.^^t•L18RARYQ/:. %0:!i'IV3JO'^ University Research Library This book is DUE on the last date stamped below ■■-■ - ■: iS2r NOV 2 1925 Oct ■" ' ,;v -JL 29 2929 OCT i« 1*'^ npT ♦""USiMf Form L-9-15))i-8,'24 '^^'%m ?.i tfiTT. mt m SEP 1955 X X !■ roi'thpifce VESUVIUS Eruption ol A|>iil, u/jO. I'.iiiibsion of gas, ashes, and sand as seen from the Observatory. )0 MAURY-SIMONDS PHYSICAL GEOGKArHi PHYSICAL GEOGRAPHY BY M. F. MAURY. LL.D. LATE SUPERINTENDENT OF THE NA\'Al. OBSERVATORY, WASHINGTON, D.C. REVISED AND LARGELY REWRITTEN BY FREDERIC WILLIAM SIMOXDS, Ph.D. PROFESSOR OF GEOLOLiV IN THE UNIVERSITY OF TEXAS /7577 NEW YORK •:• CINCINNATI •:• CHICAGO AMERICAN BOOK COMPANY ■tiy 1908 Copyright, 1908, by FREDERIC WILLIAM SIMONDS. Entered at Stationers' Hall, London, maury-simonds phys. geog. \44 PREFACE The advance of geographic science has been so great during the last decade that a thorough revision of the older text-books has become imperative. To the end that Maury's Physical Geography may maintain its position, it has been the writer's privilege not only to revise, but largely to rewrite that well- known book. In so doing an attempt has been made to pre- serve as far as possible the plan of the older work — a plan that has met the approval of a generation of teachers — and, at the same time, to modernize the text thoroughly. In the matter of illustrations, the present volume will be found exceedingly attractive and the adoption of a smaller page will add much to the reader's comfort. In the preparation of this edition, acknowledgments are due to many persons, especially to Dr. William J. Battle and Dr. William T. Mather of the University of Texas — the former, for the use of some of his excellent photographs of Egyptian scenery ; the latter, for timely suggestions which have added materially to the accuracy of the text. Acknowl- edgments are also made to Mr. Sterling R. Fulmore for Ha- waiian, Australian, and New Zealand views ; to Professor A. J. Henry, of Washington, B.C., for cloud views ; to Mr. W. E. Seright, of Stafford, Kansas, for the unique photograph of a tornado ; to President D. S. Jordan, of Leland Stanford Junior University, for California earthquake views ; and to Professor S 6 PREFACE H. L. Fairchild, of the University of Rochester, for photo- graphs of drumlins, kames, and eskers. The diagrams and most of the maps have been drawn by the writer or, under his direction, by Mr. N. P. Pope. FREDERIC W. SIMONDS. The University of Texas, Austin. CONTENTS Introductory PART I. — THE EARTH CHAPTER I. The Earth and the Solar System . II. The Shape, Size, and Density of the Earth III. The Motions of the Earth IV. Terrestrial .Magnetism V. Internal Heat of the Earth VI. Volcanoes .... VII. Earthquakes II i8 23 32 40 46 60 PART II.— THE LAND VIII. The Land Masses 70 IX. Relief of the Land 75 X. Relief Forms of North a.nd South America . . 95 XI. Relief Forms of Europe. .Asia. Afrk a. and .Australia 114 XII. Islands 128 PART III.— THE WATER XIII. Properties of Water XIV. Waters of the Land . XV. Drainage .... XVI. The Sea and the Oceans . X\'II. Wa\es. Tides, and Currents 136 140 165 179 CONTENTS PART IV. — THE ATMOSPHERE CHAPTER XVllI. Physical Properties of the Atmosphere XIX. Climate .... XX. Atmospheric Circulation XXI. Storms .... XXII. Moisture of the Air XXIII. Rain XXIV. Hail, Snow, and Glaciers XXV. Electrical and Optical Phenomena PAGE 200 2IO 2l8 229 239 249 258 27s PART v. — LIFE XXVI. Animals and Plants ....... 280 XXVII. The Distribution of Useful Plants .... 288 XXVIII. The Distribution of Animals 292 XXIX. Man 311 XXX. Geographical Distribution of Labor .... 322 APPENDIX XXXI. Physical Geography as a Science 328 INTRODUCTORY Physical Geography deals with the world in the present stage of its existence. It considers the machinery which makes day and night, seedtime and harvest ; which lifts the vapor from the sea, forms clouds, and waters the earth ; which clothes the land with verdure and cheers it with warmth, or covers it with snow and ice. Physical Geography, moreover, treats of the agents that cause the wonderful circulation of waters in the sea; that diversify the continents with mountains, hills, plains, and valleys, and embellish the landscape with rivers and lakes. It views the earth — its surface, its waters, and its enveloping atmosphere — as the scene of operation of great physical forces, which by their united action render possible the life of plants and animals ; and studies the life of the globe, both terrestrial and aquatic, noting particularly the circumstances which are favorable or adverse to its development. It has been found convenient to present the topics treated in the following order : — I. The" Earth. II. The Land. III. The Water. IV. The Atmosphere. V. Life. _Of_NEPTytvlE_ The Solar System PART I. — THE EARTH I. THE EARTH AND THE SOLAR SYSTEM /7377 The Solar System. — By the ancients the earth was regarded as the center of the universe. Men saw the sun in the same part of the heavens morning after morning, and when his light faded at night they saw the stars in nearly the same positions as on the preceding night. • Hence they concluded that the sun and stars all move around the earth once in 24 hours. Careful observation seemed to confirm this idea. Astronomers watched the heavens; they mapped the stars; they recorded, from night to night, the places of the brightest among them. As a result, they found that the position of some remains unchanged with reference to that of their companions, while the position of others varies perceptibly. The former were called fixed stars ; the latter received the name planets, from a Greek \yord meaning zvanderers. For several centuries, ho.wever, astronomers have known that the ancient idea was a mistake. The sun, not the earth, is the center around which the planets revolve, and the earth itself is a planet. The planets are not self-luminous, but shine by reflected sunlight. Their paths of motion, or orbits, are nearly circular, and they all journey around the sun in nearly the same plane. In their regular order, beginning with that nearest to the sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. With the exception of Mercury and Venus, they are attended by one or more moons, or satellites. The sun, planets, and satellites, together with a number of small planetary bodies 12 THE EARTH AND THE SOLAR SYSTEM called asteroids, or pla7ietoids, which revolve in paths between Mars and Jupiter, constitute the Solar System, so named from the Latin sol, the sun. Within the limits of the Solar System there are also comets and meteoric swarms. The former are celestial bodies usually consisting of a head, with a very bright spot which gradually shades into a less luminous portion, or coma, and a tail, or streamer. GiAcoBiNi's Comet, December 29, 1905 From photograph by Professor E. E. Barnard, Yerkes Observatory. Owing to the movement of the camera, which was kept focused on the comet during the exposure, the stars appear as lines instead of points. Comets seem to be composed of matter in a highly rarefied state, for even sinall stars are visible through them. Some, from their movements around the sun, must be considered members of the Solar System ; others appear as casual visitors, passing never to return. The Henderson, North Carolina, Meteorite Two views. From proceedings of the U. S. Nat. Mus., Vol. 32. 13 H THE EARTH AND THE SOLAR SYSTEM The meteoric swarms seem, in some instances, to follow the orbits of cer- tain comets ; in others, the number of meteors is so great as apparently to fill the entire circuit of their own orbits. In either case, when they encounter the atmosphere of the earth, there is a brilliant clisjDlay of shooting stars, the so-called meteoric showers. The Sun. — The sun is also a star. From it the planets derive both heat and light. This vast ball, or sphere, is more than a million times as large as the earth. Were the earth placed at the sun's center, ^ ~~~~^ the latter body would reach so far into space as to extend nearly 200,000 miles beyond the orbit of the moon, or almost 440,000 miles beyond the earth's surface. The sun is in an intensely heated con- dition, and clouds of incandescent gases project outward from its surface for thou- sands of miles into space. From examina- tions made with the spectroscope it is known to contain many substances entering into the composition of the earth. Origin of the Solar System. — The sun and the planets are composed of the same kinds of matter and have similar forms and motions. Many astronomers and philosophers have tried to combine these facts and others into an explanation of the origin of the Solar System. Such explanations are termed hypotheses. Of these hypotheses at least two merit attention ; namely, the lubiilar ■a\\<\ \\\ posits may be due to the warping of the earth's crust. In such cases the level areas exposed along the shore are also desig- nated as lake plains. In some parts of the world, too, lake plains have resulted from desiccation, or the drying up of the lake waters, due to climatic changes. Where arid conditions still prevail, these old lake bottoms now form desert plains. Interior or Inland Plains are those lying within the continents. More or less inclosed by mountains and drained by large rivers, they partake of the general character of valleys, but are on a grander scale. Their origin is not due to river action, but rather to the great forces of upheaval whereby continents have been BASE LEVEL AND PENEPLAINS 8 1 elevated and mountains formed. Broadly speaking, the surface of these plains is rolling or undulating, but many areas of con- siderable extent are quite level. The great central plain of North America, lying in the basins of the Mississippi and Mac- kenzie rivers, and the combined plains of the Orinoco, Amazon, and Plata rivers in South America, afford excellent examples of this class. That portion of the interior plain of the United States lying at the base of the Rocky Mountains is known as the ''Great Plains." It is treeless, owing to the arid conditions prevailing there, and on account of its unusual altitude is often classed as a plateau. While its appearance is that of an extended prairie region, it should not be confounded with the true prairies lying at a lower altitude and nearer the Mississippi River. They are fertile areas of treeless land susceptible of high cultivation. Base Level and Peneplains. — When a stream has cut its channel down to the level of the body of water into which it empties, it can excavate its bed no deeper. It has reached its lowest point, or base level. Such a stream, if it flows across a plain, will now begin to meander, cutting away its banks later- ally. As this proceeds, the inequalities of the plain will even- tually disappear until the plain itself is base-leveled. To indicate a stage preceding that just described, in which the divides between the streams may still be recognized as low, rounded, but inconspicuous hills and swells, the term peneplain (almost a plain) is employed. It has frequently happened in geologic time that plains, plateaus, and even mountains, by the incessant action of the erosive agents, have been reduced to the peneplain or base-level state. Plains the Centers of Civilization. — Owing to their fertility and ease of cultivation, plains have been, throughout the history of man, centers of population, civilization, and power. The imperial glory of Nineveh and Babylon, the culture of ancient Egypt, the enduring prosperity of China, and the unrivaled wealth of India, all owe their origin to the rich soil brought by the rivers from the hills. 82 RELIEF OF THE LAND Plateaus or Table-lands are broad, elevated uplands. As stated by Gilbert, "they may be indefinitely bounded; they may be limited on all sides by cliffs overlooking adjacent areas ; or descending cliffs may limit on one side and ascending cliffs or slopes on the other." The names employed suggest flat- ness. Some plateaus, as the Llano Estacado of Texas, are as level as the prairies. Generally, however, plateaus present a highly diversified surface, hills and even great mountains rising from them. The plateau of Tibet consists of plains and wide basins, some of which contain large lakes, engirdled by ranges of gigantic snow-clad mountains. The aspect presented also by the great plateau lying between the Rocli^ Mountains and the Sierra Nevada in our own country, is that of a vast uplifted mass from which the mountains rise ; while the Bolivian plateau, in South America, with the tower- ing peaks of the Andes embosoming its upland lake, singularly resembles the plateau of Tibet. In elevation plateaus vary greatly. Low plateaus, like the desert of Sahara, are from looo to 3000 feet in height. The loftiest in the world are the plateau of Tibet, 10,000 to 15,000 feet high, and the Bolivian plateau, averaging about 12,000 feet. Kinds of Plateaus. — According to their origin plateaus may be divided into two groups: diastropJiic plateaus, those result- ing from the great forces of upheaval ; and vulcanic plateaus, those resulting from the outpourings of molten rock or lava. Diastrophic plateaus, like the plains bordering the continents, have been elevated above the level of the sea. In many instances they are composed of stratified rock, sandstones, lime- stones, and shales. Oftentimes the strata or layers have suf- fered little, if any, displacement, the whole area having been lifted bodily. In some regions, however, the rocks have been broken, by faulting, into great blocks, now arranged like a series of steps, each of which gives rise to a plateau of a different altitude. This structure is particularly characteristic of the KkOSION (>K HIAIEAUS 83 plateaus trenched by the Grand Canyon of the Colorado River in Arizona, which have been termed broken plateaus. Sed Level" Broken Plateaus Part of a section from west to east across the plateaus north of the Grand Canyon of the Colorado. P'lom Powell. Vulcanic plateaus have been formed by the coolinc^ of great lava floods. In the best-known examples the molten rock seems to have welled up through fissures in the crust now com- pletely concealed beneath the successive outpourings. In the northwestern part of the United States there is a vast area, not less than 150,000 square miles in extent, embracing portions of northern California, Nevada, Idaho, Oregon, and Washington, covered with these surface flows or sheets. Where cut by the Columbia River the aggregate thickness of the sheets composing this plateau is found to exceed 3000 feet. Erosion of Plateaus. — By the action of rain and flowing water plateaus are gradually worn away, or eroded. Streams originating upon or crossing a recently elevated table- land deepen their channels until canyonlike valleys are formed. In this manner a plateau is dissected. As the stream wear continues, tributaries are extended, canyon walls undermined, and valleys broadened. In the meantime the intervening land, or ridges, assume somewhat of a mountainous aspect, the rather uniform sky line serving in a general way to indicate the surface of the former plateau. As stream dissec- tion and erosion continue, the ridges become lower and less con- spicuous until they finally disappear, save here and there a M.-S. PHYS. GEOG. — 6 84 RELIEF OF THE LAND flat-topped hill, or mesa, capped with a layer of hard, resisting rock. The plateau has now reached the zvorn-doivn stage. Plateaus cut by canyon valleys may be classed as young ; those well dissected by stream ways, with intervening hills or "mountains," as viature ; and the worn-down plateau, as old. The Bad Lands of South Dakota Illustrating the effects of erosion upon soft rocks in an arid region. Unprotected by vege- tation, the valley vi'alls are readily sculptured by water action notwithstanding the scanty rainfall. Plateaus Unproductive. — The plateau regions of the world are for the most part unproductive. Many of them are absolute deserts. Hence few plateaus have ever become centers of population and power. It is interesting, however, to observe that the table-lands of Mexico, Peru, and Tibet have each been the seat of a civilization peculiarly its own. MOUNTAINS 85 The desert plateaus have undoubtedly their part to perform in the economy of nature. They are not wastes in the sense of being wasted or useless areas. Their effect upon the rainfall and its distribution is most important. It will be more fully considered when we treat of the moisture of the air. The Matiekiiokn, or Mont Cekvin This celebrated peak has an altitude of 14.705 feet. From stereograph. Used by per- Mountains. — The higher and more conspicuous elevations of the earth's crust are termed mountains. Although they some- times stand singly, as Etna or Vesuvius, more often they are 86 RELIEF OF THE LAND joined together in the form of a connected series called a range or chain. Mountain chains seldom occur solitary. Usually two or more are parallel, or nearly so, forming a mountain system. Of this the Andes, the Alps, and the Appalachians afford striking examples. Descriptive Terms. — Isolated summits are called peaks. The top of a ridge from which there is a descent in opposite direc- tions is known as a crest. The slopes of a ridge or peak con- stitute its flanks. A ridge or group of ridges presenting a serrated or notched sky line is called a sierra. Sharp-pointed peaks are spoken of as horns, a term especially used in Alpine regions. The Formation of Mountains. — Mountains have been formed in at least four ways : by folding or crumpling, by faulting, by vulcanism, and by erosion. .\ Representation of the Effects of Contraction upon an Outer, Yield- ing Spherical Covering In A the interior of the sphere, a, is shown before coniractit>n. The coat b fits closely upon if. In B the interior of the sphere, a, is shown after contraction. The non- shrinking coat, h, in order to fit upon it is now thrown into folds. The amount of contraction is shown V)v a comparison of Ihe radius in . / with that in B. (i) The folding process is thought to be a result of contrac- tion. The crust of the earth is regarded as a spherical shell or coat, now practically cool, surrounding a heated, but cooling rHK l-oRMMIoN ()!• NKjL'NIAINS 87 and therefore shrinking, interior. Under the influence of grav- ity the crust is drawn downward, that is, toward the center of the earth, and thus a larger spherical surface is made to fit closely upon a smaller. This can be brought about only by the folding, crushing, and breaking of the crust. Although serious objections have been brought against this An Ui'WARu Fold of the Ea kin's Ckust (Anticlink), near Hancock, Maryland theory, the fact remains that many of the most prominent mountain systems are composed of folded, crushed, and dis- turbed strata, as is well exemplified in the Appalachian and Jura Mountains. (2) In the region of the Great Basin, between the Sierra Nevada and the Rocky Mountains, there is found a type of mountain structure due primarily to faulting : long, narrow ridges with a cliff, or scarp, on one side and a gentle slope on the other. Here it would seem that a great plain had been up- heaved in the form of a mighty dome which, owing to tension, or stretching, was traversed by numerous cracks or fissures. RELIEF OF THE LAND Finally, by the collapse of the dome, the long, narrow, parallel blocks were displaced or faulted and each became a mountain ridge. (3) The formation of ordinary vulcanic mountains has already Diagrammatic Illustration of Block Mountains The tilted blocks are carved into hills, and mountains and cut by narrow, canyon-like gojges, while the valleys between them are filled with wash, sand and gravel, brought down from the adjacent heights. The streams in such a region either are lost in the sands or flow into lakes, permanent or temporary. been illustrated in the description of volcanoes, the cones of which are built up by the ejectment of cinders and ash, the outpouring of lava, or by both of these processes. There is, however, a type of vulcanic mountain of quite a different structure. Through a fissure, or conduit, in the earth's crust, not reaching the surface, Ideal Section of a Laccolite. S, sheets ; D, dikes. After Gilbert. molten matter from below has been forced, which, spreading out, lifts the overlying strata bodily upward in the form of a dome. Later this elevation is eroded or worn away, exposing VALLEYS 89 in many places the interior igneous filling, known as a laccolite. Such mountains are said to have a laccolitic structure. (4) As already stated, dissected plateaus may give rise to a rugged country. Here the mountains may be flat-topped, with summit scarps or cliffs, and sloping flanks covered with rock waste (talus), or they may be rounded off and subdued as in The Border of the Edwards Plateau on the Colorado River, West of Austin, Texas the region of the Allegheny plateau bordering the Appalachian Mountains on the west. Valleys are depressions through which usually water courses run. Every mountain range is intersected by valleys, and every mountain system has valleys separating its parallel ranges. The valleys intersecting ranges are called transverse. Those lying between parallel ranges, and having therefore the same general direction, are called longitudinal. In regions of folded mountains the formation of valleys is largely due to the upheavals and depressions which have dis- turbed the surface of the earth. The formation of valleys is 90 . KELIKF OF THE LAND Grand CamvoxN of the Colorado really a part of the process by which mountains are made. The action of running water has, of course, widened and deepened them. Valleys traversing plains and plateaus have been formed by GENERAL ELEVATION OF THE LAND 91 the erosive action of water. Of such valleys the most extraor- dinary in the world are the canyons of our Western rivers. That of the Colorado is a gorge shut in by ahnost perpendicular walls of rock. It is from 3000 to 6000 feet in depth and 300 miles long. Canyons are among the most impressive evidences of the age of our earth. Thousands of years would be a brief period for the work of wearing away solid rock by running water to the depth of more than a mile as in the case of the (irand Canvon of the Colorado. A Watkr Gap The Narrows of Wills Mountain, Maryland. Cumberland in the foreground. From Geological Survey of Maryland. The heading together of transverse vallcNs renders it possible to cross lofty mountain ranges. Human ingenuity and indus- try have improved these natural courses of travel, or passes, as they are called, and some of them have been made marvels of engineering skill. The Simplon, Saint Bernard, and Saint Go- thard passes, crossing the Alps, are among the most noted. The Alpine railroad tunnels have, to a large extent, taken the place of the passes. In the eastern portion of the United States the narrow transverse valleys, through which streams flow, are termed li'ater gaps. General Elevation of the Land. — Among the best evidences of continental elevation are those furnished by raised sea 92 RELIEF OF THE LAND beaches, water-worn caves, and terraces now found far above the seat of wave action, and by the occurrence, at various elevations, of coral reefs and the shells of marine animals still adhering to the rocks upon which they grew. In some parts of Great Britain (geologically a part of the Eurasian continent) raised sea beaches, five or six in number, are found at different levels up to lOO feet, and on the Norwe- gian coast there are numerous ice-cut ter- races, which repre- sent successive old shore lines. Modern coral rock has been reported by Alexan- der Agassiz as occur- ring in Peru at the height of 3000 feet above the sea level, and raised coral reefs are found in several places fringing the Red Sea. The above are a few of the many ex- amples that could be cited illustrating the elevation of the land masses with reference to the sea level. General Subsidence of the Land. — In many parts of the world there is evidence of the sinking or subsidence of the land. This is shown in drowned valleys, estuaries, and fiords, and in the submerging of forests as well as of the works of man. The sinking of the west coast of Greenland is a familiar example. Here the inhabitants fasten their boats to poles or piles driven off the shore. After long intervals, by the subsi- A iJKDWNKi) River — Chesapeake Bay CAUSES OF RELIEF 93 dence of the bottom, the poles disappear beneath the surface of the water and must be reset. The stumps of cypress trees show submerged forest land on the coast of South Carolina and Georgia; and near the head of the Bay of Fundy, in Cumberland County, Nova Scotia, the stumps of pine and beech trees, still embedded in the soil on which they grew, are covered to the depth of 25 to 35 feet at high water. v* The coast of New Jersey also may be cited as a region of At the Head of Chesapeake Bay Elk and Bohemia rivers from Elk Neck. From Geological Survey of Maryland. subsidence, the estimated rate being about two feet a century ; and the estuaries known as the Hudson River and Chesapeake Bay represent the drowning of former river valleys by subsi- dence. The fiords of the northern coasts furnish examples of the invasion of glaciated valleys by the sea due to crustal sinking. Causes of Relief. — What force or forces may have caused the general elevation of continents we cannot with certainty tell. On the principle that Hke effects are due to like causes we should conclude that the elevation of the continents and the formation of folded mountains were produced by similar forces ; namely, those resulting from interior contraction and consequent crustal deformation. Whatever may be our conclusions on this 94 RELIEF OF THE LAND point, it is clear that the forces have been at work for ages, at times silently and gently, again with sudden displacements and earthquakes, raising some portions of the earth's surface and depressing others. Effects of Relief. — The elevations of the earth's surface, although comparatively insignificant, are to be regarded as im- A Norwegian Fiord Loen Lake. portant regulators of climate. Not many hundred feet added to the relief of a country would suffice to alter its physical aspects entirely, converting vineyards into pasture lands, or pasture lands into regions of perpetual snow. Reverse changes would result from a corresponding diminution in the average elevation. Again, relief is the great regulator of drainage. If the sur- face of the earth had been a dead level, without hills, plateaus, and mountains, there would have been no water courses. The whole land would have been one broad marsh incapable of drainage, and unsuited for human occupation. X. RELIEF FORMS OF NORTH AND SOUTH AMERICA General Features of Continental Relief. — There are certain features of relief that belong to all the grand divisions of the continents: i. They are bordered by mountains. 2. They are traversed in the direction of their greatest length by a great moun- tain system. 3. In each there is usually a subordinate mountain system. 4. In each there is usually a depressed central area. The line of direction taken by the principal mountain ^system is termed the superior or main axis of elevation. This line is not, however, in any case centrally placed, as the word axis might seem to imply, but far to one side of the grand division, which it thus divides into two unequal slopes. The subordinate mountain system follows the inferior axis of elevation. North America conforms closely to the general principle of continental relief. It has a superior and an inferior highland, between which there is a rather low, basin like interior. The superior highland is known as the Pacific highland, the inferior as the Atlantic highland, and the interior region as the great central plain. While these three divisions constitute the main features of relief, when considered more in detail it will be found that they include many topographic forms which give rise to surface expressions characteristic of the grand division. The Pacific Highland extends from the Isthmus of Panama to the Arctic Ocean. Its general course is northwest and south- east. Its inner border, facing the interior of the continent, con- sists of many mountain ranges with lofty peaks, which are collectively known as the Rocky Moiin^ins. Its outer border, facing the Pacific Ocean, also consists^ of mountain ranges, 95 96 RELIEF l-ORMS OF NORTH AND SOUTH AMERICA The Relief of North America The heavy black lines upon this and the following maps represent, in a general way, the extent and direction of the mountain chains. The elevations and depressions are indi- cated by the buff and green colors. The buff, according to the depth of its tint, repre- sents elevations of greater or less altitude. The green indicates lowlands. THE K(K"KV MOUNIAINS 97 chiefly the Sierra Nevada and the Cascade Mountains. Be- tween the boundaries here given, within the territory of the United States, lies an elevated plateau region, which consists SIERR4 NEVADA APRALACHIIN MTS. Profile of North America from West to East of three physiographic divisions : the Columbia plateau, or that drained by the Columbia River; the Great Basin, or that with an interior drainage represented by such streams as those flowing into the Great Salt Lake and the Sink of the Humboldt River ; and the Colorado plateau, or that drained by the upper and middle portions of the Colorado River of the West. ■■ ^^^^^^^^^^^m B^H^B A Rocky Mountain Summit— Pikes Peak The Rocky Mountains exhibit great variation in structure. Many of the ranges seem to have resulted from the upheaval of the older or crystalline rocks, shouldering off the stratified rocks which now rest upon their flanks in a highly inclined 98 RELIEF FORMS OF NORTH AND SOUTH AMERICA position. This is especially true of the ranges facing the Great Plains. Mountains have also resulted from crushing, folding, and faulting, and the evidence of igneous action is not wanting. The magnitude of the Rocky Mountains will be better under- stood when it is known that within the state of Colorado alone there are 30 or more peaks each having an altitude exceeding two and one half miles. The whole region of uplift has been cut and carved, worn, and remodeled by the action of snow and ice (glaciers), rain, Gateway, Garden of the Gods, Colorado and flowing water. Thus the present form of these mountains has been wrought — the peaks, domes, and ridges. Rising above the timber line, the higher, barren, rocky summits, ex- posed to the wasting action of the elements, are covered with a mantle of coarse fragments — they are rocky mountains in fact as well as in name. ^\\^ parks and gardens are features worthy of special mention. The former are sheltered valleys, surrounded by mountains, the best known being North, Middle, South, and San Luis parks; the latter are valleys of erosion formed by the wasting THt ROCKY MOUNTAINS 99 away of the softer portions of the upturned strata on the flanks of the mountains, the harder strata forming an inclosing wall. The Garden of the Gods, at the foot of Pikes Peak, near Colo- rado Springs, and Monument Park furnish excellent examples of the effects of erosion on strata of varying degrees of hard- ness. Within the Dominion of Canada the Rocky Mountains still rise as a lofty barrier between the great central plain and the The Bridge of Sighs — an Example of Erosion, Monument Park, Colorado Pacific Ocean. Here are found numerous living glaciers spread- ing from the snow-clad summits. Being nearer the Pacific, these mountains are more bountifully watered than the ranges within the United States, and consequently more heavily timbered. Many large rivers have their sources in the Rocky Mountains. The Missouri and Arkansas and their numerous tributaries, together with the Rio Grande, represent the Gulf drainage. The Fraser River in Canada, the Columbia, and the Colorado have their origin on the west side of the mountains. The latter rivers are remarkable for the depth to which they have excavated their chan- nels in their course to the sea. Plateaus and even mountains have been deeply trenched, forming the most wonderful canyon gorges in the world. lOO RELIEF FORMS OF NORTH AND SOUTH AMERICA The Sierra Nevada and Cascade Ranges form the western but- tress of the Pacific highland. The Sierra Nevada lies within the state of California, extending from Mount Shasta, near its northern boundary, in a southeastern direction, skirting the valleys of the Sacramento and San Joaquin rivers ; the Cascade Mountains extend northward from Mount Shasta through the states of Oregon and Washington into the Dominion of Canada, following a course parallel to the Pacific coast. The Sierra Nevada ranges have an interesting history. Originally elevated by a crumpling of the earth's crust, they were eroded until represented by mountains of very low altitude. Later they again became the scene of a great upheaval. Faulted and broken into great blocks, their crest was moved farther east- ward and the rugged mass left with a steep slope facing the east and a rather moderate declivity facing the west. This second elevation was accompanied by lava floods which, issuing from great rents and fissures, coursed down the mountain sides, filling the old river channels. As a consequence of this a readjustment of the streams followed and new valleys were excavated. Between Lake Tahoe and Owens Lake the Sierra Nevada attains its greatest altitude, culminating in Mount Whitney. To the highest portion of this region the name of HigJi Sierra has been given. Here are found numerous living glaciers filling depressions or cirques on the north side of high summits. They are all of small size and confined to altitudes exceeding 10,000 feet above the sea level. The Cascade Mountains were in the past the seat of extensive volcanic action. Of the many beautiful cones which crown their summit Mount Hood is probably the most conspicuous. The highest peaks, including Mount Shasta, Mount Hood, Mount Rainier, Mount Baker, and the Three Sisters, are snow- capped and support living glaciers. Here as in other regions of high altitude the upraised mass has been deeply dissected. The Columbia Plateau is a region of lava floods. The entire area between the Rocky and the Cascade Mountains has been THK (OI.IMISIA I'l.AIKAU lOI literally buried beneath a vast outpouring of igneous matter, forming, when cooled, a great lava plain from which, in places, old mountain summits rise in islandlike masses. The flowing lava by obstructing the stream ways caused the formation of many lakes. Later these were drahied and their deposits now form rich agricultural lands. In its course through the lava beds, the Snake River, for several hundred miles, has excavated a deep canyon, forming a Mt. Hood from Lost Lake. Height 11,22^ Feet barrier of considerable magnitude. In this gorge there are points where the irregularities of the older land surface are en- countered ; these have also been deeply eroded by stream wear. Near the head of the canyon the river flows over a lava preci- pice, forming a magnificent cataract known as Shoshone Falls. That this region has not been entirely free from diastrophic movements is shown by the Blue Mountains, which have been formed by the breaking and upheaval of a portion of the lava plain. M.-S. PHYS. GEOG. — 7 I02 RELIEF FORMS OF NORTH AND SOUTH AMERICA The lava floods of the Columbia plateau are among the greatest known in the history of the earth. They are exceeded only by those of the peninsula of India. The Great Basin includes a large area lying between the Wasatch Mountains and the Sierra Nevada, characterized by its interior drainage and wide-spread aridity. Its width, in an east-and-west direction, is fully 500 miles and its length 800 miles. In its northern portion it attains a general altitude of 4000 to 5000 feet, with mountains rising still higher. In its southern portions its altitude is greatly reduced, and in Death's Valley, in southern California, it is several hundred feet below the sea level. Its surface is diversified. There are large, level desert plains as well as mountains and valleys. As has been already stated, the crust of the earth has here been profoundly fractured and faulted, and the Basin ranges, trending north and Section illustrating the Structure of the Basin Ranges. After Russell. south, have resulted from the upheaval and tilting of the long, narrow blocks. As they now rest they present a precipitous front in one direction and slope off gradually in the other. The valleys between the mountains have been deeply filled with rock waste, which, issuing from the gorges, has spread out in the form of wide fans. The streams of the Great Basin either end in salt or alkaline lakes or are evaporated or absorbed before reaching them. During times of storm mountain torrents, upon reaching the valleys, owing to their increased volume, spread out, forming temporary lakes. These soon evaporate, and there are left mud plains, or playas. Such mud deposits are common in many parts of Nevada. Formerly the amount of precipitation in this region was much greater than at present and there existed large lakes now THE GREAT BASIN 103 extinct. Their old shore lines have been traced for many miles and their old terraces and delta deposits have been care- fully studied. One of these lakes, of which Great Salt Lake is a remnant, spread out over a large part of the western half of Utah. It has been named Lake Bonneville. Another exten- sive lake existed in the northwestern part of Nevada, of which Map of Portions of Utah and Nevada showing the Areas formerly OCCUPIED BY the EXTINCT LAKES BONNEVILLE AND LaHONTAN Pyramid, Winnemucca, Humboldt, North and South Carson, and Walker lakes are remnants. To this inland sea the name of Lake Lahontan has been given, " The bare mountains reveal their structure almost at a glance, and show dis- tinctly the many varying tints of tlieir naked rocks. Their richness of color is sometimes marvelous, especially when they are composed of the purple trachytes, the deep-colored rhyolites, or the many-hued volcanic tufa so common in western Nevada. Not un frequently a range of volcanic mountains will exhibit as many brilliant dyes as are assumed by the New England hills in autumn. On the desert valleys the scenery is monotonous in the extreme, yet has a desolate grandeur of its own. and at times, especially at sunrise and sunset, great richness of color. ... As the sun sinks behind the western peaks and the shades of evening grow deeper and deeper on the mountains, every I04 RELIEF FORMS OF NORTH AND SOUTH AMERICA ravine and canyon becomes a fathomless abyss of purple haze, shrouding the bases of gorgeous towers and battlements that seem encrusted with a mosaic more brilliant and intricate than the work of the Venetian artists." — I.e. RUSSKLL. The Colorado Plateau occupies the region between the Wa- satch and the Park Mountains. On the north it is bounded by the Uinta range and on the south it extends into Arizona and New Mexico. Through it the Colorado River has cut its canyon. Here the earth's crust has been extensively faulted, and by the upheaval of great blocks, embracing many square miles of area, minor plateaus have been formed. As these blocks have been slightly tilted, their upturned edges form scarps or cliffs, which, by the erosion of their softer layers or strata, have retreated until the plateaus in places resemble a series of steps or ter- races. The higher scarps rise a thousand feet or more, and some of them follow quite closely the fault lines. That vulcan- ism has not been absent is shown by the occurrence of cinder cones, laccolitic mountains, and table mountains capped with igneous rock. The Atlantic Highland comprises the Appalachian mountain system and the plateau of Labrador. It extends from Labrador nearly to the Gulf of Mexico. The Appalachian Mountains in their northern course consist of a number of disconnected groups such as the White Moun- tains of New Hampshire, the Green Mountains of Vermont, and the Adirondack and Catskill Mountains of New York. To the southward they are composed of several well-marked and nearly parallel ranges, separated into two belts by the Great Appa- lachian Valley, a pronounced depression extending from Pennsyl- vania to Alabama. The belt lying nearer the coast is composed largely of older rocks in the form of gneisses, schists, and granites, collectively known as crystalline rocks, while the inner belt is made up of stratified rocks, much folded, compressed, and overthrust. To hav-e produced such results it is reason- able to suppose that the force exerted must have been very great. iHE ailantk: highland 105 The Appalachian Mountains also have an interesting history. Originally elevated at the close of the Carboniferous or Great Coal-making period, they were subsequently much worn and eroded until a lowland was formed. Then, at a later period, came reelevation with so slight disturbance that many of the old streams were able with slight modifications to retain their former courses, which now, much deepened, cross many mountain ranges. View in thk Southern Appalachians Richland Valley from Junaluska Mountain, North Carolina. From United States Geo- logical Survey. Such is notably the case with the Susquehalina, Potomac, James, and New rivers. In the meantime the tributaries of these streams have been very active removing the softer and more soluble rocks, thus leaving the harder rocks in relief. In this manner, rather than by folding, the existing ridges have been produced. The general elevation of the Appalachians is about 3000 feet above the sea, but the culminating points. Mount Mitchell, in North CaroHna, and Mount Washington, in New Hampshire, are over 6000 feet high.^ 1 Mount Mitchell, 671 1 feet; Mount Washington, 6279 feet. I06 RELIEF FORMS OF NORTH AND SOUTH AMERICA The Relief of South America riii: iKMKAi. ri.Aix 107 Toward the interior the Apijalachiaiis are bordered by more or less dissected uplands known as the Allegheny plateau; on the seaward side they descend to the gentle undulating Piedmont belt, which, si)uth of New England, is followed bv a rather broad coastal plain. The Central Plain extends from the Gulf of Mexico to the Arc- tic Ocean. The Height of Land, a low east-and-west ridge near the northern boundary of the United States, divides it into two parts. The drainage of the northern portion is to the Arctic Ocean and Hudson Bay ; that of the southern portion is to the Gulf of Mexico. As the streams of the latter part are mainly tributary to the Mississippi River, it is usually known as the Mississippi basin. Tlie .Mississippi basin bears a strikinij resemblance to a coastal plain. It occupies the site of an ancient interior sea. As the crust here has never suffered .serious disturbance, there is a complete absence of the more striking features of relief. As far south as the mouth of the Ohio River this region has been subiected to glacial action (see page 269). The soils are deep and very fertile. They have originated in part from materials transported by glaciers, in part from stream and lake deposits, and in part from the wasting of rocks due to weathering. In the middle West there are large areas of prairie land, some e.xceedingly level, others rolling. On the east the prairies merge with the wooded region as they approacli tlie Allegheny plateau, and on the west they pass imperceptibly into the higher or Great Plains region. Along prairie streams there is usually a rather luxuriant growth of trees and vines. South America. — The general features of relief as exhibited by South America are similar to those of North America. There is a superior or Pacific highland and an inferior or At- lantic highland, with low central plains between them. The Pacific highland includes the Andes Mountains, with their long, high valleys, and the lofty BoHvian plateau. The Atlan- tic highland, severed by the valley of the Amazon, includes the Guiana and Brazilian highlands. By many the Andes are regarded as the direct continuation of the Pacific highland of North .America, which, in crossing the Isthmus of Panama, is reduced to a series of rather low hills. ■%i*. I08 RELIEF FORMS OF NORTH AND SOUTH AMERICA While such close relationship cannot be established between the Atlantic highlands of the two grand divisions, each includes in its make-up crystalline and the older stratified rocks. The Andes are remarkable for their great length, equal to one sixth of the earth's circumference, for their height, and for their regularity of form. South of Aconcagua these mountains con- sist of a single chain, the highlands of the coast being separated from them by a broad valley. Farther south, owing to subsi- dence, the higher parts of the western ridges appear as islands and peninsulas. Between 27° south latitude and the equator parallel eastern and western ranges inclose valleys and plateaus, ,0 ftlllimani BRAZILIAN HIGHLAND Profile ok South America from West to East wonderful in height and extent, separated by transverse ranges or mountain knots. Of the table-lands, the Bolivian plateau is broadest and highest, and, like the Great Basin of North Amer- ica, has an interior drainage. Upon it is situated Titicaca, the largest lake in South America and the highest in the western hemisphere. North of the Desert of Atacama to the center of Colombia this great mountain system is crowned with hundreds of snow- capped peaks and studded with smoking volcanoes. For the entire distance there is not a mountain pass or gap below 12,000 feet in altitude, while the loftiest peaks exceed 19,000 feet, — Chimborazo, 20,498; Cotopaxi, 19,613; Antisana, 19,335; and Cayambe, 19,186 feet. The northern portion of the Andes consists of three or four ranges separated by deep valleys occupied by the Magdalena River and its tributaries, which drain into the Caribbean Sea. The westernmost range, decreasing in height, blends with the Panama hills. THE ATLANTIC HIGHLANDS • IO9 Very important in its bearing upon the physical geography of the continent is the singular proximity of the Andes to the west- ern coast. Their greatest distance from it scarcely exceeds 100 miles. Chimbokazo This magnificent Andean peak rising above the valley of Quito attains the height of 20,498 feet above the sea. The Atlantic Highlands of South America are those of Brazil and Guiana. Th)e Brazilian Highland is a broad plateau region traversed by nearly parallel ranges of moderate elevation. Their loftiest peaks are from 5000 to 10,000 feet high. Rising above the sea on one side and above the plains on the other sides, this great triangular area, embracing 700,000 square miles, has been termed the " Brazilian Island." Its drainage is mainly inland, to the Amazon and Plata no RELIEF FORMS OF NORTH AND SOUTH AMERICA systems. Only one important river, the Sao Francisco, flows directly into the Atlantic, and then only after a course of a thou- sand miles behind mountain barriers. The Highland of Gniajia is a plateau supporting several closely set ridges, the most important of which are the Parime Mountains. Maravaca, the culminating peak, is nearly 10,000 feet high. The Central Region of South America, like that of North America, is a well-marked depression lying between the superior and inferior highlands. It is called the Great Central Plain. It consists of the river basins of the Orinoco, the Amazon, and the Plata. These are divided by ridges so low and so narrow that the three together may not unfairly be considered as formi ig one great basin. The following curious facts will show.how nearly alike tlieir level actually is. The Cassiquiare. which rises between the Amazon and the Orinoco, forks, after running some distance, and sends otf one l:)ranch to the south to unite with tiie waters of the Amazon, the other to unite with those of the Orinoco on the north : it thus connects these two river basins by a water way that permits the Indians to pass in their canoes from either of the two great rivers i.ito the other. P'urthermore. in the Brazilian province of Matto (irosso there are two springs side by side, and within a few feet of each other. From one the water flows into the Amazon, from the other into the Plata; and so close are the navigable waters of these rivers to each other, that, with a single portage of a few miles, the voyager, ascending the Plata from the sea, may return to ^•■'e ocean again, either through the Amazon or the -Orinoco. Silvas of the Amazon. — The valley of the Amazon is not only of great e.xtcnt, but it is very level. Lying within the tropical rain belt, it is one of the best watered regions of the world. This, together with the warm climate and rich alluvial soil, has been productive of remarkably dense forest growths known as silvas. So close together are the trunks of the trees and so great the tangle of vines that were it not for the water ways this region would be quite impenetrable, as paths are cut with difficulty. During the rainy seasons the lower portions of the valley are flooded far and wide and the waters even flow through the tree tops. On the other hand, during the dry seasons the waters so LLANOS I 1 1 far recede as to leave strips of meadow land exposed, their long submergence having effectually checked the forest growth. Llanos. — West of the Guiana highland the low valley of the Amazon passes imperceptibly into that of the Orinoco, and the forest growth, so characteristic of the former, soon gives way to a treeless or prairie region. During the wet or rainy season these plains are more or less flooded, but later, when the water recedes, they are covered with a luxuriant growth of coarse grass resembling great meadows, hence the name llanos which has been applied to them. During the dry season, how- ever, they present a very different aspect : The Orinoco no longer fi\\s its banks, but, much shrunken, courses its way seaward; the grasses and other vegetation have withered away ; the once green plains have taken on a parched and desertlike appear- ance ; and the smaller streams have ceased to flow. The Chaco and Pampas. — The third of the great South American basins is that of the Plata. Lying south of the Amazonian basin, it is separated from it by a low and almost imperceptible divide. Its northern portion is wooded and in its forests and swamps are found both wild animals and In- dians. Famous as a hunting ground, this region is known as The Chaco. Roughly located, it lies west of the Paraguay River and north of the Pilcomayo. The larger part of the basin, however, is in the form of almost level plains, although occasionally relieved by hills and low mountains. They are the pampas. The higher plains vary in altitude from 3000 to 600 or 700 feet. They are bordered along the Plata and the Parana by low alluvial plains. The pampas vary somewhat in their surface features. In the south they are barren and sandy ; north and west of the Cordoba Hills there are numerous saline basins, and in the region of Buenos Aires there are rich farming lands. Not- withstanding the widespread barrenness, much of the country is covered with nutritious grasses, so that the pampas of Argen- tina rank among the greatest a:razing: lands of the world. liM»^ ^^ ^ ^ iJ C . ,:m^^s (112) V I A Jf The Red .«i Eurasia ("3) XL RELIEF FORMS OF EUROPE, ASIA, AFRICA, AND AUSTRALIA Europe, like North and South America, has its superior and inferior highlands and its low plain, but the arrangement of these features differs from that prevailing in the New World in two well-marked particulars : ( i ) the main axis of elevation extends east and west, not north and south, as in the case of the Rocky Mountains and the Andes; (2) the mountain chains do not exhibit the characteristic parallelism shown by those of the New World. The Superior Highland of Europe stretches across the south- ern portion of the grand division, from the Atlantic to the Black Alps Profile of Europe from South to North Sea, and, if we regard the Caucasus as its eastern prolonga- tion, it reaches the shores of the Caspian. Beginning with the Pyrenees, its western termination, it culminates in the Alps. Eastward of the Alps it divides into two important branches, a northern, consisting of the Car- pathian Mountains, and a southern, consisting of the Dinaric Alps and the Balkans. These ranges inclose the Danube basin. In addition, the Apennines of Italy and the moun- tains of Greece are included in this system. The Alps, which cover an area of about 90,000 square miles, are the most celebrated of all the mountain systems in the world. Their historic and poetical associations, the grandeur and beauty 114 THE ALPS 115 of their varied scenery, the number and extent of their <;laciers, and their accessibility to travelers invest them with an interest unrivaled by the loftiest summits of other lands. Occupying a central position between France and Germany on the north, and Italy on the south, they can be reached in a few hours from any of the great cities of Europe. Owing to The Jungfrau from Wengernali' This snow-clad Swiss summit is a most imposing sight. Its altitude is 13,760 feet. Dur- ing the summer months avalanches of ice are of common occurrence, falling from the heights into the deep valley beyond the line of trees in the foreground. their varied attractions they are visited by so many thousands annually, that they have been called, not inappropriately, " the playground of Europe." " As we climb the Alps." .says a distinguished scientific writer, '" peak rises behind peak, crest above crest, with infinite variety of outline, and with a wild grandeur which often suggests the tossing and foaming breakers of a stormy ocean. Over all the scene, if the air be calm, there broods a stillness which makes the majesty of the mountains yet more impressive. No hum of bee or Il6 RELIEF FORMS OF EUROPE twitter of bird is heard so high. No brook or waterfall exists amid those snowy heights. The usual sounds of the lower ground have ceased. Now and then a muttering like distant thunder may be caught, as some loosened mass of snow or ice falls with a crash into the valleys ; or the wind brings up from below in fitful gusts the murmur of the streams which wander down the distant valleys." The highest peaks of the Alpine system are Mont Blanc, 15,730 feet; Monte Rosa, 15,217 feet; and the Matterhorn, 14,705 feet. The Pyrenees, which extend for a distance of about 250 miles from the Mediterranean to the Bay of Biscay, present a much greater uniformity of arrangement than the Alps. Their average height (8000 feet) is not greatly inferior to that of the Alps (8000 to 9000 feet); but their highest peak. Mount Maladetta, 1 1,168 feet, is far below the towering masses of Mont Blanc and Monte Rosa. The passes of the Pyrenees, however, are higher and less practicable than those of the Alps. The Carpathian and Balkan Mountains. — The Carpathians separate the plains of Hungary from the great low plain of Northern Europe. Their greatest elevation is about 9000 feet. Through the southwestern extension of these mountains, known as the Transylvanian Alps, the Danube River has cut a long and picturesque passage obstructed by numerous rocky ledges, the chief of which, the Iron Gate, is nearly a mile in width. The former dangers to navigation at this point have been removed by the construction of a canal. South of the Iron Gate the mountain barrier merges with the Balkans, which, becoming an east-and-west range, is terminated by the Black Sea. The highest summits of these mountains do not exceed 7000 feet. The Dinaric Alps connect the Balkans with the Alps proper. The Caucasus range resembles the Pyrenees in that it lies be- tween two large bodies of water, the Caspian and the Black seas, and in the further fact that it is well defined. On the north are the great Russian plains and on the south the river Kur. The length of these mountains is about 700 miles and their width PENINSULAS 1 1 7 varies between 70 and 120 miles. Mount Elburz(i8,526 feet), the most conspicuous peak, exceeds Mont Blanc in height, and the entire range is high, with a snow-clad crest and glaciers. This great mountain barrier forms a part of the boundary between Europe and Asia. Peninsulas. — High Europe throws out three mountainous projections toward the south : the Iberian or Spanish Peninsula on the west, the Italian in the center, and the Grecian on the east. The Iberian or Spanish Peninsula is a great plateau surmounted by several parallel ranges. The Pyrenees, which are the principal of these, form the dividing line between France and Spain. In the Italian Peninsula we find the Apennines, an important prolongation of the Alpine system. These are more famed for their beauty than for their altitude. The volcanoes of Vesuvius, Etna, and the Lipari Islands are consid- ered as belonging to this chain. The Grecian Peninsula, like the Italian, boasts of no very elevated ranges. Its mountains are famed less for their height than for their historic and poetic associations. They were the mythic homes of the gods of ancient Greece. The throne of Jupiter rested on Mount Olympus. The Inferior Highlands comprise the ranges of Scandinavia and the Ural Mountains. The Scandinavian mountains consist, for the most part, of a broadly elevated region along the western coast of the penin- sula. Formerly these mountains were much higher than now and indented by many deep valleys. By subsidence these val- leys have in their lower portions become arms of the sea known as fiords. As they afford safe anchorage and often extend far inland, sometimes even a hundred miles, they are commercially of great value. On such bodies of water many seaports have been established. The Scandinavian highlands terminate in North Cape, a great bluff, nearly a thousand feet in height, facing the Arctic Ocean. This point is visited annually by many tourists for the purpose of beholding the "midnight sun." The Ural Mountains form a natural boundary between Eu- rope and Asia. They extend southward, along the meridian ii8 KEl.lKF FORMS OF KUROPE of 60° east 1500 miles, from the Arctic Ocean nearly to the Caspian Sea. Low Europe consists of a vast plain lying northeast of the superior highland. It is bordered on the northwest by the mountains of Scandinavia, and on the northeast by the Ural North Cape from the West The nortliern end of tlie Scandinavian highlands. range. It extends from the Arctic Ocean to the Black Sea, and westward as far as the Bay of Biscay. The Valdai Hills, having an altitude of about a thousand feet, mark the highest point of a swell which separates the rivers flowing into the Baltic and White seas from those which enter the Black and Caspian. THK SUPEKIUK HKiHLAND OK ASIA 1 19 The range of this plain in latitude is so great and, as a direct consequence, its climate so varied, that it presents several well-marked aspects. The northern portion is treeless and of tlie general character of the lands border- ing the Arctic coasts in both hemispheres. Farther south forest lands appear, which still farther south give way to rich prairie lands excepting in regions bordering the Caspian, where saline conditions prevail. The Superior Highland of Asia consists of two portions : ( I ) the various mountain chains which radiate from the central elevated region known as the plateau of Pamir; and (2) the plateau of Tibet. The Pamir is called by the Asiatics the "roof of the world." In shape it may be regarded as an irregular square. From three of its corners great chains project. The southeast corner is the starting point of the great ridges of the Himalaya, the Karakoram, and Kuen-Lun. From the northeastern corner the Thian Shan range takes its origin. From the southwestern starts the line of the Hindu Kush. The plateau of Tibet lies between the Himalayas on the south and the Kuen-Lun Mountains on the north. It is the loftiest table-land in the ivorld, having an extreme elevation of about 15,000 feet. 30000 HIMALAYA MTS. .i* 25000 20000 15000 10000 i^ J~ THIAN SMAN ^ /I MTS. 5000 .jJiJ^mW ua^ ^^ SIBERIAN PLAIN Fkomi.e ()!• .Asia ikdm .soi i a 10 NOriu The Himalayan Range stretches eastward from the Pamir in an unbroken course for a distance of 1500 miles. Its breadth varies from 150 to 350 miles, and its mean height has been esti- mated at 6000 feet higher than that of the Andes. Over 40 of its peaks rise to an altitude of 23,000 feet, and more than 70 reach 20,000 feet. Mount Everest, with an elevation of 29,000 feet, is, so far as known, the highest mountain on the globe. I20 RELIEF FORMS OF ASIA The Himalayas present the grandest possible mountain scenery ; deep gorges wrapt in perpetual twilight gloom ; frightful precipices ; somber for- ests of rhododendrons and pine trees ; higher up, vast glaciers filling the ravines, and ice and snow covering the ridges which rise one above another to such sublime heights as must ever secure their summits immaculate from the footsteps of man. Everything is colossal ; but the Himalayas lack the smiling valleys and sheltered lakes which impart such picturesque charm to the Alps. They possess the grandeur without the amenity, the magnificence without the variety, which mark the less elevated European system. The passes of the Himalayas, instead of leading through low gaps and over gentle declivities, rise up into the regions of perpetual snow and ice, and are so difficult as to be of little avail for the purposes of commerce be- tween the people on the opposite sides. They are on an average 10,000 feet higher than those of the Alps, and nearly 4000 feet higher than those of the Andes. We cannot be surprised that India and Siberia are practically farther removed from each other than if they were separated by an ocean, nor even that the opposite slopes of the Himalayas are occupied by men of different races. The Karakoram, Kuen-Lun, and Thian Shan Mountains. — The Karakoram range traverses the plateau of Tibet, and is supposed to have a greater average height than even the Himalayas. It contains Mount God win- Austen (height, 28,278 feet), believed to be the highest summit next to Mount Everest in the v^^orld. The Kuen-Lun range separates Tibet and eastern Turkestan, and is prolonged by the Chinese range of the Pe-Ling. The Thian Shan range forms the northern boundary of the plateau of eastern Turkestan. Some of its peaks attain the height of 20,000 feet. The Hindu Kush extends in broad, massive ranges westward for 400 or 500 miles. A depression then occurs. The range, however, is really continued in the Elburz Mountains, which form the northern boundary of Persia. The general direction of the great mountain chains of the superior highland region is east and west. The Inferior Highlands comprise the Altai Mountains and their northeastern continuations, together with the Great Khin- Gan range, and the ranges of southeastern Asia, and, finally, the subordinate plateaus of the grand division. THE ALTAI AND THE KHIN-GAN MOUNTAINS 121 The Altai and the Khin-Gan Mountains. — The Altai Moun- tains, extending in a northeasterly direction, are continued in the Yablonoi and Stanovoi ranges. They separate the desert wastes of Mongolia from the plains of Siberia. Some of their peaks are 12,000 feet high. "Although far less extensive and elevated than the Thian Shan, the Altai still bears comparison with the European Alps, if not in the height of its peaks, diversity of its forms, abundance of its snow or rich vegetation, at least in the development of its ranges and the length of its valleys." — Reclus. The Khin-Gan Mountains, with their southern offshoots, form the eastern barrier of the great Desert of Gobi. The Plateaus of Asia are a prominent feature of the grand divi- sion. They extend in a series from the shores of the Red Sea nearly to the Pacific Ocean. In general they are arid and rainless, sandy, stony, and barren. In the spring their surface is thinly sprinkled here and there with grass and herbs, but in the sum- mer and autumn it is, for the most part, dry and sterile. The sheltered valleys are, however, in many cases exceed- ingly fertile. In such valleys there is a settled population, but outside of them the plateau region may be described as the home of roving herdsmen and marauding Bedouin. North of the Kuen-Lun Mountains are two plateaus, eastern Turkestan and the Desert of Gobi. These are shut in on the north by the Thian Shan and Altai Mountains. The average elevation of eastern Turkestan is about 2000 feet above the sea level ; that of Gobi, about 4000 feet. Entering Gobi from Tibet, we should descend fully 9000 feet. The triangular plateau of the Dekkan in India rises to the average height of about 3000 feet. The sides of the triangle are the eastern Ghats, the western Ghats, and on the north the Vindhya Mountains. The plateau of Iran or Persia, including large portions of Afghanistan and Baluchistan, is shut in by the Elburz and Hindu Kush Mountains on the north, by the Zagros chain on the south, and the Sulaiman on the east. It rises from 3000 to 4000 feet above the sea level. The plateau of Armenia, with Ararat (about 17,160 feet high) for its culmin- ating point, rises to the westward of Persia. The plateau of Asia Minor lies westward of that of Armenia. It has an average elevation of 2500 feet. The Taurus ranges bound it on the south. The plateau of Arabia forms the southwestern projection of Asia. 122 RELIEF FORMS OF ASIA The Great Lowland of Asia lies to the north. It extends from the shores of the Arctic Ocean southward to the base of the Altai Mountains and the adjacent ranges, and comprises the Kirghiz Steppes and the Siberian Plain. It is a part of the almost continuous depression which extends through I-'urope and Asia, from the North Sea to Bering Strait, a distance of more than 5000 miles. The Kirghiz Steppes are wide and monotonous tracts, covered in spring with rough grass, parched with drought in summer, and bleak and desolate in winter. The Dead Sea, Paeestink This remarkable salt-water lake occupies the deepest known depression of the land below sea level. Its length is 47 miles; its greatest width does not exceed 10 miles; its sur- face is 1292 feet below that of the Mediterranean Sea ; and its greatest depth is 1310 feet. From the eastern and western margins of the sea the land rises precipitously in the form of great limestone cliffs. The Siberian Plain consists of prairies and piny forests in its southern portions; of swanipy tundras on its northern edges. m\ the: grand division of africa 123 Inferior in size to the Siberian Plain, but vastly more impor- tant for their influence upon the history of the human race, are the plains of China and India. They support nearly one half the population of the globe. Two remarkable depressions are found on this grand division. One is occupied by the Dead Sea, the surface of which is 1292 feet below the level of the ocean ; the other by the Caspian, the surface of which is 84 feet below. The Grand Division of Africa obeys less closely the general law of continental relief. It has, however, mountain ranges along the coast, while a plateau region of less elevation occupies the interior. Its superior highland, lying on the east, is broken by rivers into pronounced segments. Notwithstanding that its mean elevation is said to exceed that of Europe and even Asia, its mountains can scarcely be compared with the Alps in magni- tude, much less with the Himalayas. The Superior Highland consists of an elevated region which extends from the Isthmus of Suez to the Cape of Good Hope. One important portion of it, the plateau of Abyssinia, attains an elevation of 7000 to 8000 feet. The culminating points, however, are the snowy heights of Kenia, Kilimanjaro, and the Ruwenzori Mountains (about 19,000 feet), near the equator. South of these elevations occur the Livingstone Mountains (5000 to 10,000 feet), walling in Lake Nyassa; and nearly at the southern extremity of the continent lie the Snow Mountains, which may be considered as vast terraces ascending from the sea toward the interior. The plateau of Abyssinia has been described as a '• block " of the older crystalline rocks, gneisses, and scliists. capped with lava sheets. Its surface has been profoundly eroded, and in places the accumulation of volcanic matter is said to form high mountains. Lake Deml^ea occupies a depre.ssion 3000 feet below the general level and is regarded as the chief source of the Blue Nile. The Inferior Highlands include the ranges which border the northern and western coasts. The Atlas Mountains on the north consist of three or four parallel ranges which ascend from 124 RELIEF FORMS OF AFRICA The Relief of Africa the Mediterranean stage by stage, and increase in height to the westward. The Kameruns and the mountains near the headwaters of the Niger are the principal elevations on the west. The Kameruns are volcanic. They attain at some points the height of nearly 13,000 feet. THE IMKKIOR 125 The Interior of the i;rancl division may be regarded as a vast plateau bordered by the various coast ranges. Low plains are to be found onh' along the coast. I^f% /[ \ ^ In -^ 1 9 1 -■mtf^^^^^^j -A-"^-^^^ M ^ A CAKAVAiN UN IHE DESKRT OF SAHAK.\ The plateau region may be divided into two sections: (i) that portion which consists of prairies and fertile river basins ; and (2) the arid Sahara. The Sahara stretches east and west 3000 miles, north and south ijCENE UN THE DtaKRl OF SaUAKA 1000, covering an area of 2^ millions of square miles. It is not an absolute level. Its average elevation is about 1200 feet, but it contains areas which are 4000 or 5000 feet in height, and has a mountain range one of whose peaks is nearly 8000 feet 126 RELIEF FORMS OF AUSTRALIA The Relief of Australia high. Southward of Tunis are found depressions, some of which are lOO feet below sea level. They are marshy regions for most of the year, but when the winter rains fall they receive the drainage from the mountains, and thus become broad, open lakes known as chottes {shots). The surface of the desert con- sists, in some places, of sharp stones, in others of gravel, in others again of shifting sand. »The latter when driven before the wind is arranged in long, huge billows called dimes. Here and there over the desert are found fertile spots or oases where water may be obtained either from springs or wells. Australia somewhat resembles Africa in its relief. It has an elevated border and a depressed interior. The superior highland lies along the eastern and southeastern shores. It includes the Blue Mountains and the Australian AUSTRALIA 127 Alps, culminating in the latter, the loftiest peaks of which are about 7000 feet high. Inspiration I'oim, Bi.i k Moumain.s, New Soiin Wales, Aisikaeia Photographed by Sterling R. Fulmore. The inferior highland borders the western and northwestern portions of the continent. Of the central lowland the basins of the Darling and Murray rivers are best known. Of the remainder much is desertlike. A characteristic feature of the lowland is its inland salt lakes, which cover large areas during the rainy season, but shrink to saline marshes or completely disappear during the dry season. SIAI£ RORMAL SCMOOi, UOS AKGEUES, CRlt. M.-S. I'HYS. GEOG. ■ XII. ISLANDS Classification. — As distinguished from continents the smaller land masses rising above the" sea are termed islands. They vary greatly in size, from the mere protrusion of a rocky or low-lying mud or sand bank, a few square feet in area, to land masses hundreds of square miles in ex- tent, which, in their general character- istics, are not unlike the continents them- selves. According to their origin and structure islands may be classi- fied into two groups : ( 1 ) continental; (2) oceanic. Continental Islands, as their name im- plies, rise from the submerged continen- tal borders and not from the deeper parts of the ocean's floor. At earlier periods in the earth's history many of them were actually parts of the continents from which they have been separated by setthng (subsidence), wave wear (erosion), or a combination of both. 128 The British Islands and the Submarine Plat- form ON WHICH THEY REST. After Geikie. The tinted area is less than 100 fathoms in depth. OCEANIC ISLANDS 129 Sea exploration and soundings show that the British Islands rest upon a submarine platform which cannot be regardeid as other than an extension of the mainland of Europe. This, together with their geologic structure, goes to show their intimate re- lation to the existing con- tinent, of which, in fact, they form a part. Other coastal islands have resulted from the cotistriictive action of the waves by which mud banks, sand spits, and reefs have been thrown up. Once above the water, their growth is aided by the springing up of coarse grasses and other forms of vege- tation which gradually collect and hold in place additional matter. Along the Gulf coast of Texas long barrier is- lands, broken by occa- sional inlets, have been built up by the waves driven shoreward by the prevailing winds. The filling up of shallow sounds and the present growth of islands is also well illustrated along the coast of North Carolina. Map OP' THE Coastal Portion of North Carolina In this partially drowned region the outer sand reefs, in the form of long, narrow islands, almost completely close the entrances to Albemarle and Pamlico sounds. The inclosed bodies of water are being gradually filled by the silt and sand brought from the land by river action. Oceanic Islands are situated far from the continents. They rise from the deeper portions of the ocean's floor. In structure they are strikingly unlike most continental islands, being either volcanic or coralline. The former often rise thousands of feet 130 ISLANDS above the sea level, while the latter are low-lying and devoid of surface relief. Oceanic islands of the first group are the tops of volcanic peaks which rise above the sea through their own upbuilding ; the islands of the second group are brought to the surface by the upbuilding of coral reefs from high submarine volcanic or other platforms. Volcanic Islands are arranged, as a rule, along the great bands or belts of volcanic activity which trav- erse the globe. Most of them are found within the vol- canic belts of the Pacific and the Atlantic. There are, however, exceptions to this general rule, many volcanic islands being situated quite irregularly. The volcanoes upon islands in the Pacific belt are among the most active in the world ; those in the Atlantic belt are far less active, and many are either extinct or bordering on extinction. Volcanic islands are formed by the accumulation of materials thrown out by submarine volcanoes. Sometimes such islands are formed very suddenly, as in the case of Graham Island, in 1831, and that off the island of Santorini, in the Mediterranean, in 1866. Coral Islands are found especially in the southern Pacific and Indian oceans. They are a result of coral growth and wave action. The coral animal is -a. polyp — not an in.scct, but an Brain Coral In this figure there is shown a coral skeleton, that is, "dead coral," which is composed of carbonate of lime, the substance of limestone. The living portions of coral, the polyps, are soft and fragile, and when removed from the sea water soon dry up and disappear. (t>KAl, ISLANDS 131 animal imich lower in the scale oi lile — which secretes from sea water a skeleton composed of carbonate of lime, the sub- stance of limestone. Many polyps are usually supported in common by a single skeleton, which may be of a delicate branching' form or a great rounded mass or head. Begin- ning" in water not exceeding 20 fathoms, more often 6 or 7 fathoms, the reef-building coral by the growth and accumu- lation oi its hard parts lays the foundation of what may be- come a reef or a coral island. In all cases this coral growth rises from a submarine platform which not infrequently is the submerged summit of a volcanic peak. Polyps thrive best when immersed in pure sea water; accordingly they exhibit the greatest profusion on the exterior or seaward side of a reef. As they approach the surface, the finer and more delicate skeletons are broken by the dashing of the waves, and their fragments, settling down among larger coral heads, fill the interstices and serve eventually to cement and solidify the reef. Finallv the level of low tide is reached and the upward growth of the polyps is checked. The further upbuilding of the reef now becomes the work of the waves — a v^^ork of destruction and of construction. Portions of coral growth are torn from their beds, broken up, ground as sand on a beach, and swept into a long ridge. The ridge, heaped up by successive additions of broken coral, finally becomes so high that it overtops the waves, and an island is formed. The next stage is the appearance of vegetable life. Floating wood lodges among the coral fragments. It decays and forms mold. Seeds, such as cocoanuts, not injured by salt water, are wafted to the newly formed islet ; others may be carried thither by birds. Under the stimulus of a tropical sun they grow, and in time cover the dead coral mass with living green. The breadfruit and cocoa palm are the most important of the forms of plant life that flourish upon such islands. No large animals live upon them, and, on account of their small areas, they can sustain only a limited population. 132 ISLANDS Coral Reefs may be classed as (i) fringing reefs; (2) barrier reefs; (3) atolls. Fringing reefs occur near the shore line surrounding islands or skirting the coasts of continents. Many Pacific islands furnish examples of such reefs, as well as the eastern coasts of Africa and South America within the equatorial belt. Barrier reefs are quite like fringing reefs, but farther removed from the land. They represent a later stage of reef develop- Atoll ment when, by the action of the waves and the growth of coral, the reef formation has advanced seaward. In the meantime the inner side of the reef has been slowly dissolving away, leaving an ever-increasing interval of shallow water between it and the land. In some instances it is possible that fringing reefs may have been transformed into barrier reefs by the gradual subsid- ence of the sea bottom, whereby the reef, growing upward to the surface, appears at a considerable distance from the shore. This is illustrated by the diagrams on page 133. The great barrier reef off the northeast coast of Australia is 1250 miles long and from 10 to 90 miles wide. The island of New Caledonia and many others are protected from the sea by similar reefs. An atoll vs, a belt or strip of coral reef inclosing an expanse of water called a lagoon. ORIGIN OF ATOLLS 133 Diagrammatic Formation Atoll Illustrations of OF Barrier Reek THE AND Atolls are usually nearly ov'al or circular, but in many cases they are quite irregular in shape. Sometimes, as in the case of Whitsunday Island, they are complete rings; but most frequently on the side not exposed to the prevailing winds there are one or more breaks, form- ing inlets. The atolls are almost innumer- able. There are nearly a hundred of them in the Dangerous Archi- pelago, which lies to the westward of Tahiti. Thev are not more than half a mile across, from the sea to the lagoon. In their highest parts they are only a few feet above the water; still, they resist the utmost fury of the waves. They are thickly covered with vegetation. Section of mountain rising above water, forming an island ; RR, section of fringing reef resting on slopes ; A, height of sea level as shown in II below ; B, height of sea level as shown in III below. II Origin of Atolls. — Many of the reefs and atolls rise from very great depths ; but the polyps are most vigorous in water not deeper than 60 feet ; and in water that is more than 150 feet deep they cease to live. The ques- tion, therefore, arises, how can the foundations have been laid for certain reefs and atolls, which stand in water not less than a mile and deep .'' Darwin suggested an answer which enables us to understand not only how atolls in deep water may have originated, but also how atolls in general have been formed. It is well known to geologists that the level of the ocean bed is subject to change. It may be upheaved, or, again, it may subside. Darwin conjec- tured that as fast as the coral reef was built up toward the L, section of mountain rising above water after partial submergence ; RR, sections of barrier reef resting on slopes. Ill L, section of same mountain after complete submergence ; RR, sections of same reef now forming an atoll. half 134 ISLANDS surface, it was carried down by the subsidence of the ocean bed. Let us notice the successive steps of this process. There is reason to beHeve that in those parts of the ocean where atolls now abound, high mountains once towered. These mountains were islands. The polyps built encircling reefs around them. But in many cases, as they built up, a gradual subsidence took place, until the islands them- s' selves disappeared beneath the '---., ^ ..• ■ ■ waves. This subsidence, on the one hand, and this building up, on the other, may have continued for ages, and to the extent of thousands of feet, so Theoretical Section of an Atoll ' RR, reef; 6-. summit of island; 6', former that where the mountains then summit of island. were, there may now be deep waters and low atolls. Thus the mountain tops were replaced by the lagoons, and the en- circling reefs became coral islands. Tahiti affords an illtistration of tiiis process. It is a volcanic island witli a fringing reef, the foundations of wiiich rest upon the submarine slopes of the Lsland. It exhibits the appearance which must have been presented by existing atolls before the subsidence of the ocean floor had carried down beneath the surface of the sea the mountainous islands formerly inclosed by them. Other views, however, have been advanced, among them those of Sir John Murray of the Challenger Expedition, showing that in the explanation of the origin of barrier re.efs and atolls sub- sidence IS not necessary. Through wave, action any summit rising above the sea may be leveled so as to form a submarine platform upon which a reef may secure a foundation. If the eminence, usually a volcanic peak, is not completely leveled, there remains an island sur- rounded by a barrier reef. This reef is all the time broadening its foundation by the addition of its own waste and thus pushing outward into the deeper water. Should it take on an annular form, inclosing a lagoon, with or without an island, it forms an DlSlKIBUriON Oh Ci)RAL I 35 atoll. Such a coral island has resulted from simple reef building without subsidence. Murray entertains the view also that the lagoon may be deepened b\ the solvent action of sea water upon the dead coral. Distribution of Coral. — The reef-building polyps are con- fined to tropical waters which have a temperature of not less than 68°. The central part of the Pacific Ocean is the scene of their greatest activity. They are also found in many portions of the Indian Ocean, in the Red Sea, and the Persian Gulf. Except among the West Indies, at the Bermudas, and off the coast of Brazil, there are none in the Atlantic. The area within which they are at work is not less than 25 millions of square miles. PART III.— THE WATER XIII. PROPERTIES OF WATER Composition and Properties of Water. — Pure water is composed of two gases, oxygen and hydrogen, united in the proportion of one volume of the former to two volumes of the latter. It is represented by the chemical symbol HgO. Among the properties of water that especially interest the geographer are the following : (i) It changes its forms with remarkable readiness ; (2) it expands when passing into the solid state ; (3) it has great capacity for absorbing heat ; (4) it has great solvent power. Forms of Water. — Water exists in three forms or states : the solid, the liquid, and the gaseous. Changes of temperature of ordinary occurrence cause it to pass from one to another of these. As a solid it may fall gently as snow, muffling the young plants and screening them from the biting winds of winter, or as ice it may cover the surface of lakes and rivers, protecting aquatic forms of life as snow does the plants and insects of the land. As a vapor it passes off from the surface of the seas, lakes, and rivers, and even from the land itself, into the atmos- phere. Mantling the earth with an invisible screen, it prevents the too rapid escape of its warmth at one time ; or, assuming the form of clouds in the sky, shields it from the too great heat of the sun at another, and when still further condensed it falls as rain, supplying water to springs and rivers and necessary moisture to animals and plants. Expansion of Water. — Water expands when passing from the liquid state to the solid. This is probably due to the fact that its particles, when crystallized, do not fit so closely together as 136 J CAPACITY OF WATER FOR ABSORBING HEAl' 137 before. When cooled, it follows the general law, and contracts until it reaches the temperature of 39.2° F. Below this it disobeys the general law, and expands till it reaches 32°, its freezing point. Then suddenly it hardens into ice, and attains its maxi- mum expansion. Since ice is more expanded than water, it is lighter than water, and, as we all know, floats. Were ice heavier than water, it would sink as fast as it was formed, and our river channels and shallow lakes would be filled with solid ice from the bottom to the top. Another important consequence of the expansion of water when freezing is that it exerts a force that is practically irresist- ible. It sunders the solid rock from the foundations of the mountains, and crumbles it into fragments. Interesting examples of the effects of the force exerted by freezing water may be found on rocky hillsides. During thaws the crevices of rocks be- come filled with water. As the weather grows cold, this water freezes and splits the rocks. Iron water pipes are sometimes burst by the freezing of the water in them during extremely cold weather. Capacity of Water for Absorbing Heat. — Two effects may be produced by the application of heat to a body: (i) a rise of temperature which is generally accompanied by expansion of the body ; thus an iron rod placed in the fire grows warm, and at the same time becomes longer and thicker ; (2) a change of form ; in this case the heat given to the body changes it from a solid to a liquid, or from a liquid to a vapor, without altering its temperature. We are familiar with the fact that a kettle of boiling water may be kept boiling for a long time before all of the water is changed into vapor, yet during that time its temperature has not changed, although it has absorbed a large amount of heat. If the vapor thus formed be condensed to a liquid, it may be shown experimentally that the same amount of heat will be given out as was originally absorbed. Heat which causes change of form without altering the temper- ature is called latent heat ; that which is absorbed by a solid 138 PRC^PF.RTTRS OF WATKR when melting being known as the latent heat of iiwltiito;, and that which is absorbed by a Hquid when becoming a vapor, as the latent heat of 7'aponsatioii. Take a lamp which affords enough heat to raise the temperature of one pound of water 1° a minute and let us call that amount of heat a iiint of //eat. Now set in a vessel over the lamp a pound of ice at 32°. It will immediately begin to melt, but the heat does not warm the ice or the water ; it only melts the ice. At the end of 143 minutes all the ice will be melted, but the temperature of the water will still be 32° and no more. Now. what has become of all the heat received from the lamp during these 143 minutes? It has gone to convert the solid into a liquid and is therefore called latent. The latent heat of melting ice is therefore 143 units. Now let the lamp continue burning as before. In 180 minutes the temperature will be raised from 32"^ to 212° and the water will then begin to boil. 180 units of heat have therefore been re- quired to raise the temperature of the water from its freezing point to its boil- ing point. If now the boiling water be kept over the lamp it will not become hotter but will gradually change into vapor and at the end of 966 minutes more it will have boiled away. Thus the latent heat of evaporation of water is 966 units. In other words it takes as much heat to melt one pound of ice as it would to heat 143 pounds of water one degree, and as much heat to change one pound of boiling water into vapor as it would to heat 966 pounds of water one degree. Water is pecuhar in that its latent heats of melting and evap- oration are larger than those of any other substance and this is of special importance in its relation to natural phenomena. Evaporation and Condensation. — From the above statement it will be seen that evaporation exerts a cooling influence because ice or water on becoming vapor renders heat latent. Condensation of water, on the other hand, exerts a warming influence. As has been frequently noticed, the intense cold is mitigated just before a snowstorm. This is due to the conden- sation of vapor into snow. It has been computed that from every cubic foot of vapor condensed, and frozen into snow, heat enough is set free to raise more than 100,000 cubic feet of air from the temperature of melting ice to summer heat. Nature makes great use of these counter ]:)roperties, the evapo- ration and condensation of water. She stores away the heat of CIRCULATION' OF WATKR 1 39 the torrid zone anion<^ the particles of vapor, thus cooling the atmosphere. Transported by winds to other regions, they are there condensed into rain and their heat set free to warm the air and modif\' the climate. The Solvent Power of Water is another property of great im- portance. The forms of plant and animal life are largely built up of materials which enter them in solution. Water acts as a vehicle for conveying these materials into the living system. It is essential, therefore, to the maintenance of life. Moreover, by the solution of mineral substances water pro- motes rock decay and the general disintegration of the earth's crust. All waters })crcolating through rocks or flowing upon the surface are more or less charged with mineral matter held in solution. Circulation of Water. — The readiness with which water changes its form and passes from the liquid state to that of vapor, and from the vaporous to the liquid state again, is the means whereby a constant circulation is carried on from the sea to the land, and from the land to the sea again. It waters the thirsty lands ; it fills the springs and replenishes the rivers. Thus some portions of the rainfall find their way back to their home in the sea through river channels ; other portions, evaporated, rise in the atmosphere and again being cooled descend as rain or snow. And thus most of the waters of the globe come out of the sea as from a reservoir and to it they are later returned. XIV. WATERS OF THE LAND Ground Water and Springs. — Only a portion of the rain which falls upon the land finds its way directly into the creeks and rivers leading to the sea. The larger part sinks into the earth, Diagrammatic Illustration of a Common or Gravity Spring a represents an impervious layer above which are the porous beds b, c, and d. Rain wafer percolating the soil and porous beds appears as a spring s, where the bed a is cut by the valley. where it is known as ground water, though sooner or later much of it again reaches the surface, chiefly in the form of springs. Many rocks are porous, and most rocks are traversed by cracks and especially by joints, consequently surface water percolates downward until its further progress is impeded by an impervious layer. Flowing, now, over the top of that layer in the direction of its incUnation, the water wi"!! appear as springs, or a line of seepage, wherever the topography is such as to furnish an outcrop, as on the side of a hill or valley. Should the rocks be alternately porous and impervious and incline or dip toward a fault fissure appearing at the surface at a lower level than their outcrop, then, under certain condi- tions, as when the opposite wall of the fissure is composed of compact or non-porous rock, the water will completely fill the fissure and will be forced out at the surface under more or less pressure. 140 J GROUND WATER AND SPRINGS 141 DiagrjVMMATIC Illustration of a Fissure Spring In the figure above the porous beds p,p and the impervious beds c,c,c, outcropping on the right and dipping to the left, on ac- count of a fissure of displacement or fault, abut on an impervious mass m. The rain falHng upon the outcrop creeps downward through the pervious beds/,/ until the fissure is reached, where the water is forced to the surface as a spring s by the pressure of that in the reservoirs r,r,r behind it. As will be shown later, the principle is identical with that of the artesian well. ^;' --^ .^ ^^r 4 *?•"•■■■ ■ -if ;f^'^m ^^?fi^ ■K" '~'^ An Appalachian Mountain Spring This beautiful spring, surrounded with ferns and other forms of vegetation, is one of many on the Black Mountains of North Carolina. From United States Geological Survey. The springs above described represent two types : (i) common or gravity springs ; and {2)fissiire springs. 142 WAVERS OF THE LAND Tlie depth to wliich percolating water descends is surjjrising. From a deep well sunk in a certain district of France, pieces of leaves were thrown up b}- the first gush of water from a depth of about 400 feet. These leaves were comparatively fresh. They were ascertained to liave come from a distance of about 150 miles from the spring. From the percolation of water through the earth arises one of the greatest difficulties in mining operations. Before the invention of steam pumps many coal pits in England were abandoned because, as the miners said, tliey were dnnvncd. From the Comstock mine 3.500.000 gallons of hot water had to be pumped every 24 hours. Artesian Wells are so called from the province of Artois in France, where they were first used. As in the case of fissure ^ -P c p c Section of an Artesian Basin /, /, porous beds; c, c, impervious beds above and below/,/, inclosing the reservoir, r ; L, water level; If, artesian well. springs, their source of supply is porous, usually sandy, beds inclosed by impervious layers. The porous beds act as reser- voirs, and their outcrop may be many miles distant from the region in which the wells are sunk. Formerly it was thought that artesian conditions prevailed only in basins, as illustrated in the figure above, and that when the upper confining layer was penetrated by boring, the water should rise, fountain like, in the air. Theoretically it should reach the height of the water level in the reservoirs, but practically, on account of adhesion, friction, and the resistance of the air, this is not attained. It will be readily understood that the larger the number of wells sunk in a given basin, the more the pressure is reduced by the increased outward flow which lowers the height of the water in the reservoir. It must be kept in mind that by "reservoir" is not meant a cavity filled with water, but a porous rock, as a bed of sand or gravel, saturated with water. Through such a reservoir water flows which has fallen on its outcrop as rain. i AKIESIAN WELLS «43 AKfKsiAN Conditions akisinc i kom iiii-: I'assage ok Hokols Waikk-iikarinc; Beds into Imperviois Beds />, porous beds; c,c, impervious beds above and below tiie porous water-bearing beds inclosing the reservoir ; c' , the region where the pervious beds gradually pass into impervious beds; r, reservoir; L, L, water level ; H', artesian well. It is now well known that a complete basin does not furnish the only artesian condition. Beds inclining or dipping in one direction may grad- ually pass from a porous into a com- pact and more im- pervious state, and if inclosed, as in the preceding case, a reserv^oir may be formed as indicated in the figure above, from that part of the confined beds which is porous. This res- ervoir likewise, when penetrated, will fur- nish flowing wells until by over-boring the pressure is re- duced. Moreover, the same results may be attained by the penetration of in- ,•1 11 artesian WEI.I. Al WOONSOCKET, Sol Til DAKOTA clmed porous beds ^, , ,. , , , . , ^ ,, . ,^ ' The height of the column is 97 feet. From L^nited States properly inclosed, " Geological Survey. -M.-i. HHVs. ueol;. — 9 144 WATERS OF THE LAND which thin out and disappear at some point beyond the artesian area, as in the figure below. c Artesian Conditions arisini; from the thinning out of Water-bearino Beds /, porous beds thinning out at jr ; r, reservoir; /., Z,, water level ; H^, artesian well. Although originally applied to flowing wells, the term arte- sian is not now so restricted, but may be applied to any deep well, whether flowing or not, which has its source at a consider- able depth below the surface and depends upon the rainfall at a more or less distant point. Artesian wells have been of the greatest value in many countries, especially in arid and semiarid regions, where they have furnislied water not only for drinking purposes, but for irrigation as well. In Algiers through bor- ings put down by the French an abundance of water has been olitained on the margin of the Sahara. In many parts of the United States artesian wells are in common use, es- pecially in California and Texas. In some instances the water is obtained from beds dipping beneath the sea as on the Atlantic and Gulf coasts. Rivers receive their waters (i) directly from the rainfall as it runs off the surface in the form of wet-weather tributaries ; (2) from springs; (3) from the melting of snow fields and glaciers. Most rivers are said to originate in springs, each of which pours forth a contribution in the form of a little streamlet. Influenced by gravity, streamlets seek a lower level, and uniting, form creeks and rivers the volumes of which are often greatly increased by sudden rainfalls and the melting of snow over a large area. In a similar manner a number of tributaries' blending together make one great water course. Such a water course, with its tributary streams, is called a river system. Erosion means the eating or wearing away of the materials Ek( )SIOX •45 which form the earth's exterior. This is brought about chieriy in two ways: (i) by the solvent power of the water; and (2) by its mechanical action when in motion. These two combined remove the more soluble and softer rocks with ease; and even the hardest cannot with- stand their action. If the soluble par- ticles of a rock are dissolved by water, the rock disinte- grates and crumbles awav. When, there- fore, a stream runs i n c e s s a n 1 1 )^ over such a constantly dissolving and disin- tegrating rock, it is clear that erosion will make rapid progress. Moreover, the rocky fragments torn from the stream bed by the mechan- ical action of the flow- ing water, especially where there is a marked descent, are whirled against one another and the bottom and sides of the channel. Thus as the river flows on, the fragments of rock become smaller and smaller. In the upper course of the river they may be of considerable size, but in the lower course they are reduced to sand and silt. The erosive action of rivers is most impressively illustrated by the excava- tion of rocky gorges. That of the Niagara and the canyons of our Western rivers are |)erhaps the most striking examples that can be offered. Tlie Falls of Niagara, it is evident, were at one period about seven miles Chakacikkistic Bed of a Mountain Stream Hickory Nui Creek, North Carolina. 146 WATERS OF THE LAND lower down the stream than at present. The vast volume of water that passes over the diff, now falling from the height of 160 feet, both directly and indirectly is a powerful eroding agent. By it the gorge has been cut back- ward from the Ontario scarp towards lake Erie. Transportation. — The finer particles of eroded matter are carried along by the river in suspension ; that is, simply mixed with the water. The coarser portions are rolled onward by the current. This twofold action constitutes transportation. A river will transport eroded matter to a greater or less dis- tance, and in greater or less quantity, in proportion to the ve- locity and volume of its current. Water moving at the rate of eight inches per second will carry along ordinary sand. If the velocity be increased to 1 2 inches, it will roll along fine gravel, while a current having a speed of three feet a second can sweep along pieces of stone as large as eggs. In floods masses of rock ^as large as a house have been moved. f'^ As to the quantity of matter transported, it is estimated that of ykible sediment the Rhone carries into the Mediterranean more than 36,000,000 tons annually, and of salts invisibly dissolved, more than 8,000,000 tons. The amount of silt carried into the Gulf of Mexico by the Mississippi in one year would make a col- umn one mile square and 241 feet high, and if the sand and gravel urged along the bottom be added, 268 feet. The removal of this matter from the surface of the valley reduces its average level one foot in 4638 years. Deposition. — The materials borne or rolled along by rivers are deposited at various points in the channel. The finer por- tions, called silt, familiar to us as muddy sHme,are carried down as far as the mouth of the river. Farther up the stream sandy particles come to rest; still higher, gravel is deposited ; and finally, in the upper course of the river we find stones of greater or less size. It is obvious that deposition will depend very largely upon the slope of the river bed and the rapidity of the current. Any- thing that checks the latter favors deposition. I DKPOSITION '47 Changes in river courses are a frequent effect of deposition. They occur especiallx' in ri\ers that flow through alluvial lands. Very often the course of such streams is marked by what arc termed uicandcrs, or sharjD curves resem- bling the letter S. The lower Missis- sippi presents a strik- ing illustration of this. In some cases portions of the land are carried from one side of the river to the other, giving rise to important ques- tions of ownership. Sometimes, too, when a river is unusu- ally high, it may cut for itself a straight course instead of following its old curves. The portion of the former channel that is thus abandoned, closed by silt at each end, be- comes a lake, cres- centic in shape, com- monly called a " cut off " or an oxbow. Among the important deposits of rivers are those that occur at or near their mouths, whether they flow into the sea or a lake. Here the current is checked by contact with the larger body of water, and, as a consequence, the silt which is readily Meanders, M, and Oxbow Lakes, O, ok Mississippi 148 WATERS OF THE LAND held in suspension by the moving water, now settles to the bot- tom. In this way bars are formed. The Mississippi, and all the rivers of the United States that flow directly into the Atlantic Ocean, have bars. A Ml \Mii IvIm; SiKi.wt, Cri-)()KED Ckki-k, Cai.ifoknia Crooked Creek is a tributary of Owens River in eastern California. Pts valley has been cut in volcanic rocks. In the waste-fiJled portion the stream has taken on the mean- dering condition of maturity. The manner in which such streams broaden their valleys is well shown by the meander extending to the left from the center of the picture. From photograph by Willis T. Lee, United States Geological Survey. So great is the amount of .solid matter brought down by the Mis.sissippi that a bar no le.s.s than two and a quarter miles in breadth was formed off one of its outlets called the South Pass. Fleets of vessels more than 50 an number might sometimes be seen, detained on the bar for weeks, waiting for a chance to go to sea, or to enter the Pass. The operation of towing a ship into the deep waters of the Gulf occupied days, and in some cases weeks. In 1875 Captain Eads, by the authority of Congress, constructed yV///V.y, or long walls, which narrowed and confined the current, and thus gave it greater velocity, and, of course, greater power to scour out the channel and carry off the sediment into deep water. The mouth of the Danube has been deepened by jetties so as to admit vessels of 20 feet draught. DEPOSITION 149 Again, when a river encounters a lake or other body of still water, where the silt deposited is not washed away by strong currents, there is gradually built up a fan-shaped deposit, through which, later, the stream may flow in several channels or distributaries. Such a deposit, from its resemblance to the Greek letter (A) of that name, is called a delta. The Mississippi, the Nile, the Ganges, the Orinoco, the Dan- ube, the Volga, and many other rivers which flow into in- land seas or gulfs protected from the sweep of the tides and ocean currents, are famous for their deltas. But where there is a very strong littoral or shore current, it sweeps off the sedi- ment as fast as it enters the sea, and o iH' 1 iik xNii.i- The delta of the Nile has the typical A-shape. Delia of 1 hk Mississippi The lightly shaded portion is covered with shallow water. ISO WATERS OF THE LAND there is no delta formed. This is the case with the Amazon, the Plata, and with all the American rivers that empty into the Pacific Ocean. The area of deltas is often very large. That of the Missis- sippi is about 13,000 square miles. One third of it is still in process of formation, being as yet only a sea marsh. Section of the Mississippi Sediment is deposited not only upon the beds of rivers, but also upon their ijanks. This has the etTect of raising the banks above the general level of the neighboring country. In some portions of their course both the Mississippi and the Po are above the adjacent fields. The land, therefore, slopes from the river on either side, and one goes up to it instead of down to it. Rapids. Cascades, and Waterfalls. — These terms are employed A Diagrammatic Illustration of Rapids The arrow indicates the direction of stream flow. The outcropping rocks are seen in section. to denote the more or less violent descent of streams in their passage from a higher to a lower level. Rapids are formed wherever the stream bed is in the form of a series of steps, as from the successive outcropping of hard strata or where a stream plunging down a declivity is more or less imj)eded by barriers of hard rock. The rapids above and KAPIDS, CASCADES, AND \VA lERI- ALLS '51 A DiACkAMMAllC ILIASI KAl ION OK CASLAUbS The hard layers foi ni miniature table rocks over which tiie water falls. The softer, thin bedded rocks below are easily eroded so that each cascade represents a temporary stage in gorge formation. below Niao^ara Falls and the rapids of the Saint Lawrence River afford excellent examples of this form of stream descent. A cascade is a low perpendicular or nearly perpendicular waterfall, usually one of a series by which a stream rather abruptly reaches its lower level. Frequently cas- cades result from the al- ternation of hard and soft strata in the stream bed. Falls of the cascade type are especially character- istic of the lake region of central New York. The glens and gorges about the heads of Cayuga and Seneca lakes afford many beautiful examples. The typical waterfall is perpendicular, resulting from the abrupt descent of a stream over a preci- pice. In regions of strat- ified rocks the plunge may be over hard rock Cas.a,>k in niv. Catskm.i.s 152 WATERS OF THE LAND ( Thk American and Luna Falls, Niagara, from below In tin; foreground is the " Rock of ARes," one of the largest of the fallen limestone fnigments. RAl'IDS. ( AS( Alii;>. AMI WMKKIAI. '53 \\ iiiki.i uui, Kaiiijs, Niagara Ri\kk From a photograpli. layers (table rock) which are underlain by softer beds. Such is the case at Niagara. Here the harder upper rock is a limestone 80 feet thick. Beneath it there is a softer rock, of about the same 54 WATERS OF THE LAND Gkkat Falls of iul Vkllowsio.nl From pliotograpli by Haynes. I.AKKS 155 thickness, made up of very thin layers, known as shale. As the limestone is undermined by the breaking up of the shale by frost and water action great fragments of the table rock drop into the abyss below, and thus the falls gradually retreat up stream. Other forms of per- })cndicular falls, as in the \'osemite, are caused by streams leaping into a great valley excavated b\' glacial action. In regions of igne- ous rocks waterfalls often result from the unequal resi.-i'tance of the layers forming the stream bed. A very hard layer, such as basalt, overlying soft and non-resisting layers, will give rise to the typical per- pendicular fall as in the case of the Sho- shone Falls of the Snake River. In rather unusual instances dikes or walls of hard igneous rocks form the barrier over which streams are precipitated, as exempli- fied in the Lower or Great Falls of the Yellowstone. The Victoria Falls of the Zambezi in Africa are the most remarkable in the world. They are more than a mile wide and over 400 feet in perpendicular height. The river plunges into a nar- row ravine running diagonally across the river bed. Lakes. — The formation of lake basins has been ascribed to many causes, some of which are as follows : ( i) great (diastropJiic) movements of the earth's crust, especially those producing large; IrnAiA Fai.i,. Xkw York This is a fall of the cascade type. 156 WAI'ERS OF THE EAND downward folds; (2) the obstruction of drainage by the elevation of mountains ; (3) subsidence, as in certain regions affected by earth- quakes ; (4) the damming of valleys by glacial barriers (moraines) Niagara Falls in Wintlr The severity of the winter is shown by the great accumulation of ice Ijelow the falls. left upon the retreat of the ice; (5) depressions in glacial drift due to the melting of isolated patches of ice ; (6) glacial erosion ; ( 7) volcanic action. Lake Superior is thought to occupy a great downward fold of the earth's crust, or syncline. Most of the lakes in mountainous regions have resuhed from orographic movements. The lakes of the -sunk country" near New Madrid. Mo., sprang into existence as a result of the well-knownearthquake of i8[i-i2. In Switzerland and other mountainous regions small lakes behind ghtcial bar- riers are known. The numerous lakelets and ponds in glacial drift, as in Mas- sachusetts, are due to the melting of isolated patches of ice which were left surrounded or buried in debris upon the retreat of the glacier. Some of the lakes of central and western New York, as Cayuga Lake, .seem to be due. in part at least, to the formation of rock basins by glacial erosion. Crater Like, in the Cascade Range of southern Oregon, and similar Jakes in other parts of the world, (jccupy extinct volcanic vents. KkESII-WArKk A\l» SALl-WAlKk lAKKS 157 Fresh-water and Salt-water Lakes. — In regions where the precipitation or rainfall exceeds the evaporation, lake basins 'f^ ^^ MH witk M MH ^^R.^^ ^ 91 ^M 8^-- I^^SH hI |^^^^B|Un|M^«-'%^|M ^^^^^^^^HK^ .ii.^K'; ^ <^^^^^^^^^^H f^^W^^i H^^ ill ^^^H.<:iK.- P^la ^^ift^E fl ^^^^^^^^ ^^B ^^^ <)d^^^^l 1 J YosEMiTE Falls, C.\i,ifornl\ The height of tlie upper falls is about 1500 feet. will be filled with water which, overflowing the rim or breaking through the barrier at some weak point, pushes onward to the 158 WATERS Ob THl:; LAM) sea, cutting, it may be, a channel through hard rocks; hence the presence, oftentimes, of rapids, waterfalls, and gorges. In the case of lake basins situated in arid regions, which are characterized by great warmth and dryness, the amount of water Cnstle of Chillon, Cake Geneva. Dent du Midi in the background. evaporated is sometimes equal to that which is supplied, and sometimes greater. As fast as the water is poured into these basins by the rivers it is carried away in the form of vapor. Such basins are not filled to overflowing, and consequently have no outlets. The water of lakes having no outlets is commonly salt. The water of lakes having outlets to the sea is fresh. The reason for this will be readily understood from the following explanation. Rivers carry into lakes many substances in solution, of which one of the most common is chloride of sodium, or common salt. This IKtSll-WArEK AND >AL1' WAIK LAKES 159 is Drcsent in ordinal-)' river water, although it cannot be tasted ; l)iit if a large quantity of such water were evaporated, a small amount of salt would be left behind. Thus it is clear that if a lake have an outlet, not only is its superfluous water removed, but the salts dissolved in such water are also taken out. I'HE Dead Se.v On the other hand, if a lake have no outlet, then, while the water brought in is removed by evaporation, the salt intro- duced remains behind. Thus lakes having no outlet may be compared to the evaporating vats or troughs in which, as at many points on the shores of the Mediterranean, sea water is boiled, or evaporated by solar heat, in the manufacture of salt. The water passes off, the salt remains. Hence, year after year, salt lakes become Salter. Conspicuous examples of salt lakes are the Great Salt Lake and the Dead Sea. Both of these are heavily charged with saline ingredients. The water M.-S. PHYS. GEOG. — lO i6o WATERS OF THE LAND of the Dead Sea is about one fifth heavier than that of the ocean, and sustains tlie human body, so that it cannot sink in it. From its great salinity the Dead Sea is often called the Sea of Salt. But the Jordan, which supplies it, is of course fresh. The Dead Sea is situated in a depression remarkable for its intense heat, and the reo-ion in which the Great Salt Lake lies is very remarkable for the dryness of its atmosphere. In the case of both these lakes, therefore, evaporation proceeds at an enormous rate. Cayuga Lake from Cornei.i, Heights, Ithaca, N.Y. Inland Seas. — Some inland bodies of sn1t water, however, have evidently been at one time parts of the ocean. These are properly designated inland seas. The most remarkable of them are the Caspian and Aral. When the Arctic Ocean extended, as geologists believe it did, southward as far as the mountains of Persia, these two seas and many neighboring bodies of salt water were included within its limits. Seals abound in the Caspian, and sturgeons, herrings, and other sea fish in both the lakes. Like other salt lakes, these inland seas have no outlet. The DESKCATKD t)K EVAPORATED LAKES l6l Volga, the largest river in Europe, and the Ural pour volumes of water into the Caspian, yet its level does not rise. Lake Aral receives the Amu and Syr rivers, yet its level seems actually to be lower than formerly. Many small salt lakes entirely evaporate during the summer, and leave their beds covered with saline incrustations. From the Crater Lake, Oregon This unique body of fresh watt-r is situated in the Cascade Range of southwestern Oregon. Occupying a depression, known as a caldera, formed by the subsidence or caving in of a great volcanic summit — Mount Mazama — its surface is 6,239 '^^^ above sea level. Its shape is somewhat elliptical, its diameters being 6\ and 4J miles respectively. Its depth approximates 2,000 feet. A single island, in the form of a cfnder cone, rises aijove its waters. There is no outlet, the steep walls of the caldera rimming the lake on all sides. dry bed of Lake Elton, in the Caspian region, 100,000 tons of salt are annually gathered. Desiccated or Evaporated Lakes. — Salt and alkaline lakes are usually the remnants of larger bodies of water which have greatly shrunken or almost disappeared on account of the arid- ity brought about by climatic changes. The former existence of such lakes is shown b)' easily recognized basins and shore lines, as in the case of Lake Bonneville, in Utah, and Lake La- l62 WATKRS OK THE LAND hontan, in Nevada. Great Salt Lake is a survival of the former, while Carson, Pyramid, Winnemucca, Humboldt, and other lakes fill depressions in the basin of the latter. A Caldera, Canary Islands Calderas or " caldrons " are large craterlike depressions which often measure several miles in diameter. In sime instances they seem to have resulted from violent eruptions, during which volcanic summits have been blown completely away; in others, they have evidently been formed by the subsidence or caving in of volcanic cones. See Crater T.ake. The waters of Lake Bonneville, which were fresh, flowed into Snake River. Lake Lahontan had no outlet and its waters were probably never fresh. As these lakes diminished in volume, the water became more and more concen- trated, until tlie mineral matter held in solution was precipitated. The first substance deposited was, carbonate of lime in the form of tufa. This is found along the ancient shores of Lake Bonneville and in much greater abundance along those of Lake Lahontan. Great Salt Lake is rich in salt (sodium chloride) ; the Nevada lakes are not. As an explanation of this difference, it as been suggested tliat Lake Lahontan had probably been evaporated to dry- OFIICKS OF l.AKKS ■^>3 ness. truly i/t'sura/t'(/,dnd\.hdi later, underslightl\ t'liaii;^(.:(l climatic cunditions, whicli permitted the formation of smaller bodies of water, the salt beds that must have existed were buried under clav de])osits. and therefore do not affect the waters of the present lakes. Offices of Lakes. — Lakes act as lesei'voirs and thus often- times prevent the flooding of rivers. The waters of the upper Ui'PKK Lake uf Kii.i.ak.nkv, Ikkianh The Iraki's of Killninev are famous for their beauty. They He in tlie souihui'Stern part of Ireland about 35 miles nortlnvest from Cork. tributaries of a stream, swollen by recent and heav\' rains or b)' the rapid melting of snow, upon reaching a lake spread out and are held back, in consequence of which the flow at the outlet is not greatly increased. As the inundations of the lower Missis- sippi are mainly due to the floods of its tributaries, there being no intervening lakes to hold back the surplus waters, it has been proposed to regulate its flows by the erection of impounding reservoirs on its headwaters. Furthermore, lakes act as settling basins. The water flowing 164 WAIKRS ()!• rilK LAND into a lake may be laden with sediment, even the finest glacial silt, but the water flowing from it will be clear, containing no matter held mechanically in suspension. Hence it follows that a lake may become completely filled with detritus brought in by flowing streams. When this stage has been reached, the lake gives place to a plain through which the supplying stream meanders. This is illustrated in a small way by the accumula- tions deposited in the reservoir behind an old dam. Geographical Distribution of Lakes. — In North America are found the vast bodies of fresh water which are called the "Great Lakes." Lake Superior, a member of this group, is the largest body of fresh water in the world. Its area is over 30,000 square miles. The surface of this great inland sea has an altitude of 602 feet, but its bottom extends below the sea level 406 feet. The northern part of the Great Central Plain of the continent abounds in lakes of greater or less magnitude. In the basin l>etween the Rocky Mountains and the Sierra Nevada there is a region of saline lakes. In Europe, the great lake region lies in northern Russia and Scandinavia. Ladoga and Onega, Wener and Wetter, are the largest lakes of the grand division. Those of the Alps, Como, Miiggiore, Geneva, and others are comparatively small, but famed for their beauty. Asia is noted for the size and number of its salt lakes. The Caspian Sea, Lake Aral, and the Dead Sea are examples. Of fresh-water lakes Asia has few. Lake Baikal, however, 400 miles in length, may be compared with our own Lake Superior. Africa rivals North America in the magnitude of her great lakes. Victoria and Albert Nyanza, Tanganyika and Nyassa, are the largest. South America has one lake of importance, Titicaca. Aus- tralia is noted for its salt lakes. Eyre, Torrens and Gairdner each exceed 100 miles in length. XV. DRAINAG?: Advantages of Drainage. — The drainage of the land depends primarily upon its relief. Those countries best adapted for human habitation are well drained. Crops do not flourish on cold, damp soils, nor can human health and strength be main- tained where the ground is always wet. As is well known, the vicinity of swamps is especially unhealthful. For this reason a very large area of the sunny peninsula of Italy, called the Campagna, once densely populated, is almost uninhabited. From the days of ancient Rome it has remained, owing to the level nature of the land, and the consequent absence of any stream into which the waters might be directed, a vast swamp and a breeding ground of pestilence. It is now being reclaimed. How Drainage is Effected. — Rivers are the channels through which the water carried from the sea in the form of vapor and rained upon the land finds its way back to the sea. Every running stream may therefore be regarded as a kind of rain gauge, which measures, in a general way, the quantity of rain that falls upon the valley which it drains. The region drained by a river system is called the river basin. The basins of large streams are hundreds of thousands of square miles in area. That of the Mississippi contains nearly 1,250,000 square miles. The limits of a river basin are defined by what are termed zuatersheds ; that is, water divides, j//r^/ being from a German word meaning to divide. A watershed is a line of elevation, some- times lofty and sometimes low, which, like the ridge of a roof, divides the rain as it falls, and causes one portion to descend one slope of a country or continent, and the other portion another. 165 1 66 r)RAiNA(;t: If on a map of North America you trace a pencil line round the sources of all the rivers that pour into the Mississippi from the Appalachian slope on the one side, and from the Rocky Mountain slope on the other, 30U will have marked out the watersheds which define the eastern and western limits of the Mis- sissippi basin. The mountains and slopes of every country determine in a Inrge measure the number of its water courses, their length and direction, and the velocity of their currents ; in a word, their capacity for carrying off superfluous rain water. Inundations. — The inundations or floods which occasionally submerge large areas of land, and are so destructive to life and property, occur where the quantity of water to be removed exceeds the capacity of the draining rivers. Many rivers, as the Nile, the Orinoco, and the Mississippi, are sub- ject to periodical over- flow. So extensive are the inundations of the Po that the Italian engineers have actually proposed a scheme for cutting an artificial channel to be used in case of cmergenc}'. The chief causes of floods are to be -found in seasonal changes. They affect the rainfall and cause the melting of snow both on high mountains and in river basins. The sudden disappearance of winter snow is always accompanied by swollen streams. The meltinL; (ifsiKAv in Ft- nnsylvania. Oiiid, Indiana, antl Illinois, togellicr with copious sprint^ rains, are annuall\' followed hv a marked rise in ihe Ohio Fl.OODKD LaNUS at SINCAC, Nl'.W JKKSEY, ON THK Passaic Rivkk Fiom United States Geological Survey. NOR 111 A.Ml-.RICA 167 and its tributarifs. and wlicn the snows of the Rocky Mountains begin to nielt, the western tributaries ot the Mississippi are Hooded and that stream experiences the "June rise." North America. — The boundin^^ waters of North America are the Arctic Ocean, the Pacific Ocean, and the Atlantic, including the (nilf of Mexico. These receive the drainage of the grand division. The great watershed is the Rocky Mountain system. It acts like the ridge of a roof, shedding the water to the east and to the west. All the region lying westward of it is drained into the Pacific and into Bering Sea by the Colorado, the Columbia, the Phaser, the Yukon, and other rivers of less im- portance. East of the Rocky Mountains the grand division is divided into four .slopes: a northern, inclining toward the Arctic Ocean ; a northeastern, toward Hudson Bay ; an eastern, toward the Atlantic ; and a southern, toward the Gulf of Mexico. The largest river draining to the Arctic is the Mackenzie. The Saskatchewan-Nelson is the chief system draining to Hudson Bay. To the south lies the great basin of the Missis- sip])i, the drainage of which is poured into the Gulf. This basin embraces the enormous area which lies between the Rockv Mountains and the Appalachians. The amount of water carried by the Mississippi from this region into the Gulf of Mexico every second is 675.000 cubic feet, enough to cover about iS acres of ground to the depth ot a foot. We can see from this how soon tlie .Mississippi basin would become a desolate swamp. If it were a dead levt-l untrenclied by its mighty system of rivers. The eastern slope of the grand division, including the terraced plateau occupied b}' the Great Lakes, is drained by the Saint Lawrence and by a series of rivers, large and small, which flow from the Api)alachians to the Atlantic. South America. — The drainage of South America, like that of North America, is maiiil\- effected by three river systems. The l68 DRAINAGE crest of the Andes is the great watershed. It lies along the western edge of the grand division. Hence the drainage has in general an easterly flow. The eastern slope embraces nearly the whole of the grand division. It is divided into three great river basins, those of the Orinoco, the Plata, and the Amazon. The last contains the greatest river system on the globe. The Amazon discharges six times as much water as the Mississippi. In respect to volume it is the largest river in the world. It rises in the beautiful little lake of Lauricocha, high up among the Andes. Descending by falls and rapids, it reaches the region of the silvas, and then becomes a stream navigable for large steamers from the foot of the mountains to the sea, a distance of about 2200 miles. So great is the force of its current that its fresh waters are carried a dis- tance of about 200 miles from the land. An ocean current passing near its mouth sweeps away sediment as fast as the river brings it down. Thus the river's own current and the ocean current prevent the formation of a bar. The western slope of South America is steep and narrow. There is no room for. long rivers, and no water for large rivers. The Pacific receives only a few small mountain torrents, fed by the melting snows of the Andes. Europe. — From a point in the Ural Mountains at about latitude 61° north, to the Valdai Hills, thence in a southwest- ward direction through central Europe down to the southern shores of Spain, an irregular line may be traced which will separate Europe into two great slopes. The one inclines to the northwest, the other to the southeast. All the rivers have one or the other of these two general directions ; and the grand division is drained into the Mediter- ranean, the Adriatic, the Black, and Caspian seas on the one side ; or into the Atlantic and Arctic oceans, and the North, Baltic, and White seas on the other. The region of the Alps is drained by four streams, the beauti- ful Rhine of the Germans, the Rhone, the Danube, and the Po ; the drainage of the low jjlains is accomplished by a number of rivers, among which the Volga, the Don, the Dnieper, and the Dniester are conspicuous. ASIA 169 Asia. — The grand division of Asia, like that of Europe, may be regarded as consisting of two great slopes, one having a general incline toward the north, the other toward the south and east. Beginning on the western shore of Asia Minor, a line may be drawn to Mount Ararat, thence along the crests of the Klburz and Hindu Kush Mountains, thence northeastwardly to the Sea View on the River Nile Water carriers filling their " skins." of Okhotsk, which will represent the great watershed of the grand division. Southeast of this line the Euphrates and Tigris, the Indus, Ganges, the Yangtse, the Hoang, and Amur carry the drainage to the southward and eastward into the seas and bays of the Pacific and Indian oceans. On the northern side of the line nearly every important river flows in a northerly direction into the Arctic Ocean. Africa. — The drainage of Africa is accomplished in the main by the four great river systems of the Nile, the Niger, the 170 DRAINAGE Kongo, and the Zambezi. Much of the surpkis water of the grand division, however, is removed by evaporation. The most interesting feature in the drainage system of Africa is the river Nile. But for it Egypt would be as barren as the Great Desert of Sahara. The river is formed by the junction of two streams called the White and the Blue Nile. The former issues from the Equatorial Lakes. The latter rises among the hills and the table-lands of Abyssinia. During June. July, and August the rains pour down in torrents upon the regions drained by these streams. Each is flooded. Uniting at Khartum, the descending torrents reach Cairo by the middle of June, and during the latter part of summer and in the autumn the land of Egypt is uijder water. As the flood subsides, a layer of fertilizing sediment is deposited upon the soil. Most of it has been washed down from the Aby.ssinian hills by the Blue Nile, which takes its name from the color which the sediment imparts to its waters. Australia is scantily supplied with rivers. The Mui-ray and its tributaries are the only water courses of importance. Dur- ing times of drought the latter cease to flow and the main stream is greatly shrunken. XVI. THK SKA AND THK OCEANS Extent of the Sea. — Less than three fourths of the earth's surface is covered by water. This surface comprises, in round numbers, an area of. 197,000,000 square miles, of which about 55,000,000 are land and 142,000,000 water. All of the land, ex- cept 13,000,000 square miles, is on the north side of the equator. The northern hemisphere therefore contains approximately three fourths of all the known land, and two fifths only of the water surface, of the world. The extent of water that is visible to the eye at one time is not great. If we stand on the shore and look seaward, oar view is closed in bv a line in which sea and sky appear to meet. To this line we give the name horizon; that is. bounding line. Its distance from us depends on our elevation. If wl- occupy a position which is elevated six feet above the sea level, our horizon will be three miles oflF. If we ascend a bluff or lighthouse, and so gain a point about 100 feet high, our horizon will be 12 miles distant. Saltness of the Sea. — Various solids ai-e found dissolved in sea water. Of these the most abundant is common salt. Others are certain compounds of lime, magnesium, potassiinn, and iodine. The solid matter may be estimated on an average as about one thirtieth ])art of the whole bv weight. Though there is little variation from the average, it seems to be well ascertained that there are areas, as within the region of the North Atlantic trade winds, for example, where the pro- portion of saline matter is greater than elsewhere. This may be expected, since evaporation ^ is there at its maximum. On the other hand, the pn)portion of salts is reduced where great rivers empty into-the sea or where great bodies of ice melt. ' Evaporate a >mall portion of sea water until it is very much concentrated. Then warm a drop of this concentrated fluid on a piece of glass, and put it instantly under a microscope. You will see ihe saline sulistances, which have given the sea water its peculiar taste, crystallizing in regular shapes, as the water gradually dries from the glass. 171 \ 1/2 THE SEA AND THE OCEANS Saltness of partly Inclosed Bodies of Water. — Theoretically, owing to excessive evaporation, the waters of the Mediterranean Sea ought to contain a greater proportion of saline matter than the adjacent Atlantic, and such is said to be the case off the coast of Tripoli, where they are subject to rapid evaporation by the hot winds from the Libyan desert. In the Red Sea, too, there is a concentration of saline matter. No streams of any consequence flow into it, and, almost com- pletely landlocked, it is subject to excessive evaporation; so that it exhibits a degree of saltiness found only in some salt lakes. In higher latitudes, where the evapora- tion is not so great, and where there is a large inflow of ter- restrial water, land- locked seas are less salt than the adja- cent ocean. Some parts of the Baltic, for instance, are al- most fresh. Color of the Sea. — The sea is green or blue ; it is sometimes colored here and there by reddish, or whitish, yellowish, or crimson patches, according to the tints imparted by the color of the bottom, by the shadow of the clouds, by the ingredients of its waters, or by its myriads of organisms. In certain parts of the Indian Ocean the waters, as seen from a distance, are black. In the Mediterranean, in the Gulf Stream, and between the tropics generally, the sea waters are dark blue ; along the shores and near the mouths of great rivers and in coral seas they are green. Pho.sphoresceni' Sea I'lK iS^lloRESCKNTK / 5 Thus the sea assumes here and there various shades of color; yet its waters, when viewed by the tumblerful, are as clear as the purest crystal. Phosphorescence. — In most parts of the sea the water is phosphorescent. The phosphorescence is caused by certain minute living bodies which, like glowworms and fireflies on the land, have the power of emitting light, some in flashes, and some in a steady glow. These little creatures, invisible to the naked eye, are as multitudinous as the sands on the shore. In .\kctic IcK Breaking out of Etah. Peary expedition. From Bulletin of the Piiilarlelphia Geographical Society. In tropical seas and in certain waters they tip the waves with flame, and cover the sea after dark with sheets of light. As the ship plows these waters, she leaves a bright streak far behind in her wake. Though we cannot see the dolpliin and other fish, as they s]iort in the depths of these phosphorescent seas, yet, by the streaks they leave beliiiid. 74 THE S1£A AND THE OCEANS we can often track them through tlie water, as we do rockets t^hrough the air. As they chase each other in the mazes of their .sport, these threads of light are, to those who are fortunate enough to see them, among the most pleasing wonders of the deep. They are particularly beautiful in the liarbor of Callao. The Temperature of the Sea is in general highest near the surface. In the equatorial waters the average surface tempera- ture is about 80° F., sometimes rising in the Indian Ocean to 90°, and in the Red Sea to 94°. Toward the bottom the tempera- ture is depressed. Indeed, near the bottom all over the globe deep sea water seems to be about as cold as that of the polar seas. During the Arctic winter the sea is frozen to the depth of several feet, form- ing floe ice, through which, by the action of the tides, currents, and winds, temporary channels or leads are opened. Taking advantage of these water ways, the explorer or navigator urges his ship onward. Oftentimes, however, the channels are closed with prodigious force and his vessel nipped if not crashed. As a result of this ice movement barriers of broken or pack ice are formed which may reach the height of 100 feet. The Oceans. — The sea is one immense body of water encir- cling the globe. It is, however, divided by the intervening land masses, or continents, into smaller bodies, called occajis. Of these the Pacific is the largest. It contains more than half the water of the sea. Next in size, but only about half as large as the Pacific, is the Atlantic. The Indian is the third in area. The Arctic is properly only an extension of the Atlantic, while the Antarctic hardly deserves to be regarded as distinct from the main body of the sea. The form of each ocean basin depends upon the shape of the inclosing continents. The Pacific approaches the oval ; the Atlantic has been compared to a long- trough ; the Indian is triangular; while the polar oceans are very irregular. Of all the oceans the Atlantic is the most marked by inden- tations of its shores. The Asiatic edges of the Pacific and Indian oceans are also well supplied with bays and border seas. Depth of the Oceans. — Two questions comiected with the Util'TH OF 1 UK ( K IIANS 175 subject ot ocean basins have been made matter of accurate in\'estigati(>n — their depth and the configuration of their bottom. so 40 LONGITUDE 30 FROM 20 GREENWICH WEST EAST 10000 - a J ' ' a i 5 2 i ^ 3 f 5; =0 LABRADOR _^j ,, ^ R." ? £ 1 S' ||[|i|[|[|l[ll . ^M 1 1 s m ^^P :oooo iiliiiiiii^ 1^^ i 3^^^ \'K,KriC.\I. SKi riuN 1)1 1111 AllA.Nlli ( )* h.\-N Al 52 NiiKIII i,\lll,la on the riglit. upward movement of its waters. A mass of water moved in this way is called a wai'r. The elevated portion of the water is called the crcs/ ; the distance from one crest to another is the breadth ; the depression between two crests is called the trongJi. '79 i8o \VA\1.;S, IIDKS, AM) CLKI-IKMS The rolling in of waves upon the beach produces the impres- sion that the entire body of water is moving toward the land. As we shall see, however, when we come to consider the sub- ject of tides, it may actually be receding. We must, there- fore, distinguish between the motion of the waves and the motion of the water. If we produce a ripple upon the surface of water in a basin, bath, or pond, the ripple will travel from edge to edge of the water, and communicate an undulating or wave movement to each portion of the surface. But the water itself has no progressive movement. BKEAKKKS U.N THE SHORE Coionado Beach, California. Point Lomaon the right. From ]5hotograph l)y H. R. Fitcli. The action of a breeze upon a field of wheat, or tall grass, illustrates the matter very forcibly. The wind passes over the field, and each stalk and blade bends alternately down and up, thus forming depressions and wave crests. Yet there is no onward movement of the stalks. Those portions of the water, tiowever, which actually reach the shore, do possess an onward movement. Instead of being driven against an adjoining mass of water, they encounter the solid bottom. Thus the lower part of their mass is retarded, while the upper part moves onward, curls, and dashes as a dn^aker upon the beach. The Height of Waves depends mainly upon the force of the wind and the depth of the water. In general they are not more Tin; VELOCITY OF WAVE MOVEMENTS i8i than 8 or lo feet high. The highest known are those off the Cape of Good Hope, where they are said to attain the height of more than 40 feet. The bell of a lighthouse on one of the Scilly Islands, east of Lands End. was wrenched off by a breaker, at the height of 100 feet. The Velocity of Wave Movements depends ( i ) on the velocity and force of the wind ; and (2) upon the depth of the water and its freedom from obstructions. In the open sea the advance of \\'AVK Action on Partly Submerged Rocks, San Diego Couniy, California From photograph by H. R. Fitch. a wave movement is more rapid than in one obstructed with islands. The rate of ordinary wave travel is from 1 5 to upwards of 50 miles an hour. The wave movements of the ocean are incessant. Even where a perfect calm prevails, there is a ceaseless movement of the water, which, like a great pulse, keeps the surface constantly rising and falling. This heaving is commonly known as the ground swell of the ocean. Waves affect the surface chiefly. The highest waves in a storm have no appreciable effect in water more than a quarter 182 WAVES, TIDES, AND CURRENTS of a mile in depth. A wave 40 feet high and a quarter of a mile in breadth would not, in all probability, disturb the smallest grain of sand lying on the sea bed at a depth of 200 fathoms. Force and Work of the Waves. — The heaviest billows beat against the shore with enormous force. They undermine and level cliffs, they dash great rocks to pieces and grind the frag- ments into gravel and sand which, distributed along the shore, form the beach. Sand is the common beach material, though in \\A\ K A< riDN k\ 111' Aiii AMI. 1,\ JuLLA, San DiEi;o Cuuntv, Cali- fornia Note also the sandy beach in the foreground and the high surf in the center of the picture where the waves strike the submerged rocks. From photograph by H. R. Fitch. times of storm bowlders may be thrown up by the waves or broken down from cHffs and headlands. The shore has often been likened to a mill where the grinding of rocks into sand is a ceaseless operation. Under the influence of waves beaches may be extended into spits or points, and sand thrown up as barrier islands. The lat- ter are especially well illustrated by the long, narrow sand bar- riers of the Gulf coast of Texas. Under certain conditions waves also act as transporting agents. The presence of silicious sand on the lower coast of Florida, where the rocks are coralline limestone, is thus accounted for. lilt TIDES l8- The Tides are great vvavelike movements. They differ from wind waves, (i ) in their extent ; (2) in their regularity ; (3) in their cause. In a general way it may be said that two large waves, each having its crest and its depression, together encircle the globe from north to south. These two ceaselessly chase each other over the broad expanse of the sea, occasioning two elevations and two depressions of its waters in the course of about 25 hours.^ From the fact that these elevations and depressions occur with regularity about one hour later each day, and thus rudely mark the time, they are called tides, from the Anglo-Saxon tid, time. Pi!— 1 WM H ^^HBR^fflmn ^^^^^ir ^^^B ^""^ ^^BBbh HB^H^SiH^Hi^BB^^B h^B^H^^^IhB Wk ^^^^^^^H >^ \j^^^^B^H9H llllllg^WM hHH| ^^P^'' li ^^^B 98PBB jpTilJll jfiBMKtfL'i tfiff > n V l/vJiliil^r^Tr^ flilMftilh^ll^ ^^tt Bki ^^B ^m ^SBSi ^H^^HBH I^H^HB l^B^mMi Hi0^ ^S^^H^H mbm| ^^9 ^^HHn^nQwf fj 1 ■9HHHH liii^^ 1^^ ^IH SlKIN'. lll'l-- The elevation or rising of the water is called high ox flood tide ; its depression or falling, loiv or ebb tide. These occur alternately every six hours. Cause of Tides. — The tides are mainly due to the influence of the moon. The sun also has a tide-producing power, but it is insignificant compared to that of the moon, owing to the fact that. the sun is 400 times farther off. The moon is comparatively near the earth. Let us sec then how, in consequence of this, she affects its waters. The earth and moon may be regarded as two bodies revolving about a com- mon center of gravity c, which, owing to the greater mass of the earth, as compared with that of the moon, lies 1000 miles ^ The exact time is 24 hours 52 minutes, or what is known as a lunar clay, the time between the crossing of the meridian of a place by the moon and her appearance on the same meridian ngain. 1 84 WAVKS, TIDKS, AND CURRENTS within its circumference. The two bodies are exactly balanced at their centers, but the surface of the earth at B is 7000 miles from the common point about which the earth and moon revolve, in consequence of which there is developed a throwing off or centrifugal force, known to every schoolboy who has used a sHng or whirled a bucket of water over his head, which partly High Tide at Ostend, Belgium Ostend is noted us a pleasure resort, its Ijeach affording excellent opportunities for bathing. In front of the buildings is a protecting wall. The hill-like elevations at the right are dunes. overcomes the force of gravity and permits the outward bulging of the water in the form of a tidal wave. At A, however, in addition to the slight centrifugal tendency resulting from the movement about T, the tidal wave is generated by the direct attraction or pull of the moon. Halfway between the tidal wave crests or high tides, there are depressions, as represented in the illustration. These occur where the water is drawn away to form the high tides. CAl'SK OK 'IIDKS .85 They create the low tides. Like the high tides, they take place twice in a lunar day, at intervals of a little more than 12 hours. Evidence that the moon chietiy is concerned in causing the tides is found in the fact that high tide at any place occurs nearly at the time when the moon is over the meridian of that place. l\l>E Al (JSlt.Mi. IlKl.CII M The receding waters liave left a broad beach, now thronged with visitors. In ihe back- ground at the left, standing high above the water, is seen the landing pier. A marked phenomenon of the tides is that the intensity of the movement varies. Three days after full and new moon the flow or rise of the water is far greater than usual. This is explained by the fact that when the moon is new, as in the illustration on page 183, and when she is full, the sun and moon combine their tide-producing forces, forming what are known as "the spring tides. During these the flow is at its maximum. When, on the other hand, the moon is entering her second and her fourth i86 MOVKMENT OF IHE TIDAL WAV?: 1 87 quarters, the two forces do not act in harmony, and as a con- sequence the neap tides result, in which the height is much less than in the spring tides. Movement of the Tidal Wave. — Were it not for the interfer- ence of the continents and the variations in the depth of the sea, a tidal wave might be expected to follow the apparent course of the moon about the earth. Such a wave would then move from east to west with its crest extending in a north-and- south direction. The sea, however, is divided by the land into great oceanic basins of varying depths. By the continents the wave is deflected from its course, and according to the depth of the w^ater its velocity is increased or diminished, being accelerated in the deeper water and retarded in the shallower. The movement of the tidal wave is shown on a chart by means of cotidal lines which connect all places having high water at the same time. They therefore represent the crest of the tidal wave. Speed of Tidal Wave. — Since the tides follow the moon, they have to travel round the earth from east to west in the same time that she appears to revolve round it; namely, 24 hours and 52 minutes. The tidal wave, therefore, in equatorial seas, would, if it were unobstructed, and could pursue a direct course, travel at the rate of 1000 miles an hour. It must be borne in mind, liowever. that the water in miciocean has only an imperceptible progressive motion; it is the undulation, not the water, that travels at this high rate of speed. The waving grain, as it bends to the breeze, causes an undulation that travels across the field faster than you can run: but the stalks are rooted ; thev only sway backward and forward to the breeze. So it is with the deep sea and its swell. When, however, the tidal wave comes near the shores, where the water is shallow and confined, a change occurs. The un- dulation is retarded, but the motion of the water is vastly in- creased, and it sweeps as a current along the continental shores and up the bays and rivers. The current gains in speed as the tidal wave loses, i88 WAVES, TIDES, AND CURRENTS fi« ^u. .&J \\ Is *L Ari.AiNTic CoAsr Timcii Mean height, in feet. The current often attains unusual speed in passing headlands, and then the term race is commonly applied to it. Such an accelerated current moves from six to eleven miles an hour. Height of Tides. — In the middle of the Pacific Ocean the rise of the tide is sometimes less than a foot ; in the Atlantic, near Saint Helena, about three feet. On the other hand, be- tween the converging shores of narrow seas and bays the water is sometimes heaped up to the height of from 25 to 40, and, in the Bay of Fundy, from 50 to 60 feet. The Mediterranean and the Red seas, how- ever, with their narrow entrances, almost cut off the tidal wave, so that in both the ebb and flow are very slight. The greatest rise in the Mediterranean is about 1.2 feet. This seldom occurs. In the Caribbean Sea and Gulf of Mexico, likewise, the tides are rarely three feet. high, owing probably to the fact that these sheets ot" water are protected from the tidal wave l)y the West Indies. Very great differences exist be- tween the tides at various points of the same coast. On the shores of Florida the rise is not more than about three feet. It increases as we go northward, until we reach the Bay of Fundy, where it attains its maximum. At some points on the shores of Great Britain there are tides of great height and strength, while at others riDKS ()!■ RIVERS; BORES 1 89 close by, the rise and fall are barely perceptible. The rise and fall at Liverpool are 28 feet; in the ^Bristol Channel, 40 feet; at Wicklow, on the opposite Irish coast, only 2 or 3. To account for these differences various causes may be sug- gested : the form of the bottom, the projection of headlands, the narrowing of channels along which the tidal current is forced, and the position of those channels with reference to the direction of the tidal wave. A glance at the map shows, for example, that were the tidal wave propagated from the northeast instead of the southwest, the Bay of Fundy would cease to have remarkably high tides. The peculiarities of a sliore are sometimes such as to cause a complete sundering, or division of tlie tidal waters. Two currents are tluis formed. In some cases these meet again after their division and give rise to a 2(j/iirl- pool. Charybdis in the Straits of Messina, and the Maelstrom among the Lotbden Isles, are illustrations of this phenomenon. Tides of Rivers ; Bores. — The tides of some rivers present interesting peculiarities. They enter certain river channels with extraordinary velocity. People crossing the dry bed of the river Dee, in England, are sometimes overtaken and drowned by the inrushing water. The case of the Amazon is of special interest. The tides ascend tliis river to a greater distance from tixe sea than in any other river of the world. They are felt 700 miles up slrea.r • and the sin- gular phenomenon is presented of there being several tides in the river at the same time ; for before the flood of one has reached the end of its 700 miles' journey, several other tidal waves, each in succession bringing high tide with it, have had time to enter. A tidal wave of great height sometimes enters the mouth of a river and ascends its channel as a perpendicular wall of water. Such a tidal wave is known as a bore. Among the most remark- able are those of the Hugli at Calcutta, the Garonne in France, the Tsien-tang in China, and the Amazon. At certain times bores 12 to 15 feet high come rushing into the channel of the Amazon on the top of the tide. Sometimes as many as five, 30 or 40 c^.;>f. -^ su|^ace;guri __i . , 1 laO Longitude 20 West 'M from GO Greenwich 30 (190) (19") 192 WAVES, TIDES, AND CURRENTS miles apart, dash up the river, capsizing small craft as they go and spreading consternation among the watermen. The bore of the Tsien-tang is even greater than that of the Amazon. It spans the river with a feather-white and roaring wall of water. 20 feet high, and travels at the rate of eight miles an hour. The Currents of the Sea. — There are rivers in the sea. They are of such magnitude that the mightiest streams of the land are rivulets compared to them. They are either of warm or cold water, while their banks and beds are water of the oppo- site temperature. Fo-r thousands of miles they move through their liquid channels unmixed with the confining waters. These movements are called currents. The mariner can sometimes detect them by the different color of their stream, while, if they give no such visible sign of their existence, he can trace them by testing their temperature with his thermometer. Classification and Course of Currents. — The chart on pages 190, 191, exhibits a general view of the horizontal currents. ( 1 ) There is an Equatorial Current sweeping from east to west on each side of the equator, and well-nigh encircling the globe ; (2) There is a slight eastward Counter Current not far from the equator ; (3) There are Polar Currents setting from the polar regions toward the equator ; (4) There are Return Currents setting from the equator toward the poles. The chart also shows that as in the case of the tidal wave, so in the case of oceanic currents, the shores of continents and islands have marked effect in modifying their normal courses. These are also modified by the rotation of the earth. If two trains are moving on parallel tracks in the same direction and with the same speed, an object thrown or a ball shot "point blank" from one to the other inay strike the point aimed at. But if the train from which the ball is shot be going 35 miles an hour, and the other only 15, the ball from the first will strike in advance of the point aimed at. If the direction of the trains CLKKKMS (^F 11IL-; A 11. Wilt" 193 be eastward, then the ball will strike a certain flislann- to the east of tiie point aimed at. This is what occurs when water starts from the eqiuUoi toward the poles. It rotates toward the east at the speed of 1000 miles an hour. Passing to either pole, therefore, it has a hi Off Cape Horn it divides. One branch pa.sses into the Atlantic ; J CI RK I. NTS OK TFIK INDIAN OCEAN I97 the other, the Hionbouit or Peruvian Currefit, enters the Pacific. The Humboldt Current carries its cool Antarctic waters all aloni;- the west coast of South America from Patagonia to the (ialapagos Islands. These waters, when they touch the equator, are still too cold for the growth of the coral polyp. Hence the whole western coast of South America is without coral reefs or coral foruiation of any kind ; though in the same latitudes, at a distance from the coast, where the waters are warm, coral thrives in the greatest abundance. Near and at the equator the Humboldt Current is deflected to the westward and becomes part of the Equatorial Current of the Pacific. Currents of the Indian Ocean. — The Indian Ocean has no such well-defined system of currents as the Atlantic and Pacific. North of the equator the direction of the flow is determined by the monsoons. South of the equator an Equatorial Current, emerging from the East Indian Archipelago, sweeps to the westward. Reaching Madagascar, it branches. The eastern fork passes to the southward and merges with the Antarctic Drift. The western flows along the eastern coast of Africa as the Mozambique Current. Leaving the Mozambique Channel, it becomes the Agullias Current, and south of the Cape blends with the Antarctic waters. A brancli of the Antarctic Drift, setting to the northwestward, and becom- ing the West Australian Current, pours its icy flow into the Indian Ocean. Causes of Oceanic Circulation. — The chief causes of oceanic circulation are to be found in the winds which, brushing the sur- face of the water, give ri.se to superficial currents. These, fol- lowing the direction of the prevailing winds, are further modified by the shape of the land masses. In this manner there arc formed in the sea five great eddies, those of the northern hemi- sphere moving in a clockwise direction ; those of the southern hemisphere in a counter-clockwise direction. The trade winds blowing incessantly to the westward, and meeting over the equatorial regions, impart to the waters be- 198 WAVES, TIDKS, AND CURRENTS neath them a gentle but continuous westerly movement, hence the Equatorial Current, while farther to the north and to the south, under the influence of the prevailing westerly winds, the currents bear to the eastward. In those parts of the Indian Ocean that are within the mon- soon district the currents are controlled by the monsoon winds. For six months they flow in one direction, for six months in the other. Some winds produce irregular currents. Such effects have been observed upon rivers, ponds, or canals, in piling up the water on one side or at one end, and by blowing it away from the other. In great storms at sea the winds may drive the water before them and pile it up above its usual level. It has been held that oceanic circulation is largely due to differences in the specific gravity ^ of the waters in various parts of the sea. That it does exert some influence seems probable, especially in the interchange of water between the equatorial and polar regions. Sea water when heated expands. A given volume of such heated water, if it contain the same proportion of salts as an equal volume of colder salt water, will weigh less. On the other hand, when sea water is chilled, it contracts and becomes heavier. The surface temperature of sea water in polar seas is about 35° F; in equatorial, about 80°. This difference of temperature is permanent, and sufficient to produce a marked variation in the sj^ecific gravity of the water in the two regions. Wherever the waters in one part of the sea differ in specific gravity from the waters in another part, no matter, from what cause the difference may arise, or how great may be the distance between two such parts of the sea, the heavier water will flow, ' Two bodies arc said to differ in specilic gravity when equal volumes of the two differ in weight. A gallon of salt water, for example, weighs more than a gallon of freshwater. A jiint of water weighs about a pound; a pint of quicksilver weighs about thirteen pounds. ^ .. SAKCiASSU SEAS 1 99 by the shortest and easiest route, toward the lighter ; and the lighter, in its turn, will seek the place whence the heavier came. Sargasso Seas. — An interesting evidence of the circulation of the oceanic waters is to be found in what are known as Sar- gasso Seas, so-called from sarga::o, the Spanish name for sea- weed. These are vast collections of drifting seaweed, which gather in those portions of the different oceans which are most free from the influence of currents. If bits of cork or chips, or any floating substance, be put into a basin, and a circular motion be given to the water, all the light substances will be found crowding together near the center of the pool where there is the least motion. Like such a basin is the Atlantic Ocean, with its Equatorial Current and its Gulf Stream. The Sargasso Sea is at the center of the whirl. The Sargasso Sea of tlie Atlantic embraces an area of several hundred thousand square miles : and though tiie weeds are all afloat and held by noth- ing, yet the Sargasso remains where it was over 400 years ago, when Columbus passed through it on his first voyage to America. During Maury's researches connected with the " Physical Geography of the Sea," the existence of four other Sargassos was established : namely, one in the Indian Ocean, two in the Pacific, and another in the Atlantic. (See Chart, pp. 190. 191.) PART IV. — THE ATMOSPHERE XVIII. PHYSICAL PROPERTIES OF THE ATMOS- PHERE The Composition of the Atmosphere. — Wherever we go on the surface of the earth we perceive that air is present. If we ascend above the mountain tops, or pierce the loftiest clouds, it is still with us. It envelops the earth. The entire mass of the air is commonly spoken of as the atmosphere. It is transparent, and, unlike water, is a mixture of gases and not a chemical compound. Its chief ingredients are oxygen and nitrogen. These elements are present in the pro- portion of 21 parts by weight of the former to 79 parts by weight of the latter, or approximately i to 4. In addition there are also present in the air carbon dioxide in small amount, and in lesser degree the rarer gases argon, krypton, and helium. F"urthermore, ordinary air contains water vapor and dust in vary- ing amounts as a result of its interaction with the hydrosphere and the lithosphere. Not only does oxygen form a part of the atmosphere, hut chemically combined with hydrogen it forms watw. and in combination with several other elements such as silicon, carbon, calcium, and aluminum constitutes the outer portion of the lithosphere. O.xygen is, therefore, the most widely distributed of all the chemical elements. It is, moreover, the vivifying agent of the atmosphere, being essential to the existence of living things. Nitrogen, of which the atmosphere is largely composed, is to the chemist •' inert" ; that is, it does not combine strongly with other elements. In this particular it is the opposite of oxygen and consequently does not enter con- spicuously into the formation of the earth's crust. Its function in the atmos- phere seems to be largely that of a diluting agent, thus preventing the Xuo great activity of the oxygen. Carbon dioxide, though normally present in the atmosphere in a small 200 ORIGIN OF Till-: ATMOSI'HKRK 20I amount, is essential to plant life. It is exhaled by most forms of animal life and is at times generated in great abundance in volcanic regions, especiallv where vulcanicity is dying out. in large amount carbon dioxide is suffocating rather than poisonous, cutting otf the supply of oxvgen which is essential to life. Invisible water vapor is another substance found in greater or less quantitv in the atmosphere. It results from evaporation, and is one of the forms assumed by water in its circulation. When chilled, this vapor collects in the form of minute drops, forming clouds, and upon further cooling, may be ]Meci])itated as rain. hail, or snow. Dust is one of the most common impurities of the atmosphere ; and although usually confined to the layers over the land surfaces, it is in some instances, as after certain volcanic eruptions of the explosive type, wafted for long distances in the upper regions of air and even far over the sea. Furtliermore. it mav be held in meclianical suspension, if sufficiently fine, for a long period — it mav' be several moiitlis. A heavy rainfall cleanses the atmosphere by washing the mechanically suspended particles from it, hence in arid and semiarid regions the air is more heavily charged with dust than elsewhere. Dust, it will be seen, is to the atmosphere what sediment is to water. The agitation of the wind pollutes the air with dust just as the stirring of the bottom of a pond pollutes the water with mud. From what has laeen stated it is obvious that the atmosphere over the sea is freest from contamination by solid matter. A microscopic examination of dust deposited from the atmosphere shows it to be composed of a great variety of substances, both mineral and organic, including certain disease- bearing germs. Origin of the Atmosphere. — If the earth onVinated in the nuinner set forth by the nebular theory, we can readily conceive that in its early stages, on account of the prevail- ing high temperatures, much matter now in the form of solids and liquids was in a vaporous or gaseous state, and that, as a result of such condition, many substances were included in the atmosphere which are not now present. It may be conceived further that by chemical combination and by condensation from cooHng — processes continued through a long period of time — the atmosphere would become much reduced in volume and, at the same time, simpler in composition. It is especially noteworthy that, according to this view, the primitive atmos- phere must have contained within its body the elements of the 202 PHYSICAL PROPERTIES OF THE ATMOSPHERE primeval sea, or the first hydrosphere, which came into exist- ence as a condensation from it. On the other hand, it is held by the advocates of the planetesimal hypothesis that " the substances of the atmosphere and ocean were originally a part of the planetesimals and helped to form the earth's mass," and that they were subsequently forced to the surface by the compression due to gravity and the heat involved in that process. Weight of the Air or At- mospheric Pressure. — Though a gaseous body, the atmosphere is influenced by gravity. Air, therefore, has weight, from which follows atmospheric pressure. The famous Galileo was the first to point this out. A pump maker wished to know from him .why a pump would not raise water from a well which was more than 32 feet deep. Galileo concluded that it was because a column of water 32 feet high is as much as the weight of the air can balance. Everywhere upon land and sea this pressure is felt. If the atmosphere were undisturbed and of the same density through- out, or if it were of a uniformly decreasing density, we might expect it to exert upon all points at the sea level the same pressure. And this it practically does, notwithstanding the fact that it is a medium subject to numerous and, at times, sudden disturbances which do not fail to manifest themselves TOKKICKI.I.I'S liXPKklMKM' THE MERCURIAL BAROMKIER in pressure variations. The average atmospheric pressure at the sea level is 14.74 pounds (for con- venience usually stated 15 pounds) to the square inch of surface, a pressure exceeding a ton to the square foot. The Mercurial Barometer. — This is an instru- ment used for measuring atmospheric pressure. Its construction is based upon a well-known ex- periment of Torricelli, a celebrated pupil of Galileo. He filled a tube, about three feet in length, with mercury. He then carefully inverted the tube, covering its open end with his thumb, until in- serted in a vessel of mercury. When released the mercury fell until it was about 30 inches in height. This column was sustained by the weight of the air. In Green's Standard Barometer, here shown, the glass tube containing the mercurial column is, for protection, inclosed in a brass case. To the upper end of the case is attached a ring (A) for the sus- pension of the instrument ; to the lower end is appended, by means of a flange ( /: ), the cistern. Through a slot (B) in the case the top of the mer- curial column may be seen (obscured in the figure by the vernier which moves in the slot) and its height determined by a scale graduated in inches and tenths of inches. For convenience and more accurate reading the scale is provided with a vernier moved by a milled head (C). As mercury is affected by heat, the reading of the instrument must be corrected for various temperatures, hence a thermometer (D) is attached to the case. The cistern consists of an upper portion in the form of a glass cylinder through which the surface of the mercury and the lower end of the barometric tube may be seen. The lower portion of the reservoir, also protected by a brass case, consists of a wooden 204 PHYSICAL PROPERTIES OF THE ATMOSPHERE receptacle terminated with a kid bag which forms the bottom of the mercury-containing vessel. At the lower extremity of the cistern case there is an adjusting screw, worked by a milled head (F), the upper end of which presses against a button at- tached to the kid bag. When the button is pressed up, the capacity of the cistern is diminished ; when it is withdrawn, the capacity is increased. To use the barometer the adjusting screw should be raised or lowered until the surface of the mercury just touches the end of the ivory peg (*), which establishes the zero point of the scale. Variations in Atmospheric Pressure. — Variations in atmo.s- pheric pressure are occasioned by changes of level and by changes in the weight of the air. ( 1 ) Effect of CJiangc of Level. — In ascending a mountain, the explorer passes through a certain proportion of the atmosphere, and is, of course, relieved from a portion of its pressure. For the first 10,000 feet of ascent the barometer falls 10 inches — an average of one inch to every 1000 feet of ascent. For the second 10,000 feet the barometer would fall about 6.7 inches, the amount of its fall constantly decreasing as he ascends. Mr. Glaisher in his balloon reached a height of 37,000 feet, and then the barometer went down to seven inches. The lowest reading of the barometer ever observed upon a mountain was 13.3 inches, at an elevation of 22,079 ^^et, on the summit of Ibi-Gamin, in Tibet. It is easy to see that the amount of fall furnishes a means of measuring heights of moun- tains, and altitudes to which balloons ascend. An interesting consequence arising from tlie \veigl>t of the atmosphere is the fact that the l)oiling point is lowered at high elevations. At about the level of the sea, water boils at 212^ F. At Quitt). i i.ooo feet high, the boiling point is 194°. On the top of Mont Blanc, nearly 16,000 feet high, it is 180". This results from the diminished pressure to which water is subjected at great elevations. It has the inconvenient effect of making it impossible in such situitions to cook i^y boiling. (2) Effect of Change in Weight of the Atmosphere. — A fall of barometer occurs, also, when the column of air above any area be- i'i<(ii:Ai;i.i: iii.K.iir m iiii \i .\u,)sriiKkK 205 comes lii;"htcr than usual. This takes place when there is more than the ordinary aim)unt of vapor in the air; because vapor is lighter than dry air. Consequently, the greater the projM^rtion of vapor in the air, the lighter that air will be. A Ion.' barometer therefore usually indicates a moist, rainy atmosphere. A high baroDteter indicates that the atmosphere is heavy ; either because it is dry or because it is dense. The density, or compactness, of the air of course diminishes with the height. On lofty mountains it is highly rarefied, which means that its particles, being relieved from pressure, are more widely separated from one another than at lower levels. Persons a.scendin,i( to great elevations sometimes experience a singular (lifficultv. The walls of the blood vessels burst, and there is a flow of l)lood from the nose and ears. This iiuil de iiiontai^m\ ov ///<>// ///n/// snA'/ii'ss. as, the French call it. is seldom feh at a lower level than 16.000 feet, and balloon ascents have been made to a height of 29.000 feet before any serious inconvenience has arisen from this cau.se. Lines drawn through places whicli have the same barometric pressure at any gi\en time are called /si>/>(irs. from tlie Greek I'sos. equal, and /xrros. weight. Probable Height of the Atmosphere. — The height of the atmos- phere has not yet been definitely determined. Calculations based upon the decrease of atmospheric pressure for increase of altitude seem to indicate that at the height of about 50 miles the air would become too light to affect the barometer appreciably. This would apparently fix the outer atmospheric limit. On the other hand, there is reason for thinking that the atmosphere has a height much exceeding 50 miles. It is believed that meteors be- come visible only after entering the atmosphere. Observations made upon the same meteor from different points afford data for the calculation of its height. But since the meteor is luminous, this height must represent a distance within the atmosphere. From calculations of this character it is now thought that the atmosphere may even exceed 100 miles in height. While in its outer layers the atmosphere must exist in an extremely rare- fied state, there is the possibility that some of its rarer elements may exceed the greater limit given above. 206 PHYSICAL PROPERTIES Ol- THE ATMOSPHERE Atmospheric Temperature. — The process by which the air is warmed is complicated and for that reason can be best understood by the separate consideration of each step. (i) A portion of the radiant heat emitted by the sun is inter- cepted by the earth. In its passage through the atmosphere a part of this heat is absorbed, thus increasing the tcvipcraturc of that body. (2) The layer of air resting directly upon the terrestrial areas, which have become heated by the impingement of radiant heat, are warmed by contact with the heated surfaces (conduction). (3) The lowest stratum of air, thus warmed and expanded, is crowded from its position and borne upward by the settling of the cooler, and therefore heavier, air. In this manner currents are established (convection) which circulate to a limited height; that is, until the warm ascending air is cooled to the temperature of the air above it. (4) Of the radiant heat falling upon the water areas a large part is reflected, and passing outward through the atmosphere again contributes to its warming by partial absorption. This also may become a source of atmospheric movement. ( 5 ) On the other hand, while the land areas are poor reflectors, they emit radiant heat from which, as it passes outward, the air exacts a contribution. (6) In the heating of the lower atmosphere the absorption of radiant energy by the dust particles plays an important part. As they become heated, they in turn heat the air that surrounds them. (7) Another .source of atmospheric heat which must be taken into consideration is the absorption of heat radiated from the earth by watery vapor. In this particular watery vapor is said to be more efficient than any other atmospheric ingredient. Clouds act as a protective covering, thus preventing the too rapid cooling of the lower atmospheric layers and the disas- trous results that would arise from it. Temperature of the Air as affected by Night. — It is during the day that the heat effects of solar energy are most pronounced. SEASONAL VARIATION IN TEMFERATURE 20/ At night the heated land surfaces are cooled by radiation, for like other good absorbers, they readily part with their heat, which radiated outward into the air serves in part to prevent its too rapid cooling. As the land cools, the adjacent air also cools by radiation to it, and the layer resting directly upon the ground is further cooled by contact (conduction). This is well illustrated during the winter season when the warming of the ground in the daytime is not sufficient to prevent its freezing at night. Then the air in contact with the frozen surface is itself reduced in temperature. Water, on the contrary, is a good reflector of solar heat, a poor absorber, and likewise a poor radiator. The little warming that takes place on the surface of the oceanic areas is not readily lost by radiation, in consequence of which there is not the reduction of temperature at night noticed on land surfaces, nor is the air in contact with the water so thoroughly chilled by conduction. Hence it follows that the range of atmospheric temperature over the water is not so great as over the land. Seasonal Variation in Temperature. — The temperature of the air nearest the earth also varies with the season, being warmer in summer and cooler in winter than in either spring or autumn. ^" The amount of radiant heat received by any portion of the earth's surface depends upon the directness of the solar rays. When they fall vertically they give rise to the greatest heat effects ; as their inclination increases these effects diminish. At the time of the vernal equinox the direct rays fall upon the equator. As spring merges with the northern summer the direct or vertical rays fall upon portions of the earth's surface succes- sively nearer to the Tropic of Cancer until at midsummer xjune 21) their northern limit is reached, after which, as has been already explained (see p. 27), their recession southward begins. \ During this season the heat received by the earth is furthermore increased by the long exposure due to the lengthened days. In the meantime the amount of heat lost by radiation during the night is greatly diminished, owing to the shortness of that inter- 208 PHYSICAL I'ROPERriES OF THE ATMOSPHERE val. Thus the surface warms to summer temperature. Under these conditions, without diminishing the importance of other processes, special emphasis must be placed upon the heating of the lower atmospheric layers by their contact with the heated land areas. Although midsummer is June 21, the highest temperatures are usually experienced some weeks later. This is due to the fact that the earth, warmed in excess of its radiation, is still receiving radiant heat. As the season advances, however, on account of the increased inclination of the solar rays and the shortening of the days, high temperatures cannot be maintained, hence the earth becomes cooler. This and the attendant phenomena serve also to reduce the temperature of the air. In the winter season the radiation from the earth is in excess of the warming due to the sun's energy. The earth now becomes chilled, and as a consequence the temperature of the air in con- tact with it is likewise lowered. Just as the heat of summer comes later than midsummer, so the cold of winter comes later by a few weeks than midwinter (December 22). Instruments used for Measuring Temperature. — The instru- ments used for measuring the hotness or temperature of the air, as well as that of other bodies, are termed tJicnnonieters. The ordinary forms are based upon the expansion and contraction of liquids when influenced by heat or cold. Practically the liquids employed are limited to mercury and alcohol — to the former on account of its high boiling point and to the latter on account of its low freezing point. In the less common metallic ther- mometers the measurement is made through the unequal expan- sion of thin strips of different metals, and in one instrument, at least, through a combination of the expansion of a liquid and the elasticity of a metal. Tlie mercurial thermometer is that in common use. It consists of a capil- lary glass tube having at one end a bulb or reservoir. In the process of manu- facture both the bulb and the tube are filled with mercury which is heated to the boiling point. The tube is then .sealed When cooled the mercury wiU settle, filling the l)ull) and a part of the tube. IXSTKUMEXTS USED VOR MtASL'klXLi I K.Ml'KK.Vl I Ki: 209 The methods of graduating the mercurial thermometer or making t\.e saile 1)\ which it is to be read, are as follows : Two points are selected as standards — the freezing point and the boiling point of distilled water, the latter under the pressure of one atmosphere, for the boiling point varies according to atmospheric pressure. These standards have been selected, as they can be easily established on any thermometer. According to the Fahrenheit scale (marked F. or Fahr. on the thermometer) the freezing point has been arl)itrarilv placed at 32^ and the boiling at 212 . from which it follows that iSoMntervene between the two standard points. .According to tlie Centigrade scale (marked C. on the thermometer), which is simpler, tiie freezing point has been placed at 0° and the boiling point at 100". The degrees of this scale, it will be seen, are larger than those of the preceding, the relation being 100 to 180. These are the scales in common use. and they may be either stamped upon the ther- mometer case or etched upon the glass tul^e. The latter plan is preferable and is pursued in graduating the best instruments. Cheap thermometers are useful in a general way, but accurate readings should not be expected from them. Furthermore, if trustworthy results are to be obtained, the thermometer must be properly located. It should never be placed where the air will be influenced by any warming body, and especially should it be protected from the direct rays of the sun. If possible, it ought to be hung in a shelter, raised above the ground, and placed apart from buildings, so constructed as to permit the ready cir- culation of the air. When this cannot be done, the shelter may be built out from the north window of a building, if in other respects the location is desirable. XIX. CLIMATE Weather and Climate. — The atmospheric conditions prevail- ing at a place during a given time — a day, a month, or even a year — constitute its ivcatJier. Within this term are included various elements ordinarily perceptible to the senses, such as temperature, moisture or dryness, clearness or cloudiness, the presence or absence of wind. Climate is more comprehensive, as it includes " an aggregate of weather conditions " based upon observations extending over a series of years. The longer the periods of observation, the more valuable become the data upon which climate is established. The chief elements of climate are temperature and moisture, of which the more important is temperature. The principal causes which modify temperature are, distance from the equator; distance from the sea; prevailing winds and ocean currents ; and height above the sea level. Distance from the Equator. — The first and most apparent cause of the differences in climate is the distance from the equator. This has two effects: As the distance increases, (i) the average annual temperature falls; and (2) there are greater contrasts between summer heat and winter cold. As the area within the tropics receives the vertical rays of the sun, it is the region of the greatest heat. Between the tropics and the polar circles the sun's rays fall obliquely and therefore e.xert a feebler power. Within the polar circles the inclination of the sun's rays is greatest, hence, except during a brief period of a few weeks, excessive cold prevails. The contrasts between summer heat and winter cold are mainly due to variations in the length of the day, and these depend on distance from the equator. Within the tropics there DISTANCE FROM THE SEA 211 is comparatively little difference between the two periods of day and night through the year. Only twice in the year, at the equinoxes, are they equal for other parts of the globe. As the sun passes northward from the equator, the day lengthens over the northern hemisphere, until, within the Arctic circle, the sun does not set at midsummer. The same phenome- non occurs in the southern hemisphere, after the sun passes southward of the equator. Since there is very little difference between day and night at the equator, the temperature within the tropics is nearly uni- form throughout the year. North and south of the tropics there are important differences between day and night, in consequence of which climatic con- trasts are found in all regions outside of the tropics. Within the polar circles these contrasts are at their maxi- mum. The Arctic summer, strange to say, is exceedingly warm. It is marked by a rapidity of plant growth that is marvelous. In a few weeks crops mature which require twice that length of time in latitudes much nearer the equator. But, on the other hand, the winter cold is correspondingly excessive. Distance from the Sea. — In certain countries climate is affected more by distance from the sea than by distance from the equator. The climate of a region adjacent to the sea is called an insular or maritime climate. The climate of a region remote from the sea is called an inland or continental climate. Certain causes moderate insular climates. (i) Water absorbs heat much more slowly than the land, and therefore remains, in hot weather, comparatively cooler. Hence the summer temperature of a country bordering on the sea is lowered. (2) On the other hand, water parts with its heat by radiation much more slowly than the land, and therefore remains in cold weather comparatively warmer. Hence the winter of a mari- time country is moderated. (3) Vapor is incessantly rising from the sea, and, being con- M.-S. PHYS. GEOG. — 1 3 212 CLIMATE densed, falls as rain or snow upon the land, and this liberates latent heat. (4) The vapor in the atmosphere of a maritime climate pre- vents the escape of heat. It acts as a blanket. A familiar illustration of this is the fact that frost rarely occurs on cloudy nights, (5) Again, the process of evaporation goes on more rapidly in hot weather than in cold, and this has the effect of moderat- ing the summer heat of a maritime country. For the above reasons, insular or maritime climates are equable, or free from extremes. Inland or continental climates are the opposite of maritime. They are subject to great extremes, intense heat in summer and excessive cold in winter. Two reasons may be assigned for this : — ( 1 ) Countries far from the sea are without its cooling influence upon their summer heat, and they have no reservoir of warmth to compensate for their rapid radiation of heat in winter. The continent of Asia affords the most striking instances of the excessive character of inland climates. The Russian army advancing toward Khiva in 1839-40 experienced vicissitudes of temperature from a heat of over 100^ F. to a cold of 45° below zero. At Werchojansk, eastern Siberia, the culminating point of excessive climate in all the world is reached. The extreme temperature of 90.4° below zero has been observed there. The soil is permanently frozen to the depth of 380 feet. In the month of June the Lena is free from ice; the surface soil has thawed for three or four feet ; and the warmth of the short summer is such that grain will ripen in the shallow stratum of soil above the frozen mass. The mean temperature of July at Yakutsk is 69°, the same as at Paris. (2) The comparative dryness of the air of an inland region contributes to create extremes. This is strikingly illustrated by the climate of the Sahara. The air there is perfectly dry. No vapor hinders the reception of heat by day or its loss by night. Travelers who have suffered from intense heat during the day have found the water in their canteens frozen before morning. Prevailing Winds and Ocean Currents. — The climate of a country is also greatly modified by the prevailing winds and the HEIGHT ABOVE THE SEA LEVEL 213 neighboring ocean currents. If the prevailing winds come from the sea, they temper the extremes of heat and cold. If a cold current bathes any portion of the shore, it lowers the tempera- ture ; a warm current raises it. The British Isles and the province of Labrador are the same distance from the equator, and in many parts the same height above the sea. Yet such is the difference of climate between them, that Labrador is covered with snow for nine or ten months every year, and is so cold as to be almost uninhabitable ; while in England the ground is rarely covered with snow, and the pastures are green all the winter. Both countries are in the regions of westerly winds ; but in Labrador they come from the land, and are dry and cold ; in England they come from the sea, and are laden with moisture and warmth. The shores of Labrador are washed by a cold Arctic current ; those of Great Britain by the w^arm waters of the Gulf Stream and Atlantic Drift. The climates of western Europe, from North Cape to the Strait of Gibraltar, are modified by the sea winds and the in- fluence of the Drift. Norway stretches beyond the 70th degree of north latitude ; yet the west- erly winds are so richly laden with warmth and moisture from the waters of the Drift that the harbor of Hammerfest. latitude 70^^40', is never frozen, even in the severest winters. But cross the Scandinavian mountains, and there is encountered at once, if it be winter, the severest cold. In this short distance ' from the warm waters and the west winds of the Atlantic, the Russian lakes and rivers, the gulfs and bays of the Baltic, are found closed to navigation every year from November till May. Climatic conditions similar to those which affect the western shores of Europe are found upon the western slopes of Oregon, British Columbia, and Alaska. Westerly winds prevail, and they are laden with moisture from the Pacific Ocean. The result is that here, as in Norway, open harbors and evergreen hills are found in the high latitudes of Alaska and other parts of our northwest coast. Height above the Sea Level. — Among other circumstances, climate depends upon heii^ht above the sea. A change of ele- 160 180 160 140 120 100 160 180 160 110 120 100 80 60 10 ("4) 20 40 t>0 au 100 liO 110 IGO CO 80 lUO 120 IIU 160 C2I5) 2l6 CLIMAIE vation of a few thousand feet at the equator produces a change of temperature as great as would be experienced in sailing 6000 miles to the frozen regions of the poles. The island of Cuba and the Mexican mountain of Orizaba are in the same latitude. The summit of the mountain is cov- ered with snow all the year ; the island with fruits, flowers, and evergreens. The reason why elevation above the sea level causes reduc- tion of temperature is that the radiation of heat goes on from elevated parts of the earth's surface more freely than from its lower portions. Two causes may be assigned for this : (i) ele- vations are comparatively small, and therefore have a smaller store of heat; (2) the air and vapor upon elevations are rare- fied, and hence little hindrance to radiation is presented. The general rule as to the effect of elevation is this : for every one hundred yards of perpendicular ascent there is a decrease of one degree in the temperature; so that, even at the equator, by ascending to the height of about 16,000 feet above the sea, one may reach the snow line. Isothermal Lines. — From thermometric observations made in all parts of the world, the actual distribution of temperature over the globe has been ascertained. To show this, Humboldt constructed a series of lines called isotJiernis, or lines of equal heat. These are drawn round the globe so as to connect all places which have the same mean temperature during the year or any given part of the year. ^\ Isothermal lines are far from coinciding with the parallels of latitude. Let us take by way of illustration the line in the northern hemisphere indicating the mean annual temperature of 50°. (See chart, pp. 214, 215.) It passes through Oregon on the Pacific shores, and leaves the Atlantic coast between New York and New Haven. It bends northward in crossing the Atlantic, and in Europe passes near Liverpool, Vienna, and Odessa, and in Asia, near Pekin. The summer isotherms cross Great Britain as east-and-west h'nes. The winter isotherms are nearly north-and-south Hnes. ZONES OF TEMPERATURE 21 7 We are not to conclude, however, that because the same isothermal line passes through two places, they have a climate identically the same. Of two such places one may have an extremely hot summer and a correspondingly cold winter. The other may have a climate free from extremes. Yet both may have the same average yearly temperature. San Francisco and Washington have the same mean annual temperature, while their climates differ greatly. Again, the same isothermal line passes through New York and Dul)lin. Yet the climates of these places have no resemblance. The mean winter temperature of Dublin is 6' above that of New York ; while the summers of the two places are so unlike, that whereas grapes and Indian corn are successfully cultivated in the vicinity of New York, they will not ripen in tiie open air at Dublin. Zones of Temperature. — By means of isotherms we define the zones of temperature. They are indicated by the colors on the chart. The true Torrid Zone is bounded by the iso- therms of 70° on either side of the equator. The true Tem- perate Zones extend from the isotherms of 70° to those of 32° ; the Frigid Zones from these to the poles. XX. ATMOSPHERIC CIRCULATION Winds. — A body of air in motion is called a wind. The rate of motion and the direction of winds vary greatly. By means of an instrument called the anemometer, it has been as- certained that the velocity of a light wind is 5 miles an hour ; of a stiff breeze, 25 miles; of a storm, 50 miles ; and of a hurricane, 80 to 100 miles, or even 100 to 150 miles. Again, the direction in which winds blow is so con- stantly changing that they are often spoken of as fickle, inconstant, and uncertain. There is, however, order in the movements of the atmos- phere. The fickle winds are obedient to laws. There are causes that make them blow with greater or less rapidity ; there are reasons why they blow now north or south, now east or west. Winds are named according to the quarter from which they blow. A west wind comes from the west; an east wind from the east. Anemometer This instrument, which is used for determin- ing the velocity of the wind, is placed in an unobstructed, elevated position, as above the roof of a high building. It consists of four hollow hemispherical cups mounted vertically on arms which are attached to a vertical axis. The lower portion of this axis communicates the motion of the rotating cups, by means of an endless screw, to a series of dials which register the number of revolutions. Cause of Winds. — The chief cause of winds is the unequal distribution of heat in the atmos- phere. The underlying principle is illustrated by the following examples, 218 GENERAL CIRCULATIOX OF THE ATMOSPHERE 219 If a fire is lighted on the hearth, the air within the chimney will be heated and forced upward by an indraught of cooler and heavier air from all parts of the room. This continues as long as the fire burns. The same occurs when a bonfire is lit, or a house is on fire. I'A'ery child knows that " the sparks fly upward to the sky." They are carried up by the hot ascending currents. The air above the fire is expanded, rendered lighter, and driven upward by currents of cool air that come rushing in from all sides. These, when heated, ascend with such force as to carry up clouds of smoke and sparks. This unequal distribution of heat, as in the warming of the air within the chimney while that in the room is comparatively cold, establishes a system of air currents. If there are no obstacles in the way and if these currents are neither chilled nor heated in their course, they will go straight toward the mouth of the chimney. Chairs and tables as well as other objects in the room will deflect them and cause more or less irregularity in their direction. To prove that such currents really do flow, place a lighted candle in the doorway of a room in which a fire is burning. The flame will be drawn inward by the current. Now what occurs in the air of a room w^hen a fire is kindled on the hearth takes place in the atmosphere. Some portions of it are always more heated than others ; and the unequal distri- bution of heat establishes a system of currents. The heated surface of the earth warms the air above it. This air, forced up by the surrounding cool air, ascends as a current ; and streams of cooler, heavier air flow in. In proportion to the size of the area heated, the volume of the inflowing currents will be greater or less, and in proportion to the difference of temperature between the heated air and the inflowing currents, the rapidity of their flow will be greater or less. General Circulation of the Atmosphere. — Turning now our attention from these simple illustrations to the general circulation of the atmosphere, we find that within the tropics there is per- petual summer. Here the air is heated and filled with watery vapor, while the air on either sidejs co^l^and comparatively dry. liOS HI^GBliES, CRli. 220 ATMOSPHERIC CIRCULATION What must be the effect of this unequal distribution of heat and vapor ? There can be but one answer : it creates a general circulation of the atmosphere. In the first place, as in the case of the fire upon the hearth, the heated, moist air of the tropics is pressed upon by the heavier air on either side. It is forced upward, and there is an indraught both from the north and the south to supply its place. Circulation of the Atmosphere If the earth were at rest, and if its surface were covered with water, the inflowing currents would go straight from the polar to the equatorial regions. ] There would then be a simple circu- lation of light air from the equator to the poles, and of heavy air from the poles to the equator. The winds would be steady and unvarying. But the earth is not at rest, and its surface, instead of being uniformly covered with water, is varied by land masses of greater or less magnitude and elevation. The rotation of the earth and CONSTANT OR TRADE WINDS 221 the influence of its land masses are two causes which largely affect the circulation of the air and render it exceedingly com- plicated. Winds are classified, according to the regularity with which they blow, as cojistant, variable, and periodical. Constant or Trade Winds. — Certain of the winds blow with- out interruption in the same direction and at nearly the same rate. So constant are they that vessels often sail in them for days without, as the sailors say, " changing a stitch of canvas." It was the steady blowing of these winds which so alarmed the crew of Columbus on his first voyage to America, and led them to fear that they would never get back to Europe. From their always pursuing one trade, i.e. path, or from their importance to navigators, these winds have been called trade winds, or the trades. If the earth had no daily motion, these winds would blow on one side of the equator from the north; on the other side from the south ; and in both instances, directly into the equatorial regions. But, in consequence of diurnal rotation, the air, when it arrives at the equator, is in a region which is moving toward the east 120 miles an hour faster than in latitude 30°, where it began to blow as trade winds. In thus passing from regions of lesser velocity to a region of greater velocity the trade winds are deflected toward the west, becoming in the northern hemi- sphere northeast winds and in the southern, southeast winds. Variable Winds. — North and south of the trades are the zones of the so-called variable winds. They extend from the parallels of 30° north and south, to the polar circles. Within these limits the prevailing direction of the winds is counter or oppo.site to that of the trades; that is, from the southwest in the northern, and from the northwest in the southern hemisphere. For this reason these winds are called coiDiter trades. They are also known as anti-trades and prevailing tvesterlies. Their origin is thus explained : While the trades blow stead- ily from the poles, there must be return currents from the equator to the poles, otherwise the polar regions in time would 222 ATMOSPHERIC CIRCULATION be destitute of air. When the upward current at the equator has risen to a considerable elevation it divides and flows toward the poles, one part going toward the north, and the other toward the south pole. These two streams of air remain upper currents as far as the northern and the southern limits of the trade winds; that is, about as far as the parallels of 30° north and south. Here, for the reason that their temperature has fallen below that of the air inflowing from the poles, they descend and blow as surface winds. They become variable, since they are fre- quently interrupted by great swirls or cyclonic movements following in the same general course ; that is, from the south- west to the northeast. That the upper currents above alluded to do flow out northward and southward from the equatorial regions is abundantly proved. Sometimes volcanoes, as we have already learned, eject vast quantities of dust. Not unfrequently this passes into very elevated regions of the atmosphere ; and instances are on record of its being carried sometimes for hundreds of miles in a direction opposite to that of the surface winds. Conseguina, in Nicaragua, is in the region of the northeast trades. Dur- ing the eruption of 1835, its ashes were carried to the island of Jamaica, distant 800 miles to the northeast. No other explanation of this seems possible, than that an upper current was blowing above the surface winds, in an opposite direction. In 18 1 5, ashes from a volcano in the island of Sumbawa, near Java, were borne to the island of Amboina, 800 miles to the northeast, although the southeast monsoon was then at its height. This again proves that there must have been a powerful current toward the northeast, above the southeast surface wind. It is clear, therefore, that return currents flow from the equator to the poles. Were it not for the earth's rotation, the counter trades would move straight to the poles. They are, however, influenced by that force and so deflected as to blow from the southwest or west. This is explained as follows: In the equatorial regions, these winds have acquired the rapid rotary motion toward the east which belongs to that portion of the earth. Hence, when they reach the latitudes nearer the poles, they are blowing east- THE CALM BELTS 223 ward with a velocity far more rapid than that belonging to those regions, and thus become westerly or southwesterly winds. The polar winds are currents of cold air making their way from the poles toward the equator. Their direction is similar to that of the trade winds, northeast in the northern hemi- sphere, and southeast in the southern hemisphere. Coming from the equator, the counter trades bring moisture and warmth ; the polar winds are dry and cold. The trades, counter trades, and polar winds, though treated separately, are really only parts of a great atmospheric move- ment which is ceaselessly accomplishing its unending circuit from the equator to the poles, and from the poles back to the equator. The Calm Belts. — Between the northeast and the southeast trade winds there is a belt of calms encircling the earth known as the Equatorial Calm Belt. The name is not altogether good, for throughout the entire region a vast current of air is ascend- ing. It is therefore an area of low barometric pressure, and is calm only in the sense of being comparatively free from the horizontal movements of the atmosphere or those that are ordinarily recognized. The portion of this belt resting upon the sea is the most difficult part of the ocean for sailing vessels to cross. By sailors it is called the doldrums. Ships are sometimes detained here many days. Between the trades and counter trades, in each hemisphere, there are also belts of atmosphere marked by the prevalence of calms. The belt in the northern hemisphere is known as the Calms of Cancer ; that of the southern, as the Calms of Capricorn. These calms, where they occur on the ocean, are termed by sea- faring men horse latitudes. Here, unlike the Equatorial Calm Belt, the air currents are descending and the area is one of high barometer. The position of all the calm and wind belts above described is not invariably fixed. They all move northward and south- ward, following the apparent course of the sun. They reach 224 ATMOSPHERIC CIRCULATION their farthest northward limit in autumn, their farthest southern limit in spring. The Periodical Winds are those which blow for a certain time in one direction, and then for an equal or nearly equal time, in the opposite direction. They are the land and sea breezes and the mojisoons. Along the coast of most countries there is a breeze from the sea by day and from the land by night. The rays of the sun heat the land more readily than they do the water. The warm rocks, sand, and soil heat and expand the air in contact with them, rendering it light. Pressed upward by the cooler air^of the sea, it rises. Currents then rush from off the sea to supply the place of the ascending columns, precisely as the indraught to a furnace supplies the rush up the chimney. Thus a sea breeze is produced. At night this action is reversed. The land has the property of radiating, that is, of parting with, its heat more rapidly than the water, hence the land by night grows cooler than the sea. It then cools the air above it. But the air over the sea remains comparatively warm and light and is therefore pressed upward by the cool air from the land in the form of seaward-blowing currents. They constitute the land breeze. Were it not for these refreshing breezes, many countries along the seacoast would be uninhabitable. / Monsoons are winds which blow from a certain direction for part of the year, and for the rest of the year from quite an- other quarter. They are land and sea breezes on a grand scale. Instead of alternating with day and night, they alternate with summer and winter, hence their name, from an Arabic word meaning season. The most famous monsoons are those of southern Asia. In India they blow from the northeast for six months of the year, and from the southwest for six months. During the summer the sun plays upon the great deserts and inland basins of central Asia. Those dry and barren wastes glow like furnaces, and the heated air ascends from them in THE PERIODICAL WINDS 225 immense columns. A disturbance is created which is felt to the distance of 2000 or 3000 miles from its center. Cooler air rushes in from the sea on three sides of the continent. Along the coasts of Siberia it comes from the north. P^rom China round the south of the continent to the Red Sea, it comes from the Pacific and Indian oceans ; that is, from the southeast, south, or southwest. In this region, which is largely in the zone of " trades," the effect is so great as actually to reverse the trade wind and cause it to blow in the contrary direction. In the winter the center of Asia is a region of low tempera- ture. Its atmosphere is dry, cold, and heavy ; that of the seas south and east of the continent is moist, warm, and light. The light air is pressed upward by the heavy, and ascends into the upppr regions of the atmosphere. Currents then blow from the land toward the sea. In consequence of this we have, during the winter in India, ?he northeast monsoons, which are really the northeast trades blowing' with augmented force and velocity ; on the Chinese coast we have the northwest monsoons. The summer or the southeast and southwest monsoons, hav- ing passed over the sea, are laden with moisture, and are the wet monsoonsj^ They give its wet season to southern Asia. The northeast and northwest monsoons are for the most part dry, because they come from the land. During their prevalence it is the dry season. The changing from the dry winds to the wet is called in India the "bursting " of the monsoon. The southwest monsoon sets in generally toward the end of April, a steady wind sweeping up from the Indian Ocean and carrying with it dense volumes of vapor. The atmosphere becomes close and oppressive. Flashes of light- ning play from cloud to cloud. The wind suddenly springs up into a tempest. Then a few great heavy drops of rain fall ; the forked lightning is changed to sheets of light, and suddenly the flood gates of heaven are opened, and not rain, but sheets of water, are poured forth, refreshing the parched earth, carry- ing fertility over the surface of the country, filling the wells and reservoirs, and replenishing the dwindling rivers and streams. The whole land from Cape Comorin to Bombay seems suddenly recalled to life. 226 • ATMOSPHERIC CIRCULATION Certain other winds resembling the monsoons are those of Australia, the Gulf of Guinea, and the Mediterranean. They are sometimes called minor monsoons. The winds of Australia blow landward in the hot months ; seaward in the cold season. They are largely controlled by the great desert of Australia at the one season and by that of Gobi at the other. During the South Temper- ate summer the Australian desert is the hotter. During the South Temperate winter Gobi is the hotter. Each thus becomes in turn the controlling area. The Australian monsoons, however, do not compare in regularity with those of India. Over the Gulf of Guinea and the Mediterranean periodical winds blow in summer in opposite directions ; the winds of the Gulf of Guinea come from the southwest, those of the Mediterranean — known to the ancient Greeks as the Etesian winds — are from the northeast. Both are due to one cause, namely, the intense heating of the Sahara. This produces an upward current of heated air and an inrush of cooler air from the Gulf of Guinea on the one side, and from the Mediterranean on the other. The periodical winds of Mexico, Central America, and the Brazilian waters, and those known in Texas as " Northers," are due to causes similar to those of the monsoons. Among the periodic winds of less importance are the return currents from deserts. These are laden with heat, sand, and dust. From the Sahara currents flow northward and southward. Those from the south enter Egypt, and blow for a few days at a time during a period of 50 days. Hence they are called khamsin, an Arabic word meaning fifty. During their prevalence the air is filled with blinding dust and the midday sun is darkened. By such a wind of unusual violence, the army of Cambyses, 50,000 in number, is said to have been destroyed, when on its way to attack the oasis and temple of Jupiter Ammon. Crossing the Mediterranean, the desert wind scorches the vegetation of southern Europe. It is known as the sirocco. The tops of mountains chill the surrounding air. This some- times descends as a cold wind into the warmer regions below. Thus from the snowy heights of the Andes the cold pamperos sweep over the Pampas of the Plata, the icy puna descends upon the table-land of Peru, and the chilling Diistral descends from the Alps to the shores of the Mediterranean, causing great discomfort to sick and well. SURFACE EFFECTS OF WINDS ■^-V Surface Effects of Winds are especially well shown along sandy coasts and in arid regions. By the constant blowing of the wind sand is ac- cumulated in rounded ridges, like snowdrifts, called dunes. These heaps are by no means stationary, but advance with the wind, some- times overwhelming Sand Ijlm Showing the general level surface and the steep lee slope encroaching on a pine forest. * forests and converting arable lands into barren wastes. Large dunes are found on the southwest coast of France. Here for r^--?^--;;^- ^.'^i _5r« Surface of Dune, Dune Park, iNniANy? Showing the destruction of a forest by dune invasion. (From United States Geological Survey.) 228 ATMOSPHERIC CIRCULATION the distance of 150 miles they cover a strip several miles wide, attaining in some instances the height of 300 feet. At the head of Lake Michigan and on its eastern shore are found large dunes. On the Pacific coast, near the Golden Gate and else- where, the drifting of the sand has been prevented by the culti- vation of certain plants. The heaping up of sand ridges in desert regions through wind action is also common, as in Africa, Arabia, and the Great Basin. Moreover, blowing sand is an agent of abrasion and by it even rocks are worn away. Among other surface effects of wind mention may be made of the stripping of land surfaces, the transportation of dust, and the destruction of forests. XXI. STORMS General Description. — Storms and tempests are sudden and violent disturbances of the atmosphere. At sea they are among the most grand and terribly sublime spectacles in nature. A wind becomes a storm when it attains the velocity of 50 miles or more an hour. The great storms of the West Indies and of the Indian Ocean are called hurricanes ; those of the China Sea, typhoons. These storms, which are alike in cause and character, together with the great eastward-moving swirls of the temperate regions, may be considered under the general name of cyclone. This word, de- rived from the Greek kuklos, circle, refers to the fact that they consist of columns of air revolving round a perpendicular axis. Sketch to illustrate the Lower- atmospheric Circulation in a Hurricane The inward spiral at the base is the surface wind. (After Everett Hayden in National Geographical Magazine^ At the same time they have a progressive motion of greater or less rapidity over a certain portion of the surface of the earth. Cause of Storms. — The general cause of all such atmospheric disturbances is the same in principle as that of ordinary winds. 229 230 STORMS COURSEOF CYCLONE IN Northern Hemisphere ^a^e COURSEOF CYCLONE IN Southern Hemisphere Course of Cyclones It is a difference or inequality of pressure or weight, in different regions of the atmosphere. The principle may be thus stated : Into an area of low barometer a wind must always blow from an area of high barometer. When from any cause the weight of the atmosphere in a locality is diminished, an ascending current results. Currents of colder and heavier air rush in to supply the deficiency. The force and velocity of the currents thus created will be greater or less ac- cording to the dif- ference of atmos- pheric pressure, or the "gradient," as meteorologists call this differ- ence. The larger the gradient, the more violent will be the resulting wind. Suppose there is but one area of low barometer and one of high ; the result will be a simple wind moving in one direction. If, however, the one area of low barometer is surrounded by areas of high barometer, it is evident that there will be an inflow of air from all directions. Such currents do not collide at the center, but, in obedience to LAWS OF STORMS 231 a force arising from the earth's rotation, are de- flected to the right in the northern hemisphere and to the left in the southern.^ They there- fore circle round this area, thus forming a cy- clone. The course of the atmospheric currents during a disturbance of this kind is shown in the diagram on p. 229. Laws of Storms. — Cyclones obey the fol- lowing laws: — ( I ) The wind revolves in opposite directions according as the cyclone is in the northern or southern hemisphere.; In the northern the direc- tion of revolution is from right to left, or against the hands of a watch. In the southern it is from left to right, or with the hands of a watch. As the wind constantly re- volves, it constantly changes its direction at any given place in the storm track. On oppo- site sides of the center it has opposite directions. Hence it is easy to understand why NORTHERN HEMISPHERE VVindEast SOUTHERN HEMISPHERE VJind West Wind East Storm Cards Showing direction of whirl in both hemispheres. ^ Ferrel's law. M.-S. PHYS. GEOG. 14 232 STORMS the wind changes as soon as the storm center passes. This is shown by the " storm cards." The rate of revolution, or "velocity of the wind," is from 50 to 150 miles an hour. (2) The storm, while revolving, has a progressive motion. The direction of this motion is determined by the prevailing winds. In general it is northwest and southwest within the zones of the trades, and northeast and southeast/in those of the counter trades. / The course of tropical cyclones is well defined. North of the equator they move northwestwardly up to about latitude 30° N. Here they turn to the northeast. South of the equator they pursue the reverse course ; starting near the tropics, they advance toward the southwest, and near the parallel or 27° they turn to the southeast. From this it will be seen that the pathway of cyclones somewhat resembles the curve called a./) a ra do /a. (See diagram, p. 230.) The rate of travel varies from i to 70 miles an hour. (3) The storm center is an area of calm and also of low barometer. The arrival of the storm center at any point is indicated by the barometer. The descent of the mercury in tropical storms often amounts to two inches. It is sometimes so rapid that it can be detected by the eye. This fall of the barometer occurs at the storm center for two reasons : ist, because the center is an area of warm, humid air; 2d, because the center is an area of rarefaction. The air particles which are nearest the vertical center of the cyclone are apparently repelled outward from that center by their centrifugal force. This makes the air in the center less dense, or, as we commonly say, rare- fies it. Under such conditions the barometric column sometimes falls as low as 27.5 inches. Anti-cyclones. — Closely associated with cyclones are vast bodies of air the condition of which is the reverse of that of the cyclone. To such bodies of air is given the name anti-cyclone; that is, opposite of the cyclone. The cyclone is warm, moist, and light. The anti-cyclone is VALUE OF STORM LAWS 233 cold, dry, and heavy. Hence the area over which an anti- cyclone prevails is one of high barometer. Occasionally in an anti-cyclone the mercury will rise to 31.25 inches. Again, while in a cyclone air currents flow inward from the circumference toward the center, in the anti-cyclone currents flow outward from the center toward the circumference. Value of Storm Laws. — A knowledge of the laws of storms is of the utmost value to the navigator. By observing the direction of the wind he may learn in what direction the storm center is from him. The rule is : Turn your back to the wind and the low barometer is always to your left in the northern hemisphere, and in the southern hemisphere to your right. This will appear by examining the diagram on page 231, and imagin- ing yourself with your back to the arrowheads. If the sailor knows where the storm center is, he can steer away from it. Again, if he finds his barometer sinking rapidly, an inch or more below its usual height, he knows that he is in the storm center. Obviously it will be well to trim the sails and prepare for a gale. The center of calm will soon pass beyond and a tempest strike his ship. The Areas of Storms differ in size and shape. In Europe they are nearly circular ; in the United St-ates, their shape is usually an elongated oval. They are seldom less than 600 miles in diameter. They average twice that amount. Tornadoes and Whirlwinds differ from hurricanes and ty- phoons, (i) in duration ; and (2) in extent of area. In passing over any point, tornadoes seldom occupy more than a few seconds. Their breadth varies from a few yards to a mile or two, though their destructive effects are usually con- fined to a narrow path. The rate of their progressive motion is commonly about 30 miles an hour, and the length of the'ir course 25 or 30 miles. An approaching tornado has the form of a funnel-shaped cloud pointing downward. A noise, perhaps due to electricity, and not unlike that of a train of cars, is heard ; thunder, light- ning, hail, and rain occur. 234 STORMS A partial vacuum is formed by the centrifugal force at the center. Sometimes when the end of the funnel dips down and touches a building, the vacuum resting over it so relieves the building from atmospheric pressure as to cause a sudden expan- sion of the air con- tained in it. The walls of the building then burst asunder as by explosive force. Tornadoes sweep everything before them. Houses and other buildings are lifted up bodily, and lanes called " wind roads " are cut through the forests. Large trees are up- rooted and whirled about like stubble. The region of North America most frequently visited by tornadoes is the Mis- sissippi Valley. Dur- ing the past 50 years more than 600 have occurred there. In the deserts of Asia and Africa, as well as in the region of the Great Basin of North America, whirlwinds sometimes draw up into their central core large quantities of sand and dust. They thus become moving columns of sand, 500 to 700 feet in height (as observed with sextant), and are known as " dust whirlwinds," ^■■i^^l QUI 5P"r' •■* •'♦*' A lOKNADO The tornado here shown is from a photograph taken by Mr. W. E. Seright at Stafford, Kansas, about 5 : 30 P.M., April 12, 1906. It was the last of six or seven similar manifestations which occurred within the radius of three or four miles the same afternoon. When photographed the cloud was probably a mile distant in a northeast direction. J DISTRIBUTION OF STORMS 235 The Simoom, or " poison wind," appears to be a desert whirl- wind intensely hot, and so rarefied as to be suffocating. At sea, especially in cer- tain parts of the ocean, waterspouts occur. These are tall moving columns of water. Scientific opinion is divided as to their cause. Some think that they are produced like the dust whirlwinds of the desert, by a revolving air current which draws up the spray of the waves into its core of low pressure. Others think that the water comes solely from the clouds. The cut seems to suggest the latter view. Two actual, careful observers of the spout photographed drew, however, opposite conclusions from their observations. Distribution of Storms. — The most violent storms occur in the vicinity of mountainous islands. The Pacific is the most tranquil of the oceans. In those portions of its trade- Waterspout as seen ekom Oak Bluffs ^ (Cottage City), Mass., August 19, 1896, wind regions where there at 1:02 p.m. are no islands, and where monsoons do not prevail, storms are almost unknown. The typhoons are confined to the southeast coasts of Asia and the East India Archipelago. 236 WEATHER FORECASTS 237 The South Atlantic, along the coast of intertropical Brazil, is almost stormless, whereas, in corresponding latitudes in the North Atlantic, among the West Indies, terrific hurricanes occur. The portions of the Indian Ocean especially subject to hurricanes are the Bay of Bengal and the neighborhood of Mauritius. Weather Forecasts,^ — During the last 50 years observa- tions upon the force and direction of the wind, the course and character of storms, the pressure of the atmosphere, the amount of rainfall, the temperature and moisture of the air, have disclosed certain general principles or laws of the weather. Knowing these laws, and knowing by telegraphic reports the weather conditions prevailing throughout the country, it is possible to predict from day to day, with considerable accu- racy, the approach of storms, or of cold or hot weather. Most of the great storms of the United States travel in a northeasterly direction. They may be conveniently classed as those which come from the Pacific Ocean and those which come from the Atlantic. The storms of the Pacific penetrate to a greater or less dis- tance into the country, and often cross it entirely. The storms from the Atlantic are first felt either at some southerly point on the Atlantic seaboard, or on the shores of the Gulf. Generally they come in from sea by the way of the Gulf, pass northward through the Mississippi Valley, and then turn to the northeast. J Over 50 years ago Maury urged upon the attention of the government of the United States, and those of European nations, the desirability of having systematic meteorological observations carried on by all nations at sea. As the result of his efforts the United States government invited all the maritime states of Christendom to a conference, which took place in Brussels, 1853. The suggestions made were adopted. But the ideas of Maury were not limited to the ocean. In the preface to the second edition of his "Physical Geography of the Sea," published in 1855, he says : "It is a pity that the system of observations recommended by the conference should relate only to the sea. The plan should include the land also, and be uni- versal." The present " U. S. Weather Bureau " with its well-organized Signal Service is the crowning result of his labors in this direction. 238 STORMS Those which make their appearance first on the Atlantic seaboard are the western halves of cyclones, which, pursuing their parabolic course, first north- westwardly and then northeastwardly, happen partially to embrace our shores within their area. These western half-cyclones consist of northeast and northwest gales. The eastern halves of the same storms, consisting of gales from the southwest and southeast, are at sea. The storm center pursues a course nearly coinciding with our shore line. The transient and uncertain character of tornadoes renders it impossible to make exact predictions regarding them. Ordinary storms, however, are so far regular that, in a large proportion of cases, their course, after they have once manifested themselves, may be foretold with some degree of accuracy. The Weather Map. — The following description of the Weather Map is taken from a publication by the Chief of the United States Weather Bureau (see map, p. 236): "This map presents an outline of the United States and Canada, and shows stations where weather observations are taken daily at 8 A.M. and 8 p.m., seventy-fifth meridian time. These obser- vations consist of readings of the barometer, thermometer (dry and wet), direction and velocity of the wind, state of weather, amount, kind, and direction of the clouds, and amount of rain or snow, and are telegraphed to Washington and to many of the Weather Bureau stations throughout the country for publi- cation on maps and bulletins. Solid lines, called isobars, are drawn through points having the same atmospheric pressure ; a separate line being drawn for each one tenth of an inch in the height of the barometer. Dotted lines, called isotJierms, connecting places having the same temperature, are drawn for each 10 degrees of the thermometer. Heavy dotted lines, inclosing areas where a decided change of temperature has occurred within the last 24 hours, are sometimes added. The direction of the wind is indicated by an arrow flying with the wind, or opposite to the ordinary vane. The state of the weather — whether clear, partly cloudy, cloudy, raining, or snowing — is indicated by the circular symbol. Shaded areas, when used, show where rain or snow has fallen since the last observation." J XXII. MOISTURE OF THE AIR Humidity. — More or less moisture is always present in the air. It exists as vapor. This vapor is invisible, yet its presence is often recognized by the sensation of dampness. The amount of vapor in the air is greater over the sea and other large bodies of water than over the land. It is dissipated by heat and con- densed by cold. In arid regions the moisture available is less than the capacity of the air to hold, hence the air is dry. The presence or absence of moisture in the atmosphere has a marked effect on climate. Great humidity is enervating and not con- ducive to mental or physical exertion ; temperature sensations are exaggerated ; human activities curtailed. Dry air, on the contrary, is bracing, and higher temperatures can be endured without discomfort. Evaporation. — One of the most remarkable properties of water is the readiness with which it passes from one of its states to another. Whenever it assumes the form of vapor it is said to evaporate, and the process of evaporation goes on at all tempera- tures and under all circumstances until the air is saturated. When the point of saturation has been reached, it can hold no more moisture. You may have observed water drying in the streets and roads after a rain, or clothes hanging on the line frozen stiff, and yet becoming dry ; or you may have seen a light fall of snow disappear in freezing weather. These were cases of evaporation. Evaporation is accelerated and increased under the following conditions : — (i) By high temperature. From this it follows that the maxi- mum of evaporation is found within the tropics ; the minimum at the poles. Furthermore, that evaporation takes place during the day, and in the warmest part of the day 239 240 MOISTURE OF THE AIR (2) By diminution of pressure. In a vacuum there is almost no pressure, and there evaporation takes place almost instan- taneously. Hence on the tops of high mountains, where the pressure of the atmosphere is very much diminished, evaporation goes on much more rapidly than it does at the sea level, where the full pressure of the entire atmosphere is felt. Indeed, mountain peaks may be so high as to be entirely free from snow, while a belt of snow girdles the lower part of the mountain. The reason of this appears to be that at certain alti- tudes and under certain conditions snow evaporates so rapidly that it cannot accumulate. Aconcagua in Chile sometimes appears with its bare and bleak top peering above a girdle of snow. (3) By a dry condition of the atmosphere. Warm dry air will absorb far more moisture than that which is cool and damp. If air be near the point of saturation, it is clear that evaporation will be retarded ; but if the air be dry, it will be accelerated. (4) By wind. If a wind blows upon the surface of water, evaporation is accelerated. As fast as one portion of the air be- comes charged with vapor, it is removed, and a fresh portion takes its place. Condensation and Precipitation. — Vapor returns to the liquid or solid state and is deposited upon the earth by the pro- cesses called condensation and precipitation. When condensed, it assumes the form of dew, white or hoar- frost, fog or cloud, hail or snow. The great cause of precipitation, or the removal of moisture from the atmosphere, is loss of heat. The atmosphere can contain more or less vapor in a state of absorption in proportion to its temperature. If the temperature is 50°, a cubic foot of air can absorb about two grains' weight of vapor. At the tempera- ture of 70°, that is, with an increase of only 20° of heat, the proportion of vapor is about twice as great. From this it is easy to see why reduction of temperature causes precipitation. Suppose a cubic foot of air saturated with mois- ture to be reduced in temperature, even very slightly ; it is ob- HOW DEW IS FORMED 241 vious that its capacity for moisture will be at once reduced, and a certain portion of its vapor must be precipitated. The temperature at which the deposit in such cases begins to take place is called the (/cw point. How Dew is Formed. — On clear and calm nights, the grass, the leaves, and other objects rapidly radiate their heat and grow Cirrus Streamers with Low Cumulus on the Horizon, Washington, D.C. From photograph by Professor A. J. Henry. cool. They chill the surrounding air. It can no longer contain the same amount of moisture as when it was warm. Hence a portion of it is condensed and deposited upon the leaves in the sljape of fine drops of water. We often say " the dew begins to fall,'' though, strictly speaking, it does not fall. It is deposited upon the grass precisely as, on a hot summer's day, the moisture is deposited on the outside of a pitcher of ice water. Clouds check radiation, and hence on cloudy nights less dew, or perhaps none at all, is deposited. You must have noticed that dew and hoar frost, which is mois- 242 MOISTURE OF THE AIR ture condensed at a temperature below the freezing point, are deposited on some objects more copiously than others. This is because some radiate heat more rapidly, and therefore chill and condense more quickly the vapor that floats above them. Fog. — Vapor coming in contact with cool air, if chilled below Cirrus Clouo merging into Cirro-stkaius, Washington, D.C. From photograph by Professor A. J. Henry. the dew-point, assumes the form of fine watery particles which we call mist ox fog. It may also have been observed that in a clear, calm, and frosty morning the springs, ponds, and rivers " smoke." This phenomenon is identical with that exhibited by the steam which issues from the teakettle, the locomotive, and the steamboat. The " smoke " is a miniature fog. Often, too, fogs are seen upon the surface of rivers in early morning, which vanish before noon. The morning air, being CLOUDS 243 cool, cannot absorb this moisture, but later in the day when its capacity has been increased by warming, it readily absorbs the fog. The most foggy sea in the world is that part of the North Atlantic Ocean that lies on the polar side of latitude 40" ; and the most foggy place is on the Grand Banks of Newfoundland. DOI KI.E-TURRETED CUMULUS, LOWKR POK I.MAC kl\l R From photograph by Professor A. [ Henry. Vapor rises rapidly from the warm water of the Gulf Stream. Near the Grand Banks the Gulf Stream meets the icy Labrador Current. Owing to the chilling influence of this current, the vapor is condensed into fog as fast as it rises. Though fogs are most frequent in summer, they occur on the Grand Banks at all seasons, producing in winter the exquisitely beautiful silver fogs of New- foundland, which garnish the forests of that island with frostwork. Clouds. — A cloud is simply a mass of mist or fog floating high in the aJr instead of near the ground. 244 MOISTURE OF THE AIR Clouds present a very great variety of appearance, and hence are divided into seven classes : three simple, cirrus, cumulus, and stratus ; four compound, cirro-cumulus, cirro-stratus, cumulo- stratus, and cunuilo-cirro-stratus or uimbus. The cirrus or curl cloud consists of white wavy lines or curled 1 " ?E ^^ \ wara g^i^ray^ j^^Sff^ijfe^'^" \ -^ B^^'^^ikc^^^ *^^^". \ • -J ^ J8 ■ 1 iH^^gutUiimK^^ Cirro-cumulus Cloud, "Mackerel Sky," Washlncjton, D.C. From photograph by Professor A. J. Henry. bands. It is the lightest of all cloud forms, and attains the highest elevations, floating four or five miles above the surface of the earth in regions of perpetual frost. It is supposed to consist of minute crystals of ice such as we see in the snowflake, and may be defined as frozen fog. Cirrus clouds are often heralds of the cyclone. These nimble forerunners have been observed 8oo miles in advance of a storm. They sometimes cau- tion the mariner, before his barometer gives any intimation of the approaching tempest. CLOUDS 245 Cumulus clouds derive their name from the fact that they are heaped up, like vast mountains towering one upon another. They are often of glistening whiteness. They abound in the tropics, and frequently appear in the sky of temperate latitudes during the summer, when evaporation is rapid. Of all cloud forms they are perhaps the grandest. Out of CUMULO-STRATLS, KNOXVILLE, TENN. them darts the lightning which makes our thunder storms so magnificent. Stratus clouds appear in the shape of long layers or ribbons. They are seen most frequently in the evening, and, when tinged by the rays of the setting sun, they form those islets of gold which render the sunset sky so beautiful. The compound clouds combine the features of the simple ones from which they are named. The Cirro-cumulus is made up of fleecy masses of cirrus which roll themselves up into rounded shapes. These cause the mottled appearance commonly known as a "mackerel sky." 246 MOISTURE OF THE AIR The Cirro-stratus consists of layers of cirrus clouds. They are often so arranged as to resemble a shoal of fishes, all swim- ming parallel to one another. This cloud, like the cirrus, is often the precursor of storms. The Cumulo-stratus is formed of heaped clouds resting on layer clouds. Like the cumulus, its general mass is often quite CUMTLUS AND NlMBUS, SEASCAPE (United States Weather Bureau.) dark and threatening, while its edges are bright with sunshine that is behind the clouds. The Nimbus is simply a cloud of any kind from which rain falls. Heaped clouds, and curls and layers blend together, lose their characteristic features, and form one dense leaden mass. It often overspreads the whole heavens. When clouds rest on the tops of mountains, they are actually in contact with the earth ; often indeed they are below the sum- mit of the mountain. Their average elevation, however, is about half a mile. At times they cannot be less than four or five miles high. Cl.dUDS 247 The velocity of cloud movement, when accurately estimated by observers, is found to be far more rapid than we should sup- pose from the apparent rate of the "passing cloud." It has been found that cirro-cunuilus and cirrus clouds which seem to be moving at a leisurely rate are often traveling 75 to 100 miles an hour. This is of very great interest, for it indicates to us the velocity of the upper currents of the atmosphere. Clouds screen the earth from exxessive heat in summer, while as a mantle they keep it warm in winter by checking radiation. Plants and animals are distressed by the intense heat of the noonday sun. But the more powerful the ray, the more rapid is evaporation.. Soon vapor enough is lifted from the earth to form the mitigating clouds. They over- shadow the land, and plants and animals rejoice in their shelter. M.-S. PHYS. GEOG. — 1 5 ■RI XXIII. RAIN General Statement. — The first form assumed by the moisture of the upper air when condensed is that of cloud. If, however, the process of condensation continues, and vapor exists in abun- dance, it is easy to see that the tiny water particles which make up the cloud will increase in size, until they are too heavy to float, and will fall as raindrops to the earth. The general cause of rainfall is that a certain volume of vapor- laden air has been chilled below the dew-point, so that it has no longer the same capacity for moisture as before. This may be brought about in several w^ays : (i) The moist air maybe driven against lofty mountain slopes and cooled by contact; (2) it may be chilled by being mixed with a mass of colder air ; (3) it may be chilled by expansion, as when carried upward by ascending currents of heated air, wafted over high mountains, or drawn into the center of a cyclone. Expansion has the effect of cool- ing air and condensing its vapor. This last cause produces the heaviest rainfalls for short periods. Distribution of Rain. — Rain is very unequally distributed over the earth. (i) The rainfall is greater on land than at sea. (2) It is greater in mountainous than in level regions. (3) It is greater in the torrid than in any other zone. The average annual quantity, at the equator is eight feet. It diminishes, however, on either side as we approach the poles. This follows from the fact that the torrid zone, being the hottest, is that of the greatest evaporation. Dry air cools about 1° for each 183 feet of ascent; but if moisture is present, as soon as condensation takes place, the latent heat set free reduces the rate of cooling. 249 250 REGULA'rORS OF RAIM \l I 25 1 These are the general facts regarding the distribution of rain. We must now consider more in detail how this distribution is brought about. Regulators of Rainfall. — The great regulators of rainfall are mountains, deserts, and winds. Each of these has an important part to perform in the distribution of rain over the surface of the earth. Mountains are the great condensers of vapor. If mountain chains face winds coming from the sea, the land lying between them and the sea is well w'atered. As they rob the winds of their moisture, not unfrequently the region lying beyond them is rainless. Thus the Himalayas face the southwest monsoon, as it comes freighted with vapor from the' Indian Ocean. They make India one of the most productive countries in the world ; but the plateaus lying to the north of them are almost rainless. On a smaller scale the Western Ghats act in the same way. They, too, lie in the pathway of the monsoons, and intercept and con- dense their vapors. The annual rainfall upon their tops amounts to about 260 inches, while the country on the east of them receives less than 30 inches. But perhaps the most striking illustration of the influence of mountains upon rainfall is to be found in the case of the Khasia hills, on the northern shores of the Bay of Bengal. They in- tercept the southwest monsoons as they Come burdened with vapor from the bay. The result is that the winds, as they slant up the hills into the higher and cooler air, have their moisture at once precipitated as rain, of which about 500 inches fall there in the year. In South America the influence of the Andes is familiar. The northeast and southeast trades come from the sea saturated with vapor, and so go into the interior, rising, and cooling, and dispensing showers as they go, until they reach the crest of the Andes. Here the cold and expansion are sufficient to precipi- tate almost all the remaining moisture. Thus the eastern side of these mountains, within the trade-wind region (see Chart of 252 RAIN the Winds), is abundantly watered, while the western is dry. Hence it is that Peru is a rainless country. South of the mouth of the Plata, the reverse takes place. There the prevailing winds are from the west. They come from the Pacific, reeking with moisture, and water the western slopes of the Andes, causing the excessive rains of southern Chile, while the eastern slopes are comparatively dry. In our own country the Cascade Range and the Sierra Nevada have a similar influence. They lie in the pathway of the westerly winds which come loaded with moisture from the Pacific. They act as condensers, and bring down the copious showers which give fertility to the Pacific slope. In moiintainless areas, like the Dakotas, rain and snow are caused by currents of cold air descending from tlie upper regions of the atmosphere. They reduce the temperature with surprising rapidity. Pouring into a warm atmosphere, they condense its moisture, and a rainfall or snowfall is the result. In many cases deserts are the directors of the winds, and thus become regulators of the rainfall. India is in a region in which the northeast trade winds blow over the land and are rainless. Were it not for the deserts of central Asia, which have the effect of drawing in the southwest monsoons (see p. 224), India would be as arid as Gobi. In Africa the Sahara produces the monsoons which blow from the Indian Ocean upon that continent. By June, the desert is heated sufficiently to bring in the sea winds. The rainy season then begins, and lasts till late in autumn. The periodical overflow of the Nile is due to rain resulting from the condensation of vapor brought from the sea by the African monsoon. Thus Egypt owes its fertility in some degree to the burning sands of the Sahara. North America has its deserts and its monsoons, though they are far less marked than those of the Old World. The table-lands of Mexico, Arizona, the dry plains of Texas, New Mexico, and the neighboring regions, are heated by the summer sun to such a degree, that the air resting upon them becomes rarefied, and ascends, the cooler air RAINS CLASSIFIED 253 from far and near coming in to restore the equilibrium. Thus a southeast monsoon is created in the Gulf of Mexico, and a southwest one in the Pacific. Both of these winds blow toward the land, and bring the rains to Mexico, so that one side of that country is watered from the Pacific, and the other from the Atlantic Ocean. As a general rule winds are dry, if they have traversed the land or if they are journeying toward the equator. Winds are wet, if they have traversed the sea or if they are journeying from the equator. Land winds are dry for the simple reason that they have so little opportunity to take up moisture. Thus the northeast monsoons which sweep over the inland regions of Asia are the dry monsoons. The westerly winds of our own country, from' the Sierra Nevada to the Atlantic, are dry winds. They bring our fair weather. Again, a wind that is blowing toward the equator is dry, because, entering warmer latitudes, it is gaining capacity for moisture with every degree of its progress. The trade winds, for example, blow toward the equator. You perceive, therefore, that they are going from cooler to warmer latitudes. Their temperature is increased by the way, and with increase of temperature there is increase of capacity for moisture. The trade winds, therefore, take up more water from the sea than they return to it. They are evaporating winds. .Sea winds and winds blowing toward the poles are rainy. The counter trades go toward the poles. They are traveling from warmer to cooler latitudes. Their temperature is de- creased by the way, and therefore there is a decrease in their capacity for moisture ; they deposit more than they take up. They are, therefore, rain winds. Rains Classified. — The winds are classified according to the regularity with which they blow, as constant, variable, and periodical. It is proper, therefore, to classify the rains which they bring in the same way. Hence, according to the nature of the supplying winds, the rainfall in any given region is con- stant, periodical, or variable. 254 RAIN The constant rains are confined to a belt near the equator, about 5° wide. In this belt there are almost daily showers. The cause is clear. The northeast and southeast trades meet near the equator. They are so completely saturated with moisture that the sailor hanging out his clothes in the morn- ing, is often surprised to find in the evening that they have not dried in the least. Under the vertical rays of the sun an as- cending current is produced which carries the vapor-laden air into the higher regions of the atmosphere. Here the vapor is cooled and condensed ; and hence the frequent thunder showers of this region of constant precipitation. Within the tropics, to the north and to the south of the narrow belt of Constant Rains, lie the zones of Periodical Rains. In the New World the periodical rainfall is closely connected with the annual movement of the Equatorial Calm Belt and its accompanying Cloud Ring. The Calm Belt travels northward and southward, following the apparent annual movement of the sun in the heavens. It is farthest south in March, and farthest north in September. During the time that it is passing over a place, it gives to that place its rainy season. After it has passed, there is scarcely a drop of rain until it comes again. Let us follow the Cloud Ring in its journey from south to north, and we shall readily understand its movements, and the rainy seasons that depend upon them. The time is February; it is then over Guayaquil (Lat. 3° S.), and then the rainy season there is at its height. It commences its movement for the north in March. Quitting the skies of Guayaquil soon after, it leaves them bright and clear with the commencement of the dry season. In a little while it has traveled as far as latitude 4° N. It then overshadows Bogota, where the rains begin in April or May. In June it is over Panama, and hence a rainy season prevails there : and so the Cloud Ring continues on to Mexico, reaching Mazatlan, just under tiie tropic, about September, when it commences its march toward the south, so as to be again at Guayaquil by February or March. It is clear that on its return from north to soutli the Cloud Ring must give KXCESSIVE AND DEFICIENT RAINIAl.l, 255 to certain places a second rainy season because, in coming and going, it passes over them twice. In the Old World the periodical rains are occasioned by the monsoons or reversed trades. For about six months, in south- ern Asia and central Africa, copious rains fall. When the mon- soons change, the dry season sets in, and scarcely any rain falls until after six months, when the wet monsoon begins to blow again. Within the two belts of Periodical Rains the year is divided into rainy seasons and dry. In general terms, the rainy season in the northern belt may be said to begin with April and last till October, while the dry season extends from October till April. In the southern belt this order is reversed — the dry season lasting from April till October, and the season of rain from October till April. It is not to be supposed that during the rainy season there is an incessant fall of rain. In Mexico, for instance, the rainy season is the most delightful portion of the year. As a rule the nights and mornings are clear and beautiful, and the weather fine, with a few hours of rain after three or four o'clock p.m. North and south of the belts of Periodical Rains, the rains become variable ; that is, they are irregularly distributed through the year. In some countries they occur mainly during the sum- mer, in others during the winter; in others, again, during the spring and autumn. This condition prevails throughout the temperate regions. Excessive and Deficient Rainfall. — Owing to the influence of local causes, there are regions of excessive and deficient rainfall. The regions of excessive rainfall, with few exceptions, lie within or near the tropics. Cherrapunjee, in the vicinity of the Khasia hills in India, receives annually about 500, and in some years 600, inches — or a depth of 50 feet — a greater amount, so far as we know, than any other place on the globe. Parts of the British Isles, the coasts of Guinea and Senegambia. eastern Africa and India, are all remarkable for their heavy rainfall. In the New World, Brazil, Guiana, Venezuela, the West India Islands, Central America, southern Chile, and the Pacific shores of Alaska are all regions of excessive rainfall. 256 RAIN The Primitive Method of Ikku.aiion practiced by the Egyptian 1 i,\^\.ms The water is raised in vessels attached to " sweeps " with counter weights at the opposite ends. EXCESSIVE AND DEFICIENT RAlNIAl.l. 257 The rainless or almost rainless regions are the great belt of deserts extending across Africa and Asia, from the Atlantic nearly to the Pacific ; the Great Basin in North America, lying eastward of the Sierra Nevada ; Peru, together with the north- ern part of Chile, portions of Argentina lying eastward of the Andes, and the interior of Australia. Cultivation in all dry countries is carried on by means of irrigation. For this purpose tanks liave been constructed in India at vast e.xpense. The Peru- vian farmers avai' themselves of the mountain streams that are fed by the snows of the Andes; while the peasant of Egypt, like his forefathers, supplies his fields and gardens from the waters of the Nile. (For irrigation in United States, see p. 320.) XXIV. HAIL, SNOW, AND GLACIERS Hail. — Moisture, descending through the cold upper regions of the atmosphere, is sometimes frozen and becomes hail or snow. When examined carefully, hail has been often found to consist of concentric layers of ice, incasing one another like the layers of an onion. In size, hailstones vary. At times they are as large as mar- bles, or even hens' eggs, so that severe hailstorms may occasion very great damage to crops. The formation of hail is not well understood. The sudden ascent of moist air into the cold upper regions of the atmosphere is probably the most common cause of this phenomenon. Glaisher, in his balloon ascension, found the temperature, at the height of three miles, i8° F. ; at four, 8° ; at five, — 2°. The temperature at the surface was 59°. Snow. —The moisture that falls from the clouds, frozen in flakes, is called snow. When examined, it is usually found to consist of exquisitely formed crystals, which are generally in the shape of a six-pointed star. (See illustration.) Snow rarely occurs within the limits of about 30° north and south latitude, except on high mountain tops. It is naturally more abundant as we approach the poles. It is also in general more abundant where the climate is inland, than where it is maritime. Paris has, on an average, 12 snowy days in the year; St. Petersburg, 170. Snow is perpetual, however, ev^en at the equator, upon all heights greater than about three miles above the sea level. The line above which snow is always found is called the snow line. It varies in altitude from many causes. 258 I SNOW 259 Whatever tends to elevate the temperature of any locality tends also to elevate the snow line. Hence a low snow line means a cold climate. While at the equator the snow line is 16,000 feet high, at the Straits of Magellan it is only about 4000, and in Norway about 5000. The use of snow is twofold : (i) it protects the earth and the crops planted in late autumn from the intense cold and the injurious effects of frost. Sometimes there is a difference of 40° between the temperature of the ground a little below the surface and that of the snow that covers it; (2) falling in vast SiNUU Crvstals quantities on the great mountain ranges, as the Himalayas, the Alps, and the Rocky Mountains, it serves as a perpetual feeder of the rivers. The quantity of snow that falls on an extensive range of mountains, such as the Alps, is very great. Aga.ssiz observed a fall of 57 feet in si.x months at the Hospice of Grimsel, and observations during twelve years near the Pass of the Great Saint Bernard showed an annual snowfall varying from 12 to 44 feet. It has been estimated that the average annual snowfall on the Alps amounts to 60 feet, which is equivalent to six feet of water. A large part of the snow, as already stated, gradually melts and flows 26o HAIL, SNOW, AND GLACIERS thi'ough the river courses to the sea. Other, though smaller portions, consohdated into ice, descend the mountain slopes into the valleys as glaciers. Frequently masses of snow are loosened from their beds and plunge down the steep declivities with frightful velocity, forming avalanches. Sometimes the echo of a loud word is enough to disturb an overhanging mass and hurl it into the valley below. Lffkcts ok an Avalanchk A scene in the Selkirk Mountains of British Columbia. Many instances are on record of the appalling destruction wrought by this scourge of the Alps, whole villages having been overwhelmed and hundreds of lives destroyed by a single avalanche. Thick forests are the best protec- tion against danger from this source, and in former times the penalty of death has been adjudged against any who should destroy a single tree of the pro- tectinji barrier. GLACIERS 261 Glaciers are vast masses of ice either spreading out over the surface, as in Greenland and the Antarctic regions, or filling valleys, as in the Alps and other snow-clad mountains. A Snow-clad Summit— Mont Blanc, "The Monarch of the Alps" This mountain has an altitude of 15,730 feet. In the foreground is seen the village of Chamounix. Note the glacier extending downward into the valley. In regions where the snowfall exceeds the loss by melting, the accumulated snow gradually becomes compacted by par- tial melting and by the pressure of its own weight. Moreover, that which occupies the higher levels gradually creeps down- ward to the lower — to the edge of the plateau in the case of an ice sheet, or down a valley in the case of a mountain glacier. 262 HAIL, SNOW, AND GLACIERS Should we follow a ravine downward from a snow-clad crest, we should find the snow growing more and more solid under our feet until we reached the snow line. Below this the com- pacted snow would appear as ice. Following the ravine to a still lower level, we should observe that the ice mass filled it from side to side and terminated at length among gardens and pastures, a stream of water gushing from its cavernous extremity. Other glaciers, smaller in extent, and containing comparatively little ice, never reach the lower valleys. Mek de Glace — Sea of Ice This celebrated glacier is formed by the union of several branches descending from the Mont Blanc range. The compacted snow above the snow line is called the nhw (na-va). It is in general about half the density of ice, or more than three times that of snow. Glacial Motion. — Solid and immovable as these mighty masses of ice appear, they are really in motion. Long before glacial motion was suspected by scientific men, it had been known to the mountaineers that blocks of stone lying upon the surface of glaciers moved slowly downward. A large number of carefully conducted observations have GLACIAL MOTION 263 been made, which prove not only that the glacier has motion, but that its motion closely resembles that of a river. It is swiftest in the center, and slower, owing to the friction, near the sides and bottom. Notwithstanding this movement, the termination of the glacier retains about the same position from year to year, because it is melted away as fast as it moves downward. Kkanz Josef Glacier, New Zealand This glacier lies on the western slope of the Southern Alps. Its length is 8\i, miles. The rapidity of the motion of a glacier depends upon the season of the year, the size of the glacier, and the inclination of its bed. The motion is more rapid in summer than in win- ter, in the daytime than at night, and in a large and deep glacier than in a small one. The average rate per year for glaciers of the Alps varies from 25 to about 100 yards. The middle of the Mer de Glace was found by Tyndall to 16 M.-S. PHYS. GEOG. 264 HAIL, SNOW, AND GLACIERS move 20 to 33 inches a day in summer. The rate is about half as much in winter. The following figures express in yards the motion, during one year, of a row of poles set in a straight line across the glacier of the Aar, by Professor Agassiz : — 5. 20. 48. 55. 62. 64. 67. 6g. 79. 68. 64. 54. 47. 39. 21. II. I. The central part, therefore, moved about 80 yards a year. The great glaciers of Greenland and Alaska move at various rates, 60 or more feet a day. Some glaciers, notably that of the Rhone, tell their own tale of their movement down the valley. On their surface concen- The Mum Glacier, Alaska This great ice-stream, which results from the union of many tributaries, enters an inlet of the sea. Its water front is about a mile wide and rises perpendicularly 250 feet or more. From it masses of ice break away which float off as small icebergs. Since the above photograph was taken the extremity of the glacier is less accessible to tourists on account of the shoaling of the inlet. trie curves are seen bulging toward the lower end of the glacier. These show, as clearly as a line of stakes, the more rapid movement of the central portion of the glacier. Owing to the slowness of glacier motion, it may be a century or more before what is now the upper end of the glacier will get to the foot of the mountain. Theory of Glacial Motion. — Various theories, none of which is in all respects satisfactory, have been advanced to account THEORY OF GLACIAL MOTION 265 for glacial motion and the accompanying phenomena. The first thing to be accounted for is the motion itself. Two causes for this may be given : (i) gravitation ; (2) expansion within the glacier. It is probable that both these take part in producing the motion. Gravitation, or the weight of the glacier, would naturally draw the mass down the slopes of the valley. E-xpansion within the glacier needs explanation. When the water from the melted surface of the glacier percolates down- ward into the interior of the mass, it encounters a temperature of 32° F. It freezes and of course expands. Its expansion must take place in the direction of least resist- ance, which, owing to gravity, is toward the lower end of the valley. The following facts must now be considered : first, that the ice of a glacier accommodates it- self to the shape of its inclosing valley very much as a river does to its channel ; and, second, that after fracture its parts reunite. These phenomena are explained by what is known as regelatiou or second freezing. If we pound a mass of ice into fragments and then moisten the broken surfaces, the fragments will readily freeze compactly together again. This is what occurs in a glacier. In passing through narrow gorges it is crushed and broken, and in ghding over steep '^s^ •* Crossing Franz Josef Glacier, New Zealand Note the irregularities of the surface in the form of pinnacles which have resulted from superficial melting. 266 HAIL, SNOW, AND GLACIERS CREV ASSESS irregularities in its bed it is cracked and splintered. The lower parts break away from the upper, and fissures of great depth called crevasses are formed, as shown in the following illus- tration. But after the ice /^?*:^~ has been thus broken and splint- ered or sundered by crevasses, it re- unites and forms one compact mass. The crevasses admit warm air, and their walls are perhaps slightly thawed, or the ice on the top of the glacier being melted, water trickles down and moistens the fractured surfaces. In this con- dition the mass of fragments is com- pressed by its con- fining valley walls, the sundered portions are brought together again, and regelation occurs. Underpressure ice melts at a lower temperature than 32° Y. If a wire weighted at each end is caused to cut through a block of ice, water will be seen flowing round the wire, while, in the cut behind or above the wire, it is found to be frozen. This experiment has an important bearing upon the phenomena of glacier motion. Pressure is obviously exerted by certain portions of the A Crevasse This fissure was encountered in making an ascent of the Jungfrau, Switzerland. From stereograph. Used by permission. I MORAINES 267 glacier upon others, especially when the glacier is squeezed within gorges. If this pressure reduces the melting point from 32° F. to 28°, the mass being above the latter temperature, it is easy to see how the onward movement of the glacier would be facilitated by reason of its partial liquefaction. Moraines. — The rocks and debris brought down from the slopes of the ravine by the action of the frost and by av'alanches accumulate on the sides of the glacier, forming dark bands of earth and stones, varying in size ac- cording to the character of the rock encountered. These bands are called mot-aines. Occurring at the sides they are called lateral moraines. At the confluence of two glaciers, the moraines which skirt the two sides that join are united, and form a medial ^moraine. If another glacier unites with this again, a second medial moraine is formed in the same man- ner. The earth, stone, and bowl- ders brought down on the glaciers form, at the lower end of the glacier, where the ice melts and leaves them, immense deposits called tcr- In Moraines (a, b, c, d, e).o¥ the Mer de Glace the above cut it will be seen that the Glacier du Geant unites first with the Glacier des Periades, and from their junc- tion the dotted line shows the medial moraine formed from the right moraine of the G6ant glacier and the left moraine of the Periades. Where the glacier thus re- inforced receives the Glacier de L6chaud, another medial moraine is formed; and a third where the Tal^fre adds its tributary stream. By the junction of these is formed the Mer de Glace. minal moraines. Bowlders of Transportation. — In some regions of the earth the surface is strewn with bowlders derived from distant sources. They evidently once formed a part of an old moraine, and their 268 HAIL, SNOW, AND GLACIERS presence is explained by the transporting power of glaciers. As the ice melted they were deposited in their present positions and sometimes so gently as to form the so-called rocking stones that may be swayed back and forth if pushed by the hand. These transported bowlders vary greatly in size. They may weigh hundreds of tons, but usually they diminish in size as the A TRANSFUKlKli (jl,H lAL BOWLDER, YELLOWSTONE NA'WONAL PaRK This massive bowlder of granite is 24 feet long, 20 feet wide, and 18 feet high. To have reached its present position, near Inspiration Point, it must have been carried from 30 to 40 miles. distance from their origin increases. A belt of country extend- ing from the Baltic to the Black Sea is strewn with bowlders rent from the Scandinavian mountains. The Glacial Period. — The former existence of extensive ice sheets over the northern portions of Europe and North America is evident. Among the proofs may be cited the following : the occurrence of smooth and polished rock surfaces ; striations and DRUMLINS, ESKERS, AND KAMES 269 grooves similar to those found in regions known to have been glaciated ; old moraines ; transported soils and bowlders ; valleys filled with transported rock waste ; ice-eroded rock basins now forming lakes. The time of this ice invasion in the earth's history dates from an age just preceding the probable advent of man. So exten- sive were the altera- tions of surface fea- tures then produced that sufficient time has not yet elapsed to ob- literate the evidence. Drumlins, Eskers, and Kames. — In cer- tain glaciated areas, as in central New York, central and eastern Massachusetts, and southern Wisconsin, there are found hills and ridges of glacial debris or //// having an oval or elongated oval form and smooth, rounded surfaces. Their longer axes lie in the direction of the ice movement, as will appear from an ex- amination of the striae and grooves on the neighboring rocks- Such elevations have been termed dntuilins. Their height varies, but rarely exceeds 100 to 200 feet; their length also varies, ranging from a half a mile in the short forms up to a mile or even two miles in the more elongated forms. These hills are of a morainic character and often constitute the most prominent features of a landscape. Map showing the Area of North America covered by ice in the glacial period Salisbury. Geological Survey of New Jersey. 2 70 HAIL, SNOW, AND GLACIERS Glacial Grooves at Kingston, Iowa — Iowa Geological Survey In these groovings the movement of the ice body in four directions is recorded. Another topographic feature of glacial origin is seen in the winding or sinuous deposits of washed sand and gravel which Drumlin, Savannah, Wayne County, New York The right-hand end has been notched by the wave cutting of Lake Iroquois, the predeces- sor of Lake Ontario. From photograph by Professor H. L. Fairchiid. glacip:rs as kivkr sources 271 form well-defined ridges, not often exceeding 50 feet in height and usually of less elevation. They are known as cskers. Their origin is somewhat obscure, but it is thought that they represent deposits of debris in subglacial streams flowing in tunnels or deposits in canyonlike gorges cut in the ice by stream wear and melting. Closely related to drumlins and eskers are mounds or knolls of sand and gravel, glacial debris, which has been more or less stratified through water action. These deposits have been termed kames. The materials of which they are composed were evidently deposited adjoining the ice by streams issuing Side View of Esker, Pittsford, New York From pliotogrgph by Professor H. L. Fairchild. from glaciers and, whenever the ice melted, left in the form of mounds. Glaciers as River Sources. — The glacier, as it imperceptibly glides down the mountain, is melting all the time, and the traveler upon its rugged surface may hear, far down in its creviced depths, the sound of running water, which gathers volume from a thousand trickling streamlets, and at last issues forth, the never failing source of some noble river. The Rhine, the Rhone, and many tributaries of the Danube and Po spring from glaciers in the region around the Saint 2/2 HAIL, SNOW, AND GLACIERS Gothard ; and every one of the hundreds of glaciers found among the Alps nourishes some stream. The Ganges, in India, leaps out from under a glacier, a torrent 40 yards in width. Distribution and Size of Glaciers. — Glaciers of enormous size are found in the Arctic and Antarctic regions. In the Old World the grandest glacier region of the Temperate Zone is that of the Himalayas. The glacier of Bepho, in one of the .'. (iKoup OF Kames, Mendon Ponds, Monroe County, New York From photograph by Professor H. L. Fairchild. valleys of the Karakoram range, is t,6 miles in length — about four times as long as the Mer de Glace — and covers hundreds of square miles in area. Many others in the same region are of nearly equal extent. It is estimated that the number of large glaciers in the Alps is about 500, and that the surface constantly covered by snow, neve, and ice is more than 1000 square miles. The thickness of the Alpine glaciers is believed to range from 200 to 800 feet. ICEBERGS 273 The Pyrenees and the Scandinavian mountains contain glaciers, and large ones exist in the Caucasus. In the New World, Greenland and Alaska have glaciers far surpassing in magnitude those of the Old World. The Hum- boldt Glacier, in Greenland, is more than 60 miles in breadth and 300 feet deep. The Malaspina Glacier of Alaska, according to Russell, has an area approximating 1500 square miles. He has described it as "a vast, nearly horizontal plateau of ice." A-N li.KlJKK Glaciers are also found upon Mount Shasta, upon Mount Rainier, and in the Selkirk Range in Canada. The Andes, except at their southern extremity, are destitute of them. As distinguished from valley glaciers, continental glaciers or ice sheets cover the entire surface over large areas. They are great snow and ice plains or, if sufficiently elevated, plateaus. At present they occur in Greenland and the Antarctic regions. The ice sheets of the Glacial Period were undoubtedly of this type. Icebergs. — The glaciers of the polar regions are not melted into rivers like those of temperate latitudes, Their lower ex- 274 HAIL, SNOW, AND GLACIERS tremity, therefore, is pushed out into the sea, and masses, often of great size, are broken off from time to time by the buoyancy of the water and borne away by ocean currents. These are called icebergs. On the polar side of 55°, soutli, the sea, all the way round the earth, is studded more or less thickly with icebergs. During his Antarctic voyage in 1841, Sir James Ross sailed 450 miles along an unbroken barrier of ice. It stood 180 feet out of the water, and was aground in water 1500 feet deep. Admiral D'Urville fell in with an ice mass off the Cape of Good Hope 13 miles long and 100 feet high. Maury met with them as near the equator as 37° south latitude. Indeed, icebergs come from the unexplored Antarctic regions in sufficient number to stud an area as large as the continent of Asia ; for navigation is endangered there by ice throughout an area of not less than 15,000,000 square miles. On the north side of the equator icebergs are found only in the Atlantic; never in the Pacific Ocean. They drift out from their nurseries in the polar regions with the cold currents, which bear them southwardly until they dis- appear in the warm waters of the Gulf Stream. They frequently lodge on the Banks of Newfoundland, where they greatly imperil navigation. XXV. ELECTRICAL AND OPTICAL PHENOMENA Atmospheric Electricity. — Concerning the precise nature of electricity we are ignorant. Although known only by its mani- festations or effects, it has been defined as a "powerful physical agent." Among the phenomena attributed to it are shocks more or less violent, heating and luminosity, chemical action, attraction and repulsion, etc. Electricity is of two kinds, posi- tive and negative. The former is that developed on a glass rod by rubbing it with a silk cloth ; the latter that developed on a stick of sealing wax by rubbing it with a flannel cloth. Bodies charged with like electricity repel, while bodies charged with unlike elec- tricity attract each other. By the use of suitable instruments it has been shown that ordinarily the atmosphere is charged posi- tively and that the presence of electricity is by no means confined to showery weather or thunder storms. During cloudy weather it may be either positive or negative, but during thunder or snow storms it may change from one to the other with great rapidity. The electric discharge known as lightning is a visible mani- festation of atmospheric electricity. It may occur between a charged cloud and the earth or between two oppositely charged clouds. It would seem that the cloud units or vapor particles are individually electrified and that upon condensation into drops the amount of electricity equivalent to that spread over the surfaces of the component vapor particles is, in the case of each drop formed, spread over a surface of much less area. From this it follows that each drop becomes more highly charged than its component units or is at a \{\g\\Q.x potent ta I. A cloud is formed of a vast number of water drops. As they further unite by condensation the potential of the cloud becomes still greater ;' that is, the amount of electricity for a given sur- face area is increased more and more. If, under such condi- 276 ELECTRICAL AND OPTICAL PHENOMENA tions, the cloud should approach the earth, a disruptive dis- charge through the intervening air may take place or the same phenomenon may occur upon the approach of two oppositely charged clouds. Lightning flashes are of several kinds — stream lightning, zig- zag lightning, sheet lightning, and ball lightning. Stream lightning consists of a broad, straight flash. Zigzag lightning consists of flashes passing between two bodies of air or clouds, or between a cloud and the earth. Since different portions of the air have different conducting powers, and the electricity fol- lows the path of least resistance, the course of the lightning natu- rally becomes zigzag. Sometimes the flash is forked. Sheet lightning, fre- quently called heat lightning, appears as a glow of light illumi- nating vast clouds and ZIGZAG LIGHTNING, FROM A PHOTOGRAPH ^^^^ j^^.^^ ^^^^^ ^^ the sky. It is probable that this kind of lightning is the reflec- tion of the lightning of some distant storm. Ball lightning appears in the shape of globular masses of fire, which explode with violence. It is of rare occurrence. Thunder is thought to be occasioned b}' the sudden rushing together of the portions of the atmosphere that have been divided by a flash of lightning. It is not often heard at a greater distance than fourteen miles. Occasionally, however, in level regions such as the prairies, it may be heard at a very much greater distance. The flash is seen instantaneously, because light travels about 186,000 miles in a second. The sound requires about five seconds to travel one mile. Hence if, after seeing the lightning, we count the number of seconds, or pulse THE AURORA 277 beats, until we hear the thunder, it is easy to ascertain how near the flash has been to us. In general the electricity does not pass from the air to the earth, but only from one portion of the atmosphere to another. When a discharge to the earth does occur, the effects are often very destructive. The strongest trees, if struck, are rent and stripped of their branches, the sap being suddenly converted into steam, and an explosion actually taking place. Animals and men who are struck are almost always killed. The Aurora. — Another phenomenon, in which atmospheric electricity apparently plays an important part, is the illumina- tion, often a magnificent display of color, frequently seen near the polar regions of the earth. It takes on a variety of forms. Sometimes it is simply an arch of light spanning the sky from east to west near the horizon, with quivering streamers of white, green, or crimson light, shooting fitfully to the zenith. Some- times mere masses of colored light are observed. Again the whole heavens are flushed. In the northern hemisphere it is called the aurora boiralis {" Northern Lights ") ; in the southern hemisphere, the aurora australis (" Southern Lights "). Of the two displays the'former is better known. The zone of its greatest brilliancy is slightly irregular, lying, for the most part, between the parallels of 60° and 70° north latitude. It follows roughly the Arctic shore line of the Eastern Hemisphere, but in the Western Hemisphere it passes southeast from Alaska to Hudson Bay, thence south of Greenland and Iceland to the northern shores of Scandinavia. Auroras are more frequent as we approach the poles. Within the tropics they are almost unknown. Their law of distribution seems to be the reverse of that which governs the distribution of lightning. The following facts show that the aurora is an electrical phenomenon: — (i) The delicate shades of rose, purple, and violet, which characterize the more brilliant auroras, can be produced experimentally by passing currents of electricity through vacua in Geissler tubes or receivers. 2/8 ELECTRICAL AND OPTICAL PHENOMENA It has been computed, from observations of a large number of auroras, that the beams do not usually approach nearer to the earth's surface than 50 miles, and sometimes extend from it to the distance of more than 250. At such altitudes the atmosphere must necessarily be very attenuated, like that through which the electricity is passed in the experiments alluded to. (2) Direct evidence of the electric character of the aurora is found in the effect produced upon telegraph wires during an auroral display. The aurora has sometimes caused the instruments to work, as though it had been a battery. Sometimes it completely interrupts their work. (3) The magnetic needle, also, is frequently disturbed during auroras in a degree corresponding to their brilliancy. Saint Elmos Fire. — In storms at sea the masts and yards of the ship are sometimes tipped with balls of electric light. They are due to elec- tricity passing without noise, when the clouds are low, between the clouds and the tips of the spars of the ship. Optical Phenomena. — The most impor- tant of all the optical phenomena connected with the atmosphere is also the most com- mon. It is the diffu- sion of light. This is brought about by reflection and refraction. By the former, light is propagated from particle to particle in the atmosphere. By the latter, it is retained above the horizon when the sun has actually gone down, and it is bent into the atmosphere before he has actually risen above the horizon. Refraction and reflection give rise to the exquisite variety of colors which deck the morning and evening sky. They also occasion the phenomena of rainbows, parhelia (commonly called sundogs or mock suns), paraselenae (or moondogs), halos, and miragre. Saint Elmo's Fire A OPTICAL PHENOMENA 279 The rainbow is an arch of colored light which spans the heavens during a storm. It is seen only when the sun is shining at the same time that rain is falling. The descending drops separate the white sunlight into its ele- mentary colors. Hales are rings of prismatic colors round the sun or moon. They are really circular rainbows, probably due to the refracting power of the ice crystals com- posing cirrus clouds. Mirage. Another effect of refraction and reflection is commonly called iiiirage. It is often observed in the desert. Distant villages seem under its in- fluence to be near to the spectator or to be suspended in the heavens above. Sometimes the traveler thinks he is approaching a pool of sparkling water, and hastens to quench his thirst, when he finds that he has been pursuing a mirage. Mirage is also observed at sea. distant ships being seen elevated above their true position, or even inverted in the air. M.-S. I'HVS. GEOG. — 1 7 PART v.— LIFE XXVI. ANIMALS AND PLANTS: THEIR RELATIONS AND DISTRIBUTION Inorganic and Organic Bodies. — In the preceding chapters at- tention has been especially directed to the land, the water, and the air. They constitute the inorganic or lifeless portions of the earth. The following pages treat of living bodies, including Man himself. As such bodies are possessed of parts adapted to certain ends, — for example, lungs for breathing, feet for walking, eyes for seeing, — they are said to possess organs having certain func- tions, hence all such bodies are organic. It is customary, there- fore, to speak of mineral matter as inorganic and of living matter, or that formed through the process of living, as organic. Of living things two grand divisions are recognized : plants and animals. In the study of Physical Geography it is necessary to consider, first, the relations of each of these divisions to the other ; and secondly, their distribution and its causes. Animals and Plants. — In their higher forms animals and plants are easily recognized, but lower in the scale of life the distinguishing characters of each become less marked until eventually forms are encountered which are recognized as ani- mals or plants with the greatest difficulty and at times with much uncertainty. The higher animals differ from the higher plants in many particulars, among which mention may be made of the following : They have a nervous system ; they are not fixed in position, but possess the power of voluntary motion ; they have an internal cavity adapted to the digestion of solid food. The higher plants, on the other hand, are without a nervous system ; they are fixed 280 ANIMALS AND PLANTS 281 in j5osition, that is, the}' are without the power of voluntary motion ; and their nourishment, unlike that of animals, being liquid or gaseous, does not require a digestive cavity. In con- sequence of these distinctions common animals and plants are Victoria Regia rarely confused. When, however, the lower forms of animals are reached, especially those which are attached or fixed to for- eign objects during the whole or a part of their lives, then there is great danger of mistaking them for plants. The sea anemone and the coral polyp, for instance, are both plantlike in appear- ance, the spreading tentacles about their mouths presenting a flowerlikc fringe. 282 ANIMALS AND PLANTS Plants, in general, differ from animals in their power of trans- forming inorganic matter into living matter. Animals do not possess that power. Hence for their food animals are dependent, either directly or indirectly, upon plants. Animals feeding upon plants are herbivorous ; those feeding upon other animals are carnivorous. Where there is neither grass nor other vegetable growth, herbivorous animals cannot live; and where they are not found, carnivorous animals, which feed upon them, cannot exist for want of a food supply. General Facts concerning Distribution. — It is a familiar fact that the same kinds of plants and animals are not found every- where. Some forms are widely distributed, others are restricted to very narrow limits. The region within which any plant or animal is found is commonly called its geographical range. The dandelion and buttercup blossom even amid the glaciers of Greenland. The orange, the date, and banana grow only within or near the tropics. The gigantic water lily called the Victoria Regia has been found only in the basins of the Amazon and Orinoco. Range Dependent on Climate. — Certain climatic conditions render it possible or impossible for the various species of living forms to exist. Of these conditions by far the most important are temperature and moisture. The peculiar plants and animals of the torrid zone would ob- viously die, if placed amid the cold of the Arctic circle ; while it is equally certain that the polar bear and his associates would become extinct, if they were exposed to the scorching heat of the tropics. The early geological history of the globe furnishes striking illustrations of this principle. The entire assemblage of animals that we now lincl upon the earth did not simultaneously spring into existence. Those species first ap- peared which were suited by existing climatic conditions. Low forms of ani- mal life prevailed at first, and then higher and higher successively, until such conditions arose as were favorable to the life of Man. and then, at length, his creation took place. Moreover, many of the animals that once abounded have entirely disap- peared. Their existence is attested only by fossil remains. Lynxes, bears, MODIFICATIONS BY CLIMATE 283 ami hyenas once roamed over the fields of England, and crocodiles swarmed in its rivers; huge mastodons, larger than the modern elephant, flourished on what are now the banks of the Hudson, and browsed amid the forests of Si- beria. Their tusks are dug up at the mouth of the Lena and upon the islands of New Siberia, in such quantities as to form an article of regular commerce, under the name " fossil ivory." The climatic conditions favorable to their existence have ceased, and their race has therefore ])ecome extinct. Modifications by Climate. — It would follow as a natural con- clusion from the fact that plant and animal life are largely de- pendent on physical conditions, that changes in these conditions should bring about changes in the plants and animals affected by them. Such we find to be the fact. Modifications of a very extraordinary nature can be affected by varying the " environ- ment " of a plant or animal, and allowing the new environment to be permanent during a sufficient length of time. Many of our most valuable food plants have been thus transformed. The grains in general are believed to have been originally wild grasses. Our own Indian corn presents a very interesting illustration of climatic modification in a vegetable form. In the South and the Northwest it often attains the height of 12 to 15 feet. As we advance northward through its belt of cultivation, along the At- lantic slope, its height diminishes, until, in New England, it is not usually more than about five feet high. Again, the appearance and quality of its grain have been singularly modified. It is a familiar fact that we have a number of varieties, field corn, sweet corn, pop corn, with white, yellow, brown, and even black grains. Similar illustrations might be given of the modifications of animal forms by changes in their physical conditions. The Shetland pony and the race horse came from one original stock. The terrier, the greyhound, and the mastiff had a common parentage. Zones of Vegetation. — Since the extent of the geographical range of plants depends mainly on temperature and moisture, it follows that the surface of the earth may be divided into zones of vegetation. These will correspond more or less closely with the 284 ANIMALS AND PLANTS zones of temperature. They will of course be defined not by lines of latitude, but by lines of heat, or isotherms. The principle of division is this, that within belts or zones having a certain average annual temperature, certain plant growths will flourish ; beyond the limits of such zones these characteristic forms disappear, and others are found which are suited to the prevailing temperature. Thus each zone has its characteristic forms of plant life. Although in naming the zones of vegetation the same terms are employed as in the ordinary divisions by lines of latitude, it should be borne in mind that the signification of the terms has been slightly changed in order to accord with lines of tempera- tnre. Horizontal Zones. — The surface of the earth may be divided into the following horizontal zones of vegetation: (i) an equa- torial zone ; (2) two temperate zones ; (3) two polar zones. The Equatorial Zone extends north and south of the equator, and is bounded by the annual isotherms of 70°. It is the zone of greatest heat and most abundant moisture, and consequently of most luxuriant vegetation. The characteristic growth of this belt is that of the palms. The trees do not lose their leaves in winter. The Temperate Zones extend northward and southward of the equatorial, and are bounded by the isotherms of 32°F. Here the tropical palms disappear, or are replaced by dwarfed repre- sentatives of the family. The characteristic forms are those of the deciduous forest trees, — those which shed their leaves in autumn and renew them again in spring, — of which the oak, the chestnut, and others belonging to our own forests are familiar examples. The colder parts of these zones are marked by the abundance of conifers (pines, larches and spruce, and juniper trees). The Polar Zones extend north and south from the temperate. Within them the average annual temperature is not higher than 32°F., and in many portions it is below 5°. The warmer parts of these zones contain vast forests of spruce, pine, and larch. The HoKTZONTAl. ZONKS 285 A Group of Date Palms A scene in the town of Luxor on the Nile. colder portions are characterized by the growth of dwarfed birch, alder, and willow trees. But beyond certain limits trees 286 ANIMALS AND PLANTS wholly disappear, and only the lower forms of plant life, mosses and lichens, remain. Vertical Zones. — Since, by ascending sufficiently high, even in equatorial regions, one can pass through every variety of climate, torrid, temperate, and frigid, it is evident that there must be vertical as well as horizontal zones of vegetation. On the lower slope of the Andes, for example, are found regions of palms and bananas, tree ferns and vines. These correspond to the zone of equatorial vegetation. Higher up are encountered the deciduous trees of the temperate zone. Still farther up if \ there is a re- 7 JlI\.3^.''\. ^ion closely re- S ■••.-A^:/|^.Tos; ;. A Region of Lichens. semblillg the '^''WSS^^^^^Z^^^^- Arctic zone: I . ^ 2^^^ ^£^^'^^\ ^'^^^^^ Region. Conifers are ^' ""iSSlfSlW'Si^^ the prevailing .i ^^*^ ^ 9^ s;/^^5^f^ Limit of ordinary large trees type, while de- i y \\A''\l^^'^*f\\^lVt(^'^^^^^'^^^^^'^^ ciduous trees S 'y^^^J'^^^'i'y)^^^^^ are represent- y ixl.^il^^A^:02^^^:^}^ Regionof Palms cd by shrubs ~ < t^--? /-' ''^' --^■^^'-.iv ^^.^''■g.-,., and dwarfed Vertical Zones of Vegetation specimens. Near the snow line trees of every kind disappear, and mosses and lichens are the only forms of vegetation that can with- stand the perpetual cold. The Flora of the Sea. — The flora of the sea differs from that of the land in color. It is less inclined to green. The plants of the sea are brown and yellow, pink and purple, green, orange, and violet, with all intermediate shades. The vegetation of the sea has, like that of the land, a vertical and a horizontal distribution. Both are determined mainly by the temperature of the water and the nature of the sea bed. In the deepest parts of the ocean nothing but microscopic forms of vegetable life of the simplest kind (called diatoms) occur. The smaller algae or seaweeds scarcely exist below the i THE FLORA OF FHE SEA 287 depth of 300 feet ; the larger are not found deeper than about 60 feet below the surface. The horizontal range of many marine plants is coextensive with the sea. Others, like land plants, have limited ranges. Among the most interesting kinds of algae are the Macrocystis pyrifcra, the H Unnllcea utilis, and the Gulf Weed. The Macrocystis pyrifera measures 700 feet in length. Tliis weed is Hlce a cord. It attaches itself to the rocks, and grows from the bottom in the littoral waters of many covmtries, and especially along the northwest coast of America. Few, if any, forms of vegetation have a wider geographical range than this weed. After all traces of plant life on the land have ceased, on approaching the poles, it is still found flourishing in the water. The WUrinllcEa utilis grows in the waters of the Falkland Islands and ad- joining regions. The surf often twists it into cables several hundred feet long and as thick as the human body. This, like the Macrocystis pyrifera, fastens itself to the rocks, in stormy waters, with such tenacity that sometimes, in the attempt to tear it away, large bowlders are brought up adhering to its roots. Plants of this species surround Kerguelen Land with such a tangled mass that rowboats find it difiicult to get through it. The Straits of Magellan are so thick with these weeds that they fouled the rudder and so entangled the propellers of the first steam vessels that passed through these waters as seriously to interfere with the navigation. Among the most widely distributed forms of marine vegetation is the Gulf Weed {Fiicus nataiis). It is not known whether it grows at the bottom or near the surface of the sea. It is always found afloat, living and growing, but without any signs of roots. It lies so thick in the Sargasso Sea as completely to hide the waters in many places and give the sea the appearance of a drowned meadow. XXVII. THE DISTRIBUTION OF USEFUL PLANTS Food Plants. — It will be of interest to consider the geo- graphical distribution of those plants that are of the greatest importance to man. Of these, the grains or cereals, as they are called (barley, rye, wheat, Indian corn, rice, and millet), deserve first attention. Certain of them have, of all plants, the widest geographical range. Barley is cultivated in Europe as high as 70° north latitude, and on the Asiatic table-lands at an elevation of 13,000 feet. Rye will grow in all regions between 67° north and south latitude. Wheat has a range almost equal to that of rye. It ripens in North America as far as latitude 55", and in Europe, owing to the influence of tempering winds and currents, as far as latitude 64^. In Mexico and the Andean region its culture begins at the height of about 2500 feet and is successful as high as 10,000. Upon the Himalayas it is cultivated as high as 12,000 feet above the sea. Indian corn will grow and ripen in the open air, from the parallel of 45° or 50° north to the corresponding parallel south. Its range embraces two thirds of the earth's surface. In the torrid zone neither wheat nor Indian corn do well at the sea level, though they j^roduce finely on the mountain sides. Rice is limited in its geographical range by the parallels of 45° north and 35° south. This belt covers more than half the surface of the earth. The plant thrives best in low and swampy ground, and is the chief cereal cultivated in China and japan. Its grain is the principal article of food for one third of the entire human race. Millet is the most prolific of the cereals. It is adapted better than any other to the vicissitudes of a tropical climate. In 288 FOOD PLANTS 289 Egypt, Arabia, Turkey, and Italy it is an important article of food, and in India it, and not rice, is the staple food grain. Nearly allied to the cereals as an article of diet is the potato. It has a range almost equal to that of barley. It is probably a native of Chile or Peru, but will grow in Iceland. In the ]o\v. damp, and hot portions c^f the ecjuatorial region Bkeadfrlm r wheat and corn are replaced by rice and the banana, manioc or mandioca, and the breadfruit. The banana, indigenous in the regions of intertropical Amer- ica, is, as an article of food for the masses, what rice is to the Hindu, the potato to the Irish, and wheat to the European. An acre of ground planted in bananas requires less cultivation and yields more abundantly than any other food plant. Hum- boldt estimated the yield to exceed that of the potato 44 times. 290 THE DISTRIBUTION OF USEFUL PLANTS and that of wheat 133 times. The banana flourishes 4000 feet above the sea. Manioc or Mandioca is a native of South America. It is also extensively grown in Africa and other tropical regions. Its large turniplike root, dried and grated, is known as cassava, and purified as tapioca. It is an article of food for a large part of the population of South America. Breadfruit is characteristic of the islands of the Pacific. Its fruit furnishes the natives with food somewhat resembling bread. Sugar cane, so far as we know its history, seems to have been a native of India or China. It grows in the warm latitudes of every continent. Beverage Plants. — The chief plants which yield beverages, tea, coffee, and cacao, are grown in warm re- gions ; tea in China and Japan, India, and Ceylon ; coffee in southern Asia, central Africa, and the tropical portions of North and South America. Cacao is a native of the trop- ical regions of North and South America. Spices and Narcot- ics. — The geograph- ical range of the spices, such as cin- namon, nutmeg, gin- ger, pepper, cloves, and allspice, or pi- mento, is narrow. It is confined to a few degrees north The East Indies are specially the NUTMEi; and south of the equator, region of the spices. The important narcotics, tobacco and opium, are natives of PLANTS USED FOR CLOIHING 29 1 warm regions, but their geographical range extends into the temperate zones. Plants used for Clothing. — The principal plants which are used for textile fabrics and clothing are cotton, flax, and hemp. Cotton, the most important of them all, will grow and mature well at moderate heights, anywhere between the parallels of 37.^° north and south. This belt being 75° of latitude broad, and extending entirely round the earth where its circumference is largest, gives for this plant a geographical range that em- braces more than half the earth's surface. The United States, Brazil, India, and Egypt are the chief cotton-growing countries. Flax and hemp are confined to the climates of the temperate zone, and are brought to their greatest perfection between the parallels of 25° and 50° north. The Medicinal Plants, such as yield sarsaparilla, jalap, castor oil, quinine, gums, and balsams, are almost all indigenous to the torrid zone. Foremost among them stands the cinchona, from which quinine is obtained. Is is a native of the eastern slopes of the Andes, flourishing in a belt that extends through Bolivia, Peru, and Equador, from 3000 to 9000 feet above the sea level. It has been successfully acclimatized in India. Useful Trees. — The ornamental woods and dyewoods, such as mahogany, rosewood, sandalwood, and logwood, are confined to the torrid zone. The oak, walnut, chestnut, maple, ash, with pines, firs, and cedars, belong to the cooler latitudes. The geographical range of the oak extends from the tropics to the verge of the frigid zone. The timber trees of the tem- perate zone are replaced in the torrid by the teak and bamboo. XXVIII. THE DISTRIBUTION OF ANIMALS General Statements. — Animals, like plants, require a certain temperature for the maintenance of their life. Furthermore, no animal except Man can inhabit regions in which nature does not spontaneously provide for it suitable food ; and hence the fauna of every country is dependent on its flora. For these two reasons the distribution of animals, like that of plants, depends mainly upon climate. Zones of Animal Life. — In view of this fact it is usual to divide the earth's surface, in relation to its fauna, into the equa- torial, temperate, and polar zones, as has been done in treating of the distribution of plants. The Equatorial Zone is characterized by the abundance of its forms of animal life. It is the zone of lions, tigers, rhinoceroses, elephants, camels, crocodiles, poisonous serpents, and birds of the most brilliant plumage. The temperate zones, on the other hand, are distinguished by the number of their useful animals, such as the ox, cow, horse, sheep, and goat. The eagle, turkey, and pheasant are among the birds. In coloring, the animals of temperate regions are far less brilliant than those of the Equatorial Zone. In the Arctic regions (for of the Antarctic we know little) are found the fewest species, although the individuals are numerous. The reindeer, musk ox, white and brown bear, wolves, white foxes, and sables are the chief land animals. The seal, walrus, and whale frequent the waters. Reptiles are unknown. Ducks and gulls abound. Zoological Regions. — It is obvious that any division of the earth's surface into zones characterized by peculiar fauna and flora is necessarily far from exact. Although the distribution 292 I ZOOLOGICAL REGIONS 293 of life on the globe is mainly dependent on climate, it is not so altogether. For, in the first place, many species overlap, being found in more than one zone. The dog is the com- panion of Man in every zone ; sugar cane grows in both torrid and temperate regions. And in the second place, however alike in climate different portions of the earth's surface may be, they do not nec- essarily have the same flora and fauna. The isotherms of the United States traverse also the Empire of China. Yet there are marked differences between the forms of plant and animal life which characterize the two regions. The iso- therms of 68° F. pass through Australia, South America, China, and the Gulf region of the United States. But the vege- tation and animal life of these regions are strikingly diverse. From these considerations scientific men have been led to seek a mode of division more in harmony with existing facts than that represented by zones, and the plan proposed by the eminent Chimpanzee From photograph. Used by permission of the New York Zoological Society. (294) 30 Longitade 60 130 Greenwich 150 (29S) 296 THE DISTRIBUTION OF ANIMALS naturalist Sclater, and more exactly defined by Mr. Wallace, seems to be the most satisfactory thus far devised. According to this division the surface of the earth is made up of six regions, each of which has certain forms of life peculiarly its own and not found elsewhere, although it may have Barbaky Lion From photograph. Used by permission of the New York Zoological Society. many species in common with other regions. The following are the names of the regions with their leading characteristic forms. (i) The NortJicni Old World Region includes all of Europe, all temperate Asia north of the Himalayas, and northern Africa down to the Tropic of Cancer. Here we find the bear, wolf, deer, horse, cow, and camel, the wild goats, the eagle, the corn- crake, and bustard. Peculiar to this region are almost all the known species of goats and sheep, moles and dormice ; and among birds the night- ingales, magpies, and almost the entire group of pheasants. (2) The Ethiopian or African Region Qmhr2iCQs> Africa south of the Tropic of Cancer, southern Arabia, and the island of Madagas- ZOOLOGICAL REGIONS 297 car. Here we lose sight of certain forms familiar in the Northern Old World Region, bears, deer, moles, and true pigs ; and camels and goats, except in the desert regions, are equally wanting. Peculiar forms are the gorilla, chimpanzee, and baboon, the hippopotamus and giraffe, the guinea fowls, most of the weaver birds, and the secretary bird. HirPOPOTAMLS From photograph. Used by permission of the New York Zoological Society. Madagascar and the neighboring islands, though classed as parts of the Ethiopian region, have a fauna peculiar to themselves. This insular sub- region is one of the most wonderful in the world from a zoological point of view. It is especially characterized by the abundance of lemurs (nocturnal animals somewhat resembling monkeys, but very small) : while most of the groups in which Africa is especially rich — apes, lions, leopards, giraffes, ante- lopes, and elephants — are wholly wanting. Some of the birds are entirely unlike all other known species. (3) The Indian Region comprises India, Indo-China, and the East Indian Islands as far as the Strait of Macassar. Peculiar to this region are the orang-outang, thetiger.tbe honey bear, the civet, and flying lemurs ; and among the bright-feathered 298 •IIIK DISIRIBUTION OF ANIMALS birds, the argus pheasant, the peacock, the trogon, and the curi- ous little tailor birds. (4) The Aiistralian Region consists of Australia, New Zealand, Polynesia, and those of the Malayan islands that lie east of the Strait of Macassar. This region has a fauna of marked peculiarity. It is notable for the absence of forms elsewhere al- most universal. The higher mammalia of other regions are re- placed by mammals (such as the duck mole) that lay eggs ; and by marsupials (that is, animals with a pouch for holding their young). Of these none are found elsewhere, except the opossum of North and South America. Among the marsu- pials of Australia are the kangaroo, the tree kangaroo, and the wombat. The bird life of this region is rich in handsome and peculiar forms, such as the beautiful bird of paradise, the crimson lory, the lyre bird, the bower bird, the emu, and the cassowary. (5) The North American Region includes North America and adjacent islands north of the Tropic of Cancer. The fauna of this area and that of- the Old World region present marked dissimilarities. Here we do not find native THREE-HORNEM GlKAllh Copyright, 1905, by New York Zoological Society. U.sed l)y permission. ZOOLOC.ICAL REGIONS 299 the horses, asses, cows, sheep, pigs, hedgehogs, and dormice of the Old World. They are replaced by the bison (nearly extinct), raccoons, opossums (marsupial), prairie dogs, and From photograph. Used by permission of the New York Zoological Society. skunks. The thrushes, wrens, robins, and finches are rep- resented by new families. Among animals peculiar to this region are the grizzly bear, the pouched rat, the mocking bird, the blue jay, the blue crow, and the rattlesnake. It is hardly necessary to say that many Old World forms have been introduced. (6) TJie South American Region embraces South America and that portion of North America and the outlying islands which are south of the Tropic of Cancer. Of all the regions this is the most remarkable for the fewness of the forms which it contains in common with others. No M.-S. PHYS. GEOG. — 18 500 KAN(.K OF DRALHilir ANIMALS 301 horse or ass, ox, sheep, or goat is a native of South America. The wild cattle and horses which now roam over its plains and pampas are the offspring of animals introduced by Europeans. This region is equally remarkable as containing a greater number than any other of forms which are strictly its own. Among these are the sloth, the armadillo, the llama, the alpaca l| Gklai (jka\ Kangaroo From photograph. Used by permission of the New York Zoological Society. and chinchilla, the blood-sucking vampire bat, the prehensile- tailed monkey,^ and the destructive boa-constrictor. Here alone we find the condors, toucans, todies, rheas, curas- sows, and mot-mots. The forest-clad slopes of the Andes are alive with the murmur of 400 species of humming birds, some of which pass their existence near the limits of perpetual snow. Range of Draught Animals. — Of special interest is the geo- graphical range of those animals which Man employs as draught animals or beasts of burden. The horse, the ass, and the ox, either native or introduced, are found wherever grains and grasses grow. Beyond the 1 Monkeys whose tails are capable of grasping the branches of trees. 302 THE DISTRIBUTION OF ANIMALS limits of these food plants the reindeer and the dog become the draught animals. The reindeer is fitted to browse upon Arctic mosses, and has the instinct of searching for them SiLVEK-rip Grizzly Bear From photograph. Used by permission of the New York Zoological Society. beneath the snow. He presents one of the most striking cases of an animal adapted to the peculiar conditions of his habitat. In the equatorial regions of the Old World we find the ele- phant serving as a beast of burden ; while to the northward, especially in desert regions, the camel and dromedary are employed. The cushioned foot of tlie camel enables him to tread firmly upon the shiftint^ sands of the desert, while his capacity for carrying an extra supply of water adapts him wonderfully for journeying through its dry and thirsty wilds. In South America, where, to traverse the continent, the traveler has to scale the snowy heights of the Andes, there — UAXGE OF DRAUGiri" WIMAl.S 303 Soirrn Amf.rican Condor From photograph. Used by permission of the New York Zoological Society. A Beast of Burden 304 THE DISTRIBUTION OF ANIMALS and not in North America, where the mountains have gaps that the buffalo could cross — was found the llama, the camel of the New World, the only beast of burden in use among the' native Americans at the time of the discovery of the continent. Malay Tiger From photograph. Used hy permission of the New Yorlc Zoological Society. The llama, with the alpaca and vicuna, which are different species of the same genus, have their habitat along the edge of the snow line on the Andes, where the atmospheric pressure is not more than eight or ten, instead of fifteen, pounds to the square inch. This diminished pressure of the atmosphere has very marked effects upon both man and beast. To one from the lowlands, respiration, in these elevated regions, is difficult. Mules are used for the transportation of merchandise be- tween these places and the seaboard, but never ascend beyond a certain height. At the elevation of 5000 or 6000 feet they are met by the llamas of the table- land, and the cargoes are exchanged. Without the camel and the llama Man, in the early stages of civilization, could have neither crossed the deserts of the Old World, nor scaled the cloud- capped mountains of the New. Among the fastnesses of the Himalayas, and upon the bleak heights of the LIMITED RANGE OF SOME ANIMALS 30s plateau of Tibet, the beautiful m^' serves as a beast of burden. He is to be seen browsing at an elevation of 17,000 feet above the sea. What the camel is to the Arab, what the llama is to the Peruvian, the yak is to the native of Tibet. Limited Range of Some Animals. — Many animals are con- fined to a very narrow geographical range by causes that are r\vo-TuEi> Sloth From photograph. Used by permission of the New Yoik Zoological Society. in some cases quite obscure. The little chinchilla, with its beautiful fur, has its habitat on the Andes of Chile and Peru, 8000 to 12,000 feet abov^e the sea. The chamois inhabits the belt of the Alps which lies between the trees and the snow line. The Kashmir goat, noted for its fine wool, is restricted to the valleys of the Himalayas. The ostrich of Africa, the rhea of South America, the emu of Australia, the cassowary of New Guinea, the aptery.x of New Zealand, are birds which neither fly nor swim. Their gee 306 THE DISTRIBUTION OF ANIiMALS graphical range therefore is very limited. The same was true of the dodo of Mauritius and the aepyornis of Madagascar. Animals of limited range are the most likely to become ex- tinct. The apteryx is nearly so ; the dodo has become so boLTH American Llama From photograph. Used by permission of the New York Zoological Society. within two centuries ; and the aepyornis became so at a very recent period, for one of its eggs (eight times as large as that of an ostrich) was found and brought to Europe in 185 1. Fauna of the Sea. — As with the animals of the land, so with those of the sea — different species have their geographical range, both vertical and horizontal, beyond the limits of which the conditions necessary for their existence are not found. This, however, is less rigidly true with regard to the fauna of the sea than that of the land. It is quite obvious that temperature must be the main element which determines the habitat of marine animals. Other matters, such as the nature of the sea bottom, have a minor influence. —b^—J-^' sf-^X ^ 3 \% t / ■ -^' f ' I'll i \l lis ^' \ it 307 3o8 THE DISTRIBUTION OF ANIMALS Life of Tropical Waters. — The waters of the tropics, like the shores which they bathe, teem with the greatest variety of animal forms. Many of the fish and crustaceans are decked with colors of surprising brilliancy. The sperm whale inhabits the warm waters of this zone, and is most abundant in the Pacific Ocean. Flying fish, alba- core, bonito, and sharks are all in- habitants of inter- tropical seas. Pearl oysters, also, with corals and sponges, are found in this belt. Life of Cooler Waters. — In the cooler seas of the temperate and x\rctic regions we find the greatest abundance of fish that are of value to Man. All the famous food fisheries in the world - those of the cod, the herring, the mackerel, and others — are in the waters of cold currents. Al'll-.KVX From Nicholson and Lyddecker. The Grand Banks of Newfoundland, the fisheries of the North Sea, and those of the Pacific coasts of America. China, and Japan, all lie within the range of the cold flow from the north. It is to the presence of the cold current along our Atlantic seaboard that our own fish markets owe their celebrity. The right whale is found in the cold waters of polar seas. Those of the torrid zone are as impassable to him as a sea of flame. So true is this that the right whale of the northern hemisphere and the right whale of the south- ern are restricted each to his own zone. Although the seal may be found in all latitudes, his favorite haunts are the islands of Alaska, the shores of Labrador, and the bays of southern Chile and Argentina. Other inhabitants of polar waters are the sea lion, ^ TlIK l-I.ORAS OF rilK /( tOl,0( ilt Al . KKCIONS 309 hunted for liis I'lii. and llic walrus, hunted for his ivory tusks, which are superior to those of the elephant, and the narwhal, or sea unicorn, whose ivory horn is eight or ten tVet in length. Various depths are suited to various species of marine animals. The reef- building polyp cannot flourish at a greater depth than about 150 feet below the surface. Lower down, in depths so great as 1500 or even 2400 fathoms, living forms are found, but they are of a low order — foraminifera, sponges, starfish, and mollusks. The bathymetrical range of such creatures is surpri.s- ingiy great. The Floras of the Zoological Regions. — The floia of each region may not perhaps be so distinctly marked as the fauna. Wtsr l.MMAN Boa From photogiapli. Used by permission of the New Nork Zoological Society. There will naturally be much overlapping, many species being very widely diffused, and some being common to all parts of the globe. Still, we ought to find some characteristic floral peculi- arities in each region. The Old World region is the native home of all the cereals excepting maize, of the apricot, the cherry, the apple, the pear, the olive, the cork oak, and sycamore iig. The EtJiiqpiaii region has among its peculiar vegetable forms the baobab, the oil palm, and coffee. The Indian region is characterized by the banyan, the fig, the mango, cinnamon, the guttapercha and teak trees, and the sweet potato. 3IO THE DISTRIBUTION OF ANIMALS The Australian region has a flora very distinct from that of all others. The leaves of the trees are of a peculiar bluish green hue, and strangely present their edges to the sun, arranging themselves vertically instead of horizontally. The eucalyptus or gum trees, of which there are 400 varieties, are probably the loftiest trees in the world. Many are 400 feet high. One monster was felled which measured 480 feet. The beefwood trees are remarkable. Instead of leaves, of which they have none, they have sheaths inclosing their branches. They thus resemble in structure the " horsetail " with which we are familiar. The NortJi Anierican region is the native home of the mag- nolia, the live oak, the Sequoia gigantca (giant trees of Cali- fornia), and persimmon. Nearly 400 species of trees are peculiar to this region. The South American region is distinguished by the multi- tude of its parasitic forms. Peculiar to it are the cinchona, the cacao, the manioc, the potato, the sarsaparilla, the Victoria Kegia, and the passion flower. XXIX. MAN Range of Human Habitation. — Man dwells in every zone and at nearly all altitudes. He is literally cosmopolitan. Unlike the irrational animals, he can to a large extent overcome the force of external conditions. He can protect himself from the severity of the winter's cold, and maintain his existence amid the snows of the Arctic regions ; and on the other hand he can endure the fierceness of intertropical heat. Thus his horizontal range -is almost unlimited. He has, again, an ample vertical range. The lowest place where men have established permanent dwelling places is in the valley of the Dead Sea, 1300 feet below the sea. The highest is at the convent of Hanle, inhabited by twenty Tibetan monks, 16,533 feet above the sea. These limits include a vertical range of more than three miles. The Unity and Diversity of the Human Family. — Wherever Man is found, he presents the same essential features of body and of mind. No such differences sunder men as those which exist between the horse and the lion, the eagle and the ostrich. The human family is of one blood. Still the heat and cold to which man is habitually exposed, the food upon which he lives, and the physical conditions generally by which he is surrounded will, in the lapse of time, produce certain effects upon his bodily and intellectual organization. Hence we find wide diversities characterizing different portions" of the human family. Men differ in color, in feature, in mental and moral peculiarities, industrial habits, social and govern- mental institutions. Division into Races. — Some ethnologists divide the great human family into three, some into five, others into six or even a larger number of races. 3" (312) L. L.P0ATE3 ENCR'G CO., N.Y. (3'3) 314 MAN The five great races of mankind, as generally recognized, are the Caucasian or white, the Mongolian or yellow, the Negro or black, the Malay or brown, and the Indian or red. The Caucasian Race derives its name from the Caucasus range of mountains, because of the tradition that the region traversed by these mountains was the birthplace of the race. The chief divisions of the Caucasians are: (i) the Indo- European, comprising the Hindus, Persians, Circassians, Sla- vonians, Teutons, and Celts ; and (2) the Sem- itic families, of whom the Hebrews and Arabs are the most important. The term Indo-European is derived from the fact that this division of the race has established itself all the way from India to the farthest bounds of Europe. Nine tenths of the peo- ple of the United States, as well as all the peoples of Europe, exxept the Lapps, Finns, and Mag- yars, and the Turks proper, belong to the Caucasian race. Both of the Americas are governed by it. Africa is controlled by it. In Asia, it dominates from the shores of the Mediterranean, through Arabia, and Persia, and along the southern slopes of the Himalaya Mountains beyond the banks of the Brahmaputra. The Caucasians are the most symmetrical in figure, comely in person, and beautiful in feature, of all the branches of the human family. The numerous divisions and subdivisions of the race vary in complexion according to the region they occupy. The extremes are the Germans with their flaxen hair, blue eyes, and Caucasian THE MONGOLIAN RACE 315 fair skin, and the Hindus with raven locks, black eyes, and olive- brown or brownish black skin. The face of the Caucasian is oval, the head ample"; the hair full and often curled or wavy. In intellect this race ranks first. With very few exceptions all the leading thinkers of the world have been Caucasians ; and without any exception all the great discoveries of recent times have been made by members of this family. To this race has been assigned the task of civilizing and enlightening the world. Its social habits and its governmental institu- tions, its educational sys- tems and its religious views, are those which most conduce to the ele- vation and happiness of mankind. Wherever the white man establishes himself he speedily becomes dominant; while the com- munities of other races into which he introduces himself are commonly subjected to a gradual process of extinction. The Mongolian Race derives its name from the Asiatic tribe of Mongols. The Chinese, Indo-Chinese, Japanese, Tibetans, Samoyedes, and Turks in Asia, the Finns, Magyars, and Lapps in Europe, and the Eskimos of the Arctic regions of North America are branches of this race. The color of the Mongolian is olive-yellow. His face is broad, with wide and flattened nose, and small, obliquely set eyes. His hair is straight, coarse, and black. In stat- ure he is somewhat below the ordinary standard of the Caucasian. Mongolian 3i6 MAN In intelligence and moral character he ranks next to the Caucasian. Branches of the Mongolians, as the Eskimo, are very low in the intellectual scale. Not so the Chinese and Japanese. It is true that, in the past, they have displayed the mental inactivity which marks the Mongolian in general. They remained for ages just where their ancestors had been. A great change, however, is going on. The establishment of a constitutional form of government by the Japanese, and their adoption of many im- l^ortant features of European civilization, entitle them to rank among the progressive nations of the world. The same may be said in a less degree of the Chinese. Something also must be said in commendation of the native civilization of both these great Mon- golian communities. China has had a Govern- mental system which has stood the test of ages. Japan, too, has been a prosperous and well-ordered state for generations of which we have no count. In religion the Mongolians are generally Buddhists. The Negro Race is so called from the color of its skin (Latin, iiigcr, black). It occupies nearly the whole of the African continent. The hair of the Negro is short and curly ; his nose is flat, wide, and upturned ; his cheek bones are prominent, and his lips thick. The moral and intellectual status of the Negro in his native land is low. When brought into contact, however, with the Nkcro THE MALAY RACK 317 Caucasian race, he shows himself capable of considerable ele- vation. The native Australians, though classed by some ethnologists as a separate race, may properly be regarded as a branch of the Negro family. They are probably the most degraded members of the human species. Before the European settler they are rapidly dying out. The Malay Race is held by some to be a branch of the Mongolian. Its characteristics are, however, sufficiently marked to entitle it to separate classification. The Malays occupy a part of southeastern Asia and most of the islands of the Pacific. The Malay peninsula, Sumatra and Java, Borneo, Celebes, For- mosa, the Philippines, New Zealand, and the Polynesian Islands, all had this race for their aborigines. The members of the Malay race are of medium height, with well-proportioned limbs. Their color varies from olive-yellow to brown or black. Their hair is coarse and black. Intellectually and morally the Malayan is of a low order. Some of them, however, have a written language and a legal code. They are true sea rovers, and prone to piracy. The American Indians constitute what some ethnologists designate as an offshoot of the MongoHan race. At the time of Columbus they had spread all over North and South America. Some of the better known tribes are the Chippeways, Da- Mai.w 3i8 MAN kotas, Apaches, and Cherokees in North America ; the Caribs, the Araucanians, and Patagonians in South America. The American Indian is copper-colored or red, and therefore he is often called the Red man. His hair is black, coarse, and straight, his cheek bones prominent. In person he is tall and lithe. He is remarkable for his endurance of fatigue and his disregard of pain. Intellectually and morally he occupies a medium position among the races of mankind. The Incas of Peru and the Aztecs of Mexico were found in a remarkable state of civilization by Pizarro and Cortez; and there are, in Central America and in New- Mexico and Arizona, interest- ing memorials of a long-for- gotten civilization which had its home in those regions. The Montezumas of Mexico had their halls, their acade- mies and schools, their zoo- logical and botanical gardens, their calendar and their monu- ments Their capital, at the time of Cortez, vied with the Amekican Indian wealthiest cities of Europe. Conditions Favorable to Civilization. — From this brief re- view of the races it will be seen how powerful has been the influence of physical circumstances upon Man. Some portions of the human family have remained hopelessly barbarous; some have received civilization from others ; and some, again, have originated a civilization of their own — an iridigcnons civi- lization. Wherever this last has occurred, it has invariably been neither at the poles, nor in the hot lands of the tropics, but rather in a middle ground between the two. It is here that conditions best adapted to man's physical development are found. MAN'S INFLUENCE UPON T'HVSICAL GE0(JKA1'IIY 319 An indigenous civilization has never had its origin under the blighting blasts of the Arctic regions. Life there, from the cradle to the grave, is a continuous struggle for mere sub- sistence. The body is so pinched and starved by cold and hunger as to prevent the development of the mind. Neither do the moist and overheated climates of the torrid zone appear to be favorable to mental development. There the rainy season and the constant heat dwarf and enervate the body. Cold may not pinch, nor hunger gnaw, yet fever racks the frame ; and the mind, in its first and feeble steps toward civiliza- tion, is crippled by the ills of the body. Body and mind, more- over, lack in the torrid zone, by reason of its superabundant productiveness, the great stimulus to human exertion, — necessity. Man, to be civilized, must be beyond the reach of climatic extremes. Man's Influence upon Physical Geography. — While, however, we notice the influence of physical geography upon Man, we must also notice the influence of Man upon physical geography. Although, like the brutes, he is strongly impressed by his material sunoundings, he is unlike the brute creation in this : They cannot modify the conditions which surround them ; he can. The methods to which he resorts are mainly three : ( I ) Drainage, (2) Irrigation, (3) Extension of the range of useful plants and animals. In many cases skill and perseverance triumph over natural difificulties that seem insuperable. Immense changes are wrought by artificial drainage. Super- fluous water, instead of being left to form marshes, saturate the soil, and be taken up by evaporation, is carried off under- ground through the drain pipes ; consequently, the air is not so largely impregnated with moisture as formerly, and the soil, instead of being constantly chilled by evaporation, is rendered warm, genial, and productive. This result is particularly noticeable in England and Scot- land, where very extensive areas have been drained and brought under cultivation. M.-S. I'HYb. GEOG. — I9 320 MAN Holland has been reclaimed from the sea. The water has been diked out ; and many parts of the country that were the bottom of tiie sea are now dry land, and though below the level of the sea, form the home of industrious and happy communities. Years ago there were " drowned lands" along the lower banks of the Mississippi, subject to overflow, and uninhabitable, embracing an area larger in the aggregate than the state of New York. Many of these lands have now been reclaimed by means of levees. The dike lands of Nova Scotia and New Brunswick have been reclaimed from the sweeping tides of the Bay of Fundy. They are probably the finest hay lands in the world. Some of them have been cropped 200 years. They are as sure to yield as the fields of Egypt. By Man's agency in using the waters of the Nile for irrigation, Egypt became in olden time the granary of the world. Canals conveyed the water to lands not reached by the flood. And to-day the Egyptian peasant is using with profit the devices employed by his ancestors more than 3000 years ago. Sharply contrasted with these, as a result of modern engineering, is the great dam at Assuan by which an ample water supply, for irri- gating purposes, has been afforded to a large territory. Much of the country yields three crops every year. In India and Ceylon vast districts of country are rendered fer- tile by the use of reservoirs, constructed ages ago for collecting water in the rainy season, but even on a larger scale by the gigantic systems of irrigation constructed by the English. The dry regions of our own country also are now largely irrigated. In Utah, California, Arizona, New Mexico, and other far Western states the wilderness has been, by this means, trans- formed into a garden. Some single "canals" with their distrib- uting channels carry water to 150,000 acres. Races of men, species of animals, and families of plants have been carried from one country to another, and their geographi- cal range enlarged. Indian corn, tobacco, and the potato, with many other plants, the turkey, and other animals, were indigenous to America. They have been carried to the Old World and acclimated. On the other hand, the horse and cow, the sheep, hog, goat, ass, and MAN'S IMLLKN'CE Ul'OX I'lIYSlCAL tiKoi IRAl'IIV 3_M Other animals of the Old World, with wheat, oats, rye, barley, and rice, the sugar cane and coffee, and a great variety of other plants have been transported to America. A few stray cattle and horses, escaping to the pampas and llanos of South America, multiplied exceedingly. So wonderfully did they increase that, upon the jiampas, they were slaughtered by millions for their hides, horns, and tallow. XXX. GEOGRAPHICAL DISTRIBUTION OF LABOR Distribution of Labor Dependent on Physical Geography. — Every nation has industries peculiar to itself. These, to a large extent, have their root in geographical circumstance, or in dif- ference of climate. To show how human labor, when unaffected by tariffs and untrammeled by legislation, would naturally distribute itself over the earth in obedience to geographical law, let us suppose two families to have been planted originally on the earth, one at the equator, the other in the Arctic regions. How different, on account of their geographical surroundings, would be their occupations ! The intertropical family would seek the shades of the groves, pluck the ripe fruit overhead, require little clothing, and be ex- empt from undergoing the hardships of toil to earn their daily bread. With little exertion on their part nature would supply their wants. The Arctic family, on the contrary, would be clothed with skins and furs ; the earth would produce no grain or vegetables for them. They would live by the chase and the bounties of the sea. Now, suppose these two families gradually to extend themselves, the one toward the north, the other toward the south, meeting midway near the isotherm of 50°. The occupations of both, as they continued to approach this middle ground, would no longer be directed, on one side mainly toward the sea, and on the other exclusively to the soil ; but would become more and more diversified. The necessities of the southern family would compel them to resort to sundry active occupations, some to the manufacture of clothing, others to the fabrication of implements for husbandry ; indusiriils ok ruF. uxri'F.i) states 323 others again to seafaring. Novel opportunities would present themselves to the northern community, and induce them like- wise to subdivide their labor. They would divert a portion of it from the sea and the chase, and devote themselves to a greater or less extent to agriculture, to the forest, the mine, and the factory. Such a diversitv of occupation really exists among men. The middle latitudes, embracing regions lying not far from the isotherm of 50°, form a belt encircling the earth, where human occupations are most diversified. In some parts of this belt the tending of flocks and herds and the raising of stock are the chief industrial pursuits ; in other parts agriculture, in others mining, manufacturing, seafaring, and lumbering ; in some, all of these occupations, or several of them, are combined. To the south of this middle ground, the attention of the people is devoted more and more to the field and the forest ; to the north, more and more to hunting and the sea. Along this middle ground are found the most active seafaring and commercial peoples in the world, the greatest manufactur- ing nations, and the largest cities. Within its belt are included most of the United States, Japan, the populous parts of China, and all the great commercial, min- ing, and seafaring communities of Europe. It is now easily perceived that there are geographical reasons why the people of South America, of Africa, India, and of the tropical and subtropical regions of the earth should, in the main, be agricultural or mining in their industries rather than seafar- ing or manufacturing. In general it may be laid down as a rule, that the industries of every country are connected with its geography, and that human labor is distributed, largely, in obedience to certain phys- ical conditions. Industries of the United States. — A brief survey of the indus- tries of our own country will serve well to illustrate this law of the geographical distribution of labor. Let us observe in the first place how the principle applies to 324 GEOGRAPHICAL DISTRir.UTIOX OF LABOR our various agricultural pursuits. Climate, of course, furnishes the predominant reason why different products are raised in different parts of the country. But we shall notice that other minor causes are not without their influence. In the valley of the Mississippi, which may be regarded as the great agricultural region, there is found as we advance northward from Louisiana, a succession of climatic belts, and a corresponding variety of crops engaging the attention of the husbandman. First of all, near the borders of the Gulf of Mexico, comes a belt in which sugar and rice are important crops. Leaving this belt, we enter regions, one after another, specially adapted to the cultivation of cotton, tobacco, corn and wheat, hemp, the grape, and orchard fruits. If the journey lie along the Atlantic slope from Florida to Maine, we find a similar succession of belts and products ; but with this striking difference, owing to the influence of the sea, namely, that the climates are milder and the belts broader. In the " Tide-water Country " these belts are so widened that rice cultivation is carried up into North Carolina, cotton is raised in Virginia, and figs in Maryland — all much farther north than on the west of the Appalachians. In the tide-water country of Georgia and the Carolinas, rice is an important article of cultivation. There is a geographical reason for this. Rice fields, in certain stages of the crop, must be flooded, for which purpose the tidal creeks and rivers of the seaboard afford excellent facilities. At the same time Louisiana has become the first rice-growing state in the Union. In the Mississippi delta the river is high above the cultivated ground. Consequently a supply of water can be obtained by simply tapping the river. In the southwest- ern parishes, away from the river, and on the coastal plain of Texas, large areas of low and level lands are irrigated from sur- face reservoirs and wells. The agricultural pursuits of the Pacific slope, owing to its physical peculiarities, differ from those of the Atlantic. No rice or cotton is cultivated. Hut the region is unsurpassed for its INDUSTRIES or NEW EXC.I.AND AND (.1 I.F S I A TKS 325 wheat and fruit crops ; the olive, vine, and orange yield abun- dantly, while stock, raising and wool growing are profitable employments. Considering now the various other industrial pursuits of our people, we find it to be the rule that Physical Geography has largely determined how the occupants of each section shall employ themselves. Here we view far-reaching grass-covered plains which naturally suggest the occupations of stock raising, dairying, or wool grow- ing. Elsewhere we traverse forests famed for lumber, ship timber, and naval stores. In yet another region we observe that attention is directed to the great lakes or water courses for fish and fowl ; or to the interior of the earth for minerals ; or to commerce, manufacturing, and navigation. All these occupations are, it is true, adopted according to individual fancy, yet they are clearly prompted and controlled by geographical influences. Industries of New England and Gulf States Contrasted. — A very striking illustration of the law of geographical distribu- tion of labor is obtained when we contrast the leading occupations of such widely separated sections of our country as the Gulf states and New England. In the former there is no " wintry weather." The husband- man may labor in the field all the year long, and the soil yields abundantly- In New England, on the other hand, the ground is covered with snow, or is frozen hard, during four or five months in the year. How is New England industry to ply its hand during this period ? It cannot till ; neither can it stand idle. Forests upon the mountains, ships upon the sea, quarries of valuable stone, and above all factories of every description fur- nish ample employment for the industrious population. New England is preeminently devoted to manufacturing. Its polished granites and marbles are distributed everywhere along the At- lantic seaboard for building and ornamental purposes ; its manu- factures find a market in every part of our own country and are 326 GEOGRAPHICAL DISTRIBUTION OF LABOR exported to the far-distant seaports of China and Japan and the islands of the seas. Louisiana, and her sister Southern states, on the other hand, want laborers for their harvests of cotton, corn, sugar, rice, naval stores, hemp, tobacco, etc. There are, therefore, inducements peculiar to each of these two sections which allure the people of one to this branch of industry, the people of the other to that, according to geographical conditions. In one, these inducements lead to the sea and the factory ; in the other, they point to the bosom of the earth. Mining and Manufacturing. — If coal and the useful metals are found in any region, manufacturing interests will sooner or later be developed. It is in no small degree owing to her vast deposits of coal and iron that Great Britain occupies her extraordinary position as a manufacturing nation. Pennsylvania, Ohio, Ala- bama, Illinois, the Virginias, Maryland, Michigan, and other states similarly rich in the useful minerals, are actively engaged in mining and metallurgy. Fishing and Commerce. — Again, people are maritime in their habits from physical reasons ; partly because they are adjacent to the sea, and partly because, owing to the conditions which sur- round them, the bounties of the sea are to them more enticing than thebounties of the land. Hence it is found that the seafaring populations of the world belong chiefly to those countries where, either from the poverty of the soil, the severity of the climate, or the high price of food, it is easier for some of the population to make a living by braving the sea than by delving on shore. Ships at sea are not manned by sailors from the Mississippi Valley and the Southern states, where lands are cheap, climates mild, and where the soil is lavishly kind ; but rather by men from New England, .Great Britain, and the countries of north- western Europe, where, largely on account of geographical con- ditions, the laborer finds it in many cases easier to make a living at sea than on shore. Commerce originates between nations to satisfy needs. Arti- cles required for food and shelter, comfort or luxury, being FISHING AND COMMERCE 327 irregularly distributed over the globe, it becomes necessary that human industry should be partly directed to the exchanging of the natural and artificial products of one region for those of another. To this end many routes of commerce have been es- tablished, necessitating the investment of great capital in rail- roads, steamships and other vessels, and at the same time giving employment to a vast multitude of people. APPENDIX XXXI. PHYSICAL GEOGRAPHY AS A SCIENCE Scope of Physical Geography. — The earth is not young. Like a hving being, it is a product of evokition or growth. In the course of its development it has passed through many stages. The interaction of sea and land, rock decay and denu- dation, transportation and deposition of sediment, vulcanicity and glaciation, elevation and subsidence, earth folding and fault- ing, animal and plant life, have all contributed to its present form. Yet the earth as we know it is not a finished product ; change and remodeling are still taking place ; the forces of the past, in varying degree, are still at work. It is, however, as the abode of man, chiefly, that the earth merits our attention. The relation of man to his environment or surroundings is a practical matter, and should we define Physical Geography as the study of the earth and its phenomena in the present stage of their existence with special reference to that relationship, we have before us a field of the widest scope. The Relation of Physical Geography to Other Sciences. — It is only by a knowledge of the earth in its present condition that Man has been able to interpret its past history. Physical Geography is, therefore, a most important adjunct to geology. Indeed, there is no well-marked line of division between these sciences which, in many instances, occupy common ground. Geology, however, is usually confined to a consideration of the history of the earth and its inhabitants as recorded in the rocks. But this seems arbitrary in view of the fact that the earth is a unit. It were better that Physical Geography should constitute the latest chapter of geology. 328 HOW rilVSKAI, (^.KOC.k.MMIV SlIOll.l) RE STl'DIl H 329 Like geology, Physical Geography rests iij)on a fouiuhition of other sciences. To explain the phenomena of the earth it has oftentimes been necessary to invoke assistance from astron- omy, chemistry, physics, zoology, botany, and mineralogy ; for the earth is one of the planets, it consists of matter, it is in- habited by animals and plants, and is, for the most part, com- posed of mineral substances. How Physical Geography should be Studied. — In the ele- mentary study of Physical (jeography the text-book occupies an important position. Not only is such a work a record of the observations and conclusions of those who have made a specialty of earth phenomena, but also a manual of guidance for those who desire to acquaint themselves with the subject. Moreover, at the outset the student should understand that although the ability to memorize a text may add much to his information, it is by no means an index of his scientific attainments. If the best results are to be obtained from the study of Physical Geography, he should, as far as possible, verify the data and conclusions of the author. By training of that kind he may become competent to make independent observations and from them deduce proper conclusions. Then, and not till then, has he reached that degree of culture which is truly scientific. His local or home surroundings become now an ever-present field of research. Nowhere in the world is the opportunity for geographic investigation denied him. Lines of investiga- tion open in many directions : He may observe winds, clouds, rainfall, temperature, and other weather conditions and note their bearing upon climate ; he may study the effects of rock weathering or decay and the topographic features arising from erosion ; he may face the problems of stream dissection, current action, delta formation, cascades and waterfalls in the rill formed by a passing shower ; he may learn something of Nature's processes by observing the effects of storms and floods. These and many other fields of inquiry equally inviting lie within the reach of all students. Furthermore, every local- ity has its special phenomena : For example, wave action may 330 PHYSICAL GEOGRAPHY AS A S( H'.NCE be studied by those living upon the sea coast or near lakes and ponds; ice action by those living in the colder regions of the earth ; glaciers and glacial motion by those living in Alpine regions ; and vulcanicity and earthquakes by those living in volcanic regions or parts of the earth subject to crustal disturb- ances. Maps, Models, and Other Illustrative Materials. — There are, however, fields of geographic inquiry which ordinarily lie be- yond the reach of most students, as the expense of investigation is too great or the region to be examined too remote or too inaccessible. To this class belong deep-sea research, electro- magnetic observations, Arctic exploration, the investigation of high mountain ranges, the exploration of desert regions, and the like. Such forms of research can be carried on only under the auspices of the government or of well-endowed private institutions. The student of geographic tastes should embrace every opportunity to travel. There are problems worthy of his best thought and effort within the boundaries of his own state. But for the elementary student this also is usually impracticable, hence the necessity of a geographical collection in every school or college. This should include a set of the most recently published maps of the continents ; a good atlas, selected folios, atlas sheets and charts from the publications of the United States Geological Survey and the United States Coast Survey ; relief models of the continents ; the Harvard Geographical Models ; and a relief globe such as the Jones Model. In ad- dition, if possible there should be included a set of lantern slides or photographic views. Such illustrations are extremely valuable to the student, as they convey to him an exact im- pression of the regions or phenomena under consideration. He should, moreover, have access to other books than the text, but their number will depend upon the resources of the individual or the school. In higher institutions a similar equipment, but in an enlarged form, should constitute the furnishings of a geographic labora- tory. Here the number of relief maps and models should be MAPS, MODELS, AND OIHEK ILI.ISTR VIIVK MAIKRIALS 33 1 greatly increased, especially by the addition of duplicates of the many excellent models prepared under the auspices of the United States Geological Survey and other departments of the national government. The collection of maps should also be made more complete, and embrace not only political, but topographic and geologic maps as well. If not found in other departments of the institution, some of the more common in- struments for weather observation should be added, such as a mercurial or aneroid barometer, a themometer, a vane, anemom- eter, and rain gauge. This laboratory should be furnished with tables suitable for map work, cabinets for the storage of maps, photographs, and other geographic matter. While the facilities afforded by such a laboratory may increase many fold the value of Physical Geography as a study, they do not sup- plant the necessity of actual observation in the field. INDEX Abyssinia, plateau of, 123. Aconcagua, 48. Active volcanoes, 50. Adirondack Mountains, 104. .■Epyornis, 306. Africa, drainage of, 169, 170. rainfall of, 252. relief of, 123-126. Agonic lines, 38. Agulhas current, 197. Air, currents of, 219. moisture of, 239. ■weight of, 202. Alaska, climate of, 213. Albacore, 308. Alcohol in thermometers, 208. Aleutian current, 196. Alexandria, 25. Algae, in hot springs, 42. sea forms of, 287. Allegheny plateau, 107. Allspice, 290. Alluvial plains, 78. Alpaca, 301, 304. Alps, 114-116. Altai Mountains, 121. Amazon River, no. description of, 168. no delta, 150. .'\ndes Mountains, 107-109. Anemometer, 218. Angle of dip, 36. Animal life, zones of, 292. Animals, aquatic, 307. distribution of, 292. higher. 280. lower, 281 modified by climate, 283. Antarctic drift, 196, 197. Antarctic Ocean, 174. currents of, 195. Anticline, 87. Anti-cyclones, 232. Antisana, 108. Anti-trades, 221. Apennines, 117. Appalachian Mountains, 104-107. Apple, 309. Apricot, 309. Apteryx, 305,308. Aquatic animals, 307. Arabia, 121. Aral, Lake, 160, 161. Ararat, 121. Arctic Ocean, 173, 174. currents of, 195. Argon, 200. Argus pheasant, 298. Arica earthquake, 64. Arid region, erosion in, 84.' Armadillo, 301. Armenia, 121. Artesian wells, 142-144. temperature of, 41. Artificial magnet, 32. Ash trees, 291. Ashes, volcanic, 50, 53. Asia, drainage of, 169. relief of, 1 19-123. Asia Minor, 121. Ass, 301. Asteroids, 10, 12. Atlantic coast tides, 188. Atlantic drift, 213. .\tlantic highlands, 104-107, T09 .Atlantic Oc^an, 174-178. 333 334 INDEX Atlantic Ocean, currents of, 193, 194. Atlas Mountains, 123. Atmosphere, 70. circulation of, 219. composition of, 200. Atmospheric electricity, 275. Atmospheric pressure, 202. Atmospheric temperature, 206. Atolls, 132-135. Attractive power of earth, ^^. Aurora australis, 277. Aurora borealis, 277. Australia, flora of, 310. great barrier reef, 132. relief of, 126, 127. Australian Alps, 126, 127. Australian current, 196. Autumnal equinox, 27. Avalanche, 260. Axis of the earth, 23. direction of, 25. Axis of elevation, 95. Baboon, 297. Bad lands, 84. Baikal, Lake, 164. Balkan Mountains, 116. Balsams, 291. Baltic Sea, climate of, 213. saltness of, 172. Bamboo, 291. Banana, 289. Banyan, 309. Baobab, 309. Barbary lion, 296. •Barley, 288. Barometer, mercurial, 203. Barrier islands, 182. Barrier reefs, 132. Bars, 148. Basin, 165. Basins of geysers, 42, 43. Bath, temperature of springs at, 41. Bay of Fundy, tides in, 188. Bear, 292, 296, 297, 299, 302. Beefwood tree, 310. Belted coastal plain, 78. Bepho, 272. Beverage plants, 290. Bird of paradise, 298. Birds, 292, 300. Bison, 299. Black Stream, 196. Blanc, Mont, 116, 261. Block mountains, 88, 102, 104. Blue crow, 299. Blue jay, 299. Blue Mountains, Australia, 126. Boa-constrictor, 301, 309. Bolivian plateau, 82, 108. Bonito, 308. Bonneville, Lake, 103, 161-162. Boothia, 34. Bores, 189. Bower bird, 298. Bowlders, transported, 268. Bowlders of transportation, 267. Brahmaputra, delta of, 79. Brazil current, 193. Brazilian highland, 109. Breadfruit, 289. Breadth of wave, 179. Breakers, 179, 180. Breezes, land and sea, 224. Bridge of Sighs, 99. Bristol Channel, tides in, 189. British Columbia, climate of, 213. British Islands, 128—129, 213. Broken plateaus, 83. Brown bear, 292. Budapest, temperature of well at, 41. Bustard, 296. Cacao, 290, 310. Caldera, 29, 161, 162. Calendars, 29. California earthquake, 63, 66—69. Calms, belt of, 223. of Cancer, 223. of Capricorn, 223. i INDEX 335 Calumet-Hecla mine, temperature of, 40. Camel, 292, 296, 302, 303. Campagna, 165. Cancer, Tropic of, 30. Canyon, 90, 91. Capricorn, Tropic of, 31. Caracas earthquake, 65. Carbon dioxide, 200. Carbonate of lime, 42. Carnivorous animals, 282. Carpathian Mountains, 116. Carson Lakes, 103. Cascade, 151. Cascade Mountains, 100. Caspian Sea, 123, 160, 161. Cassava, 290. Cassiquiare River, no. Cassowary, 298, 305. Castor oil, 291. Catskill Mountains, 104. Caucasian race, 314. Caucasus, 116. Cayambe, 108. Cayuga Lake, 156, 160. Cedars, 291. Centigrade scale, 209. Centrifugal force, 20, 184. Centrosphere, 22. Cen'in, Mont, 85. Chaco, III. Chain, mountain, 85, 86. Chamois, 305. Change of seasons, 29. Charleston earthquake, 63. Cherr)', 309. Chestnut, 291. Chimborazo, 47, 48, 109. Chimpanzee, 293. China, plains of, 123. Chinchilla, 301, 305. Chottes, 126. Cinchona, 291, 310. Cinnamon, 290, 309. Circulation, oceanic, 197. ! Circulation of the atmosphere, 218, 219. of water, 139. Cirques, 100. Cirro-cumulus cloud, 244. Cirrus cloud, 242, 244. Civet, 297. Civilization, 318. Climate, 210. affected by ocean currents, 212 affected by winds, 212. at Werchojansk, 212. continental, 211. inland, 211. insular, 211. maritime, 211. of Alaska, 213. of British Columbia, 213. of Cuba, 216. of England, 213. of Labrador, 213. of Norway, 213. of Oregon, 213. of Orizaba, 216. of Sahara, 212. Climatic belts, 324. Clothing, plants used for, 291. Cloud, definition of, 243. Cloud Ring, 254. Clouds, classes of, 244. formation of, 201. Cloves, 290. Coast line, 72-74. Coastal plains, 76. Coffee, 290, 309. Colorado, Grand Canyon of, 91. Colorado Plateau, 104. Columbia Plateau, 100. Coma, 12. Comets, 10, 12. Commerce, 326. Comstock lode, temperature of, 40. Condensation of water, 138, 139, 240. Condors, 301, 303. Conduction, 207. 336 INDEX Constant rains, 254. Constant winds, 221. Continental climate, 211. Continental elevation, 91. Continental islands, 128, 129. Continental relief, 95. Continents, 70. Contraction, eflfects of, 86. Convection, 206. Coral islands, 130-135. Coral, reefs, 131, 132, 197. sand, 178. Corals, 308. Cork oak, 309. Corn, 324. Corncrake, 296. Coronado Beach, 179, 180. Cotidal lines, 186. Cotopaxi, 47, 50, 108. Cotton, 291, 324. Counter current, 192. Counter trades, 221. Cow, 292, 296. Crater, 46. Crater Lake, 156, 161. Craters, or basins, of geysers, 43. Crest, mountain, 86. Crest of wave, 179. Crevasse, 266. Crimson lory, 298. Crocodiles, 292. Crumpling, 86. Cuba, climate of, 216. Cumulo-stratus, 245. Cumulus, 243, 245. Curassows, 301. C'urrent, Arctic, 213. Currents, ocean, 192-198, 212. Curvature of the earth, 18. Cut-off, 147. Cyclones, 229, 230. Dangerous archipelago, 133, Danube River, delta.s, 149. jetties of, 148. Date palms, 285. Day, lunar, 183. sidereal, 28. solar, 28. Day and night, lengths of, 26. Dead Sea, 122, 123, 159, 160. Declination, magnetic, 37. of the needle, 36. variations in, 38. Dee, tides of the, 189. Deer, 296. Deficient rainfall, 255. Deformation, crustal, 93. Dekkan, 121. Delta, 78, 79, 149. Delta plain, 79. Delta shore lines, 79. Dembea, Lake, 123. Density of the earth, 21. 'Denudation, 77. Deposition, 146-150. Desert plateaus, 85. Deserts, regulators of rainfall, 252. Dew, 241. ' ~' Diastrophic plateaus, 82. Diatoms, 178, 286. Dip of strata, 77, 78. Dip of the needle, 34. Dipper, 24. Dissected plateaus, 83. Distributaries, 149. Distribution of animals, 292. of rainfall, 248, 249. Diurnal variations, 38. Dodo, 306. Dog, 293, 302. Doldrums, 223. Dormant volcanoes, 50. Dormice, 296. Drainage, 165-170, 319. Draught animals, 301. Drift, Antarctic, 196, 197. Atlantic, 213. Dromedary, 302. Drowned mines, 142. INDEX 337 Drumlin, 269, 271. Dry season, 255. Dublin, temperature of, 217. Duck mole, 298 Ducks, 292. Dunes, 126, 227, at Ostend, 184. D'Ur\'illa;a utilis, 287. Dust, in atmosphere, 200, 201, 206. volcanic, 50. 54. "Dust whirlwind," 254. Dyewoods, 291. Eagle, 292, 296. Earth, a magnet, i^. and the universe, 17. an oblate spheroid, 20. a planet, 11. attractive power of, :i:i. axis of, 23. curvature of, 18. density of, 21. fluidity of, 45. interior of, 45. • internal heat of, 40. magnetic pwles of, 33. magnetism of, 32. motions of, 23. nucleus of, 22. revolution of, 23, 25. rotation of, 23, 25. Earthquakes, 60-69. causes of, 66—69. flistribution of, 65. duration of, 61. .sea waves caused by, 63, 64. East Australian current, 196. Ebb tide, 183. Eclipse of the moon, 19. Edwards plateau, 89. Egypt, floods of, 170. Elburz, Mount, 117. Elburz Mountains, 120. Electricity, atmospheric, 275. Electro-magnet, 32. Elephants, 292, 302. Elevation, continental, 91. effect of, 216. Elton, Lake, 161. Emu, 298, 305. luigland, climate of, 213. Epicentrum, in earthquakes, 60. Flquator, 23. magnetic, 34. Equatorial Calm Belt, 223. Equatorial current, 192, 193, 194, 196, 198. Equatorial zone of animal life, 292. vegetation, 284. Equinox, autumnal, 27. vernal, 26, 207. Equinoxes, 76, 27. Eratosthenes, problem of, 24. Eroded plateaus, 83. Erosion, 75, 83, 86, 99, 144-146. Eruptions, volcanid, 51-55. Esker, 271. Estacado, Llano, 82. Estuaries, 92, 93. Eucalyptus, 310. Europe, coast line, 73. drainage of, 168. relief of, 114-118. Evaporation, 138, 139, 239. Everest, Mount, 119. Excessive rainfall, 255. Extension of plants and animals, 319. Extinct volcanoes, 50. Fahrenheit scale, 209. Fault, 60, 66. Faulting, 86. Field magnetic, ;^^. Figs, 309, 324- Finches, 299. Fiords, 93, 94, 117. Firs, 291. Fishing, 326. Fissure springs, 141. Fixed stars, 11. 338 INDEX Flanks, mountain, 86. Flax, 291. Flood plain, 78. Flood tide, 183. Floods, 166. Fluidity of earth, 45. Flying fish, 308. Flying lemurs, 297. Fog, 195, 242. Folding, 86. Food plants, 288. Foothills, 76. Force of waves, 182. Forests, submerged, 93. Foxes, white, 292. Franz Josef glacier, 263, 265. Frigid zones, true, 217. Fringing reefs, 132. Fumaroles, 49. Ganges, delta of, 79. Garden of the Gods, 98. Gardens, 98. Garonne, bore of, 189. Geysers, 42. Ghats, 121. Giacobini's comet, 12. Ginger, 290. Giraffe, 297, 298. Glacial grooves, 270. Glacial motion, 262. causes of, 265. theory of, 264. Glacial period, 268. of North America, 269. Glaciers, 261. as river sources, 271. continental, 273. distribution of, 272. size of, 272. Globigerina, 178. Goats, 292, 296. Gobi, Desert of, 121. Godwin-Au.sten, mountain, 120. Gold Hill mines, temperature of, 40. Gorilla, 297. Gradient, 230. Graduating thermometers, 209. Graham Island, 47, 130. Grand Banks, fogs of, 195. Grand Canyon, 90, 91. Grand divisions, 71. Grand Geyser, 43. Grapes, 324. Gravity, specific, 198. Gravity springs, 141. Great Basin, 102. Great Geyser, 42. Great gray kangaroo, 301. Great Lakes, 164. Great Plains, 81. Great Salt Lake, 103, 159, 162. Grecian Peninsula, 116. Green Mountains, 104. Greenwich, 24. Gregorian calendar, 29. Gregory XIII, Pope, 29. Grenelle, temperature of well at, 41. Grizzly bear, 299, 302. Grooves, glacial, 270. Ground swell, 181. Ground waters, 140-144. Guiana, higliland of, no. Guinea fowls, 297. Gulf Stream, 193, 194, 213. Gulf weed, 287. Gulls, 292. Gums, 291. Gu.shers, 42. Gutta-percha, 309. Hail, 201, 258. Halo, 278. Hammerfest, climate of, 213. temperature of, 195. Height, of the land, 75. of tides, 188. of waves, 180. and temperature, 213, 216. Helium, 200. IXDKX 339 Hemp, 291, 324. Henderson meteorite, 13. Herbivorous animals, 282. Hercules, constellation, 17. High barometer, 205. Highlands, 76. High Sierra, 100. High tides, 183. Hills, 76. Himalayas, 119, 120. Hindu Kush, 120. Hippopotamus, 297. Honey bear, 297. Hood, Mount, loi. Horizon, 171. Horizontal zones of vegetation, 284. Horns, 86. Horse, 292, 296, 301. Horse latitudes, 223. Hot springs, 41, 42. Humboldt current, 197. Humboldt Lake, 103. Humidity, 239. Humming birds, 301. Hydrosphere, 21, 22, 70. Hypothesis, nebular, 14, 15, 45. planetesimal, 14, 16, 202. Iberian Peninsula, 117. Ice, lighter than water, 137. melting point of, 45. Icebergs, 273. Iceland, geysers in, 42. Inclination of needle, 34. India, flora of, 309. plains of, 123. rainfall of, 251. Indian corn, 288. Indian Ocean, 174. currents of, 197. Indians, American, 317. Indigenous civilization, 318. Industries of United States, 323. Inferior highlands, 95, 117, 120, 123. Inland climate, 211. Inland seas, 160, 161. Inorganic bodies, 280. Insular climate, 211. Interior plains, 76. Internal heat, 40. Inundations, 166. Iran, plateau of, 121. Iron Gate, 116. Irrigation, 256, 319, 320. Islands, 128-134. barrier, 182. continental, 128. coral, 130-134. oceanic, 129. volcanic, 130. Isobars, 205. Isoclinic lines, 36. Isogenic lines, 36. Isothermal lines, 216. and life, 293. map, 214-215. Italian Peninsula, 117. Jalap, 291. James River, 105. Japan, earthquakes in, 64, 65. Japan current, 196. Jetties, 148. - Julian calendar, 29. Jungfrau, 115. Jupiter, II. year of, 26. Kamerun ^Mountains, 124. Kames, 271, 272. Kangaroo, 298, 301. Karakoran Mountains, 120. Kashmir goat, 305. Kenia, Mount, 123. Khamsin, 226. Khajia hills, rainfall of, 251. Khin-Gan Mountains, 121. Kilauea, 46. Kilimanjaro, Mount, 1,23. Killarney Lakes, 163. 340 INDEX Kirghiz Steppes, 122. Krakatoa, 54. Krypton, 200. Kuen-Lun, 120. Kuro-Shiwo, 196. Labor, distribution of, 322. Labrador, climate of, 213. Labrador current, 196. Laccolite, 88. Lagoon, 132. Lahontan, Lake, 103, 162. Lakes, 155-164. causes of, 155, 156. desiccated, 161-163. distribution of, 164. extinct, 103, 161-163. offices of, 163. salt, 158-162. Land, distribution of, 70-72. Land winds, 253. Latent heat, 137, 138. Lateral moraine, 267. Latitude, 23, 24. Latitudes, horse. 223. Lava, 49, 50, 54, 55. Leap year, 29. Lemurs, 297. Lightning, 275. kinds of, 276. Lions, 292, 296. Lisbon earthquake, 65. Lithosphere, 21, 22, 70. Liverpool, tides at, 189. Livingstone Mountains, 123. Llama, 301, 304, 306. Llano Estacado, 82. Llanos, 76, iii. Logwood, 291. Loma Point, 179, 180. Longitude, 23, 24. Longitudinal valleys, 89. Low barometer, 205. Low tide, 183. Lowlands, 76. Lunar day, 183, 185. Lyre bird, 298. "Mackerel sky," 244, 245. Macrocystis pyrifera, 287. Magdalena River, 108. Magnet, 32. Magnetic declination, 37. Magnetic equator, 34. Magnetic field, 33. Magnetic needle, ;^;^. Magnetic north pole, 34. Magnetic parallels, 36. Magnetic poles, 7,7,. Magnetic storms, 38. Magnetism, terrestrial, 32. Magpies, 296. Mahogany, 291. Maladetta, Mount, 116. Malay race, 317. Malay tiger, 304. Mai de montagne, 205. Man, races of, 311, 314. range of, 311. Mandioca. See Manioc. Mango, 309. Manioc, 289, 290, 310. Manufacturing, 325, 326. Maple, 291, Maravaca, no. Marine deposits, 176-178. Maritime climate, 211. Marlin, temperature of well at, 41. Mars, II. Marsupials, 298. Materials for Physical Geography, 330. Matterhorn, the, 85, 116. Mauna Kea, 48. Meanders, 147, 148. Medial moraine, 267. Medicinal plants, 291. Mediterranean Sea, saltness of, 172. Melting point, 45. Menam valley, overflow of, 79. Mercurial barometer, 203. INDKX 341 Mercurial thermometer, 208. Mercury (quicksilver), 198, 203, 208. Mercurj' (planet), 11. year of, 26. Mer de Glace, 262. Meridians, 23. Mesa, 84. Meteoric swarms, 12, 14. Meteorite, Henderson, 13. Middav lines, 23. Millet,' 288. Mineralization, 42. Miner\a Terrace, 42. Mines, temperature of, 40. Mining, 326. Mirage, 279. Mississippi basin, 107. Mississippi River, amount of water in, 167. banks of, 150. delta of, 79, 149, 150. erosion by, 146. floods in, 163, 166. jetties of, 148. meanders of, 147. Mistral, 226. Mitchell, Mount, 105. Mocking bird, 299. Mock suns, 278. Moisture of the air, 239. Moles, 296. Mongolian race, 315. Monkeys, 301. /l^Ionsoons, 198, 224. effect of, 225. minor, 226. Mont Blanc, 116, 261. boiling point at, 204. Mont Cervin, 85. Mont Pelee, 54. Monte Rosa, 116. Monument Park 99. Moon, eclipse of the, 19. Moondogs, 278. Moons, II. Moraines, 267. Motions of the earth, 23. Mot-mots, 301. Mountain chain, 86. Mountain crest, 86. Mountain flanks, 86. Mountain knots, 108. Mountain peaks, 86. Mountain range, 86. Mountain sickness, 205. Mountain system, 86. Mountains, 76, 85, 95-127. formation of, 86. regulators of rainfall, 251. block, 88, 102. Movements, earth, 75. Mozambique current, 197. Musk-ox, 292. Narcotics, 290. Natural magnet, 32. Neap tides, 187. Nebula, 15. Nebular hypothesis, 15, 45. Needle, magnetic, ^^^. declination of the, 36. dip of the, 34. Negro race, 316. Neptune, 11. year of, 26. Neutral line (magnetic), ;^^. New Caledonia reefs, 132. New Madrid earthquake, 65. New River, 105. New Style, 29. New Zealand, springs in, 42. Newton, 25. Niagara Falls, 145, 152-156. Nightingales, 296. Nile River, 80, 169, 170. delta of, 149. Nile valley, overflow of, 79, 80. Nimbus, 246. Nitrogen, 200. North .America, drainage of, i()~ 342 INDEX North America, flora of, 310. glacial period, 269. rainfall of, 252. relief of, 95-107. North Cape, 117, 118. North Carolina, coastal map, 129. North Pacific current, 196. North pole, 24. North star, 24. Northern Hemisphere, 71. "Northers," 226. Norway, climate of, 213. Nucleus, earth's, 22. Nutmeg, 290. Oak, 291. Oases, 126. Oblate spheroid, earth an, 20. Ocean currents, 190, 191. affect climate, 212. Oceanic circulation, 197. Oceanic Islands, 129. Oceans, 1 71-178. See Sea. Oil palm, 309. Old Faithful Geyser, 44. Olives, 309, 325. Olympus, Mount, 117. Ooze, 178. Opium, 290. Opossums, 298, 299. Oranges, 325. Orang-outang, 297, 299. Orbits, 10. Orchard fruits, 324. Oregon, climate of, 213. Organic bodies, 280. Orinoco River, i ro, iii. delta, 149. Orizaba, climate of, 216. Orkney Isles, temperature of, 195. Ostend, 184. Ostrich, 305. Ox 292, 301. , Oxbow, 147. Oxygen, 200. Oysters, 308. Pacific current, 196. Pacific Highland, 95, 107. Pacific Ocean, 174-178. Pamir, 119. Pampas, 76, in. Pamperos, 226. Papandayang, 58. Parallels, 23. magnetic, 36. Paraselenae, 278. Parhelia, 278. Parime Mountains, no. Parks, 98, 99. Passes, 91. Passion flower, 310. Peacock, 298. Peaks, mountain, 86. Pear, 309. Pelee, Mont, 54. Pe-Ling Mountains, 120. Pepper, 290. Periodical rains, 254. Periodical winds, 224. Persimmon, 310. Peruvian current, 197. Pheasant, Argus, 298. Pheasants, 292, 296. Phosphorescence, in sea, 173. Physical features, 75. Physical geography, influenced by man, 319. manner of studying, 329. related to other sciences, 328. scope of, 328. Piedmont belt, 100. . Pikes Peak, 97. Pimento, 290. Pines, 291. Plain, delta, 79. Plains, 76. Planetesimal hypothesis, 14, 16, 202. Planetesimals, 16. INDEX 343 Planetoids, lo, 12. Planets, 11. relative sizes of, 16, 17, 21. Plants, distribution of, 282. higher, 280. medicinal, 291. used for clothing, 291. Plata River, no, in. no delta, 150. Plateaus, 76, 82-84. of Africa, 123-125. of Asia, 119, 121. of North .America, 97, 100-104. of South America, 109, no. Playas, 102. Po River, 150, 166. Point Loma, 179, 180. Pointers, 24. Poisonous serpents, 292. Polar currents, 192, 196. Polar winds, 223. Polar zones of vegetation, 284. Poles, 24. magnetic, ;^;^. Polyps, 130, 131, 197. Pope Gregory XIII, 29. Position, 23. Potato, 289, 310. Potomac River, 105. Pouched rat, 299. Prairie dogs, 299. Prairies, 76, 107. Precipitation, 240. Prehensile -tailed monkey, 301. Prevailing winds and climate, 212. Problem of Eratosthenes, 24. Pumice, 50. Puna, 226. Pyramid Lake, 103. Pyrenees, 116. Quartz, 41. Quicksilver, weight of, 198. Quinine, 291. Quito, boiling point at, 204. 3^2, 313, 314. Raccoons, 299. Race, tide, 188. Races of mankind, Radiolaria, 178. Rain, 201. cause of, 249. classitication of, 253. constant, 254. deficient, 255. distribution of, 248, 249. excessive, 255. periodical, 254. regulators of, 251. Rainbows, 279. Rainless regions, 257. Rainy season, 255. Range, geographical, 282. mountain, 86. of draught animals, 301. Rapids, 150, 153. Rattlesnake, 299. Reclaimed land, 320. Red clay, 178. Red Sea, saltness of, 172. Reefs, coral, 131, 132, 197. Reflection of light, 278. Refraction of light, 278. Regelation, 265. Regions, zoological, 292. of life, 296. Reindeer, 292, 302. Relief of the land, 75. causes of, 93. continental, 95. effects of, 94. forms of, 76. of Africa, 123-126. of Asia, 1 19-123. of AustraHa, 126, 127. of Europe, 11 2-1 19. of North .\mcrica, 95-107. of South America, 107- in. Reservoir, underground, 142. Return currents, 192. Revolution of the earth, 23, 25. 344 INDEX Rheas, 301, 305. • Rhinoceroses, 292. Rhone River, matter transported by, 146. Rice, 79, 288, 289, 324. River basin, 165. River plains, 76. River system, 144. Rivers, 165-170. sources of, 144, 271. tides of, 189. Robins, 299. Rocky Mountains, 97. Rosa, Monte, 116. Rosewood, 291. Rotation of the earth, 23, 25. Ruwenzori Mountains, 123. Rye, 288. Sables, 292. Sahara, 125. cHmate of, 212. Saint Elmo's Fire, 278. Saint Gothard tunnel, temperature of, 40. Saint Michael, springs at, 41. Salt, in sea, 171, 172. Sand, volcanic, 50, 53. Sand dune, 125, 227. Sandalwood, 291. San Francisco earthquake, 63, 66, 68, 69. Santorini, 130. Sao Francisco River, no. Sargasso Seas, 199. Sarsaparilla, 291, 310. SateUites, 11. Saturation, point of, 239. Saturn, 11. and his rings, 15. Scales, thermometer, 209. Scandinavian Mountains, 117. Sea, 1 71-178. bottom of, 175-178. color of, 172. Sea, currents of the, 192. depth of, 174, 175. extent of, 171. phosphorescence of, 173. saltness of, 171, 172. temperature of, 174. Sea waves, earthquake, 63, 64. Sea winds, 253. Seal, 292, 308. Seasonal variation in temperature, 207. Seasons, change of, 29. Secretary bird, 297. Secular variations, 38. Sequoia gigantea, 310. Serpents, poisonous, 292. Sharks, 308. Sheep, 292, 296. Sheet lightning, 276. Shooting stars, 14. Shore lines, delta, 79. Shoshone Falls, 155. Siam, rice crop of, 79. Siberian Plain, 122. Sidereal day, 28. Sierra, 86. Sierra, High, 100. Sierra Nevada, 100. Silica in geysers, 43. in springs, 41. Silicious ooze, 178. Silt, 146. Silvas, 76, no. Silver-tip grizzly bear, 302. Simoom, 235. Sinter, 41. Sirocco, 226. Skaptar Jokul, 54. Skunks, 299. Sloth, 301, 305. Snake River, loi, 155. Snow, 201, 258. uses of, 259. Snow line, 258. Snow Mountains, 123. i IN'DKX 345 S )ft rocks, erosion of, 84. Solar day, 2S. Solar system, 10, 11. origin of, 14. Solstice, winter, 27. Solstices, 26. South America, drainage of, 167, i6vS. tlora of, 310. rainfall of. 251. relief of, 107 11 1. South magnetic ix)le, 34. South pole, 24. Southern Hemisphere, 71. Spanish peninsula, 117. Specific gravity, 198. Sperm whale, 308. Spheroid, oblate, 20. Spices, 290. Spits, 182. Sponges, 308. Spot period of the sun, 39. Spring tides, 183, 185. Springs, 140, 141. hot, 41. algae in, 42. Standard time, 28. Stars, fixed, 11. shooting, 14. Steppes, 76, 122. Storm cards, 231. Storm laws, value of, 233. Storms, 229. • areas of, 233. cause of, 229. distribution of, 235. laws of, 231. Storms, magnetic, 38. Strata, dip of, 77, 78. Stratus cloud, 245. Stromboli, 50, 52. Submerged forests, 93. Subsidence of land, 92. Sugar, 324. Sugar cane, 290, 293. Sulaiman Mountains, 121. Sun, 14. spot period of, 39. Sundogs, 278. Superior, Lake, 164. SujDerior highland, 95. Sus(|uehanna River, 105. Sweet ]x)tato, 309. Sycamore tig, 309. System, mountain, 86. Table-lands, 76, 82. Tahiti, 134. Tailor birds, 298. Tea, 290. Teak, 291, 309. Telegraphic plateau, 176. Temperate zone, of animal life, 292. Temperate zones, of vegetation, 284. true, 217. Temperature, atmospheric, 206. measuring, 208. seasonal, 207. of zones of, 217. of artesian wells, 41. of Calumet-Hecla mine, 40. of Comstock lode, 40. of Gold Hill mines, 40. of Gulf Stream, 194. of Hammerfest, 195. of Orkney Isles, 195. of Saint Gothard tunnel, 40. of Werchojansk, 212. and climate, 210. and height, 213, 216. Terminal moraine, 267. Terraces, 92. Terrestrial magnetism, 32. Thermal springs, 41. Thermometer, 203, 208. Thian Shan, 120. Thrushes, 299. Thunder, 276. Tibet, plateau of, 82, 119. Tidal wave, movement of, 187. Tides, 183. 346 INDEX Tides, height of, i88. neap, 187. spring, 185. of rivers, i8q. Tide-water country, 324. Tigers, 292, 297, 304. Till, 269. Time, standard, 28. Titicaca, Lake, 108, 164. Tobacco, 290. Todies, 301. Tomboro, 58. Tornado, 234. Tornadoes, 233. Torricelli's experiment, 202. Torrid Zone, true, 217. Toucans, 301. Trade winds, 221. Transportation, 146. Transporting agents, 182. Transverse valleys, 89. Tree kangaroo, 298. Trees, useful, 291. Trogon, 298. Tropic of Cancer, 30. Tropic of Capricorn, 31. Trough of wave, 179. Tsien-tang, bore of, 189, 192. Tufa, 162. Turkestan, 121. Turkey, 292. Tuscarora deep, 175. Universe, earth and the, 17. Upward fold, 87. Uranus, 11. Ural Mountains, 117. Valdai Hills, it8. Valleys, 89. Vampire bat, 301. Vapor, water, 201. Variable rains, 255 winds, 221. Variations, diurnal, 38. Variations in declination, 38. in pressure, 204. secular, 38. Vegetables modified by climate, 283. Vegetation, zones of, 283. Velocity, of clouds, 247. of wave movements, 181. Venus, II. Vernal equinox, 26, 207. Vertical zones of vegetation, 286. Vesuvius, 48, 50-53, 54. Victoria Falls, 155. Victoria Lake, 164. Victoria Regia, 281, 310. Vicuna, 304. Vindhya Mountains, 121. Volcanic cones, 46-48. Volcanic islands, 129, 130. Volcanoes, 43, 46-59. causes of action, 58-59. cla.ssified, 50. distribution of, 55-58. eruptions, 51-55, 58. products, 48-50. Volga, delta, 149. Vulcanic plateaus, 82. VulcanLsm, 86. Walker Lake, 103. Walnut, 291. Walrus, 292. Washington, Mount, 105. Water, absorption of heat, 137. circulation of, 139. composition of, 136. evaporation and condensation of, 138, 139- expansion of, 136. forms of, 136. properties of, 136-139. solvent power of, 139. Waterfalls, 151- 15 7. Water gap, 91. Waters of the land, 140-164. Watershed, 165. INDEX 347 rocky headland, Waterspxnit, 235. Wave, tidal, 187. Wave action, on 182. on submerged rocks, 181. Wave movements, velocity of, 181. Waves, 179. force of, 182. height of, 180. Weather and climate, 210. Weather forecasts, 237. Weather map, 236. description of, 238. Weaver birds, 297. Welh, temperature of artesian, 41. Werchojansk, climate of, 212. \\'est Indian boa, 309. Westerlies, prevailing, 221. Whale, 292, 308. right, 308. Wheat, 288, 324. Whirlpool, 189. Whirlwind, 233. "Whirlwind, dust," 234. White bear, 292. White foxes, 292. White Mountains, 104. Whitsunday Island, 133. Wicklow, tides at, 189. "Wind roads," 234. Winds, 218. alTect climate, 212. cause of, 218. constant, 221. periodical, 224. |X)lar, 223. surface effects of, 227. trade, 221. variable, 221, 255. Winnenucca Lake, 103. Wolf, 292, 296. Wombat, 298. Wrens, 299. Wyoming, springs in, 42. Yak, 305. Yellowstone, Falls of, 155. Yellowstone National Park, springs and geysers in, 42, 44. Yoseraite Falls, 155, 157. Zagros Mountains, 121. Zambezi River, falls on, 155. Zenith, 24. Zigzag lightning, 276. Zones, of animal life, 292. of temperature, 217. of vegetation, 283. Zoological regions, 292, 294, 295. Job.5.!!.l.^ for Mend hy.^....Timc.L±::.y:..^..'J.9..l)!f:^ [Unusual mending time charged extra] Stab bi5*'.l..No.Sect../-2.-..