPHY IN TRINITY COLLEGE, HARTFORD, CONN., AND AUTHOR OP ELEMENTS OF METEOROLOGY, ELEMENTS OF ASTRONOMY. ETC. PHILADELPHIA: PUBLISHED BY E. H. BUTLER & CO. 1870. Entered, according to Act of Congress, in the year 18C7, by S. Augustus Mitchell, in the Clerk's Office of the District Court for the Eastern District of Pennsylvania. MITCHELL'S NEW SERIES OF GEOGRAPHIES Have received the highest praise from the most expe rienced teachers and educators in the United States, for their faithful accuracy, for being always up -with the current state of geographical knowledge, and for the striking beauty of their copper-plate maps.

They are widely used and highly approved in schools of every State in the Union. The series consist of Mitchell's New First Lessons in Geography; Mitchell's New Primary Geography; Mitchell's New Inter mediate Geography; Mitchell's New Geography and Atlas of Forty-four Maps; Mitchell's New Physical Geography, by Prof. Brocklesby; Mitchell's New Outline Maps; aud Mitchell's New Ancient Geography. MITCHELL'S OLD SERIES OF GEOGRAPHIES are published as usual and brought down to the present date, and consist of Mitchell's Primary Geography, revised edition ; Mitchell's Geography and Atlas, revised edition; Mitchell's Ancient Geography and Atlas; and Mitchell's Geographical Question Book. MITCHELL'S NEW OUTLINE MAPS.— A new series of Outline Maps, designed to accompany Mitchell's New School Geographies, carefully constructed, as follows:— 1.

The Hemispheres, size, 24x28 inches; 2. North America, 24X28; 3. The United States (double size), 28X48; 4. South America, 24X28; 5. Europe, 24X28; 6. Asia, 24x28; 7. Africa, 24X28. These Maps are sufficiently large to give the general features of political and physical geography,—including the Political Boundaries and the Principal Localities, the Mountain-Chains, the River-Courses, the Plateaus, and the Plains. These features are all accurately set forth, and are so re presented as to be recognized at a glance. These maps are strongly mounted, yet so light and portable that they can be carried about the school room, or from one room to another, and hung up, without disturbing the exercises of the school. They are sold, carefully enclosed in a portfolio, at the low pkice of ten dollars a set.

Preface

It is hardly necessary, at the present time, to vindicate the right of Physical Geography to a prominent piaee among the studies pursued in our schools, academies, and higher institutions of learning ; for our best educators now appreciate its importance, and regard it as a constituent part of the science of Geography. In the following work the writer has endeavored to unfold concisely, yet in their completeness, the principles and facts of Physical Geography, and has sought, by the mode of presenting them and by freshness of illustration, to uphold the intrinsic interest of this department of science. In respect to the arrangement of the several divisions of the subject, their natural and obvious order has been adopted. In the j:>reparation of this treatise the standard works on Physical Geography have been consulted, — such as the splendid folio Atlas of Johnston, that of Petermann and Milner, and the treatises of Humboldt, Herschel, Somerville, Ansted, and others.

Recourse has also been had to the United States Explorations and Surveys, Maury's Nautical Charts and Sailing Directions, various Encyclopædias, numerous scientific works, and books of travels and researches. In fine, from all sources, both public and private, which have been ascessible to the author, facts and illustrations have been drawn. The attention of the student is directed throughout the subject to the truth that the globe is not a mere collec tion of matter existing under various forms, but an organized body, filled with a wondrous mechanism, in which all the parts and systems are exquisitely adapted to each other; and that the physical phenomena of the world reveal in their harmonious action a unity of plan and purpose, and display in an infinite variety of ways the Power, Wisdom, and Goodness of the Almighty Designer.

Trinity College, December 2, 1867. CONTENTS PAGE PAGE Meteorology ......••• 88 The Atmosphere 88 Thermal Phenomena 89 Aqueous Phenomena ....... 96 Climate 105 Optical and Luminous Phenomena .... 108 Electrical Phenomena . . . . . . 113 The L,ife os the Globe, aud its Distribution 118 Geographical Botany 118 Geographical Zoology 1 29 Ethnology 143 Physical Phenomena of the United States . .150 Extent, Coast-Line, Inlets, Capes, etc. . . 150 Geology, Mountains, Mountain-Slopes . . . 151 Table-Lands, Plains, Volcanoes .... 152 Lakes and Rivers 154 Meteorological Phenomena, Climate, etc. . . 156 Geographical Tables 162 Pronouncing Vocabulary 163 Introduction ......... 5 The Earth regarded as a Planet .... 6 The Structure of the Earth 9 The Central Mass of the Earth, and its Crust 9 Land .......... 16 Continents 17 Islands 19 Mountains, Valleys, and Passes .... 23 Table-Lands, or Plateaus 31 Plains ........ 34 Volcanoes . 42 Earthquakes . 46 Caverns and Natural Arches 52 Mineral Productions '54 Water — Land System .58 Springs A .. 58 Lakes 62 Rivers 65 Water — Oceanic System ... 73 The Ocean 73 Oceanic Motions 77 LIST OF COPPEK -PLATE MAPS. 1.

The Globe, showing its Continents, Islands, Mountain-Ranges, Table-Lands, Plains, etc. . . 40, 41 Comparative Heights of the Chief Mountains above the Sea-Level. a. Map of the World, showing the Distribution of Volcanoes, and the Regions subject to Earthquakes 50 Principal Volcanic Series of the New World. Principal Volcanic Series of the Old World. ». Hydrographic Map of the World, showing the Oceans, Seas, Lakes, and the River-Systems . . 76 4. Map of the World, showing the Temperature of the Ocean and the Advance of the Tidal Wave . 80 5. Map of the Ocean-Currents 87 Vertical Section of the North Atlantic Ocean from Senegambia to Mexico. Chart of the Basin of the Atlantic Ocean, from the Deep-Sea Soundings of the United States Navy. 6. Map of Winds and Hurricanes, showing their Distribution over the Globe, and their Influence on the Routes of Navigation 92 Map of the Hurricane-Tracks in the Atlantic Ocean.

Map of the Hurricane-Tracks in the Indian Ocean. 7. Rain (Hyetographic) Map of the Would . . 98 Amount of Rain in the Zones. Rain-Map of India. 8. Meteorological Map of the World, showing, by Isothermal Lines, the Mean Annual Temperature of the Air at the Earth's Surface . . . .116 9. Map of the World, showing the Geographical Distribution of the Most Important Trees, Fruits, Grains, and Spices 122 Distribution of the Most Important Plants, according to Altitude — Western Hemisphere. Distribution of the Most Important Plants, according to Altitude — Eastern Hemisphere. 10. Zoological Map, showing the Distribution over the Globe of the Principal Birds and Reptiles . 134 ll. Zoological Map, showing the Distribution over the Globe of the Principal Mammalia . . 138 12. Ethnographic Map of the World, showing the Distribution of the Principal Races of Men . 148 13. Physical Map of the United States . . .161 Heights of the Principal Mountains in the United States.

Introduction

. 1. Physical Geography is that science which treats of the surface and atmosphere of the Earth, with its various forms of life and the laws of their distribution. Its limits, however, are not rigorously defined, inasmuch as our knowledge of the existing condition of the globe must evidently be imperfect unless we are somewhat acquainted with its previous history, and are aware of the mighty convulsions through which it passed before it received its present organization and became fitted for the abode of man. 2. Nor must the connection of the earth with the solar system be forgotten ; for the secret influences of the sun control its motions, quicken its countless germs .of life, and fill it with abundance and beauty. The department of science under consideration, therefore, extends, more or less, into the domains of Astronomy and Geology. 3.

Physical Geography is embraced under six general divisions, to wit: — I. The Earth regarded as a Planet. II. The Structure and Formation of the Earth III. The Land. IV. The Water. V. The Atmosphere and its Phenomena; or, Meteorology VI. The Life of the Globe, and its Distribution. 1. Of what does Physical Geography treat? Why are not its limits rigorously defined? 2. What connection has the earth with the solar system? What sciences are connected with Physical Geography ? 3. Under what general divisions is Physical Geography embraced ? 4. Terrestrial Sphere.— For the purposes of description and of fixing the positions of places, geographers have conceived the earth to be divided by certain imaginary lines, and the globe thus intersected is called the terrestrial sphere. These lines are the axis, meridians, equator, parallels of latitude, tropics, and polar circles.

PART FIRST THE EARTH REGARDED AS A PLANET. 5. Axis of the Earth.— The axis of the earth, or polar diameter, is that diameter upon which it revolves, as will be presently shown. Its northern extremity is the north pole of the earth, and its southern is the south pole.

Chapter I

1. The Earth is one of the planets1 of the solar system, and the third, so far as we know, in the order of distance from the sun. The position of the earth's axis determines that of each of the other fictitious lines. Every plane passing through the centre of 2. Form of the Earth. — The earth appears, at the first view, to be nothing more than a vast broken plain, swelling into mountains, sinking into valleys, and spreading out into lakes, seas, and oceans; but careful researches have removed this erroneous impression, and proved, beyond a doubt, that it is nearly spherical in form. The proofs are as follows : — NORTH POLE. i. When a vessel sailing from the shore speeds over the ocean, and gradually lessens in the distance, her hull first sinks below the horizon, the lower sails next disappear, and the last objects seen are the tops of the masts.

SOUTH POLE. GREAT CIRCLES. SMALL CIRCLES. the earth divides it into two equal parts, termed hemispheres, and its section is called a great circle. All other sections are small circles, and divide the earth into unequal parts. The circumferences of all circles, great or small, are divided into three hundred and sixty equal parts, called degrees, each degree into sixty equal parts, called minutes, and each minute into sixty equal parts, called seconds. Degrees are designated by the following character, °; minutes, thus, ' ; II. Navigators have repeatedly sailed around the earth by con stantly advancing in the same direction, arriving at length at the port from which they departed. in. The visible portion of the earth's surface is always circular, wheresoever an observation is taken. That this fact proves the earth to be spherical will be evident from the following illustration.

If we take an orange to represent the earth, and cut a smooth slice from any side of it, the outer surface of the slice may be considered as the portion of the surface of the earth seen at any time by a spectator. seconds, thus, ". 6. The Equator is a great circle perpendicular to the axis, extending east and west, and dividing the globe into hemispheres, the northern and southern; any diameter in its plane is an equatorial diameter. Meridians are great circles passing through the poles of the earth perpendicular to the equator. Parallels of latitude are The bounding line of this surface is seen at a glance to be the circumference of a circle. If, instead of a spherical body, like an orange, a lemon is taken, and a slice cut from the side, the shape of the slice will be oval. In a lunar eclipse the shadow of the earth is cast upon the moon, and appears circular. iv.

We have said that the earth is nearly spherical. If it were a sphere, the length of a degree would be the same in every latitude ; but the various measurements of arcs of meridians, made by astronomers, in different parts of the world, with wonderful accuracy, all show that a degree increases in length from the equator to the poles. This fact proves that the earth is flattened at the poles; and to such a solid, mathematicians give the name of an oblate spheroid. The varying rates of the vibrations of a pendulum in different lati tudes establish the same point. 3. Size of the Earth. — It has been found from the most recent researches and calculations that the equatorial2 diameter of the earth is 7926.708 3 miles, and the polar* diameter 7899.755 miles,— the differ ence being 26.953 miles. The length of the equatorial circumference is 24,902.487 miles.

MERIDIANS PARALLELS OF LATITUDE. small circles parallel to the equator. Of these, two are termed tropics, and two others, polar circles. The tropic of Cancer is about 23° 27' north of the equator, and the tropic of Capricorn about 23° 27' south of the equator. The north polar, or Arctic, circle is about 23° 27' from the north pole, and the south polar, or Antarctic, circle about 23° 27' from the south pole. 1 From the Greek word planetes, a wanderei-; a heavenly body that changes its place. 1 See Articles 5 and 6. 3 The English statute mile is 1760 yards long; the English geographical mile is one-sixtieth of a degree of latitude, and about 2025 yards in length, — one-seventh greater than the former. In this work, wherever the words mile and miles occur without any designation, the English statute mile is understood. 4 See Articles 5 and 6. 7.

Zones. — Zones are those divisions of the earth's surface which are included between the tropics, the tropics and the polar circles, 1. What is said of the earth, and of its position in the solar system? 2. What is the form ofthe earth? Give the proofs. Is the earth a sphere? What is its true form, and how proved? 3. Give the length of the equatorial diameter. That of the polar. Give the length of the equatorial circumference. 4. What is the terrestrial .sphere? What are the principal imaginary lines ofthe earth? 5. What is the axis of the earth? What are the poles? What does the position of the axis determine? How is the globe divided by a plane passing through its centre ? What are great circles ? Small circles ? How are the circumferences of all circ es divided and subdivided ? 6. What is the equator ?

What are meridians, parallels of latitude, tropics, and polar circles? What are the respective posi tions of the tropics, and of the polar circles ? 7. What are zones, and how many lLYQ [11616 aa' THE EARTH REGARDED AS A PLANET. degrees of longitude vary in length at different latitudes. Thus, at the equator the extent of a degree is about 69 miles ; at the 20th parallel, nearly 64.8 miles; at the 40th, about 52.8 miles; and at the 80th parallel, only 12 miles; vanishing to nothing at the'poles. and the polar circles and the poles. They are five in number : the space between the tropics is called the torrid zone ; that included by yorth Pole. 9. Motions of the Earth. — The earth has two motions : first, a daily revolution about its axis from west to east, causing the grateful vicissitudes of day and night; and, secondly, a yearly revolution around the sun in the same direction, which gives rise to the changing seasons.

These views were held by Pythagoras, a Greek philosopher, five hundred years before the Christian era, but were rejected by succeeding astronomers, who regarded the earth as stationary, around which all the heavenly bodies were supposed to revolve every twenty four hours. This error continued for about two thousand years, when the true theory was revived by Copernicus, in the sixteenth century. the tropics and polar circles, the north temperate and the south temperate zone; and the remaining surface, lying between the two poles and the polar circles, are severally named the north frigid and the south frigid zone. The zones have received their respective appellations on account of the different degrees of heat they receive from the sun. The cause of this will be evident when we speak of the seasons. 10.

Daily motion. — The fact that the earth revolves upon its axis rests upon the following proofs : — i. It is impossible, from the laws of centrifugal force, that the heavenly bodies should revolve daily about the earth ; but perfectly consistent with these laws to consider their motion as apparent, and due to a real motion of the earth. 8. Eatitude and Eongitude. — The position of a place on the earth's surface is determined by its latitude and longitude. The latitude of any place is its distance from the equator, measured, in de grees, minutes, and seconds, on a meridian passing through the place. Latitude is reckoned north and south from the equator to the poles, — a distance of 90 degrees. n. The flattening of the earth at its poles is the legitimate effect of its rotation. Newton, assuming the earth to revolve upon its axis, proved its figure to be that of an oblate spheroid, before the fact was shown by actual measurements.

Regions north of the equator are in north latitude, and those south of the equator in south latitude. If two or more places are situated, for instance, on the 20th degree of south latitude, they are said to be on the same parallel, because the same circle passes through them. Degrees of latitude increase in length from the equator to the poles, the length of a degree at the equator being 68.7 miles, but at the poles, 69.4 miles. in. Balls descending from the summit of a high tower fall east of the point whence they started ; the top of the tower, and of course the balls, moving more rapidly eastward than the base, as they are farther from the axis of the earth than the latter, and consequently have a greater centrifugal force. In 1804, thirty balls were dropped from Michael's Tower, in Hamburg, from the The longitude of any place is the distance between a meridian passing through that place, and another meridian, taken as a standard, this distance being measured on the equator in degrees, minutes, and seconds. height of 235 feet, when the deviation from a perpendicular was found to be one-third of an inch.

The annexed cut illustrates this proof. A ball being dropped from B does not take the direction of the perpendicular BB', but that of the inclined line BD. IV. The diminished weight1 of bodies at the equator indicates a centrifugal force resulting from the rotation of the earth. A body re moved from the poles to the equator would lose by this force -jggth of its weight. v. The pendulum experiment of Foucault proves the daily motion of the globe. The standard meridian of the early geographers passed through the isle of Ferro,— the most westerly of the Canary Isles. In most of the kingdoms and states of Europe, that meridian is taken as a standard which passes through their principal observatory. Thus, the French reckon longitude from the observatory of Paris, and the English from that of Greenwich, which is the standard generally adopted in America.

Longitude is reckoned east and west from the standard meridian, being mea sured in each direction from 0° to 180°. Places lying west of the assumed meri dian are said to be in west longitude, up to 180°; those to the east, in east longitude, to the same extent. This point is illustrated in the annexed figure, where the circle CEDB represents the equator, and A the pole of the earth. . vi. All the planets, that afford the astronomer any means of deter mining the question, are found to revolve on their axes ; and it is reasonable to infer that the earth, which belongs to the same system, also revolves on its axis. This axis is its shortest or polar diameter, the length of which, as already stated, is 7899.7 miles. Upon no other diameter can the globe permanently rotate : every other is unstable ; for if a globe 1 A body removed from the equator to the poles gains T5Tth of its entire weight ; 3£uth is due to the flattening of the earth at the poles.

The difference between T|Tth and -j^th, equal to still remains to be accounted for ; and the rotation of the earth does account for it. In consequence of the convergence of the meridians to the poles, How are they situated ? Why are the zones termed torrid, temperate, and frigid ? How is the position of a place on the earth's surface determined? 8. How is latitude measured and reckoned ? Are the degrees of latitude all of the same length ? What is longitude, and how measured ? What is said of the standard meridian ? How is longitude reckoned ? What is said respecting the length of a degree of longitude? Give instances. 9. How many motions has the earth? What were the views of Pythagoras ? What those of succeeding astronomers ? When was the true theory of the earth's motions revived? 10. Give the proofs of the earth's rotation.

Upon what diameter does the earth revolve ? Can it revol vh permanently on any other? What is the velocity of the earth on its axis? begins to revolve on any diameter except the shortest, it changes its rotation till it eventually revolves on the latter. The velocity of the earth on its axis is about 1000 miles an hour at the equator. the days and lengthening the nights, in the northern hemisphere, and producing the contrary effects in the southern. On the 22d of September it again passes through the poles, when the days and nights are once more equal in length all over the world. This is the time of the autumnal equinox in the northern hemisphere, and of the vernal in the southern, — spring commencing in the latter region, and autumn in the former. 11. Annual 'lotion. — The annual revolution ofthe earth around the sun is inferred from the following considerations : — i. From the fact that all the other bodies of the solar system pos sess this .notion, and there is no reason for believing that the earth constitutes an exception.

The earth still sweeping forward in its annual course, the circle of illumination gradually withdraws from the north pole, and ex tends beyond the south pole, lengthening the nights and shortening the days in the northern hemisphere, and causing the opposite results in the southern. II. The squares of the times of the revolutions of the planets about the sun are proportional to the cubes of their average distances from this orb. The earth, on the supposition that it is in motion around the sun, is included in this law. in. The phenomenon termed the aberration of light can be ex plained only by the annual motion of the earth. On the 21st of December this change has attained its full extent: the rays of the sun then strike the earth beyond the south pole to the Antarctic circle, and the regions within this circle now enjoy a continual day ; but in the northern hemisphere the solar beams reach only the Arctic circle, and this zone is now veiled in the gloom of a constant night. 12.

The Ecliptic is the orbit, or path, which the earth describes in its yearly revolution, and is so named because the eclipses of the sun and moon happen in, or near, its plane. The distance of the earth from the sun is 95,300,000 miles ; the length of its orbit, 598,000,000 miles; and its orbitual velocity, 1138 miles a minute. It is now the time of the winter solstice in the northern hemi sphere, when winter begins, and of the summer solstice in the southern, when summer opens, — the longest day now occurring in the latter hemisphere, and the shortest in the former. 13. The Seasons. — The change of seasons is owing to three causes : — i. That the sun illumines but half of the globe at a time. n. That the axis of the earth is inclined to the plane of the ecliptic. in. That the direction of the axis is always the same.

The inclination of the axis to a perpendicular to the ecliptic is about 23° 27'. On the 20th of March the direction of the sun's rays is perpendicular to the earth's axis, and the bounding line that divides the enlightened from the dark hemisphere, and which is called the circle of illumination, reaches from pole to pole. As the earth revolves on its axis, every place on its surface is now half the time of one rotation in darkness, and the other half in light ; and the days and nights are equal in length all over the globe. This is the time of the ver nal equinox1 in the northern hemisphere, and of the autumnal in the southern, — spring beginning in the former and autumn in the latter. The subject of seasons is illustrated by the annexed cut, where the twelve globes represent the position of the earth in its orbit in the successive months of the year, DCL the equator, and NCS the axis, — N being the north pole, aud S the south.

The earth moving on its course, the circle of illumination gradually overlaps the north pole more and more, and recedes from the south pole, — the days increasing in length and the nights decreasing, in the northern hemisphere, and the reverse occurring in the southern. 14. Solar Influences. — The sun, by its attraction, keeps the earth in her orbit, and, in conjunction with the moon, sways in tides the waters of the ocean. On the 21st of June the circle of illumination reaches its utmost limit, the rays of the sun then extending 23° 27' beyond the north pole to the Arctic circle, and falling short of the south pole by the same amount, just grazing the Antarctic circle. Within the former circle now reigns continual day, and within the latter unbroken night. His beams illumine the globe in its ceaseless circuit, transforming, by their manifold powers, what would otherwise be a mass of dead and inert matter into a world glorious in life, grandeur, and beauty.

The sunbeam, by its chemical power, its light and heat, moulds the crystal, wakens the sleeping seed, and, quickening the pulse of life throughout the world, clothes it with verdure, bud, bloom, and fruit, all glowing with the rich and varied hues of light, while every form of animal life rejoices beneath its cheering rays. In the northern hemisphere it is the beginning of summer, and the time of the summer solstice,2 when the day is longest and the night shortest. In the southern hemisphere it is the period of the winter solstice, when winter commences, and the night is longest and the day shortest. Moreover, by its heat, it lifts the waters into the air, to descend in fertilizing showers, and gives rise to the winds which distribute the treasures of rain all over the world. Such are a few of the influences of the sun, whicli will be more fully unfolded in the subsequent chapters of this work ; for the energies of this mighty orb pervade all the realms of nature embraced by the subject of Physical Geography.

As the earth departs from the summer solstice, the circle of illu mination returns by degrees to the north and south poles, shortening 1 From the Latin œquus, equal, and nox, night. 2 From the Latin sol, sun, stare, to stand; because the sun now appears to be stationary in the heavens, as regards its apparent motion north or south. 11. Give the proofs of the annual motion of the earth. 12. What is the ecliptic? What is the distance of the earth from the sun, the length of its orbit, and its orbitual velocity ? 13. To what are the seasons owing? What is the inclination of the earth's axis to a perpendicular to the ecliptic? Describe in full the changes of the seasons. Explain the seasons by the cut. 14. What is said of the influence of the sun upon the earth? THE STRUCTURE OF THE EARTH. mean rate of 1° Fah. for every fifty-five feet of descent, alter which the change was more rapid, being 1° Fah. every forty-four feet.

PAET SECOND. The hot springs that occur in various parts of the globe, and which are generally found to have their sources very deep below its surface, attest likewise the existence and progressive increase of its internal heat. THE STRUCTURE OF THE EARTH. 1. The subject of the Structure of the Earth may be appro priately divided into two heads: — lst. The Central Mass of the Earth, and its Crust. 2d. The Formation of the Earth. But, above all, volcanoes, which in every clime are seen, from time to time, pouring out their fiery streams of melted rock, ex hibit the most striking proof of the intense heat of the central portions of the earth. According to Humboldt, granite would be melted at the distance of about twenty-four miles below the surface of the earth, if the temperature constantly increased to this depth at the rate of 1° Fah. for every fifty -four and a half feet. 4.