Eclectic Physical Geography

Preface

. The aim of this book is to indicate briefly what we know or sur mise concerning the proximate causes of the more common and familiar phenomena observed at the earth's surface. Even thus re stricted, the field of inquiry encroaches to a greater or less extent upon the domains of all the branches of science. Since the study of Physical Geography precedes that of the sciences in most of our schools, it has been thought advisable to present, in the form of an introductory chapter, a condensed state ment of the more important and fundamental scientific conceptions regarding the properties and phenomena of matter and energy, such as inertia, gravitation, cohesion, affinity, and heat, light, magnetism, and electricity. This chapter may be studied or simply read, at the discretion of the teacher.

The order of treatment of the different parts of the subject proper is that which seems most natural and rational. After describing the relations of the planet to the solar system, its movements and their effects, the atmosphere is at once considered, not only be cause it forms the true outer layer and envelope of the earth, but because its action is the proximate cause both of all details in the relief of the land, and of the more conspicuous phenomena of the sea. The sea is next discussed, since it forms an intermediate layer between the atmosphere and three fourths of the earth's solid surface, and since the peculiarities in the relative position, composition, and relief of the land masses can be appreciated only after some acquaintance with the depth and character of the bottom in different regions of the sea.

In the treatment of the land, which then follows, the methods by which its surface contour is constantly modified by atmospheric agencies .are explained at greater length than is usual in current text-books, while the influence of subterranean agencies in changing the elevation of the land is carefully considered. Climate, being the average local condition of the atmos phere, as determined largely by the peculiarities of the surface upon I'KKFAI E. which it rests, is appropriately treated after that surface has been discussed, and fittingly precedes the concluding chapters on life. These chapters embrace a brief description of the more conspicuous phenomena of the organic world. The close dependence of plants and animals upon their inorganic surroundings and upon each other is pointed out, as well as the remarkable series of facts which is held by many scientists to indicate that all organisms are of kin.

In a study of this kind it is well to remember that, with all the scientific knowledge of the nineteenth century, we are still profoundly ignorant of the ultimate causes of things, while our ideas of proximate causes are constantly being revised and changed as our acquaintance with nature increases. The broadest scientific gener alizations of one generation are apt to be swept away or greatly modified by the next, and our descendants will doubtless regard the science of to-day much as we regard that of the ancients. Yet, notwithstanding its crudities and absurdities, ancient alchemy gradually developed into modern chemistry, which has been of inesti mable value to man ; and in the same way, the more perfect knowledge of the future is to be acquired only through familiarity with the imperfect theories of to-day.

The maps in the book have been carefully prepared in various projections, each adapted to portray most accurately the special feature under consideration, and, with the cuts and diagrams, are inserted to illustrate, and not simply to beautify the text. The acknowledgments of the author are due to the United States Geological Survey, Coast and Geodetic Survey, Signal Service, and Hydrographic Bureau for maps and information courteously sup plied. He also takes this opportunity to acknowledge gratefully the valuable assistance rendered in revising the proof-sheets of the introductory chapter, by Prof. T. H. Norton, of the University of Cincinnati ; of the chapters on the atmosphere and climate, by Prof. Cleveland Abbe, of the U. S. Signal Service, and Prof. W. M. Davis, of Harvard College ; and of the chapters on the land by Capt. C. E. Dutton of the U. S. Geological Survey.

Cincinnati, fiuly, 1888. CONTENTS. PAGE Introduction. — Some General Laws of Nature ... 7 Part I. — The Earth as a Planet. Chapter I. — The Solar System 35 II. — Movements of the Earth .... 43 Part II.— The Atmosphere. Chapter III. — Composition, Weight, and Heat ... 55 IV. — Moisture of the Atmosphere .... 66 V. — Movements of the Atmosphere ... 78 VI. — " " " " (Continued) . 90 VII. — Luminous Phenomena ..... 100 Part III.— The Sea. Chapter VIII. — Depth, Composition, and Temperature . . 109 IX. — Waves and Tides 122 X. — Currents and Deposits 135 Part IV. — The Land. Chapter XI. — Divisions of the Land 149 XII.— Surface of the Land 161 XIII.— Structure of the Land 180 XIV.— Springs 195 XV.— Streams. 205 XVI.— Work of Streams 216 XVII. — Glaciers and Lakes ..... 231 (v) VI CONTENTS. PAGE Chapter XVIII. — Mountain Structure and Land Sculpture . 248 XIX. — Earthquakes 264 XX.— Volcanoes 278 Part V. — Weather and Climate.

Chapter XXI. — Weather and Climate 293 Part VI. — Life. Chapter XXII. — The Various Forms of Life .... 313 XXIII.— Distribution of Life 328 XXIV.— Man 350 Index 373 List of Maps and Charts. Abnormal Temperatures of Isothermals, United States . 309 the World . . . 305 Lake Region United States . 239 Biological Regions . . 334 Magnetic Meridians, North- Continental Plateau . -152 era Hemisphere . . 31 Currents and Floating Ice Malay Archipelago . .156 of the Sea . . .138 Map Projections . . 53-4 Delta of Mississippi and Nile 228 Rain-fall on Land Surface Depths of the Sea . . 1 1 2-3 of the World ... 76 Drainage Basin of Missis- Rain-fall of United States . 307 sippi River . . . 207 Range of Annual Tempera- Drainage Basin ofthe Oceans 209 ture of World . . 300 Earthquakes in the U. S. . 267 Storm Frequency and Paths 91 Glaciers and Glaciated Re- Surface Africa and Australia 175 gions .... 238 Surface of Euro-Asia . 173 Isobars and Winds Northern Surface of North and South Hemisphere ... 87 America . . .167 Isobars and Winds Southern Tornado Frequency in the Hemisphere ... 85 United States ... 98 Isothermals, Northern Hemi- Vegetation regions of World 332 sphere .... 63 Volcanic regions of World . 289 Isothermals, Southern Hemi- Weather Chart of eastern sphere .... 65 United States . . .

Introduction

. SOME GENERAL LAWS OF NATURE. Show me thy ways, O Lord, teach me thy paths. — Psalm xxv: 4. Laws of Nature. — Nothing in nature is permanent ; every thing is constantly changing. Day changes into night, fair weather into foul, plants and animals die and decay, and even the solid rocks gradually wear away into soil or sand. These changes do not occur by chance, but each is the result of some definite cause, and, under similar circumstances, precisely the same effects are produced by the same causes. The invariable relations between causes and resulting effects constitute the laws of nature. Physical Geography seeks to trace the operation of the laws of nature upon the earth ; upon the air, the water, and the land ; upon plants, animals, and even upon man. Matter is the general name given to the material of which any body, such as rock, water, or air, is composed.

Kinds of Matter. — The number of substances in the world is almost infinite ; yet most of them are compound substances, and can be broken up into a comparatively few distinct kinds of matter, from which no other kind can be obtained, and which are, therefore, called simple sub stances, or elements. niVSICAI. GEOGRAPHY. Constitution of Matter. — All matter is conceived to be built up of minute particles, called molecules. A molecule is the smallest fragment of any substance that can exist by itself. A molecule of a compound breaks into the simple substances of which the compound is com posed ; and a molecule of a simple substance breaks into still smaller fragments, called atoms, which are too small to exist by themselves, but large enough to unite with other atoms of the same or different kinds of matter to form a simple or a compound molecule.

Molecules are too small to be visible even with the aid of the most powerful microscope. Some idea of their extreme smallness may be gathered from Sir William Thomson's estimate that if a drop of water were magnified to the size of the earth, its molecules, so magnified, would be about as large as base-balls. Common Properties of Matter. — All matter of what ever kind is indestructible, impenetrable, and possesses inertia. By virtue of the first quality, it is absolutely impossible to destroy a single atom or molecule in nature. A substance may disappear, but new substances are always formed of its constituent atoms. By virtue of the second quality, two particles can not occupy the same space at the same time. A nail driven into a board Fig- '■ does not penetrate the molecules of the wood : it simply forces them aside Inertia. — All matter resists being set in motion, and, when moving, resists any change in the rate or direction of its motion.

Hence, no body can either start into motion or stop when moving unless something outside of itself pulls or pushes it powerfully enough to overcome this resistance. This resistance of matter is called its inertia. The inertia of bodies increases with the amount of matter they contain. Thus, if two balls of iron, a large one and a small one, be suspended by long cords, the large one will require a more powerful pull or push to start it to swinging or to stop it than the small one. If a ball of cork, of the same size as one of the iron balls be sus pended, it will require a less powerful pull or push to start or stop it than the iron ball. The iron ball, therefore, though of the same size, contains a greater quantity, or mass, of matter, and possesses greater inertia than the cork ball. Forces of Nature. — A pull or a push of any kind or strength always tends to overcome inertia, and is called a force.

There are three great natural forces by whose varying action the few elemental substances are gathered and held together into the infinite variety of groups or bodies of nature. These forces are Gravitation, Cohesion, and Chemical Affinity. Gravitation is a force which is constantly acting upon all matter in nature. By virtue of this force, each mole cule of matter tends to attract, or pull toward itself, every other molecule, however distant. Since each molecule exercises this attraction upon others, a body composed of a great number of molecules, or of a large mass of matter, exercises a stronger attraction than bodies of fewer molecules or less mass. The mass of the whole earth is so enormous that its attraction quite overpowers that of de tached bodies near its surface ; these, therefore, if unsup ported, yield to the attraction of the greater mass, and move or fall toward the earth.

If the body is sup ported, the attraction of the earth causes it to push or press against its support. This pressure is called the weight of the body. Some bodies ascend instead of falling — as smoke or a balloon in the air, or a cork or oil under water. This is not because the earth does not attract them, but because an equal bulk of the air or water immediately above the body contains a greater mass of matter, and is, therefore, more strongly attracted by the earth than the body itself. The body and the greater mass of air or water above it con sequently exchange places — the greater mass sinking, and forcing the smaller mass to rise. When two bodies are weighed in the same place and under similar conditions, the heavier always contains the greater mass of matter even if it is much the smaller body.

Thus, i cubic foot of rock, 2 cubic feet of water, 8 cubic feet of cork, and i, 600 cubic feet of air have about the same weights and the same inertia, and, consequently, are equal to each other in mass, though the bulk of the cork is four times that of the water, and eight times that of the rock. If the bulks were equal, the rock would weigh twice as much as the water, the cork one fourth as much, and the air but one eight hundredth as much. The specific gravity of a sub stance is such a comparison of its weight with that of an equal bulk of some other substance, usually water, taken as a standard. Thus, the weight of water being called one, the specific gravity of rock is two, of cork one fourth, of air one eight hundredth. Fig. 2 Distance. — Although the attraction of gravitation acts between bodies, however far apart they may be, the power or intensity of this force decreases very rapidly as the distance between the bodies increases.

Thus, gravity acting from B is distributed over four times the space at 2D, and nine times the space at 3Z? that it is at \D; hence, if the distance between two bodies is doubled or trebled, the mutual attraction of gravitation which they exert on each other is decreased to one fourth and one ninth respect ively ; in other words, tlie intensity of gravitation varies in versely as the square of the distance between the bodies. This law applies to sound and to radiant heat and light as well as to gravitation. The effects of Gravitation arc almost infinite in num ber, and many of them are familiar to every one. In general, gravitation gives weight to all substances in nature — even to such light and invisible substances as air — and therefore this force is one of the causes of all phenomena in which the weight of bodies plays a part.

The rising of vapor through the heavier air, and the falling of rain through the lighter air ; the moving of heavy air, as wind, to a region where the air is lighter ; and the downward flow of streams over the sloping surface of the land are thus all caused by the attraction of the enormous mass of the earth upon the relatively insignificant masses of matter near its surface. The effect of the earth's attraction, however, is not confined to the neighborhood of its surface. The nearest heavenly body, the moon, is much smaller than the earth ; it contains but one eightieth as much matter. Though 240,000 miles distant, the attraction of the larger earth pulls this body constantly from the straight course which its inertia influences it to follow, and causes the moon's path or orbit to become nearly circular around the earth.

The moon's attraction upon the larger earth is imperceptible on the solid land, but it heaps up the waters of the sea to form the tides. But the attraction of gravitation extends to all distances. The sun is a body whose mass is 300,000 times as great as that of the earth and moon together. The attraction of this vast mass, exerted through a distance of 92,000,000 miles, overcomes the earth's inertia, and causes the earth and the other planets of the solar system to move around the sun in nearly circular orbits — just as the earth influences the movement of the moon. The effect of the sun's attraction upon the earth is seen in the regular recurrence of the seasons, and the regular variation in the length of the day and night. Each fixed star is, probably, like our sun, the cen^r of a system of planets.

Each of these systems, as a whole, has, like the solar system, a motion of its own through limitless space, which is modified and regulated according to the mass and distance of the various systems by this universal force of gravitation. Cohesion, like gravitation, is an attractive force which may act on every molecule in nature. But it is unlike gravitation in three important particulars: (i) it acts only be tween individual molecules, and not between masses ; (2) it acts only between molecules of the same kind of matter ; and (3) it acts only when the molecules are exceedingly close together, — so close that they seem to be in absolute contact. It is the force of gravity acting between the mass of the earth and the mass of a stone which causes the stone to fall to the earth ; but it is the force of cohesion acting between the millions of individual stone molecules which causes them to stick together and form the solid mass of stone.

A man lifting a bucket from a well, or carry ing a heavy basket, is thus overcoming the force of gravity ; while a woodman chopping down a tree, or a machinist filing a piece of iron, is struggling against the force of cohesion. State of Aggregation. — It is believed that between the molecules of all bodies two antagonistic forces are con stantly struggling for mastery : the attractive force of cohesion, and a repulsive force, which results in what we call "heat." When the attractive force is the stronger, the molecules cohere (stick together) and form a solid; when the two forces are about equal, the molecules move about, over, and beside each other, and form a liquid ; when the repulsive force is the stronger, the molecules fly farther apart, and form a gas. It thus depends simply upon the relative intensities of cohesion and heat between the molecules of any substance, whether that sub stance takes the form of a solid, a liquid, or a gas.

Ice, water, and steam, for example, may be produced from the same molecules by simply making them colder or hotter. It is believed that there is no substance which may not exist in any one of the three states of ag gregation, — a solid, a liquid, or a gas. . Crystallization is a peculiar effect of cohesion frequently seen in rock, cast iron, snow, and very many other solids. When a substance passes slowly and quietly from a liquid to a solid state, the molecules generally arrange themselves in a peculiar manner, assuming certain definite geometrical shapes. These shapes vary in differ ent substances, but remain constant in substances of the same kind. If water, for instance, be examined when solidifying, ox freezing, delicate needles of ice will be observed shooting out over the sur face and forming six-pointed stars or little six-sided figures.

These are ice crystals, and, if observed in freezing water in any part of the world, the ice-needles are always found to form angles of just 6o° with each other. If a solution of table salt be allowed to solidify, the salt takes the form of little cubes with exquisitely smooth sides, and clean, square angles. These are salt crystals. In general, every substance forms crystals, which are always the same in the same Fig. 3. — 1. Quartz. 2. Gypsum. 3. Salt. 4. Calcspar. 5. Feldspar. substance, but different in shape from the crystals of other sub stances. Crystallization is explained by supposing that the cohesive force of molecules is not exerted equally on all sides, but is stronger in certain definite directions, and that there are differences in this respect between the molecules of different kinds of matter.

The power of Cohesion is, of course, greatest in solids, but it varies in different substances. The cohesive attraction is so strong that it requires a pull of ioo.ooo to 170,000 lbs. to break a steel bar 1 inch square. 50,000 to 100,000 lbs. " " " iron " " " 4,000 to 20,000 lbs. " " " wooden " " " 500 to 1,000 lbs. " " "stone. ' It is the great power of the cohesive force between ice molecules that causes the bursting of water-pipes when the water in them crystallizes, or freezes. The molecules of water and of many other substances occupy a greater space when the absence of heat allows cohesion to arrange them in the form of crystals, than when, heat being present, it over comes cohesion and arranges the molecules so that they slide over each other in the form of a liquid. Hence, the contents of a water pipe expands as it changes from a liquid to a crystallized form.

It expands with a force which, at the ordinary temperature of freezing water, produces an outward pressure of more than 2,000 pounds on each square inch of the interior of the pipe, and this pressure in creases rapidly as the temperature falls. Few pipes can withstand this pressure, and, consequently, they burst. If the pipe is strong enough, however, to prevent the expansion, the water can not freeze, but remains liquid. Adhesion is a force similar to cohesion, except that while cohesion acts only between molecules of the same kind of matter, adhesion acts only between molecules of different kinds. No body can become wet when plunged into water, if the adhesion between the molecules of the water and the body is weaker than the cohesion between the molecules of the water. Grease is such a substance, and, therefore, does not become wet.

Capillary Attraction is an instance of adhesion, and is so named from the Latin word capillus, a hair. When one end of a fine, hair-like tube is plunged into any liquid that will adhere to the material of which the tube is made, the attraction of adhesion causes the liquid to rise in the tube a short distance above the level of the liquid outside the tube. The finer the bore of the tube, the higher will the liquid rise in it. If the corner of a towel be allowed to remain for a short time in water, the towel, for some distance above the surface of the water will be found to be wet, the minute spaces between the strands of the threads having acted as so many tubes in which the water rises by capillary attraction. Capillary attraction plays a very important part in nature ; it enables the soil and rocks to retain water, it forms one of the means by which plants are supplied with their liquid food, and it is called into requisition in distributing some of the animal juices throughout the body.

Chemical Affinity, like gravitation, is an attractive force, and, like cohesion, acts only at imperceptible distances. But it is an atomic force ; it acts, primarily, only between atoms, and when these atoms are of different kinds of matter, a substance is produced entirely different from either of the atoms. The difference between affinity and cohesion is thus very apparent ; cohesion increases the mass of a substance by adding together many minute particles of the same substance ; affinity produces a new substance by combining still more minute particles of totally dissimilar substances. Elements. — It has been said that an element or simple substance is composed of but a single kind of matter ; that is, if an element could be broken up into its atoms, all the atoms would be exactly alike in all particu lars.

There are about seventy known elements ; of these, fifty-five are called metals, such as aluminium, calcium, potassium, iron, copper, gold, etc. The remaining ele ments are called metalloids; some are solids at ordinary temperatures, such as silicon, carbon (charcoal), phosphorus, and sulphur; one is a liquid, — bromine; and others are gases at ordinary temperatures, such as oxygen, hydrogen, and nitrogen. Compounds. — Every substance in nature is composed of one or more elements in a free state, or is a chemical combination of two or more elements. Such a combination produces a compound substance. Air is composed chiefly of oxygen and nitrogen mixed together in the free states. Water is a chemical compound of the two ele ments, oxygen and hydrogen ; quartz ox flint, of oxygen and silicon; limestone, of oxygen, carbon, and calcium ; bread, meat, and most foods, of oxygen, hydrogen, nitrogen, and carbon, together with minute quantities of various other elements.

Oxygen is far the most abundant element on the earth. At ordinary temperatures it is a gas — colorless, tasteless, P. G.—2. FIIYSICAL GEOGRAPHY. and odorless, and a trifle heavier than air. Oxygen is essential to all life, both animal and vegetable. Oxygen forms about by weight of all rocks of the earth. $ ' " water. " I • air. § ' vegetable matter. | " ' animal matter. Oxidation and Combustion. — The affinity of oxygen for most of the substances in nature is so strong that it is constantly combining with them when they are exposed to the air with its large quantity of free oxygen. The process is called "rusting," "rotting," or "burning" in different instances, all of which are covered by the general term oxidation. Oxidation always produces heat, as is the case with most chemical combinations.

When the heat is great enough to produce light, the process is called combustion. A familiar instance of oxidation is the "rusting" of iron in the air. The oxygen of the air unites with the surface iron to form the new substance, oxide of iron. The burning of fuel is really the same process, only the chemical affinity between the carbon and hydrogen of which most fuel is composed, and the oxygen of the air, is much greater than that between iron and oxygen ; the heat produced by their union is great enough to produce light, and the process is consequently called combustion. Decomposition is the breaking up of a compound into its elements or into simpler compounds. The affinity be tween different elements varies in strength. Whenever elements having a stronger affinity for each other than for those with which they happen to be combined, are brought by any means sufficiently close together for affinity to act, the weak combinations break up, and the ele ments, liberated by the decomposition, recombine accord ing to the strength of their mutual affinities to form other substances, which, under similar circumstances, decompose and recombine into still other compounds.

In this way, the atoms and molecules are kept in circulation. Gunpowder is nothing but certain weak combinations containing elements that have a strong affinity for each other, artificially placed so close together that a slight heat causes the weak combinations to decompose and leave certain of their ingredients free to unite in a strong combination. Kinetic Energy. — One or more of these three great attractive forces — gravitation, cohesion, or affinity — is thought to be, directly or indirectly, the cause of all motion in the universe ; and every one of the innumerable changes that are constantly taking" place in matter around us, is thought to be the result of some kind of motion of that matter, — either a visible motion of its mass as a whole, or an invisible motion of its molecules or atoms.

Matter in motion always imparts some kind of motion to other matter with which it comes in contact. This im parting of motion is called doing work. Matter in motion is, therefore, said to have the power to do work, or to possess kinetic (active) energy. The quantity of work a body in motion is capable of doing, — or the amount of kinetic energy it possesses, — depends more upon the rapidity of its motion than upon its mass ; for, while doubling the mass only doubles the energy, doubling the speed increases the energy four times ; thus, energy increases with the mass of a body but with the square of its velocity. That is, a hundred-pound cannon ball, moving with a certain speed, possesses no more energy than a one-pound ball moving ten times as fast. Potential Energy. — It often happens that the expenditure of kinetic energy upon a body places it in such a position that, though not in motion, it would move and do work if unrestrained.

A body in such a position is said to possess potential (possible) energy. A bent bow, a hoisted weight, or a wound-up watch spring possesses potential energy. Potential energy is thus simply stored-up kinetic energy, since it exists only in bodies on which kinetic energy has been expended. Upon the removal of restraint, the body immediately moves, and the potential energy is converted back again into exactly the amount of kinetic energy which was expended in its production. Conservation of Energy means that the total amount of energy in the universe is an unchangeable quantity. Energy, therefore, can not be created or destroyed, but it is constantly eluding observation by changing its form, or by entering and leaving different masses of matter. It is frequently apparently destroyed either (i) when it changes from a kinetic to a potential form, — as when the kinetic energy expended in lifting a heavy weight is changed into potential energy of the weight when the latter stops moving just before falling ; or (2) when masses in visible motion impart a portion or all of their motion and energy to invisible molecules, — as when a falling weight strikes the earth, and its motion, as a tnass, stops.

In this case, if the weight and the place struck were carefully examined, they would be found to have undergone certain changes in consequence of the blow ; they would be hotter than before, and they might have become luminous, or other changes might have taken place. These changes — heat, light, etc., — are simply the results of molec ular energy arising from the invisible motions imparted to the molecules by the collision which stopped the visible motion of the weight. If the energy causing all the changes that occurred in consequence of the blow could be collected, it would be found to equal the amount which the weight possessed when it struck the earth, and exactly this amount of energy is passed on to other matter by the molecules be fore they regain their former condition. Nature of Heat and Light. — Heat and light are the results of a certain kind of insensible motion of the mole cules of matter.