Oass-JjclB SS Book. — *Syg COPYRIGHT DEPOSIT «/ GEOLOGY By Thomas C. Chamberlin and Rollin D. Salisbury, Professors in the University of Chicago. {American Science Series.) 3 vols. 8vo. Vol. I. Geological Processes and Their Results. Vols. II and III. Earth History. (Not sold separately.) A COLLEGE TEXT-BOOK OF GEOLOGY By Thomas C. Chamberlin and Rollin D. Salisbury. {American Science Series.) 8vo. PHYSIOGRAPHY By R. D. Salisbury. (American Science Series.) 8vo. The same. Briefer Course. i2mo. The same. Elementary Course. i2mo. ELEMENTS OF GEOGRAPHY By Rollin D. Salisbury, Harlan H. Barrows and Walter S. Tower, of the Department of Geography, The University of Chicago. (American Science Series.) i2mo. MODERN GEOGRAPHY By Rollin D. Salisbury, Harlan H. Barrows and Walter S. Tower, of the Department of Geography, The University of Chicago. (American Science Series.) i2mo. HENRY HOLT AND COMPANY, Publishers New York and Chicago AMERICAN SCIENCE SERIES. MODERN GEOGRAPHY FOR HIGH SCHOOLS BY ROLLIN D. SALISBURY HARLAN H. BARROWS AND WALTER S. TOWER Of the Department of Geography, the University of Chicago NEW YORK HENRY HOLT AND COMPANY 1913 <&!< <\ Copyright, 1913 BY HENRY HOLT AND COMPANY STfje ILakrstUe $rrss R. R. DONNELLEY & SONS COMPANY CHICAGO ©CU343148 2/> / PREFACE For several years there has been a widespread demand for a course in general geography in high schools. This book is designed to serve as the basis for such a course. All rational work in general geography must be founded on physiography, and this fact has determined the organization of the material of this book. Physi- ographic processes and features are treated briefly, however, while their relations to life, and especially to human affairs, are developed at greater length. The book has been prepared with the conviction that the chief object in geography teaching should be preparation for everyday life, for citizenship in the widest sense. Hence the authors constantly have sought (i) to make the text explanatory rather than merely descriptive, so that it may afford training in clear thinking; and (2) to emphasize the relations of earth, air, and water to man's activities and interests, so that the knowledge gained may be directly useful. The principles developed have been applied at greatest length to the United States, because this country is of most interest and importance to American students. Furthermore, space forbade the application of these principles in detail to other countries. The larger aspects of economic and commercial geography are covered in connection with such topics as soils, minerals, waterways, water power, harbors, and the distribution and development of industries and cities. It is hoped, therefore, that the book may be found useful by teachers of commercial geography, as well as by those who have sought to " humanize" high school physiography. The illustrations are intended to serve as the basis for classroom discussions and quizzes, and should be studied and interpreted as carefully as the text itself. The questions may be used for written work or for classroom discussion. The answers to most of them are not to be found in the text, but can be reasoned out by students who have followed the text with understanding. The physical maps at the end of the book afford the means of locating most of the places and features mentioned in the text. vi PREFACE Teachers using this book will find it helpful to have the authors' Elements of Geography. The larger volume discusses in greater detail many of the topics of this one, and gives numerous references to supplementary material. A list of books on geography and related subjects which might well be in a high school library is given at the end of this book. CONTENTS CHAPTER I. II. III. PAGE IV. VI. VII. vin. IX. x. The Nature of Geography Earth Relations The Solar System The Earth as a Planet Maps and Map Reading Terrestrial Magnetism Relief Features of the Earth Relief Features of the First Order . Relief Features of the Second Order Subordinate Topographic Features Comparison of the Continents The Nature and Functions of the Atmosphere General Conceptions .... Composition . .... Relations of the Different Constituents to Life Climatic Factors: Temperature . General Conslderations ' . Seasons . Relation of Temperature and Altitude Representation of Temperature on Maps Ranges of Temperature Climatic Factors: Moisture Importance of Atmospheric Moisture Evaporation ..... Humidity ..... Climatic Factors: Pressure and Wind Pressure ..... Representation of Pressure on Maps and Charts Winds ..... Winds and Rainfall Storms and Weather Forecasting Weather Maps Cyclones and Anticyclones . Weather Forecasting . Local Storms Tropical Climate General Characteristics of Tropical Climates Types of Climate Within the Tropics The Future of the Tropics . Types of Climate in the Temperate (Intermediate) Zones General Characteristics of Climates of the Temperate Zones . . Types of Climate 4 4 5 15 18 19 19 21 23 24 27 27 28 29 34 34 4i 44 45 52 56 56 56 59 66 66 67 72 76 81 81 85 93 95 98 98 101 112 113 114 117 Vlll CONTENTS XI. Climate of Polar Regions . General Considerations The Antarctic Region . The Arctic Regions XII. The Oceans General Considerations Temperature of the Sea Movements of Sea-Water The Life of the Sea XIII. The Materials of the Land and Their Uses General Constitution . Soils .... Mineral Products and Their Uses Conservation of Mineral Resources XIV. Changes of the Earth's Surface Due to Internal Forces Slow Crustal Movements .... Earthquakes Vulcanism ....... XV. Modification of Land Surfaces by External Agents The Work of the Wind .... Ground-Water The Work of Streams . . The Work of Ice XVI. The Uses and Problems of Inland Waters Navigation Water Power ...... Irrigation ....... Reclamation of Swamp and Overflowed Lands Water Supply XVII. Mountains and Plateaus and Their Relations to Life Mountains Plateaus ........ XVIII. Plains and Their Relations to Life .... Life in Well-Watered Plains of Muddle Latitudes Life in Semi-Arid Plains Life in Arid Plains ...... Life in Arctic Plains ...... Life in Humid Plains of Low Latitudes XIX. Coast-Lines and Harbors ...... XX. Distribution and Development of the Leading Industries of the United States .... Agriculture . . . . . Forest Resources and Lumbering The Fishing Industries .... Mining, Quarrying, Etc. .... Manufacturing Industries .... XXI. Distribution of Population; Development of Cities Factors Affecting Density .... Cities 399 LIST OF PLATES AT END OF VOLUME Plate I. Plate II. Plate III. Plate IV. Plate V. Plate VI. Plate VII. North America United States South America Europe Asia Africa Australia IX MODERN GEOGRAPHY CHAPTER I THE NATURE OF GEOGRAPHY Ancient and modern geography. Geography has been studied since ancient times, for people always have wanted to know about the earth on which they lived; but the conception of geography has changed greatly as years have gone by. In olden times it was re- garded as a description of the earth. It included an account of the countries into which the earth is divided, their physical features, such as rivers, mountains, and plains, and their inhabitants and products. Modern geography is concerned especially with the effects of physical features, such as land forms, water, and climate, on living things. Divisions of geography. It is clear that there are two main parts to the study of geography: (i) The physical features of the earth (land, water, air) which affect life; and (2) the ways in which different forms of life respond to their physical surroundings. Various groups of physical phenomena may be the subjects of special study. Thus the phenomena of the atmosphere are considered in meteorology and climatology; those of the waters in oceanography and hydrography; and those of the lands in physiography, as some would define that term. Similarly, earth relations to life may be studied with special reference to plants {plant geography), to animals {animal geography), or to man {human geography). Relations to other subjects. The study of these different phases of geography brings it into contact with many other sciences. The form, size, and motions of the earth are matters of astronomy as well as geography; the origin and characteristics of land forms and the distribution of useful minerals are matters of geology as well as geography; the effects of physical conditions on plant and animal 2 THE NATURE OF GEOGRAPHY life are phases of botany and zoology as well as geography; the distri- bution of mankind, man's subdivision of the earth into political units, and many other matters, relate geography closely to history; and man's present activities, influenced by geographic conditions, are factors of political economy. Importance of human geography. Most interest attaches to the study of the earth in its relations to man. Human activities are so many and varied, and are influenced in so many ways by physical conditions, that special study often is made of related effects. Thus economic geography traces the influence of natural factors in the pro- duction of things useful to man. The relations of land forms, soil, and climate to the raising of crops is an example. Commercial geography considers the influence of natural factors in the transporta- tion and exchange of various commodities, as the trade in tropical fruits between warm regions and those too cold to raise them. His- torical geography is concerned with the influence of physical condi- tions on past events. Political geography traces the influences of lo- cation, topography, climate, and natural resources on the develop- ment of countries. The basis of other studies. Since geography shows the many ways in which the earth is related to the life of man, it is important as the basis of many other studies. It is especially important in connection with the study of history, for in all ages the conditions under which people lived have influenced their occupations, their stage of development, and their relations to the rest of the world. The better geography is understood, therefore, the easier it is to under- stand the meaning of historical events. The Jews in Palestine never became seamen because the nearest coast had no good harbors, while their neighbors, the Phoenicians, on a more favorable coast, were the first good sailors, and for many years were influential in Mediterranean districts outside their own country. Russia has striven for more than two centuries to secure satisfactory seacoasts, and as a result has been led into several wars with her neighbors. Great Britain, difficult to invade because an island, was able at an early date to use her natural resources to great advantage, and became the leading nation of the world in manufacturing and com- merce. In our country, slavery developed chiefly in the South, mainly because the conditions of field labor there favored it more than in the North. These examples suggest the close connection between geography and some important facts and phases of history. EARTH CONDITIONS AND LIFE 3 Geography is related no less intimately to present events. The distribution of people over the face of the earth, the manner in which they live, and their grouping in countries and cities always bear some relation to earth conditions. Many old cities, like Venice, were located where defense against invasion was easy. Most new cities were located with respect to natural advantages for manufacturing or commerce. Food, dress, shelter, occupations, industries, prod- ucts, trade, and many other facts and conditions of life are in- fluenced by physical surroundings. Deserts have little vegetation and few animals, for water is scarce. Since man depends on plants and animals for food and clothing, and largely also for shelter, desert populations are small. Tropical natives wear little clothing and eat little meat, largely because bodily temperatures are maintained easily without either. They have little commerce, because their wants are few. The people of middle latitudes, on the other hand, must adapt them- selves, in the matter of food, clothing, and shelter, to extremes of heat and cold. Their wants are therefore many and varied. Com- plex industries and world commerce are needed to satisfy them. The United States is the greatest producer of foodstuffs, because of the great extent of favorable surface, soil, and climate — resources which a progressive people have used to advantage. Several coun- tries of western Europe have advantages for extensive manufacturing, such as supplies of coal near good seaports; but they cannot produce all the raw materials needed for their factories, nor all the food for their factory workers. Hence large quantities of raw materials and food, like cotton and copper, flour and meat, are exported yearly from the United States to these European countries. An understanding of the larger relations between physical con- ditions and life in general is necessary for an understanding of the effects of the physical surroundings of man on his interests and activities. This in turn helps one to understand the affairs of the world, and therefore is important to good citizenship. CHAPTER II EARTH RELATIONS The Solar System Members of solar system. The solar system includes the sun and all the bodies which revolve about it (Fig. i). There are eight planets, of which the earth is one. To us, all the planets except our own appear as stars, but in their motions they differ from other stars. Commencing with the nearest to the sun, the planets are, Fig. i. Diagram of the principal members of the solar system. The size of the bodies is exaggerated greatly as compared with that of the sun and the orbits. The central body is the sun; the others are the planets. in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. All but Mercury and Venus have satellites correspond- ing to our moon. Saturn has nine of them. Besides the planets and their satellites, the solar system includes numerous other bodies (mostly asteroids) which have little influence on the earth. The sun is more than i ,000,000 times as large as the earth, and very hot. From it the earth receives nearly all its heat and light. The other planets shine only by reflected sunlight. Beyond the great system to which the earth belongs there are many thousands of stars, each of which may be compared to our sun, though many of them are vastly larger. The planets. The planets are all of similar form, all rotate on axes, and move in nearly circular paths about the sun in the same direction, but they are strikingly unlike in some respects. Jupiter, 4 THE FORM OF THE EARTH 5 the largest, has a diameter more than ten times that of the earth, while the diameter of Mercury, the smallest planet, is only about one- third that of the earth. The innermost planet revolves about the sun in 88 days, the outermost in 165 years. The shortest rotation period of a planet is less than 10 hours, while that of Venus is nearly 225 days. From the standpoint of life, the earth is the most favored of the planets. Indeed, the conditions of heat and light would prevent the existence of such life as we know on most of the other planets. The Earth as a Planet Form. The form of the earth is very much like that of a sphere, but since it is not exactly a sphere, it is called a spheroid. The form has been determined in various ways: (1) Ships have sailed around it. This proves that it is everywhere bounded by curved surfaces, but it does not prove that it is a sphere or even a spheroid, for it would be possible to sail around it if it had the shape of an egg. (2) When a vessel goes to sea, its lower part disappears first, and when a vessel approaches land, its highest part is seen first from the land. By people on the vessel, the highest lands are seen first, and the low ones later; the spires and chimneys of buildings appear before the roofs, and the roofs before the lower parts. Like (1) above, these facts show only that the earth has a curved surface. But from whatever port vessels start, and in whatever direction they sail, objects on land disappear at about the same rate. This means that the curvature of the surface is nearly the same in all directions. A body whose curvature is the same in all directions is a sphere, and a body whose curvature is nearly the same in all directions is nearly a sphere. (3) Again, the earth is sometimes between the sun and the moon. It then casts a shadow on the moon (making an eclipse), and this shadow always appears to be circular. In these and other ways it is known that the form of the earth does not depart greatly from that of a sphere. (4) That the earth is not exactly round, however, is shown in various ways. For example, a body weighs slightly more in high latitudes than in low latitudes. This means that it is nearer the center of the earth in the high latitudes than in the low; or, in other words, that the earth is not a true sphere. (5) Certain mathematical calculations not given here (for one of them, see p. n) prove that the curvature of the earth's surface is less in high latitudes than nearer the equator. 6 EARTH RELATIONS Consequences of the earth's form. The spheroidal form of the earth facilitates travel and transportation. It aids commerce in another important way. The attraction of the earth causes bodies to have weight. Because the earth is nearly round, gravity is nearly equal everywhere upon its surface, and, as we have already seen, the weight of a given object is therefore nearly constant. If the weight of things varied greatly from place to place, this variation would interfere seriously with trade between different parts of the world. Size. The circumference of the earth is nearly 25,000 miles, and its diameter nearly 8,000 miles. Since the earth is not a perfect sphere, its various diameters and circumferences are not exactly equal. Its longest diameter is 7,926.5 miles and its shortest nearly 27 miles less (7,899.7 miles). The area of the earth's surface is nearly 197,000,000 square miles. Motions The earth has two principal motions : (1) It rotates on its shortest diameter, called its axis, and (2) it revolves around the sun. The axis is an imaginary line, and its ends are the poles. The circumfer- ence midway between the poles is the equator. Rotation. The rotation of the earth from west to east gives us day and night, for one side of the earth and then the other is turned toward the sun during each rotation. The time of rotation, about 24 hours, determines the length of a day (day and night). Human activities are in general adjusted to the turning of the earth, the succession of daylight and darkness affording convenient intervals for work and rest. In those parts of the earth where the intervals of light and of darkness are many days (instead of hours), this habit of regularity of work and rest is less general. During the long period of light, the hunting people of Greenland, for example, cease their work or seek rest only when fatigue overtakes them. During the long period of darkness they have no regular work or exer- cise, and are much less vigorous than in the period of light. The long " night " ot polar regions is very trying to the health and strength of people accustomed to a period of light each day. The period of rotation furnishes also a natural unit for measuring time. Again, the rising and setting of the sun, due to the earth's rotation, give us a simple system of directions. Revolution. The earth revolves about the sun in a little more than 365 days, and the period of revolution fixes the length of the year. MOTIONS OF THE EARTH 7 The path of the earth around the sun is its orbit. The orbit of the earth is not a circle, but a curve called an ellipse (Fig. 2), and the distance of the earth from the sun varies from time to time. When Perihelion Aphelion Fig. 2. The orbit of the earth is an ellipse, with the sun in one of the foci. the earth is nearest the sun {perihelion), the distance between them is about 3,000,000 miles less than when they are farthest apart JUNE 21 ^^ Fig. 3. Diagram showing the position of the earth with reference to the sun at the solstices and equinoxes, and the inclination of its axis. {aphelion). The earth is nearest the sun (about 91,500,000 miles) in the early part of the winter of the northern hemisphere (about January 1st), and farthest from it (about 94,500,000 miles) early in the summer. The motion of the earth through space during its 8 EARTH RELATIONS revolution about the sun is at the rate of about 600,000,000 miles a year, or more than 1,100 miles each minute. The earth's axis is inclined toward the plane of its orbit about 2^/2 degrees (Fig. 3). This position of the axis, together with the motions of the earth, has much to do with the distribution of the heat and light received from the sun, with the changes in the length of day (daylight) and night, and with the seasons.. Latitude, Longitude, and Time Latitude. The equator has been denned as the circle about the earth midway between the poles. Circles parallel to the equa- tor are parallels. The number of parallels which might be drawn is very large, though only a few are represented on maps. The length of parallels varies greatly, those near the equator being longer, Fig. 4. Parallels and meridians. and those near the poles shorter. The north and south lines that pass from pole to pole on the earth's surface are meridians. All meridians come together at each pole. A few meridians and parallels appear in Fig. 4, which shows the earth in two positions. The left-hand part of the figure shows the half of each parallel represented and the whole of each meridian. The right-hand part shows the relation of parallels to the North Pole. The distance between the equator ^nd either pole is divided into 90 parts, called degrees (written 90^. Each degree is divided into 60 parts, called minutes (60') . Each minute is divided into 60 parts, called seconds (60"). Distance north or south of the equa- tor may therefore be determined from a globe or map by means of parallels. The system of parallels and meridians is made possible by the form of the earth and its rotation on its axis. LOCATION OF PLACES ON THE EARTH North Pole Distance north or south of the equator is called latitude. North latitude is north of the equator, and south latitude is south of it. The degrees, minutes, and seconds are numbered from the equator toward the poles. The latitude of the equator is o°. Latitude i° N. is one degree north of the equator,- and latitude 90 N. is at the North Pole. Latitude i° S. is one degree south of the equator, and lati- tude 90 S. is at the South Pole. Longitude. Position on a parallel is indicated by means of the meridians which cross it. The number of possible merid- ians is very great, but, as in the case of parallels, only a few are commonly shown on maps. One meridian, that passing through Greenwich, England, where the British Royal Obser- vatory was established in 1675, is usually chosen as the merid- ian from which distances east and west are reckoned (Fig. 5). This meridian is the meridian of o°, and is sometimes called the prime meridian. Distance east or west of this meridian is known as longitude. Places east of longitude o° are in east longitude, and those west of it are in west longi- tude. East and west longitude respectively are regarded as extending 180 from the meridian of o°; that is, half-way around the earth. The position of a place on the earth 's surface may be fixed exactly by means of meridians and parallels. If a place is in longitude 30 E., its distance east of the meridian o° is known. If at the same time it is in latitude 30 N., it must be on the parallel of 30 N. where it is crossed by the meridian of 30 E. So convenient and accurate is this method of locating places and reckoning distance, that parallels and meridians are used in many places as boundaries between states, counties, and townships. The poles are the only places which have latitude but no longitude. Since all meridians come together at the poles, the poles cannot be said to lie either east or west of the meridian of Greenwich. At the South Pole Fig. 5. Diagram showing the position of the axis of the earth, the poles, the equator, the meridian of Greenwich, and the meridian of 180 . IO EARTH RELATIONS North Pole the only direction is south, and at the South Pole the only- direction is north. Longitude and time. There is a definite relation between longitude and time. Since the earth turns through 360 in 24 hours, it turns 15 in one hour, and 15' of longitude in one minute of time. The sun therefore rises one hour earlier at a place in longitude o° than at a place in the same latitude in longitude 15 W., and one 4 lr - Fig. 6. Map showing standard time belts of the United States in Dec., 191 2. hour later than at a place in the same latitude in longitude 15 E. Similarly, noon comes an hour earlier in longitude o° than in longitude 1 5 W., and an hour later than in longitude 15 E. All places on a given meridian have noon at the same time and midnight at the same time, and such places are said to have the same time; but places on dif- ferent meridians have different times. St. Louis is about 15 farther west than Philadelphia, and Denver is about 15 west of St. Louis. When it is noon at Philadelphia it is about eleven o 'clock at St. Louis and ten at Denver. When it is one o 'clock at Philadelphia it is noon at St. Louis and eleven o'clock at Denver, and when it is noon at Denver it is one o 'clock at St. Louis and two at Philadelphia. The variations of time with changes of longitude become apparent when long journeys are made either east or west. Thus a watch which STANDARD TIME BELTS n has the correct time in New York has not the correct time when it is carried to Chicago. To avoid the difficulties of time-keeping growing out of travel, the railroads of the United States have adopted a sys- tem of standard time. Under this system the country is divided into north-south belts of convenient width (Fig. 6), and in each belt all railways use the same time. The railway time in adjacent belts differs by one hour. By this system, clocks and watches do not show correct local time except on one meridian of each belt. The irregular boundaries of the belts are due to the adoption of the nearest impor- tant railway points as the places for changing time on east and west journeys. Lengths of degrees. The length of a degree of longitude, as measured on the surface of the earth, is the V360 part of a parallel. Since the parallels are very much shorter near the poles than near the equator, the length of a degree of longitude is less in high than in low latitudes. At the poles, where the length of the parallel becomes zero, the length of a degree of longitude also becomes zero. At the equator, a degree of longitude is a little more than 69 (69.16) miles. Degrees of latitude are measured on meridians. They also vary in length. The length of a degree of latitude is about 68^ miles in India, while in Sweden, the most northerly place where a degree has been measured, it is 69X miles. All measurements which have been made show that the length of a degree of latitude, measured on the earth's surface, increases as the poles are approached. At the poles it is calculated that it must be about 69^ miles. In the United States, the average length is about 69 miles. The increase of length of the degree toward the poles means that the earth is flattened there. This means that the earth is a spheroid. Inclination of Axis and its Effects The sun's rays illuminate one-half of the earth all the time. The border of the illuminated half is called the circle of illumina- tion (Fig. 7). All places on one side of the circle of illumination have day, while all places on the other side have night. If the axis about which the earth rotates were perpendicular to the plane in which the earth revolves about the sun, the circle of illumination would always pass through the poles. Under these conditions, half of the equator and half of every parallel of latitude would be illuminated all the time, as in Fig. 7. If the half of each parallel were always illuminated, the days and nights would be equal everywhere, for it 12 EARTH RELATIONS takes just as long for a place at A (Fig. 7) to move to B (six hours, half of a twelve-hour day) as for it to move from B to A' (half of a twelve-hour night). Since days and nights are not equal at all sea- sons in most parts of the earth, it proves that the axis on which the earth rotates is not per- pendicular to the plane of its orbit. Again, if the earth rotated on an axis perpendicular to the plane of its orbit, the sun always would be equally high at any given place at the same hour of the day. But this is not the case. In the United States, for exam- ple, the sun is much higher above the horizon at noon in summer than in winter. The same is true in all lati- tudes similar to those of the United States. This variation of the an- gle at which the sun's rays strike the same place at dif- ferent times, as well as the unequal lengths of days and nights in most places, is the result of the inclination of the axis on which the earth rotates as it revolves around the sun (Fig. 3). The position of the axis is constant throughout the year. The effect of the inclination of the axis is illustrated by Fig. 3, which represents the earth in four positions in its orbit. On March 21st, the half of each parallel (the half toward the reader) is illuminated. At this time, therefore, days and nights are equal everywhere. On June 21st, more than half (the part not shaded) of every parallel of the northern hemisphere is illuminated, and there the days are more than 12 hours long and the nights correspondingly less. In the southern hemisphere the nights are longer than the days. On September 2 2d, the days and nights are again equal everywhere, for the circle of illumination divides every parallel into two equal parts. In the figure, the lighted part is away from the reader. On December 2 2d, more than half of each parallel in the southern hemisphere is in the light, and there the Fig. 7. Diagram to illustrate the fact that half of the earth is lighted by the sun at any one time. The parallel lines at the right show the direction of the sun's rays. The part of the earth not shaded is lighted by the sun; the other half is in darkness. The line between the illuminated half and the half which is not illuminated is the circle of illumination. This diagram represents con- ditions at the time of an equinox. EFFECTS OF INCLINATION OF EARTH'S AXIS 13 days are longer than the nights, while in the northern hemisphere the nights are longer than the days. Twice during the year, therefore, on March 21st and September 2 2d, the days and nights are equal everywhere. These times are known as the equi- noxes. The equinox in March is the vernal equi- nox; that in September is the autumnal equinox. When the earth is in the relation to the sun shown in the position marked June 21st, Fig. 3, the days are longest in the northern hemisphere, the sun is highest in the heavens at noon, and its rays fall perpendicularly on the surface of the earth farther north (23 27'+) than at any other time. This is the summer solstice (Fig. 8). The winter sol- stice occurs six months later, when the sun 's rays strike the earth vertically 23^"° (nearly) south of the equator (Fig. 9), and when the days of the southern hemisphere are longest and those of the northern shortest. Figs. 7, 8, and 9 also show that the days and nights are always equal at the equa- tor, since the equator is always bisected by the circle of illumination. Days and nights are not always equal in any other Fig. 9. Fig. 8. Diagram illustrating the effect of inclination of the earth's axis on the length of day and night. In the figure, more than half of every parallel of the northern hemisphere is illuminated. The days in the northern hemi- sphere are therefore more than twelve hours long, since the half of each parallel is the meas- ure of 180 of longitude, and 180 of longitude corresponds to twelve hours of time. Similarly less than half of every parallel of trie southern hemisphere is illuminated, and the days are therefore less than twelve hours long. Fig. 9. The relation of the earth to the sun's rays at a time six months later than that represented in Fig. 8. The conditions of day and night in the hemispheres are reversed. 14 EARTH RELATIONS Sp&A latitude, unless at the poles, where there is one day (or period) of six months of light, and one night (or period) of six months of darkness. The relative duration of daylight and darkness, and the angle at which the sun 's rays strike the earth, are the chief causes of changes of seasons. Thus at the equator, where the hours of day and night are always equal, and the sun's rays nearly vertical at all times of the year, seasons differ but little, while toward the poles, say in Lat. 6o°, where days and nights are very unequal most of the time, seasons differ greatly. It will be seen, therefore, that most of our methods of reckoning years, seasons, days, distances and posi- tions, weights, and direc- tions depend on the various earth relations. Apparent motion of the sun. The effect of the in- clination of the axis of the earth is to make the sun ap- pear to move north and south once during each revolution of the earth about the sun. That is, the revolution of the earth about the sun, while it rotates on an in- clined axis, makes the sun appear to move from a place where its rays are vertical 23^° (nearly) north of the equator (direction 5, Fig. 10), to a place where they are vertical 23^° (nearly) south of the equator (direction W), and back again, in one year. The result, so far as the earth is concerned, is as if the sun moved from S, which corresponds to the time of the summer solstice, to Sp & A, which corresponds to the time of the autumn equinox, then to W, which corresponds to the time of the winter solstice, then back again to Sp & A, which corresponds to the spring equinox, and finally to S, while the earth is making one circuit about the sun. When the sun is vertical at points north of the equator, the days are longer than the nights in the northern hemisphere, and the sun 's rays strike the surface in the northern hemisphere more nearly ver- tically than they do in the southern hemisphere. The greater number of hours of sunshine and the more nearly vertical rays explain the Fig. 10. Diagram illustrating the appar ent motion of the sun. MAPS AND MAP READING 15 warmth of our summer, even though the earth is then farthest from the sun. In high latitudes, as in western Canada, the long period of sunlight (16 to 18 hours) is an important factor in the successful cultivation of crops, in spite of the short summer. When the sun is vertical at the equator, days and nights are equal everywhere, and when the sun is vertical south of the equator, days are longer than nights in the southern hemisphere, and the sun's rays are more nearly vertical there than in the northern hemisphere. The northernmost parallel where the sun's rays are ever vertical is called the tropic of Cancer. The corresponding southernmost parallel is the tropic of Capricorn. The tropics are nearly 23^"° (23 27'+) from the equator, because the axis of the earth is inclined by that amount toward the plane of its orbit. The sun is vertical at the tropic of Cancer at the time of the summer solstice, and at the tropic of Capricorn at the time of the winter solstice. The parallels just touched by the circle of illumination at the time of the solstices are the. polar circles. They are as far from the poles as the tropics are from the equator. They are therefore in latitude about 66>^°. The one in north latitude is the Arctic circle, and the one in south latitude is the Antarctic circle. Within the polar circles the differences of the seasons are chiefly a matter of daylight and darkness. Between the tropics there are no changes of seasons like those of the United States. Hence it is only between the polar circles and the tropics that there are four seasons of the year, to be called truly spring, summer, autumn, and winter. c^-~ Maps and Map Reading What is known of the earth 's surface may be represented in vari- ous ways — by globes, models, and maps. Globes have the great advantage of showing without distortion the distribution of land and sea, and other large surface features. It is not practicable, however, to make them large enough to show minor features, and, even apart from this, they are not suited to all purposes. Models, or relief maps, reproduce on a small scale the unevenness of the earth 's surface. In order that the elevations may stand out clearly, their height is exag- gerated greatly on most models, which are likely, therefore, to give false impressions. Map projections. The necessity of representing part or all of the earth on a flat surface led very early to the making of crude maps. i6 EARTH RELATIONS Fig. ii. Map representing relief by hachures. (U. S. Geol. Surv.) It is, of course, impossible to show the rounded surface of the earth on a flat surface without exaggerating or reducing certain parts, so that each of the many methods {projections) devised from time to time for representing the meridians and parallels of a globe on a plane surface, involves more or less distor- tion. Almost all sailing charts and many maps of the entire world are made on Mercator's projec- tion (Fig. 39), named for the inventor. A map on Merca- tor's projection is accurate at the equator, but exaggerates areas more and more as the poles are approached. Thus Greenland (Fig. 39) appears to be about half as large as North America on a Mercator's map, while in reality it is less than one-fifteenth as large. Representation of relief on maps. The surface of the land is uneven, and it is a matter of importance, in many cases, to show the unevennesses {relief) on maps. This is done in various ways. One method is by shading — different colors or shades representing different elevations (see maps at end of book). Another method is by hachures (Fig. 11) — lines drawn in the direction in which the land slopes. Where slopes are steep, the lines are made short and heavy; where gentle, longer and lighter. Such maps give only a general idea of the form of the land. Much more exact information may be had from contour-line maps. In order to read contour-line maps, it is necessary to know that contours are lines drawn on maps to express relief, and that any given line runs through points of the same elevation above sea-level. This will be understood readily by reference to Figs. 12 and 13. Fig. 12 shows a model of an ideal landscape viewed from above, on which lines have been drawn connecting places of equal elevation. In Fig. 13 the above lines are shown alone; this is a contour map of the region represented by the model. By comparison of the model and map it will be seen that where the slopes of the former are steep WAYS OF REPRESENTING RELIEF ON MAPS i7 the lines of the latter are close together, and vice versa. The vertical distance between two adjacent contour lines is the contour interval. The contour interval varies on different maps. In regions of low Fig. 12. Model of ideal landscape. (U. S. Geol. Surv.) Fig. 13. Contour map of the area shown in Fig. 12. (U. S. Geol. Surv.) relief an interval of 10 or 20 feet generally is used; in mountainous areas an interval of 500 or more feet has to be used in some cases in order to avoid having the lines too close together to be read. In the map of Fig. 13, the interval is 20 feet, the exact value of the 10c 1 8 EARTH RELATIONS and 200 foot lines being indicated. By counting the lines it will be seen that the top of the hill to the left of the river is more than 260 feet above the level of the ocean in the foreground. It cannot be 280 feet high, however, for no 280 foot line is drawn. A comparison of the model and map will show also how valley depressions are repre- sented by contours. Terrestrial Magnetism The earth is a great magnet, and, like the small magnets with which we are familiar, has two poles. One of these poles is called the North Magnetic Pole and the other the South Magnetic Pole. One end of the compass needle points toward one of these poles, and the other toward the other. If we were to follow the directions pointed by the compass needle, we would be led to the North Magnetic Pole in the one case, and to the South Magnetic Pole in the other. The magnetic poles are far from the geographic poles, the true north and south points, and they are not exactly opposite each other. Their positions appear to shift a little from year to year, but the change is not known to be great. The North Magnetic Pole is in latitude about 70 N., and in longitude 97 or 98 W., while the South Magnetic Pole is in latitude 72 25' S., and longitude 155 16' E. Questions 1 . The horizon of a given observer increases as he rises. What does this prove concerning the shape of the earth's surface at that place? What further inference could be made from the fact that as he ascends his horizon remains circular? 2. At places east of a given point the sun rises and sets before it does at that point. At places toward the west it rises and sets after it does at the station in question. What does this indicate as to the surface of the earth? 3. Why do the sun's rays never fall vertically in latitudes higher than 23^°? 4. Certain crops are said to mature faster in western Canada than farther south in the United States. Suggest a logical reason for this. 5. How would the seasons at Chicago (42 N.) be changed if the axis of the earth were inclined 45 , rotation remaining as now? 6. Two cities about 690 miles apart, on the same meridian, are located in latitude 42 N. and 32 N., respectively. From these facts determine approximately the circumference of the earth. 7. What is the difference in longitude of two places having a difference in time of six and one-half hours? 8. -What is the difference in local time between New York City (74 W.) and Chicago (87 36' W.)? 9. The altitude of the sun at a given place at noon at the time of equinox is 50°. What is the latitude of the place? 10. In what latitudes is the altitude of the sun 20 at noon at the time of equinox? n. In what latitudes has the sun a noon altitude of 30 at the time of the summer solstice? 12. What is the altitude of the sun at the equator at noon at the time of the summer solstice? CHAPTER III RELIEF FEATURES OF THE EARTH The surface of the land is uneven. The lowest lands are below sea-level, and the highest point (Mt. Everest, in the Himalaya Moun- tains) is more than five and one-half miles above sea-level. The relief of the land surface is therefore not far from six miles. Com- pared with the diameter of the earth, even the loftiest mountains are slight elevations, for the height of Mt. Everest above the sea is equal to only V1436 part of the polar diameter of the earth. On a globe 10 feet in diameter this would correspond to one- twelfth of an inch. The sea bottom also is uneven, and its relief is a little greater than that of the land. Since the highest points of land are nearly six miles above the sea, and the lowest parts of the sea bottom about six miles below, the relief of the surface of the solid part of the earth (lithosphere) is almost twelve miles. If its surface were even, the water of the ocean would cover the whole earth to the depth of about 9,000 feet. Relief Features of the First Order Continents and ocean basins. The average elevation of the lands above sea-level is a little less than half a mile, while the average depth of the oceans is about two and one-half miles. Were the height of lands in middle and high latitudes equal to the average depth of the Mountains. gateau ^~v s\ — d/^„„„ Fig. 14. Diagram to show the distinction between an elevated continental area and an ocean basin. The steep slope (much exaggerated) at the left of the ocean basin is the line of contact between the two, and is the real border of the continental area. The ocean covers the lower part of the continental tract, namely, the continental shelf. The diagram also shows the general relation between low mountains, such as the Appalachians, a low plateau, and a coastal plain. The continental shelf is a continuation of the coastal plain. 19 2o RELIEF FEATURES OF THE EARTH oceans, much of each continent would be too high and cold to support a dense population. The continents and the ocean basins are relief features of the first order. The oceans have an area (143,000,000 square miles) more than two and one-half times as great as that of the lands (54,000,000 square miles). About most continental borders, the water is shallow (less than 600 feet) for some miles. The bottom beneath this shallow water is the continental shelf (Fig. 14). At their sea-ward edges, the continental shelves descend, by rather steep slopes, to the ocean basins. Por- tions of the continental shelves have been built up from deeper water by the deposition of sediments washed down from the land; other parts are due to the sinking of former land areas; and still others are the result of the wearing back of the land by waves. Many islands stand on the continental shelves, and represent higher areas whose lower surroundings have sunk, or been cut by waves, below sea-level. In many cases a slight elevation of the continental shelf, or a slight lowering of the sea, would join these islands to the mainland. Thus a rise of 300 feet would trans- form most of the area of the Baltic and North seas into land, and unite Great Britain with the continent. Such a change would modify greatly conditions in Great Britain. Separation from the continent has freed the United Kingdom from the need of a large standing army, and favored the development of extensive sea interests, which required the maintenance of a large navy to protect them. Most islands of the ocean outside the continental shelves are volcanic cones, or coral islands associated with them. Their combined area is only about three-fourths that of the state of Illinois. Fig. 15. Land and water hemispheres. Grouping of the continents. The northern hemisphere con- tains more than twice as much land as the southern. If the earth be PLAINS, PLATEAUS, AND MOUNTAINS 21 divided into two hemispheres, one with its center in England and the other in New Zealand (Fig. 15), the first would contain about six-sevenths of all the land, and might be called the land hemi- sphere, while the other would contain only about one-seventh of the land, and might be called the water hemisphere. Even in the land hemisphere, however, the water would cover rather more than half the surface, while in the water hemisphere it would cover about fourteen-fifteenths of it. Since the northern hemisphere contains two-thirds of the land, and a still larger proportion of the productive land, it has always supported a vast majority of the human race. Relief Features of the Second Order The more strongly marked features of the continents and of the ocean basins are relief features of the second order. The continental areas are made up of plains, plateaus, and mountains. Some of their relations are shown in Fig. 14. Plains. Plains are the lowlands of the earth. They may be but a few feet above the sea, or they may be hundreds or thousands of feet above it; but if so high as a thousand feet, they are in most cases far from the sea, and distinctly lower than some of the other lands about them. Plains differ widely among themselves, not only in height, but in position, size, shape of surface, fertility, origin, and in various other ways. Different names are given to various sorts of plains, the names being intended to call attention to some one feature. Coastal plains border the sea, and interior plains axe far from it, or are separat- ed from it by high lands. The plains of the Atlantic and Gulf coasts illustrate the first class, while a large part of the area between the Appalachian Mountains and the Rocky Mountains is a great interior plain (Plate 1). Plateaus. Plateaus are highlands with considerable summit areas; but no great elevation is necessary to make a flattish area of land a plateau. In general, a plateau is so situated as to appear high from at least one side. Thus if a coastal plain rises gradually from the sea to a height of 200 feet, and then rises by a steeper slope to another broad tract of land which stands 200 feet higher (Fig. 14), the upper tract would be called a plateau. The Piedmont Plateau, which lies between the Appalachian Mountains and the Atlantic Coastal Plain, is not very high, but it is enough higher than the Coastal 22 RELIEF FEATURES OF THE EARTH Plain to be distinctly set off from it. A large part of this plateau is, however, not so high as much of the great interior plain of the continent. Some plateaus lie between mountains on the one hand and plains on the other, as in the case of the Piedmont Plateau. Others lie be- tween mountains, as the plateaus of central Asia (Fig. 16), Mexico, Caucasus Mts. Himalaya Mts. Nan-Shan Mts. Fig. 1 6. Section across Asia, showing plateau between the Himalayas and the Nan-Shan Mountains. Sierra Ui "f a Ro ^ Mts r*- Mu - /V~— ^_, />^- ^C\^ ^__ Mississippi Basin s^~— — _^__ Fig. 17. Section across North America, showing plateaus between the moun- tains in the western part. and western United States (Fig. 17). Other plateaus rise directly from the sea, as Greenland and parts of Africa. The total area of plateaus is great, though less than that of plains. Mountains. Mountains are conspicuously high lands with slight summit areas (Fig. 18). The tops of the loftiest mountains are be- tween five and six miles above the sea, but most mountains are not half so high. The highest mountains tower above any plateaus, but many mountains are lower than the highest plateaus. Few mountains reach the height of the Plateau of Tibet, 15,000 to 16,000 feet. Mountains are unlike plateaus of similar elevation in having little area at the top. In the case of mountain peaks, this is shown by the name. A mountain ridge may be long, but in most cases its top is narrow. Numerous peaks or ranges near together make a moun- tain group or chain; but even in great mountain groups there is no large expanse of land at the summit level. Where mountains rise abruptly to great heights above their surroundings, they are the most impressive and awe-inspiring features of the earth. In not a few cases they rise from low, warm plains to such heights that their summits always are covered with snow. Nowhere else are such extremes of climate found so close together. MINOR TOPOGRAPHIC FEATURES 23 Mountains are the third of the three topographic types of the second order, as they appear on the lands of the earth. In this group- ing of mountains, only great groups or systems of mountains, such as the Appalachians, the Rockies, the Alps, the Himalayas, and the Andes, are considered. Most mountain ranges are situated near the edges, rather than in the interiors, of the land masses, and most of the loftier mountain chains are not far from the shores of the greatest ocean. The conti- Fig. 18. Mountains rising conspicuously above a plain. Southern California. nental slopes to the Pacific Ocean are therefore shorter and steeper than those to the Atlantic and Arctic oceans. About one-third of the land drains to the Atlantic Ocean, one-sixth to the Arctic, one- seventh to the Pacific, and one-eighth to the Indian. The drainage of the rest of the land (22%) fails to reach the sea, and is lost in dry interior basins. Subordinate Topographic Features The surfaces of most plains and plateaus are uneven, while the very name of mountain suggests ruggedness. Irregularities of surface consist of elevations, such as ridges and hills, above the general level, and of depressions, such as valleys and basins (depressions without outlets) , below it. The elevations and the depressions are bordered by slopes, which, when very steep, are called cliffs. Ridges, hills, valleys, basins, flats, and cliffs affect mountains, plateaus, and plains; but in most cases they are more pronounced in mountains and plateaus than 24 RELIEF FEATURES OF THE EARTH on plains. These minor unevennesses of surface are topographic features of the third order. The key to their history is found in changes now taking place on the land (Chapter XV) , or in those which have taken place in recent times. Comparison of the Continents The position, form, size, and general relief of the continents are of fundamental importance, since these things determine, in large measure, their fitness for human occupation. Europe (Plate IV), the smallest continent except Australia, lies almost entirely in the north temperate zone. It widens rapidly toward the south, so that its east and west extent along the line of the Mediterranean, Black, and Caspian seas is nearly three times that along the Arctic Ocean. No other continent has an outline so irregular. Great arms of the sea extend far inland, modifying climate and helping commerce by bringing most parts of the continent into close contact with the sea. More than half of Europe is less than 600 feet above sea-level, and only one-sixth is over 1,500 feet. Many rivers serve as natural high- ways into the interior. Some of those in the west are unfrozen throughout the year. Europe has no tropical section, and no dry desert. Asia (Plate V), the largest of the continents, is nearly 4^ times the size of Europe, and nearly 5^ times as large as the United States. It extends somewhat farther north than Europe, and much nearer the equator. Less than one-fourth of Asia is below 600 feet above the sea, and about one-sixth is above 6,000 feet. The average elevation is nearly three times that of Europe. A central region of high pla- teaus and mountains receives little rain, and is of slight value to man. The longest drainage slopes are toward the Arctic. Because of these things, one-half of Asia is relatively inaccessible. Asia has only about one-third as long a coast-line as Europe in proportion to its area. Its great size and relatively compact form make it the conti- nent of climatic extremes. From a physical standpoint Europe and Asia form one continent (called Eurasia), but for historical and other reasons they usually are separated. Australia (Plate VII) is only a little larger than the United States, and is divided almost in halves by the tropic of Capricorn. The coast, though less regular than that of Africa and South America, has few harbors compared to Europe and North America. Because THE CONTINENTS COMPARED 25 of its position, size, compactness, and topography, much of Australia is arid (p. 106). Australia is the most isolated of the continents. About two-thirds of Africa (Plate VI) are within the tropics. Broadly speaking, the continent consists of a great plateau, bordered in places by a narrow coastal plain. At the south, the plateau is 3,000 to 5,000 feet above sea-level; at the north, 1,000 to 2,000 feet. Only one-eighth of the land (less than in any other continent) is below an elevation of 600 feet. The rivers descend in rapids or falls to the coastal lowlands. More than one-third of the continent is desert, while other large areas are semi-arid. Africa has the most regular coast of any continent. Europe, with the most irregular outline, has more than six times as much shore-line as Africa, in proportion to its area. Although one of the most ancient civilizations had its seat in Egypt, Africa has remained to our own day the "dark conti- nent." The conditions indicated above have helped greatly to bring this about. The fact that much of the coast is without harbors, and that navigation of even the larger rivers is interrupted near their mouths by falls and rapids, delayed exploration, conquest, and commerce. Both the vast deserts and the dense equatorial forests retarded native progress, and discouraged European settlement. Like Africa, South America (Plate III) is largely within the tropics and is very compact, with few great indentations, peninsulas, or is- lands. On the other hand, the proportion of desert is much less, and of lowlands much greater. Two-fifths of South America are below 600 feet, and two-thirds under 1,500 feet. In North America (Plate I), as in Europe, most of the land is in middle latitudes. Unlike Europe, North America presents its greatest width to the cold polar seas. North America ranks next to Europe and South America in the relative extent of its lowlands. Nearly one-third of the continent is below 600 feet, and nearly two-thirds below 1,500 feet. The vast interior plain stretching from the Arctic Ocean to the Gulf of Mexico has an unequaled system of navigable waterways. Except Europe, North America has the longest shore- line in proportion to its size. The greatest indentation, the Gulf of Mexico, affects the climate of eastern United States profoundly (p. 85). Except in the far north, most of the indentations have commercial importance. 26 RELIEF FEATURES OF THE EARTH Questions i. South America and Africa have few islands about their borders. What does this suggest concerning the width of their continental shelves? Does it prove anything about the width? 2. Soundings along the eastern coast of the United States have shown that depressions like river valleys extend across the continental shelf from the mouths of various rivers. What do such depressions suggest concerning the history of those parts of the continental shelf where they occur? 3. From the comparison of the continents given on pages 24-25, which ones appear best fitted to contain the most advanced nations? Which ones seem least fitted to do so? 4. Most people live on plains. Would it therefore be better, from the human standpoint, if the earth were without mountains? Reasons? CHAPTER IV THE NATURE AND FUNCTIONS OF THE ATMOSPHERE General Conceptions Relation tp rest of earth. Air is essential to the life of the earth, and to most processes in operation on the earth 's surface. It helps to distribute moisture, it makes the extremes of heat and cold less than they would be if it did not exist; and it is a leading factor in the formation of soil. Furthermore, the atmosphere is not merely an envelope of the rest of the earth, for it goes down into the soil and rocks as far as there are holes and cracks, and its constituents are dissolved in the waters of sea and land. Weight of air. When the atmosphere is still, we are hardly conscious of its existence, but many familiar phenomena show that air is very substantial. Thus wind, which is only air in motion, may be so strong that trees and buildings are blown down by it. A wind blowing 30 miles an hour exerts a force of nearly 60,000 pounds on the side of a house 60 feet long and 20 feet to the eaves. The pressure of still air, that is, its weight, is nearly 15 (14.7) pounds on every square inch of surface at sea-level. In other words, its weight is equal to that of a layer of water completely covering the earth to a depth of 33 feet. Density. The atmosphere is made up of gases. The particles of which the air is composed are nearer together at low altitudes than at high altitudes. At its bottom, the air is pressed down by all the air above; at the height of 1,000 feet the air is pressed down by all above that level, and so on. Hence the lowest air is under most pressure and is densest. One-half the atmosphere (by weight) lies below a plane about 3.6 miles above sea-level, and three-fourths of it below a plane 6.8 miles above the same level. Nearly three-fourths of the atmosphere lies below the top of the highest mountain. It is partly because the air is less dense at high levels that mountain- climbing is difficult. The body is not accustomed to the lessened pressure, and it causes discomfort. 27 28 NATURE AND FUNCTIONS OF THE ATMOSPHERE Height. The actual height of the atmosphere is not known, though something is known about it (Fig. 19). (1) The greatest altitude reached by any mountain-climber is about 24,000 feet. This shows that the air extends to a height of more than four and one-half miles. (2) Men have gone up more than six miles in balloons. In some cases, the men in the balloons became unconscious before this height was reached, and in other cases, where oxygen was carried for breath- ing, the chief discomfort was from cold. Balloons without men have risen eighteen miles. At this tf ,gh Clouds (Wmiles) Highest Mou mtain (6 m,le s ) ■ Hi|hes^_Mo_u_ntain_Ascent_ (4% ^jjj- - -, low Cjouds ('/smi/e ) Fig. 19. Diagram to show relative altitudes in the atmosphere. height the air is still dense enough to carry the balloon. This shows that the air extends up more than eighteen miles. (3) On almost any clear night "shooting stars" may be seen. Shooting stars, or me- teors, are small, solid bodies which come into the earth's atmosphere from space outside. They are very cold when they enter the atmosphere, for the temperature of space is very low (probably about — 45q°F.). In passing through the atmosphere, meteors are heated by friction with the air, and when they get red-hot, they may be seen. The height at which they begin to glow has been calculated in some cases, and found to be, at a maximum, nearly 200 miles above sea-level. This shows that the atmosphere is much more than 200 miles high, for the meteors must have come through the rare, cold, upper air a long distance before becoming red-hot by friction with it. From these considerations it appears to be certain that the air extends more than 200 miles above the rest of the earth, but how much more is unknown. Except for a few miles near its bottom, it is, of course, very thin (rare). Composition Principal constituents. The composition of the atmosphere is nearly the same at all times and at all places where it has been ana- lyzed. In its lower parts, at least, it is made up chiefly of two gases — (1) nitrogen, which makes up about 78 per cent of dry air, and (2) IMPURITIES IN THE AIR 29 oxygen, which makes nearly 21 per cent. Some scientists think its composition at great heights may be very different from that below. Besides these two gases, there are several lesser constituents, two of which, carbon dioxide and water vapor, are very important. The former makes up about 3 /ioooo by weight of the whole atmosphere, and its amount is nearly constant from day to day, and from year to year. Water vapor is water in particles too small to be seen. The total amount in the atmosphere is not known to vary much, but the amount varies greatly from place to place, and it varies much from time to time in the same place. Even in the driest deserts the air is never without water vapor. Several other gases exist in the air, but among them ozone only is known to be of much importance. The gases of the air are mixed with one another, and each of them retains its own qualities in the mixture. Oxygen behaves much as if no nitrogen were present, and the nitrogen as if there were no oxygen. Impurities. The air always contains some gases which are impurities, though they are not necessarily harmful to life. Some such gases arise from the burning and decay of organic matter, others from chemical processes used in manufacturing, and still others from volcanic and other vents in the earth's crust. Although the total amount of gas which enters the air in these ways is small in comparison with the volume of the atmosphere, it would seem very great if stated in terms of weight or volume. For example, it is estimated that at least 1,000,000,000 cubic feet of natural gas escape unused into the air each day in the United States. Quantities of gas are poured into the air, too, from chimneys. The air always contains, as impurities, numerous solid particles, such as dust, and germs or other organic matter. These vary in amount and character from place to place, and from time to time. Relations of the Different Constituents to Life Nitrogen. Nitrogen is inactive. Though it enters the lungs with oxygen in breathing, it does not appear to be of direct use to animals. Indeed, its chief function in relation to life is often said to be "to dilute the oxygen." It is important to note, however, that indirectly nitrogen is of great importance to both plant and animal life. Most plants use the small quantities of nitrogen com- pounds in the soil. Nearly all crops, if grown year after year in the same place, take out so much of the nitrogenous matter as to decrease 3 o NATURE AND FUNCTIONS OF THE ATMOSPHERE the fertility of the soil. A few plants, such as clover, alfalfa, peas, and beans, add nitrogen to the soil. Certain bacteria associated with these plants take nitrogen from the air and combine it with other elements, and the plants then store it in their roots, stalks, etc. It is therefore important to grow nitrogen-fixing plants in rotation with other crops, and turn them under the soil. Oxygen. Oxygen from the air is consumed all the time by ani- mals. Air-breathing animals take it from the air directly, and water- breathing animals take it from the water in which it is dissolved. Oxygen is used by plants also, especially by green plants, and it is used wherever combustion (burning) or decay is going on, for com- bustion is primarily the union of oxygen with carbon, and decay is very slow combustion. The heat developed by combustion (as of coal) warms houses, and produces steam to run trains, drive machinery, and serve man in many other ways. Oxygen from the air combines with various constituents of rocks to form new com- pounds, and in so doing helps to form soil (p. 162). In spite of the fact that oxygen is being consumed all the time, its amount does not appear to grow less from year to year. It must, therefore, be supplied to the air about as fast as it is used up. Plants break up the carbon dioxide of the air into carbon and oxygen, and set some of the oxygen free. This is the greatest source of supply. Small amounts of oxygen also reach the atmosphere from volcanic vents, and in other ways. It will be seen that plants, through their relation to oxygen and nitrogen, play an important part in supplying animals with both these elements. Carbon dioxide. The carbon dioxide of the air, though a small constituent, is extremely important. It is being made constantly by the burning of all kinds of fuel and by the decay of all organic matter. It is also added to the air by the breathing of animals. Every 1,000,000 human beings breathe out about 2.5 tons per hour. It also comes out of many volcanic vents in great quantities. From these various sources, carbon dioxide is supplied to the atmosphere rapidly. About three-fourths of common soft coal is carbon. The carbon of a ton of such coal, united' with oxygen from the air (3ms. of carbon unite with 8lbs. of oxygen), would make more than 2^ tons of carbon dioxide, all of which goes into the atmosphere. A ton of hard coal, which contains more carbon, would produce still more carbon dioxide. Nearly a billion tons of coal are mined each year, and most of this is burned. When all sources of carbon dioxide are considered, it seems safe to say that carbon dioxide is being supplied to the atmosphere at the rate of about 75 tons per second. CARBON DIOXIDE AND LIFE 31 Because of its close relations to combustion, respiration, and decay, the amount of carbon dioxide in the air of cities is greater than in the open country. The amount in the air of London occasionally becomes five times the normal quantity, while in badly ventilated schoolrooms, theaters, and workshops, it is sometimes ten times the normal amount. The conditions which increase the amounts of carbon dioxide in city air usually increase the amounts of various other harmful gases. Such conditions are injurious to health. The widespread movement to "purify city air," largely by doing away with smoke, is an attempt to remedy these conditions. In spite of constant additions, the amount of carbon dioxide in the air does not increase permanently enough to be noted. This gas, therefore, must be taken out of the atmosphere about as rapidly as it comes in. It is taken from the air chiefly (1) by green plants, of which it is the main food, and (2) by uniting with mineral matter in the solid part of the earth. It supports not only most plants, but indirectly most animals, for the latter feed on vegetation, or on other animals that live on plants. By uniting with mineral matter it helps to form soil. The carbon dioxide of the air has still other important functions. The earth is radiating heat into space all the time, somewhat as a hot stove radiates heat into its surroundings, and carbon dioxide has the power of holding much of this heat. It therefore serves as a blanket to hold in the heat of the earth, and, thin as the blanket is, it is more effective, in this respect, than the denser blanket of oxygen and nitrogen. If it were thicker, the temperature would be still higher. It is thought possible that at certain times in the distant past, as when magnolias grew in Greenland, the amount of carbon dioxide in the air may have been greater than now; and that at other times, when the climate was cold in low latitudes, the amount may have been much less than now. Water vapor. The water vapor in the atmosphere is a variable quantity. It is all the time entering the atmosphere by evaporation, and it is all the time being condensed and precipitated from the atmosphere as rain, snow, etc., to be again evaporated, condensed, and precipitated. The larger part of both water vapor and carbon dioxide is in the lower part of the atmosphere. Like much of the carbon dioxide, the water vapor is making continuous rounds. Its precipitation supplies the water for wells, the flow of springs, the maintenance of lakes, streams, and glaciers, and for the life of plants 32 NATURE AND FUNCTIONS OF THE ATMOSPHERE and animals. The bodies of animals, including human beings, are about four-fifths water. The tissues of annual plants are three- fourths water; of perennials, nearly half. To produce a bushel of corn, from 10 to 20 tons of water are required. The amount of water vapor which the atmosphere is capable of containing at any time depends on temperature; but other things, such as the available supply, help to determine the amount which there is in the air in any one place. Like the carbon dioxide, the water vapor of the air helps to keep the earth warm. Dust. All solid particles held in the air are dust. They are not ordinarily seen except on dry, windy days, but dust from the air is constantly settling everywhere, indoors and out, whenever the air is dry. Dust may be seen readily indoors if a room is darkened and light allowed to enter through a narrow crack or small hole. Even air which appears clear may in this way be seen to contain countless particles of solid matter. The amount of dust is sometimes very great, as over cities and in dry and windy regions. During the fogs of February, 1891, it was estimated that the amount of dust, deposited on roofs in and near London was six tons per square mile. Dust-polluted air is believed to favor diseases of the lungs, like tuberculosis. Some years ago a method was devised for counting the dust particles in a given volume of air. The result showed that in the air of great cities there are hundreds of thousands of dust particles in each cubic centimeter of air (a cubic centimeter is less than J /i6 of a cubic inch); and. that even in the pure air of the country, far from towns and factories, there are hundreds of motes per cubic centi- meter. Like carbon dioxide and water vapor, most of the dust is found be- low an altitude of 10,000 feet. Its relative absence at high altitudes increases the intensity of the sunshine there by day, and helps to bring about low temperatures at night. Dust particles in the atmosphere are important in several other ways. They scatter the light of the sun in such a way as to illuminate the whole atmosphere. Without dust in the air, all shady places would be in darkness. The sun would appear, probably in dazzling brilliance, shining from a black sky in which the stars would be visible even in the daytime. The blue color of the sky and the sunset and sunrise tints are influenced by the dust in the atmosphere. Dust particles also serve as centers about which water vapor condenses. QUESTIONS 33 Questions i. State the conditions (all of them) which would tend to make the country air dusty at a given point in northern United States. 2. What conditions favor an increase in the amount of dust in the air of cities in summer? In winter? 3. Compare and contrast the purity of the air (1) over oceans and over lands; (2) in dry and in moist regions; and (3) at high and at low altitudes. 4. Would you expect the average amount of carbon dioxide to be greater in the air of cities or of the open country? Why? What processes tend to equalize the amount over country and cities? 5. Give at least three reasons why the amount of carbon dioxide in the air (especially of great cities) tends to vary in amount between summer and winter. 6. Why do people accustomed to low altitudes breathe very much faster in high altitudes? 7. Indicate various ways in which the extreme elasticity of the air favors human activities. CHAPTER V CLIMATIC FACTORS: TEMPERATURE General Considerations Besides the composition of the atmosphere, various other things connected with it are of great importance to life. The things which make up climate (climatic factors) are especially important. The chief climatic factors are (i) temperature, (2) moisture, and (3) air movements, or wind. Importance of heat. Were it not for the effect of the atmosphere on temperature, life could not endure the heat of day or the cold of night, and the earth would be a desolate, lifeless waste. The tem- perature which most concerns land life is the temperature of the air in which it lives. The air is warmed chiefly by the sun. The heat- ing power of the sun is proved by the fact that days are warmer than nights, and that sunny days are warmer than cloudy ones. The rare exceptions to these general facts need not be considered now. Measurement of heat. Variations of temperature from time to time and from place to place are so important that it is necessary to have some easy way of measuring and recording them. Temperature is measured by the thermometer, which consists of a glass tube of uniform diameter, except for a bulb at the lower end. The bulb and the lower part of the tube are filled with some liquid, generally mercury, and this is heated until it boils. The boiling mercury fills the tube and expels all air, and while it is boiling the tube is sealed, the heat being withdrawn at the same moment. On cooling, the mercury contracts and fills the lower part of the tube only. Whenever the temperature rises, the mercury expands and rises in the tube, and when the temperature falls, the mercury contracts and sinks. The amount of rise or fall of the mercury shows the amount of change of temperature. A scale is marked on the tube so that the temperature may be read from it. Two scales are in common use — the Fahrenheit (F.) and the Centigrade (C). On the Fahrenheit scale the temperature of boiling water (at sea-level under normal pressure) is marked 21 2 ; on the Centigrade scale, ioo° (Fig. 20). The tempera- ture of melting ice (freezing point) is marked 32 on the former scale, and o° (zero) on the latter. Between the freezing and the boiling point on the Fahrenheit scale there are 180 degrees, and on the Centigrade scale 100 degrees. It follows that i° C. js equal to i4/ s ° F. Zero on the Fahrenheit scale is 32 below the freezing point, and 20 below zero Fahrenheit (written — 20 F.) means 52 (32°+ 20 ) 34 HEAT FROM THE SUN 35 below the freezing point. The Centigrade scale is simpler than the Fahrenheit, and is used generally in scientific work and in most European countries. We often have occasion to use the temperature of a given place at a given time, as that of New York at noon on July 4th; but we also have occasion to use the records of temperature in other ways. From a sufficient number of temperature records, spread properly over a year, an average temperature for that year may be obtained. Similarly, averages for shorter periods, as seasons, months, and days, are possible, called average seasonal, monthly, and daily temperatures. The average temperature of one year for a given place is, as a rule, somewhat different from that of the preceding or following year. The average temperature for a goodly number of years gives its mean annual tem- perature. Similarly, it is necessary to take the averages for many Januarys to get the mean monthly temperature for that month. The highest temperature during any period is its maximum temperature and the lowest, its minimum temperature. Sun heating : insolation. The northern and southern hemispheres receive the same amount of heat from the sun each year, but, because of the inclination of the earth's axis, they do not receive the same amounts at the same seasons. Both receive the same amounts of heat per day only at the times of equinox. The amount of heat received by the surface of land and water is far less than the amount coming to the top of the atmosphere, for much is absorbed in passing throug the air. (1) Other things being equal, any part of the earth should get most heat per day when the sun shines there the greatest number of hours. During a part of the summer of the northern hemisphere, latitudes above 66j4° have sunshine continuously (except for clouds) for more than 24 hours. So far as hours of sunshine are concerned, therefore, these latitudes should then receive more heat per day than other parts of the earth. If there were no atmosphere, the surface of the earth at the North Pole would receive, on the 21st of June, about one-third more heat during 24 hours than the surface of an equal area at the equator. But the amount of heat which reaches the bottom, of the air'aX. the pole on the 21st of June is much less than that received at the bottom of the atmosphere at the equator. Fig. 20. Diagram to represent Fahren- heit and Centigrade scales. 36 CLIMATIC FACTORS: TEMPERATURE \ / . Equator -^2 N \ V \ V \ \ Y \ \ \ — ' I ~L / /■ / / ^ X -^2 y (2) Other things being equal, the surface of the land or water gets most heat where the sun 's rays are most nearly vertical, because (a) the rays are there most concentrated, and (b) they pass through a less thickness of the air. This is shown by Fig. 21. A given bundle of rays, 1, falling vertically on the surface, is distributed over a given area, while an equal bundle of rays, 2, falling obliquely on the surface, is spread over a greater area, and therefore heats each part less. The rays oblique to the sur- face, 2, have passed through a greater thickness of air, and more of their heat has been ab- sorbed by it before they reach the surface of the land or water. These facts help to explain why the surface at the poles does not get warmer than an equal area at the equator, even with months of continuous sunshine at the former places, and but 12 hours at a time at the latter. The snow and ice of polar regions prevent them from getting warm, even during the months when much heat is received (p. 37). The angle at which the sun 's rays reach the earth varies from place to place, and from time to time at the same place, because of the inclination of the earth's axis. This is illustrated by Figs. 8 and 9, which have been explained. Distribution of insolation. From Fig. 10, which has been studied, we see that when the sun's rays come to the earth from the direction W (perpendicular 23^° south of the equator), they are more oblique than at any other time in the northern hemisphere, and less oblique than at any other time in the southern hemisphere. At the same time the days are longer in the southern hemisphere than in the northern. Hence there are two reasons why the southern hemi- sphere receives more heat than the northern at this season, namely (1) more nearly vertical rays, and (2) more hours of sunshine. After the time (winter solstice, December 2 2d) when the sun's rays are vertical at 23^° S., they become perpendicular to the sur- Fig. 21. Diagram to illustrate the unequal heating at the bottom of the atmosphere, due to the angle at which the rays of the sun reach the surface of the earth. The dotted line may be taken to represent the outer limit of the atmos- phere. DISTRIBUTION OF SUN'S HEAT 37 face in latitudes farther and farther north, and on March 21st they are vertical at the equator. Days and nights are then equal every- where, because all parallels are cut into two equal parts by the circle of illumination (p. 12), and the sun's rays are equally oblique in corresponding latitudes north and south of the equator. Any latitude in one hemisphere is then receiving the same amount of heat as the corresponding latitude in the other hemisphere. This condition would be permanent if the axis of the earth were not inclined. After March 21st, the sun continues its apparent journey north- ward until June 21st, when its rays are vertical at the tropic of Cancer, 23^° N. The days of the northern hemisphere are then longest and the nights shortest, and the rays of the sun are less oblique in this hemisphere than at any other time. At this time, therefore, the northern hemisphere is being heated more than at any other. From June 21st to December 2 2d, the sun appears to move so that its rays become vertical farther and farther south, and the preceding changes are reversed. The latitudes where the sun's rays fall vertically range from the tropic of Cancer to the tropic of Capricorn; and the sun's rays are, on the average, least oblique between these limits. This is why low latitudes are, on the whole, warmer than high latitudes. The density of the atmosphere also affects the amount and in- tensity of the insolation received by the surface of the earth. On mountains the less density of the air means more intense sunlight, and a greater amount of heat per unit of land surface, than is received at sea-level (p. 39). One effect of this is seen in the rapid growth of plants on mountains in early summer. Distribution of temperature. The temperature of one place is not necessarily higher than that of another because it receives more heat. The region about the North Pole does not get very warm, even when it receives much heat, because much of the heat received is used in melting ice and in warming ice-cold water, which is warmed very slowly, and flows away as soon as the heating is well begun. Mountain tops are also generally cold in spite of the intensity of inso- lation there. After the heat from the sun has been received by the earth, it is re-distributed to some extent, with the general result that the parts which get more by insolation share their heat with the parts which 38 CLIMATIC FACTORS: TEMPERATURE get less. The distribution of actual temperature, therefore, differs much from the simple distribution which insolation would give. There are three ways in which the air receives, loses, and transfers heat. These are radiation, conduction, and convection. (i) Radiation. The sun always radiates heat, and the surface which its rays strike is warmed by absorption of the radiated heat. A body need not be glowing hot, like the sun, or like fire, to radiate heat. The radiators in our houses radiate heat when they contain hot water or steam. The body which radiates heat is itself cooled. Thus hot iron soon cools in the air, because it radiates its heat. The land warmed by the absorption of heat radiated from the sun during the day is cooled by the radiation of its heat at night. The absorp- tion of heat by day and its loss by night give variations of temperature between day and night. If the day is long and the night short, ab- sorption of heat from the sun by day exceeds radiation by night, and the land tends to become warmer, as in spring and early summer. If the day is short and the night long, radiation of heat will be greater than absorption, and the land will become colder, as in autumn and early winter. (2) Conduction. If one end of an iron poker is put in the fire, the other end becomes hot. The heat passes from one end to the other. This method of passing heat along is conduction. Any cold body in contact with a hot body is warmed by conduction. The hand is warmed by conduction when placed on anything which feels warm ; it is cooled by conduction when placed on something which feels cool. The bottom of the air is warmed by contact with the land (that is, by conduction) wherever the temperature of the land is higher than that of the air. Conduction from the land to the bottom air has an im- portant effect on the temperature of the air just above the ground. (3) Convection. When a kettle of water is placed on a hot stove, the water in the bottom is heated by conduction, that is, by contact with the hot kettle. The heating of the water causes it to expand, and when the water in the bottom of the kettle expands, it becomes lighter than the water above. The heavier water above sinks and pushes the lighter water below up to the top. This movement is convection. Another illustration of convection is afforded by stoves, fireplaces, and furnaces. A thin sheet of light paper may be held up for a moment by the rising air over a hot stove, or even carried up if the convection current is strong enough. Again, as the air in a chimney is heated, it expands and becomes less dense than the air I CONVECTION CURRENTS 39 Fig. 22. The first rise of air, as a result of heating, is due to the expansion of the part heated. Fig. 23. The permanent heating of the air over a region gives rise to per- manent convection currents. about it. The cooler, denser air about the base of the chimney or stove crowds in below the expanded air in the chimney, and .pushes it up out of the chimney. Since the air entering the chimney from below is being heated and expanded all the time, the up-draught con- tinues as long as there is fire. Every draught from a chimney is an example of convection. When the surface of the land is warmed by the absorption of heat from the sun, it warms the air above both by conduction and by radiation. The lands of low latitudes are heated more than others. The heated air over the heated land expands. If the air in a given region were expanded as shown in Fig. 22, the air at the top of the expanded column would flow away, much as water would un- der similar conditions. After this takes place, the amount of air at the base of the column h will be less than the amount at the same level outside the heated area, and air from outside the heated column will flow in. This inflow will push up the column of expanded air, and further overflow above will cause further inflow below. If the heat- ing continues, a permanent convection current is established in the heated area (Fig. 23). Such movements of air are important not only in distributing temperature, but also in causing winds, clouds, and storms. The atmosphere is heated (1) by the absorption of the sun's rays as they come through it, (2) by the absorption of heat radiated from land and water, and (3) by conduction from warm land or water to the lower air. The amount of heat absorbed by air from the direct rays of the sun depends on the distance the rays travel in it, that is, on the obliquity of the sun's rays (Fig. 21). When the sun is vertical at the equator, its rays pass through about twice as much atmosphere in latitude 6o°, and about ten times as much in latitude 85 , as they do in latitude o°. The amount of absorption of sun-heat by the air, therefore, varies with latitude. About half of it is absorbed by the air at the equator, and about four-fifths at the poles, as compared 4 o CLIMATIC FACTORS: TEMPERATURE with the total amount which would reach the earth in those latitudes if there were no atmosphere. In general, the amount of heat absorbed by the atmosphere is more than 50 per cent of the total amount coming to the earth from the sun. The heat radiated into the air from below is absorbed by the air much more readily than that coming from the sun directly. The lower air consequently is heated by radiation from below more than by direct insolation. / After heat is received from the sun, therefore, it is re-distributed by radiation, conduction, and convection. Movements of air (winds) and movements of water (especially ocean currents) also distribute heat. Without these movements of air and water, the average tem- perature of the equator would be much higher than now, and that of the poles much lower. These changes would be destructive to many forms of life. Temperature of land and water. Land is heated by insolation four or five times as fast as water, for several reasons : (1) A given amount of heat raises the temperature of soil and rock more than that of water. (2) Water is a good reflector, while land is not; the latter, there- fore, absorbs a larger proportion of the heat of the sun 's rays. The amount of heat reflected from a water surface increases with increasing obliqueness of the sun's rays. At the equator, 40 per cent of the insolation goes into heating the water; in latitude 6o°, less than 5 per cent. A familiar result of the reflection of heat from water appears in the intensity of sun-burn received on water. Snow-covered land and bare white sand reflect heat much as water does. • (.3) Land radiates heat more readily than water does. (4) Convection movements take place in water as soon as its surface is heated. This prevents excessive heating at any one point. The land, on the other hand, is without movements of convection. (5) There is more evaporation from a water surface than from land, other conditions being the same, and evaporation cools the surface from which it takes place. A wet soil, receiving the same amount of the sun's rays, remains cooler than a dry soil. The hot sand of the desert is an example of this effect on the warming of the land. (6) Light and heat penetrate water, but not soil and rock to any great extent. The heat of insolation is therefore distributed through a greater thickness of water than of soil. Being confined to the surface of the soil, the temperature of the latter is made higher. CONTRASTS OF SEASONS 41 Since the temperature of air tends to be the same as that of the surface on which it lies, the presence of land or water is an important factor in determining the temperature of the air above. Seasons In Middle Latitudes In middle latitudes, the seasons are four — spring, summer, autumn, and winter. Each season has characteristics of its own, but each grades into the one which follows. In the United States, March, April, and May are commonly called the spring months; June, July, and August the summer months; September, October, and November the autumn months; and December, January, and February the winter months. In the southern hemisphere, spring comes in September, October, and November; summer in December, January, and February, and so on. The vernal equinox of the northern hemisphere is the autumnal equinox of the southern, and the summer solstice of the northern is the winter solstice of the southern. The definition of the seasons given above is based on temperature, the warmest three months being summer, and the coldest three, winter. The seasons are sometimes defined in a different way. Thus spring is sometimes regarded as the time between the vernal equinox and the summer solstice; summer the time from the summer solstice to the autumnal equinox, and so on. Summer and winter temperatures. The summer heat of middle latitudes is due (1) to the high altitude of the midday sun above the horizon, giving less oblique rays with a shorter path through the atmosphere, and (2) to the long days and short nights. More heat is received during the long day than is lost during the short night. The reverse of these conditions accounts for the cold of winter, though during the winter of the northern hemisphere the earth is 3,000,000 miles nearer the sun than in summer. A consideration of Figs. 3 and 9 will make it clear why the seasons are reversed in the two hemispheres. One result of this difference of seasons in opposite hemi- spheres at the same time is that crops in the middle latitudes of the southern hemi- sphere are harvested in our late winter and early spring, when the northern supplies of certain things are running low. Hence there is important trade between the two hemispheres, places in each hemisphere being benefited because their crops ripen in the cold season of the other. Warmest and coldest months. Since the northern hemisphere receives most heat at the time of summer solstice, and least at the time of winter solstice, it would seem at first that these dates, respec- tively, should be the times of greatest heat and cold; but this is not the 42 CLIMATIC FACTORS: TEMPERATURE case. Again, since corresponding latitudes in the two hemispheres are being heated equally at the time of the equinoxes, it would seem, at first, that corresponding latitudes in the two hemispheres should have the same temperature at these times; but this, again, is not the case. In our own latitudes, for example, March 2 ist (vernal equinox) is much colder than September 2 2d (autumnal equinox). The explanation of these conditions is found in the fact that the temperature of any given place at any given time does not depend entirely on the amount of heat received from the sun at that time. In our latitudes, the soil, rocks, lakes, and rivers receive more heat during the long days of summer than is lost during the short nights. At the end of summer, therefore, heat has been stored up in them. At this. time of year, the northern hemisphere has a temperature higher than that which it would have if it depended entirely on the heat received from the sun each day. On the other hand, the tem- perature at the time of early spring is lower than that which the daily heating would seem to produce, because the cold of the winter just past has not been altogether overcome. Some of the snow and some of the ice of lakes, ponds, streams, and soils, in middle and high latitudes, is still unmelted. The snow and ice keep the lower part of the air cool. For similar reasons, the summer solstice is not the hottest time of year. The time of greatest heat lags behind the time of greatest heating. In middle latitudes the lag is about a month; but it is more over oceans than over lands, because land is heated and cooled more readily than water. For this reason places near bodies of water usual- ly have later and colder springs than places not so situated. Under such conditions, April in the northern hemisphere may be as cold as November. In the same way, the time of greatest cold does not come till after the time of least heating. In Tropical Latitudes The seasons in low latitudes are unlike our own. At the equator, the sun 's rays are vertical twice each year — at the times of the equinoxes. Twice a year, too, the sun 's rays are vertical 23^2° from the equator, once to the north and once to the south. The equator, therefore, has two seasons, occurring at the time of our spring and autumn, which are somewhat warmer than two other seasons occur- ring at the time of our summer and winter. The variations in temperature are much less than in middle latitudes, for the length CONTRASTS OF SEASONS 43 of day and night never varies at the equator, and does not vary much in any part of the tropics. The angle of the sun's rays, too, varies less than with us. At the equator, therefore, there are four di- visions of the year, but their differences of temperature are slight. Toward the margins of the tropical zone, the variations of tem- perature are greater than at the equator, but far less than in middle latitudes. In much of the tropical zone, wet seasons alternate with dry ones, and in such places, differences in moisture are more im- portant than differences in temperature. In High Latitudes In high latitudes, the seasons are still different. About latitude 6o°, for example, the differences in the seasons are similar to those of the central part of the United States, except that they are greater, because of the greater variation in the length of day and night. In latitude 63 , the longest day of summer and the longest night of winter are about 20 hours each, as compared with a little over 15 hours in latitude 40 . The long nights of winter in latitude 63 mean much lower temperatures than in latitude 40 at that season. On the other hand, the long hours of sunshine in summer make it possible, in favored localities, to grow Crops as far north as latitude 6o°, even where it is only four months from snow to snow. In latitude 75 N., which may be taken as typical of polar regions, there are four natural divisions of • the year, one (summer) when daylight is continuous, one (winter) when darkness is continuous, one (spring) when there is alternating day and night, with the days lengthening, and one (autumn) when there is alternating day and night, with the nights lengthening. The lengths of the seasons defined in this way are not the same. There is a common notion that in polar regions there is a day of six months and a night of six months each year, but this is not correct. There is a six-month day and a six-month night at the poles only. In latitude 78 , about half way between the pole and the polar circle, there is continuous daylight and continuous darkness for periods of about four months each. In latitude 70 the periods of continuous darkness and of continuous light are two months each, and so on down to 24 hours at the polar circle. Though the name summer may be applied to one part of the year in high latitudes, places north of latitude 6o°-65° are not warm enough in summer for the growth of cereal crops. Vegetation is confined to grasses, stunted shrubs, lichens, and mosses. 44 CLIMATIC FACTORS: TEMPERATURE Relation of Temperature and Altitude High altitudes are colder than low levels in the same region, (i) because the air is thinner, and (2) because it contains less water vapor, carbon dioxide, and dust. For these reasons it absorbs less heat from the direct rays of the sun, and less of that radiated from below. The temperature of the air on top of a mountain may be much lower than the temperature of the air at its base, in spite of the fact that insolation is much greater in the former position. The average decrease of temperature is about i° F. for each 330 feet of rise, or 16 for each mile, for the altitudes where observations have been taken. One mile of ascent, therefore, means about the same decrease of temperature as a journey of 1,000 miles (about 15 of latitude) toward the poles. Tropical highlands, like those of Mexico or Bolivia, in latitudes 18 to 19° N. and S. respectively, are cooler than some places at sea-level in middle latitudes. For this reason, some countries in the tropics can produce not only tropical crops, but also those characteristic of other regions, and by living at the higher elevations, the people may escape the uncomfort- able heat of tropical lowlands. In middle latitudes also vegetation varies with the altitude. Thus, in the low mountains of Pennsylvania, the ridges bear coniferous trees (pines, etc.), sugar maples, and similar types, while the valleys between have the honey locust, gum, and walnut, which need a warmer climate. The low temperatures of certain mountains and high plateaus of the middle zones do not favor dense populations. On the other hand, the cool climates of various high lands in the tropics have favored white settlements. During the hot summer months the capital of India was transferred each year from Calcutta (the capital until 191 1), near sea-level, to Simla in the Himalayas, at an elevation of 7,000 feet. Certain elevated places in the Philippines, like Baguio, the summer capital, will have increasing importance as health and pleasure resorts during the hot period. The difference in vegetation and in human conditions between the sunny and shady slopes of mountains is striking in many cases. Thus at a place near Zermatt, in the Alps, barley and rye are grown on a sunny southern slope 6,900 feet above sea-level, while a few hundred yards away, northern slopes, even below the level of the grain fields, have arctic-alpine vegetation and snow-banks. In some of the valleys in the Alps, most of the people live on the sunny slopes. CHARTING TEMPERATURE DATA 45 Where mountains are covered by snow throughout the year, their surfaces are never warmed above a temperature of 32° F. , the melting temperature of snow. All the heat received beyond that necessary to raise them to this temperature is spent in melting and evaporating snow, not in raising the temperature of its surface. Yet in spite of the freezing temperature, travellers over the snow-fields may be sun-burned, as if exposed to midsummer sun at lower altitudes. Part of this effect is due to the greater intensity of insolation at higher altitudes, and part of it to the fact that snow reflects heat much as water does (p. 40). Representation of Temperature on Maps It is important to have some means by which temperatures in different places and at different times may be studied readily. For large areas it is most convenient to have the temperatures shown on maps. Maps showing temperatures are thermal maps. On such maps temperatures and their distribution commonly are shown by lines, each of which connects points having the same temperature. Such lines are isotherms, and maps showing isotherms are isothermal maps. A line connecting places having the same average annual temperature is an annual isotherm. Lines connecting places of the same average seasonal or monthly temperature are seasonal or monthly isotherms. Fig. 24 shows annual isotherms. The map does not give exact average temperatures for places between the lines, but tempera- tures for such places can be estimated from the map. At the extreme north there is the isotherm of o° F., which barely touches North America. The average annual temperature of places on this line is o° F. The isotherm of io° F. lies south of the isotherm of o° F. The average temperature of places between these two iines is more than o°, and less than io°. South of the isotherm of io° follow, in order, the isotherms of 30 , 50 , 6o°, and 70 . The lowest isotherm shown on the chart in the southern hemisphere is that of 30 , lying south of all lands except Antarctica. The latitude of this isotherm corresponds nearly to the latitude of the isotherm of 30 in the northern hemisphere. Next toward the equator from the southern isotherm of 30 is the isotherm of 50 , followed by those of 6o° and 70 . Thus the map shows a relation between latitude and annual temperatures, the highest temperatures being near the equator. Annual isotherms do not show all we may want to know about the temperature conditions of a place. An annual isotherm of 50 F., for example, does not tell us whether the temperature is about 50 F. 4 6 CLIMATIC FACTORS: TEMPERATURE ~ *; yy f/% „ ^r ^*- >* yy y / y . f ^ ' J ^~ ^ — ^- __— —^ / y / / / / s y . ' * v y ^_^^' y / / / / / / / ( ( " y > ' / / ( ' ( K L^ / / \ v — — *"" ^ • / \ ^- mtt- :rn- y X £aot. Fig. 42. Diagram illustrating the general movement of air currents in a cyclone of middle latitudes. The upper air moves mainly toward the east, in the direction of the prevailing winds. the direction toward which the prevailing winds of middle latitudes blow. This upward movement has an important effect on precipita- tion (p. 85). (3) Cloudiness and precipitation. An open circle on the shaft of an arrow (Fig. 40) indicates clear skies, a half-blackened circle (as in Wyoming) shows that the sky is partly cloudy, while a black circle (as in Montana) indicates general cloudiness. An R on the shaft of an arrow (as in California) indicates rain, and an 5 in the circle on the shaft of an arrow (as in New York) shows that snow is falling. Amounts of precipitation are given in the printed table with the other data for each station. (4) Temperature. As indicated above, the broken lines of a weather map are isotherms. The isotherms of Fig. 40, and of the weather maps which follow, show two distinct features: (1) they WEATHER OF CYCLONES AND ANTICYCLONES 85 have little relation to parallels, and (2) all of them bend northward where the pressure is low, and southward where the pressure is high. These features are less pronounced on maps showing storms of less intensity. Cyclones and Anticyclones Characteristics of highs and lows. Highs and lows are some- times much more pronounced than those shown in Fig. 40. In the low of Fig. 43 the pressure ranges from 29 at the center, to 30.1 in the East, and to 30.5 in the West. So great a range of pressure within the United States is uncommon. The isobars are closer together in this figure than in Fig. 40, and therefore indicate stronger winds. Cloudy skies prevail in the southeastern part of the cyclone. Highs as well as lows may have great area. Fig. 44 shows a high, or anticyclone, more than 2,000 miles across, with a great range of pressure. The isotherms of this chart, like those of the preceding, stand in very definite relations to the isobars. Denver, in the anti- cyclone, is about 30 colder than the southern part of Maine, which is 3 farther north, but on the western border of a cyclone. Near centers of low pressure, rain or snow falls in many cases, while around centers of high pressure there is, as a rule, no precipita- tion. The chief reason for rain or snow about a low is that the inflowing, rising air expands and is cooled (p. 60), and so gives up some of its moisture. In the northern hemisphere, southerly winds to the southeast of storm centers are, in general, blowing from warmer to cooler places, and this may result in rain or snow. The prevailing winds which control the outflow in the upper part of a cyclone (Fig. 42) tend to carry the rainfall to the east of its center. The circulation of winds around cyclonic areas is the real factor in drawing moist air northward from the Gulf of Mexico, and in giving abundant rainfall east of the Mississippi River. In an anticyclone there is a descending spiral movement of air. The descending air comes from an altitude where the air is colder than that at the bottom of the atmosphere, and hence brings a low temper- ature. Winds from anticyclones generally bring clear weather, but cold air moving down and out from an anticyclone may mingle with warm air about it, so as to cause some of the moisture of the latter to condense, giving rise to clouds, or even to precipitation. Movements of cyclones and anticyclones. Highs and lows do not remain in the same place from day to day. This is shown by 86 STORMS AND WEATHER FORECASTING Fig. 43. Weather map for January 16, 1901, showing a very pronounced low. Fig. 44. Weather map for December 9, 1898, showing a high of great size. MOVEMENT OF STORMS 87 Figs. 45-47, which are the weather maps of three successive days. In these figures areas of precipitation are shown by shading. In Fig. 45 there is (1) a low along the Atlantic coast; (2) a high central over Iowa; (3) a feeble low north of Montana; and (4) a high in Oregon. The map of the succeeding day (Fig. 46) shows (1) that the low of the Atlantic coast has disappeared (moved to the east) ; (2) that the high of the interior has moved to West Virginia; (3) that the low which was north of Montana has moved to Dakota; while (4) the high of the Oregon coast remains about where it was. The map of the next day (Fig. 47) shows (1) that the high of the Virginias has Fig. 45. Weather map for September 24, 1903. .The shading on this and succeeding maps indicates areas of precipitation during the preceding 24 hours. moved on, but not so far as on the preceding day; (2) that the low which was over North Dakota is now north of Lake Superior; (3) that the high of Oregon has moved east to Idaho and Montana ; and (4) that a weak low has developed in Oklahoma. The rate of progress of a storm is not the same as the velocity of its winds. The velocity of the wind depends on the differences in pres- sure. A weak cyclone, that is, one in which differences of pressure are not great, gives rise to weak winds, even though the center of the storm moves rapidly. A strong cyclone, that is, one in which the 88 STORMS AND WEATHER FORECASTING Fig. 46. Weather map for September 25, 1903. Fig. 47. Weather map for September 26, 1903. PATHS OF STORMS 89 differences of pressure are great, gives rise to strong winds, even though the cyclone itself may move forward slowly. The rate at which cyclones move varies with the season, the average being about 37 miles per hour in winter and 22 in summer. Storms may move at twice these rates, however, or at less than half their usual speed. The course of a cyclone may be shown on a single map, as in Fig. 40. The row of arrows shows that the low of Maine has moved from western Canada. The mean tracks of cyclones and anticyclones Fig. 48. Chart showing the mean tracks of cyclones (light lines) and anticy- clones (heavy lines), and their average daily movement (broken lines). for the United States are shown in Fig. 48. The broken lines on this map, marked 1 day, 2 days, 3 days, and 4 days, show the average daily progress of storms which come from the northwest. Some anticyclones enter the United States from the Pacific, while others start north and northwest of Montana, or, at any rate, are first reported from there. Cyclones start in various places. Many of them appear first near the places where anticyclones start, but others appear first in Colorado, the Great Basin, Texas, and elsewhere. The passage of a cyclone or anticyclone involves changes in the direction of the wind, and usually also changes of temperature, go STORMS AND WEATHER FORECASTING humidity, and cloudiness. Thus in Fig. 46 the wind at St. Paul is southeasterly, though this city is in the zone of westerly winds. The next day, after the storm center has moved forward to a position northeast of St. Paul (Fig. 47), the wind is northwesterly. An east wind is. often the first sign of an approaching cyclone; and since many cyclones bring rain, an east wind generally is taken as a sign of approaching rain throughout much of the United States. Cyclones are, on the whole, more frequent and better developed in winter than in summer. They do not affect the air to great heights. Even when the great whirl or eddy is 2,000 miles across, its height (depth) is rarely more than 4 or 5 miles. The origin of the cyclones and anticyclones of middle latitudes is not well understood. Winds and temperatures incidental to cyclones and anti- cyclones. During the passage of a cyclone, the air to the southeast of the storm center is drawn from warmer (lower) to cooler (higher) latitudes. In midsummer this often gives rise to a hot wave, though not all hot waves are associated closely with cyclones. Similar winds are known as the sirocco in the western Mediterranean region, and by other names elsewhere. In eastern United States, numerous sun- strokes and deaths from heat prostration accompany some hot waves in their progress across the country. Air to the northwest of a cyclone moves from cooler (higher) to warmer (lower) latitudes. In winter, this may give rise to cold waves. These cold winds are known as northers in the southern part of the United States, and sometimes as blizzards in the northern part, though this name usually implies heavy snowfall and high wind, as well as low temperature. When warm, moist air is forced up over mountains, it precipitates some of its moisture (p. 77). The precipitation sets free heat, so that the rising air is cooled much less than it would be otherwise. Beyond the crest of the mountains it descends, and is warmed in the process. It is warmed much more (often twice as much) in the descent than it was cooled in the ascent. It may, therefore, descend as a hot wind. Such winds are known as chinook winds in the United States, especially just east of the Rocky Mountains. The chinook winds temper the rigorous winters of certain parts of the north- western states and the Canadian provinces east of the mountains. They fre- quently evaporate a foot or more of snow in a few hours. For this reason they are sometimes called "snow eaters. 1 ' These winds make winter grazing possible over large areas which otherwise would he covered heavily with snow. Chinook win f DESTRUCTIVE TROPICAL STORMS 9i sometimes develop with great suddenness. In some cases the temperature has been known to rise 8o° in six or eight hours under their influence. The chinook winds of summer are sometimes so hot and drying as to wither vegetation, and occasionally to destroy crops. Tropical cyclones. Cyclones sometimes start in tropical regions, and follow courses very different from those of the cyclones of middle latitudes. Most of the cyclones of this class which reach North Fig. 49. Course of West Indian storms for August-October, 1878-1900. The heavy line indicates the mean track. America originate in or near the West Indies, and they are most com- mon in late summer and early autumn. They follow a northwesterly course until the latitude of Florida is reached. Here they commonly turn to the northward, and later to the northeastward, following the Atlantic coast. The heavy line of Fig. 49 shows the average path of tropical cyclones {hurricanes) for a period of years. Tropical cyclones are stronger than those of intermediate latitudes; that is, the pressure at the center is lower and the winds are higher. Many of them do great damage along coasts, both to shipping and to low coastal lands. The great storm at Galveston in September, 9 2 STORMS AND WEATHER FORECASTING 1900, resulted in a loss of 6,000 lives, and damage to property esti- mated at more than $30,000,000. Much of the destruction was due to water driven by the high winds over the low island on which Galveston stands. An expensive sea-wall (Fig. 50) has since been built, and the level of the city raised, to prevent the recurrence of such a disaster. In September, 1906, a West Indian hurricane swept the Gulf coast of Florida and Alabama, and then passed inland, with damage to shipping and crops estimated at 15 to 25 millions of dollars. Islands which lie near cyclone tracks suffer severely. Porto Rico, for example, has been devastated five times within the last century. The storm of 1899 was probably the worst. Coffee, sugar-cane, and tobacco crops were destroyed almost completely, more than 3,300 lives were lost, and the property Fig. 50. A cross-section of the Galveston sea-wall, showing plan of construc- tion and relative dimensions. The right-hand side faces the sea. damage was estimated to be not less than $35,000,000. During this storm 23 inches of rain fell in 24 hours. These tropical storms are so violent that sailing vessels once within the storm's grasp rarely escape. For this reason there has been much careful study of these storms. Sailing directions, giving instructions how to escape from them, are now a part of the equipment of every vessel frequenting the oceans where tropical cyclones occur. In the Atlantic, tropical cyclones occur north of the equator, though not south of it ; in the Pacific, they occur both north and south. They occur in the later part of the hot season, and are believed to originate in strong convection (p. 38) currents. Fortunately tropical cyclones are much less frequent than cyclones of middle latitudes. FORECASTING THE WEATHER 93 Weather Forecasting Weather predictions. Weather predictions are based on the facts shown on weather maps. As a rule, official predictions are made only for the 36 or 48 hours immediately following the hour when the map is made. Take, for example, the map of the 25th of Septem- ber, 1903 (Fig. 46). Rain accompanies the cyclone which is central over Dakota. Since this storm has, for the last 24 hours, been moving a little south of east at the rate of about 40 miles an hour, it is fair to presume that it will move in this same general direction at a similar rate for the next 24 hours. If, in this time, it advances to the Lake Superior region, it probably will bring with it weather similar to that which it is now giving to the region where it occurs. Hence, on the 25th, the prediction might be made that rain is to be expected in about 24 hours in the region around the head of Lake Superior. On the 26th the prediction might be made that the low which is central north of Lake Superior (Fig. 47) will move on to the Gulf of St. Lawrence by the succeeding day, and that increasing cloud- iness and rain will accompany it. Rain for the region about Lake Huron and the area east of it may, therefore, be predicted for the 27 th. Temperature changes as well as changes in cloudiness and precipi- tation may be predicted. Thus in Fig. 45 the isotherm of 50 bends southward notably in the high, central over Iowa. As the high moves east, it probably will carry the low temperature with it. Hence it is safe to predict that the temperature will fall in the area into which the anticyclone is to move. The map of the succeeding day (Fig. 46) shows that the temperature of western Virginia has fallen from about 6o° to about 40 along the path of the high, while areas much farther north are warmer. Fig. 46 also shows that North Dakota and Alberta have a tempera- ture of 50 , that is, a temperature io° warmer than that of western Virginia. It will be noted, too, that the relatively high temperature of Dakota, Montana, and Alberta goes with a low. As the cyclone moves eastward, the temperature along its path probably will rise. This is shown by the map of the next day (Fig. 47), which shows a temperature of about 50 north of Lake Superior. The same map shows how the isotherm of 40 bends to the southward in front of the high which is central over western Montana. As the high of Montana moves eastward, it will be likely to carry a low temperature with it. 94 STORMS AND WEATHER FORECASTING From this map, therefore, it may be predicted that the temperature in Nebraska, Kansas, Iowa, and Missouri will be lower. The time when the rain which a storm may bring to any given place will fall is calculated from the rate at which the storm is moving. In the same way, the prediction of the time of arrival of a cold wave which an anticyclone may bring is based on the rate of progress of the anticyclone. This rate is known in advance by telegraphic re- ports. Predictions concerning the weather may be made more readily for the central and eastern parts of the United States than for the western part, for the storms have been under observation longer before they reach the central and eastern states. Failure of weather predictions. Weather predictions, even for short intervals, often fail. The reasons are many, among them the following: (i) Cyclones and anticyclones sometimes depart widely from the courses they commonly take. In such cases, the places the storm was expected to pass do not have the weather which was predicted for them. Thus a storm may be in line for St. Paul, to which it is expected to bring rain and a rising tem- perature; but instead of keeping its course, it may turn off to the northward, and the rain which was predicted for that city falls farther north. (2) Storms change their rate of advance, and so arrive earlier or later than predicted. (3) Storms sometimes appear and disappear without warning. (4) A storm sometimes changes its character, becoming weaker or stronger. It then does not bring to the places it passes the w r eather predicted for them. Value of weather forecasts. In spite of all mistakes, the warnings of storms, floods, cold waves, etc., sent out by the Weather Bureau, have been of great benefit. It has been esti- mated that property valued at $15,000,000 was saved in 1897 by warnings of impending floods. In 1910 the estimated saving was $1,000,000. In September, 1903, vessels valued at $585,000 were held in ports temporarily; along the coast of Florida, by storm warnings. The loss of the Boston steamship City of Portland, with all on board, in the great storm of November 28, 1898, was due to a failure to heed storm warnings which kept all other craft in port. Warn- ings led to the protection of Si, 000.000 worth of fruit about Jacksonville, Florida, in 1901, with an estimated saving of half this amount. Other warnings of cold in 1901 were estimated to have been the means of saving more then §3,000,000 worth of property. Shipments of perishable products, like most fruits, may be damaged badly if freezing temperatures are encountered unexpectedly in transit. Mer- THUNDER-STORMS 95 chants handling such products are saved much trouble and inconvenience by infor- mation from the Weather Bureau concerning the temperatures for which their shipments must be prepared. The annual saving of property in these various ways exceeds, several times over, the total cost of the Weather Bureau. Local Storms Thunder-storms. Thunder-storms are frequent in the United States. They are most common in warm regions, and in warm seasons. Further, they are most common on days which are unusually warm, and during the warmer parts of these days; but there are occasional thunder-storms in the winter, and there are thunder- storms at night. The first indication of a thunder-storm is usually a large cumulo- nimbus cloud, which, in the zone of the westerly winds, generally appears in the west. It moves eastward, and as it reaches the place of the observer, there is usually a smart breeze, or thunder -squall, rushing out before it. Shortly after the squall the rain begins to fall. The rainfall may be heavy, and the drops large, but the downpour does not usually last more than an hour, and in many cases much less. A second thunder-storm sometimes follows close upon the first. Lightning is due to the discharge of electricity from one part of a cloud to another, from one cloud to another, or from the cloud to the ground. When light- ning discharges approach the ground, they seek exposed objects in some cases and cause loss of property, chiefly through fire, and occasional loss of life. The thunder following the lightning is due to vibrations in the air caused by the electrical dis- charge. It sometimes happens that lightning at a great distance lights the clouds over a region where the electric discharge itself cannot be seen. This lighting of the clouds is often called heat lightning, because it is more commonly seen in hot weather than at other times. The rainbows which accompany or follow many thun- der-storms are due to the effects of the drops of water in the atmosphere as the sun's rays pass through them. In middle latitudes, most thunder-storms occur during the passage of cyclones, though they do not accompany all cyclones. They are more common on the south sides of cyclones than elsewhere, and many of them occur at a considerable distance from the center of the main storm. In middle latitudes, most thunder-storms move from west to east, while in the zone of trade-winds they move from east to west. In both cases they move with the prevailing winds. Much of the precipita- tion from summer cyclones is connected with thunder-storms. Hence localities having most of their rain during the warm season depend largely on thunder-storms for moisture. Not infrequently violent thunder-storms give precipitation in the form of hail. 96 STORMS AND WEATHER FORECASTING Tornadoes. When a convection current is very strong, and has a very small diameter, the whirl becomes so intense in some cases as to cause great destruction. A whirling storm of this sort is a tornado. Tornadoes, like thunder-storms, are phenomena of hot weather. They are rather less abundant in the later part of the summer than in the earlier part. They are more likely to occur in a cyclone than in an anticyclone. Tornadoes are associated in most cases with hot days, and with the warmest part of the day. The atmospheric pressure in the center of a tornado is usually much lower than in the center of a cyclone. In a very strong tornado, the pressure at the center may be a fourth less than that of its sur- roundings. This is one reason why the tornado is so destructive. During its passage, the pressure may be reduced from the normal amount, 14.7 lbs. per square inch, to three-fourths of this, or to 11 lbs. per square inch. If such a tornado passes over a closed building in which the air pressure is 2,117 1 DS - P er square foot, the pressure on the outside becomes 1,584 lbs. The walls are therefore pushed out with a force of 533 lbs. per square foot, and unless they are very strong, they will fall, as if the building had exploded. In some cases only the weaker parts, such as windows, yield. Not only is the pressure at the center of the tornado very low, but the area of the low pressure is very small. While a cyclone may be 1,000 miles or more across, few tornadoes exceed 1 ,000 feet in diameter at the sur- face of the land, and many are only a few yards wide. The re- sult is that the winds are violent. Estimated by the size and weight of the objects moved, their velocities have been thought to Fig. 51. Funnel-shaped cloud of a tornado, Solomon, Kas. (U. S. Weather Bureau.) hour. reach 400 or 500 miles per With this velocity, or even a velocity much less, trees are over- turned, buildings unroofed or blown down, and bridges hurled from their foundations. DESTRUCTION BY TORNADOES 97 A tornado is often seen first as a funnel-shaped cloud (Fig. 51), the point of which may be far above the ground. As the funnel moves forward, its lower end may rise or fall. The cloud is due chiefly to the condensation of moisture in the sharp convection current, and the funnel shape is due to the expanding and spreading of the air as it rises. The tornado is, of all storms, the most destructive, but, in most cases, it has a very narrow track, and does not work destruction for a very great distance, rarely more than 15 to 30 miles. One of the most destructive, though not one of the most violent, tornadoes of recent times was that at St. Louis, May 27, 1896. It accompanied a thunder- storm in the southeastern part of a cyclone, central some distance northwest of the city. The destruction of property in and about St. Louis was estimated at about $13,000,000. A more violent tornado was that at Louisville on the 27th of March, 1890, just before nine o'clock in the evening. Many weak buildings were wrecked, 76 persons were killed and about 200 injured in Louisville alone, and the loss of prop- erty was estimated at about $2,500,000. Questions 1. Explain the apparent contradiction in the fact that northeast winds, in most areas of the United States, are part of a storm coming from the west. 2. Show by a series of diagrams, in their proper order, the weather changes which would take place at a given station on three successive days under the following conditions: (1) On the first day the storm center (low) is approaching from the southwest; (2) on the second day at noon the center is 200 miles away, directly to the south; (3) on the third day it has moved on in the normal direction, and at the normal rate. Diameter of the low, 1,000 miles. Make similar diagrams for the same place for a storm following a track 200 miles to the north of the station. 3. Make rules for forecasting temperature when the weather map shows isotherms running (1) east and west, and far apart; (2) north and south, and close together. 4. Indicate what truth, if any, there is in the following weather proverbs: (1) "Too cold to snow." (2) "A white frost is a sign of a fair day to follow." (3) "Rainbow in the morning, sailors take warning; rainbow at night, the sailors delight." 5. Suggest other weather proverbs which you have heard, and show whether or not they have any basis of truth. 6. Why are large dealers in grains, cotton, and tobacco interested in the daily weather map? 7. Suggest some of the changes in the climate of the United States which would result (1) if the Rocky Mountains ran east and west, along the entire length of the Canadian boundary; (2) if the area of the Gulf of Mexico were land. CHAPTER IX TROPICAL CLIMATE Extent of tropical regions. The tropical zone, as usually defined, is limited by the tropic of Cancer on the north and the tropic of Capricorn on the south. Other definitions of this zone have been suggested, as (i) the zone where the trade- winds blow, and (2) the zone where the palm tree grows, the palm being taken as the type of tropical vegetation (Fig. 52). Defined by parallels, the tropical zone covers about two-fifths the area of the earth. About one- third of all the land — in round numbers, 17,000,000 square miles — is within the tropics. This third of the land sup- ports about a third of the people of the earth — in round numbers, 500,000,000. Much tropical land is desert, and much is covered with dense forests (Fig. 53), and these parts are but sparsely peopled; but the fertile areas which are cultivated support dense populations. In Java, for example, 30,000,000 people live in an area two-thirds that of Pennsylvania. About one-seventh of North America and one-sixth of its people are in the tropics. The tropical part of South America is much larger, nearly three-fourths of the continent and of its people being between the Caribbean Sea and the tropic of Capricorn. No part of Europe is in the tropics, and only about one-fifth of Asia is tropical, but this fifth supports fully half the population of the conti- nent. Three-fourths of Africa are in the tropical zone and two- thirds of its people, and about half of Australia and one-fourth of its people. The area of ocean within the tropics is about 70,000,000 square miles. The large proportion of water in this zone gives much of the land a marine climate. Relatively small areas, in the wider parts of the continents, show true continental conditions. General Characteristics of Tropical Climates The most striking thing about the climate of tropical regions is its uniformity. The weather does not change frequently, as in middle latitudes. Atmospheric conditions are so nearly uniform 98 TEMPERATURE CONDITIONS IN THE TROPICS 99 month after month that weather and cli- mate are almost the same. Now and then hurricanes and typhoons occur in some parts of the zone. Uniformity of temperatures. The temperatures of the tropics are even more uniform than the other elements of cli- mate. (1) The noon altitude of the sun varies much less than in other zones, and (2) the length of day and of night is always nearly the same. As a result, the amount of insolation never varies much, and since it is always large, the temperature is always high, except at high altitudes. Annual changes. Many tropical places have a range of less than io° between the mean temperatures of the warmest and coldest months, and a range of less than 15 is characteristic of most tropical lands. On the oceans, and on some lands, the range is insignificant. At Bogota, Colombia, the coolest month is less than 3 cooler than the warmest. Buitenzorg, Java, has an annual range of only i.8°. Toward the edges of the tropical zone, the annual range of tem- perature is greater, especially inland. Thus at Nagpur, in the interior of India, Lat. 2i°9 / , the range is 27. i°. Diurnal changes. In many parts of the tropical zone, the difference in tem- perature between day and night is greater than that between the warmest and the coolest months. Near coasts, the tem- perature rarely falls below 70 at night, or rises above 90 by day. Inland, the range is much greater, and in dry regions far from coasts it is as much as 6o° or 70 in some places (from 50 or 6o° at night, to a maximum of 120 by day). In places, ff ^ ff+ 44 w 00 o o "3 "3 Pi 3 ^° N. and S. There is, however, no marked change in climate as these boundary lines are crossed. The intermediate zones contain a little more than half (52.7 per cent) the area of the earth. Southern hemisphere. The total land area of the south tem- perate zone is only about 4,000,000 square miles (Fig. 57), and its population not more than 20,000,000. In other words, the lands of the south temperate zone, taken together, have an area about one- third larger than that of the United States, and a population less than one-fourth as great. About one-fourth of South America (1,800,000 square miles) and about the same proportion of its people (10,000,000) are south of the tropic of Capricorn. More than half of Australia and about three-fourths of its people (3,000,000) are in the same zone. Because of aridity this part of Australia is less important than the correspond- ing part of South America. New Zealand, but little more than 100,000 square miles in area, has a population of about a million. About 7 per cent of Africa lies south of the tropic of Capricorn. This area (700,000 to 800,000 square miles) has hardly more than 4 per cent of the people (5,000,000 to 6,000,000) of the continent. The area of ocean in the south temperate zone is about twelve times as great as that of the land (Fig. 57). Hence much of this zone has a marine climate, which is much less variable than the climates of the north temperate zone. Northern hemisphere. Nearly half of all land is in the north temperate zone, and the area of land there (26,000,000 square miles) is about equal to that of water (Fig. 58). In North America, all the 113 ii4 TYPES OF CLIMATE IN TEMPERATE ZONES •a * \ '8 <\ ; Bi \ i J [I j\ t ^ 1 - w t \ \\ „••-. \ ^^Va 1 \ \ W U K i 1 / ° 3 \ ~\ f-8 United States except northern Alaska, most of Canada, and part of Mexico, are in this zone. So also are nearly all of Europe, most of Asia, and part of northern Africa. This zone contains the greatest nations, and the majority of civilized peo- ple. Because of the greater expanse of land, continental climates are more pre- valent than in the southern hemisphere. Only in certain broad aspects can the climates of the northern and southern intermediate zones be discussed together. General Characteristics of Climates of the Temperate Zones Variability. There are several types of climate in these zones, and their differ- ences are perhaps as striking as their likenesses. Variability is the distinguish- ing feature of most of them. They vary in (i) temperature, (2) direction and veloc- £ ity of wind, and (3) amount and distribu- tion of rainfall. In general, the variability is less in the southern hemisphere than in the northern. Sun influence. The fundamental cause of variability in these zones, as contrasted with the uniformity of tropical climates, is the great variation in (1) the altitude of the sun during the year, and (2) the length of day and of night. The sun never is overhead at any place in these zones, and during at least a part of the year it is many degrees from the zenith at noon (pp. 13-14). There are, accordingly, great differences in the amount of heat received at different times, and the year is divided into seasons which vary much in temper- ature. 3 o O 10 X ._ U-, O ag 5 ~ o TEMPERATURES OF INTERMEDIATE ZONES 115 Winds. The prevailing (westerly) winds of these zones are much less regular in direction and velocity than the trade- winds of the tropical zone, and are inter- rupted much by cyclonic storms, which vary greatly in frequency and strength. Temperature ranges. The factors noted above lead to great variations of temperature from day to day, from season to season, and from place to place. The great and sudden variations of tempera- ture make the term temperate singularly inappropriate for these zones. The weather at least is often most intemperate. In contrast with the conditions in the tropical zone (p. 99), observations through many years are necessary to get a correct idea of the climate. The yearly range of temper- ature in most places is far greater than the daily range. In the same latitude, conditions vary widely from place to place, both with respect to variation of temperature and the time of greatest heat and cold. Inland, the highest and lowest temperatures of the year generally .occur about a month behind the highest and lowest noon-alti- tudes of the sun, and the temperatures of the warmest and coldest months may be 50 apart, even in middle latitudes (as Chicago). Spring and autumn are much alike so far as temperature is concerned. Near the sea, the highest and lowest tem- peratures are about two months after the solstices, while spring is cold and autumn is warm. The maximum temperatures in summer in many cases exceed those of some tropical stations, and the lowest temperatures in winter approach polar cold. Summer weather is almost tropical, i l '"%. ■ \~H: &§ E S SJ n6 TYPES OF CLIMATE IN TEMPERATE ZONES and winter weather polar, in many parts of these zones. Weather and climate are therefore very unlike, so far as temperature is concerned. The average annual range, however, is as low as 20 in some places, even in comparatively high latitudes. Hence, in this zone, latitude is not a sure index of climate. North temperate zone. The great expanses of land lead to marked contrasts in temperature between the two margins of this zone, within which some of the highest as well as some of the lowest known temperatures occur. The mean annual range varies from as little as 1 6° in southern California (San Diego, near the sea), to as much as 8i° in northwestern Canada (Fort Chippewyan, far from the sea to windward). Near the tropical margin of this zone, summers and winters are not extreme, and springs and autumns are long. Toward its pole- ward margin, on the other hand, the differences between summer and winter are great, and the transition seasons are short. Hence the length of the growing season for plants differs greatly in different parts of the zone, with important effects on life. The variations of temperature are accompanied by variations in rainfall. In tropical lowlands, where temperatures always are high, it makes little difference to vegetation when rain comes; but where there are seasons of radically different temperatures, rain is useful to plants in summer, but not in winter. There are two general types of seasonal rainfall in the temperate zones, the marine or winter type, and the continental or summer type. In general, windward coasts and islands have the former, while interiors and leeward coasts have the latter. Both the variations of temperature and the distribution of rain- fall have far-reaching effects on life, some of which may be pointed out. Civilization, which apparently began near the tropics, has moved steadily outward (especially northward), until its chief centers are now in the middle latitudes of the northern hemisphere (p. 114), where the seasons are commonly regarded as responsible for much of the energy, thrift, and industry which have brought about this advanced development. The change of seasons stimulates effort. In summer, the conditions of life in many parts of the temperate zones are almost as easy as in tropical regions. Summer is a time of abundance, and winter a time of scarcity, in nature's supplies. In summer, it is necessary to provide food, clothing, and shelter for the winter, when nature does not provide. In order to live, therefore, SUB-TROPICAL CLIMATE 117 man must plan for the future, and to secure the things he needs requires regular effort; but with planning and effort, it is possible for him to secure what he needs. These conditions lead to mental, physical, and industrial development, and such development is the basis for advance in civilization. South temperate zone. The limited extent of land in the south temperate zone gives it a climate far less variable than that of the corresponding northern zone. Types of Climate The north temperate zone is a patch-work of climatic types, whether the division is based on temperature or on rainfall. The south temperate zone, with its smaller land areas, mostly near the sea, has few important types of climate. The chief types of climate of both hemispheres are determined by (1) the distribution of land and water, (2) winds, and (3) altitude. With insolation, these factors control both temperature and rainfall. The following important types of climate are recognized: (1) That of windward coasts in low latitudes, the sub-tropical type; (2) that of windward coasts in high latitudes (above 40 ) ; (3) that of continental interiors, a type which varies much, especially in amount of rainfall; and finally, (4) the modifications, particularly of (3), brought about by altitude. I. WINDWARD COASTS IN LOW (BELOW 40°) LATITUDES General characteristics. The chief features of sub-tropical climates are moderate temperatures, with small annual and large diurnal ranges. In these respects the climate resembles that of the tropics. The rainfall is rather light in most places (Fig. 39), and is greatest in winter. The summers are dry. This climate is typical- ly sunny, with a maximum of cloudiness in winter. Distribution. The sub-tropical type of climate is found in latitudes affected alternately by the trade-winds, the tropical belts of high pressure, and the westerly winds. It is developed best on islands and on the western (windward) coasts of continents between the parallels of about 25 and 40 . It prevails over much of the land of the south temperate zone and is widespread about the Mediter- ranean Sea, extending from Spain on the west through Italy and the n8 TYPES OF CLIMATE IN TEMPERATE ZONES southern part of the Balkan Peninsula into western Asia, as well as across the northern part of Africa. The wide extent of the sub- tropical climate about the Mediterranean has led to the name "Med- iterranean climate." In North America, this type of climate is almost confined to the coastal part of California, south of San Fran- cisco. The climate of southern California may be taken to illustrate the type. Southern California The southward migration of the wind systems in winter brings southern California under the influence of westerly winds. The northward migration of the wind systems in summer brings it in turn under the influence of (i) greatly weakened westerlies, (2) the tropical high pressure belt, and (3) the northern margin of the trade- winds. Temperatures. The latitude is high enough to prevent a long continuation of temperatures as high as those of the tropics, and nearness to the sea prevents the seasonal extremes characteristic of most places in the temperate zones. Freezing temperatures are rare in low altitudes. Daily ranges of temperature are greater than yearly ranges. On the whole, the temperature of southern California is much like that of tropical lands at moderate altitudes. In some ways the sub-tropical type of climate is the best in the world, and is described frequently as being like " perpetual spring." It is healthful, as shown by the popularity of southern California, where Pasadena, Riverside, San Diego, and other cities duplicate, on a small scale, the noted resorts in the Riviera of southern France and Italy. The sunny skies (68 per cent for San Diego) help greatly to make these places popular, especially in autumn, winter, and spring. The dry season (summer) may be disagreeable because of (1) the heat, (2) the drying up of vegetation, and (3) fogs and dust. Many places in California have least sunshine in the dry season on account of fogs. The absolute lowest temperature at San Diego is 32 , and the absolute maximum 101 . Such variations are characteristic of tropical lands where the average annual range is not more than 15 to 20 . Interior stations show greater average ranges and more marked extremes, because they are farther from the sea. Their mean maxima are higher, their mean minima are lower, and the fre- quency of both high and low temperatures is much greater. MARINE CLIMATE 119 Rainfall. As in most similar localities (Fig. 39) the precipita- tion in southern California is rather low, and there is a marked winter maximum. The summers are almost rainless for a period which varies considerably from place to place. The interior valley of California is dry at all times because the coast ranges have taken the moisture out of the winds from the ocean. The dryness increases the range of temperature in the valley. Rainfall and Crops During the dry season, most vegetation dries up unless irrigated. Where water is available, the abundance of sunshine and the favor- able temperatures lead to extensive irrigation, as in southern Califor- nia and in the favored parts of southern Europe, western Asia, and northern Africa. Most of the crops of these latitudes, however, are grown during the rainy winter season and harvested in spring, before, or soon after, the beginning of the dry season. Winter crops are made possible by the temperatures of that season. Winter wheat is a common cereal crop, as in Italy, southwestern Australia, and California, while barley, resistant to both heat and dryness, was long the chief cereal in such climates. Corn cannot be grown without irrigation, for it needs a high temperature (such as that of the dry season) during growth. The characteristic crop of the sub-tropical climate is fruit. Oranges, lemons, olives, grapes, and other fruits are produced abundantly in southern California and in Mediterranean lands. There is possibility of frost, however, and frost-fighting is an important part of the business of the California fruit grower. In many sub-tropical localities, fruit-drying is an important industry, favored by the dry, sunny weather which follows the ripening of the fruit. 2. WINDWARD COASTS IN LATITUDES ABOVE 40°; MARINE CLIMATE Location. The marine type of climate in this zone is controlled by prevailing westerly winds, blowing almost constantly from ocean to land. The climate is cool, damp, and rainy. The change from the sub-tropical type of climate is gradual, and in some ways the two types are not very unlike. In the western hemisphere, this type of climate is developed best (1) in Chile, south of latitude 40 and west of the Andes Mountains, 120 TYPES OF CLIMATE IN TEMPERATE ZONES and (2) near the coast from San Francisco to the Arctic Circle. It is modified greatly even east of the low coast ranges. In the eastern hemisphere, neither Africa nor Australia extends into latitudes high enough to have this type of climate; but it affects parts of Tasmania and most of New Zealand. It affects the coast of Europe from France to the Arctic Circle, and extends far inland because there is no continuous north and south mountain range to take the moisture from the westerly winds. The change from marine to continental conditions here is very gradual. From the British Isles, the annual rainfall decreases gradually eastward, the winter maximum gives way to spring and summer maxima, and the ranges and extremes of temperature become more marked. If the marine influence did not reach far inland, the densely populated and highly developed countries of western Europe, especially north of latitude 50 , would be far less important than now. The temper- ing effect of the westerly winds on the climate of western Europe is increased by the relatively high temperature of the central and eastern parts of the North Atlantic Ocean. Temperatures. The variations of temperature are less than in the same latitudes elsewhere. Thus the yearly range of tempera- ture at Sitka, Alaska, Lat. 57 , is only 25 , hardly more than that in some parts of the tropics, and at Thorshaven, in the Faroe Islands, Lat. 62°,the range is only 14. 2 . In this respect, this type of climate resembles the sub-tropical type, though the actual temperatures are lower (Why?). It is the only really temperate climate of the inter- mediate zone. Regions having a marine climate have mild winters and cool summers, and their average yearly temperatures are higher than those of other regions in the same latitude. For example, Ireland, which represents perhaps the extreme case, is 30 or 40 too warm for its latitude, 55 N. Rainfall and humidity. Places freely exposed to westerly winds get much rain in winter, when the land is cooler than the sea. In summer, low lands are warmer than the ocean and receive little rain, though the dry season is much shorter than in lower latitudes (Why?). Mountainous western coasts have abundant rainfall, high humidity, and much cloudiness all the year. In some places fogs occur almost daily, and in extreme cases, as along the coast of Alaska, they may last for weeks at a time. Evaporation is extremely low. MARINE CLIMATE AND LIFE 121 Though the maximum precipitation is in winter, little of it is in the form of snow, except at high altitudes. Effect on life. Cool summers, abundant moisture, and much cloudiness, prohibit the growth of many kinds of crops. For example, wheat and corn are not grown in the typical marine climate of western North America and northwestern Europe. Wheat requires a dry, sunny harvest season, and so its growth near the coasts in question is confined to places where topography modifies marine conditions, as in eastern Washington and eastern England. Corn needs a higher temperature and more sunshine than the marine climate affords. Oats, rye, and barley, however, are grown successfully in a cool, cloudy, damp climate. This is a chief reason why oats have fur- nished the staple food of Scotland. Various crops are grown near the northern limit of the intermediate zone in northwestern Europe and in Alaska. In Norway, rye, oats, barley, and potatoes are grown successfully within the Arctic Circle. In Alaska, barley, potatoes, cabbages, and turnips have been grown at Ft. Yukon, in latitude 66° 30'. The marine climate is also favorable for grass, which in some places grows ten or eleven months in the year. For this reason, the raising of live stock is or may be important in this climate. In the British Isles, for example, the grazing in- dustry has long been the leading phase of agriculture. Mild tem- peratures and abundant moisture make Ireland always green (Emer- ald Isle), and the raising of cattle is a chief industry. Marine climate also favors the growth of heavy forests. Good examples of such forests are found in northwestern United States (p. 370), where lumbering is an important industry and forest prod- ucts are leading articles of trade. In the same region, mountains near the coast cause heavy precipitation, much of which is in the form of snow. The melting of the snow in summer keeps the streams full when the rainfall is least, and mountain streams afford water power (p. 290) for manufacturing. Among native tribes, forest conditions lead to hunting and fishing as regular pursuits. The change of climatic conditions with increasing latitude has resulted in striking contrasts in man's activities. In the northern part of Chile, for example, there is a coastal desert at the margin of the trade-wind zone. Here conditions have favored the accumulation of guano and nitrate deposits, which have been the basis of important industries and commerce, and the cause of bitter strife between Chile and Peru. South of the desert, the sub-tropical type of climate has led to irrigation and the growth of fruits. Still farther south, where the climate is of the type under consideration, grazing and the raising of cereal crops and vegetables 122 TYPES OF CLIMATE IN TEMPERATE ZONES are the chief occupations. In the extreme southern part, the heavy rainfall from the westerly winds supports luxuriant forests, and forest industries and fishing are the chief occupations. Similar contrasts exist along the western coast of North America from California northward, and along the coast of Europe from Spain to Norway. 3 CONTINENTAL CLIMATES Regions affected. This type of climate, as its name implies, is found inland from windward coasts; but not at any fixed distance from the coast. We have seen already that the marine climate extends far from the western coast of Europe (p. 120), and but a very short distance from the west coast of the Americas (p. 119). In the south temperate zone, the continental climate is found only in southern Argentina. North America and Eurasia, on the other hand, are broad in rather high latitudes (Fig. 58), and so have continental climates over wide areas. In North America, there is a sharp contrast between the marine climate of the western coast and the continental climate east of the westernmost high mountains, the continental climate affecting most of the United States and Canada. In Eurasia, because of conditions already noted (p. 120), the marine climate of western Europe grades into the continental climate which affects the Russian Empire and most of China. Temperatures. The chief characteristic of the continental climate is extremes of temperature. These extremes are due largely to the fact that land absorbs and radiates heat much more readily than water does. The winters are cold, the cold increasing (1) with the latitude, and (2) with increasing distance from the sea to windward. In latitude 45 , in North America, the lowest temperatures are about — 30 , and near the northern limit of the zone they reach — 6o° or even less. A great area in northeastern Asia, far from the ocean to windward, has extremely low temperatures in winter. In the United States, the temperature never falls to — 40 , except in the extreme northern part and in high mountains, and there but rarely; but, except in the Gulf region, there is no large area east of the Pacific coast where temperatures io° to 20 below freezing do not occur every year. The summers are hot. July averages of 6o° are found even beyond the northern margin of the zone, and maximum temperatures of 8o° to 90 are found close to the Arctic Circle. In the southern part of the zone, the summer temperatures are tropical. The annual ranges of temperature are very great, especially in the northern part of the north temperate zone. In northwestern CONTINENTAL CLIMATE 123 Canada, the difference between the lowest and the highest tempera- tures of the year has been known to reach 150 , and in northeastern Asia, 180 . In the lower latitudes the extremes are not so great; the winters are milder, and the summers are not correspondingly warmer. In our southern states only small areas ever have tempera- tures above ioo°, and in most parts of the zone the mean maximum temperatures are under 90 , or no higher than those occasionally recorded near the Arctic Circle. Cyclonic influence. A second important feature of continental climate is the variability of weather from day to day. Cyclones and anticyclones interrupt the prevailing westerly winds frequently; hence there is repeated change from clear, cold, and dry days, to cloudy, warm, and damp ones. Because of the frequent storms, the winds may, in the course of a day or two, blow from all points of the compass, and each wind tends to bring its own distinctive weather conditions. The northerly winds of anticyclones in winter carry freezing temperatures almost to the southern margin of the zone. Southerly winds, on the other hand, carry warm air to comparatively high latitudes, and temporarily may produce a summer-like tem- perature in mid-winter, even as far north as New York and Chicago. Rainfall. A third important element of continental climate is its rainfall, which is very variable, but as a rule either moderate or scanty (Figs. 39 and 59). In few places is it more than 40 inches a year, and most of it comes during the spring and summer. The fact that most rain falls when temperatures are favorable for plant growth is most important. Eurasia illustrates the effect on rainfall of distance from the windward coast. The western slopes of the British Islands have 80 to 100 inches of rain yearly; Germany and western Russia have 20 to 30 inches; eastern Russia and western Siberia, between 15 and 20 inches; while large areas of central and eastern Siberia have less than 10 inches. Arid and humid interiors. On the basis of rainfall, there are two principal subdivisions of continental climate, the one humid, and the other arid. These types merge into each other in a belt where the climate is semi-arid. Forests are characteristic of the humid climate, but they give place to grass lands where the climate is semi-arid, and to deserts where the rainfall is very slight. In a general way, moisture decreases with increasing distance from the ocean to windward; but topography and cyclonic storms modify this i2 4 TYPES OF CLIMATE IN TEMPERATE ZONES CONTINENTAL CLIMATES IN UNITED STATES 125 general relation. Altitude also is an important factor in continental climate, especially in arid regions, because highlands increase precipi- tation. Lowland deserts may give place to grassy lands at moderate altitudes, and to forests still higher. As in tropical deserts, the effect of high elevations plays an important part in the life of the arid regions. With but slight modification, the continental climates extend eastward to the oceans. Ranges of temperature are somewhat less near the eastern seaboard, and the rainfall is somewhat greater (Fig. 39). Continental Climates in the United States The interior of our country may be divided into (1) the arid region (Fig. 60), chiefly between the Sierra Nevada and Cascade mountains on the west and the Rocky Mountains on the east; (2) Fig- States. 60. Map showing arid, semi-arid, and humid regions of the United (After Newell.) the semi-arid region between the Rocky Mountains and longitude 98 to ioo°; and (3) the humid tract, lying farther east. All these regions have extremes of heat and cold. They also have great changes of temperature and humidity from day to day as a result of passing cyclones and anticyclones. The difference in the amount of rainfall, however, makes the conditions of life very different in the three regions. 126 TYPES OF CLIMATE IN TEMPERATE ZONES (i) The Arid Region The arid region (Fig. 60) includes most of tne Cordilleran section of the United States, except the high mountains. Its western margin is near the western coast, because the mountains there stop much moisture which otherwise would be carried inland by the westerly- winds. The average annual rainfall in the arid belt is less than 15 inches, and over large areas, less than 10 inches (Fig. 59). Sunshine prevails throughout the year, relative humidity is low, and evapora- tion high. The nights are usually cool even when the days are hot. The heat of summer is great, but the humidity is so low that the sensible temperatures are not very high. So far as comfort is con- cerned, the arid region has an agreeable temperature. Effects of scanty rainfall. The scanty rainfall means scanty vegetation, except where high elevations cause rain enough to support grass or timber. The rapid evaporation of ground-water leaves the alkaline substances it contains in the soil, and the slight rains are not enough to dissolve and carry these away. In some places this gives rise to alkaline soils, unfavorable for vegetation. Where not alkaline, desert soils are naturally rich, because elements important for plant food have not been leached out or used up (p. 293). Hence where water can be applied to desert lands, they are highly productive in most cases. Many mountains in the arid region receive much snow in winter, and this may afford water for irrigation. The total area which can be irrigated, however, is but a small portion of the entire arid tract (p. 293). Farming is therefore not the leading industry of arid lands. Where rainfall is enough to support even a meager growth of grasses, grazing is an important occupation. Mining is important in parts of the arid West, though aridity has little or nothing to do with the development of ores. Desert condi- tions favor the accumulation of salt deposits, as about Salt Lake, and borax deposits, as in Death Valley, California. The population of the arid section is necessarily scanty, because there is no natural basis for permanent or extensive settlement in most localities. (2) The Semi- Arid Region In the semi-arid region (Fig. 60), the yearly rainfall is between 15 and 20 inches (Fig. 50), most of which falls in spring and summer. CONTINENTAL CLIMATES IN UNITED STATES 127 The tract is without high mountains, so that there is little increase of precipitation as the result of altitude, and forests are generally absent. The region is sunny, and the temperatures are high in summer and low in winter. The sensible effects of the extremes, however, are moderated by the dryness of the air. The open charac- ter of the country favors free circulation of the atmosphere, and fairly constant winds of moderate to high velocity are more or less typical of most of the region. Effect on life. The semi-arid district is a region of grass land; there is not enough rain for most cultivated crops. Grazing conse- quently has been the most general occupation. Water is highly prized, and bitter contests have been waged over the question of its ownership. Thus the use of the waters of the Arkansas River, which flows from Colorado into Kansas, led to a long legal battle between the two stated, because there was not water enough for both. (3) The Humid Region The semi-arid region merges gradually into the humid region farther east (Fig. 60). The temperatures of the two regions are not unlike, but in the humid region cloudiness and humidity are greater, and evaporation less; hence sensible temperatures are higher in summer and lower in winter. The precipitation rarely falls so low as 20 inches per year, and most of it comes in summer. The amount of rain necessary for crops without irrigation varies with the latitude. More is needed in Oklahoma than in Dakota, because the higher temperature and lower humidity of the former cause greater evapora- tion. In the western part of this region, trees grow in the river bottoms; farther east, they become more abundant, and forests are found (or were once) over large areas. Throughout the humid region there is rain enough for cultivated crops, and it contains some of the greatest agricultural tracts of the temperate zones. Effects on life. The crops raised are determined largely by the climate. Wheat, for example, is raised most in the less rainy regions (Fig. 260), and its seed time and harvest are influenced by climate. In the north, spring wheat is grown, largely because the winters are too cold for wheat sown in the autumn. Farther south, where the winter season is shorter and milder, both winter and spring wheat may be grown, the former predominating in many sections. The harvesting of winter wheat begins in the south in June, and the harvesting of spring wheat ends in the north about the first of 128 TYPES OF CLIMATE IN TEMPERATE ZONES September. The harder varieties of wheat, rich in gluten and good for macaroni, are grown in the drier sections (p. 366), while softer varieties, less rich in gluten, but good for flour, are grown where rain is more plentiful. The best climate for wheat is one with a dry, sunny harvest season, such as that of the Sacramento Valley, California, and eastern Wash- ington (p. 121). This ideal climate is not found in much of the humid interior, where wheat is the standard crop only in a north- south belt, some ten degrees in width, just east of the 100th meridian. Even here, the climate is not so good for wheat as that of eastern Washington. East of the wheat belt, the heavier rains favor a variety of crops. Corn is the standard cereal in great areas (Fig. 259), though wheat, oats, and other crops are commonly grown in rotation with it. Corn is not grown so far north as wheat, because corn requires a higher temperature, and most varieties require a longer warm season. With corn, many other cereals, vegetables, and fruits are grown, requiring more moisture than wheat. The humid continental region is the region of greatest develop- ment in the United States. It has the major part of the population (Fig. 281), it contains most of the chief cities (p. 399), its manufactur- ing and commercial activities are greatest (p. 383), and its transpor- tation facilities are best (Fig. 279). All these things reflect the abundant yield of the soil, and this is a result, in large part, of favor- able climate. The abundance of rain and the topography of the eastern coast of the United States favor the development of swamps, and in low latitudes swamps invite diseases like those of equatorial regions (p. 103). The home of malaria in the United States is on the low plains and in the river valleys along the eastern coast south of New York. Yellow fever has been introduced many times into the Gulf and South Atlantic ports, but could not last from one summer to the next, on account of the frosts of winter. Shore towns in nearly all latitudes feel the beneficial effects of the sea-breeze (p. 74), and many important seashore resorts from New Jersey northward are the result. In the higher latitudes, the ocean affects the temperature of coastal lands chiefly by lowering the temperature in summer, because of frequent winds (sea-breezes and cyclonic winds) from the east. The July mean for Labrador, for example, is 13 or 14 lower than that for Norway House, at the IMPORTANCE OF HUMID REGIONS 129 northern end of Lake Winnipeg, near the great Canadian wheat district. In Labrador none of the cereals will ripen. The sparse population there finds its chief support in fishing, hunting, and trapping. Fishing especially is important during the summer, and when the catch is small, the people suffer greatly from want during the long, cold winter. The same factors which lower the temperature and increase the rainfall along our eastern coast increase cloudiness and fog. Places exposed freely to the sea (like Newfoundland) have conditions of humidity, cloudiness, and fog similar to those of marine climates on western coasts. Along the eastern coast, therefore, the continental climate is somewhat modified. The humid parts of the north temperate zone are the greatest cereal districts of the world. They bear the same relation to the cul- tivation of cereals that the semi-arid steppe lands, with their grassy veg- etation, hold to the live stock industry of the world. Thus the great wheat regions lie mainly between the 40th and 55th parallels. Rye, closely related to wheat in its uses and conditions of growth, replaces wheat in many places where the soils are too poor for the latter. Of the other great cereal crops in this belt, oats and barley are grown more to the north, and corn to the south. Hence, through the heart of the temperate zone is found the home of all the cereals, save rice, which serve as food for man. This arrangement of important crops influences both the distribution of population and the movement of commerce. The populous part of the temperate zone corresponds closely to the cereal belt. Much of the commerce of the world now moves along east and west routes in these same latitudes. No other country is situated so well as the United States with respect to cereal growing lands. The whole humid section in the interior of this country is exposed to sudden frost in late spring and early autumn (Fig. 61), and in either case widespread damage may result. Its southwestern part is exposed to hot winds from the south which, in exceptional cases, wither and kill crops. Droughts are common, though less frequent and less widespread than in monsoon countries. Almost every year some part of the humid portion of the United States suffers from too little rain; but severe drought rarely affects a great area, or the same area frequently. In monsoon countries like India, on the other hand, a large area suffers from drought at the same time, and the same area may suffer for a period of years. Tropical and sub- 130 TYPES OF CLIMATE IN TEMPERATE ZONES tropical Australia also has frequent and long-continued droughts which affect large areas. In spite of its extremes of climate, central and eastern United States is a highly favored agricultural region, largely because of its reliable rainfall. Near the northern limit of the north temperate zone the summers of interior lands are too short and too cold for cereals. Even in the most favored parts of continental interiors, the hardiest cereals cannot ^t , / r \\ *v ~£^' n# 2t>^. / ***■■ \v J 9 f^ i i "-I \ /Sept.15 h \^T >. V __ -*T"i -•-• 4- r -. ■ (7 '■\ -^\ J ( "/ *' J*\ ^^V^ y\ ~^S ^ A/ 001 ' ^Mayis/j Kl^ A- L y< r^i^'kfr ^#>s^iir ( r^^N-My ! \^w\ tf + ) ( /CZZcs r x V"tf^i / Novl [ t 7~~-i\ r\---->vJ^r- - -^ >. I.mV xU/v _^ i"ii^ s\._.ji i ~j?Zs / ^~r~ — \^^ AprXS ^SksLP )-^s/i&v ApM i f JnJsX v ^*$i) \ « \ r — y*f i tJv^^iL ^^>i~' lv ~ \ S r\y-vr -•+ — jy ^ S « / ^^CVo^c. ^ •■ fS^p^ h-f^z^oL yjSQ^J^ I \\ Xs ^"-^tfr%=W' X' "S" 1 " 1 71 "V->~ }~ '~^2jO>ec.l \\ \ v^^'/^^ 3 ^^ 5 ^ i^^^W^^^l • I >*c-I5 -J) \ \ JV-rvA.'' -'Z^^—rio^^A ;^g^ ^^V>*V \A \ Marehli '/V h 1 \ / Feb.l»V A F ^ \ x >Febl5 \ ) -1 \>V V DecJ5 ' :) V Ov rr Fig. 6i. Map of United States showing average dates of last killing frost in spring (broken lines) and first killing frost in autumn (solid lines). (After U. S. Weather Bureau.) be grown much beyond the 6oth parallel (Fig. 58). Dense forests disappear in most places before the margin of the zone is reached, being replaced by the scattered trees and scanty vegetation which mark the beginning of the frozen, polar wastes. Both Canada and Russia have large areas of this nearly worthless, almost uninhabited territory (p. 336). The United States, on the other hand, is neither too far north nor too near the equator. Climatically, it has the best position of any large country. 4. MOUNTAIN CLIMATES Temperature. Even moderate altitudes so affect temperature as to determine what crops may be cultivated. For example, in MOUNTAIN CLIMATE 131 the plateau sections of Pennsylvania, in latitude 40 to 42 , corn can- not be depended on to ripen at an altitude of 2,000 feet. In some of the drier, hence warmer (in summer) and sunnier, parts of the arid West, corn, under irrigation, will ripen at much higher altitudes (4,000 feet about Great Salt Lake). In general, the upper limit for even the hardiest crops does not exceed 6,000 feet, even in the lower latitudes of the temperate zone. In contrast, corn is grown in Bolivia at an altitude of 10,000 feet, and wheat even higher. The timber-line (upper limit of timber) in the United States ranges from an altitude of about 11,000 feet at the south, to 7,000 or 8,000 at the north, and the level at which snow lies most of the time is not far above these limits. Hence, so far as agriculture is concerned, the higher lands of the temperate zone are of little use. Precipitation. The effect of altitude on rainfall is the same in the temperate zone as elsewhere. It increases the amount of precipitation, and tends in many cases toward a maximum in winter. The increased precipitation at higher altitudes usually results in heavy snowfall in winter. Thus Baltimore, altitude 104 feet, has an average of 23.8 inches of snow annually, while Grantsville, Md., altitude 3,400 feet, has 71.2 inches. Summit, the top of the pass (7,017 feet) crossed by the Southern Pacific railroad east of Sacra- mento, Cal., has an average snowfall of 433 inches a year, and twice in thirty- three years the amount has reached 775 inches. Sacramento, on low land to the west, has only a trace of snow each year. Winter snowfall is an important factor in the flow of many rivers. Disastrous winter and spring floods are the result in some cases (p. 76), and in others the supply of water from melting snow is an important aid in (1) the development of water power, (2) the main- tenance of a sufficient depth of water for navigation, and (3) irrigation. Heavy winter snows and snowslides offer serious problems to railroad lines which run at high levels, and at the bases of mountains. Snow- slides are one of the things to be feared about mines in mountains, and mountain villages have been destroyed by them. Mountain conditions of temperature and rainfall favor forests, and make many mountains the sites of lumbering (p. 316). Forest trees thrive far' above the altitudes which limit crops. Even in arid regions, some areas 5,000 to 6,000 feet high have rain enough to support forests of commercial value. Many mountains serve as health and pleasure resorts (p. 317). Most mountain health resorts are visited chiefly by persons afflicted i 3 2 TYPES OF CLIMATE IN TEMPERATE ZONES with diseases of the lungs, especially tuberculosis. Mountain climate is not a cure for this disease; but the conditions in the mountains may aid in checking it, or may even enable the organs affected to throw it off. The favorable conditions are (i) the pure, dry air char- acteristic of the higher altitudes of many mountains, and (2) the de- creased density of the atmosphere, which stimulates the lungs to greater activity. In the arid parts of western United States, these conditions are associated with bright, sunny weather, which favors out-of-door life. Questions 1. Explain the absence of summer rainfall in sub-tropical climates, even with winds from the ocean. 2. Account for the morning fogs of the coast of southern California in summer. 3. Why is the Pacific Ocean not the chief source of moisture for the United States? 4. Explain the differences in climatic conditions at different points on the 41st parallel in the United States. Along the 32nd parallel. 5. Explain the increase in rainfall from San Diego northward to Astoria. (See Fig. 59 and Plate II.) 6. Why are the limits of cereals and of permanent habitations nearer the equator in Fig. 57 than in Fig. 58? 7. How does the isotherm of 50 in Fig. 57 differ from that of Fig. 58? Why? 8. Why do the lines showing average dates of frost (Fig. 61) turn northward over Lake Erie and along the south Atlantic coast? 9. W 7 hy is the snowfall in the Mississippi Valley heavier than that in the corresponding latitudes on the Atlantic coast? 10. Suggest reasons, based on climate, why there is little commerce between lands of the south temperate zone. CHAPTER XI CLIMATE OF POLAR REGIONS General Considerations Extent of polar regions. The limits of the polar regions are commonly placed at the Arctic and Antarctic circles; but they are sometimes regarded as being limited equatorward by the isotherm of 50 for the warmest month, an isotherm which marks the approxi- mate limit of the growth of trees and cereals (Fig. 62). In this dis- cussion, the latitude division is used. Thus defined, the polar regions have an area about one-twelfth that of the earth. General features of polar climate. All polar regions are alike in having the sun above the horizon for more than twenty-four con- secutive hours, and below the horizon for a similar period, once each year. Near the margins of these zones, the longest period of continuous sun is only a few days (of 24 hours each) ; but the time during which the sun does not set increases poleward, and at the poles the day (period of continuous light) is six months long (p. 43). During the period of continuous light, insolation is greater in polar regions than in low latitudes (p. 35), but the temperature of the lower air is not raised accordingly, because (1) the sun 's rays are very oblique (Fig. 21), and (2) much of the heat which reaches the surface melts ice and snow, and is not effective in warming the air. The result is a low temperature for the year, and, except for lands free from snow and ice, a low temperature at all times of the year. Temperature. Many of the recorded temperatures of January in the Arctic region range from — 40 to — 6o°, while the warmest month has an average temperature of 32 or more in many places. The maximum summer temperatures close to the margin of the zone are locally as high as 8o°, or even 90 ; but such temperatures occur only where there are large areas of land free from snow and ice. Most of the Antarctic region has a summer temperature below the freezing point even during the warmest month, so far as present records show. The annual range of temperature in the Arctic region is greater 133 134 CLIMATE OF POLAR REGIONS than that in the Antarctic, because more land in the former is without snow and ice in summer. Verhoyansk, in Siberia, just within the Arctic Circle (Lat. 67 6'), has a July mean of +6o° and a January Fig. 62. Map of North Polar Zone, showing land and water areas. Pole- ward limit of growth of cereals Poleward limit of growth of forest trees . Poleward limit of permanent habitations + + + +'+. Isotherm of 50 for warmest month . mean of — 6o°. In contrast, Hammerfest (Lat. 70 40'), on the coast of Norway, and the most northerly town in Europe, has a Janu- ary mean of 23 , and a July mean of 53 . Hammerfest shows the full effect of the ocean on the temperature of windward coasts in high latitudes. THE LIFE OF ANTARCTIC REGIONS 135 Humidity arid precipitation. The low temperatures affect the other elements of climate. They mean little evaporation, and hence little moisture in the air. The relative humidity varies from extreme- ly low, especially far from the sea to windward, to relatively high, particularly on windward coasts. The precipitation is light, prob- ably averaging less than 1 5 inches a year except on windward coasts. The Shackleton expedition to Antarctica found, from recording instruments left by a preceding expedition, that the average precipitation for six years had been the equivalent of 7 to 8 inches of rain. Most of the precipitation in polar regions is in the form of snow, and is frequently accompanied by violent winds. Rain is said to fall in most parts of the north polar region during the warmer months. In the south polar region the Shackleton expedition found all precipitation during 13 months to be in the form of snow. The great fields of snow and ice in the polar regions are not due to heavy snowfall, but to the preservation of most of that which falls. In summer, fogs are common, and are a great hindrance to navi- gators. The Antarctic Region The Antarctic region is largely ice-covered water and ice-covered land. The scattered land areas which have been discovered are probably parts of an Antarctic continent. Beyond the edge of this ice-covered land the surface rises toward the interior to heights of several thousand feet. If the south polar region were limited by the isotherm of 50 for the warmest month, it would include everything south of the 55th parallel. Temperature. The great expanses of ice and ice-water do not allow the temperature of this zone to rise much above 32 , even in summer. During this season, fog and cloud are so frequent that much insolation is cut off. Fogs and clouds are therefore important factors in keeping the summer temperatures low. The mid- winter (July) temperatures of the lower latitudes of this zone are about — 15 to — 20 , so far as recorded. The temperatures of higher latitudes are probably much lower. The seasons between winter and summer are very short. The one shows a rapid rise from the low temperatures of winter, and the other a rapid drop from the temperatures of summer. Effects on life. The Antarctic region is without most kinds of vegetation familiar to us. Some mosses and lichens are found on such i 3 6 CLIMATE OF POLAR REGIONS lands as are free from ice for a part of the year, but no form of vegeta- tion useful to man is known. The animal life is mainly marine, whales and seals being characteristic. The waters abound in lower forms of life, such as molluscs and still simpler types. On land, animal life is represented by a few species of birds and insects. Great rookeries of penguins form one of the most remarkable assemblages of bird life to be found anywhere. The albatross, gull, and some other kinds of Sea-coast birds also are found. From the standpoint of life in general, however, the Antarctic lands are as close an approach as there is to an absolute desert. The Arctic Regions In the higher latitudes the Arctic Ocean is covered with ice most of the year, though the ice is more or less broken in summer. In the lower latitudes much of the ocean is free from ice all or part of the time. Snow and ice cover all but the fringe of Greenland, and the larger part of many other islands. The Arctic portions of the conti- nents are not covered by ice and snow during the summer, and their climate is in sharp contrast (How?) with that of regions which are so covered. There is also a great contrast between the interior lands which are snow-free during the summer, and windward coasts, such as western Alaska and northwestern Norway, which are affected by the moderating influence of winds from the oceans (p. 134). Temperature. The temperatures of this zone vary widely. The lowest yearly temperatures are found where there is a permanent covering of ice. Such observations as are recorded indicate a January mean of about — 40 for northern Greenland, while its July mean is near the melting point. The continental interior of Siberia is even colder than Greenland in winter. In summer, however, this same region, being without snow or ice, becomes very much warmer than Greenland. Arctic lands free from snow in summer have great extremes of temperature, and summer maxima of 6o° to 8o° are almost typical of the margin of the zone. Temperatures of 90 or more are reported frequently from Alaska and Siberia. An extreme range of 150 for the year is common, and the highest summer and lowest winter tem- peratures recorded are more than 180 apart. The extreme and long-continued cold of winter is sufficient to freeze the water in the ground to the depth of scores of feet, and the tempera- tures of summer suffice to melt the ice in the top part only of the soil. LIFE IN ARCTIC REGIONS 137 Plant life. The relatively high temperatures which prevail on ice-free land in summer permit the growth of many kinds of plants. As compared with the temperate zone, however, the amount and variety of vegetation are meager. Stunted trees of the hardier types, such as larches, pines, birches, and willows, grow near the border of the Arctic zone (Fig. 62). The northern limit of these trees is near the 70th parallel in Siberia and northwestern Canada. Dwarf willows and birches (hardly trees) are said to occur 8° or io° farther north. Mosses, lichens, and other low types of plants abound in the Arctic tundra, which becomes a sea of mud as it thaws out during the sum- mer. In the dry places in the tundra, and on southerly slopes where drainage of the soil is good and where insolation is great, there are many flowering plants, some of which produce berries. On the west coast of Greenland, poppies grow north at least to latitude 78 . The plants of these high latitudes are rapid growers, as the short growing season would let no other plants mature. The temperatures of air and soil exclude crops from nearly all the polar region. There are a few localities, as in northern Norway and favored spots in Alaska and Siberia, where hardy cereals and some vegetables may be grown (Fig. 62). Animal life. Animals, as well as plants, are more abundant in the Arctic regions than in the Antarctic. Sea life is more abundant than land life. The larger sea animals are similar to those of the Antarctic, and include whales, seals, and walruses. All these animals are important to the people living in the Arctic region, and are the basis for certain industries carried on from places in lower latitudes. Thus, sealing and whale fishing are carried on close to the Arctic Cir- cle, and even within it. The Arctic seas also teem with smaller forms of life, such as molluscs and small crustaceans. Birds are prominent in the summer. The little auk, dovekies, guillemots, and (locally) the eider duck abound. Among land mammals, the reindeer, fox, hare, polar bear, and musk-ox may be mentioned. Arctic people. The Arctic region, unlike the Antarctic, is in- habited by human beings, the best known of whom are the Eskimos (Fig. 62). The population, however, is scanty, scattered, and, on the whole, not highly civilized. Along the southern margin of the zone, there are many small groups of people. Farther north, the groups are fewer and smaller, and more confined to coasts. The most northerly permanent settlements are on the west coast of Greenland, the northernmost, Etah, being above the 78th parallel. 138 CLIMATE OF POLAR REGIONS For all inhabitants of polar regions, life is a constant struggle. The cold means poverty of resources, a constant fight for food and clothing, and consequent inability to progress. Edible plants are absent, except in the lower latitudes of the zone, and for a short time each year. Land animals, like the reindeer, are comparatively scarce on account of the meager vegetation. Hence the people depend in large part on marine life, and most of them live along the coasts. Meat is the principal food, and is furnished by the seal, the walrus, and fish, supplemented by the reindeer, the hare, the bear, and birds. Most of this food can be obtained only during the time of light, which is therefore the hunting season. Food for winter is preserved easily because of the cold. Since fuel and means of cooking are meager, much meat is eaten raw. In north Greenland, the tiny fire — a little oil with a wisp of grass or moss for a wick — is used chiefly for melting snow and ice for drinking water. The dependence of the people on animal life makes them hunters and fishers. The hunters are partly nomadic, going about in search of game during the sum- mer, but having fixed habitations for winter. Most of the Eskimo 's clothing is of fur. Plant fibers which could be woven or braided together are unknown, except as they are brought in from other lands. The materials used in making dwellings depend on local circumstances. Where forests are accessible, as along the margin of the zone, or where driftwood can be had from the ocean, as along some coasts, wood is used. Elsewhere, the winter house is usually of stone or snow. During the hunting season, the hunters live in tents of skins. Weapons and utensils may be made from wood, if it is available; more commonly they are made from bone and hides. The use of these animal products is the characteristic feature of the arts and crafts of the Eskimos. Perhaps in no other thing is their skill shown better than in the making of their kayaks (boats), where the only materials to be had are bone, pieces of driftwood, and hides. Out of these they fashion a craft wonderfully adapted to the uses to which it is put. Looked at with reference to their surroundings, the Eskimos hardly can be regarded as backward. Probably they make better use of the things at their command than more highly civilized men could, but Arctic climate is too great a handicap to allow them to progress far. QUESTIONS 139 Questions 1. Why is rainfall relatively unimportant in affecting the distribution of people in the polar regions? 2. If the entrance from the Pacific to the Arctic Ocean were widened greatly, what would be the probable effect on the climate of polar North America? 3. Suggest reasons why the Antarctic has been less well explored than the Arctic regions. 4. Why do trees grow in higher latitudes in Asia than in North America (Fig. 62)? 5. What factors determine the course of the isotherm of 50 in Fig. 62? 6. Why is there an ice-cap over central Greenland and not over lands in the same latitude in northern Asia? CHAPTER XII THE OCEANS General Considerations Importance of the oceans. The oceans are of great importance to the rest of the earth in many ways. Their effects on temperature and atmospheric moisture have been noted (pp. 51, 57). The waves of all seas are constantly wearing away the land in some places, and ^>i Un.King. $ 550 29.5' Germy 258 13.8* France 115 6.2* Nether. 84 45* Italy 52 2& Other 120 71 = n Austral. $3 Japan 26 14* Phil.Ts. 19 I.O* China 15 OS* India 7 oa' Other 23 13< Argent *42.7 23* Brazil 24.9 1.5* Chile 9.9 05* Other 22.5 t2* Y- Br.S.APr. $11.4 CXfe' PortAfr. 3.4 0.2< Br.WAfr. 2.5 Egypt 13 Other 25 w° Fig. 63. Diagram showing destinations of exports from the United States by continents and leading countries (1910). (Values in millions of dollars; per- centages are proportions of total exports.) building new land elsewhere. On the whole, destruction exceeds building, so far as land is concerned; consequently, the ocean tends to increase its area at the expense of the land (p. 348). The oceans are an important source of food, and furnish large amounts of other useful materials. Thousands of people are em- 140 COMMERCE OVER THE OCEAN HIGHWAY 141 ployed in getting commercial products from them. Other thousands are engaged in the carrying trade on the seas. Formerly the oceans were barriers to travel and communication, but swift steam- ships and cable lines now make communication between the con- tinents easy. The voyage across the Atlantic formerly took as many weeks as it now takes days, while the happenings of this morning in Europe may be printed in the evening papers of Buenos Aires. Nine-tenths of our foreign trade is carried by vessels. Enormous quantities of goods are shipped annually to the United States from all the leading countries of the world, and from the United States to these countries (Figs. 63 and 64), over the ocean highway. Distribution and area. The oceans encircle the earth in latitude 6o° S. (Fig. 57), and the waters south of 40 S. are sometimes called Fig. 64. Diagram showing sources of imports to the United States by con- tinents and leading countries (1910). (Values in millions of dollars; percentages are proportions of total imports.) the Southern Ocean. From it the Atlantic, Pacific, and Indian oceans extend northward thousands of miles. In the northern hemisphere the land makes an almost complete circuit in latitude 6o° to 70 (Fig. 58), whence it extends southward in two great arms. North of latitude about 70 lies the Arctic Ocean, almost surrounded by land i 4 2 THE OCEANS (Fig. 62) and therefore with but narrow connections with the larger oceans. The area of the different oceans is about as follows : Arctic Ocean 5,200,000 square miles Indian Ocean 28,000,000 square miles Atlantic Ocean 35,000,000 square miles Pacific Ocean 67,000,000 square miles Southern Ocean 5,700,000 square miles Exploration of the ocean. The motions of the surface waters; such as waves and tides, may be studied from the shore, but it has taken the work of many exploring expeditions to give us our present knowledge of the depths of the ocean. The depth of the ocean is known by soundings, which are made from ships by reeling out a heavy weight held by a fine steel wire. A sounding of 3,000 fathoms (a fathom = 6 feet) can be made in about an hour. A series of soundings in any region give a fairly accurate idea of the form of that part of the sea-floor. Small samples of sediment from the bottom of the sea are brought to the surface by various sorts of apparatus. Larger samples of material from the bottom and specimens of deep-sea life are obtained by dredges. Another device, known as a water-bottle, is used to secure samples of water from various depths, while a self-registering thermometer records the temperatures at different levels. Materials of the bottom. Most of the sea-bottom is covered with soft sediment. Some of it was carried to the sea by rivers, some was worn from the shores by waves, some was blown from the land, some is made up of the shells and skeletons of organisms which lived in the water, and some consists of fine debris thrown out from vol- canoes beneath the sea. A little cosmic (" shooting-star") dust is also present. Near many shores, gravel and sand from the land cover the bottom. Beyond the gravel and sand, fine sediments, such as mud and clay, prevail; but sediments of organic origin are found in many places. Thus coral reefs and mud made by the grinding up of coral by waves are found in shallow water in many places in low latitudes. Ooze is the name applied to those soft materials of the sea-bottom composed largely of the shells and other hard secretions of tiny organisms which live in the water. Many of them live near the surface, and their shells sink when the organ- isms die. The various oozes are named from the animals and plants which con- tribute most to them. Below the depth of about 2,200 fathoms, the ocean-bottom is covered with red clay, the particles of which came from many sources. THE DEPTHS OF THE SEA 143 Most of it consists of the decomposed products of (1) materials thrown out from volcanoes, (2) dust blown from the land, (3) shells and other hard parts of marine life, and (4) meteors. Depth and pressure. The average depth of the ocean is about two and one-half miles, or nearly 13,000 feet. The depth exceeds four miles in many places, and the area of very deep water is much greater than that of very high land. The areas which are far below the average depth of the ocean are known as deeps. The greatest depth of water known, 32,078 feet, is in the Pacific Ocean, near the Philippine Islands. This depth is more than the height of the highest mountain (Mt. Everest, 29,002 feet) above the sea. There are other areas exceeding five miles in depth in the Pacific, which is the deepest ocean. The greatest depth of water known in the Atlantic is Blake Deep (27,366 feet), north of Porto Rico. In few other places in the Atlantic does the depth reach 20,000 feet. The Indian Ocean is not known to have depths much exceeding 20,000 feet, and the deepest known places in the Arctic and Antarctic seas are still less. The pressure at the bottom of the oceans is very great. At a depth of one mile, it is about a ton to the square inch, while in the greatest depths it is six tons. This pressure would crush some kinds of stone. Yet the ocean water does not become much denser (is not compressed much) even under so great pressure. Objects such as pebbles, which sink readily at the surface, sink readily to the bottom. Topography of the bottom. The surface of the land is made rough in various ways, especially by running water and winds; but most of the sea-bottom is nearly flat. In spite of its general flatness the sea-bottom has many irregularities, for there are (1) volcanic cones, some of them built up from the bottom of the deep sea to elevations far above its surface (p. 194) ; (2) steep slopes, such as those (a) between the continental platforms and the deep-sea basins and (b) about some of the deeps; (3) valley-like depressions, especially on the continental shelves; (4) great ridges somewhat like the mountain ridges of the land; and (5) broad, plateau-like swells. Submarine slopes as great as 1 mile in 8 are rare, and 1 mile in 20 not very common. The latter would make a steep railway grade. Volcanic cones are most numerous in the Pacific Ocean. Many of the valley- like depressions on the continental shelves are continuations of valleys on land. Thus the Hudson, Delaware, Susquehanna, St. Lawrence, and other valleys are continued out under the sea. Such submerged valleys are thought to have been 144 THE OCEANS formed by rivers when the areas where they occur were land. Examples of moun- tain-like swells are furnished by Cuba and the adjacent islands, which are really the crests of a great mountain system rising from deep water. Composition of sea-water. One hundred pounds of average sea-water contain nearly three and one-half pounds of dissolved mineral matter. More than three-fourths (nearly 78 per cent) of this is common salt, but nearly all other substances found in the earth's crust are present, most of them in very small quantities. If all the salts dissolved in the sea were taken out of solution and laid down as solid matter on the ocean-bottom, they would make a layer about 175 feet thick. In the past, the evaporation of water from salt lakes, perhaps cut off from the sea by changes of level, has formed important salt-beds. New York has a valuable salt industry near Syracuse, depending on such deposits of rock salt (p. 183). The mineral matter in sea-water makes it a little heavier than fresh water, and makes it freeze less readily. Its lower freezing point (26°-28° F.) often leaves the ocean free from ice when nearby bodies of fresh water are frozen over. Sources of mineral matter. Dissolved mineral matter is being carried to the sea by rivers all the time, and they have brought the sea most of its mineral matter, though some of it may have been dis- solved from rocks beneath the sea, or about its shores. The mineral matter carried in solution to the sea by rivers in a year would make nearly half a cubic mile of solid matter. Those minerals of the land which are dissolved most easily get into rivers, and thence to the sea, in greater quantity than those which are less soluble. Withdrawal of mineral matter from the sea. Of the mineral matter carried in solution to the sea, calcium carbonate, of which most shells are made, is most important to ocean life. The amount of this substance dissolved in river-water is nearly as great as that of all others. The amount of common salt in river-water is too small to be tasted; yet the amount of it in sea- water is more than 200 times that of calcium carbonate. The reason is that calcium carbon- ate is taken out of the water all the time by animals, to make shells, coral, etc., while most of the salt carried to the sea stays in the water; and this probably has been true for millions of years. Gases in sea-water. Sea-water also contains dissolved gases, the most abundant being nitrogen, oxygen, and carbon dioxide. The amount of oxygen dissolved in the ocean is more than V300 of that in the air; the amount of nitrogen about Vioo that of the air, TEMPERATURE OF THE SEA 145 while the amount of carbon dioxide in the sea is 18 times that in the air. Much of the gas in the ocean was dissolved from the atmosphere. The oxygen of the water is being used all the time by sea animals, and its supply is being renewed all the time by solution from the air. Animals and plants do not use the nitrogen dissolved in sea-water, and the same nitrogen probably stays there from age to age. The carbon dioxide is being used all the time by the plants of the sea, and some of it is constantly escaping into the air. Salinity, density, and movement. For several reasons, some parts of the sea are more salty than others. (1) The salt is left behind when ocean- water evaporates. Since evaporation is more rapid in some places than in others, the water becomes more salty where evaporation is great, as in some hot climates. (2) Where much rain falls, and (3) where large rivers enter, the sea- water is freshened. In these ways the saltness of the sea- water at the top of the ocean is changed all the time. Every change in the saltness of sea-water changes its density, and unequal density causes movement. When surface water becomes denser than that beneath, it sinks, and lighter water comes in over it from all sides. When the surface water of one place becomes less dense (fresher) than that about it, the lighter water spreads out on the surface, as oil spreads on water. Since variations in saltness are being produced all the time, motion due to unequal density is constant. Movements brought about in this way are usually very slow. Temperature of the Sea Temperature of the surface. The surface of the ocean, like that of the land, is warmer near the equator and cooler toward the poles (Fig. 65). Near the equator its temperature is about 8o° F.; near the poles, where not frozen, it is 26°-28° F. When frozen, the surface of the ice may become as cold as the air above it; but the tem- perature of the water just beneath the ice is 26 — 28 F. The de- crease of temperature toward the poles is by no means regular, as shown by the isothermal chart (Fig. 65). In the open .sea, ocean currents help to make the isotherms depart from the parallels (p. 51). Some currents are cold, flow- ing into warmer water, and some are warm, flowing into cooler water. 146 THE OCEANS Rivers help to make surface temperatures unequal, for many of them are warmer than the sea in summer, and colder in winter. Part- ly enclosed arms of the sea in low latitudes are warmer than the open ocean in the same latitude. Temperature and movement. Water expands slightly when warmed. Warm water is therefore lighter than cold water, if both are equally salt. It follows that unequal surface temperatures cause movement of the surface waters, and since the surface temperature is kept unequal all the time by unequal heating, by inflow of rivers, Fig. 65. Map showing mean annual temperatures for the surface waters of the oceans. (After Lyde.) and by melting ice, there is constant though slow movement of the surface waters. Temperature beneath the surface. Sea-water becomes cooler with increasing depth, except where the surface is at or near the freezing point. Even where the surface water is warmest, the temperature at a depth of a few hundred fathoms is below 40 F. It is estimated that not more than one-fifth of the water of the ocean has a temperature as high as 40 F., while its average tempera- ture is probably below 3c) F. Only in certain areas of shallow water, and in the partly enclosed seas of relatively low latitudes, is the tem- perature of the water at the bottom as high as 40 . WAVES, CURRENTS, AND TIDES 147 Movements of Sea- Water Causes We have seen that differences in saltness and in temperature make waters unequal in density, and so produce a slow circulation of the waters of the sea. There are other things which produce move- ment, such as (1) differences of level, (2) winds, (3) the attraction of the moon and the sun, and (4) occasional causes, like earthquakes and volcanic explosions. Inequalities of level. The inequalities of level which produce movements of sea- water are brought about chiefly by (1) the in- flow of rivers, which raises the surface of the sea near their mouths; (2) winds, which pile up the water along the shores against which they blow; (3) unequal rainfall, which raises the surface most where most rain falls; and (4) unequal evaporation, which lowers the sur- face most where it is greatest. Movements due to unequal rainfall and evaporation are too slight to be seen. Those caused by the inflow of rivers and by winds are greater. Thus, beyond the mouth of a great river like the Amazon, movement may be distinct for many miles, and waters often are piled up against a shore by winds, so that the rise is seen readily. The raising of the surface of the water caused most of the destruction in the storm at Galveston (p. 92). When the water-level along a coast has been raised by the wind, it settles back after the wind goes down. Since the causes producing differences of level are always in operation, movements due to these differences are always taking place. Winds. Winds produce movement of sea-water in another way. Where they have a constant direction, as in the zone of trades (p. 105), there is a constant drifting movement of surface water in one direc- tion. A steady movement in one direction necessitates a return move- ment somewhere else, thus producing a circulation of the sea-water. Where the circulation is in the form of distinct streams of water, they are called ocean currents. Attraction of moon and sun. Bodies attract each other in proportion to their masses, and inversely as the squares of their distances. That is, a body which weighs twice as much as another has twice the attractive force at the same distance. If one of two bodies of the same mass (or weight) is twice as far from a third body as the other is, their attractive forces on the third are as 1:4. The side of the earth toward the moon is nearer the moon ( by 148 THE OCEANS about 4,000 miles) than the center of the earth is, and so is attracted by that body more strongly than the center. The opposite side (about 4,000 miles farther away) is attracted less strongly than the center, and these differences of attraction disturb the waters of the earth. The attraction of the sun produces similar, though lesser, effects. Movements of the sea-water, known as tides, are the result. Occasional causes. Landslides along shore, earthquakes, and volcanic explosions may cause sudden and extensive movements of the ocean-water (pp. 191, 197). Low coastal lands occasionally suffer severely from movements of this sort. Types of Movement The principal movements which result from the above causes are (1) waves, with the undertow and shore currents (p. 346) which they produce; (2) ocean currents; (3) drift, or feeble currents; and (4) tides. Waves. When the wind blows over a water surface it causes waves. The stronger the winds, the greater the waves. With moderate winds, waves in open water rarely exceed 10 feet in height (from crest to trough). Ordinary storm-waves may be twice as high, while in violent storms a height of 40 or more feet is attained. Such waves breaking on the decks of vessels may do much damage. Storm- waves travel 30 to 60 miles an hour, but, save in shallow water, the water in a wave usually does not move forward (p. 346). The distance between successive wave crests is the length of the wave. Wave lengths vary from 100 feet or less, to 2,000 feet or more in severe storms. Occasionally the surface of the ocean is smooth and glassy, and yet shows long, low undulations. These are "swells," and usually represent waves caused by distant storms. On some coasts they interfere seriously with commerce. Short, "choppy" waves are especially unfavorable for small craft, and may cause much discomfort to passengers on larger vessels. In general, the longer the vessel, the less it is affected by waves; hence the advantage of the modern ocean steamships, which in many cases are twice as long (700 to 800 feet) as the average storm-wave. Currents and drifts. There are more or less distinct streams of water, or currents, in various parts of the ocean. This was known first by their effect on the course of sailing vessels. It was later proved in other ways, as by following the course of floating objects set adrift for this purpose. The course of currents is important because of their effect on navi- THE GULF STREAM 149 gation. In foggy weather, and especially near some coasts, failure to allow for the current may lead to ship-wreck. Some of the wrecks that have occurred on the Irish coast probably were caused in this way. Vessels are aided or retarded by currents, according to the direction of the voyage. Surface currents affect the movements of icebergs and floe-ice. Collision with an iceberg may wreck the largest steamship, as the Titanic, and floating ice favors the forma- tion of fog, which increases the danger of collision. For these reasons, steamship routes across the North Atlantic vary somewhat with the season, in order to avoid the floating ice. Little is known of ocean currents beneath the surface. Most of them are shallow, compared with the depth of the ocean. A current so slow as to be indistinct often is called drift. Courses and causes of ocean currents. Fig. 66 shows the general circulation of the surface waters of the sea. It represents a large part of the surface water as moving. There are equatorial currents or drifts moving westward, one on each side of the equator, in both the Atlantic and Pacific oceans. The westward-drifting equa- torial waters of the Atlantic are divided at the coast of South America. The smaller part is turned to the southwest, and the larger part to the northwest, along the border of the continent. Part of the northern branch flows through the Caribbean Sea into the Gulf of Mexico, whence it issues through the narrow strait between Cuba and Florida as the Gulf Stream. This well-defined current is fed partly by the water which enters the Gulf from the equatorial drift, and partly by that which enters from the land. In the Straits of Florida, the Gulf Stream is about 40 miles wide in its nar- rowest part, 2,000 to 3,000 feet deep, and has a maximum velocity of about five miles per hour. Farther north it becomes wider and slower, until, in the open ocean, the rate is perhaps only 10 to 15 miles per day. As it becomes slow, its boundaries become less distinct, and it is recognized by its temperature, color, and life more readily than by its motion. As it advances, the Gulf Stream turns toward the east (to the right), crosses the Atlantic, and approaches the coast of Europe in a latitude farther north than that where it leaves the coast of America. As it approaches Europe, it divides and spreads, but long before Europe is reached (about latitude 40 N.), the current has become a widespread drift of water, not easily distinguished. This favorable current and the westerly winds make the voyage for sailing vessels from this country to England much quicker than the return trip. iSo THE OCEANS That part of the equatorial drift which is turned southward along the coast of South America soon turns to the left (Fig. 66). The equatorial drifts of the Pacific follow courses similar to those of the Atlantic. The part which turns north is the Japan Current. The Indian Ocean has a south equatorial drift only, and its course corresponds to that of the southern part of the equatorial drifts of the other oceans. All currents moving toward the poles from the equatorial region are warm currents. The movement of warm waters into the polar oceans makes a return movement necessary. Cold waters moving equatorward from these oceans are turned to the right in the northern hemisphere, and to the left in the southern. The result is to throw them to the eastern coasts of the continents, where in places they form distinct cold currents. Along the east coast of North America, the Labrador Cur- rent sometimes brings icebergs south to latitude 40 , while in the warmer waters of the northeastern Atlantic, drift-ice rarely is encountered south of latitude 70 . The Labrador Current chills the air above it, and this helps to make northeast winds in New England cold. The equatorial drifts are caused and directed by the trade-winds. Outside the tropics the winds do not blow in one direction all the time, and so do not produce persistent drifts or currents. In regions of strong monsoon winds, as about India, the drift of the surface waters changes with the wind. If the ocean covered all the earth, the westward drift of equatorial waters caused by the trade-winds would go round and round the earth. But the continents deflect the waters, turning them north and south. Once turned in these directions, the waters would tend to follow the coasts but for the deflecting influence' of the earth 's rotation. Where the sea is so shallow that the moving water touches bottom, the topography of the bottom influences the course of move- ment. Ocean currents therefore appear to be started chiefly by the winds, and to be directed by winds, lands, and the rotation of the earth, and, to a less extent, by the topography of the bottom. Ocean currents and atmospheric temperatures. Without ocean currents, the isotherms over the sea would follow the parallels some- what closely, except near the continents (p. 51). Under such conditions, the temperature over the ocean in the latitude of the British Isles and northward would be io° F. or more lower than now (Fig. 65). Ocean currents do not themselves warm or cool the land; but the air over a warm current is warmed by THE CURRENTS OF THE SEA 151 iS2 THE OCEANS the water, and is then blown to the land. Even without the Gulf Stream, the western coast of Europe would have a milder winter climate than the eastern coast of North America in the same latitudes (p. 51), but the drift of warm water into the North Atlantic makes the winter temperature of Europe north of latitude 50 considerably warmer than it would be otherwise. Thus the harbor of Hammer- fest, Norway, Lat. 76 , is affected by ice little more than that of New York, Lat. 40 . The Japan Current likewise lessens the cold of winter on the northwestern coast of North America. Warm currents often help to cause fogs, both at sea and on land. When wind blows over a warm current, it takes up a large supply of moisture. If it then blows over colder water, it is cooled, and some of its moisture is condensed, producing a fog. Fogs are common along the Gulf Stream, especially where the adjacent land or water is much cooler than the current itself. Fogs are more abun- dant about Newfoundland than farther south, because the difference between the temperature of the Gulf Stream and its surroundings is greater there than farther south. Tides. Along most coasts the ocean-water rises and falls twice every day, or, more exactly, every 24 hours and 52 minutes. The rise and fall of the water are the tides. The tide rises for about six hours, when it is high or flood tide, and then falls for about six hours, when it is low or ebb tide. In most places there is a distinct interval of little or no movement (" slack water") when high tide changes toward low, and vice versa. The rise and fall amount to several (3 to 6) feet in most places. In bays which open broadly to the sea, but are narrow at their heads, the range is sometimes 20 or 30 feet, and in rare cases, as in the Bay of Fundy (Figs. 67 and 68), 50 feet or more. Where bays have a narrow entrance and widen within, the tidal range is small. Tides are absent in small lakes, and are feeble in large lakes and in seas connected with the ocean by a narrow passage, such as the Mediterranean Sea and the Gulf of Mexico. In many shallow harbors the tides have an important effect on navigation (Figs. 67 and 68). Even some of the most important ports depend on the rise of the tide for the movement of their com- merce. Thus at Liverpool vessels arriving at low tide must wait, in many cases, for high tide, before the water is deep enough for them to dock, and vessels must arrange hours of departure to match high tides. Where the tide runs in among islands, or passes through narrow straits, it causes distinct currents (tidal races), eddies, and whirlpools, \ TIDES AND COMMERCE 153 like the famous Maelstrom near the Lofoten Islands. Sailing vessels frequently have serious difficulties with tidal races, as at Hell Gate, New York, and in Vineyard and Nantucket sounds, off the coast of ■^ 1 Fig. 67. Low tide at Wolfeville, Bay of Fundy, Nova Scotia, Sept., 1903. In March, 1904, the end of the pier was washed away in a storm, and the light- house was damaged. (Roland Hayward.) Massachusetts. Fishermen commonly speak of the tide as " coming in," or " going out," and time their movements to take advantage of In many ways tides are more important to navigation than ocean it. 4 JJLT Fig. 68. High tide at the same place shown in Fig. 67. (Roland Hayward.) currents, and much effort is devoted to charting them for the benefit of navigators. The tide runs far up many rivers. At Troy, some 150 miles up the Hudson River, the range of the tide is more than two feet, and tides ascend the St. Lawrence nearly 300 miles. 154 THE OCEANS It is at least two thousand years since the moon was first thought to cause the tides, but only about two hundred years since Newton explained how the moon produces them. Without attempting to give a full explanation of the tides, some of the principles involved may be understood. If a weight is attached to a string and whirled, it tends to fly away in a straight line. It is prevented from doing so by the string, which holds it in its circular path. The tendency to fly away is what Fig. 69. Diagram to show the tendency of the moon to raise the water on the side of the earth toward the moon and on the opposite side at the same time, producing two high tides. is called centrifugal force. The earth and moon attract each other (p. 147), and would fall together but for the centrifugal force due to their motions. At the center of the earth, and at the center of the moon, the attraction between these bodies is exactly balanced by the centrifugal force due to their revolutions. The result is that neither falls toward the other. But on the side of the earth nearest the moon the attraction is stronger than at the center of the earth (p. 148), and is greater than the centrifugal tendency. The attraction of the moon, therefore, tends to make the earth bulge out on the side nearest the moon. On the opposite side of the earth the attraction is weaker than at the center, and is less than the centrifugal force. Here, too, the earth tends to bulge out. The solid part of the earth is so rigid that it does not rise enough to be felt or seen. But the waters of the ocean . Fig. 70. Diagram to show the relative positions of the earth, moon, and sun, at the time of new moon ( = spring tide). Size of moon (M) and earth (E) great- ly exaggerated. move easily, and rise a little, and the rise takes place on opposite sides of the earth at the same time. This makes the. high tides. Between the high tides the water sinks a little, making the low tides. The rotation of the earth makes the tides appear to move about the earth. If all the earth were covered with water, its surface would have two great tidal bulges or waves at the same time (Fig. 60). The highest part of one would be a point directly under the moon, and the highest point of the other would be opposite the first. Each wave would cover half the earth, and the borders of the two would meet in a great circle, where the surface of the water would be lowest. If the moon were not revolving about the earth, high tide at any place would come every 12 hours. But the moon moves forward in its orbit about the earth, THE CAUSE OF THE TIDES 155 so that it takes 24 hours and 5 2 minutes for a given place to have the same relation to the moon that it had the day before. This makes the period between successive high tides 12 hours and 26 minutes. The movements of the tides are not so simple as the outline above would imply. Many things interfere. The continents stop or divert the advance of tidal waves, and the waves travel more slowly in shallow than in deep water (Why?). Since tides are retarded most near land, their advance is here most irregular. For these reasons, the time of high tide at most places differs from the time when the moon Fig. 71. Diagram to show the relative positions of the earth, moon, and sun, at the time of full moon (= spring tide). crosses their respective meridians. This difference in the time of arrival of high or low tide may be determined for any harbor, and is called the " establishment of the port." At New York, for example, high water arrives 8 hours and 13 minutes after the moon passes the meridian. Tables showing the "establishment" of different ports are of great value to navigators. The sun also attracts the earth, and tends to cause tides. If there were no moon there would still be small tides produced by the sun. The tides which we know Fig. 72. Diagram showing the tendency of the sun and moon to produce tides on opposite parts of the earth at the time half way between new moon and full moon, and half way between full moon and new moon. are the combined effects of moon and sun, but the moon's tides are much the stronger. The sun strengthens the tides when sun and moon work together, and weakens them when they work against each other. When sun and moon stand in the relation to each other and to the earth shown in Fig. 70 (new moon), each tends to make high tides at A and at B. When the relations are those shown in Fig. 71 (full moon), the result is the same. At these times, and each occurs once a month, high tides are higher, and low tides lower, than at other times. The tides of such times are called spring tides. They have no relation to the spring season. When the earth, moon, and sun have the relative positions shown in Fig. 72, and this occurs twice each month, the tidal influences of the sun and the moon are 1 56 THE OCEANS opposed to each other, and the result is that high tides are not so high, nor low tides so low, as under other conditions. The tides of such times are known as neap tides. Spring tides have nearly twice the range of neap tides in many places. In the open ocean and along precipitous coasts, the tide is like other waves, merely a rising and falling of the water. Like other waves also, the water of the tidal wave moves forward when it ap- proaches shores where the water is shallow. In shallow waters near the coast, tides alternately cover and expose wide expanses of sandy beach or mud flats, as the case may be. The water-line at low tide may be a quarter of a mile or more from its position at high tide. Tidal currents may be effective agents of erosion, maintaining deep channels in harbors, to the great ad- vantage of commerce. By the circulation they cause, tides in some cases help to remove filth which otherwise would accumulate in harbors. Sewage disposal is always easier for cities near tide-water. On the other hand, the sediment drifted about by tides may be de- posited in harbors. This makes expensive dredging necessary, in order to maintain a sufficient depth of water for shipping. The frequent shifting of the deposits renders it impossible to indicate the channel on the pilot charts of some harbors. The large volume of water rising and falling in tides has led to many attempts to develop tidal water power. Small tide-mills are used for grinding grain and other purposes at various places in western Europe, and a few larger power plants have proved useful, as in the Seine estuary. The Life of the Sea Animals and plants abound at and near the surface of the sea, and at the bottom where the water is shallow. A bucket of water dipped up from the surface of the ocean almost anywhere will con- tain hundreds or even thousands of minute plants and animals, though most of them are too small to be seen without a microscope. Liv- ing things are present, but not in great numbers, at the bottom of the deep sea; but in the water between the uppermost ioo fathoms and the bottom, there is little life. The temperature, the depth, the clearness, the saltness, and the quietness or roughness of the water, influence the life which it con- tains, in ways easily understood. The depth of the water has little or no effect on plants and animals which float or swim near the sur- face; but at great depths the supply of oxygen is slight, and there THE LIFE OF THE SEA 157 is not light enough so that animals can see much below 50 fathoms. In the great body of the ocean darkness reigns, and green plants, which depend directly on sunlight, cannot live in darkness. Though the pressure of the water at the bottom of the ocean is very great (p. 143), the animals living there can stand it because their bodies are full of liquids under the same pressure, and these great pressures within their bodies balance the great pressures without. If an animal from the bottom of the deep sea were brought suddenly to the surface it would explode (Why?). Even when raised slowly, they sometimes explode as they near the surface. Some animals, such as the polyps which make coral, live only in warm regions. Others, such as narwhals and seals, are found only in cold waters. Still others are found in both warm and cold waters. The unequal distribution of ocean temperatures by warm and cold currents influences greatly the character of marine life in different parts of the sea. In many ways the life of the sea is in strong contrast with that of the land. Thus most familiar land plants are fixed in position, but many sea plants float. Most land animals are free to move about, while many of those in the sea, such as polyps and barnacles, are fixed through most of their lives. Many which are not fixed move about but little, either lying on the bottom or burrowing into it. Some, on the other hand, as many of those in the surface waters, appear to be moving always. All the great groups of animal life are represented in the sea. Even warm-blooded mammals (whales, seals, walruses, etc.) abound in frigid waters, among icebergs and ice-floes. Some of them, like the seals and walruses, do not spend all their time in the water, but frequently crawl up on the ice or land. Not only are there many varieties of marine plants and animals, but the largest modern animals (whales) live in the sea. Many sea plants, too, are of great size. Some sea-weeds are six inches in diam- eter, and some have a length greater than that of the tallest trees. The total value of food products — fish, oysters, clams, crabs, lob- sters, etc. — derived from the sea probably is not less than $500,000,- 000 per year. The best fishing regions are found where large areas of shallow water, as over broad continental shelves, furnish extensive feeding and breeding grounds for vast numbers of fish. The most important region of this sort is the area of shallow water about the British Isles, including the North Sea. The British fisheries employ 158 THE OCEANS more than 100,000 men, and yield an annual catch valued at more than $50,000,000. Similar conditions led to the development of im- portant fisheries from New England (p. 375). Other sea animals furnish other articles of commerce. The seal furnishes fur and oil; the whale, oil and whalebone; and the hide of the walrus makes exceptionally strong leather. Coral and sponges, products of animal life, are also articles of commerce. Sea-weed was Fig. 73. Coral formations, Samoa. (Muir and Moodie.) used formerly as the chief source of soda and of iodine. Some varieties still are gathered in large quantities on the coast of Massachusetts and Europe, to be used as food under the name of " Irish moss." Coral reefs. The little polyps (Fig. 73) which secrete coral live where the water (1) is 120 feet or less in depth, (2) is never colder than about 68° F., (3) has the saltness of normal sea- water, (4) is free or nearly free from sediment, and (5) is subject to some movement by the wind. Where these conditions exist, polyps thrive and make reefs, and the reefs may become islands. Polyps flourish along the borders of many tropical lands, and in some places far from shore. Coral reefs are of several classes. Those which are separated from the land by a somewhat deep channel or lagoon are barrier reefs. Those close to the land are fringing reefs. Rudely circular reefs CORAL REEFS AND ISLANDS 159 inclosing a central lagoon are atolls. The chief importance of coral reefs is their relation to navigation. Atolls frequently afford shelter to vessels in distress. Submerged reefs, however, are dangerous, and long barrier reefs may hamper commerce seriously, as along the east coast of Australia. The use of pink or red coral for jewelry leads to important coral " fishing" in the Mediterranean, whence much of the product goes to India. Most of the natives of coral islands are backward in civiliza- tion, because of the limitation of their resources. Questions 1. Why is agriculture possible on a limited scale in Alaska, and not in the same latitudes in Labrador, Greenland, and Baffin Land? 2. Why is Alaska less favorable for agriculture than Norway? 3. Why is the climate in latitude 50 , on the west coast of South America, less favorable for farming than that in latitude 50 on the west coast of North America? 4. Why are isotherms (Fig. 65) affected less by ocean currents in the southern hemisphere than in the northern? 5. Why is the water along the equator in the Pacific Ocean warmer toward the western border of the ocean? What does the principle involved suggest in regard to the surface temperatures in the Gulf of Mexico? 6. Why are steamer routes across the Atlantic farther south in summer than in winter? 7. In order to enter a shallow harbor, is a vessel more likely to have to wait for flood tide at the time of neap tides or at the time of spring tides? Why? 8. On which side of the Gulf Stream, in latitude 45 , are fogs more com- mon? Why? 9. Are fogs more likely to occur over a warm current, or over a cold one? Why? 10. What inference might be drawn from the fact that polyps once lived within the Arctic Circle? n. What changes in geography are implied by the fact that polyps once lived in eastern Wisconsin? CHAPTER XIII THE MATERIALS OF THE LAND AND THEIR USES General Constitution The mantle rock. The loose material such as soil, clay, sand, and gravel, which covers most of the land, is called mantle rock, because it forms a mantle over the solid rock beneath. Mantle rock varies in thickness from a few inches to scores or even hundreds of feet. It is formed by the decay and breaking up of solid rock, and for this reason is called also rock waste. Soil is the uppermost part of the mantle rock, which serves as a source of food for plants. It varies in thickness from two or three inches to as many feet, and locally, much more. Soil consists of small particles of minerals, usually mixed with partly decayed vegetable matter {humus) . Both mineral and organic matter are necessary parts of a good soil, but their proportions vary greatly. In color, soil may be yellow, dull red, gray, brown, or, when much humus is present, black. It may be either clayey and compact, or sandy and porous. In order to support plant life, soil must contain both air and water. Air always is present in sufficient amount, unless crowded out by excess of water, as in some swamp soils. On the other hand, the necessary amount of water may be lacking, as in deserts. Such soils are barren, even though perfect from the physical and chemical stand- points. In western United States, large areas of barren land need only water to be of great value. In excavations, as for cellars, wells, railway cuts, and the like, soil may be seen to grade down, in many places, into subsoil, which is different in color and texture from the soil above. In most places the subsoil is much thicker than the soil, though it may be absent altogether. Solid rock. Beneath the subsoil is solid rock (Fig. 74). This extends down to great depths, probably even to the center of the earth. In interior United States, solid rocks may be seen chiefly in quarries, mines, along the courses of certain rivers, and in a few 160 THE SOIL A FUNDAMENTAL RESOURCE 161 other situations; but in eastern Canada, in western Scandinavia, among high mountains generally, and in many other places, they come to the surface over large areas. Such places have little value from the standpoint of agriculture, even though other conditions are favorable. Soils Importance to man. Man, depends, directly or indirectly, on soil for most of that which he eats and wears. Products of the soil furnish the principal articles of commerce, and its cultivation con- Fig. 74. Diagram showing soil grading into solid rock beneath. stitutes the chief basis of civilization. These relations, too, are last- ing ones. Whether the United States shall in the future support a numerous, well-to-do, progressive population, or a sparse, under-fed, and non-progressive one, is largely a question of whether the soil of the country is kept abundant and fertile. In 1900, more than a third of the wage earners of the United States were employed in farming. The Making of Soils We have seen that most soils are formed by the decay and break- ing up of solid rocks. All changes which make solid rock crumble are processes of weathering. The weathering of rock prepares it for transportation by wind and water. Chemical processes. The oxygen, carbon dioxide, and water vapor of the air are active chemically. The meaning of chemical l62 MATERIALS OF THE LAND — THEIR USES action is illustrated by the rusting of iron. Iron rust is composed of iron, oxygen, and water. Oxygen and water from the air enter into chemical combination with the iron. While all three of these substances are in the rust, the rust does not look like any one of them. The union of oxygen with any other substance, as iron, is oxidation. The union of water with another substance is hydration. Iron rust is therefore oxidized and hydrated iron. If rusting is allowed to continue, iron is, in time, "eaten away"; that is, it crumbles to pieces. In this case, as in many others, chemical change produces physical change. Many rocks contain iron which may be oxidized and hydrated. When such rocks are exposed to the air, therefore, the iron in them is changed (rusted), and this tends to make the rock crumble. Other chemical changes tend to produce the same result. Some of the substances made by chemical changes in the rocks are soluble, and if they are dissolved and carried away by waters passing through the rock, the rock from which they are taken is left more porous, and weaker. Some rock-making minerals are soluble without chemical change, so that solution is one of the most important means by which rocks are made to crumble, and by which soils are formed. Mechanical proc- esses, (i) When water freezes, it ex- pands about one-tenth of its volume, and in doing so exerts great force. When it freezes in rock cavities which it nearly fills, it acts like a wedge, and may pry the rock apart and break off pieces. This process of rock-break- ing is most important when there is abundant moisture, and where the changes of temperature above and below the freezing point of water are fre- quent. Rock-breaking is a first step in the making of soil from rock. Fig. 75. Surface of bowlder scaling off under changes in temperature. (Taff, U. S. Geol. Surv.) HOW SOIL IS FORMED 163 (2) Where solid rock has no covering of loose material, as on many steep slopes, it is heated by day and cooled by night, and the daily changes of temperature may be great. Rocks ex- pand when heated and contract when cooled, and under daily heating and cooling their surface parts break and scale off (Fig. 75). The breaking of cold glass when touched with hot water, or of hot glass when touched with cold water, involves the same principle. The shattering of rock by heating and cooling is very common, particularly in high moun- tains. Thus the upper part of many a mountain is covered with broken rock (Fig. 76), so insecure that a step may loosen many pieces and start them down the mountain. Great piles of such debris (called talus) bury the bases r HP"^ 1 "*! m ■ : ;+< 1 ' ' 1 L" ft 1 V:*^ Fig. 76. Summit of Granite Peak, Wa- satch Mountains, showing broken character of the rock. (Church.) Fig. 77. View showing long talus slopes. (Russell, U. S. Geol. Surv.) i6 4 MATERIALS OF THE LAND— THEIR USES of some mountains to the depth of hundreds of feet (Fig. 77). This debris tends to decay, gradually forming soil, after which, if other conditions are favorable, the slope is occupied by plant life. (3) The growth of roots in cracks in the rocks may enlarge the openings, and so help to break the rocks (Fig. 78). (4) The multitudes of burrowing animals make openings in the ground, and bring large quantities of loose material to the surface, where it is exposed to air and water, and is by them changed to soil. (5) Rivers wear the bottoms and sides of their channels, and so help reduce solid rocks to fine material. (6) Glaciers grind and crush masses of rock into such fine mate- rial that some of it is called "rock flour." Much of the mantle rock of northeastern United States was ground up by ancient glaciers (p. 2 5i). (7) In many dry regions, wind- driven sand wears exposed rocks and forms much fine, loose material, capable of becoming soil. Classes of Soils In the paragraphs which follow, the term soil is used to include the subsoil also, where the distinction between them is not important. Soil which remains above the solid rock from which it was formed is residual soil (Fig. 74). On the other hand, transported soil has been brought from its place of origin to its present position by some of the agents (wind, water, or ice) which transport materials on the surface of the earth. In general, transported soils are richer than residual soils, though this is not always the case. Residual soils. All kinds of rock decay, and the decayed rock, properly weathered, becomes soil. Residual soils vary greatly in fertility, much depending on the character of the parent rocks. Thus most sandstones weather into poor soil. Shales produce clay soils of greater average fertility, but in some cases they are heavy, and hard to work. Limestone soils are, as a class, very fertile, but if their Fig. 78. A tree growing in a crack in the rock. The growth of the tree widens the crack. Sierra Nevada Mountains, California. CLASSES OF SOILS 165 limey constituents are dissolved out, as they may be, the soil is less fertile. Transported soils. Transported soils are much less uniform in composition and texture than residual soils. In many cases they represent material gathered from a large area, and are entirely unlike the rocks on which they rest. Sediment transported and deposited by rivers is alluvium, and soils formed on alluvium are alluvial soils. Such soils in the flood-plains and deltas of great rivers, when not too wet, are commonly of great fertility. The rich soil of the great alluvial fan (p. 235) of the Hwang-ho, in China, supports one of the densest populations in the world. Ancient civilizations were confined so generally to rich flood-plain soils that the period before 800 b. c. has been called the Fluvial Period. Eolian soils are formed from sand or silt deposited by the wind. Eolian deposits cover large areas in various regions (p. 202). While the sand is loose, and being blown about, it is hardly soil and offers little chance for agriculture. For this reason, part of an extensive area of sand-hills in western Nebraska has been set aside for a National Forest. It is believed that certain trees which can get along with little moisture may be grown there, and that the entire sand area, now almost worthless, may be covered with a profitable forest. Large areas of land have been reclaimed in this way in southwestern France. Wind has deposited loess in certain regions. Loess is a loam, of buff or gray color, coarser than clay, and finer than sand. Soils formed from loess are very fertile when well watered. Some of the best farming lands of the Rhine, Danube, and other European river basins have loess soils. Similar soils occur in some parts of the Mississippi Basin, particularly along parts of the Mississippi and Missouri rivers. Before the Civil War, the counties of Missouri covered with loess contained a larger percentage of slaves than most of the rest, and grew large quantities of tobacco. The loess-covered counties of eastern and southeastern Nebraska produce most of the corn, wheat, oats, and alfalfa grown in the state. They are settled more thickly, and have more improvements, than most of the rest of the state. Much of the mantle rock of Canada and northern United States was brought to its present position by the great ice-sheets which once covered the region (p. 251). This material is called drift. Soil formed from drift varies much in character and fertility. Some of i66 MATERIALS OF THE LAND — THEIR USES it is too sandy and some is too stony to be farmed with success, but much of it is of excellent quality. Since the glacial drift was made not very long ago (as geology reckons time) by the grinding up of rocks of many kinds, the soils made from it are likely to contain all the mineral elements needed for plant food. The Removal of Soils Relation of gain and loss. It has been estimated that in the United States it may take, on the average, 10,000 years to form a foot of residual soil (833 years for an inch). Slow as this rate is, it is faster than the average rate at which soil is removed by surface waters, winds, etc. If soil were removed faster than it is formed, the land would in time be without soil, as it is now in some places, espe- Fig. 79. View in the Apennine Mountains, near Florence. Shows the shall low, stony soil which remains after the loam has been washed away. By removing the slight protective cover of vegetation, the sheep promote further erosion. (Sketch from photograph by Willis.) daily on steep slopes. With the clearing away of forests and the plowing of land for agriculture, the rate of soil erosion was increased greatly, and it now exceeds the rate of soil formation over large areas. From parts of the Apennine Mountains (Fig. 79), Dalmatia, Pales- tine, and China (Fig. 80), where the land was cultivated for centuries, the soil has been washed away, and the land is now barren. This shows what must be expected in some parts of this country, if the washing away of soil is not checked. The Mississippi River carries, LOSSES FROM SOIL EROSION 167 on the average, more than 1,000,000 tons of the richest soil matter into the Gulf of Mexico every day. The work performed each year by the Missouri River in transporting material toward the sea is estimated to be equivalent to 275,000,000,000 ton-miles (a ton-mile is a ton carried a mile). All the railroads of the United States carried 800,000,000 ton-miles of freight in 1909. The annual loss to the 21 country from the washing and leaching of soil is estimated at some Fig. 80. View in the western part of the province of Chi-li, China. The erosion has been aided in places by recent deforestation. (Willis, Carnegie Insti- tution.) $500,000,000. Although the land, even of eastern United States, has been cultivated but a short time compared with that of Europe, yet nearly 11,000,000 acres once farmed have been abandoned. More than one-third of this area has been ruined for farming by the erosion of the soil. It has been estimated that the area thus ruined would, if covered by fertile soil, be capable of supporting a population greater than that of any one of the twelve least populous states. Doubtless the total loss to the country from the partial destruction of soil is even greater. Nor is this all. (1) The soil carried away may do much harm where it is deposited. (2) Streams which carry much sediment deposit some of it in their channels, thus interfering with navigation. (3) The clogging of river channels also helps to cause floods. (4) Res- 168 MATERIALS OF THE LAND — THEIR USES ervoirs, such as mill-ponds, may be filled with sediment, interfering with manufacturing. (5) Streams are polluted, interfering seriously with their use as a source of water supply for cities, and making- expensive filtering plants necessary. Factors controlling soil erosion. Several factors influence the rate of soil erosion. (1) It is greater on steep slopes than on gentle ones. Lands in the southern Appalachians have been cleared of forests and cultivated where slopes are so steep that the soil was washed away in eight or ten years, and the land abandoned. (2) It varies with the amount and distribu- tion of rainfall. The more the rainfall and the more rapidly it falls, the more rapid the erosion of the soil. The greatest storm of a year may wash away more soil than all the other rains of that year. (3) It is influ- enced by the presence or absence of vegetation, and in the case of cultivated land by the kind of crop. Bare soils, and those devoted to widely-spaced plants, wash faster than grass lands and forest lands. (4) It is affected by the texture of the mantle rock and solid rock. (Which would favor greater wash, compact or porous soil? Compact or porous material below the soil?) Prevention of soil erosion. There are various ways of reducing soil erosion. The more important are the following: (1) Deep and frequent tillage increases the power of the soil to absorb rain, and so reduces the amount of water running directly off over the surface. This is highly desirable apart from its effect on erosion, for few places have water enough to produce maximum crops. (2) Plowing and planting along contours (p. 16) produce little depressions and ridges at right angles to the slope. These tend to check erosion (How?). Plowing up and down a slope, on the other hand, increases erosion (Why?). (3) On steep slopes, wash may be reduced by making- a series of terraces or benches. Terracing is practiced in parts of the Fig. 81. Terracing in western North Carolina. (Sketch from photograph by N. C. Geol. Surv.) MINERAL PLANT FOODS 169 Piedmont Plateau (Fig. 81) and elsewhere in the South, and in many countries of Europe and Asia (p. 312). (4) The soil should be kept covered with vegetation as much as possible throughout the year. (5) Grasses tend to prevent wash in several ways (How?). (6) On slopes exceeding 18 or 20 in steepness, the soil is protected best by trees (Fig. 82), and, in general, such land should be devoted to forests. Lessening soil erosion is one of the most important prob- lems of conservation, and it depends very largely on individual land-owners. Mineral Plant Foods Proper care of the soil calls for (1) the prevention of erosion so far as possible, and (2) the keeping in the soil of the mineral mat- ters needful for plant food. The mineral sub- stances of importance are phosphorus, potassium, calcium, and silicon, though a few others are used in small quantities. Besides these mineral substances, plants need carbon, hydrogen, oxygen, and nitrogen. Different crops draw unequally on the mineral foods of the soil, and when one crop is grown on the same ground year after year, the soil may become poor in one or more of these foods, and its productivity be reduced. The almost exclusive cultivation of tobacco injured the soil in parts of colonial Virginia. This helped to send thousands of farmers west of the Appalachian Mountains in search of new land. Southern Wisconsin was primarily a wheat region from the 1830's to the 1870's, when the diminishing yields and the competition of the new, rich soils farther northwest led to the raising of other crops, and the adoption of better methods of farming. Where crops of different kinds are raised, one after another (rotation of crops), the soil remains in better condition; but unless the essential elements taken from the soil by plants are returned in some way, its fertility must diminish. Fig. 82. View showing effect of roots in hold- ing soil. San Juan Mountains, Colorado, near Silverton. (Fairbanks.) 170 MATERIALS OF THE LAND — THEIR USES " Worn-out" farms are common in the South and East, and even in parts of the Upper Mississippi Basin. Land may be kept from wearing out by giving it the elements it lacks, that is by fertilizing it. In some parts of the southeastern states, where the soil was made poor by the long-continued growth of cotton or tobacco, no crops are grown without the use of fertilizers. Natural processes tend to add to the soil the substances essential to plants. New soil is formed by the weathering of underlying rocks (p. 161), and ground- waters bring mineral matter in solution from below, which they may deposit near the surface, enriching the soil. In most cases, these processes of soil renewal and enrichment fail to balance the loss which results from the common methods of farming. While certain natural processes tend to enrich soils, surface and under- ground waters may also erode and leach them (p. 211), thereby reducing their pro- ductivity. The supplies of most of the elements which plants need are abundant in the air, the ground- water, or the soil. Hydrogen and oxygen are the constituents of water, and oxygen makes one-fifth of the atmosphere. The air contains an unlimited supply of nitrogen, but most plants get their nitrogen from compounds of that substance in the soil or in fertilizers (p. 29). Next to oxygen, silicon is the most abundant element in the earth's crust. Most rocks contain a little calcium, and limestone contains much. Carbon is derived from the carbon dioxide of the air. Potassium is a constituent of many common rocks, and there are large deposits of potassium compounds in various places. Wood ashes contain potassium, and for this reason they are good for land. Unlike the foregoing, phosphorus is a relatively rare element, and already the original amount in the soil has been diminished seriously in many parts of the United States. Guano, chiefly from islands off the west coast of South America, is an important source of supply, though little is imported into the United States. The bones of do- mestic animals are a second source, and the manufacture of phosphate fertilizer is an important industry at the great slaughtering centers. The bones of buffaloes, killed in great numbers years ago, have been gathered up by the train-load from the western plains and used in the same way. Enormous quantities of phosphorus are now lost in the sewage of great cities, and in the leaching of farm manure. This phosphorus should be returned to the soil, so far as possible. Some European countries are far ahead of the United States in this matter. Finally, the United States possesses the greatest known deposits of phosphate rock (rock containing much phosphorus), and because DISTRIBUTION OF SOILS IN UNITED STATES 171 phosphorus is to be a critical factor in the fertility of soil, these de- posits constitute one of the most important mineral possessions of the nation. In the Southeast, there are deposits in South Carolina, Flor- ida, Tennessee, and Arkansas. The first three of these states furnish nearly all the phosphate rock now mined in the United States. In addition, there are far greater deposits in Idaho, Wyoming, Utah, and Montana. There is, unfortunately, much waste of the poorer phosphate rock in mining — material which, if saved, would be of great value in the future. Unfortunately for the United States, too, increasingly large amounts of phosphate are being exported. It is not to be inferred from the above discussion that fertility of soil is deter- mined solely by its chemical composition. Its productivity is influenced also by (1) its physical condition (coarseness, fineness, etc.), (2) its water content, (3) the organic matter (humus, etc.) which it contains, (4) the minute organisms (especially bacteria) at work in it, (5) the presence of toxic bodies (the accumulated excreta of plants) , and by other factors. Furthermore, the yields obtained from a given soil are affected greatly by (1) the quality of seed sown, (2) the effectiveness of cultiva- tion, and, in many cases, by such things as (3) harmful insects, (4) plant diseases, and (5) weather conditions. The reduced yields of many long-cropped soils probably are due in part to causes other than the impoverishment of the mineral elements of plant food. General Distribution and Use of Soils in the United States The principal physiographic provinces of the United States are shown in Fig. 83. Since the settlement and development of these provinces have been influenced profoundly by the topography of the land and the character of the soil, the larger provinces may be considered briefly. The Atlantic and Gulf Coastal Plains. Much of the Coastal Plain is less than 100 feet above sea-level, though some parts of it are considerably higher. The underlying rocks are imperfectly cemented gravels, sands, clays, marls, and lime- stones. Along the coast there are extensive marshes, where most of the soil is too wet to cultivate. The draining of these swamps has been begun, as for example on the delta and lower flood-plain of the Mississippi, and when it is completed their rich soils will support many people (p. 301). Elsewhere, the soils of the Coastal Plain present great variety. Over the marls and limestones they are fertile, and over the sands, gravels, and clays, they are much less productive. Many sandy tracts, as in parts of southern New Jersey, have remained wooded and sparsely settled to the present. In the Carolinas such belts, called "barrens," long helped to separate the life of the tidewater country from that of the Piedmont Plateau. In contrast with the sandy areas, the bottom lands of the rivers, where not too wet, and the belts of limestone soils are the garden spots of the South. Here most cotton was grown before the Civil War, and most slaves were owned (p. 325). Here the negro population is densest to-day. It probably is true that the rich soils of many parts of the Coastal Plain, and the genial climate of the South, were re- sponsible for the continuance of slavery in the United States to the time of the Civil War. 172 MATERIALS OF THE LAND — THEIR USES The New England Hills. There is no continuous coastal plain in New England. The most important lowlands have developed on weak rocks in the Connecticut Valley, about Narragansett Bay, and around Boston. On these low- lands the early history of Connecticut, Rhode Island, and Massachusetts centered. To-day, the Boston Basin contains about half the people of Massachusetts, and one-fourth those of all New England. Apart from these lowlands, most of New England is hilly. Much of its glacial soil is thin and poor, and in many places stony. It has been estimated that in some parts it took, on the average, one month for a man to remove the stones from each acre of glacial drift, to get it ready Fig. 83. States. Map showing the principal physiographic subdivisions of the United for farming. Many of the early settlements were made in areas of stratified drift (p. 266), where the bowlders were fewer and the land flatter. The unfavorable soils and the harsh climate prevented a high development of agriculture in New England, which was without a single staple crop for export, such as colonial Virginia had in tobacco, and South Carolina in rice and indigo. By the close of the seventeenth century, more than half the people of New England were engaged in industries other than agriculture, and it is said also that more than half the time of the farmers was given to non-agricultural work. For two centuries the life of New England was dominated by industries centering in the ocean — chiefly fishing, shipbuilding, and the carrying trade. Later, manufacturing became the leading interest. Crude methods of agriculture in early days led to the exhaustion or partial exhaustion of many lands which were originally good for farming. When the lands (eased to produce good crops they were deserted. Much has been written and said of the abandoned farms of New England, but in recent years many of them have been brought under cultivation again, and with the improved methods of to-day they are producing satisfactory returns. It seems certain that many of the DISTRIBUTION OF SOILS IN UNITED STATES 173 abandoned farms will be reclaimed. Much of the rough, infertile upland, however, probably can be used to best advantage in the future for forests. The Piedmont Plateau. The Piedmont Plateau has an elevation varying from 250 or 300 feet at its eastern edge, to about 1,000 feet in places along its western margin. The higher lands have a rather poor, residual soil, but many of the valleys have rich, alluvial bottoms. The Appalachian Mountains. The soils of the larger valleys are fairly fertile. This was strikingly true, originally, of the limestone soils of the Great Appalachian Valley, which, under various names, extends from Georgia to New York. This great valley was one of the first areas west of the Blue Ridge to be settled, and it soon became an important grain producing section. During the Civil War, the Confederate armies drew large quantities of supplies from its fertile fields. The upper slopes of these mountains are steep, and covered with soil which washes easily when the forest is removed. A National Forest is to be established in the southern Appalachians, and the steeper land devoted permanently to forestry. In the future, the country must look to Appalachian forests for much of its supply of hardwood. The Cumberland-Alleghany Plateau. The surface of this plateau is much dissected by valleys cut in the nearly horizontal layers of rocks. In general, relatively level land and fertile soil are found only in the valley bottoms. The hills have steep slopes, and their soils are infertile. Except where mineral resources have attracted settlers, the plateau is sparsely settled. Lake and Prairie Plains. Most of the surface of this area is covered with glacial soil (Fig. 170), the composition of which is influenced greatly by the nature of the underlying rocks. Thus in Michigan and Wisconsin there are large areas of sandy drift over sandstone, where attempts at farming, following the removal of the pine forests, have met with little success. There are also hilly belts {moraines, p. 258) in the northern part of the area, where the stony soil is used largely for wood- lots and pasturage. There is also much marsh land, unfit for agriculture until drained. In general, however, the soils of this region, especially the prairie soils between the Missouri and Ohio rivers on the south and southwest and the Great Lakes on the north, are of great fertility. No other equal area in the United States is so important agriculturally (Fig. 257). Iowa, Illinois, Ohio, and Indiana, in the order named, are the first four states in the percentage of improved land to total area. The prairies generally were avoided by the first settlers, who regarded the absence of trees as evidence of poor soil. Even after their fertility was known, the larger prairies were not settled far back from the main streams until the building of railroads provided means of transportation. The Great Plains. The surface of this province rises from an elevation of about 1,000 feet at the east, to more than 5,000 feet at the west. Most of the region has a deep and rich soil. At the north, the soil is of glacial origin (Fig. 170) ; farther south it is (1) partly alluvial, having been spread widely by depositing rivers flowing eastward from the Rocky Mountains, (2) partly residual, and (3) consider- able areas in the eastern part of the tract are covered with loess (p. 165). The eastern part of the area is very productive, but the western part has too little rain for ordinary farming. Here agriculture must depend on (1) irrigation, which is possible over small areas, (2) "dry farming" (p. 329), and (3) the cultivation of drought-resisting plants, such as durum wheat and kaffir corn. Over large areas grazing probably will continue to be the chief interest (p. 329). 174 MATERIALS OF THE LAND — THEIR USES The Rocky Mountains and Western Plateaus. In the different parts of this great region all kinds of rocks are found, in all sorts of positions. The soils vary as greatly as the rocks, both in origin and composition. Glacial soils are found at the north, and throughout the region in many mountain valleys. Great areas Fig. 84. Map showing the best use to which it is thought the land through- out North America may be put. (Zon, U. S. Forest Service.) BUILDING STONES AND CLAYS 175 of alluvial soil fringe the bases of many of the mountains, where withering streams from the uplands have deposited their sediment. Some of these deposits have a thickness of hundreds and even thousands of feet. The steep slopes are flanked also by great piles of talus (p. 163), most of which do not support much plant life. Where the mountain slopes are not too steep, there are residual soils, and these also cover great areas of the plateaus. Over most of the region, systematic tillage of the soil has not been possible because of (1) too great height, (2) the steepness of the slopes, or (3) lack of ade- quate rain. Most of the land is therefore best suited to grazing, and, especially in the mountains, to forestry. Irrigation is making agriculture possible in many rather small areas (p. 293), especially in valleys and on other lowlands. In some such places, there is a dense population. Nowhere else in the world is fruit-raising carried on more intelligently or with better results, and probably nowhere else in the world has farm land sold at such high prices. Small, choice orchards have been sold at $4,000 and $5,000 per acre, and prices half as high are not rare. The Pacific Ranges. As farther east, the soils of the mountain slopes can be used best for forests, for which, except at the south, there is enough rain. Among the mountains there are many fertile valleys with glacial or alluvial soils, and between the ranges are the great waste-filled valleys of the Willamette River and of central California. The rich, alluvial soils of the latter probably have given the state larger returns than its gold mines. In the southern part of the province, the value of even the best soil depends on irrigation, and unfortunately there is water enough to irrigate only about one-tenth of the land. Irrigated land, with groves of oranges or lemons, sells for very high prices, while non-irrigable land is worth but little. Toward the north, with increase of rainfall and with lower tempera- tures, the necessity of irrigation is less. Fig. 84 shows, in a general way, the best use to which it is thought the land throughout North America may be put, and serves to illustrate many of the larger points stated in the preceding paragraphs. Mineral Products and Their Uses Building Stones and Clay Building stones. The principal building stones are granite, limestone, marble, slate, and sandstone, though not all rocks of these kinds are useful for building. The strength of the rock, its color, ease of splitting and dressing, and durability all enter into the problem. Not all good stone is available, for much is too far from a market. Cement is taking the place of building stone to a very large extent. Granite is distributed widely in the United States, and is quarried in a large way in several of the Atlantic States. Limestone is quarried in many states, largely for local use. From a few famous quarries, such as those at Bedford, Indiana, it is shipped to all parts of the United States. Much limestone is burned for lime, and much is used for mortar, cement, railroad ballast, etc. The growth of the 176 MATERIALS OF THE LAND — THEIR USES cement industry has been remarkably rapid. In 1890, the United States produced less than 350,000 barrels of Portland cement; in 1911, more than 79,500,000 barrels. Much marble is used as an ornamental building stone. Until recently, it has been quarried on a large scale only in the East. Vermont supplies about four-fifths of all the marble used in the United States for ornamental work, but Colorado promises to become a great producer. Slates are used chiefly as roofing material, but also for various other purposes. The production of slate, like that of marble, is confined largely to the East, and is most important in Pennsylvania, Vermont, and New York. Sandstone is used for buildings, bridges, and other purposes. It is distributed widely in many states, so that many small quarries serve local needs. A few popular kinds of sandstone, such as the brownstone from Pennsylvania and the vicinity of New York City, have wider markets. Gypsum is used extensively for building-plaster and certain cements. It is used also as a land fertilizer, and in other ways. Clays and clay products. Clays have a wider distribution than most other economic rock materials, and are used in making many things. Among these are pottery of various grades, tiles, terra cotta, brick, and Portland cement (made from a mixture of clay and lime rock). Every state produces clay products, Ohio, Pennsylvania, New Jersey, and Illinois leading in the order named. The total value of the products of the clay-working industries of the country exceeded $162,000,000 in 191 1. Substitution of mineral products for wood. Brick, stone, and cement are being substituted more and more for wood in build- ings, sidewalks, bridges, piers, etc. This is highly desirable, because these materials are (1) more durable, (2) less liable to fire, and (3) their use lessens the drain on the forests. Mineral Fuels Coal. After soil, coal is the most important of the mineral resources. Together with iron, which is next in importance, it has made possible the extraordinary industrial development of the United States. Germany and England also have become great manu- facturing nations largely because of their extensive deposits of coal and iron. The United States has more and better coal than any other country, so far as known. Fig. 85 shows the general distribution of its coal fields. Their combined area is about 500,000 square miles, COAL SUPPLY OF THE UNITED STATES 177 or about 16 per cent of the area of the country. Their wide distribu- tion is a matter of great importance, since the largest item in the cost of coal is the cost of transportation. The amount of coal in the United States at the beginning of 191 1 was estimated at more than 3,062,800,000,000 tons. About one-third of this, however, is accessi- ble only with difficulty, and by no means all of it is of good quality. / { ( L e Ij^C r^T^^ /r\^ nil V \ L_^j% / « 1 ' ka ^h ^7 ••3? I— / •" * ' 5 , ,{ ^/l /■ XWCWV COAL FIELDS WM DOUBTFUL . co/u /-/ftos \ K 1 coat (/A/of» Y CC£P COVER Fig. 85. Map showing general distribution of coal fields in the United States. (U. S. Geol. Surv.) It is estimated that more than 99 per cent of the original supply of coal in the United States is still in the ground. The mining of coal in the United States began to be important about the middle of the last century, and the output has nearly doubled each decade since. The 496,000,000 tons mined in 191 1 was about V17 of all mined to the end of that year. If the output should continue to increase at the same rate, the entire known supply would be exhausted in less than 150 years. For various reasons, howxver, our supply of coal will last much longer than this. Never- theless, it is highly desirable (1) to avoid, so far as possible, the waste of coal; (2) to substitute water power for steam power (gen- erated by the burning of coal) wherever practicable; and (3) to use coal in the most efficient way possible. The waste in mining coal has amounted to about 50 per cent of the quantity produced; that i 7 8 MATERIALS OF THE LAND— THEIR USES is, about 250,000,000 tons were wasted in this way in 191 1. This is more coal than was mined in the United Kingdom (the second coal-producing country) in 1905. Much unburned coal passes off as smoke. The average steam engine does not develop into power more than 6 to 10 per cent of the heat energy of the coal. In making electric light from coal, only a small part of one per cent of the energy of the coal is utilized. Much of this waste can be Fig. 86. Map showing general distribution of petroleum and natural gas fields (the black areas) of United States. (Day, U. S. Geol. Surv.) avoided, and some progress in this direction has been made already. One effect of the burning of large quantities of coal is to increase the amount of carbon dioxide in the air (p. 30). Indeed, it has been estimated that the amount may be doubled in this way in the next 1,500 years. It will be remembered (p. 31) that this probably would make the climate much milder. Pennsylvania, West Virginia, Illinois, and Ohio lead in mining coal. They have produced about ^4 of all the coal mined in the United States. Petroleum. Petroleum was discovered in large quantities in west- ern Pennsylvania in 1859. The field which includes this original area extends from New York to Tennessee (Fig. 86), and has produced more petroleum than any other. The output is now decreasing, SUPPLY OF IRON IN THE UNITED STATES 179 however. Most of the petroleum of this field is of high grade. The large Ohio-Indiana field was the second to come into use (about 1885). Most of the others are of recent development. In 191 1, California produced most petroleum, and Oklahoma and Illinois ranked second and third. The total output of the country during this year was more than 220,000,000 barrels. Since i860, as much petroleum has been produced each nine years as in all preceding years, and should this rate continue, the supply, so far as it can be estimated in known fields, would be exhausted by about 1935. Should the present output continue without increase, the calculated supply will last until about the year 2000. Crude oil is used for fuel, for the prevention of dust on roads, and for some other purposes. From it various oils are manufactured for lighting and lubricating purposes, and many by-products are obtained. In view of the probable early exhaustion of the supply, petroleum should be used only for those purposes for which it is best adapted. Its most essential use is for the making of oils for lubricating the bearings of all kinds of machinery. For this purpose, no satisfactory substitute is known. On the other hand, the use of petroleum as fuel in locomotives and for the development of power in factories is in most places unnecessary, and should be discouraged. Natural gas. Natural gas is the most perfect fuel. So far as known, the United States has a greater supply than any other nation, and it occurs in more than half the states (Fig. 86). It is believed, however, that the natural gas now known will be exhausted within the next twenty-five or thirty years. In spite of this, and in spite of its great value, enormous quantities (estimated at 1,000,000,000 cubic feet daily) are allowed to escape from the ground unused. A large part of this waste can be prevented. Metals Iron. Some iron was mined in this country in the colonial period. The production was unimportant, however, till 1850. Since then it has increased rapidly, so that the output during the decade ending with 1909 amounted to 52.6 per cent of all the iron ore that has been mined in the United States. It was estimated recently that the available iron ore (that usable under existing conditions) in the United States amounts to nearly 4,800,000,000 long tons (a long ton is 2,240 lbs.), and that in addition there are low grade ores, part or all of which will be useful in the future, 180 MATERIALS OF THE LAND— THEIR USES amounting to more than 75,000,000,000 long tons. Like coal, iron ore is distributed widely (Fig. 87), but by far the most important deposits of our country are in the Lake Superior region, especially in northern Michigan and Minnesota. This district contains about 73 per cent of the available ore of the United States, and about 95 per cent, of the low-grade reserve. It had produced, to the end of 191 1, more than 530,000,000 long tons of iron ore — considerably more ^r^^--^ 1 .i I ^Yy^. p-5^3^ j I* *• / * i* #7' - 1 \ '/ * • • 1 m \ji -v ^"^K ) 1 n * \ Fig. 87. Map showing general distribution of iron ore in the United States Some of the smaller areas contain more and richer ore than the larger ones. than half the total amount produced in the United States. In recent years it has furnished about 80 per cent of the entire output of the country. In 1910, the United States produced more than 56,800,000 long tons of iron ore — nearly half the world's production for the year. In 191 1, however, the output was only about 41,000,000 tons. If the iron ores of the United States continue to be mined at the increasing rate of the last few decades, the known deposits of high grade will all be mined in about ninety years. Several considerations, however, make it certain that the supply of ore will last much longer. Furthermore, iron, unlike coal, can be used again and again. For example, old rails are made over into new ones or into other things. The great problem in conserving the supply of iron is therefore to use it again and again, keeping the stock as nearly intact as possible. There is little waste of iron ore in mining. COPPER, GOLD, AND SILVER 181 Copper. The existence of copper on the southern shore of Lake Superior (Keweenaw Point) was known to the Indians at an early date. As late as 1845, however, the entire output in the United States amounted to only 100 tons a year, and not till 1867 did copper begin to be used in large amounts. Its use has increased rapidly in recent years, about 550,000 tons being produced in 1911. Nearly three-fifths of the entire amount produced in the United States have been mined in the last ten years. Michigan, long the leading copper state, is now outranked by Arizona and Montana. Some nine other states, most of them in the West, produce copper, several of them in large amounts. Copper ores are scattered so widely, and are so irregular in their occurrence, that the supply has not been estimated accurately. It is thought, however, that the known copper ore, usable at existing prices, will be exhausted in Michigan in fifteen or twenty years, and in Montana and Arizona in even less time.- Should the value of copper increase, lower grade ore could be used. Even now, at the Michigan mines, only twenty-two pounds of copper are obtained, on the average, from each ton of ore. New discoveries of copper are made from time to time, and for this and other reasons, copper ore will last much longer than the time suggested above. Copper is used chiefly for making wire and brass. These uses involve little unavoidable waste, and the same copper may be used repeatedly. Gold. The production of gold was unimportant in the United States until after its discovery in California in 1848. The leading gold-producing states are California, Colorado, and Nevada. Each produces about 1,000,000 ounces (an ounce is worth about $20) of gold per year. Alaska is also a heavy producer. The amount of gold which remains to be mined cannot be estimated. It already is practi- cable to mine very low grade ore. In some cases, for example, a ton of ore is mined and milled to recover one-eighth of an ounce of gold. Gold is used chiefly as coin and bullion, and in the arts. Most of its uses involve little waste or loss of the gold itself. Even were the supply used up, the loss would be much less serious than that of coal or iron. Silver. Neither the amount nor the duration of the silver deposits of the United States can be estimated. Nevada, Montana, and Utah are (19 10) the leading silver-producing states, followed by Colorado and Idaho. Like gold, silver is used chiefly for coin and 182 MATERIALS OF THE LAND — THEIR USES in the arts. Its use in photography is an interesting and a rapidly increasing one. In general, there is little waste or loss in its use. Lead and zinc. Lead was known to the Indians of the Missis- sippi Valley before the coming of the whites, but the deposits of the region were not worked effectively until the early 1820's, when a period of great activity in mining began. This culminated in Illinois and Wisconsin about 1845. During the next few years many of the miners went to the iron fields of Lake Superior, and to the gold fields of California. Lead was discovered later in various western states, in many places in association with silver. Missouri is the leading lead-producing state, followed by Idaho and Utah. The known supply of lead is very limited. Much is lost need- lessly by the prevailing methods of mining, milling, and smelting. About one-third of the lead produced in the United States is used in making paint. Lead used in paint can be used but once, and more abundant things will have to be substituted for it increasingly in the future. Zinc is associated in many places with lead, and for years was regarded as valueless by lead miners. The first zinc plants were erected in Illinois in the 1850's, but for twenty years the produc- tion was small. In recent years it has increased very fast, and the output of the last decade equaled that of all earlier years. Mis- souri leads, by a large margin, in its production. There is great waste of zinc in mining, concentrating, and smelting. About two-thirds of that produced in this country is used for galvanizing iron. Like lead, it is used also for making paint. Most of the rest is used (with copper) for making brass, and for sheet zinc. In 191 1, the United States produced 406,000 tons of lead and 271,000 tons of zinc. Aluminum. Aluminum is by far the most abundant of the metals. It is a constituent of many rocks, and makes up more than 8 per cent of the earth's crust. It is light, strong, malleable, ductile, is a good conductor of electricity, takes and retains a high polish, and does not corrode easily. These properties fit it for many purposes, but the difficulty and expense of separating it from its combinations long prevented its extensive use. It is extracted on a commercial scale only from bauxite, a relatively scarce mineral. When it can be obtained cheaply from clay, of which it forms a part, its use wiU be increased enormously. CONSERVATION OF MINERAL RESOURCES 183 The production of aluminum in the United States increased from &$ pounds in 1883 to about 47,000,000 pounds in 191 1. It is used for making a constantly increasing variety of things, such as cooking utensils, castings, wall " paper," ceiling panels, paints, varnishes, and wire. Doubtless in the future it will replace iron, copper, and some of the other metals for many purposes. Salt Salt is indispensable to man, and fortunately the supply is prac- tically inexhaustible. (1) In arid regions there are many lakes with no outlets into which streams bring minerals (including com- mon salt) that have been dissolved during the passage of the water through or over the rocks (p. 211). These things are left behind as water evaporates from the lake, which becomes more and more saline as the process continues. When the waters of the lake become saturated, further evaporation causes the minerals to begin to be precipitated from solution. Great Salt Lake is estimated to contain some 400,000,000 tons of common salt. (2) Extensive salt beds which were laid down in ancient lakes or arms of the sea are found between beds of other rock in many places. Those in central New York may have an area underground of some 10,000 square miles (lar- ger than Vermont), and single beds are in places 80 feet thick. Besides New York, Michigan and Kansas are leading salt-producing states. (3) The ocean is the remaining and greatest source of supply (p. 144). The need of salt helped to hold most of the American colonists near the At- lantic coast for along time. Not until it was discovered in the Holston and Kanaw- ha valleys (Tenn. and W. Va.), in central New York, and in Kentucky, did dependence on the coast for salt cease. In 1778, salt brought on pack animals over the Appalachian Mountains sold in southwestern Pennsylvania for £6 10s. per bushel. The same amount of salt now is worth but little more than 10 cents where it is prepared, and not more than 50 cents in the markets in most parts of the United States. Conservation of Mineral Resources The mineral resources noted above are a part of the heritage of the earth. The people of to-day have a right to use such of them as they need, in as great quantities as necessary. It is their duty, however, to use them in such a way as to insure the minimum of waste and the maximum of efficiency. This is demanded alike by the interests of the present generation, and by those of genera- i8 4 MATERIALS OF THE LAND — THEIR USES tions to come. The facts given show that many reforms are needed. The reckless waste of some of these resources is a reflection upon American intelligence. Questions i. What are the principal ways in which soil is being formed in New England? Florida? Nevada? 2. Why are the soils of the lower flood-plains and deltas of large rivers of great fertility in most cases? Are they commonly of coarse or fine texture? Why? 3. State conditions which explain why soil wash is, in some cases, much faster on one of two equal slopes than on the other. 4. Would you expect wash in winter from bare fields to be greater in northern or southern United States? Why? 5. Would it be desirable, from the standpoint of agriculture, entirely to prevent soil erosion if it were possible? Reasons? 6. Tile underdraining is in many cases effective in checking soil erosion. Why? 7. Plowing under straw, leaves, etc., was formerly a common practice. What value, if any, would this have? 8. In some of the mountainous areas of Italy, Austria, and other countries, forests are maintained in strips at right angles to the slope of the surface, while the land between is tilled. Why is this advantageous? 9. Explain in detail why plowing up and down a hill-side is unwise. 10. Other things being equal, would you expect crops to suffer more from protracted droughts on sandy or on clayey soils? Why? 11. In parts of China it is customary to plant alternate rows of leguminous plants (like peas and beans) and grains. How does this benefit the soil? 12. Steel cars rapidly are replacing wooden ones, and re-enforced concrete (i.e., cement strengthened by steel) is being used for many new bridges in place of steel. Are these changes desirable from the standpoint of the conservation of natural resources? Reasons? 13. Why are gold and silver, the "precious metals," much less essential to man than coal and iron? CHAPTER XIV CHANGES OF THE EARTH'S SURFACE DUE TO INTERNAL FORCES Slow Crustal Movements Except for occasional earthquakes and landslides the crust of the earth seems to be firm and stable, but it is in reality subject to very slow movements which, in the course of ages, produce great changes. Such movements warp both land and sea-bottom. It is probable that more of the earth's surface has been sinking or rising in recent geological times than has been standing still. Movement of coastal lands, (i) Old buildings and docks, near sea-level when built, are now under water in some places and well above the sea in others. Clearly, this means a recent change, at these places, in the relations of land and sea. (2) Beds of sediment containing sea-shells, deposited beneath the sea in recent times, are found above the water in north Greenland, on the Pacific coast of the United States, in the West Indies, on the west coast of South America, and in other places. On the slopes of Mount St. Elias, Alaska, mod- ern sea-shells have been found attached to the rocks just as they once grew, but several thousand feet above the sea. (3) On the other hand, there are drowned forests along some coasts. Thus north of Liverpool, England, many stumps may be seen at low tide standing on the beach (Fig. 88). Since trees of the kind represented by these stumps do not grow in salt-water, it is clear that the land where they grew has sunk below the level of high water. On the coasts of New Jersey and North Carolina, too, there are stumps having similar histories, several feet below sea-level. These and many other facts prove that the land and sea change their relations to each other, and that most coast-lines have been affected by such changes in recent times. The emergence of land may be due to (1) its rise, or (2) the sink- ing of the sea-level. Similarly, the submergence of land may be due to (1) its sinking, or (2) the rise of the sea. From what is now 185 i86 CHANGES OF THE EARTH'S SURFACE known it is certain that both the sea and the land rise and fall from time to time. Causes of changes in sea-level. Several things may make the sea-level rise or fall, (i) The sinking of a part of the ocean bed would lower the sea surface, while the elevation of a part of the sea floor would have an opposite effect. (2) Sediment washed from the land into the sea builds up the ocean floor, and so raises the surface of the sea. (3) Lavas poured out from volcanoes beneath the sea, and the deposits of corals and shell-bear- ing sea life, make the sea-level rise. (4) An increase or decrease in the total amount of land- water or ice would lower or raise the surface of the ocean. Since the oceans are all connected one with another, each of the above changes would affect the surface of the sea everywhere, and by the same amount. Other factors also affect the surface of the sea, and some of them make it higher in certain places than in others. Changes of level in the interiors of continents. Changes of level are perhaps as common in the interiors of continents as along coasts, but they are not detected so easily, since there is no level surface like the sea with which to make comparisons. There are raised beaches about many lakes, as about the Great Lakes and Great Salt Lake (Fig. 89) ; but raised beaches about a lake may result from the lowering of the lake, either by the cutting down of its outlet or by evaporation. They do not, therefore, prove a rise of the land. But many old shore-lines about lakes are not horizontal, as they were when formed. Some parts of the old shore-line about former Lake Bonneville (the ancestor of Great Salt Lake) are 300 feet higher than other parts of the same line. Similar tilted shore-lines are found about many lakes, and show that the land has warped since the shore-lines Fig. 88. Stumps laid bare on the beach at low tide; Leasovve, England. (From photo- graph by Ward.) CHANGES OF LEVEL 187 were formed. Other phenomena, some of them discussed later, also show movement of large interior areas. Ancient changes of level. Layers of rock, deposited long ago as sediment beneath the sea, are now found over great areas, far above sea-level. Most of the solid rock beneath the Mississippi Basin, for example, was laid down as sediment beneath the sea, as shown by the shells of the sea animals which it contains. In the Fig. 89. Shore of former Lake Bonneville, Utah. (From photograph by U. S. Geol. Surv.) Appalachian Mountains, rocks formed in the same way are found up to heights of several thousand feet; in the Rocky Mountains up to 10,000 feet and more; and in some other mountains to still greater heights. It is certain, therefore, that changes of level have been great, and that vast areas have been affected. It is also certain that great changes in the areas and in the rela- tions of land and sea have occurred many times in the distant past. Earthquakes Frequency and importance. Tremblings or quakings of the earth's surface occur frequently in many countries. Most of them are not felt, and can be detected only by means of delicate instru- i88 CHANGES OF THE EARTH'S SURFACE ments made to record them. For many years an average of several earth tremors a day have been recorded in Japan, and it has been said that some part of the earth's surface is shaking all the time. The changes made in the surface of the land by earthquakes are slight, and they are important chiefly because severe earthquakes may cause great loss of life and property. Distribution. Most earthquake regions lie near the edges of the continental platforms, though some (in Asia) are far inland. Most of them are mountainous areas, though some are lowlands. Earthquakes are perhaps most common in volcanic regions, though not all the earthquakes of such regions have been caused by volcanoes. Except along the west coast of South America, the southern conti- nents are rather free from earthquakes, or at least few are reported from them. In the northern hemisphere, earth- quakes are most common about the Mediterranean Sea, in southern Asia, in the islands east and southeast of that con- tinent, and along the western coasts of North and Central America. Some of the areas most affected by earthquakes are settled densely. Causes of earthquakes. Earthquakes are caused in various ways. During movements of the earth's crust, great cracks or fissures sometimes are formed in the surface of the land (Fig. 90). The walls of fissures may be displaced, or faulted. Faulting has caused many great earthquakes, the slipping of one great body of rock past another producing vibrations, which in some cases have spread great distances. An Alaskan earthquake in 1899 was caused by a sudden displacement of more than 40 feet, and the San Francisco disaster in 1906 resulted from a horizontal movement of 5 to 20 or more feet, along a line many miles in length. Earthquakes accompany violent volcanic eruptions, and in these cases the explosions which accompany the eruptions Fig. 90. Fissure in floor of Kilauea, Hawaii. DESTRUCTION BY EARTHQUAKES 189 doubtless cause the quaking. Great landslides and avalanches may cause slight earthquakes. Slight shocks may be caused in still other ways. It is probable that most earthquakes are incidents of the wide- spread movements to which the crust of the earth is subject, move- ments which are due chiefly to the continued fitting of the outside of the earth to a shrinking interior. In general, these movements are too slow to produce vibrations which we can feel ; but they are sufficient, in rare cases, to produce great earthquakes. Destruction of life and property. Except along the plane of slipping, the actual movement of the land surface during an earth- Fig. 91. The new library building at Stanford University, after the earth- quake of April, 1906. (Moran.) quake is very slight, in most cases only a small fraction of an inch. It is the suddenness of the shock which overthrows and destroys buildings and other objects. That a sudden but very slight movement of the ground may do this is clear from the fact that a quick, sharp tap on the side of a table may overthrow all loose objects upon it, even though the movement of the table itself is very slight. Some earthquakes in thickly settled regions have caused an appal- ling loss of life and property. The most disastrous earthquake in North America occurred in and about San Francisco in April, 1906, A large part of the city was burned by the fire which followed the shock. More than 700 lives were lost, and between 100,000 and 200,000 people were made homeless. Some 25,000 buildings (Fig. 91) 190 CHANGES OF THE EARTH'S SURFACE were destroyed in the earthquake and fire, having an estimated value of more than $100,000,000. In 1905 a great earthquake in India Fig. 92. Taal Volcano, Philippine Islands, in eruption. (Gilchrist.) destroyed nearly 1 9,000 lives and more than 112 ,000 buildings. About 1 00,000 people were killed in the earthquakes in southern Italy in 1908. TYPES OF VOLCANOES 191 In some countries where earthquakes are frequent, like Japan, much attention has been given to making buildings in such a way as to withstand the shocks. The greater frequency of earthquakes in Nicaragua was one reason for selecting the Panama route for the Isthmian Canal. When an earthquake disturbs the sea-bottom, waves are set in motion. These waves rush upon neighboring coasts, and in some cases (e. g., in Sicily in 1908) they have done great damage. Millions of marine animals and plants were killed during the Alaskan earthquake of 1899. VULCANISM Volcanoes A volcano is a vent in the earth's crust out of which hot rock comes (Fig. 92). The hot rock may flow out in liquid form (called lava), or it may be thrown out violently in solid pieces. It is gen- erally built up into a cone (Fig. 93), which may become a mound, a high hill, or even a high mountain. Quantities of gases and vapors are discharged along with the hot rock. There is a hollow, called the crater, in the top of most volcanic cones. Craters vary greatly in size, some of the larger ones being two or three miles across. While the volcano is active, an opening leads down from the crater to the source of the lava, at an unknown depth. Common phenomena of an eruption. In the explosive type of eruption, rumblings and earthquake shocks, due to explosions within the throat of the volcano, may occur for weeks or months before a violent outbreak.. During a violent outbreak, dust, cinders, and larger pieces of rock are shot forth and fall on the sides of the cone. The clouds of condensed steam and dust rising from the crater darken Fig. 03. (Marshall.) Cone of Ngauruhoe, New Zealand. 192 CHANGES OF THE EARTH'S SURFACE the sky, and torrents of rain, falling on the fine dust, may form rivers of hot mud. Liquid lava may or may not accompany the discharge of solid material. In the quiet type of eruption, the lava rises in the crater and overflows its rim or, more often, breaks out through cracks in the side of the cone. There is little or no burning in a volcano, for there is little or nothing to burn. There is, therefore, no smoke. What appears as smoke is mostly cloud, blackened by volcanic dust. The products of volcanoes. Lava is a term applied both to the liquid rock which issues from a volcano, and to the solid rock ,,-,.-> Fig. 94. Recent flow of lava from Kilauea, Hawaii. (U. S. Forest Service.) which results from its cooling (Fig. 94). Most of the solid materials blown out of a volcano are pieces of lava which became solid before they were shot out, or during their flight in the air. They include masses of rock tons in weight, and smaller pieces of all sizes down to particles of dust (commonly called volcanic ash). The dust in many cases is shot high into the air, and, being light, is scattered broadcast by the winds, some of it coming to rest thousands of miles away. The liquid lava and the larger solid pieces, on the other hand, stay near the vent. The gases and vapors which issue from volcanoes are of many kinds. Some are poisonous, and some are so hot as to be destructive to life, as in the case of Mont Pelee, in 1902 (p. 197). TOPOGRAPHIC EFFECTS OF VOLCANOES 193 Soils made by the decay of volcanic materials may be very fertile if well watered. The volcanic soils of the Spice Islands (Moluccas), Java, and other islands of the East Indies, support a luxuriant vegetation. Number. The number of active volcanoes is not known, but is estimated at 300 to 400. Something like two-thirds of them are on islands, and the rest on the continents. Distribution. The distribution of active volcanoes is shown in Fig. 95. Many are in belts, within which some are in lines. The • ACTIVE VOLCANOES RECENTLY EXTINCT VOLCANOES Fig. 95. Map showing the distribution of volcanoes. (Russell.) most marked belt nearly encircles the Pacific Ocean. The volcanoes of the West Indies and of Java and Sumatra sometimes are considered as forming branches of the main belt. Outside this belt, there are a number of volcanoes in and about the Mediterranean Sea, and there are others which are not connected with any well-marked system. Most volcanoes are in the sea or near it. Many are in moun- tain regions, though they do not occur in all mountains. Many of the active volcanoes are near the line where the continental plateaus descend to the ocean basins. Many volcanoes are in lands which have been raised or lowered recently. Topographic effects of volcanoes. Some volcanic cones are mountains of great size, like Mt. Rainier (Tacoma) in Washington, 194 CHANGES OF THE EARTH'S SURFACE Mt. Hood in Oregon (Fig. 96), Mt. Shasta in California, and Orizaba in Mexico. All. those named are so high that glaciers are found on their slopes. Vol- canic cones are far more numerous than volcanoes, for the cones of many ex- tinct volcanoes still remain. Many small islands and some large ones are due chiefly or wholly to the build- ing of volcanic cones on the ocean-bottom. The Aleutian Islands and the Hawaiian Islands were formed in this way. Iceland, too, is largely volcanic. Destruction of volcanic cones. Volcanic mountains, like all other elevations on the land, are subject to change and destruction. Fig. 96. Mt. Hood, a snow-capped mountain. Fig. 07. Portion of ("rater Lake, Oregon. (Copyright by Riser Photo Co.) DESTRUCTION OF VOLCANIC CONES i9S They may be destroyed partially by violent explosions. Again, the top of a volcanic mountain may sink, leaving a great hollow, or caldera. Crater Lake, Oregon (Fig. 97), the deepest lake in North America, is in a caldera five or six miles in diameter, and 4,000 feet deep. The lake is sur- rounded by steep walls 900 to 2,200 feet high. Since the sinking of the top, a small cone, now an island in the lake, has been built. Volcanic cones, are destroyed also by the slow processes of weath- ering and erosion (p. 306). Wind and rain attack them as soon as they are formed, but the results are not striking until the volcano is extinct and the cone stops growing. The many cones of extinct volcanoes in western United States are in various stages of destruction. Some in Arizona, California (Fig. 98), Fig. 98. Typical cinder cone, Clayton Valley, California. Fig. 99. Mt. Shasta, a typical volcanic cone furrowed by erosion, but retain- ing its general form. (U. S. Geol. Surv.) Idaho, and Oregon were formed so recently that they have been eroded but little. Fig. 99 shows a high mountain built by a former volcano. It still retains its conical form, but its steep upper slopes are cut by ravines and valleys, several of which contain glaciers. 196 CHANGES OF THE EARTH'S SURFACE Destructiveness. Like earthquakes, some volcanoes have de- stroyed great numbers of lives and much property. During an erup- tion of Vesuvius in 79 A. D., Pompeii, a city of about 20,000 people, Fig. 100. The ruins of Pompeii. (Doseff.) was buried by cinders and ashes (Fig. 100), and Herculaneum was overwhelmed by streams of hot mud. Some of the later eruptions of this volcano also have been very destructive. That of 1631 Forsaken I Lang I. Fig. 101 Fig. 102. Fig. 101. Krakatoa Island and surroundings before the eruption of 1883. Fig. 102. Krakatoa Island and surroundings after the eruption of 1883. The numbers indicate the depth of the water in fathoms (a fathom = 6 feet) in both figures. destroyed some 18,000 lives. One of the most violent and destructive volcanic eruptions known was that of 1883 in Krakatoa, an island between Sumatra and Java. About two-thirds of the island was LOSSES DUE TO VOLCANOES 197 blown away, and the sea is now nearly 1,000 feet deep where the center of the mountain formerly was (Figs. 101 and 102). Sea waves spread to Cape Horn, and possibly to the English Channel. On the shores of neighboring islands the water rose 50 feet. More than 36,000 persons perished, mostly by drowning, and 295 villages were destroyed, wholly or partially. The volcano of Pelee is on the island of Martinique, at the eastern edge of the Caribbean Sea. Its cone descends by steep slopes to the sea on all sides but the south, where there is a plain on which the city of St. Pierre formerly stood. After slumbering for more than fifty years, the vol- cano became active in the spring of 1902. On May 8th a heavy black cloud, probably composed of steam, sulphurous vapors, and dust, which had an estimated temperature of 1,400° to 1,500° Fig. 103. The ruins of St. Pierre, Mar- tinique. (Hovey.) F., swept down through a gash in the crater's rim, and out over the plain to the south- west. In two minutes it struck the city of St. Pierre, five miles distant, which was demolished at once (Fig. 103). Buildings were thrown down, statues hurled to the ground, and trees torn up. Explosions were heard in the city as the cloud reached it, and flames burst out, started either by the heat of the gases, or by the red-hot particles of rock which the gases carried. A few minutes later a deluge of rain, mud, and stones fell, continuing the destruction. Only two people out of 30,000 survived the disaster. Igneous Phenomena Not Strictly Volcanic Fissure eruptions. Lava sometimes rises to the surface through great cracks instead of through the rather small vents of vol- canoes. From such cracks floods of lava may spread over the land for hundreds of miles. Many such lava floods once occurred in Oregon, Washington, and Idaho, where the former hills and CHANGES OF THE EARTH'S SURFACE \s\- xjv? jg for \---^— 1 ) i ; L...._ i 1 Fig. 104. Lava flows of the North- west. valleys were buried, and a vast plateau 200,000 square miles or more in extent was built up (Fig. 104). In this lava plateau, the Snake River has cut a great canyon 4,000 feet deep in some places, and 15 miles wide. The walls of the canyon show that in some cases successive beds of lava are separated by layers of soil in which the roots and trunks of trees are preserved. An older and larger lava plateau, more dissected by erosion, occurs in central and southern India. Still others, now made rough by erosion, are found in northern Ireland and western Scotland. Some of the islands off Scotland are rem- nants of an old lava plateau. Intrusions of lava. Most of the lava forced upward from great depths probably fails to reach the surface, and hardens underground. Such rocks may be exposed at the surface through the wear- ing away of the rocks which overlay them. Great masses of intruded lava may bulge up the overlying strata, making domes (Fig. 105), some of which reach the size of mountains. The Henry Mountains of Utah are examples. In places, lava has been forced in between beds of rock, and into cracks in them (Fig. 106). Intrusions of lava may give rise to topographic features of importance after erosion has affected the regions where they occur, for the hardened lava is in many cases harder than its Fig. 106. Diagram showing lava which has been forced in between beds of rock (forming silk), and into cracks (forming dikes). What changes have oc- curred since the dike-rock was intruded? CAUSES OF VULCANISM 199 surroundings. Many dikes form ridges. Intruded sheets of lava, if they have been tilted from a horizontal position, may also form ridges, and these ridges may be so high as to be called mountains. The Palisade Ridge of the Hudson (Fig. 107), and most of the mountains Fig. 107. The face of the Palisade Ridge, west of the lower Hudson River. of the Connecticut Valley, are examples. The steep ridges so impor- tant in the battle of Gettysburg are smaller examples of the same sort. Causes of Vulcanism The causes of vulcanism are not well known. How the liquid rock is formed, the depth of its source, and how it makes its way to- ward the surface, are unsolved questions. The old notion that volcanic vents are connected with a liquid interior has been abandoned. It seems probable (1) that lava is being formed all the time, in spots, in the deep interior, and (2) that it is all the time finding its way toward the surface, but faster and in greater amounts at some times than at others. The places where the crust is weakest, that is, where there is movement, are the places most likely to afford the lava a place of escape. 200 CHANGES OF THE EARTH'S SURFACE Questions i. At the west end of the island of Crete, in the Mediterranean Sea, old docks, near sea-level when built, are found many feet above the water. At the east end of the island, ancient buildings are under water. Was the change in the relation of land and sea thus recorded due to movement of the sea surface, or of the land? Why could it not have been due to the other? 2. How would the coast-line of North America be changed if the bottom of the Indian Ocean were to sink enough to lower the surface of that sea 200 feet? 3. Other things being equal, which are more enduring, volcanic cones built of lava or of cinders? Why? 4. Will soil form quickly or slowly on the recent (1902) volcanic deposits of Martinique and St. Vincent? Why? 5. (1) What was the origin of the mountain in the right hand foreground of Fig. 108? The evidence? (2) Has much or little time elapsed since its formation? How told? (3) What is the probable history of the curving ridge at the left? Fig. 108. CHAPTER XV MODIFICATION OF LAND SURFACES BY EXTERNAL AGENTS The surface of the land is being changed all the time by various agents, especially by wind, by water in the ground, by running water, by ice, and in minor ways by different forms of life. The Work of the Wind Winds change land surfaces by taking dust and sand from certain places and depositing them in others. Wind-driven dust and sand may wear exposed surfaces of rock. Transportation. Desert winds often sweep up "clouds" of dust which may be seen for miles, and a single storm may move millions of tons of dust and sand. The dreaded simoon of the Sahara has been known to destroy entire caravans, death resulting from suffocation in the dust-laden air. While transportation by the wind is most important in arid regions, it is not confined to them. Dry sand and dust are blown about wherever they are exposed to the wind. Particles of dust are much heavier than air, and gravity tends to bring them down. Yet they may remain in the air for a long time (i) because they are so small that they do not fall readily, and (2) because there are many upward currents in the air which carry them up in spite of gravity. As a matter of fact, the dust of the air always is settling, and the supply is being renewed all the time. Dust in the air may be carried great distances. A severe storm in March, 1901, carried dust northward from the Sahara as far as Denmark. In 1883, volcanic dust from Krakatoa (p. 196) was carried around the earth by the upper winds in about two weeks, its progress being shown by the brilliant sunsets to which it gave rise. Abrasion. Sand blown against a rock has the effect of a sand- blast, and wears the rock away. Abundant wind-blown sand, driven 201 202 MODIFICATION OF LAND SURFACES Fig. ioq. Rocks carved by the wind. (Bastin.) What inferences may be made concerning the character of the rocks? against projecting rocks, may carve them into fantastic forms (Fig. 109). This process is of much importance in dry regions where the land is rough. In deserts and along sea coasts, telegraph poles have been cut off near the ground by wind-blown sand. In some such places, stones are piled about the bases of the poles to protect them (Fig. no). Wind deposits. Wind de- posits of sand and loess have been described (p. 165). Sand usually is blown along within a few feet of the ground, and is therefore likely to lodge about any obstacle which blocks its way. Mounds, hills, and ridges of wind-deposited sand are dunes, which range in height from a few feet to more than 400 feet. Small dunes are much more common than large ones. Dunes are found mostly near the sources of abundant dry sand. They are common ■j|? along much of the Atlantic coast of the ; j United States, where sand is washed up on the beach by waves. After drying, it is JMBfcjSta-^^^" blown about by the wind. Winds from the ■Bk&X Jk ^ V wes ^ kl° w this sand into the sea, but those BfrSj6^JK^lf^^^ from other directions, especially from the -^K "' east, drift it up on the land. Dunes abound over thousands of square miles in the drier parts of the Great Plains, as in western Nebraska and western Kansas. They are largest and most numerous in still drier re- gions, as the Sahara. In some places, dunes are the most striking feature of the landscape. Sand is blown from the windward side of a dune and dropped on the leeward side, much of the time. This continued shifting of sand to the leeward side results in a slow migration of the dune. Farm lands have been covered in this way, and forests have been Fig. no. Telegraph pole in southern Califor- nia, deeply cut by wind- driven sand. (Menden- hall, U. S. Geol. Surv.) DAMAGE DONE BY SHIFTING SAND 203 Fig. in. Dunes advancing on a forest. Little Point Sable, Michigan. Fig. 112. The last house in Riggs, Oregon, a village overwhelmed by sand dunes. (Gilbert, U. S. Geol. Surv.) 204 MODIFICATION OF LAND SURFACES buried (Fig. in). In some places sand buries buildings (Fig. 112), and causes much trouble along railways. The migration of dunes along some coasts is so disastrous that steps are taken to stop it. If a dune is covered with vegetation, its position is not likely to change so long as the plants remain, for they hold the sand. Trees, shrubs, and grasses which will grow in sand sometimes are planted on dunes to prevent further drifting (Fig. 113). This has been done at various points on the western coast of Europe, and to some extent in our Fig. 113. Sand dune reclamation, from photograph by Forest Service.) Manistee County, Michigan. (Sketch own country, as at San Francisco, where the westerly winds drift sand in from the shore. The amount of wind-blown sand not heaped up in dunes is probably far greater than that in dunes. Summary. The more important phases of the work of the atmosphere may be summarized here. (1) Of most importance is its work as an agent of weathering (pp.- 1 61-164). Through its effect on changes in temperature it helps to break rocks, and by the chemical action of its oxygen, carbon dioxide, and water vapor, it causes rocks to decay. Weathering prepares materials for removal by various agents of transportation. (2) The wind transports and deposits large amounts of fine material. Although most extensive in arid regions, this work has affected all land surfaces. Since the wind deposits much dust and sand in the sea, the general effect is to lower the lands and build up the ocean-bottoms. (3) Rocks are worn by wind-driven sand. This is most important in deserts, where the atmosphere is, in many places, the chief agent in wearing down the land. (4) By controlling the conditions of evaporation and pre- WATER UNDERGROUND 205 cipitation, the atmosphere makes possible the work of streams and of glaciers, and the existence of land life. QUESTIONS 1. Why are there many dunes on the eastern side of Lake Michigan, and but few on the western? 2. In most dune areas there are many hollows among the sand hills. In what ways are such hollows formed? 3. Why are dunes formed along some river valleys and not along others? 4. What changes in natural conditions may stop dune-building in a given region? Ground-Water general considerations The fate of rain-water. The average annual rainfall of the United States is about thirty inches. This means that a total of about 1,500 cubic miles of water (enough to cover New England to a depth of about 1,000 feet) fall as rain or snow in this country each year. It is thought that about half of this water evaporates, that about one-third of it runs off over the surface, and that the remain- ing one-sixth is taken up by plants or sinks into the ground. The ground- water surface. It is possible almost anywhere to dig wells deep enough so that they will contain water all the time. This means that the surrounding rocks are full of water below the level of the water in the wells. The surface below which the ground is full of water in any given region is the water surface or water table for that region. In swamps and marshes the water table is at or near the surface of the ground, while in arid regions it may be hundreds of feet below. In humid regions it is seldom more than 50 or 60 feet below the surface. The position of the water table also varies from time to time. It is higher after heavy rains, and lower during and after long droughts. Amount of water underground. The pores and openings in the rocks below the water surface are full of water. Some porous rocks contain one-third or more of their volume of water; very com- pact rocks contain but little. In general, rocks near the surface have more and larger pores and cracks than those at greater depths. Pores and cracks become very small at the depth of a few thousand feet, and probably none exist below a depth of five or six miles. If this is true, water does not descend to greater depths. There is water 206 MODIFICATION OF LAND SURFACES enough underground so that, if it were brought to the surface, it would form a layer probably 500 to 1,000 feet deep. Circulation of ground-water. Ground-water is moving all the time. This is shown, for example, by the constant flow of springs, and by the fact that after a well is pumped "dry," it soon fills again to the former level, because water seeps in from the surrounding rocks. Ground-water moves because the water table is not level every- where, and the water moves from places where its surface is higher to places where it is lower. The water table is kept uneven, partly HE—^-S^sKSi iWk. ^sfc. ^$&®. ,-^-JjBafWgK ' ^ — - _ _ ■ - - '.■,'■:■.....:.■:■.'..;■.: £o»rff ■■■ Fig. 114. Diagram showing the relation of the level of ground-water (the broken line) to the surface of the ground and to a lake and river. because of unequal rainfall, and partly because of the uneven surface of the land. Other things being equal, the water table is higher beneath high land, and lower beneath low land (Fig. 114). The water surface below the high land tends to sink until it is as low as that beneath the low land; but in moist climates it rains so often that the water surface under the hills almost never sinks to the level of the water in the surrounding low lands, before it is raised again by rains. Water which sinks to great depths commonly follows an irregular course. At first its movement is chiefly downward, and is rather rapid because of the many large cracks and pores in the rocks near the surface. Farther down, its movement is largely sideways (Why?). It may flow slowly for many miles along a crooked course, through small openings, before it reaches a passageway leading to the surface. Through such an opening it may issue with great force as a spring or flowing well. Fig. 115 suggests the intricate circulation of the water which issues in a deep-seated spring. Some water flows underground to the sea or to lakes, and issues as springs beneath them. Much MOVEMENTS OF GROUND-WATER 207 ground-water, too, seeps out in such small amounts that it does not appear to flow, and does not make a spring. Much ground-water is taken up by roots, passes up through the plants, and comes out through their leaves (is transpired) into the air. The amount of water returned to the air daily by forests through their foliage varies under different conditions from 1,000 to 20,000 or more pounds per acre, during the growing season. About 5,000 pounds of water are transpired by the foliage of corn-plants in the production of a bushel of corn. Again, water is evaporating from the ground most of the time, even in regions where the soil appears to be very dry. The rate at which ground-water moves depends chiefly on (1) the porosity of the rock or soil, ana (2) the pressure of the water. The rate at which water seeps through soils from irrigating ditches in the West is in most cases from one to eight feet per day; but in very porous soils it is sometimes 50 feet per day. In widespread beds of sandstone which underlie southern Wisconsin and northern Illinois, the rate of movement of ground- water is about half a mile a year. At this rate, rain-water which enters these beds 100 miles from Chicago would reach that city in about 200 years. Knowledge of the circulation of the upper part of the ground- water is important to every family using well-water for household purposes. Polluted well-water is very common on farms which might have pure and wholesome water. Great numbers of wells are so situated that ground-water moves toward them from cess- pools and stables. Largely as a result of this, typhoid fever is more common in many farming regions than in most cities. Uses and functions of ground-water. Ground-water is of vital importance in the economy of the earth and in human affairs. (1) It is important to plants. It dissolves the mineral elements of plant food and carries tnem to the roots. The amount of water available for plants is the most important factor conditioning their life in many regions. (2) Underground water supplies all springs and wells, the sources from which perhaps three-fourths of the people of the United States obtain their water for household use. Fig. 115. Diagram showing the in- tricate underground drainage which issues in a deep-seated spring. (Geikie.) 208 MODIFICATION OF LAND SURFACES The distribution of population in eastern United States was influenced greatly by running water and natural springs^ until modern methods of well-digging were developed. Absence of springs, and the use for two years of the brackish water of the James River, were one cause of the high death-rate in the Jamestown colony. A supply of wholesome water helped to determine the location of the Pilgrim colony at Plymouth, and of the Puritan settlement at Boston. Many of the stockaded villages of the early western frontier were so located as to command a supply of water in the event of an Indian siege. The settlement of certain inter- stream areas in southern Wisconsin and in Illinois was delayed for years, partly because of the difficulty and expense of digging wells. In the arid West, springs and watering places determine the location of many vil- lages and farms, and influence the course of trails and roads (Fig. 116). Their location is shown on many maps for the benefit of travelers. Because of the importance of ground-water to plant, animal, and human life, it is highly de- sirable that the water table be kept near the surface of the ground. It is estimated that in eastern United States it has been lowered from 10 to 40 feet over large areas by cutting off forests and by careless methods of tillage which have increased the proportion of the rain-water that runs off over the surface. It is estimated that at least three-fourths of the shallow wells and springs have failed in this part of the country. (3) Ground-waters bring about important changes in the character of the rocks through which they pass. These changes take place slowly, but they are going on all the time. OUTFLOWING WATERS Hillside and fissure springs. Fig. 117 illustrates two kinds of springs. In the one, water descends through a porous bed of rock, c, to a layer, a, which is compact. Much of the water flows along this layer until the latter comes to the surface (out-crops), and there the water issues as a hillside spring, s. The great majority of springs are of this class, and most of them are small. In the other Fig. 116. Map showing springs (by circles) and roads in the region of Flag- staff, Arizona. (From San Francisco Mountain Sheet, U. S. Geol. Surv.) FLOWING WELLS AND SPRINGS 209 case (Fig. 117), the water moves through the porous layer, b, under pressure, until it reaches a crack which leads up to the surface. If the crack is open, the water will follow it up to the surface, as at s', forming a fissure spring. In such a situation there will be a spring only when the opening is lower than the water surface in the layer Fig. 117. Diagram to illustrate two types of springs, as explained in text. of rock which carries the water. This sort of spring is similar to a flowing well in principle, though in the latter case the opening is made by man. Artesian wells. Formerly, artesian wells were regarded as the same as flowing wells. Now, the name "artesian" often is applied to deep, drilled wells, whether they flow or not. Fig. 118 illustrates Fig. 118. Diagram illustrating the conditions necessary for flowing wells the conditions necessary for flowing wells. They are: (1) A porous layer or bed of rock, A, under one which is not porous, and which prevents the water from escaping upward until it is penetrated by the well hole, W. The porous bed must come to the surface in a region which is higher than the site of the well; and (2) enough rainfall where the porous bed comes to the surface to keep that bed well filled with 2IO MODIFICATION OF LAND SURFACES water. Under these conditions, the water will gush up (Fig. 119), if a hole is made down to it. Flowing wells may be but a few feet deep, or they may be thousands of feet deep. Thus there is one in St. Louis nearly 4,000 feet deep, and many in New Jersey less than 100 feet in depth. Many villages and small cities get their water from artesian wells; but great cities, such as New York and Chicago, could not get enough in this way. Brooklyn obtains a part of its supply in this way, its artesian wells furnishing about 22,000,000 gallons per day. In parts of the West, artesian waters are used extensively for irrigation, as well as for domestic and other purposes. In some regions more wells have been drilled than are needed, and when not in use (in many cases this is the greater part of the time) the water from the flowing wells has been allowed to run off freely. This has reduced so greatly the pressure and the amount of water available, that villages and cities, formerly abundantly supplied from artesian wells, have been com- pelled to seek other sources of supply. This is the case, for example, in some parts of the Dakotas. In some of the arid states where the water problem is critical, as in California, strict laws exist to prevent the waste of artesian and other underground waters. Fig. 1 19. An artesian well at Lynch, Nebraska. Flows more than 3,000 gallons per minute. (Darton, U. S. Geol. Surv.) Geysers. Geysers are hot springs which erupt from time to time (Fig. 120). So far as known, they occur only in a few regions of recent volcanic activ- ity — Yellowstone National Park, New Zealand, and Iceland. From a few geysers water is thrown to a height of 200 feet or more, by steam produced at some point in the geyser tube below the top of the water. It is believed that hot volcanic rocks make the water boil, and the expansion of the steam formed causes the eruptions. (How will the cooling of the rocks affect the frequency of eruptions? What will be the final fate of existing geysers?) Although interesting, geysers are of little importance. Other hot springs. Some springs are warm, and others are hot. Where spring-water is hot, it is in some cases because it has been in contact with lava which came up from greater depths so recently that it has not yet become cold. In other cases the heat may be due to chemical changes taking place beneath the surface. There are more than 3,000 hot springs in the Yellowstone National Park, and many others in different parts of the country. MINERAL WATERS 211 Mineral and medicinal springs. All spring-water has some mineral matter in solution; but a spring is not commonly called a mineral spring unless it contains (i) much mineral matter, (2) mineral matter which is unusual in spring- water, or (3) mineral matter which is conspic- uous either because of its color, odor, or taste. Many mineral springs are thought — and some rightly — to have healing properties, and so are known as medicinal springs. Many of the famous watering-places and resorts for invalids are at hot mineral springs. The Hot Springs of Arkansas, Virginia, South Dakota, and Carlsbad (Bohemia) are examples. Many springs which are charged with gases are called mineral and medicinal, even though their waters are worthless for healing purposes. In 191 1 mineral water was sold from about 700 springs in the United States. The amount of water sold was more than 67,000,000 gallons, valued at about $7,800,000. WORK OF GROUND- WATER Solution. All water which comes out of the ground has in solution some mineral matter dissolved from the rock through which the water has passed. Pure water does not dissolve mineral matter readily; but rain-water is not pure, for it dissolves gases from the air, and in sinking through the soil takes up the products of plant decay. With these impurities in solution, ground-water dissolves most sorts of mineral matter more readily than pure water would. The amount of mineral matter brought to the surface through springs is very great. Much ground-water finds its way to rivers after it seeps out. The larger part of the mineral matter in solution in rivers has come from ground- water which has flowed to them. All the rivers of the Fig. 120. The Wairoa Gey- ser, New Zealand. Shoots 1 ,500 feet. (New Zealand Gov't Tourist Dept.) 212 MODIFICATION OF LAND SURFACES earth are estimated to carry nearly five billion tons of mineral matter to the sea in solution each year. The transfer of so much mineral matter in solution from land to sea, lowers the land. Some of the mineral matter carried to the sea in this way remains in the sea-water. Thus, most of the salt which has been carried to the sea remains there, probably, to this day. On the other hand, much of the mineral matter taken to the sea is used by sea animals (and some plants) for making their shells and bones, and these are left on the sea-bottom when the organisms die. Caverns and cavern life. By the dissolving work of ground-water, rock is made porous. Small pores and cavities are more numerous than large ones, but some of the openings made in this way, such as Mammoth Cave in Kentucky and Wyandotte Cave in southern Indiana, are very large. Such caves occur chiefly in limestone, for this is the most soluble of the common rocks. A few animals live in caves and some of them show peculiar features. They are colored less brightly than their relatives above ground. This is probably because of the absence of sunlight, which seems to have much to do with producing color in animals. Some cave animals have good eyes, some have poor eyes, and some have none. From these and other facts, we infer that the eyes of animals in dark caves tend to disappear. The organs of touch are well developed in cavern animals. In the darkness the sense of touch is much more useful than sight. In Europe, certain caverns were the homes of primitive man, as shown by the human bones and the tools which are found in them. Here, too, are found the bones of large animals which were killed for food or fur, and taken to the caves. On some of the bones of such animals, and on pieces of slate or wood, there are drawings, some of which are of animals no longer living in the region where the caves are. From this we infer that the people who lived in the caves dwelt there a long time ago. Deposition. Ground-water sometimes leaves a part of its dis- solved mineral matter in the pores and cracks of the rocks through which it flows. When cracks in the rocks are filled or partly filled by mineral matter deposited from solution, the fillings become veins (Fig. 121). Many ores of gold, silver, lead, zinc, copper, and other metals, occur in veins. Originally, most of the metals were scattered widely through the rocks. They were dissolved, and then deposited by ground-waters in the cracks and openings where they are now found. Thus ground-water has made the great deposits of most ores, so important to mankind (pp. 179-182). Ground-waters also deposit mineral matter among particles of loose sediment, cementing them into firm rock. Mineral matter brought to the surface by ground-water may WORK OF GROUND-WATER 213 be deposited there, as the result of various causes. (1) When water evaporates, the mineral matter dissolved in it is left behind. This is one reason why kettles in which water is boiled become coated with mineral matter. (2) Certain gases dissolved in water help it to dis- solve mineral matter. If water contains much gas, which later es- capes, as when the water is heated, some of the mineral matter in solution may be deposited. (3) Warm spring- water may give up what it holds in solution when it cools. (4) Microscopic plants grow in the waters which issue from some hot springs, as in Yellow- stone Park, and by some process not well understood extract mineral matter from the water, and cause it to be deposited. Solution and deposi- tion may be going on at the same time, in the same place. Thus the original material of a buried shell may be dissolved and car- ried away at the same time that other material is left in its place, pre- serving the form of the shell. In the same way, wood may be replaced by mineral matter, giving rise to petrified wood, or wood "turned to stone." Such changes probably take place slowly, the mineral matter which was in solution in the water replacing the woody matter as it decays. Fig. 121. A quartz vein (the white band) fill- ing a crack in much older rock. Muchals Caves, Kincardineshire, Scotland. Mechanical work. Mechanical wear by ground-water is slight, since ground-water rarely flows in strong streams. Indirectly, ground- water helps to bring about changes of another sort. When the soil on a steep slope becomes full of water, its weight is increased great- ly, and the water in it makes it move more easily. Under these cir- cumstances, it sometimes slides down. Such movements are known as slumping or sliding. If the slide is large, it usually is called a 214 MODIFICATION OF LAND SURFACES landslide (Fig. 122). Slumping is very common on the slopes of hills composed of clay or other loose matter. Many landslides have been very destructive. In 1903 there was a slide on Turtle Mountain, Prov- ince of Alberta, Canada. A huge mass of earth nearly half a mile square, and probably 400 to 500 feet deep, suddenly slid down the steep face of the moun- tain, into the valley below. The length of the slide was about two and a half miles, and it is estimated that the time which it took was not more than 100 seconds. The heavy rainfall of the preceding year had filled the rock with water, and the earth tremors which occurred shortly before the slide are believed to have hastened the catastrophe. Water in the soil and subsoil works with gravity in the ex- tremely slow, down- slope movement of surface material. This sort of movement is creep (Fig. 123), which is usually too ^slow to be seen. Fig. 122. A landslide, graph by Hole.) (Sketch from photo- Fig. 123. A ravine near Crawfordsville, In- diana, showing trees leaning down-slope, in part because of creep. The surface material creeps faster than that below, tipping the tree.s toward the axis of the ravine. SUMMARY From the preceding paragraphs it is ap- parent that the exist- ence and work of ground-water are matters of great importance. (1) Without water in the soil most plants could not live, and the amount available largely controls both the density and the- character of the vegetation. (2) Chiefly through its influence on plant life, WORK OF RUNNING WATER 215 ground-water helps to determine the distribution and occupations of people. (3) Ground-water is the source of all wells and springs. Ground-water, seeping out, maintains the flow of most streams. (4) Ground- water may modify the character of rocks in several ways: (a) by removing soluble constituents; (b) by depositing new mate- rial in rock cavities; (c) by replacing old material with new; and (d) by favoring new chemical combinations. These changes must have occurred on a vast scale, for ground-waters have been at work for untold millions of years. As a result, soils and useful ores have been accumulated. (5) The mechanical work of ground-water is relatively unimportant, but widespread. The creeping and slump- ing of surface material are in some cases due partly to ground-water. QUESTIONS 1. In order to contain water constantly, must wells extend farther below the surface of the ground on hill tops or in valley bottoms? 2. In order to increase the flow of water, dynamite is sometimes exploded in wells. Why does this in many cases produce the desired effect? Would it be more likely to succeed with wells in hard, brittle rocks, or soft, tough rocks? 3. Make a diagram showing (1) the surface of the ground in a hilly region con- taining a lake, a swamp, and a river, and (2) the position of the water table beneath this surface (a) after continued rains, and (b) during a long drought. 4. What effect does the irrigation of arid lands by water led in ditches from streams have on the position of the water table? How does this affect the question of the acreage which may be irrigated in years to come? 5. Why are the inscriptions on many old tombstones indistinct? 6. Describe the characteristics of a climate which should (1) hinder, and (2) favor solution by ground-water. The Work of Streams Running water is more effective than wind in changing the sur- face of the land over which it moves, largely because water is about 80 times heavier than air. The work of running water is also much more important than that of ice, because water moves more readily and affects larger areas. It is true that glaciers have been much more extensive than now at different times in the past, but this was the case, so far as known, only for comparatively short periods. On the other hand, streams are numerous in most lands, and have been for untold ages. All in all, running water is more important than all other agents- in shaping the details of land surfaces. Streams modify land surfaces (1) by moving loose material to 2io MODIFICATION OF LAND SURFACES lower levels, much of it to the sea, (2) by wearing their channels, and (3) by depositing their excess loads in various forms. These phases of river work, together with their topographic results and some of their human relations, are discussed below. The use of streams, as for commerce, manufacturing, and irrigation, is discussed in Chapter XVI. TRANSPORTATION Gathering sediment. As rain-water Hows down the slopes on which it falls, it carries particles of earth to the streams below. A stream gets much sediment in this way, if the immediate run-off flows over bare, steep slopes of loose material, and little, if it flows over slopes well covered with vegetation, such as grass land or forest. Besides the sediment brought to it by slope wash, a stream also gathers material from its bed and banks. A stream is not a single, straightforward current. When water runs swiftly through an open ditch or gutter, some of it may be seen to move from sides to center, and some from center to sides, while eddies are common. There are also many subordinate currents in the main current of a river, and they move in various directions. Many of them are caused by the unevenness of the bed of the stream (Fig. 124). Some of them a move upward and carry sediment up from the bot- tom of the stream. _ ^ Ground-water dissolves ///^~a~\\-* ^r^Tr^:.' rock slowly, and springs „. __ .„ , m bring some of this dissolved Fiiz:. 1 24. Diagram to illustrate the effect 7r * . ( \ of irregularities, a and 6, in a stream's bed, on matter to streams (p. 211 J. the current striking them. Most dissolved substances are invisible, and remain in the water even after it has become quiet. The amount of matter carried to the sea in solution each year by all rivers (p. 211) has been estimated to be about one-third as much as the sediment carried by them. Carrying sediment. Coarse materials, such as pebbles, in most cases are rolled along the bottom, while tine materials, such as mud and silt, are likely to be carried in suspension. The behavior of the fine sediment in suspension needs explanation. Mud consists chiefly of tiny particles of rock, nearly three times as heavy as water; hence they tend to sink all the time. But as TRANSPORTATION BY STREAMS 217 gravity brings them down, many are caught by upward currents (Fig. 124), and carried up in spite of gravity. It is largely by means of these minor upward currents in the main stream, that sediment is kept in suspension. Particles of sediment suspended in a stream are dropped and picked up repeatedly, and the long journey of any particle is made up of many short ones. Amount of load. The amount of sediment a stream carries depends on (1) its swiftness, (2) its volume, and (3) the amount and kind of sediment which it can get. Swift and large streams can carry a heavier load than slow and small ones. The effect of velocity on the carrying power of streams may be seen in most creeks and rivers which are wider in some places than in others. Where the channel is narrow, the current is swift, and here, in many cases, all fine material has been swept away, leaving only pebbles and larger stones in the channel. Where the channel is wider, and the current slower, the bottom of the same stream may be covered with sand or mud. By narrowing the channel of the Mississippi by making jetties near one of its mouths, in 1875, James B. Eads not only prevented further deposition of sediment there, but forced the river to clear out its own channel. This change permitted larger ocean vessels to reach New Orleans. The amount of material which certain streams carry to the sea has been estimated. For a given river, the estimate is made by calculating the average amount of water (in gallons or in cubic feet) discharged by it each year, and then determining the average amount of sediment in each gallon or each cubic foot. The Mississippi River carries to the Gulf of Mexico an average of more than a mil- lion tons of sediment a day. It would take nearly 900 daily trains of 50 cars, each car loaded with 25 tons, to carry an equal amount of sand and mud to the Gulf. This sediment represents a great loss to the country (p. 167), for most of it would make soil of great fertility, if it were on land. All the rivers of the earth are carry- ing perhaps 40 times as much as the Mississippi. CORRASION How streams wear rocks. As already stated (p. 216), streams wear (corrode) their channels. If the channel is muddy, the mov- ing water picks up sediment; if sandy or gravelly, sediment is rolled along the bottom. Many streams flow on solid rocks, and they gather load even from them. Rock exposed to water, as in the bed of a stream, decays. As it decays, it crumbles, and the crumbled parts are swept away by a swift current. Again, the sand and gravel rolled along by a stream wear its bed even if it is of hard 2l8 MODIFICATION OF LAND SURFACES rock. Subordinate currents sometimes drive the sediment in suspen- sion against the bottom or sides of the channel with similar results. The bits of sediment which a stream carries therefore become tools (Fig. 125), with which even hard rock is worn away. Clear water, flowing over firm, hard rock, wears the rock little. This is shown Fig. 125. The tools of a river. Joe River, Washington. (Tolman.) Stream-worn pebbles in the bed of the St by the fact that in many cases even large rivers flowing from lakes have " mossy" channels. (Why do such rivers have few tools?) Rate of erosion. The rate at which a stream wears down the surface over which it flows depends largely on (1) its volume, and this depends chiefly on the amount of precipitation, and on the size and topography of the area draining to it; (2) its velocity, which is determined chiefly by its slope, or gradient, and its volume; (3) the character of its bed, especially the resistance of its materials; and (4) the load which the running water carries. To work most effec- tively, the water must have tools enough to enable it to cut rapidly, but not so many that the energy expended in moving them retards its flow seriously. Since the factors named above vary greatly, the rate at which the land is being worn down is very unequal in different places. The average rate of wear for the United States is thought to be about 1 inch in 760 years; but the rate varies from RIVER VALLEYS IN HISTORY 219 an average of 1 inch of reduction in about 440 years in the Colorado Basin, to 1 inch in about 3,900 years in the basin of the Red River of the North (Fig. 126). FEATURES DEVELOPED BY STREAM EROSION River Valleys The depressions in which rivers flow are their valleys, and in the making of valleys streams have been the chief agents. River valleys centers of human activity. Most of the great valley lowlands of middle latitudes are settled densely, because Fig. 126. Rates of land reduction by stream erosion in the United States. The figures are the approximate number of years required for one inch of reduction. (Dole and Stabler, U. S. Geol. Surv.) of their fertile soils, favorable topography, and facilities for com- munication. Probably more than one-fourth of the people of east- ern United States live on alluvial lands. The valleys of the United States have been sought out for set- tlement from the beginning of its history. New York history began at the mouth of the Hudson, Pennsylvania history in the valley of the Delaware, and that of Virginia on the banks of the James. Later, various valleys became highways of expansion toward the interior. The overflow from the settlements of the coastal low- lands of Massachusetts passed over the rocky and infertile uplands 220 MODIFICATION OF LAND SURFACES to the west, to the inviting bottom lands and terraces of the Con- necticut Valley. As years passed, this great valley led settlers northward into New Hampshire and Vermont. The Ohio Valley was one of the first sections of the inte- rior to be settled, and for many years the Ohio River was a main highway of westward expansion. The upper Rio Grande Valley guided settlers northward from Mex- ico into the United States. The Platte Valley directed many fur traders and trap- pers across the Great Plains; it was fol- lowed by the Mor- mons on their way to Utah; along it ran the Oregon Trail and the first trans-continental railroad; and it was the greatest gateway into Nebraska when, in the fifties, the latter began to be settled. Many other examples of the part which valleys have played in expansion and settlement might be given. The larger rivers of eastern United States were long the great high- ways of trade and travel. Much of the Interior depended largely on the Mississippi and its tribu- taries as outlets to market, before the building of railroads (p. 274). In the future, the larger rivers of the United States probably will be used more than now for transportation (p. 287). Many valleys are grown-up gullies. Many valleys are en- larged gullies. A gully started during one shower (Fig. 127) is made Fig. 127. A gully made by a single shower. Fig. 128. . Diagram illustrating how one gully takes others as a result of growth. FORMATION AND GROWTH OF VALLEYS 221 deeper, wider, and longer by the next. As the result of repeated showers year after year and, in many places, repeated meltings 4*fefaMti^3SEE5 Fig. 1 29. Gullying in southwestern Iowa. (Iowa State Drainage, Waterways, and Conservation Commission.) of snows, the gully grows to be a ravine, and later a valley. Not all gullies, however, become valleys. Many gullies may start on one slope, but as they grow, some are so widened as to take in others (Fig. 128), and the number is reduced. Few gullies become ravines, fewer still be- come small valleys, and the number of valleys which attain great length is very small. Growth of gullies should be prevented. Much land in the United States has been ruined and much more injured, by gullies. There are many exam- Fig. 130. Brush dams built to check erosion in the southern Appalachians. pies of such land in the southern Appalachians, where, on bare surfaces, gullies form and grow rapidly because the slopes are steep, I 222 MODIFICATION OF LAND SURFACES the rainfall heavy, and much of the surface material is eroded easily. Surfaces of this sort should, as a rule, be given over to the growth of forests. But serious gullying is by no means confined to mountain areas (Fig. 129), and the problem of checking the growth of gullies is country-wide. One of the best ways of stopping their growth is by filling them with brush (Fig. 130). How valleys get streams. Water commonly flows in gullies only when it rains or when snow melts, and for a short time after- ward. But many valleys made from gullies have permanent streams, so that they are being made larger all the time. k When a valley has been deepened so that its bottom is below the T? . i^- u • j ground-water surface, Fig. 131. Diagram showing ground- water sur- & face; a, the ground-water surface in wet weather, ground-water seeps or and b, in times of drought. When a valley has been flows into it, and forms cut below a, there will be a stream in wet weather, , j -p- but it will go dry in time of drought. Whentheval- a stream - ^n^g-^ 1 * ley bottom is below b, the stream will be permanent. a represents the water surface in wet weather, and b the water surface in dry weather. The valley whose cross- section is shown by 1 does not have a stream fed by ground-water; the valley 2 has a small stream in wet weather; while the valley 3 has a permanent stream, because its bottom is below the ground-water level of dry times. Streams which are fed by lakes, and streams which flow from snow- and ice-fields which last from year to year, do not depend on ground-water, though in most cases they receive it. The deepening of valleys. Swift streams remove material from their beds and so make their valleys deeper, but many slow streams deposit more sediment than they take away, and so make their valleys shallower. Many streams deepen their valleys in their upper courses where their waters are swift, while they make them shallower in their lower courses where the flow is sluggish. As a stream deepens its valley, the gradient becomes less, and the stream flows more and more slowly. In time, every swift stream will cut its channel down until its gradient is low and its current sluggish. A stream cuts the lower end of its channel down to about the level of the lake, sea, or river into which it flows, but the channel rises from its lower end to FORMATION AND GROWTH OF VALLEYS 223 its head. The lowest level to which a stream can reduce its basin is base-level. The widening of valleys. Valleys are widened in many ways, among them the following: (1) A stream may flow against one side of its channel with such force as to undercut the slope above. Slow streams are more likely to widen their valleys in this way than swift ones, because they are turned more easily against their banks by obstacles in the channels. (2) Rain-water flowing down the slopes of a valley carries earthy material with it. This widens the valley, by slowly wearing back its slopes. (3) The loose matter which lies on the slopes of a valley creeps slowly downward, especially when wet. It may also slump down steep slopes. In these and other ways, all leys are being widened all time. After streams have cut their valleys down to low gradients, they make flats in their bottoms, by side-cutting (Fig. 132). These flats are below the level of the surface in which the valleys lie, and may become very wide (Fig. 133). Thus the Mississippi River at Memphis has a flat about 35 miles wide. Most valley flats increase regularly down stream (Why?). The lengthening of valleys. The headward growth of a gully is due chiefly to erosion by the water which flows into its upper end. The head of a gully advances in the direction of greatest wear, and this is rarely in a straight line. Most valleys are therefore crooked from the outset. The headward growth of a valley normally continues until the wear of the water flowing into its upper end is equaled by the wear Fig. 132. Diagrams of a making a flat by side cutting. in width more or less 224 MODIFICATION OF LAND SURFACES of the water flowing from the same divide (water-parting) in the opposite direction. The divide is then permanent (Fig. 134). Valleys are not all grown-up gullies. Not all valleys were formed by the growth of gullies. A vast area in northern North Fig. 133. A wide valley flat. Milk River, near the Montana-Alberta bound- ary. (From photograph by U. S. Geol. Surv.) America, for example, once was covered by a sheet of snow and ice. Most of the rivers which had existed in this area ceased to flow while the ice lay on the land. Many of their valleys were rilled, at least in places, by the drift which the ice left when it melted, and so great areas were left without well-defined valleys. The melting ice, however, supplied much water, and this flowed along the lowest lines of descent which it could reach, and made valleys along those lines. Valleys made by such waters may have permanent streams at the start, since they do not depend on ground-water. Again, the melting of the ice left many lakes in the hollows of the land it had covered, and the rainfall of the region was great enough to make many of them overflow. When a lake overflows, Fig. 134. Diagram of a divide. The crest of the divide (at A) is per- manent if the conditions of erosion are the same on the two sides. Rain- fall may lower it, but cannot shift its position horizontally. STAGES OF EROSION 225 the out-going water follows the lowest line of descent, and cuts out a valley. In these ways, rivers soon were formed on the surface from which the ice melted. Valley and river systems. Most valleys are joined by many smaller valleys. The reason is simple. The erosion of the slopes of valleys by the water flowing from them to the valley-bottoms is greater along some lines than others (Why?), and tributary gullies are started, which, growing in the same way as the parent valleys, may come to have permanent streams. These tributary valleys of the first generation come to have branches, and the process may go on until a network of watercourses affects the surface. A valley and its tributaries constitute a valley system. A stream and its branches form a river system, and the area drained by a river system is a drainage basin. Stages in the history of valleys and streams. Valleys grow in size as they advance in years. When a valley is young, it is narrow and its slopes are steep. If the land is high, the valley may have a steep gradient, in which case it soon becomes deep. Its cross-section is then somewhat V-shaped (Fig. 135, 1), and its tributaries are short. A mature valley is wider (Fig. 135, 2), its slopes in most cases are gentler, and its tributaries are longer and older. An old valley is wide, and has a broad flat and a low gradient (Fig. 135, 3). A stream also, as well as its val- ley, passes from youth to maturity, and from maturity to old age. In its youth, it is likely to be swift, unless it flows through low land. In maturity, it flows less swiftly and more steadily, and when it reaches old age, it winds slowly through its wide plain. Even an old stream, however, may take on the vigor of youth when in flood. The terms youth, maturity, and old age may be applied to river systems as well as to single rivers. Every river system, aided by weathering, has entered on the task of carrying to the sea all the land of its basin which is above base-level. So long as the river system has the larger part of its task before it, it is young. When the main valleys have become wide and deep, and the areas of upland have been well cut up by valleys, the river system is said to have reached maturity. Fig. 135. Diagram showing changes in the shape of a valley as it advances from youth to old age. 1 = youth; 3 = old age. The material in which the valley is cut is all of the same character. 226 MODIFICATION OF LAND SURFACES When the task of reducing its drainage basin to base-level is nearing completion, the river system has reached jld age. The topography of a drainage basin is youthful when its river system is youthful, mature when its river system is mature, and Fig. 136. Diagram of an area in a youthful stage of erosion. The area some distance from the sea. The bottom of the diagram represents sea-level. Fig. 137. Diagram showing mature topography in a region situated some distance from the sea. The bottom of the diagram is sea-level. The area shown in Fig. 136 will in time resemble closely the present appearance of this area. Fig. 138. Diagram showing old topography in a region situated some distance from the sea. The bottom of the diagram is sea-level. Unless the land is elevated, the areas represented in the two preceding figures will finally closely resemble this area. old when its drainage is old. In an area of youthful topography, much of the surface has not yet been much changed by erosion (Fig. 136), and the surface may be ill-drained. In an area of mature topography, much of the surface has been reduced to slopes by erosion STAGES OF EROSION 227 (Fig. 137), and is well-drained; while an area of old topography is one which has been brought down to general flatness by erosion (Fig. 138). When an area is worn as low as running water can bring it, it is a base-level plain. As streams wear the land toward base-level, they flow on diminishing gradients. Because of this, their velocity and therefore their erosive power decrease constantly. In other words, an area approaches base-level more and more slowly the nearer it gets to it, and it may take as long to wear away the last few feet above base-level as it did all the other hundreds or thousands Fig. 139. A monadnock on a peneplain. Tower, Minnesota. (Mead.) of feet that once lay above. Few, if any, areas have been absolute- ly base-leveled. The time required is enormous, and before the task is completed, an area is likely to be elevated with reference to sea-level, and the quickened rivers started upon the task of again reducing the elevated land to base-level. But many areas have been nearly base-leveled. Such plains are peneplains (almost plains) . Above their otherwise nearly level surface, occasional elevations may rise abruptly. These elevations, known as monadnocks (Fig. 139), owe their existence to (1) the greater resistance of their rocks, or (2) a favorable position among drainage lines. The time required for reducing a drainage basin to a base-level plain is a cycle of erosion. As implied above, cycles of erosion commonly are brought to an end by relative uplift of the land before they are completed. The terms youth, maturity, and old age, as used in geography, apply to stages of development, and not to periods of years. Thus a small river, working on soft material, may bring its valley to old age in less time than that required for a large stream, opposed by resistant rocks, to bring its valley to maturity. 228 MODIFICATION OF LAND SURFACES Influence of stage of erosion on human activities. The den- sity of population of a region and the condition and activities of its people are influenced greatly by the stage which it has reached in its topographic development. Many young rivers are inter- rupted by falls and rapids (p. 230) which afford water power for manufacturing, but interrupt or prevent navigation. Many young rivers, too, are not available for commerce partly because they flow in narrow valleys, far below the level of the surrounding coun- try. In parts of western United States, it is also impracticable to lift the waters of such streams to the neighboring uplands for purposes of irrigation. Thus the waters of the Colorado River can be used for irrigation only in the upper part of the river system, or below the Grand Canyon, and the larger irrigation projects of southern Idaho are related definitely to breaks in the walls of the deep canyon of the Snake River. Again, very deep valleys may make travel across their courses almost impossible. In such cases, places where the valleys can be crossed may have all the importance of mountain passes, controlling the courses of trails and roads. The Denver and Rio Grande Railroad crosses the Green River in eastern Utah where there is a gap in the canyon wall, a gap that earlier fixed the course of the Spanish Trail. Roads may run in any direction over young plains whose valleys are shallow. Nearly all the land of such plains can be farmed, so far as topography is concerned. The poorly drained inter-stream flats may require ditching or tile draining, however, as in parts of Iowa and Illinois. Where relief is great, early maturity is least favorable to most human activities. The larger rivers may be navigable, but most of their tributaries are likely to have steep gradients, with falls and rapids. At this stage, run-off is at a maximum, and streams are most subject to floods. Many of the larger rivers are crossed at ferries and fords, for bridges are hard to maintain. Good sites for river towns may be few. Wagon roads and railroads follow the narrow ridges between the valleys, or the flats of the larger streams. Farming is difficult on the steep valley slopes, where soils are likely to be thin and easily washed away. In general, the population of such regions is sparse and non-progressive, having little contact with the outside world. Mineral deposits or other special resources may create in- dustrial centers, whose progress serves to emphasize the backward- ness of the region as a whole. These conditions are illustrated in parts of the Cumberland and Alleghany plateaus (p. 173). STAGE OF EROSION AND HUMAN ACTIVITIES 229 Old rivers are, as a rule, free from rapids and falls, and in most cases have gradients so gentle that they do not afford good water power. While these conditions favor navigation, the latter may be interfered with by sand bars (p. 237) and the shifting and crooked courses of the channels. Much of the land of the broad flood-plains of old rivers is swampy and of little use until drained, but is then of Fig. 140. The canyon of the Yellowstone. (Hillers, U. S. Geol. Surv.) great fertility (Why?). While floods are most numerous in valleys whose slopes are steep, they are more likely to be disastrous to prop- erty on the broad, low flats of older rivers, such as the lower Mississippi (P* 2 37)« On the gentle inter- valley slopes of an old area, the soils are likely to be deep (Why?); their fertility depends chiefly on the character of the underlying rock. The area of land which can be farmed is, as a rule, much greater in topographic old age than in ma- turity. On peneplains, as on youthful plains of low relief, travel is easy in all directions. Wagon roads and railroads are not confined to certain courses by topography. 230 MODIFICATION OF LAND SURFACES Canyons and gorges. Valleys which are narrow and deep often are called gorges if small, and canyons if large. The Colorado Canyon is the greatest canyon known. Its depth is about a mile, and it is eight to ten miles wide at the top. Its sides are step-like, because of the unequal hardness of the rock of the canyon walls. The harder strata are the cliff-makers. The Yellowstone (Fig. 140), Snake, and Columbia rivers have wonderful canyons in some parts of their courses, and so has the Arkansas River where it flows through the Rocky Mountains. The canyons of many smaller and less well- known rivers are al- most equally striking. A narrow valley means that the processes which have made it deep have outrun the processes tend- ing to make it wide. Val- leys are deepened rapidly when their gradients are high and their streams strong. They are widened slowly (1) when the climate is arid, so that there is little slope wash, (2) when the stream is so swift that it does not meander, and (3) when the material of the sides is such that it will stand with steep slopes. Therefore (1) great "altitude, (2) arid climate, (3) swift streams, and (4) rock which will stand in steep slopes, favor the making of canyons. In other words, young valleys in plateaus and mountains (as in western United States) are likely to be canyons. (How can there be large, strong streams in dry regions?) Some of the ancient cliff-dwellers made their homes in the recesses of canyon walls (Fig. 141), probably because these positions could be defended easily. Canyons must change into valleys of another type, for the stream in the canyon will in time cut down to its base-level. The valley will then stop growing deeper, but widening will still go on, and the narrow valley will become so wide that it will cease to be a canyon. Rapids and falls. The bed of a stream may be steeper at some points than at others, and there the stream flows more rapidly. The quickened flow constitutes a rapids; or, if the water in a stream's bed drops over a cliff, it makes a waterfall (Fig. 142). Waterfalls and rapids are important chiefly because they render the power of the streams available to man for purposes of manufacturing, lighting, Cliff dwellings, southwestern Colorado. RAPIDS AND FALLS 231 transportation, etc. (p. 288). Many electric railroads and many industries depend for power on electricity developed by falls and rapids, and railroads and fac- tories of all sorts are likely to depend on this sort of power still more largely in the future. Rapids and falls interfere with navigation, or prevent it alto- gether (p. 228). Waterfalls come into existence in various ways. A river flowing on the high gradient shown in Fig. 143 is likely to be an eroding river. It will wear its channel faster at A , where the rocks are soft, than just above, where they are hard, with the result shown in Fig. 144. The continued wear of the water in such a case would cause the rapids at A (Fig. 144) to become steeper, and in time the descending water would become a fall (Fig. 145). In this case, the rapids and falls de- pend on inequalities of hardness in the bed of the stream. This is a common way in which falls and rapids origi- nate. A landslide or lava flow may form a dam, over which the water falls or flows in rapids. Most of the waterfalls of the United States are due to glaciation (pp. 256, 265). Falls and rapids are undergoing constant change, although the change is usually very slow. Many falls are moving slowly up-stream, because the water undermines the hard layer of rock over which it drops (Fig. 145). As a fall moves up-stream, it becomes lower in many cases (Fig. 145). It is clear that such falls will disappear if they recede far enough. If the hard rock over which the water drops is in the position shown in Fig. 146, the fall will not recede, though it will become lower, and will disappear when the stream cuts down to base-level, where the fall is. (What would be the effect of re-eleva- tion of the basin?) Rapids and falls are temporary features of streams, and, like canyons, are marks of youth. In time, therefore, all existing rapids and water- falls will disappear. Fig. 142. Falls of the Black River, Wisconsin. (Smith, Wis. Geol. Surv.) 232 MODIFICATION OF LAND SURFACES Narrows. Many valleys are narrow where they cross a tilted layer of hard rock. Such a place in a valley is a narrows, or water- gap (Fig. 147). The Delaware Water-Gap through Kittatinny Mountain (Pa.-N. J.) is a well-known example. Fig. 145. Figs. 143, 144, i45 of a waterfall. Diagrams to illustrate the development and extinction • Why will the waterfall cease to retreat up-stream when it reaches C-B, Fij . 145? What changes will occur after it reaches this placer Narrows sometimes serve as gateways through mountains, and so control lines of travel. The narrows of Wills Creek in Wills Mountain, Maryland, may serve as an example. In the early days of American history, Fort Cumberland was built at this narrows to guard the important pass through the mountains, and Washington's and Braddock's roads ran west through it. At the present time, the Cumberland National Road (Fig. 215) and an important railway make use of it. PIRACY AMONG RIVERS 233 Accidents to streams. Streams are subject to many accidents. If the land through which they flow sinks so that its slope is reduced, they flow less rapidly, or may even cease to flow. If the lower end of a valley sinks below sea-level, the sea-water enters and forms a bay, drowning the lower end of the river and its valley. If the streams along a coast end in bays, we infer that the coast has sunk, and that its rivers and valleys have been drowned. Thus Delaware Bay and Chesapeake Bay are drowned valleys. If the basin of an old stream is raised so that the gradient of the stream becomes greater, its velocity is increased, and it again takes on the character of youth. Such streams are said to be rejuvenated. Fig. 146. Diagram of water- falls developed on vertical beds. Fig. 147. Lower Narrows of the Baraboo River, Wisconsin. The valley- widens beyond the gap, the same as in the foreground. If by headward growth one valley reaches and enters another where the latter is at a higher level, it may steal the water which other- wise would flow down the higher valley (Figs. 148 and 149). The stream which steals is a pirate. The stream stolen is diverted, and the stream which has lost its upper water is beheaded. Piracy has been rather common among rivers, espe- cially in mountain regions. In the Figs. 148, 149. Diagrams to Appalachian region, for example, illustrate stream piracy. there are few large streams which 234 MODIFICATION OF LAND SURFACES have not either increased their waters by piracy, or suffered loss by the piracy of others. Piracy is favored by inequalities of hardness, for streams which do not cross hard rock deepen their channels more readily than those which do (Fig. 150). When a stream is diverted from a narrows, the water-gap becomes a wind-gap. Wind-gaps are common in most mountain regions which have advanced to late maturity. Cumberland Gap, in the southeastern corner of Kentucky, is an example. It afforded many Fig. 150. A case of stream piracy in Pennsylvania. The upper part of the present Wiconisco Creek formerly was tributary to Deep Creek, joining the latter at "A." (From Millersburg and Lykens, Pennsylvania, Sheets, U. S. Geol. Surv.) What enabled Wiconisco Creek to behead Deep Creek? What was the prob- able origin of the mountain gap at "B'7 Is future piracy likely to occur in this region? Why? of the early emigrants the best route across the mountains, and during the last quarter of the eighteenth century probably more than 300,000 people passed through it to settle in the West. The many wind-gaps of the Blue Ridge Mountains were important in the early westward movement of population, and again in the campaigns of the Civil War. DEPOSITION BY STREAMS Causes of deposition. Streams may become overloaded in various ways, and so be forced to deposit their excess sediment: (1) Their carrying power may be reduced by a decrease of gradient. The change may take place suddenly, as at the base of a steep slope, or it may take place slowly, as a stream flows through a valley whose slope becomes gradually less. (2) Their carrying power may be WHY STREAMS DEPOSIT 235 diminished by decrease of volume. Streams flowing through arid regions may receive little water, and lose much by evaporation and by soaking into the dry earth. Many streams in the West leave the mountains bank-full, to wither and disappear on the lower lands. Many also have much of their water withdrawn for purposes of irrigation. (3) Tributary streams with high gradients may bring to the main streams more sediment than the latter can carry away. -^.r-— - m ^^, ~~ mm~*-^ w.'«> ', '', J$L$F. .B:^ " v-^| ' ^ ■• .':^V V "T ""• rirtiir'rfi* 11" ■ ifti .r _ luU ^r ■ I f' * mffl^ s - " i-f* xj^ '<<&$£& ■■::■■"-'■■:.- fS^jJ^^'S; *"s?^j2a Hfip^aL ^ : <^HP%r v ' Is^fe^- ! ::#- ■ -^m^ Fig. 151. Alluvial fan at the mouth of Aztec Gulch, southwestern Colorado. (U. S. Geol. Surv.) (4) Many rivers deposit at their mouths, where the current is checked. Deposits at the bases of steep slopes. Every shower washes fine sediment down the slopes of hills and mountains, and much of it is left at their bases, where the velocity of the water is checked suddenly. At the lower end of every new-made gully on a hillside, there is a mass of debris which was washed out of the gully itself (Fig. 127). Material in such positions accumulates in the form of an alluvial cone, or a gentler sloping alluvial fan (Fig. 151). The rivers descending from the Sierras to the valley of California have built great fans along the foot of the range, and most of the rivers coming out of the Rockies to the plains east of them have done the 236 MODIFICATION OF LAND SURFACES same thing. Many of the fans of streams descending from the west- ern mountains are miles across. Fans made by neighboring streams may grow until they unite to form a compound alluvial Jan, or a pied- mont alluvial plain. Such plains exist at the bases of many mountain ranges. Their alluvial deposits may be hundreds of feet thick. Many alluvial fans and piedmont alluvial plains are valuable for farming. (In general, which would be more valuable, the higher Fig. 152. Cultivated alluvial fan near Riverside, California. or the lower portions of alluvial fans? Why?) In parts of southern California, for example, such lands are so valuable that farms are very small and highly improved (Fig. 152). Water is supplied (1) by wells, through which the fan is made to yield up the water it has absorbed, or (2) by irrigating ditches which connect with a stream or reservoir at a greater height. Many villages in mountain valleys are situated on alluvial fans. The agricultural settlements of Utah spread southward from the vicinity of Great Salt Lake along the piedmont alluvial plain at the west base of the Wasatch Mountains. Most of the cities and villages of the state are within this belt. Deposits in valley bottoms; flood-plains and man. The gradient of a stream generally becomes less toward its mouth, and FLOOD-PLAINS AND MAN 237 so it happens that sediment is spread for great distances along valley bottoms. Some of it is left in the channels, and some is spread over the low lands along the streams, making alluvial plains. Streams sometimes deposit sand bars in their channels, especially in low water. Bars, and the tree trunks and snags which they often catch and hold, hinder navigation, especially when rivers are low. In earlier years, many steam- boats were wrecked by such obstructions in the Missouri and Mississippi rivers. Later, large sums of money were spent in removing snags and dredging channels. Alluvial plains along large rivers are almost flat, though they slope gently down-stream, and many of them have natural levees. This term is applied to the low ridges along the banks of the channel (Fig. 153). In times of flood, the current in the main channel is swift; but so soon as the water spreads be- yond its channel, its velocity is checked be- cause its depth sud- denly becomes less, and it promptly abandons much of its load. Dur- ing the period of over- flow, the edges of the channel current are checked by the slower moving flood-plain water, and this causes further deposition on the banks of the channel. Repeated deposition in this position gives rise to levees. Embankments have been built by man upon the natural levees of some rivers to prevent the flooding of the valley flats, and to permit the settlement of the bottom lands. Louisiana alone has spent more than $35,000,000 since 1865 in levee building, and is expending now about $800,000 a year in this way. (Why must the protective levees be built higher and higher as time passes?) In spite of such improvements, floods are unfortunately frequent. The damage which they did to buildings, bridges (Figs. 154 and 155), railroads, etc., in the United States in 1908 was estimated at more than $237,- 000,000, though not all this damage was done on the flood-plains of large rivers. Impressive as this estimate is, it takes no account of the great damage done to the land itself, nor is it possible to measure the suffering and reduced efficiency of the people living where there have been great floods. In early days, most of the people in Louisiana and Mississippi lived in narrow belts along the levees of the Mississippi and its Fig. 153. Diagram showing natural levees. 238 MODIFICATION OF LAND SURFACES Fig. 154. Railway bridge over the Nolichucky River at Unaka Springs, Tennessee. (From photograph by Glenn, U. S. Geol. Surv.) Fig. 155. Same place as shown in Fig. 154 after the bridge and piers were swept away by the flood of May, iqoi. (From photograph by Glenn, U. S. Geol. Surv.) TOWN SITES AND RIVERS 239 Fig. 156. The Rio Grande near Browns- ville, Texas. branches. The land here was high enough and dry enough to be farmed, very fertile, and close to the streams which were the great highways of that time. The plantations were narrow along the streams, and extended back, at right angles to them, until the land became too low and wet to cultivate. A stream in an alluvial plain is likely to wind about, or meander (Fig. 156). This is the result of the low velocity of such a stream, for sluggish streams are turned aside easily. Were such a stream made straight, it would become crooked again, for the banks of all streams are less firm at some places than at others, and the stream would cut more at those places. Once started, meanders tend to become more and more pronounced (Fig. 157) until, probably in some time of flood, the stream cuts through the neck of the meander and straightens its course. When a stream has cut off a meander, the abandoned part of the channel may remain for a time unfilled with sediment. If it contains standing water, it becomes the site of an oxbow lake or bayou (Fig. 156). In meandering, a stream sometimes reaches and undermines the valley bluff, thus widening its valley flat. This is, indeed, the most important process in the widening of valley flats (p. 223). Towns grew up early on the bluffs of the lower Missis- sippi at points where the river touched the side of its valley. In this way the location of Natchez, Vicksburg, Mem- phis, and other places was determined. Such sites, overlooking and controlling the river, were bones of contention between Spain and the United States during the dispute over the southwestern boundary, from 1783 to 1795. The same physio- graphic features located the Confederate defenses in the Civil War at Columbus (Ky.), Ft. Pillow (Tenn.), Vicksburg (Miss.), Grand Gulf (Miss.), and Port Hudson (La.). By shifting their courses, as the result of deposition and meander- Fig. 157. Diagram showing development of a meander. 240 MODIFICATION OF LAND SURFACES ing, streams have affected human interests in many other ways. Vil- lages which grew up on the banks of navigable rivers because oi the river trade, in some cases have been left far from the streams by changes in the positions of the latter. Such villages usually decline when the streams withdraw their patronage. Other places built on river banks have been preserved at great expense, while some have been washed away. The Mississippi River flows over the site of Kaskaskia, one of the most important French settle- Fig. 158. A delta in a lake in Switzerland. (From photograph by Robin.) ments in the upper Mississippi Valley, and the first capital of Illinois. The Missouri River destroyed Franklin, Missouri, an outfitting place in the 1820 's for the trade across the Great Plains to Santa Fe. Many streams have been used as boundaries between counties and states. In numerous cases the shifting of the stream has led to boundary disputes, for, by the cutting off of meanders, tracts of land have been shifted from one state to another. In the case of the Missouri River, there have been disputes between Nebraska and South Dakota, Nebraska and Iowa, and Nebraska and Missouri. The Supreme Court finally decided that when the Missouri develops a cut-off, the boundary line does not shift with the river, but remains where it was. Again, many boundaries have been defined as following the "main channels" of streams. Where there are several channels, which is the case in many rivers, the question may arise as to which one is the main channel. Furthermore, the main channel at one time may be a subordinate channel at another time. These conditions have led to disputes over the ownership of islands in different rivers. The objections to rivers as boundaries are most serious where they form inter- national boundaries. Thus the shifting of the Rio Grande makes it a poor bound- ary between the United States and Mexico. In addition, so much water was taken from the Rio Grande for irrigation in southern Colorado and New Mexico that there was little water for Mexican farmers below El Paso. Mexico protested to the United States, and finally it was arranged that the United States should build DELTAS AND THEIR RELATIONS TO MAN 241 a great reservoir on the Rio Grande north of El Paso, to store the water of the river, and that Mexico should receive a certain fixed amount of water from this reservoir each year. Most flood-plains are very fertile, but many are too wet to be cultivated without drainage. About one-sixth of Arkansas, for ex- ample, is swampy, but most of its swamp area is rich alluvial land. When drained, the wet lands of the United States will form one of the greatest resources of the nation (p. 300). Deltas and their relations to man. Where a stream flows into the sea, or into a lake, its current is checked promptly, and ^•^^wS'^^--^'-^-" :; ? '■'\r J> '- \ "S^'^"'^^ b (jjjjK ^\ ' £/■% J \^[Pontchartrair&. ^S^T -* ^ tt-4 V5$k\ ^T r^L ' '^-~ s^hM ^4 , ''^W^ i\v & \ '■ - - ;: ' ^z\ '\^ >N-r \ ' C r^i \ m c35 ^&^*°£2,J^ Jrvk Fig. 159. The lower part of the delta of the Mississippi River. soon stopped entirely. Its load therefore is dropped, and if not washed away by waves and currents, makes a delta (Fig. 158). That part of a delta above the surface of the water in which it is built is like a nearly flat alluvial fan. Deltas may be built where one stream flows into another, especially where a swift stream with much sedi- ment joins a slow one. Much land has been made by the growth of deltas. Thus the Colorado River has built a great delta across the Gulf of California near its former upper end. In the arid climate of the region, the shut- off head became a nearly dry basin, the lowest part of which is about 300 feet below sea-level. The soil being good, water alone was needed 242 MODIFICATION OF LAND SURFACES Fig. 160. Delta of the Nile River. The dotted area is desert. to make this area fertile, and the results that have followed the irrigation of parts of it. justify its new name, the "Imperial Valley." Figs, dates, and other tropical products grow here luxuriantly. The deltas of the Mississippi (Fig. 159), the Nile (Fig. 160), and the Hwang-ho (Fig. 161) rivers are among the large and well-known ones. The delta of the Ganges and Brahmaputra has an area (above water) of some 50,000 square miles (nearly as large as Illinois). While rivers have made much delta land, it is to be remembered that the material of which they are composed has been removed from vastly larger areas, and that much of it was rich soil. It is probable that the loss to man through the removal of such material is far greater than the gain resulting from its deposition. The surfaces of most deltas are nearly fiat, and the streams which cross them often give off branches, called distributaries, which flow independently to the edge of the delta, and are subject to frequent changes. These changes sometimes affect commerce in a vital way (p. 351). The distributaries of the Mississippi offered the English in the War of 181 2, and the Federals in 1862, several pos- sible lines of approach to the vicinity of New Orleans. The necessity of watching these different lines scat- tered the men and the resources, and weakened the resistance of the de- fenders of the city. By cutting the levees and flooding the lower land, General Jackson was able to increase greatly the difficulties of the English. J) el la of the Hwang-ho. Most delta land away from natural levees is low and wet, and must be diked and drained before it can be farmed. The soil of great deltas is deep (What determines its thickness?), and in most cases rich in the mineral elements of plant food. Some deltas, like that of the Hwang-ho, support dense populations. Delta lands are, however, subject to disastrous floods. It is estimated that the flood of the Hwang-ho ALLUVIAL TERRACES 243 River in September, 1887, drowned more than a million people and caused the death of many more by disease and famine afterward. Previous to 1853, the Hwang-ho had flowed for many years into the Yellow Sea south of the Shan-tung promontory (Fig. 161). In that year, it shifted its course in flood time, forming a new channel leading northeast into the Gulf of Pechili, 300 miles north of its former mouth. Other changes at earlier times, running as far back as 2293 b. c, are recorded in the annals of Chinese history. Lakes exist on many large deltas. Some are former sections of the shifting streams, and some (Fig. 159) are portions of the sea or lake in which the delta is built, portions that were surrounded by the deposits or shut in between them and the former shore-line. Delta cities have peculiar problems, as illustrated by New Orleans. For a long time, floods were of almost yearly occurrence. In 1849, for example, 220 in- habited squares were flooded and 12,000 people were driven from their homes. Street improvement was difficult; there were no paving stones save those brought as ballast in ships. As late as 1835, only two streets were paved for any consider- able distance. On the other streets, carriages in wet weather sank to the axle in mire. The question of a domestic water supply was an early and pressing one, and for a long time the practice was general of building cisterns to catch the rain- water. The city could not easily empty its sewage into the Mississippi, for the banks of the river are above the houses. Under these conditions, the city was for years a very unhealthful place. In recent years these disadvantages have been largely overcome. New Orleans now pumps its sewage into the river, cisterns are condemned, many streets are well paved, and the city is much more healthful than formerly. Alluvial terraces. When a river which has an alluvial flat is reju- venated (p. 233), the stream sinks its channel below the level of the flat. The remnants of the old flood-plain are then alluvial terraces (Fig. 162). Such terraces are also formed in other ways. Thus if a stream is sup- plied for a time with an excess of load, it aggrades (builds up) its valley. If, later, the excess of sediment ceases, the stream sets to work to re- move that which was temporarily laid aside in its flood-plain. The material of many alluvial terraces is gravelly or sandy, and their soils vary greatly in value. Many towns and cities are built on alluvial terraces. (What advantages would such locations have over sites on flood-plains? On the edges of valley bluffs?) The leading towns of the Platte Valley in Nebraska are on terraces near the mouths of tributary valleys. (Of what significance is the last fact?) In the middle Illinois Valley, every town is on a terrace, and every terrace has a town. Terrace sites were chosen for most of the first settlements of the Connecticut Valley, such as Hartford, Weathersfield, and Windsor. 244 MODIFICATION OF LAND SURFACES Summary. From the physiographic standpoint, the mission of running water is to wear the land to base-level. The material it Fig. 162. Terrace of the Columbia River. (Willis.) carries toward and to the sea is prepared for transportation largely by the agents of weathering, and in subordinate amount is worn from the solid rocks by the streams themselves. The irregular wearing down 163, [64. Drainage maps of contrasted areas of equal size. of the land produces most of the familiar relief features of the surface. Their characteristics are determined by several factors, especially QUESTIONS 245 by the character and position of the rocks from which they were carved, and the stage of development which they have reached. On its way to the sea, the waste of the land is often laid aside by over- loaded streams, forming topographic features subject to later destruc- tion by eroding waters or by other agencies. All phases of river work affect human interests vitally. Much can be done by regulating and controlling streams to increase their prevent usefulness and their doing damage. QUESTIONS i. In what parts of the United States would a valley need to be deep to have a permanent stream? 2. What are all the conditions which may help to make the flow of streams (i) regular, and (2) irregular? 3. Why do streams carry more and coarser material during floods than at other times? 4. Is the bed of the upper St. Lawrence River being eroded much? Why? 5. (1) Why is the rate of erosion in the Colorado Basin so rapid (Fig. 126), especially in view of the fact that a large part of it is in an arid region? (2) Why is the rate in the basin of the Red River of the North relatively so slow (Fig. 126)? 6. Why are steep slopes charac- teristic of arid climates? 7. What is the age, in terms of erosion, of the area shown in Fig. 80? 8. (1) Interpret the contrasted drainage shown by Figs. 163 and 164. (2) In what stage of erosion is the area shown by Fig. 163? (3) Does Fig. 164 indicate the stage of erosion which that area has reached? Why? 9. (1) What topographic features are shown in Fig. 165? (2) Compare and contrast the northern and southern parts of the area as to (a) the climate, (b) the character of the rocks, and (c) the work of the streams. 10. In general, what stream-built features are (1) most, and (2) least endur- ing? Why? 11. State all the important ways in which (1) stream erosion and (2) stream deposition affect human interests. Fig. 165. 246 MODIFICATION OF LAND SURFACES The Work of Ice Snow is perhaps the most common form of ice, but ice on ponds, lakes, and rivers is familiar to all who live where winters are cold. In middle latitudes the water in the soil and rocks freezes in winter, often to a depth of several feet. In some parts of the world, too, there are glaciers. In most of its forms ice has some effect on the surface of the land. Ice on lakes and rivers. Most lakes and rivers in middle lati- tudes are frozen over for several months each year. This is in some cases a great disadvantage from the standpoint of commerce. The upper Mississippi River is closed to navigation for more than four months of the year. The open season on the upper Great Lakes lasts about seven months. The St. Lawrence River is closed by ice about five months each year, and is difficult to enter during another month. Hudson Bay and its tributary rivers are closed even longer. It was a great disadvantage to the French colonies of interior Canada that they were shut off completely from the mother country .for nearly half the year, and it is a serious disadvantage to Canada to- day that her two main gateways from the Atlantic Ocean are closed so much of the time. The inland waterways of England and France are open throughout normal years; those of Germany and central Russia are closed more often, and for longer periods the farther they are from the Atlantic. Those of northern Russia are closed for five or six months. (Why are the waterways of western Europe so in contrast with those of North America in corresponding latitudes?) In some cases, the ice of rivers and lakes serves a good purpose. Fishing villages formerly were built on the ice in such places as Sagi- naw Bay, Michigan, and are still common in the gulfs of Bothnia and Finland. When frozen over, many northern rivers serve as roadways for local business. The cutting and packing of ice for sale during the following summer is an important industry on many lakes and rivers in northern United States. Ice on the sea. In high latitudes ice forms on the sea where the water is shallow, and in polar regions it becomes several feet deep, even on the open sea. Sea-ice is broken up in the summer, and t he floating pieces are called floe-ice. When the floes are crowded together, they make ice-packs, some of which are hundreds of miles 5. Ice-packs arc obstacles to polar navigation, and make most of the north coast of Russia and Siberia useless even in summer. FORMATION OF GLACIERS 247 The closing of ocean harbors and of seas connected with the ocean, like the closing of inland waters, is a great hindrance to com- merce. The North Sea has a tremendous advantage over the Baltic in this regard. The shores of the latter are hampered by ice each winter, while those of the former are edged with ice only during the most severe weather. The key to Russian expansion since the days of Peter the Great has been the attempt to secure ice-free harbors. EXISTING GLACIERS General Conditions for glaciers. Where it is so cold that snow lasts from year to year over any considerable area, the snow constitutes a snow- field (Fig. 1 66) . Snow-fields occur in mountains in nearly all latitudes, and in polar regions even down to sea-level. Where snow accumulates Fig. 166. Snow-fields in Alaska. Russell Fiord at right of view. (Brabazon, Canadian Boundary Commission.) to great depths and lies long on the surface, it changes to compact ice, and becomes an ice-field. The beginning of this change is distinct in banks of snow which last for some weeks. Such banks are made up of coarse granules of ice, sometimes as large as peas. The change from flakes of snow to granules of ice is due, in part, to the melting of the snow and the re-freezing of the water. If there is much snow, it is compressed by its own weight, and after being compacted in this way, the freezing of the sinking water binds the granules together. When the amount of ice made from snow becomes great enough, it moves out slowly from the place where it was formed to lower and warmer places. When it begins to move, it becomes a glacier. 248 MODIFICATION OF LAND SURFACES Functions of glaciers, (i) One mission of glaciers is to return to lower and warmer levels moisture which otherwise would be locked up indefinitely as snow and ice. (2) Like rivers, glaciers wear the land and move the resulting waste toward the sea. (3) Long after glaciers it o Fi /v 167. A valley glacier in the Cascade Mountains, Washington. (Willis, U. S. Geol. Surv.) have melted away, some of their effects on the conditions of life remain, because of the changes they made in topography, soil, and drainage. Thus past glaciation is a leading factor in the geography of northern United States and northern Europe. (4) Glaciers tend to maintain a relatively uniform volume in the streams which flow from them, and in various mountain regions such streams afford great amounts of power. TYPES OF GLACIERS 249 Types of glaciers. Glaciers have various forms, depending on the amount of ice and on the shape of the surface beneath and around them. If the snow-field which gives rise to a glacier is at the upper end of a mountain valley, the ice moves down the valley as a valley glacier (Fig. 167). In high latitudes, snow-fields and ice-fields may lie on plains or plateaus. When the ice in such situ- ations begins to spread, it moves in all directions from its center. Such glaciers are ice- caps or ice-sheets. Very large ice-caps sometimes are called continental glaciers. The main ice-caps of Antarctica and Greenland (Fig. 168) are large, but small ones are found on various promontories along the coast of Greenland, on Iceland, and on some other Arctic islands. Glaciers occur also at the bases of some mountains, being formed by the union of the spreading ends of valley gla- ciers. Such glaciers are pied- mont glaciers. Of these types, valley glaciers are most com- mon and most familiar, but the large ice-caps contain much more ice. Map of Greenland ice-cap. Valley Glaciers Distribution. The chief re- Fi< gions of valley glaciers are the high mountains of Eurasia, the southern Andes, and the higher moun- tains of northwestern United States and western Canada. In Alaska, high mountains near the coast receive abundant precipitation from the ocean winds. The heavy snowfall on the upper slopes feeds many glaciers, some of which reach the sea. The glaciers of Switzerland are known best and help to attract thousands of tourists to that country each year. In 1910, Congress created Glacier National Park on the Continental Divide in northwestern Montana (Fig. 224). It is about 2 5 o MODIFICATION OF LAND SURFACES sixty miles in length and contains more than sixty glaciers. This may become one of the best known and most visited of our National Parks, for the mountains and glaciers offer the chance for mountaineering of real Alpine character, the streams abound in trout, and the mountains still shelter enough game animals to become an important game refuge. The park contains one of the most beautiful portions of the Rocky Mountains lying within the United States. Size. There are nearly 2,000 glaciers in the Alps, only one of which has a length of ten miles. Less than 40 have a length of five miles, while the great majority are less than one mile long. Only a few are so much as a mile wide, and none are more than a few hundred feet thick. Larger glaciers occur in the Caucasus Mountains and in Alaska. Seward Glacier in Alaska is more than 50 miles long, and is three miles wide at the narrowest place. The glaciers of western United States south of Alaska are not so large as the larger glaciers of the Alps. Movement. The ice of a glacier is wasting all the time, both by melting and evaporation. In spite of this, many glaciers remain about the same size year after year. This is because the loss by melting is replaced by advance from the snow-fields, from which the ice creeps down the valleys until it reaches a place so warm that the melting at the end balances the forward motion. Most glaciers move very slowly. Of those whose rate of advance has been measured, few move more than two feet a day, and very few as much as seven. The rate of movement depends chiefly on (1) the thickness of the moving ice, (2) the slope of the surface over which it moves, (3) the slope of the upper surface of the ice, and (4) the topography of its bed. (What combination of conditions would favor most rapid movement?) The exact nature of glacier movement is a disputed question. It was thought formerly that glaciers flowed somewhat as stiff liquids do, but it is very doubtful if the motion is really flowage. Ice-Caps As already stated, ice-caps may lie on plains or plateaus, and may be large or small. Greenland has an area of 400,000 to 600,000 square miles, and all but its borders is buried beneath one vast field of ice and snow (Fig. 168). Except on a narrow border of a mile or so at the edge of the ice-sheet, not even a bowlder or a pebble interrupts the great expanse of white. The thickness of the Greenland ice is not known, but, where thickest, it is probably thousands of feet. Near its margin the ice is much crevassed, but the interior is fairly smooth so far as known. The ice of this great field is creeping slowly outward. The rate of THE POLAR ICE-CAPS 251 movement never has been measured, and is probably not the same at all points, but it has been estimated not to exceed a foot a week. This ice-cap is, in one sense, more of a desert than the Sahara, since it is inhabited even less than the latter. Where the edge of the Greenland ice-cap lies a few miles back from the coast, the rock plateau outside it has many valleys leading down to the sea. Where the edge of the ice-cap reaches the heads of these valleys, ice moves down them, making valley glaciers. Many of the latter reach the sea, where their ends are broken off and float away as icebergs. This is the source of most of the bergs (Fig. 169) seen from steamers which cross the North Fig. 169. An iceberg. Atlantic. Some are so large that they float far to the south before they are melted. Since they are sometimes surrounded by fog, they are a menace to ships (p. 149). The Antarctic snow-and-ice-cap is much larger than that of Greenland, but its area is not so well known. It is probably several million square miles in extent, and the thickness* of its ice probably exceeds that of Greenland. The ice descends to the sea at many points, and huge blocks of it become icebergs. Piedmont Glaciers A number of alpine glaciers come down adjacent valleys in the St. Elias range of Alaska, and spread out on a low plain at its base. So much do their ends spread that they unite to form a single body of ice, 70 miles long and 20 to 25 miles wide, called the Malaspina Glacier. Its area is greater than that of Delaware. Its central portion is free from debris, but has thousands of deep, wide cracks. A belt along the margin of the glacier .five miles or less in width is covered by rocky and earthy debris, and parts of it are clothed with vegetation. The undergrowth is here so thick that travelers have to cut paths, and on the edge of the ice there are trees three feet in diam- eter. Other glaciers of the same type occur about North Greenland. ANCIENT GLACIERS There have been times when glaciers were much more extensive than now, for various features produced only by glaciation (pp. 255- 252 MODIFICATION OF LAND SURFACES 265) are found in many places now free from ice. The latest of these periods is known as the Glacial Period. In this country, glaciers existed even in the mountains of New Mexico, Arizona, and Nevada. Fig. 170. Sketch-map showing the area in North America covered by ice at the stage of maximum glaciation. (Chamberlin.) The amount of ice in the glaciers of Utah or Colorado was then far greater than all that now exists in the United States south of Alaska. At the same time, a great area east of the Cordilleran mountain system, some 4,000,000 square miles in extent (Fig. 170), THE GLACIAL PERIOD 253 and lying partly in Canada and partly in the United States, was covered with an ice-sheet. The ice-sheet of North America originated in two principal cen- ters, one on either side of Hudson Bay. The beginning of each was doubtless a great snow-field. At first these snow- and ice-fields grew by the addition of snow, and later also by the spread of the ice to which the snow gave rise. The two ice-sheets finally became one by growing together. This great continental glacier did not origi- nate in mountains, but on high plains. When largest, the ice-sheet had the extent shown in Fig. 170, but there was an area of 8,000 to 10,000 square miles, mainly in south- western Wisconsin, over which the ice did not spread. This is known as the driftless area, because there are no ice deposits (drift) in it. In the Cordilleran mountains there was also a great body of ice that remained somewhat distinct from the one which spread from the other centers. There was extensive glaciation in Europe at about the same time. The glaciers of the Alps were then many times as large as those of to-day. On the south they extended quite beyond the mountain valleys, and spread out on the plains of northern Italy, where they left their deposits. Similar conditions existed in. the other mountains of Europe where glaciers now exist, and in some where they do not. There was also a large ice-sheet in northwestern Europe, but its area was only about half that of the ice-sheet of North America. The principal center from which the ice spread was the mountains of Scandinavia. Great ice-sheets are not known to have developed in other con- tinents during the Glacial Period, but their valley glaciers were very large. The history of the Glacial Period was not simple. After the growth of the first great North American ice-sheet, it shrank to small size, or disappeared altogether. Then followed a relatively warm period, when plants and animals lived in the region where the ice had been. Another continental ice-sheet then spread over the region from which the first had melted, and extended still farther south. As it advanced, the second ice-sheet in places buried the soil which had formed on the drift left by the ice of the first epoch. Such soils, here and there containing the remains of plants which grew in them, are one means by which it is known that there was more than one ice-sheet. A third, fourth, and fifth ice-sheet, each somewhat smaller than its predecessor, came and then melted. In other words, there were several epochs when ice-sheets were extensive, separated by epochs when they were much smaller, or when they had disappeared altogether. The ice-sheets of Europe had a similar history. 254 MODIFICATION OF LAND SURFACES Cause of glacial epochs. The development of the great ice- sheets was due to a change in climate, and especially to a reduc- tion of temperature. The cause of the cold is not known, though many explanations have been suggested. The explanation which seems most acceptable is that the change of climate was due to a Fig. 171. Glaciated surface of limestone. The view shows also the relation of drift to the bed-rock beneath. Kelleys Island, Ohio. (Stauffer.) change in the constitution of the atmosphere. An increase in the amounts of carbon dioxide and water vapor would make the climate warmer (pp. 31, 178), while any great decrease in these things would make the climate much colder. Good reasons have been suggested for variations in the amounts of these substances in the air, and also for the heavy snowfall in the regions where the ice-sheets existed. Heavy snowfall is quite as necessary as low temper- ature for extensive glaciation. LAND FORMS DUE TO GLACIAL EROSION 255 CHANGES DUE TO GLACIAL EROSION How glaciers erode. Clean ice, moving over smooth, solid rock, would erode little, but ice carrying pieces of rock in its bottom wears the surface, even when the latter is smooth and solid. Like wind and water, therefore, ice erodes by means of the rock tools which it carries. Each kind of tool does its appropriate work. Fine, earthy material in the bottom of the ice polishes the rock below, while sand and small pebbles make scratches (stria) upon it. Grooves are made by bowlders held in the bottom of the ice and forced along under Fig. 172. Glacial trough in San Juan Mountains, Colorado. great pressure. Meanwhile the tools are themselves polished, scratched, and worn smaller. The finest products of the grinding have been called rock flour. Polished and striated bed-rock surfaces (Fig. 171) are among the clearest marks of the former existence of glaciers in many places now free from ice. Changes in valleys. Mountain valleys through which glaciers pass are widened and deepened, and their walls made smoother (Figs. 172 and 173). In many cases the heads of glaciated valleys are big, blunt, and steep-sided. Most of the lakes which add so much to mountain scenery are (1) in rock basins gouged out of valley floors by glaciers (Fig. 173), or (2) behind dams formed by the deposits of the ice (Fig. 186). Tributary valleys commonly join their main valleys at the level of the latter, but the bottoms of many valleys that were deepened and widened by former glaciers are much (in some cases 500 to 1 ,000 feet) lower than the lower ends of their tribu- taries. In such cases streams descend in rapids or falls from the tributary hanging valleys (Fig. 174). Much water power is afforded 256 MODIFICATION OF LAND SURFACES by such rapids and falls in the mountains of western United States, Switzerland, and northwestern Europe. The ancient ice-sheet overrode hills and divides as well as valleys. In many cases the ice deepened the valleys more than it lowered the hills, and where this was true it increased the relief, even though it reduced the roughness of the surface. Elevations reduced and changed in shape. Hills overridden by ice-sheets are worn down and smoothed off, and the wear is Fig. 173. A valley in the Needle Mountains, Colorado, cleared of all earth and loose rock by a glacier which once passed through it. The moving ice also smoothed all the projecting points of rock. greatest on the side of the hill against which the ice moves (Fig. 175). Many small elevations were worn away entirely by the con- tinental glaciers. Ice-shaped coasts. Glaciers which descend into the sea through bays tend to gouge out the bay-bottoms, and to wear back the bay- heads. If such glaciers melt away, the sea enters to form long, narrow, steep-walled re-entrants, called fiords. Norway (Fig. 176), Scotland, Maine, and Alaska have fiord coasts, though all of them owe their characteristics in part to sinking. Many islands front CHARACTERISTICS OF GLACIAL DEPOSITS 257 these coasts, most of them representing the higher parts of the old land whose surroundings have been drowned. GLACIAL DEPOSITS General characteristics. Most of the material transported by a glacier is carried in its lower part; but some is carried in the ice above its bottom, and some on top of the ice. All of it is left, finally, Fig. 174. Hanging valley; Nunatak Fiord, Alaska. (Tarr, U. S. Geol. Surv.) on the surface of the land. The materials deposited by glaciers, called glacial drift or till, range from finest earth to huge bowlders (Fig. 177). They are not stratified, and in many places are so deposited as to form distinctive topographic features. Much of the drift deposited by the continental glaciers is a thorough mixture of many kinds of mate- rial, for it was derived from a vast area within which many kinds of rocks occur. (Com- pare glacial drift with stream deposits.) Leading types. When the end of a valley glacier or the edge of an ice-cap stays in the same place for a long time, a thick body of Fig. 175. A hill smoothed by the glacier ice which overrode it. Shore of North Greenland. (From photograph by Chamberlin.) 258 MODIFICATION OF LAND SURFACES drift is lodged beneath it, for drift is brought to this position all the time by the oncoming ice, and left there. Such a deposit is a terminal moraine (Fig. 178). All the other drift deposited by an ice-sheet is ground moraine. After a glacier melts, the area of ground moraine is Fig. 176. The Sogne Fiord, coast of Norway. (Robin.) not as great as the glaciated area, for glaciers do not carry debris in all parts of their bottoms. In general, the drift is thickest and covers the largest proportion of the surface near the margins of a glaciated area, and is thinnest and least continuous in the region from which the ice spread (Why?). For this reason, there are large areas of bare rock and of thin, bowl- der-strewn soil on the uplands of eastern and northeastern Canada. Together with a bleak climate, these condi- tions render large areas unfit for farming. Much of the material removed by the ice from Canada was de- posited in the United States. The lateral moraines are left along the sides of a valley after the valley glacier is melted (Fig. 179). Some of them are hundreds of feet high. Surface features. Because glaciers distribute their drift very unevenly, large areas once covered by ice are marked by hillocks, Fig. 177. Section of unstratified drift near Henry, Illinois. (Crane.) SURFACE FEATURES DUE TO ICE DEPOSITS 259 mounds, ^and ridges of drift, and by basin-like or trough-like depres- sions. These features are most pronounced in terminal moraines, the surfaces of which may be distinctly rough and hummocky (Fig. 180). Fig. 178. A glacier in the Cascade Mountains, Washington. Shows spreading end of glacier, crevasses in ice, and terminal moraine. (Willis, U. S. Geol. Surv.) In the Lake States, the rougher parts of the terminal moraines commonly are used for woodlots and pastures (p. 173), for the sur- face is too uneven and the soil too coarse and stony to be cultivated successfully, in competition with the neighboring prairies. Many of the hollows in the surface of the drift contain lakes (p. 261), ponds, 260 MODIFICATION OF LAND SURFACES and marshes (p. 300). It is estimated that there are \]/ 2 million acres of marsh land in Minnesota, nearly as much in Michigan, and 2^ million in Wiscon- sin. The total swamp area' for the three states is larger than the combined area of Massachusetts, Connecticut, Rhode Island, and Delaware. Nearly all this swamp land is the result of glaciation. The surface of the drift is very unlike that developed by the erosion of running water, for in the latter the depressions have out- lets, and the hills and ridges stand in a definite relation to the valleys. The drift left by the continental glacier increased the relief in some places (Fig. 181), with unfavorable results; but in most places l ;-' - ^ ^ ~7^\ ^SJI ffi^TT^fiSJffl ill l?|^ '&£*s£ ^8§liK?Sii iHHi 4m£&&tt£!^£-~' Fig. 179. A lateral moraine left by a former glacier in the Bighorn Mountains of Wyoming. (From photograph by Blackwelcler.) Fig. 180. Terminal moraine topography near Oconomowoc, Wis. (Fenneman.) it decreased relief and left the surface less rough than before (Fig. 182). This made it easier to cultivate the land and to build roads. Most of the surface between the Ohio River and the Great FORMATION AND DESTRUCTION OF LAKES 261 Lakes appears to have been made smoother. But for glaciation, much of this region probably would have a maturely eroded sur- face, not unlike that of the driftless area, and a poorer soil than it now has. Deposits beyond the land. Glaciers which descend into the sea may build subma- rine banks and even islands. Along the eastern coast of North America, these deposits may have reached the edge of the continental shelf in some places. Martha's Vineyard, Nantucket, and Long Island are composed largely of drift. The sheltered waterway behind Long Island favored the early growth of sea interests in southern New England. Fig. 182. Fig. 181. Diagram showing how a nearly level surface may be replaced by a rough one through the uneven deposition of drift. Fig. 182. Diagram showing how glacial drift may replace a hilly surface with a fairly level one. Fig. 183. Map showing the abundance of lakes in parts of the glaciated area. (From Barrett, Minnesota, Sheet, U. S. Geol. Surv.) Glacial lakes. The thousands of lakes in northern United States (Fig. 183) and Canada are nearly all of glacial origin. Some are in basins gouged out of the bed-rock (Fig. 184); some are in the 262 MODIFICATION OF LAND SURFACES unfilled portions of drift-choked preglacial valleys; and many are in hollows in the surface of the drift (Fig. 185). The terminal moraines of many valley glaciers form dams, ponding the waters of the streams above, making lakes (Fig. 186). The smaller and shallower of these lakes and ponds are being destroyed rapidly by (1) the sediment washed into them from the tributary slopes, and (2) vegetable matter. Some are being drained slowly (Why slowly?) by the erosion of their outlets. In the future, many of the shallower ones will be drained by man, that he may use their bottoms as farm land. It has been estimated that there are 8,000 lakes, big and little, in Minnesota, and that half of them will be destroyed by natural processes within fifty years. Connecticut has been credited with hav- ing had some 4,000 lakes at the close of the Glacial Period; 2,500 of them have been destroyed, and the sites of many of them now form choice garden spots. In southern Michigan and Wisconsin many early settlers located their farms on the bottoms of former lakes, attracted by the flat land and the fine, easily- worked soil. Deposits of marl occur in and about some glacial lakes. This marl is a soft, limey earth, the calcium carbonate of which is contributed chiefly by the shells of fresh-water mollusks and by lime- secreting lake plants. In parts of Mich- igan and northern Indiana, these deposits are used in making Portland cement. Fig. 184. Section of a lake in an ice-scoured rock basin. Fig. 185. Section of a lake lying in a hollow in the surface of the drift. Fig. 186. Section of a lake behind a barrier of drift. The lakes and swamps of the glaciated region make the streams flow more steadily through the year by holding back some of the water of wet times, letting it flow out in times of drought. The drift itself exerts a similar influence, for, on the whole, it is thicker than the mantle rock of other regions, and therefore absorbs more water, which it yields up slowly, making the supply of ground-water to streams more steady than it would be otherwise. Thus floods are less numerous and less dangerous, and the value of the streams for navigation and power is increased. By reducing or preventing floods, the porous drift and the lakes also greatly reduce soil erosion. Certain lakes which came into existence along the margin of the continental glacier disappeared with the ice. One of the largest of the marginal lakes (Lake Agassiz) lay in the valley of the Red LAKE AGASSIZ 263 River of the North (Fig. 187). This lake covered an area greater than that of all the Great Lakes. The water, however, was shallow. It came into existence when the edge of the retreating ice lay north of the lake, and blocked drainage in that direction. The water rose in the basin until it overflowed to the south, finally reaching the Missis- sippi River. When the ice at the north melted back far enough, a ksj SUPERIOR £ %£ Fig. 187. Map of extinct Lake Agassiz, and other glacial lakes. Lake Winni- peg occupies a part of the basin of Lake Agassiz. (U. S. Geol. Surv.) new and lower outlet was opened to Hudson Bay, and the lake was drained. Lake Winnipeg and several smaller lakes may be regarded as remnants of Lake Agassiz, for they occupy the deepest parts of the old basin. As late as 1870 the floor of extinct Lake Agassiz was almost unoccupied by farmers (Fig. 188), but during the next few years its soil was found to produce a fine grade of hard wheat, and a great tide of farm-seekers turned to the region (Fig. 189). On the nearly level lake floor it was possible to plow league-long furrows in straight lines, and later to do much of the work by such labor saving machines 264 MODIFICATION OF LAND SURFACES as the steam plow. Ft. Gary quickly grew into the city of Winnipeg, and the wheat of the region helped to make Minneapolis the leading flour manufacturing city of the United States (p. 288). The Great Lakes did not exist, so far as known, before the Glacial Period, but river valleys probably extended along their longer diam- eters. Lake basins were made as a result of (1) the deepening of these valleys by ice erosion, (2) the building up of the rims of the basins • I \\}nier2prrvyrr.:, E~!6*ol8 • • • Fig. 188. Fig. 189. Fig. .188. Map showing distribution of population in region of Red River of the North in 1870. Fig. 189. Population map of region of Red River of the North in 1880. by the deposition of drift, and perhaps (3) the down-warping of the sites of the basins. The influence of the Great Lakes on climate and on certain industries has been noted in earlier connections. Their importance as commercial highways is considered in Chapter XVI. Hundreds of the glacial lakes are of great benefit to man as pleasure and health resorts, and as sources of water supply. Many have become famous through their fine summer residences, and very many more are visited by numerous camping, boating, and fishing parties. In these ways the lakes have become large factors for good in the life of the people. Effect of ice deposits on stream courses. The deposition of drift rilled many of the former valleys. After the ice melted, the surface drainage followed the lowest lines open to it; but these lines did not always correspond with the former valleys, for some of the latter had been filled, and most of them were blocked up in some places. BENEFITS RESULTING FROM GLACIATION 265 The surface waters therefore followed former valleys in some cases, and in others flowed where there had been no valleys. In choosing their new courses, the streams in places ran down steep slopes or fell over cliffs. Many of the rapids and falls of the glaciated area, so important in the economic life of the country (p. 288), came into existence in this way. Glacial soils. In the United States, glaciation increased the amount of mantle rock, and improved the quality of the soil in many places. Much of the latter is good because it is a thorough mixture of material derived from many kinds of rock, and so is well supplied with all the mineral elements necessary for plants (p. 169). It is instructive to compare Fig. 257, showing the relation of the im- proved acreage to the total farm acreage in the different states, with the map showing the glaciated area (Fig. 170). Iowa, Illinois, Indi- ana, and Ohio are seen to lead in the relative amount of their improved land. Glaciation is perhaps the most important fact in the geography of each of these states, and it has greatly furthered their high rank in agriculture. The benefits which the states between the Ohio River and the Great Lakes received from glaciation may be illustrated further. Fig. 190 shows the glaciated and unglaciated parts of Ohio. The unglaciated part belongs to the Alleghany Plateau. It is in a mature stage of erosion, and the thin, sandy soils on the steep slopes wash easily. The first settle- ment in Ohio was made in this part of the state, at Marietta; but soon the tide of settlement set toward the more attractive glacial plains farther west and north, and the population of most of the unglaciated counties remained relatively sparse until the mineral resources of the region were developed. Many farmers in the unglaciated section turned their attention to sheep-raising when they found they could not grow grain for export in competition with the farms of the glaciated area, and grazing was long an important industry in the southeastern part of the state. About four-fifths of Indiana were glaciated. On the average, the glaciated land is worth about twice as much as the unglaciated, and the yields of staple j— — y,, i i 1 i i i ^f*^ \ fl V \\ f i f i i Fig. 190. Map showing the glaciated (shaded) and unglaciated portions of Ohio. 266 MODIFICATION OF LAND SURFACES crops bear a similar relation. The southern boundary of the region within which 4,500 bushels of corn are grown per square mile is the margin of the latest drift sheet. The situation is much the same in Illinois. The quality of the soil in places was injured by glaciation. In some of these places the drift is very thin, while in others it is very stony, so that great labor is necessary to put it in workable condition. Again, the drift may be too sandy or gravelly to make good soil, or its surface may be too rough (pp. 173, 259). Special uses of glacial deposits. Much drift clay (rock flour) is used for mak- ing brick, tile, and other clay products. Ohio has been the leading state in the clay industry for many years, because of the abundance of raw clay, part of which is drift, cheap near-by fuel, excellent shipping facilities, and nearness to great markets. About 1 ,000,000,000 bricks are made from glacial clay each year in the vicinity of Chicago. The gravel of the drift is used extensively for road making, and in the manufacture of various kinds of cements. DEPOSITS BY GLACIAL WATERS Water flows in abundance from all glaciers in the summer, and from many glaciers all the time. Stream work, therefore, accom- panies glaciation in all cases, and much of the drift left by ice is modified by water afterward. Streams which flow from glaciers carry so much sediment that in many cases they build gravelly or sandy plains beyond the ice. Such a deposit in a valley below a glacier is a valley train. Valley trains are developed best just outside terminal moraines. The Rock River, in southern Wisconsin, filled its valley with gravel and sand to a depth of 300 to 400 feet just outside the terminal moraine of the last glacial epoch. The Columbia River filled its valley to the depth of 700 feet in places with sediment washed out from the ice. Since the ice-sheet melted, parts of most of the valley trains have been carried away, and their remnants are terraces (Fig. 162). Drift terraces are common features of many of the valleys of south-flowing rivers in the glaciated area and just south of it. Streams which issue from an ice-sheet and fail to find valleys build alluvial fans. By growth, these' fans may unite, making an outwash plain, very much like a compound alluvial fan. Like valley trains, outwash plains are developed best just outside the terminal moraines of ice-sheets, and their materials are stratified. East New York, Woodhaven, Jamaica, and other suburbs of Brooklyn grew up on the outwash plain of Long Island before the terminal moraine DEPOSITS BY GLACIAL WATERS 267 just to the north was much settled. (What were the probable rea- sons for this?) Deltas may be built in lakes at the ends or edges of glaciers, and the deposits made by waters beneath the ice and at its edge take on locally the form of ridges and hillocks. As a glacier melts away, the waters produced by the melting flow over the surface of the drift which the ice had deposited, and modify it more or less by eroding in some places and depositing in others. As a result of all these phases of water work, much of the drift is stratified. Summary. Although less important, ice takes its place with air and water as one of the three agents which modify land surfaces. From this standpoint, its principal mission is the wearing of the land and the moving of the waste toward the sea. Through their wide- spread effects on topography, soil, drainage, and the distribution of plant and animal life, the ancient ice-sheets are far more important than the glaciers of to-day, as factors in human affairs. Existing glaciers are valuable to man chiefly in connection with the develop- ment of power on the streams which flow from them. QUESTIONS 1. In northern United States and Canada, would floods which occur as the river ice breaks up in spring be more likely to be disastrous on north-flowing or south-flowing streams? Why? 2. Why are there more glaciers in the Sierra Nevada and Cascade mountains than in the Rocky Mountains? Why are there more in Montana than in Colorado? 3. State all the factors which influence the size of a valley glacier. 4. Compare and contrast typical topographies due to (1) glaciation and (2) river erosion. 5. (1) What are all the important ways in which human interests have been (a) benefited and (b) injured by the work of the ancient ice-sheets in the United States? (2) On the whole, was glaciation beneficial or injurious? 6. Why are the effects of glaciation more favorable, from the standpoint of man, in northern United States than in northeastern Canada? CHAPTER XVI THE USES AND PROBLEMS OF INLAND WATERS Many ways in which streams and lakes affect human interests have been noted in preceding pages. In the present chapter, inland waters are considered from the standpoints of navigation, power, irrigation, drainage, and water supply. Navigation In the early development of many countries, lack of roads led to the use of the waterways for trade and travel. Even after roads had been built, transportation by water was much cheaper than transportation by land in most cases, and traffic continued to use waterways where ^they were available. Where railroads have come into competition with waterways, the latter in most cases have lost much of their traffic. The waterways of some countries have been protected by law against ruinous railroad competition, and certain waterways, for example the Great Lakes, furnish such favorable conditions for transportation that their traffic has grown in spite of the railroads. The average cost of hauling over the railroads in the United States declined from j 1 /^ cents a ton per mile in 1837, to less than 4/ s of a cent per mile in 1905; yet under favorable con- ditions, the cost of transportation by water is estimated to be only J / 4 to 1 /t ) that by rail. In 1909, rates for iron ore on the Great Lakes were less than one mill a ton per mile, while the rates for ore by rail were about one cent a ton for the same distance. RIVER NAVIGATION Streams were the first waterways to be used regularly for com- merce. The Euphrates and Nile were among the rivers to which men first entrusted themselves and their goods. After a time, river navigation led to coastwise navigation, but to the end of the Mediaeval Period there was little or no navigation of the open ocean. It is only in the Modern Period that navigation of the open sea has per- mitted the development of world-wide commerce. 268 THE GREAT RIVERS OF THE WORLD 269 Leading rivers of foreign lands. Because of its relief (p. 24), few of the rivers of Asia are important highways of commerce. The Yang-tze is the greatest highway. Fed by the snow-fields of the mountains of Tibet, and flowing to the Pacific through some of the most densely populated provinces of China, it is both one of the long- est rivers in the world, and one of the most important commercially. Large ocean steamers go up 600 miles to Hankow; smaller steamers ply the river 500 miles farther, to the mouth of the gorges; and native junks go up many miles more. The Hwang-ho, the other great river of China, flows through a densely settled region, but is nearly useless for navigation because of its shifting and silt-choked channel. In India, the Ganges and Indus present a contrast similar to that of the Yang-tze and Hwang-ho. The Ganges traverses the most populous and wealthy provinces, and has been of great significance throughout the history of India. It is fed by many Himalayan tor- rents, and flows for about 1200 miles across the alluvial plains of the north. Ocean steamships ascend the Hugh, one of the mouths of the Ganges, to Calcutta, and the river is used more or less for navigation to the base of the mountains. The Indus River is used but little by steamers, because of many sand bars and frequent changes in the channel. Together with its larger tributaries, it is valuable chiefly for irrigation. The great rivers of Siberia are navi- gable for hundreds of miles, but their value is lessened because they flow to the Arctic Ocean. The relief of Africa limits the navigation of most of its rivers to relatively short distances (p. .25). The Nile has regular steamboat service to the First Cataract, but navigation is not easy in the delta portion of the river below Cairo. Above the cataracts, the river is navigable throughout the year for long distances. Throughout the history of Russia its rivers have been its chief highways. Even to-day, they have greater relative importance than the rivers of western Europe, because other means of trans- portation are less satisfactory; wagon roads are poor and railroads few. Most of the Russian rivers rise in the vicinity of the Valdai Hills and follow long courses across low, nearly level plains. Their currents, therefore, ordinarily are gentle. They are navigable through- out most of their courses, and the different systems have been joined by canals, so that there is water connection between the Caspian, Black, Baltic, and White seas. While the above conditions are 270 USES AND PROBLEMS OF INLAND WATERS favorable to commerce, navigation of the Russian rivers is attended by serious drawbacks. They are ice-locked in winter (p. 246), subject to great floods in spring, affected by sand bars which hinder navigation at low stages, and most of them are tributary to inland seas. The Volga is the most important Russian river, and the largest river of Europe. Together with its tributaries, it is said to afford 7,500 miles of navigation. Its usefulness is lessened by the fact that its lower course is through a semi-arid region, and by the fact that it ends in a land-locked sea. Most of the larger rivers of central and western Europe are important commercially, and large sums have been spent to improve them and extend their connections by canals. In Germany, river transportation increased more than fivefold in the thirty years preceding 1905, although Germany has a greater railroad mileage than any other country in Europe. This is in striking contrast with the situation in the United States (p. 278). The rivers and canals of Germany (p. 287) furnish from 8,000 to 10,000 miles of navigable waterways. So much work has been done in dredging, straightening, and otherwise improving the larger rivers, that it is said scarcely one of them flows in a natural channel. The Rhine has influenced the history of Germany more than any other river, and is to-day the most important commercial river in Europe. Fed by melting snows in Switzerland and made steady in its flow by passing through Lake Constance, it flows through western Germany and the Netherlands, into the North Sea. Rotterdam, on the Rhine delta, is one of the greatest ports of continental Europe, and Cologne, though far inland, is practically a seaport. The fertile valley of the Rhine is settled densely. Commercially, the Elbe is the second river of Germany, though much less important than the Rhine. The traffic on these rivers is largely in heavy freight, such as coal and grain. The Danube has been an important highway since early times. Like many other delta-building rivers, it was difficult to enter until jetties were built at its mouth. Extensive improvements have been made also at the "Iron Gate," and elsewhere. The Rhone is the largest river of France, and its valley is the natural highway into the country from the south. Navigation in the delta portion of the stream was hindered by shallow and shifting channels, and large sums have been spent in improvements. Even now, however, the Rhone is not navigable for large ships. The Po and the Ebro are the only other THE GREAT RIVERS OF THE WORLD 271 European streams of importance flowing into the Mediterranean, and neither is used much for navigation. In Great Britain, the rivers are comparatively short, but their value is increased by the fact that their lower courses are drowned, and subject to rather high tides. The tides help to make Liverpool and London great seaports, though both are on small rivers. Like the United States, Great Britain has neglected, till recently, the question of waterway improvement. To-day transportation in Eng- land is said to be the most expensive in Europe. Fig. 191. Map showing principal streams in the United States actually used for purposes of transportation (1906). Only the parts so used appear on the map. (Data from map by U. S. Bureau of Corporations.) The Amazon is the largest river in the world, with a length of about 4,000 miles. Ocean steamers can go up 1,000 miles, and with its 29 large tributaries it furnishes more than 20,000 miles of navigable water, most of it through dense forests. The river is used to carry out tropical woods, rubber, and other products. The Orinoco is navigable for small boats to within 100 miles of Bogota, and the La Plata System is navigated by steamers for long distances. Besides the great rivers mentioned above, there are many others which serve as highways of trade and travel. Navigable streams of the United States. There are about 300 streams in the United States that are navigated more or less (Fig. 272 USES AND PROBLEMS OF INLAND WATERS 191). Their total navigable length is about 26,400 miles — more than the circumference of the earth. Only a few have much com- mercial importance now, and many are used only by small boats engaged in local trade. As Fig. 191 shows, most of the navigable streams are in the eastern half of the country. The absence of navigable waterways (Why absent?) has been a serious disadvantage to much of the West. The principal rivers, and the part which they have played in the development and commerce of the country, are discussed briefly in the following paragraphs. Most attention is given to the Mis- sissippi System, because it is by far the most important. Atlantic Rivers of United States On the Atlantic slope there are nearly 150 streams navigable for varying distances from the sea — in most cases only to the head of tide-water. The rivers of New England are navigable for short distances only, because of falls and rapids. The Connecticut is navigable to Hartford; the Merrimac to Haverhill; the Saco to Saco and Biddeford; the Kennebec to Augusta; and the Penobscot to Bangor. All these cities receive much freight by water. Many streams of central and northern New England are used for rafting lumber and floating logs. Although the streams of New England afford little navigation, the larger val- leys have been important highways since the settlement of the region began. They guided fur traders, lumbermen, and farmers (p. 219) into the interior. They •served as lines of advance and retreat for Indian war parties and colonial armies. General Arnold invaded Canada in 1775 by way of the Kennebec and Chaudiere valleys. To-day many of the valleys are followed by railroads. Boston was handicapped greatly in its commercial development by the fact that no large, navigable river came to it from the interior. The Hudson is the most important, commercially, of the tribu- taries to the Atlantic from the United States. Because the Hudson Valley is drowned, deep water extends 100 miles inland, and the river is navigable 50 miles farther, to Troy. The belt of relatively weak rocks along which the Hudson Valley developed contains, farther north, Lake Champlain and the Richelieu River. This long, narrow lowland, which extends from New York City to the St. Lawrence River near Montreal, was called by the Indians "The Grand Passway." General Burgoyne (1777) and General Prevost (1814) used it to invade the United States. When the Champlain Canal was opened between the Hudson River and Lake Champlain. water transportation was possible throughout its entire length. The Mohawk Valley and the low plain to which it leads furnish an easy route between the Hudson River and Lake Erie; the highest point is only 445 feet above sea-level. RIVERS AS FACTORS IN COLONIAL LIFE 273 Its drowned-valley harbor and good connection with the interior have been leading factors in the growth of New York City. South of the Hudson River, most of the larger rivers are navigable to the "fall line," where the streams, in passing from the hard rocks of the Piedmont Plateau to the weak rocks of the Coastal Plain, have developed falls and rapids. Along this line are Philadelphia, Balti- more, Richmond, Petersburg, Raleigh, Columbia, Augusta, Macon, and Columbus (Fig. 192). Ocean-going vessels ascend the Delaware River to Philadelphia, and smaller boats go up to Trenton. Several drowned trib- utaries of Chesapeake Bay, itself a drowned valley, have some commercial importance. The drowned streams of the Vir- ginia region were deep enough for the light-draft boats of the colonial period, and served the settlers as roadways. The early plantations were arranged in narrow belts along the stream courses. For a century, travel in tidewater Virginia was largely by water; little attention was given to road building. Ships came from Eng- land direct to the wharves of many of the plantations, to exchange for tobacco the manufactured goods needed in the colony. Under these circumstances, no important collect- ing and distributing centers devel- oped. To 1700, Jamestown was the only place worthy of being called a village. In South Carolina, the streams were not drowned sufficiently to render many of the smaller ones navigable. Hence Charleston became the commercial center of the colony, and soon also the social and political center. In general, freight rates de- crease as the size of the cargo increases, and accordingly the tendency has been to build larger and larger boats. As a result, many of the streams of the Coastal Plain, once important in trade, were long since abandoned by commerce. Mississippi River System The Mississippi River has more than 50 tributaries that were navigated more or less in 1907. The navigable waters of the system aggregate nearly 14,000 miles and border or traverse 21 states. Fig. 192. Map showing leading cities along the "fall line." 274 USES AND PROBLEMS OF INLAND WATERS The Mississippi River itself is navigable for large steamers to St. Louis, and for smaller boats to St. Paul. The Ohio River, now much the most important, commercially, in the United States, is navigable throughout its length. The Missouri River is navigable for small boats to Ft. Benton, in Montana, though it is now used but little. Other tributaries of the Mississippi are navigable for varying distances, as shown by Fig. 191. Influence on early development of the West. At the close of the Revolutionary War, the Mississippi River was made the western boundary of the United States, and the supposed length of the river fixed the width (north and south) of the country at that time. It was an unsatisfactory international boundary line, for (1) its position shifts (p. 240), (2) the navigation of the river by the Americans from the east side and any foreign people from the west side would have led to friction, and (3) the river basin is a natural unit. The political unity of the Mississippi Basin was brought about by the Louisiana Purchase in 1803. Fig. 193. A typical flatboat. The early western settlers could send over the difficult mountain roads to the eastern seaports only valuable articles of little bulk and weight, such as whiskey, furs, and ginseng, or live stock, which could walk to market. For years, many thousands of hogs and cattle were driven over the mountains to Charleston, Baltimore, and Philadelphia, but salted and dried meats, flour, tobacco, and the other export products of the frontier had to go down the Mississippi River to New Orleans. Roads were few and poor, and the settler found it highly desirable to locate his farm within easy hauling distance of a navigable stream. The influence of navigable waterways upon the distribution of population is shown clearly by the census maps of 1820 (Fig. 278) and several later years. THE STEAMBOAT AND WESTERN DEVELOPMENT 275 One of the most used of the early boats on the western rivers was the flatboat, commonly 1 5 feet wide and 40 to 50 feet long (Fig. 193). While these boats served for downstream navigation, they were almost useless against the current of the Mississippi. Ordinarily they were broken up and the lumber sold at New Orleans. In these early days, freight was carried up-river largely in keel boats or barges. Most of them were equipped with oars, poles, and sails, and in many cases they were dragged upstream by men on the bank, tugging at a long rope. The average length of the trip from New Orleans to Louisville was three months, and in many cases it required four months. Influence of steam navigation on the development of the Interior. The first steamboat appeared on the Ohio River in 181 1, and within a few years it was seen that steamers could cope success- fully with the currents of the rivers of the Interior, and that they would increase greatly the commercial value of the streams (Fig. 194). Mississippi River steamboats at New Orleans. For a time, they could not be built fast enough to take care of the business. By 1850, the time involved in upstream travel had been reduced to about Vi8 of what it had been before the appearance of the steamboat. This meant, for example, that the steamboat brought New Orleans nearly as close to St. Paul, for certain purposes, as it had formerly been to Baton Rouge. In 1830 the cost of travel- ing by water from New Orleans to Pittsburgh was about % what it 276 USES AND PROBLEMS OF INLAND WATERS had been before the* days of the steamboat. In general, the steam- boat soon reduced freight charges to about K of what they had been, and finally to % and less. Because of these things, steamboat navi- gation became one of the greatest factors in the development of the Interior. The population of the Interior, commercially dependent for the most part on the rivers, increased from 2>^ millions in. 1820 to 6>i millions in 1840. Probably no single factor contributed more than the steamboat to the rapid expansion of population during these years. Thousands settled along the tributaries of the Mississippi having steamboat service, and almost over-night river towns sprang up at favored points. The total value of the commerce of the western rivers in 1850 was estimated at $550,000,000. The leading centers of steamboat trade. During the period of steamboat supremacy, the river commerce of the Interior centered largely in four cities — Pittsburgh, Cincinnati, St. Louis, and New Oder ns. For some time before the opening of the Erie Canal (1825, p. 286), Pittsburgh was the eastern gateway to the Mississippi Basin. Im- portant roads connected it with the eastern seaboard. Its position at the junction of the Monongahela and Allegheny rivers gave it many advantages. The former brought coal from West Virginia, while the latter gave it command of the white pine of western New York. The principal products of the Pittsburgh mills reflected these advantages, together with the command of iron and the products of the surround- ing farms. They were implements and machinery, iron ware, cabinet ware, lumber, furniture, flour, and liquors. These things were sent by river throughout the Interior. Cincinnati had several marked advantages for the develop- ment of river trade. Situated midway on the Ohio and near the northernmost point of the great bend of the river, it was the nearest important river town for a large and fertile region north of the Ohio. It was also opposite the Licking Valley in Kentucky. The deep channel and favorable bank of the river along the city front made it easy to handle steamboat traffic. It was connected (in 1832) by canal with Lake Erie (Fig. 200). It received by river most of the implements and supplies, or the materials for their manufacture, needed by the tributary farming region. By river the city shipped the products of her flour mills, breweries, distilleries, and slaughtering and packing houses, which had been established to use the products LEADING CENTERS OF STEAMBOAT TRADE 277 of the surrounding country. (Why was it desirable to manufacture these things near the points where the grain and animals were pro- duced?) These advantages made Cincinnati the leading city of the Ohio Valley. For years most of the capital and business enterprise of St. Louis were engaged in the river trade, though later the city became an important manufacturing point. The following were the chief advan- tages which made it, next to New Orleans, the greatest steamboat center on the Mississippi System. (1) It is situated near the mouths of the Missouri, Illinois, and Ohio rivers. (2) The Mississippi River is considerably deeper below St. Louis than above. At St. Louis, therefore, cargoes were exchanged between the lighter-draft boats of the river above and those of heavier draft plying on the' river below. Because of its commanding position near the mouth of the Mis- sissippi River, New Orleans had for years the greatest commerce of any city west of the Appalachian Mountains. The population of New Orleans more than doubled between 1830 and 1840, in spite of the growing sand bars at the mouths of the river, frequent inun- dations, and disease (p. 243). No other important American city grew so fast. But even before the Civil War, the commerce and growth of New Orleans had received several serious blows. When canals were opened between the Great Lakes and the Ohio, Wabash, and Illinois rivers (p. 286), enormous quantities of goods from Ohio, Indiana, Illinois, and even from parts of Iowa and Missouri, went to the eastern markets by way of the Great Lakes and the Erie Canal, rather than to the southern markets. New Orleans particularly was injured as an importing city. It is some 1500 miles farther than New York from the cities of northwestern Europe, and the connection of New York with the Interior by way of the Hudson River, Erie Canal, and Great Lakes, was easier than that of New Orleans against the current of the Mississippi. The railroads continued the work of the canals, and made trade along east- west lines vastly greater than that along north-south lines. In addition to the four cities mentioned, many smaller cities and villages depended largely on river trade. Such were Louisville, whose location was determined by the rapids of the Ohio River; Nashville and Kansas City, profiting commercially (Why?) from their respective positions on the great bends of the Cumberland and Missouri rivers; and Peoria, the leading city of the Illinois Valley. 2 78 USES AND PROBLEMS OF INLAND WATERS Decline of river navigation. For years, commerce on the Mississippi River and its tributaries has been relatively small. The decline began at different times on different rivers — for example, in 1855 on the Illinois River, and about 1883 on the Yazoo River. The causes of the decline also differed somewhat, but the leading ones were of general application. (1) The channels of many of the rivers were shallow, crooked, and shifting. (2) The depth of water varied much from time to time, and from place to place. Boats suited best to the Great Lakes or coastwise trade could not be used on rivers or canals having but 6 feet of water, and boats giving the cheapest service for 6 foot channels could not be used in shallower waters, and so on. This was especially serious because of the importance of through traffic in American transportation. The great size of the United States and the contrasted products of its different parts mean that- much freight must move long distances. (3) The use of the rivers forced freight in many cases to take roundabout courses. (4) The waterways in the central and northern parts of the country were closed by ice a part of each year (p. 246). (5) Water transportation was relatively slow. (6) In general, the methods, landing places, etc., of river and canal trade have remained unimproved since the Civil War, and have been less and less able to meet the demands of mod- ern business. (7) When railroads were built throughout the Interior, these disadvantages proved fatal to river trade. The railroads at once got most of the passenger trade, and most of the traffic in perish- able and expensive freight. The rivers could, and in the future can, hope to compete only in the transportation of heavy, bulky, and non-perishable commodities such as coal, grain, lumber, building stone, and the like. It is highly desirable that the navigation of the larger rivers be improved, so that they may help the railroads in transporting the ever-increasing quantities of cheap freight (p. 287). Even since the loss of most of their business, many of the water- ways have been of importance in regulating railroad freight rates. Most of the river towns that obtained good railroad connections did not suffer greatly from the decline of river trade; but to river towns without railroads the passing of the steamboat was a serious blow, and many such places decreased in population. Present traffic. The Ohio and its tributaries now have the largest river trade in the country, and Pittsburgh is the leading inland city in the volume of its river commerce. The traffic is mainly in coal, lumber, logs, sand, and gravel. On the upper Mississippi, the FEATURES OF THE GREAT LAKES 279 declining traffic is largely in rafted logs and lumber, and in sand. The principal things transported on the lower Mississippi are coal, lumber, crude petroleum (from Louisiana), and plantation products such as cotton, sugar, and rice. In 1906, the total traffic for the entire Mississippi System, includ- ing rafts and harbor traffic, amounted to only about 30,000,000 tons. As in early days, most of the freight moves downstream. Pacific Rivers of the United States The rivers of the United States tributary to the Pacific Ocean have a combined navigable length of about 1,600 miles. None of them affords navigation far inland (Fig. 191), the San Joaquin and Sacramento rivers, especially, being nearly parallel with the coast. The Columbia is commercially the most important river of the Pacific coast. Ocean steamships reach Portland (some miles up the Willa- mette), no miles inland. As the only river rising east of the Cascade-Sierra Nevada ranges and directly- tributary to the Pacific Ocean, the Columbia was the key to political expansion on this portion of the coast. The fact that its branches approach closely the headwaters of the Saskatchewan and Missouri rivers, along which English and American explorers and fur traders advanced, was sufficient to cause a dispute between Great Britain and the United States over the Oregon country. The Colorado River is navigable for light-draft boats in its lower course (Fig. 191), but is little used commercially. COMMERCE OF THE GREAT LAKES General features of the lakes. The Great Lakes are the most important inland waterways in the world. Their shore-line in the United States is more than 4,300 miles long, if all the minor irregu- larities are measured. They are connected by canals with the At- lantic Ocean and the Mississippi System (Fig. 200). Unfortunately, the shores of the Great Lakes have few naturally good harbors. Several of the leading cities and many of the villages on them had their locations determined chiefly by the mouths of creeks or rivers. Thus Buffalo was located in part by the mouth of Buffalo Creek, Cleve- land by the mouth of the Cuyahoga River, and Chicago by the river of the same name. The entrances to these and similar streams were shallow, and easily choked by drifting sands. As a result, harbor improvements have been needed frequently throughout the history of the cities concerned. 280 USES AND PROBLEMS OF INLAND WATERS The Great Lakes afford conditions for transportation in many- ways vastly superior to those of the rivers, and their commerce has grown rapidly. The principal commodities carried on the Lakes are iron ore, coal, lumber, and grain — raw materials of great bulk, and not requiring rapid transportation. In 1910, the total domestic shipments on the Great Lakes amounted to more than 86,000,000 net tons, of which more than half was iron ore. Early navigation. Apart from their use by the Indians, the Great Lakes were navigated first by the French from eastern Canada. Their fur traders navigated the Great Lakes in light canoes which could be used also on the streams leading to and from the Lakes, and could be carried over the many portages. ^PortageS Fig. 195. Portages between the Great Lakes and the Mississippi System. Most of the lines which the French used in passing back and forth through the Great Lakes region (Fig. 195) are still of importance in trade and travel. Canals were cut across several of the old portages (compare Figs. 195 and 200), and turn- pikes and railroads followed the old lines or ran parallel to them. A number of villages and cities grew up at strategic points where the French had built forts to guard the lines of trade. Between Presque Isle (opposite the city of Erie, Fig. 251) and the Allegheny River, there ran at different times buffalo trail, Indian path, trad- er's trace, military road, turnpike, and railroad. A canal, soon abandoned, also once connected the city of Erie with the Ohio River. Long the favorite route of the French between the St. Lawrence River and the Great Lakes, the Ottawa Valley was followed by the Canadian Pacific Railroad westward from Montreal, and is to be followed by the projected Georgian Bay Ship Canal. In connection STEAM NAVIGATION ON GREAT LAKES 281 with the latter much water power will be made available, and the Ottawa Valley probably will become one of the most important industrial sections of Canada. The above facts illustrate the truth of a statement that "trade and civilization in America have followed the arteries made by geology." The first American sailing vessel appeared on the Great Lakes in 1797, but for a time the number increased slowly. In 1812 some half-dozen small schooners car- 1 1„ . s^f? 1830 > ; |UnderZpersq.niL \ ^^45 and over U r J j ,W\' t *' / \ MICHIGAN^ / ILLINOIS/" |\-— / LJ "JlT X" 1 \ 1 1 ' /" 1NDIANA ^. 1 \ \ (( ^~r^> vM%W^^k ^jji0^\ Fig. 196. ried nearly all the traffic on Lake Erie, and for several years more the business of the upper lakes was limited to that of the fur- trading stations. Further devel- opment awaited the introduc- tion of steam navigation, and the settlement of the neighbor- ing lake and prairie plains. Steam navigation and the settlement of the Great Lakes region. Beginning in the dec- ade 1820-1830 there was a large movement of population from New England and New York into the Lake region. For this there were many reasons, one of the most important being the great reduction in the expense and time involved in reaching the Interior, due to the opening of the Erie Canal in 1825 (p. 286) and the development of steam navigation on the western Lakes in the thirties. The first steamer appeared on Lake Ontario in 1816, but not till ten years later did one enter Lake Michigan, and not until 1832 did one visit Chicago. As the number of steamboats increased, passenger fares decreased, and it was soon possible to take household goods, farming implements, and stock into the Interior easily and cheaply. Fig. 197. Fig. 196. Distribution of population in the Great Lakes region in 1830. Fig. 197. Distribution of population in the Great Lakes region in 1850. 282 USES AND PROBLEMS OF INLAND WATERS A comparison of Figs. 196 and 197 will show how rapidly the nor- thern parts of Ohio, Indiana, and Illinois, and the southern parts of Michigan and Wisconsin were settled between 1830 and 1850. During this period, also, Buffalo, Cleveland, Toledo, Milwaukee, and Chicago had their first substantial growth. They served as points of contact between the agricultural Interior and the manufacturing and com- mercial East. Their prosperity depended on commerce; not till later did they come to have large manufacturing interests. The " Soo Canal " and the opening of Lake Superior. Be- fore the "Soo Canal" was opened in 1855 there was little commerce on Lake Superior, and for the most part its shores were an unsettled wilderness. The canal opened the borders of the lake to settlement, and permitted the development of their natural resources, especially the iron ore (p. 179) and lumber. The value of the canal was in- creased greatly in 1881, when the first enlargement was completed. Between 1880 and 1890, the population of the Lake Superior counties of Michigan, Wisconsin, and Minnesota increased respectively 90 per cent, 400 per cent, and 800 per cent. The canal contributed greatly to this remarkable growth. In 1896, the canal was given a depth of 20 to 21 feet, and a further enlargement is now being made. There is also a Canadian canal around St. Mary's Falls. In recent years about Vz of the total traffic of the Great Lakes has passed in or out of Lake Superior through the "Soo Canal." The tonnage passing through it during the seven months of the open season is about four times as great as that passing through the Suez Canal during the entire year. About Vs of the freight which passes through the "Soo Canal" is east-bound. Traffic in iron ore and coal. In recent years the iron ore fields of the Lake Superior region have furnished about 4 /s of the output of iron for the whole country. Fig. 198 shows the movement of iron ore on the Great Lakes. Most of the ore goes to Lake Erie ports, and thence by rail to the Pittsburgh region. Most of the iron ore goes to the coal, rather than the coal to the iron, because the amount of coal needed in manufacturing steel is greater than the amount of iron ore, and because, where now manufactured, the steel is nearer its market than it would be if manufactured where the iron is mined. As Fig. 198 shows, much iron ore also goes to the iron and steel centers near the head of Lake Michigan, especially to South Chicago and Gary, Indiana. At these points Indiana and Illinois coal (see Fig. 85) may be obtained cheaply, and they are close to great markets. TRAFFIC OF THE GREAT LAKES 283 Many boats which bring iron ore, lumber, and grain to the east- ern lake ports take back coal at very low rates. This has helped to make possible the recent establishment of the iron and steel industry at the western end of Lake Superior. It also means cheap Fig. 198. Map showing movement of iron ore on the Great Lakes in 1909. (After Birkinbine.) coal in the region west of Lakes Michigan and Superior, which is without coal resources of its own. Lumber trade of the lakes. The western end of the great northern forest of pine, spruce, hemlock, cedar, fir, birch, etc., lies in Michigan, Wisconsin, and Minnesota (Fig. 271). Lumbering began in Michigan in the early thirties, and spread westward and northward. Production increased rapidly after 1850, and for many years the Lake states were the most important lumber district in the United States, furnishing, in 1880, ^3 of the total output of the country. Logs cut in the interior were floated down the streams to the Lakes. At the mouths of the larger rivers busy towns developed 284 USES AND PROBLEMS OF INLAND WATERS where the logs were manufactured into lumber. First from the mill towns of eastern Michigan, and later from more distant points, the manufactured lumber was shipped at low lake rates to Detroit and the cities of Lake Erie. Most of the products of the Lake Michigan mills were sent through Chicago to the prairies, the settlement of which created a demand for enormous quantities of building and fence material. As the pine forests near the Lakes and along the larger rivers flowing into them were cut away, mill towns sprang up in the interior, from which more and more lumber and lumber Loading ore at Escanaba. (Copyright by Detroit Publishing Co.) products have been sent to market by rail. This change and the general decline of the lumber industry in the Lake region since 1890 (p. 372), due to the cutting away of the forests, have reduced greatly the lumber trade of the Great Lakes. In 1910, 1,208,000 thousand feet of lumber were transported on the Lakes. Movement of grain and flour. The transportation of grain and flour has been an important phase of commerce on the Great Lakes ever since the settlement of the Lake states. The movement is almost entirely from the south end of Lake Michigan and the west end of Lake Superior, to the east end of Lake Erie (Why?). Modern lake vessels. Much of the freight on the Great Lakes is carried in steel freighters, built for speed, capacity, and strength (Fig. 199). Many are 500 to 600 feet long, and have a capacity of 10,000 to 12,000 tons. One of the largest carried 13,000 tons of CANAL BUILDING IN THE UNITED STATES 285 soft coal in a single cargo, and on another occasion 422,000 bushels of wheat. Another lake vessel transported more than 323,000 tons of iron ore in 27 cargoes during the season of 1907. CANALS General considerations. The first canal in the United States was opened in 1794, but there were few of importance until the successful completion of the Erie Canal (1825) aroused general interest in canals. The period of most active canal digging extended from 1825 to 1837. Altogether, about 4,500 miles of canals have been constructed in the United States (Fig. 200). Most of them extended and supple- mented natural water- ways. The more im- portant ones were of three classes: (1) Those along the Atlantic coast, connecting bays or rivers between which the natural water routes involved much greater distances. (2) Those connecting, or begun with the intention of connecting, the leading Atlantic seaports with the Ohio River or the Great Lakes. (3) Those connecting the Great Lakes with the Mississippi System. As Fig. 200 shows, many feeders were built for the main canals. Of the 4,500 miles of canals constructed, nearly 2,500 miles, costing about $80,000,000, have been abandoned. Most of the con- ditions which contributed to the decline of river navigation (p. 278) contributed even more to the decline of the canals. They were all shallow, and the canal boats were therefore of small capacity; many of the canals varied in size in their different parts, retarding LA l( ^j£i -J \ J 1 PJ/4-- L —1 J;fct---4'-~-- ! ! r \ «.. f \-\ | ) Y ( o^ iA ^*~\/X \ \o\ Fig. 200. Map showing principal canals con- structed in the United States. Most of them are no longer used. 286 USES AND PROBLEMS OF INLAND WATERS through traffic. Most of the canal boats were towed by animals. Some of the canals were located unwisely, some were managed badly, and most of them fell an easy prey to railroad competition. The Erie Canal. The Erie Canal, connecting the Hudson River with Lake Erie at Buffalo (Fig. 200), was built by New York to control the trade of the central and western parts of that state, as well as to gain the trade of the Great Lakes region, toward which settlement was setting. Some of the products of the former sections were going down the Delaware and Susquehanna rivers to Philadelphia and Baltimore, and some were seeking the Canadian markets along the St. Lawrence River. Such a canal was needed also for military reasons. In the event of another war along the northern frontier, some way better than any existing during the War of 181 2 was needed to get supplies to the shores of the Lakes. The canal became a great highway of expansion into the Inte- rior, and a great outlet for surplus western products; it caused the rapid growth of Buffalo, Rochester, and other places along its course; it increased land values throughout the region tributary to it; and it helped to transform New York City from a market town for the Hudson Valley into the leading commercial city of the continent. The cost of transportation between Albany and Buffalo fell from $88 to $5.98 a ton in the twenty-six years after the opening of the canal. The tolls collected on the canal paid for its construction in 10 years. Until the late 1860's, the Erie Canal was the most important transportation route between the Great Lakes and the Atlantic Ocean. In 1866, the freight carried by the canal was 60 per cent of that moved across New York. Soon after this it began to decrease, and the tonnage on the canal has been small for years. The people of New York voted in 1903 to spend $101,000,000 in improving the canal, and this work is now in progress. Canals between Great Lakes and Mississippi System. It is impracticable to consider here, one by one, the different canals which connected the Great Lakes with the Ohio and Mississippi rivers (Fig. 200). In general, they injured the cities and trade of the Mississippi River (p. 277), and benefited greatly the cities and commerce of the Great Lakes. For a time, most of them were powerful factors in the development of the sections which they crossed. In addition to giving special benefits in different cases, they cheapened transportation, opened new markets, raised the prices of IMPROVEMENT OF WATERWAYS 287 farm products, lowered the cost of imported merchandise, increased land values, stimulated the growth of population, and helped build up towns and cities. Some of these canals have been abandoned, and for years the rest have been used but little. Foreign canals. Several foreign countries have systems of canals suited to modern conditions of transportation. This is true particularly of Germany. One of the important canals of Germany (the Kiel Canal) was built to permit ships to pass between the Baltic and North seas without going around Denmark. The Manchester Ship Canal allows ocean-going ships to reach the docks of Manchester from Liverpool. IMPROVEMENT OF AMERICAN WATERWAYS Why waterways should be improved. The larger rivers of the United States should be so improved as to make possible eco- nomical transportation upon them. This is desirable because (1) water transportation is normally cheaper than rail transportation, and if the cost of transportation is reduced, the price to the consumer of the things transported will tend to be lower; (2) waterways tend to keep down the rates of competing railroads; and (3) in recent pros- perous years the railroads have been unable to handle promptly the traffic of the country during the busy season. The products and trade of large sections of the country are increasing much faster than the transportation facilities of the railroads. Leading improvements needed. Among the projected improve- ments are: (1) A deep canal (at least 20 feet) between the Hudson River and the Great Lakes. The new Erie Canal (p. 286) will have a depth of 12 feet. (2) A deep inner waterway along the Atlantic coast from New England to Florida, connecting various bays and sounds. (3) A deep waterway between Lake Michigan and the Gulf of Mexico. This involves extending the Chicago Sanitary and Ship Canal (built primarily to dispose of the sewage of Chicago) to the head of naviga- tion on the Illinois River, and improving the Illinois and Mississippi rivers. Such a waterway would be of great importance to the trade between the northern and southern parts of the Interior, and, follow- ing the opening of the Panama Canal (p. 355), to the trade of the northern Interior with the Pacific coast, and with foreign countries both to the south and across the Pacific Ocean. (4) A canal to connect Puget Sound and the Columbia River. 288 USES AND PROBLEMS OF INLAND WATERS Water Power Use in the past in United States. Water power has located many manufacturing cities in the United States, and contributed largely to their growth. It was used first in a large way in New England, where it is one of the leading natural resources. Bellows Falls, Holyoke, Manchester, Lowell, Berlin, Biddeford, Lewiston, Rumford Falls, Augusta, and Bath are among the busy industrial centers created largely by water power. There are also many water power cities farther west. Grand Rapids, Michigan, a leading furniture manufacturing center, is an example. Located 40 miles inland, at the rapids of the Grand River, its first lumber mills were at a disad- vantage compared with those on the shores of the Lakes (p. 283; Why?). As a result, cabinet shops and furniture factories were soon established. (What was gained by doing this?) The power afforded by the river was soon outgrown, and the timber supply in the vicinity exhausted, but the advantages of an early start, and of established plants with world-wide reputations for furniture of superior quality, keep the city to the front. Similarly, St. Anthony's Falls and command of the forests and wheat-fields of Minnesota made Minne- apolis an important manufacturing city. Nearly Vio of the flour and grist mill products of the country are manufactured there. Water power formerly had certain disadvantages, because the mills using it had to be close to the source of the power. Coal was abundant, cheap, and easily shipped, and was used more and more for manufacturing purposes. Water power continued to be used most in connection with long-established industries, and in connec- tion with industries demanding special conditions, such as the manu- facture of paper and wood-pulp. Present conditions and future importance. In recent years there has been a great increase in the use of water power in the United States. In 1900, less than 1,500,000 horse power were devel- oped from water, and in 1908 more than 5,350,000 horse power. This change has been due largely to the following conditions, which also will help to bring about an increasing use of water power in the future: (1) There have been rapid developments in the transmission of energy in the form of electricity. Electric power developed by falls and rapids {hydro-electric power) is transmitted some 300 miles by a Colorado company. On the basis of transmission for 200 miles, a water power could, if sufficient, serve an area of 125,000 square miles. USE AND IMPORTANCE OF WATER POWER 289 In the future, few places in the United States will be beyond the reach of hydro-electric power. Power from Niagara Falls now runs street cars, lights buildings, and is furnished very cheaply for manufacturing purposes in Buffalo and other cities as far away as Utica. On the Canadian side, it is carried to various cities and villages as far away as the Detroit River. Snoqualmie Falls, Washington, furnish power for electric lights, street railways, motors, etc., in Seattle and Ta- coma, some 50 miles distant. (2) In some ways, electric power is better than other kinds for large plants, and it also has a great ad- vantage over other forms of power in that it may be carried econom- ically to the small user. (3) In many places, hydro-electric power is even now cheaper than power obtained from coal. It ^estimated that about 3/^ of the power now developed from coal in the United States could be developed cheaper by water. Furthermore, the substitu- tion would lengthen greatly the duration of the coal supply (p. 177). As the supply of coal diminishes and its cost increases, electricity developed by water will be used more and more for transportation, lighting purposes, and manufacturing. Doubtless the time is not distant when most railroads, street cars, and interurban lines will be operated in this way. In time, nearly all manufacturing industries will depend largely on water power, and it is fortunate indeed for the future of the United States that its available water power is so great. Amount and distribution of water power in the United States. In view of the part which water power is to play in the life of the nation, its amount and distribution are matters of great interest and importance. The total amount has been estimated on several bases. (1) If the amount of water available in the streams during the two weeks of lowest water were used throughout the year, and if all above that amount escaped unused, about 37,000,000 horse power could be developed. This is called the primary horse power. (2) If plants were established to develop the minimum power avail- able for the six high- water months, there would be about 66,500,000 horse power per year. (3) If the flood waters were stored in reser- voirs, so that the streams were utilized fully, there could be developed between 100,000,000 and 200,000,000 horse power. The meaning of these figures is realized best when it is remembered that now about 26,000,000 horse power are developed from coal, and only about 5,500,000 from water. The estimated distribution of water power throughout the country on the first two bases given above is shown in the table on the next page. 2 9 o USES AND PROBLEMS OF INLAND WATERS ESTIMATE OF WATER POWER IN THE UNITED STATES Horse Power Available Prima rv nr Minimum of Principal Drainages MiSm the ? £ Highest Months Northern Atlantic to Cape Henry, Va 1,702,000 3,186,600 Southern Atlantic to Cape Sable, Fla • . 1,253,000 1,957,800 Eastern Gulf of Mexico to Mississippi River 559,000 963,000 Western Gulf of Mexico, west of Vermilion River 433,760 822,650 Mississippi River, main stream 147,000 335,ooo Mississippi River tributaries from east 2,472,590 4,940,300 Mississippi River tributaries from west, including Ver- milion River 3,948,970 7,085,000 St. Lawrence River to Canadian Line -6,682,480 8,090,060 Colorado River, above Yuma, Ariz 2,918,500 5,546,000 Southern Pacific to Point Bonita, Cal 3,215,400 7,808,300 Northern Pacific 12,979,700 24,701,000 Great Basin 518,000 801,000 Hudson Bay 75, 800 212,600 Total 36,906,200 66,449,310 Improving water powers. It is highly desirable that power streams should maintain a relatively even flow. If a stream can develop 5,000 horse power during brief flood stages, and only 500 horse power the rest of the time, not much more than the latter amount can be used, and the rest is lost. Forests about the head- waters of mountain streams and systems of reservoirs hold back the storm-waters and tend to keep the flow of streams steady. They are therefore important to manufacturing, as well as to navigation and farming (pp. 166-169, 221-222). Water power in other countries. Water power is afforded by most large streams in mountain regions, and by many youthful streams in other regions, especially those that have been glaciated recently. In Europe, Switzerland is likely to be the first country to utilize fully its large water power resources. The streams of Scandinavia, Austria-Hungary, France, Italy, and Germany also afford much power. Enormous power could be developed from the streams of the Caucasus and Himalaya mountains, but this is not likely to be done in the near future. Considerable power may be obtained from the streams of eastern Australia. Canada has an abundance of water power, both in the western mountains and in the eastern part of the country. In the latter section, it is due largely to glaciation. Many other countries have more or less water power, much of which will be of value to man sometime, if not so now. WHY IRRIGATION IS PRACTICED 291 Irrigation Irrigation means the artificial application of water to land for the benefit of plants. It is practiced in many dry regions because otherwise crops cannot be grown, and it is being introduced more and more into humid regions, in order to increase the yield of crops. Even in eastern United States, there is scarcely a year when some crops do not suffer from lack of rain, and there are occasional years of serious droughts. The common statement that farming without irrigation cannot be carried on successfully where the annual rainfall is less than twenty inches is very misleading. The development of "dry farming" (p. 329) and the introduction of drought-resisting plants (p. 173) are changing some semi-arid regions into fairly productive farm lands, without irrigation. Again, much depends on the distribution of the rainfall. If it came just when the plants needed it, ten or twelve inches would suffice to grow many staple crops by ordinary methods of farming. The yields that would be obtained under such conditions could be increased greatly, however, by irrigation. Practiced since ancient times. Irrigation was practiced in Egypt 2,000 years before Christ, and probably much earlier, but the area irrigated then was much less than now. About 6,000,000 acres have been irrigated in Egypt in recent years. The ancient civiliza- tions which existed in Mesopotamia were made possible by extensive systems of irrigation. The ditches of the region have long been unused, and much land which once was cultivated is now waste. The English government has extended irrigation in India until about 50,000,000 acres are so watered. IRRIGATION IN WESTERN UNITED STATES Irrigation was practiced first in the United States in Arizona and New Mexico. In the latter, there are ditches said to have been used continuously for 300 years by people of mixed Span- ish and Indian descent. The Mormons were the first Americans (except Indians) to irrigate systematically. The conditions for irrigation were ideal on the slopes of alluvium at the base of the Wasatch Mountains, and without irrigation they could not have been cultivated. Irrigation by Americans in the Salt River Valley of Arizona began in 1867, and in southern California a few years later. 2 9 2 USES AND PROBLEMS OF INLAND WATERS Value of irrigated land. Irrigation changes unproductive, worthless, or nearly worthless land into land producing more than the average farm land in eastern United States. (Compare Figs. Fig. 20 1. The Yakima desert before irrigation. Near North Yakima, Washington. (U. S. Reclamation Service.) * \n < \Bfc> K WS&' Fig. 202. The region shown in Fig. 201, after irrigation. (U. S. Reclama- tion Service.) VALUE OF IRRIGATED LANDS 293 201 and 202.) Irrigated lands are worth $100 or $150 an acre for general farming purposes, and choice fruit lands with good orchards are worth $1 ,000 or more an acre. In general, the great value of much of the irrigated land is due to the following: (1) The soil of arid regions is likely to be rich in mineral plant foods, because for ages ground- waters have come to the surface through capillary action, and as they evaporated into the dry air they have deposited in the soil the mineral matter dissolved during their journey un- der-ground (p. 212). In some cases when irrigating waters have been turned on the land it has been found that so much of certain materials (alkaline salts or "alkali") had ac- cumulated in this way in the soil, that plants would not thrive until the alkali was partly leached out. (2) Irrigated soils, when used rightly, are durable, for soil wash can be avoid- ed largely, and the store of soluble mineral matter in the sub-soil is large. (3) Irrigating waters contain fertilizing matter in solu- tion. (4) Irrigated crops, if properly cared for, get just the amount of water II b Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec 6 18 95 4 2 7R 54 50 26 22 18 i 14 1 18 96 10 1 1 8 . ■ 1 & 1 , rm 4 "1 Me 2 J im, a tatf J m Fig. 203. Diagram showing discharge of the Boise River above Boise, Idaho, in 1895 and 1896. (Newell, U. S. Geol. Surv.) needed at just the time they need it. (5) In the warmer sections of the West, several crops a year may be grown. Area of irrigable land. As the demand for land increases with the population, it will be advisable to extend irrigation to the utmost limit. It is estimated that about 45,000,000 acres (an area the size of Missouri) are irrigable. This is only about 5 per cent of the entire arid region. The chief factors which will control the area which can be irrigated are matters of topography and rainfall. (1) The water supply comes largely from rain and snow falling on the mountains, 294 USES AND PROBLEMS OF INLAND WATERS and the mountain catchment areas are comparatively small. Further- more, only a small fraction of the rainfall of the arid region can be made available for irrigation (Why?). (2) The volume of many of the western rivers varies greatly (Why? Fig. 203), and in many cases it is necessary to build dams to hold the flood waters in reservoirs, so that they may be let out as needed during the growing season. Un- fortunately, there are comparatively few places suited for the storage of large amounts of water, and in some cases where there are good sites for dams, the areas tributary to them furn- ish little water. (3) In many places the ground is so rough that the water cannot be spread over it properly. (4) In many places the possible crops probably would not justify the expense of getting the water on the land. (5) The area which can be irrigated depends in part upon the amount of water per acre required for crops. In the case of the gov- ernment projects (p. 295), this varies from i}£ to 5^ acre-feet 1 per year. (Apart from the fact that some crops require more water than others, why should the variation be so great?) There are several reasons for hoping that the irrigable areas may prove larger than stated above. (1) Many fields are now poorly prepared for the water, so that it spreads unevenly, and more is required than would be if the land were less uneven. With the land better prepared, the water could be spread over a larger area. (2) Much more land could be watered if loss by seepage from the canals were not so great. This now amounts, on the average, to about 25 per cent of the water. The loss probably will be reduced more 'An acre-foot of water is the amount which would cover an acre of ground to the depth of one foot. Fig. 204. A canal lined with cement. Truckee- Carson Project, Nevada. (U. S. Reclamation Service.) GOVERNMENT IRRIGATION PROJECTS 295 and more by lining the canals with cement (Fig. 204). (3) The loss of water by evaporation from the canals also will be reduced. (4) Many irrigators now use much more water than is necessary to secure the largest returns. This will be corrected by legislation, and by increasing intelligence on the part of the farmers. (5) Meas- urements to determine the amount of available water have been made Fig. 205. Map showing Government irrigation projects. on only a part of the western streams, and on most of these the records cover only a few years. Further work along this line may show that the streams can furnish more water than is now supposed. (6) For much of the West detailed topographic surveys have not been made, and they may add new possibilities. Government projects. Irrigation was begun in the West by individual settlers, who led water to their fields from small rivers and creeks through ditches which they dug. Co-operation was necessary, however, before extensive areas could be watered. This has been brought about in various ways. Many so-called "irrigation districts " have been organized to reclaim arid land under state laws. Since 296 USES AND PROBLEMS OF INLAND WATERS 1894, much land has been reclaimed, especially in Idaho and Wyoming, under the Carey Act, which provides for irrigation through co-operation by the nation, state, corporations, and settlers. While much was being accomplished in these ways, it became evident that the federal government must itself undertake those projects that were too expensive, too large, or too slow in producing returns, to tempt individuals or companies. Hence Congress passed the National Reclamation Act in 1902. This act provides that money derived from the sale of public lands in the arid states shall constitute a reclamation fund. The cost of any given project is assessed against the land benefited, and is paid by the settlers in ten equal annual pay- ments. The moneys returned to the govern- ment, together with the proceeds of the sale of other lands, are used again for further recla- mation. There are some thirty government projects under way (Fig. 205), which, when finished, will irrigate more than 3,000,000 acres. The average cost to the settler probably will be $40.00 to $50.00 per irrigated acre. The success of these great projects of the government has stimulated private enterprise greatly. A few facts concerning some of the government projects will illus- trate the scope of the work. The Salt River Project (Arizona) has the recently completed Roosevelt dam, 280 feet high and 1080 feet long on top. This dam forms a lake covering 16,320 acres. The power developed by the water as it comes out is used to pump ground- water to irrigate more land, for lighting purposes, and in other ways. The storage dam for the Rio Grande Project is one of the largest in the world. It will make a lake 40 miles long, covering 40,000 acres, and con- taining 2,600,000 acre-feet of water. The water for the Truckee- Carson Project (Nevada) is stored in Lake Tahoe, a glacial lake in the Sierra Nevada Mountains. From Truckee River, the out- Fig. 206. Site of the great dam on the Sho- shone River, in Wyoming. PRODUCTS OF IRRIGATED LANDS 297 let of the lake, it is diverted into a canal and carried across to the Carson Valley to reclaim land formerly composed largely of sand dunes and alkali flats. Nearly half the area of the Klamath Project (California-Oregon) is occupied by swamps and lakes, so that it must be drained before it can be tilled. After being drained, it will need to be irrigated. The water supply for the Shoshone Project, in northern Wyoming, is derived from the Shoshone River. To regulate the flow of this river, the government has built a dam 328^ feet in height (Fig. 206), the highest structure of the kind ever built. Crops of the irrigated lands. Many different crops are grown on the irrigated lands, for the conditions affecting plant life vary greatly. Alfalfa and sugar beets are produced in many places. Hay, grain, and vegetables are staple products in Montana and Wyoming. In addition to these things, fruits are grown extensively in Idaho, Washington, Oregon, and Colorado. The great citrus fruit region is in southern California, and the raising of these fruits has increased rapidly in recent years. In 1910-n, nearly 18,000,000 boxes of oranges and lemons were shipped. The growing of deciduous fruits (peaches, pears, and the like) also has become of great importance in California, as in various other sections of the West. The shipping of these fruits in large quantities to distant markets has been made possible by the development of the refrigerator car, in which most of the shipments from California are made. In the extreme southwest, the leading products are semi-tropical fruits, cereals, and alfalfa. Population capacity of the irrigated lands. The high value of the irrigated lands encourages methods of tillage which secure maximum yields from minimum areas, and, together with the diffi- culty of hiring effective labor in the West, leads to small farms. In orchard regions, 5 to 10 acre holdings are common. On a number of the government projects, the farm unit has been fixed at forty acres. These things mean a dense rural population. The ultimate popula- tion of the irrigated lands probably will be not far from one person to an acre. Farm villages. In many ways, social conditions promise to be nearly ideal in most of the irrigated districts. The small farms will make it possible for many of the farmers to live in town, going to and from their land daily. It seems probable that each 5,000 or 6,000 acres of cultivated land will support a farm village, where the farmers will have the advantage of graded schools, public libraries, etc. On a number of the government projects, the Reclamation Serv- 298 USES AND PROBLEMS OF INLAND WATERS ice has laid out town sites about six miles apart, and set aside lots for churches, schools, and cemeteries. The town lots are sold to the highest bidders, the proceeds going to the Reclamation Fund. Irrigation promises to create many small villages, rather than a few large cities. Irrigation and the National Forests. From the standpoint of irrigation, as well as of navigation and water power, it is highly impor- tant that the flow of the streams be uniform. The preservation of forests about the headwaters of the streams helps to bring about a more even flow of water, and partly for this reason the National Forests were established (Fig. 207). Outside Alaska, these forest reserves have an area (191 2) of about 144,000,000 acres. They are cared for by the Forestry Bureau of the Department of Agriculture. IRRIGATION IN THE HUMID STATES Present situation. Irrigation is practiced in some of the humid states in growing certain crops. For example, water is pumped from wells on to the land at various points on the coastal plain between New Jersey and Florida, to irrigate truck farms. In the latter state, irrigation has been undertaken recently on a rather large scale. This is particularly interesting, since all parts of Florida receive more than 50 inches of rain a year, and some parts more than 60 inches. But much of the soil does not retain moisture well, evaporation is great, and the fruit groves and truck farms are bene- fited by watering during the drier season. Their products are so valuable that even a partial crop failure means heavy losses. Irri- gation is practiced extensively on the rice-fields of Louisiana, Texas, and the Carolinas. As yet, irrigation in the East is restricted largely to special crops which warrant relatively large expenditures, such as strawberries, raspberries, blackberries and other fruits, and certain vegetables. With these crops, a small or imperfect yield because of drought is disastrous. Future importance. It has been estimated that the yield of every important crop of eastern United States could be doubled by irrigation. It is therefore certain to be practiced more and more in the future, as the population increases and the demand for food grows. As in the West, the irrigator can apply just the amount of water needed at just the time required, and he can grow many more plants on an acre than otherwise. THE NATIONAL FORESTS 299 3 oo USES AND PROBLEMS OF INLAND WATERS Reclamation or Swamp and Overflowed Lands WET LANDS OF THE UNITED STATES The reclamation of swamp and lake areas has been referred to incidentally in other connections (pp. 171, 241, 242, 262). The matter is summarized briefly here. Area and distribution. It is estimated that the total area of swamp land in the United States is about 79,000,000 acres, most of which can be reclaimed ultimately. Swamp lands occur in many states, but the largest areas are in the states containing (1) the Atlantic and Gulf coastal plains, (2) the flood-plains of the Mississippi River and its larger tributaries, and (3) the area covered by the last ice-sheet. About half of all the area of swamp land is in Florida, Louisiana, Mississippi, and Arkansas. Status and cost of reclamation. It is estimated that nearly 16,000,000 acres have been drained, mostly in the northern interior states. In most other parts of the United States, the problem of draining wet lands received little attention until the last few years. This was due to the abundance, till recently, of good land not re- quiring drainage. Progress is now being made in Florida, Louisiana (p. 171), and other states. The cost of reclamation varies with the character of the swamp, the methods employed, and the machinery used, from $3 or so an acre, to $30 or more. In some cases ditches to carry off the water are all that is needed, and the cost is then slight; in other cases tile- draining is necessary, and then the cost depends largely on the character of the land. Along many rivers and coasts it is necessary to build dikes. The water of the swamps is then brought to certain points by drains or ditches, and pumped out over the dikes. In many such cases, rather large areas are treated as units, and improve- ments in methods and machinery have reduced the cost one-half in the last 15 years. The average cost of drainage has been estimated at $15 an acre. This is much less than the average cost of irrigating dry lands (p. 296). Results of reclamation. (1) The soils of most reclaimed swamp lands are very fertile. Since most swamp areas are of little use, it is clear that drainage greatly increases their value. The value of drained farming land varies from $20 or less an acre, to $500 and more. It depends largely on the character of the soil, the climate, transpor- tation facilities, nearness to or distance from good markets, etc. It has been RECLAMATION OF WET LANDS 301 estimated that, when drained, the swamp lands of the United States will have an average value of $60 an acre. Their present value has been estimated at $8 an acre. (2) The products of the drained lands will increase greatly the crops of the country, and will feed and support millions of people. (3) An immediate effect of the systematic draining of the swamp lands will be to increase the healthfulness of the areas concerned. The principal breeding places of malaria-carrying mosquitoes will be destroyed, and that disease practically stamped out. The present annual loss to the country from malaria, due to the reduced efficiency of the sufferers, the losses to business in the areas affected, etc., has been estimated at $100,000,000. Reclamation of lake-covered lands. Swamps merge into lakes, and many so-called lakes doubtless are included in the estimate of swamp areas already given. Ultimately, most shallow ponds and lakes will be drained. It will always be impracticable to drain some lakes, and many others will be carefully protected and preserved (p. 264). WET LANDS OF OTHER COUNTRIES Large areas of wet land have been reclaimed in Europe. Much land now farmed in Holland was won from the sea. About y$ of England was marsh or bog land in the reign of Alfred the Great (871- 901). Probably " not far from V20 of the tillable land in Europe was inundated and unfit for agriculture in the eighth century of our era." Vast areas of swamp land in various tropical countries probably will remain in their present condition for a long time. Water Supply Apart from its support of plant and animal life, the most impor- tant use of water is for home and city purposes — that is for drink- ing, bathing, and various household purposes, for sprinkling streets, flushing sewers, for fire protection, manufacturing, and the like. It is estimated that between 50 and 150 gallons of water per person are used daily in the cities of the United States. Of this, about half a gallon per person is used for drinking. Sources of water supply. (1) Rain-water, stored in cisterns and "tanks," is used extensively for drinking in the arid states, and for other purposes throughout much of the country. (2) Most of the country people of the United States obtain water for domestic purposes from underground, through ordinary wells and springs; but 3 o2 USES AND PROBLEMS OF INLAND WATERS no large city could get water enough in this way. Thousands of wells and springs have failed in recent years because the water table (p. 205) has been lowered by unwise farming and deforestation (p. 208). (3) In the Atlantic Coastal Plain, the Great Plains, and some other parts of the country where the arrangement and position of the rock strata are favorable, artesian wells (p. 209) supply large amounts of water. Sand and gravel are in general good water bearers, while clay yields relatively little water (Why?). Many wells sunk in the glacial clays of northern United States obtain their water chiefly from beds or pockets of sand and gravel in the drift. Among the solid rocks, sandstone is a good water carrier, because it is porous, and shale a poor one, because it is compact. Granite and many similar rocks are dense, and hold little water, the largest supplies being found in cracks and other openings in the rocks. (4) Thousands of lakes, particularly in the glaciated parts of the country, may serve as sources of water supply for neighboring cities and villages, and many are so used now. From the Great Lakes or their connecting rivers, Buffalo, Cleveland, Detroit, Milwaukee, Chicago, Duluth, and many smaller cities get their supply of water. (5) Many villages and cities get their water from streams. Thus New York City's supply is from streams and reservoirs in the Catskill Mountains and the uplands east of the lower Hudson River; Phila- delphia depends on the Delaware and Schuylkill rivers, Cincinnati on the Ohio, Minneapolis and St. Louis on the Mississippi, and Omaha and Kansas City on the Missouri. In recent years various cities have outgrown their supplies of water and have had to seek new supplies, in some cases at considerable distances and at great expense. Los Angeles is expending more than $25,000,000 in this way. Water is to be brought from Owens River, across the Mojave Desert and through the San Bernardino Mountains, in an aqueduct of steel and concrete some 240 miles long. New York City is expending nearly $100,000,000 to obtain an additional supply of 500,000,000 gallons a day from the Catskill Mountains, more than 80 miles away. Quality of waters. Drinking water should be reasonably clear, tasteless, and free from germs of disease. Some cities have expended large sums to guard the purity of their water. Some of them have bought large tracts of land, with their lakes, springs, and other stream sources. The waters of these tracts are then protected carefully from contamination, and carried to the cities in ways that prevent pollution on the way. Other cities have estab- lished filtering plants through which all the city water passes before WATER SUPPLY PROBLEMS 303 use. Nevertheless, the use of impure drinking water is still a leading cause of disease in the United States. Many wells receive drainage from barnyards and cesspools (p. 207), many springs used as a source of drinking water are exposed to surface wash and to pollution by stock, and many villages and cities use river and lake water con- taminated by sewage. For many industrial purposes, the value of water depends on the kind and amount of mineral matter it contains. Distilleries and breweries require water of exceptional purity. Laundries and textile mills need water which is clear, free from iron, and contains little other mineral matter. Railroad companies spend large sums in treating the waters used in their engines, so as to make them less injurious to the boilers. Knowledge of the quality of the waters of the country is so important for various reasons that extensive investigations of surface and ground waters are being made by the United States Geological Survey, and by various state and private agencies. Questions 1. Are cities more likely to develop on the inside or outside of great bends on navigable rivers? Give examples and reasons. 2. Why does the cost per ton for transportation by water tend to decrease as the size of the cargo increases? 3. Why are four-fifths of the population of New York state in the counties bordering the Hudson River and Erie Canal? 4. (1) Account for the enormous amount of water power available in the Northern Pacific district, according to the table on page 290. (2) Why do the western tributaries of the Mississippi River afford more power than the eastern tributaries? (3) Why does the Northern Atlantic district (p. 290) furnish more water power than the Southern Atlantic? 5. Explain the fact that apples and other fruits are grown in great perfection and abundance on irrigated lands around Grand Junction, in western Colorado, while in the same latitude in western Nevada attention is given largely to hardier crops, such as grain and potatoes. 6. Account for the fact that legislation concerning the utilization of stream and ground waters is more advanced in western than in eastern United States. CHAPTER XVII MOUNTAINS AND PLATEAUS AND THEIR RELATIONS TO LIFE Mountains and plateaus have been referred to frequently in earlier pages. The more important points concerning their origin, their history, and their relations to human affairs are considered in this chapter. Mountains Distribution of mountains. As already noted, mountain ranges are situated in general toward the borders, rather than in the interiors, of the continents, and most of the longer and higher systems are not far from the edges of the greatest ocean basin. The settling of the ocean basins, due to the shrinking (partly through cooling) of the earth, may have been an important cause of the uplifts which have made mountains near the edges of the continents. Leading types of mountains, (i) Fig. 208 shows several moun- tain ridges of one type, and suggests their origin. A plateau or plain was divided by giant cracks into a series of great blocks, which were displaced {faulted), the relatively elevated edges forming mountain ridges. The mountain ridges may be due to uplift, or to the sinking of the lower land adjacent to them, or to both. Such mountains are called faulted or block mountains. Block mountains in various stages of dissection occur in Oregon, Nevada, and elsewhere. (2) Mountains consisting of a series of folds formed by com- pression from the sides are a common type. In some cases the folds are open and regular (Fig. 209) ; in others they are closed, irregular, and overturned. In some cases the strata of the folds are faulted Fig. 208. Diagram of block moun- tains. (Modified after Davis.) 304 LEADING TYPES OF MOUNTAINS 3o5 (Fig. 210), and some of the faults record a vertical displacement of thousands of feet. The present topography of most folded moun- tains — for example, of the Appalachians and Juras — is controlled not Fig. 209. Open, symmetrical folds in the Appalachian Mountains. North- eastern West Virginia. Length of section, about i2>£ miles. The formation shown in solid black contains coal. (After U. S. Geol. Surv.) so much by the original folding and faulting as by later erosion and warping. (3) Many of the higher isolated mountains are volcanic cones (p. 193; Fig. 99). Many mountains have been formed also by great Fig. 210. Folded and faulted strata in the Appalachian Mountains near Bristol, Virginia. (After U. S. Geol. Surv.) intrusions of lava which have domed or lifted the overlying beds high above the level of the surrounding country (Fig. 105). In many such cases the rocks which covered the lava have been partly removed by erosion, exposing the core of intruded rocks (Fig. 211). Among the mountains produced chiefly by vulcanism and later erosion are the Henry Mountains of Utah, and the Park and Elk ranges (Fig. 212) of Colo- rado. (4) Many mountains owe their existence simply to the resistance of their rocks, which have been left standing in bold relief by the removal of the sur- rounding weaker rocks. Many mountain peaks, aside from vol- canic peaks, are of this origin. Fig 2I2 Cross-section of Elk Moun- Pike s Peak, Colorado, is a tains, Colorado. Fig. 211. An eroded laccolith. Cross- section of Mount Hillers, Utah, with ideal representation of the underground struc- ture. Compare with Fig. 105. (After Gilbert, U. S. Geol. Surv.) 3 o6 MOUNTAINS, PLATEAUS, AND LIFE well-known example. The Catskill Mountains of southeastern New York are due to unequal erosion, where the resistance of the rock is not very unequal. They are really a dissected plateau. Various other maturely dissected plateaus of considerable relief are called mountains. (5) Folding and faulting, vulcanism and unequal erosion all may be involved in the formation of lofty mountains. Many moun- tains, furthermore, have had several periods of growth, between which the upraised beds suffered great erosion (Fig. 213). The formation of mountains is a very slow process, probably occupying, for the greater ranges, hundreds of thousands or even Fig. 213. Diagram showing structure of the beds in the region of the Santa Lucia Range, California. Length of section, about 11 miles. (After U. S. Geol. Surv.) millions of years. Many mountains appear to be growing now — for example, the St. Elias Range of Alaska. Destruction of mountains. All mountains are destroyed in time by erosion, unless renewed by vulcanism or uplift. Furthermore, the erosion of mountains commences as soon as they begin to rise, and continues throughout the long period of their growth, as well as after- wards. As a result, no mountain due to vulcanism or diastrophism (crustal movements) ever had the full height which those processes would have given it, if there had been no erosion. As already pointed out, many mountains have been nearly or wholly removed by erosion, and revived again by uplift, and some of them have passed through this history several times. The length of the life of a mountain which has ceased to grow is determined largely by its height, by the resistance of its rocks, and by the character of the climate. The gentle slopes of the later life of a mountain are worn less rapidly than the steeper slopes of its earlier career, so that its old age may be longer than its youth and maturity combined. All lofty mountains are rather young, geologically speaking; old mountains have been worn low. While very old mountains are low, obviously not all low mountains are old. MOUNTAINS AS BARRIERS 307 Mountains as barriers. Mountains are barriers to the move- ment of animals and men, and to the spread of plants (Fig. 214). The effectiveness of a mountain barrier depends largely on its height, length, and width; on the number, height, and distribution of the Fig. 214. Toltec Gorge, in the mountains of Colorado. Travel even along the valley is difficult. (Denver and Rio Grande Railroad Company.) passes; and on the number of ridges, and the steepness and character of their slopes. The high, massive ranges of the Pyrenees, Caucasus, and Andes mountains form very effective barriers. The Pyrenees make the best natural inland boundary in Europe, shutting off Spain so completely from the rest of the continent that it has been said: "Africa begins at the Pyrenees." Although high, the Alps Moun- 3 o8 MOUNTAINS, PLATEAUS, AND LIFE tains have several good passes, well distributed; accordingly, they form a less serious barrier. The effect of many mountain barriers has been lessened by the building of wagon roads and railroads, the cutting of tunnels, etc. In other cases, mountains are crossed only by a few difficult trails, along which wares are taken on pack animals or by human carriers. For a long time, northern and central Europe was excluded by mountains from the culture of the leading Mediterranean countries. China is largely shut off from the rest of Asia by mountains, a fact of much importance in connection with the isolated development and backward state of that country. The Appa- lachian barrier helped to confine the English colonies to the Atlantic seaboard for a century and a half. This favored the development of compact settlements, and permitted much more rapid progress along many lines than would have been Fig. 215. Map showing course of Cumberland National Road. possible had the colonists spread themselves thinly over a vast area, after the manner of the French, who controlled the St. Lawrence gateway into the Interior. For years after the Revolutionary War, the Appalachian Mountains made commu- nication difficult between the settlements of the Interior and the seaboard. The first great step in their conquest as barriers to trade and travel was taken when the Cumberland National Road was completed from Cumberland, Maryland, to the Ohio River at Wheeling, in 181 7 (Fig. 215); the second when the Erie Canal was opened (1825). Though this canal did not cross the Appalachians, it afforded an easy route to the Interior. The third and greatest step in the conquest of the mountains was taken when four railroads were finished across them in the 1850's. These first trans-Appalachian railroads crossed the barrier at the north, where it is narrowest, lowest, and has most good passes. Until the completion of the first transcontinental railroad (1869), travel across the western mountains and plateaus was so difficult that many people going to California chose the 13,000-mile voyage around Cape Horn, or the route by way of Panama. The difficulty of crossing high, rugged mountains gives great importance to notches or passes in their ridges. Many mountain passes are water-gaps or wind-gaps; their formation has been ex- plained, and their relation to human affairs illustrated (pp. 232, 234). IMPORTANCE OF MOUNTAIN PASSES 309 Trails, wagon roads, and railroads all seek the lowest and most acces- sible passes (Fig. 216). They commonly enter the mountains along main valleys, and, where necessary, zigzag up the steeper slopes to the passes which serve as gateways through the central ridges (Fig. 217). In some cases, railroad companies have avoided the last part of the ascent by tunneling the mountain below the pass. South Pass, in central Wyoming, is the most im- portant pass, historically, in the Rocky Mountains. Through it ran the famous Oregon Trail, along which many thousands journeyed to the grain lands of Oregon and the gold fields of Cali- fornia. Truckee Pass af- fords a relatively easy route across the central part of the Sierra Nevada Moun- tains. It was used first by the California Trail, and is used now by the Southern Pacific Railroad. The Pass of Belfort, between the Vosges and Jura mountains, connects the Rhone and Rhine valleys, and with them has constituted since ancient times one of the most important routes of travel between the Mediterranean and North seas. The passes in the mountains of northwestern India have served repeatedly as gateways through which tribes and armies from central Asia have descended to plunder and conquer the people of the plains. The difficulties of travel and communication in rugged moun- tains shut their inhabitants away from the outer world, helping to retard progress. Old customs, fashions, and manners of speech are likely to be preserved by mountaineers long after they have been abandoned elsewhere. Education is backward; much of the simple clothing, furniture, etc., is home-made; trade in many cases is limited to barter, involving only the absolute essentials of life; and social intercourse is restricted seriously, favoring the close intermar- Fig. 216. Sketch-map of region about Holli- daysburg, Pennsylvania, showing the influence of mountain passes upon the course of wagon roads and railroads. (From Hollidaysburg. Sheet, U. S. Geol. Surv.) 3io MOUNTAINS, PLATEAUS, AND LIFE riage of families and the development of " clans." These conditions are illustrated among the mountaineers of the southern Appalachians Fig. 217. Road zigzagging up mountain slope in Switzerland. Rhone Glacier in middle background. (Fig. 218). They do not exist, of course, in new mountain commu- nities established by progressive people from outside, and they have Fig. 218. Homes of mountaineers in the southern Appalachians. been changed greatly in some long-settled mountains (e. g., in the Alps) by the coming of summer visitors (p. 317), and in other ways. THE SETTLEMENT OF MOUNTAINS 311 Many mountains are important climatic barriers (p. 77), and the conditions of life on their opposite sides may be very different. The western slopes of the Sierra Nevada Mountains receive much rain; to the eastward stretch broad deserts. Because most of its early mines proved disappointing, and lack of rain prevented ordinary farming in most places, the population of Nevada was always small (only 42,000 in 1900). This was the penalty of its position to the leeward of high, rain-catching mountains. Recently the population of Nevada has increased (p. 330) because of irrigation and the dis- covery of new mineral wealth. The contrast is even greater between the two sides of the Himalaya Mountains; to the south are the crowded millions of India, to the north the scattered, nomadic tribes of Tibet. The difference here is not due wholly to the mountains, but largely to the great altitude of the plateau on the northern side. The settlement of mountains. In general, the settlement of rugged mountains begins only after the more inviting neighboring lowlands have been occupied, and their populations are always rela- tively sparse. The areas of the Adirondack, Catskill, Alleghany, and other mountains in eastern United States were blank spaces on the earlier census maps (Figs. 276 and 278), and their populations are in most sections sparse even now (Fig. 281). A similar situation exists in the western mountains. Mountain areas are settled first and most thickly in their larger valleys. Here the flatter land favors tillage, soils are thicker and in most cases more fertile (Why?), the climate is milder, and the trails of the upland are replaced by roads. The inhabitants of many mountain valleys in Europe and Asia are descendants of people who sought refuge there from their enemies. The Basques, who dwell in the western valleys of the Pyrenees, are an example. In other cases, the occupa- tion of mountain strongholds has permitted people to dominate the adjoining lowlands, and levy tribute on their inhabitants. At the beginning of the Revolu- tionary War. four-fifths of the Cherokee Indians dwelt within the southern Appa- lachians, and from their mountain villages they repeatedly made sudden attacks on the frontier outposts of the whites. Agriculture in mountains. Outside the valley bottoms, con- ditions are unfavorable to agriculture in high mountains, and in many places prevent it. Many slopes are too steep to be tilled, consisting either of bare rock or having here and there a thin covering of soil which washes easily when cultivated; and with increasing height, the climate prevents the raising of crops and even the growth of trees and grasses. Switzerland is largely mountainous, and only 312 MOUNTAINS, PLATEAUS, AND LIFE about V& of its area is arable land. Only V7 of the three Alpine prov- inces of Austria is tillable. Less than l /6 of Japan can be cultivated readily. Such conditions mean a scanty food supply and a constant tendency toward over-population. They mean also that in many long-settled mountain regions the cultivable land is farmed intensively Fig. Islands. 219. Terraces made, by Ifugao Igorots, island of Luzon, Philippine in small holdings. Every effort is made to maintain the fertility of the soil, so that it may grow good crops continuously. In many mountain regions, where all the level land has long been used, the slopes, too steep for agriculture by ordinary methods, have been utilized by making terraces (Fig. 219). Low walls are built one above another on the slopes, and the spaces behind filled in and cov- ered with soil. In this way, successive tiers of nearly level benches of land (terraces) are made. Terrace agriculture is practiced in parts of India, China, Italy, Germany, France, Switzerland, and other coun- tries. In Europe, much terraced land is used for vineyards. Choice FARMING IN MOUNTAINS 313 fields with bearing vines equal in price the best irrigated fruit lands of western United States (p. 175). The crops which may be grown in mountains vary with the expo- sure, the altitude, the rainfall, the character of the soil, etc. In general, the slopes of a lofty mountain present successive climatic zones to which plant life, and animal and human life as well, are adjusted. If such a mountain is in low latitudes, its slopes may afford Fig. 220. Sheep grazing on a mountain side in Holy Cross National Forest, Colorado. (U. S. Forest Service.) conditions ranging from those of the tropics to those of the polar zones (p. 22). In the Alps, the following changes may be noted: (1) In suitable places on the sides of the lower valleys there are vineyards, olive orchards, and mulberry groves worked intensively by a relative- ly dense population. (2) Higher up, these are replaced by grain fields and pasture lands, among which there are forests of deciduous trees. This zone is less productive and settled less thickly than the first. (3) Still higher, hardy evergreen trees prevail, the proportion of useless land increases, only the hardiest grains are grown (up to about 5,300 feet) in small fields by the sparse population, and most of the land with soil is devoted to pasturage and to the growing of hay for the winter feeding of the stock. (4) Above the "tree-line" (the upper limit of tree growth is about 7,600 feet) is a belt in which some of the slopes bear grass, where cows, sheep, and goats are pastured for a 3H MOUNTAINS, PLATEAUS, AND LIFE short time in summer. (5) Finally, there is a waste of bare, rocky slopes and snow-fields, unoccupied by life which is useful to man. Stock-raising in mountains. Stock-raising is an important industry in many mountains, for slopes too steep or too rocky to be tilled, or too high for cultivated crops to ripen, may afford pasturage (Fig. 220). As suggested above, pasturing stock and growing feed for its use in winter constitute a leading industry in the higher Alps. More than half the productive area of Switzerland consists of pasture Fig. 221. Summer grazing in the High Alps. land and hay land. In spring, herdsmen take their cattle, goats, and sheep from the villages in the valleys up to the high pastures, advanc- ing, as the growth of the grass permits, close to the snow-line (Fig. 221), where the grazing season may last only six or seven weeks. In autumn, the flocks and herds are driven back by stages to the lower valleys, where they are fed in stables during the long winter. Rais- ing enough hay and other fodder for the winter feeding is perhaps the most difficult part of the industry, and this requires hard labor during the summer. Stock-raising of one kind or another is a leading occupation in the mountains of Norway, Germany, central Asia, western South America, western United States, and elsewhere. In western United States great numbers of cattle and sheep feed on the grass of the public domain (land owned by the government). The use of much of the public domain is free and unrestricted. While this has had its advantages, it MINING IN MOUNTAINS 3i5 has resulted, at many times and places, in the overstocking of the range (pasture land), and a decrease in its capacity. Some system of regulation is likely to be adopted soon. Grazing in the National Forests is regulated now. Mining in mountains. Many mountains contain valuable ore deposits, and mining is one of the most distinctive of mountain indus- tries. The original source of most of the valuable metals appears to have been the igneous rocks (hardened lavas), and great intrusions of the latter form the central cores of many mountains. The metals probably were scattered widely through the igneous rocks to begin with, and were slowly concentrated into ores in veins, largely by Fig. 222. Bisbee, Arizona, a city which grew up about copper mines. ground- waters (p. 212). These veins are, for the most part, in or near the igneous rocks. Many of them have been exposed, and so made available to man, by erosion. The iron and copper of the Lake Supe- rior region occur in the rocks of old, worn-down mountains. Much of the gold mined in the West has come from igneous rock, and from the immediate surroundings of great intrusions of lava. In north- eastern Pennsylvania the folding of beds of rock containing layers of coal helped to change the latter into "hard coal" or anthracite. Much of the coal of this region was carried away later by erosion, but much was preserved in the down-folds of the mountains (Fig. 209). More than 80,000,000 tons of this coal are mined yearly (90,000,000 in 191 1), and much of it is sent throughout eastern and central United States. Cities have grown quickly from rude mining camps following the discovery of rich mineral deposits (Fig. 222). Thus in the late 1870 's Leadville, Colorado, became a city of 15,000 people in a 316 MOUNTAINS, PLATEAUS, AND LIFE few months, though in a sage-brush valley then difficult to reach, and at an elevation of 10,000 feet. Again, important mineral de- posits may help to gather a dense urban and industrial population about the borders of the mountains in which they occur, as in the case of the Pennine Mountains of north-central England, and the Erz (meaning ore) and Riesen ranges of Germany, where mining has been carried on for many years. Mountains as forest reserves. The slopes of many moun- tains have been left largely in timber because unsuited to agricul- ture, and various mountain ranges now support important lumber Fig. 223. Modern lumber mill in the Sierra Nevada Mountains, California. (U. S. Forest Service.) industries (Fig. 223). The relation of mountain forests to the flow of streams rising in them, and to the problems of navigation, water power, irrigation, and soil erosion has been noted (pp. 169, 290, 298). These problems, together with the need of insuring a permanent lumber sup- ply, have led various countries to regulate the use and cutting of moun- tain forests, and to provide that certain areas remain forest-covered. Japan has many steep volcanic mountains, whose slopes, if uncovered, would be eroded rapidly by the heavy rains; this helps to explain the fact that nearly 3/5 of the country has been left in forest reserves, although the nation is in great need of more farm land. Among European countries, Germany, Switzerland, and IMPORTANCE OF MOUNTAIN FORESTS 317 France have skillfully managed forest reserves on mountain slopes. Some of the Mediterranean countries show the evils which may follow the cutting away of mountain forests. In Dalmatia, for example, mountain slopes once forested consist now of bare rock, and are of little use to man. In parts of eastern and northeastern China the forests are gone, and one may travel hundreds of miles without seeing a single grove on the hill sides. Even the undergrowth has been destroyed, and in places all grass and other vegetation suited to the purpose are gathered for the cattle, or eaten by goats and sheep. Serious results have followed: (1) Heavy rains cause violent floods. Valleys usually without streams may be occupied suddenly by torrents which destroy bridges and buildings, ruin fields, and then disappear within a few hours. (2) In many places not enough water enters the ground to keep the water table sufficiently near the surface for the good of plants. (3) Erosion has been increased enormously (Fig. 80). Large lowland areas are covered with coarse waste, and much fine material is swept into the sea. (4) Timber is at a premium. In the western mountains forest destruction is less advanced, and travelers report meeting long lines of coolies carrying boards down to the plains, where they are worth the equivalent of $2 to $3 each, a value which restricts their use to special purposes, such as making coffins. Most of the National Forests of the United States (p. 298) are in the moun- tainous districts of the West (Fig. 207), where the greater part of the timber is found on the mountain slopes because the latter receive more rain than the sur- rounding plateaus and plains. Congress provided in 191 1 for a National Forest in the southern Appalachians, where the maintenance of a forest cover on many of the slopes is of great importance (pp. 173, 221). Mountains as pleasure resorts. The cool, invigorating sum- mer climate and beautiful scenery of many mountains lead thousands of lowland dwellers to visit them yearly. The mountains of New England, the Adirondacks, Catskills, and parts of the Alleghanies, contain many popular resorts. With the growth of population in western United States, the mountains of that section probably will be visited more and more. Most of the National Parks (Fig. 224) and National Monuments are in the West, and a number of them contain mountains or portions of mountains of unusual beauty and interest. The National Parks, of which there are 13 in continental United States, were created by Congress, and serve various purposes; they are intended especially to be " play-grounds for the American people." In 1905 the President was given power to set aside from the public domain as National Monu- ments any "historic landmarks, historic or prehistoric structures, or other objects of historic or scientific interest." There are now twenty-eight National Monu- ments, of which the Mount Olympus, Washington, and Grand Canyon, Arizona, monuments are largest. The Alps, situated in the midst of densely settled countries, are the most beautiful mountains in Europe, and have come to be perhaps the greatest summer resort in the world. Hundreds 3i8 MOUNTAINS, PLATEAUS, AND LIFE of hotels (Fig. 225) depend upon the tourist trade, and the enter- tainment of visitors has become almost a national industry. Other mountain resources and industries. Fur-bearing animals constitute an important resource of some mountain regions. They were once a resource in many others where few are left. From about 1807 to the middle of the century, the fur trade in the Rocky- Mountains of the United States was of great value. Trading posts were estab- lished in the mountains and along the larger rivers flowing eastward from them, Fig. 224. Map showing distribution of National Parks. at which a driving business was done. St. Louis was the great depot and outfitting point of the trade. The trappers and traders were the pathfinders of the West. The fur trade is still of some importance in the mountains of western Canada. We have seen that many mountain people are forced to make most of their own clothing, implements, utensils, etc. (p. 309). In addition, many of them make special articles of superior quality for sale. In this way they eke out a living, and find work during the winter months when little can be done out of doors. From wood, metals, wool, or other raw material at hand, they make artistic wares which are suited to mountain transportation, and command ready sale. Such are the carved wooden wares of the Swiss, and the lace made by some of the Italian mountaineers. ORIGIN AND EROSION OF PLATEAUS 319 Many mountain streams afford much water power (pp. 248, 256, 290) which will be used increasingly in the future. In most cases, however, much of the energy will be carried outside the mountains in the form of electricity, to be used in the lowlands. Plateaus Distribution. As stated elsewhere (p. 21), large plateaus occur for the most part in three classes of situations. (1) Some of them are between a lower plain on one side and higher mountains on the other, Fig. 225. A summer hotel in the High Alps. (2) some are between mountain ranges, and (3) some rise abruptly from the sea, or from narrow coastal plains. Origin. Plateaus are formed in various ways. (1) Some have been built by many lava flows, like the Columbian Plateau of the Northwest (Fig. 104) and the Deccan Plateau of India. (2) Adjacent land may have been worn low or warped down, leaving a plateau. (3) The plateau may have been warped or faulted above its surroundings. The erosion of plateaus. Like mountains, all plateaus will be worn down to lowlands, if not made high again. Mature plateaus are table-lands well dissected by streams; the surface is carved into hills (or mountains) and valleys (or canyons), and slope and relief are at a maximum. Some dissected plateaus are called mountains (e. g. the Catskills, p. 306). In one sense there are no old plateaus, for, when worn low, they are plains. 320 MOUNTAINS, PLATEAUS, AND LIFE Conditions of life on plateaus. The conditions of life on high, dissected plateaus are much like those in mountains situated similar- ly (pp. 309-318), while the conditions on many low plateaus resemble closely those on neighboring plains (Chapter XVIII) . Large plateaus in continental interiors surrounded by mountains are, in general, deserts, and subject to great ranges in temperature. Accordingly, they are settled sparsely. Farming is confined for the most part to the slopes of waste at the bases of rain-catching mountains, where water may be led from the withering streams for use in irrigation. The greater part of such plateaus is uninhabited, save by bands of wandering nomads, as in central Asia, or by occasional ranchmen whose cattle and sheep graze on the thin and scattered growth of grass, as in parts of western United States. The habitability of a high plateau is influenced greatly by its latitude; while such a plateau is cold and uninviting in the temperate zone, it has a temperate climate in the tropics, where, if other conditions are favorable, it may have a population much denser than that of the neighboring lowlands. Nearly three-fourths of the people of Bolivia live at altitudes of 6,000 to 14,000 feet, and of the nine most thickly settled provinces, five are at elevations greater than 1 1 ,000 feet. Three-fourths of the population of Ecuador are found in the plateau basins of the Andean highlands, at an average elevation of 8,000 feet. There is a striking contrast also between parts of the cool plateau and the hot lowlands of Mexico. The former have relatively dense and progressive popula- tions, while the latter are settled sparsely by backward Indians. In higher lati- tudes, plateaus for various reasons are in general settled much less densely than the neighboring plains, as already indicated. The Great Basin and Columbian Plateau of western United States each contained, in 1900, only 0.5 per cent of the population of the country. In these regions the population num- bered only 1.6 and 3.2 persons, respec- tively, per square mile. The sparsest population of Great Britain is found in the Highlands of Scotland. Questions 1. (1) In what stage of erosion are the mountains shown in Fig. 226? (2) How will the slopes of these mountains be changed in the future? 2. (1) What is the age, in terms of erosion, of the mountains shown in Fig. 208? (2) What was the topographic age of the surface from which the mountains were formed? The evidence? Fig. 226. Sketch of mountainous region. QUESTIONS 321 3. (1) Compare and contrast the climate of the mountains and plain shown in Fig. 227. Why the differences? (2) What work are the streams doing in the mountains? On the plain? Reasons in each case? (3) What kinds of soil would you expect to find on the plain just west of the mountains? Why? (4) What Fig. 227. Portion of Paradise, Nevada, topographic sheet. Scale 4 miles per inch. (U. S. Geol. Surv.) does the map suggest concerning the chances for successful agriculture in the different parts of the area? 4. Compare and contrast the relations of mountains to the life of (1) primitive and (2) advanced peoples. 5. Account for the fact that houses in arid plateaus often are built with flat roofs and thick walls. CHAPTER XVIII PLAINS AND THEIR RELATIONS TO LIFE Origin and classes of plains. Various types of plains have been discussed in previous pages, and some of their relations to human affairs noted. Rivers make flood-plains (p. 236), delta plains (p. 241), and peneplains (p. 227). The ancient ice-sheets formed vast drift plains or glacial plains (p. 260). The floors of extinct lakes form many nearly flat lake plains, especially in glaciated regions (p. 262). Most lake plains are small. Extensive plains, like the Atlantic and Gulf coastal plains of the United States and the vast interior plain which stretches from the Appalachians to the Rockies, cannot in most cases be put in any of the above classes. They commonly contain many smaller plains of several or all of the types mentioned. In general, large coastal plains were once marginal sea-bottoms, and were made into land by being raised or by the sinking of the sea. Coastal plains may also be peneplains, or they may be land made by the filling of a shallow sea border by sediment washed from the land. Large interior plains are either areas worn low, or, in more cases, they are former coastal plains now separated from the sea by newer land. The changes made in plains by erosion were discussed in Chapter XV. Distribution of extensive plains. Most of the great plains of the world are in the northern hemisphere. The northern parts of the large plains which border the Arctic Ocean are of little value to man, but there are vast, fertile plains in the north temperate zone which are of great importance in the life of the world. The southern conti- nents are unfortunate in having their largest lowlands within the tropics, where climatic conditions retard human progress. General advantages of plains. From the standpoint of human occupation, plains which possess a favorable climate have distinct advantages over mountains and plateaus. In general, the slopes of plains are gentler, their soils thicker and more fertile, and they have a much smaller percentage of useless land. Their advantages 322 PLAINS AND HUMAN PROGRESS 323 of climate, soil, and topography make plains the great agricultural regions of the world. In this connection it should be remembered that agriculture is the basis of all lasting advance in civilization. Movement is relatively easy on plains, and difficult in mountains (p. 307). This means that goods and ideas circulate more readily, and that trade and culture develop more rapidly, among lowland people. In mountains, a great variety of conditions may be found within a small area, while on plains, similar conditions may prevail over large areas. It follows that most occupations of plains have a much wider distribution than those of mountains. Because of the advantages of lowlands for agriculture and trade, the great majority of the people of the world live on them. The rela- tively dense populations of the favored lowlands of the United States are shown by Fig. 281. More than °/io of the people of the country live on lands less than 1,500 feet above the sea. While this shows that most of the people live on plains, it will be remembered that there are plateaus and mountains lower than 1,500 feet, while a part of the Great Plains is much higher. Less than 1 per cent of the people live at elevations of more than 6,000 feet. Contrasts among plains. Apart from their mode of origin, plains differ in many ways. They may be large or small, high or low, rough or smooth, forested or treeless, fertile or infertile, wet or dry, and they may be in hot, temperate, or cold regions. Furthermore, there are all gradations between these extremes. These differences affect human interests in important ways, many of which have been noted. Relatively small plains protected by natural barriers, rather than large, open ones, favor early progress in civilization. A small area hastens advance to the agricultural stage (Why?), and as the population increases, laws and customs are made in the attempt to overcome the friction which goes with crowding. The isolated and protected plains of Greece possessed many advantages for early progress. On the other hand, all parts of a vast plain not protected by barriers, such as that of Russia, are open to attack. It is easy for the people of a large plain to scatter in search of game and other food, and the natural food supply may be sufficient to postpone indefinitely the development of agriculture. Extensive plains, such as those of central United States, afford excellent conditions for the further progress of a people already advanced in civilization. This is especially true where, as in the case cited, such plains have varied geographic conditions and resources in their different parts. Climate is the most important factor affecting the life of exten- sive plains, and the larger plains of the world are so distributed with reference to climate that the conditions of life in them may 324 LIFE IN PLAINS be discussed briefly under the following headings: (i) Life in well- watered plains of middle latitudes. (2) Life in semi-arid plains. (3) Life in desert plains. (4) Life in Arctic plains. (5) Life in humid plains of low latitudes. The more important direct effects of various types of climate on life were discussed in Chapters IX, X, and XL Life in Well- Watered Plains of Middle Latitudes Plains in middle latitudes having plenty of rain are the seats of advanced civilizations, and some of them support dense populations. The soil is the most important resource of these plains, and agricul- ture the most wide-spread occupation. On the whole, they have less in the way of forests, minerals, and water power, than many high- lands have, but plains are by no means without these resources. Lum- bering and mining are carried on at many points, and commerce and manufacturing are developed highly in the thickly settled sections. In the complex life of these regions, the influence of geographic con- ditions is less apparent and less direct, but not less important, than in the simpler life of the grasslands and deserts. Differences in soil, in the form of the land, in drainage, etc., have their effect on the distribution and occupations of the people. The influence of variations in soil is especially great, and may be seen in many places. In the glaciated plains of northern United States, various kinds of soil may occur within the limits of a good-sized farm. Here the intelligent farmer is likely to devote each type of soil to the particular use or uses to which it is adapted. In other places, the character of the drift over several or many square miles is determined by the nature of the underlying rock, so that, for example, an area of sandy drift, over sandstone, may lie beside an area of limey-clay drift, over limestone. In a certain region in south central Wisconsin, the condition of the people in two such areas is very different. The area of fertile, limey-clay soil is said to have been settled by people of greater means, while the sandy area was occupied by poorer people not in a position to choose. The original difference appears to have increased. In the one case, there are attractive homes with modern conveniences, large barns, many windmills, improved roads, and many well-equipped schools; in the other, many of the build- ings are old and unpainted, few farms have windmills, roads are poor, and some of the schools are in an unsatisfactory condition. The influence of soil on the distribution and activities of people may be seen on a larger scale in various parts of the Atlantic and Gulf coastal plains. In Alabama, the northern part of the state is underlain by old rocks (Fig. 228). This part was land when the area of the coastal plain was under water. Sediment washed from the old land helped to make the strata of the coastal plain. East and west across the middle of the state there is a low, nearly level belt of rich soil, weathered from the limestone beneath. This is the inner part of the coastal plain. HUMAN RESPONSES TO SOIL CONDITIONS 325 From its southern edge the ground rises rather abruptly some 200 feet, because of the outcrop of more resistant beds, and then slopes gently southward to the coast. The soils of this outer belt are much poorer than those of the inner lowland, except along the bottoms of the larger valleys, where there are deep, fertile loams. The history and present life of the state cannot be understood apart from these soil belts. The first American settlers, typical log-cabin pioneers, settled for the most Fig. 228. Fig. 229. Fig. 228. Map showing principal physiographic provinces of Alabama. Fig. 229. Map showing distribution of slaves by counties in Alabama (i860). Figures in legend indicate percentages of the total population. part in the rich inner lowland and along the fertile valley bottoms. Later, this was seen to be the section best suited to the growth of cotton, and many of the earlier settlers were pushed by the slave-owning planters north into the foothills of the mountains, or south into the sandy areas of the outer coastal plain. The inner lowland contained the largest number of slaves at the time of the Civil War (Fig. 229), and more than 3/^ of its present population are negroes. The outer zone of the coastal plain always has had a relatively sparse population, except along the larger valleys. There are still extensive pine forests where lumbering, the making of turpentine, and grazing are leading industries. Mobile is the only important city in this part of the state. It has a harbor at the drowned mouths of the leading rivers of the region, and is the natural gateway into the state from the south. 326 LIFE IN PLAINS Life in Semi-Arid Plains Large semi-arid plains occur in the belt of the trade-winds, where some of them merge into deserts, as in northern Africa and Australia. Others lie in the interiors of continents, where the prevailing winds which reach them have been robbed of most of their moisture in pass- ing over mountains. The steppes of western Asia and the Great Plains of the United States are examples. The scanty rainfall of such plains or its unfavorable distribution prevents the growth of most Fig. 230. Home of native nomad of Argentine Patagonia. (Harriet Chalmers Adams.) trees except along the streams, and restricts useful vegetation to quick- growing grasses and a few other hardy types of plants. Hunting tribes and pastoral nomads. Under primitive con- ditions, the inhabitants of semi-arid plains get their support from flocks and herds, or depend on the chase, like the buffalo-hunting tribes of earlier years on the Great Plains (p. 328). Both the pursuit of game, and the frequent need for fresh pastures with new supplies of water, cause the people to lead a nomadic life. The dwellings must be such that they can be moved easily (Fig. 230); in many cases they are tents of skins, or of felt made from wool. Personal effects and household utensils are few and light; and the most desirable form of wealth is flocks or herds, which transport themselves. LIFE IN SEMI-ARID UNITED STATES 327 The movements of many pastoral tribes are regulated by the seasons. In some cases, their flocks and herds are driven in summer into the highlands, thus escaping from the hotter plains and using more of the pasturage. The Kirghiz of Russian Turkestan regularly take their flocks in summer up into the Altai Mountains, and bring them back to the lower lands in winter. Again, the more abundant grass and water of the rainy season may permit the people to gather in considerable groups in desirable localities, while in the dry season they are forced to scatter widely, to secure food for their animals. The pastoral nomads of semi-arid plains always have been maraud- ers and conquerors, though less so than the men of the desert (p. 333). Under favorable conditions, their growing herds and flocks require more and more pasture, and from time to time compel them to move beyond the boundaries within which they formerly had roamed. On the other hand a long and severe drought, resulting in less pasturage and a failing water supply, or disease among their animals, may bring them to the verge of famine, and drive them to pillage and conquest. Mounted on horses or camels, the nomads are able to make swift attacks on the people of neighboring lands, and to retreat quickly with their booty. For centuries, portions of agricultural Russia were pillaged repeatedly by hordes of horsemen from the southeastern steppes, and the Great Wall of China was built as a pro- tection against pastoral nomads. In general, it may be said that the conditions of life in semi- arid, grassy plains rarely, if ever, permit their native tribes to develop more than a low form of civilization. Use of semi-arid plains by civilized people. Even where civilization is advanced, plains that are too dry for agriculture by ordinary methods are devoted largely to the grazing industry. Vast semi-arid areas are used in this way in the United States, Argen- tina, Australia, and Russia. By means of irrigation and special methods of cultivation, agriculture doubtless will be extended great- ly in semi-arid regions in years to come. The Great Plains. The history of the western portion of the Great Plains illustrates many of the conditions of life in semi-arid regions. Until after the Civil War, these plains were occupied by Indians dependent for a living on the great herds of buffaloes. The killing of the buffalo and the confining of the Indians to certain areas (reservations) opened the plains to the cattle industry. In the drier parts most attempts to farm by ordinary methods have been un- 328 LIFE IN PLAINS successful, though here and there streams and wells furnish water for irrigation (p. 329). Within the last few years, "dry farming" (p. 329) has replaced the grazing industry in some places. As already indicated, the buffalo was the most important factor in the lives of many Indians of the Great Plains. The chase required many quick moves, and this helped to keep families rather small, the houses light and portable, and personal property small in amount. Individual ownership of land was unknown among some of the tribes. The mythology of the Indians was tinged by their hunting and military habits. The chiefs attained their positions because of their skill as hunters or warriors. With the disappearance of the buffaloes, the hunting tribes lost their chief support, and became dependent on the white man. Great numbers of buffaloes were killed as food for the construction gangs of western railroads, and for their hides, which were in great demand in the East for robes, belting for machinery, and other purposes. They practically disappeared from the southern plains in the middle seventies, and from the northern plains a few years later. The stock-raising industry of the Great Plains began in Texas and spread north- ward. Cattle were introduced into Mexico by the Spaniards about 1525, and before the Revolutionary War there were large cattle ranches north of the Rio Grande. In the middle 1850's, most of Texas was "a vast, unfenced feeding ground for cattle, horses, and sheep." At the close of the Civil War, cattle were very cheap in Texas, but brought high prices and were in great demand in the northern cities. As a result, the practice was developed of driving cattle northward in great herds to shipping points on the railroads that were then building across the Great Plains in Kansas and Nebraska. The "cow towns," as the shipping points were called, were established beyond the farming frontier, preferably where there was a good supply of water and grass. The business shifted west and south with the advancing railroads, keeping in front of the farming zone. The banner year of the Texas cattle drive was 1884, when 1,000,000 cattle were driven out of the state. Soon after, the drives were rendered unnecessary by the extension of railroads, which took the stock to market in much less time and usually in better condition. The stocking of the northern lands occurred, for the most part, after 1870, and before the close of another decade the business had spread to the Canadian boundary. For a time, large returns were realized from feeding cattle on the public grass. Many people accordingly went into the business, and in numerous places the range (unfenced pasture land) was overstocked and the pasturage injured. One result of this in many places was the introduction of sheep, which can live on pasturage that will not support cattle. The conflicting interests of cattlemen and sheepmen have caused much trouble in some of the grazing states. The development of the grazing industry on the Great Plains had an important influence upon the growth of the slaughtering and meat-packing industry in Kansas City, Omaha, St. Louis, Chicago, and (later) South Omaha, from which meat products were sent to the urban and industrial centers of the northeastern states and Europe. In 1880, the Great Plains west of the 98th or 99th meridian were occupied only by stockmen, except along some of the larger valleys (Fig. 231). A few years later thousands of farmers moved there and began to grow wheat, using the seed and methods which they had employed farther east, where the rainfall is greater. The population of Kansas increased 250,000 between 1885 and 1888, largely in the FUTURE USE OF SEMI-ARID LANDS 3 2 9 IZDUnder2persq.Tni\ EH 2 to 6 » 6 tola " 18 and over western portion (Fig. 232). The agricultural invasion began because of heavy rains in the middle eighties, and was kept up for a few years by the advertising of railroads and the activity of town-builders and land-dealers. Then came several very dry years, and thousands were starved out of the region. Kansas lost some 200,000 people, and the western parts of Nebraska, the Da- kotas, and the eastern part of Colorado were affected similarly (Fig. 233). Mil- lions of acres returned slowly to grass, and within a few years hundreds of "cities" were abandoned by their founders. Within the last few years, another agricultural invasion of the High Plains has been in progress. A series of wet seasons, the activity of land companies, and the intro- duction of agricultural me- thods adapted to semi-arid conditions have been the le*ading causes. The out- come is still uncertain, but is not likely to be so disas- trous as the first settlement, because men know better now how to make use of dry lands. The chief uses to which the semi-arid parts of the Great Plains will probably be put in the future may be suggested briefly. (1) Farming by irrigation will be extended somewhat, but the amount of water avail- able from all sources is but a small fraction of what would be needed to irrigate all the land. (2) Dry-farming, especially with hardy, drought-resisting plants (p. 173), promises much more than irrigation for the region as a whole. Dry-farming scarcely can be said to have passed the experimental stage, and how large an area can be dry-farmed success- fully is quite uncertain. As already pointed out (p. 65), dry-farming seeks (a) to get the largest possible amount of the rainfall to enter the ground, and (b) to reduce to a minimum the loss of water by evaporation from the soil. (3) Stock-rais- ing, and stock-raising with subordinate farming, apparently must remain the leading industries over large areas. Fig. 231. Fig. 232. Fig. 233. Figs. 231, 232, 233. Maps showing distribution of population on the western Great Plains in 1880, 1890, and 1900. 33 o LIFE IN PLAINS Life in Arid Plains About Vs of the land is desert for lack of rain. By no means all dry deserts are plains; some are plateaus, and within desert plains and desert plateaus there may be ranges of high hills and mountains (p. 334), though these, in most cases, receive more rain than their sur- roundings. Many of the conditions of life are similar in arid plains and plateaus, and they are considered together. Life in cold deserts, such as parts of the Arctic plains (p. 336), differs greatly from that in dry deserts. Only the latter are considered here. The great deserts of the world are in the zones of the trade-winds, or to leeward of high mountains. Their wide distribution and vast extent, the location of some of them near well-watered and thickly- settled regions, and the relations of their people to their neighbors, always have given deserts great importance in the life of the world. Except in the relatively small areas where irrigation is possible, or to which people may be attracted by valuable mineral deposits, deserts are doomed to have scanty populations. The power of mineral deposits to bring people to deserts is illustrated strikingly in Nevada. The deposits of gold and silver first discovered there attracted thou- sands of miners and prospectors, and made Nevada a state in five years. Later, the population of the state declined greatly (p. 311), but in the last decade it has increased again (81.000 in 19 10) due to new discoveries of ore. Butte, Montana, a city of 39,000 inhabitants, is supported largely by deposits of copper that underlie less than two square miles of arid land which, without the mines, could support only a few people. Plant life in deserts. Plants require water for growth, and they lose water chiefly by evaporation from their leaves. It is clear that plants with unusual ability to get and store water, and plants which lose but little water, are best suited to deserts. Most desert plants are provided with many long roots, which enable them to get more moisture from the dry soil than would be possible otherwise, and at the same time help them to stand against the winds, often of great strength. The loss of water from the plant is reduced by such things as thick skins, corky bark, and coats of hair. Some desert plants have no leaves, and some have only a few small, rounded, and fleshy leaves. Thus the loss of water by evaporation is diminished. Many desert plants have thorns, spines, and unpleasant or poisonous juices, which help to protect them against devouring animals. Scat- tered shrubs and coarse grasses are among the leading types of desert THE ANIMALS OF DESERTS 331 vegetation. Fig. 234 shows desert plants of various kinds. The plants of deserts have little economic value at the present time. The vegetation of oases (p. 334) is. quite unlike that of the desert. After rain falls in the desert, many small, quick-growing plants spring up, some of which bear bright flowers; but soon they wither and die for lack of sufficient water. Animal life in deserts. Like certain plants, some animals have developed characteristics which help them to live in the desert. The severity of desert conditions is shown, however, by the smal-1 Fig. 234. View in the desert near Tucson, Arizona. (W. L. Tower.) number and the small variety of animals which can endure them. Like desert plants, desert animals are, as a rule, scattered. Some are very fleet of foot, and thus are able to move between widely separated watering places and to escape from their enemies. Some are slow-moving, but most of these are venomous, and all of them are able to go without water for long periods. A desert is an im- passable barrier to slow-moving animals which need water frequently. On account of the hot days and cool nights, many desert animals are more active during the night than during the day. Many of them are dull of color, and not easily seen against the barren ground. The camel is the most important animal of the arid regions of the Old World, having long been called "the ship of the desert." It is found in northern Africa and in Asia (Fig. 235), from Arabia to China, and northward to northern Mon- golia. A draft camel carries 300 to 600 pounds, according to size, the customary load being about )/$ the weight of the animal. It is said that caravans sometimes travel 20 out of the 24 hours at a steady gait of 2>£ to 3 miles an hour, halting only during the hottest part of the day. 332 LIFE IN PLAINS The camel is well suited to desert conditions. It can travel far with a small supply of food and water; it has small nostrils, which can be closed so as to prevent the entrance of the finest wind-driven sand; eyes protected against sand and sun by long, heavy lashes; and peculiar padded feet, fitted for the hot sands. The parts of the body exposed most to heat and friction are protected by great callosities. When at rest in an oasis, a camel drinks only enough for the time being, but when on the march it makes provision for many hours in advance. During weeks of rest or light work, the hump increases in size; on long journeys, the material of the hump is absorbed into the system, keeping up the strength of the animal. Human responses to desert conditions. Agriculture is impos- sible in deserts, without irrigation, and few places have enough water for that. Furthermore, grazing in many cases is possible only- Fig. 235. Camels in northwestern India. A portion of a caravan which has come through Khyber Pass from Afganistan. along the margins of the desert, or in oases. Since deserts afford little food, they can support few people, scattered widely in small groups. The conditions in deserts permit native tribes to make little progress in civilization. Along the borders of many deserts the conditions of life are a continuation of those in semi-arid grasslands (p. 326). The people wander from place to place with their flocks and herds, the size of the social group being determined by the supply of water and grass. Along the margins of certain deserts, the people sometimes do a little farming when the water supply permits, to add to the often uncertain and always restricted living afforded by their animals. We have seen (p. 331) that deserts may support considerable vegetation for a short time after rain falls. Along the edges of certain deserts, pasturage is available in the wet season, even where the surface is bare in the dry season. This may THE MEN OF THE DESERT 333 control the seasonal migrations of pastoral tribes. In winter, the Arabs find scant pasturage for their goats and sheep on the northern border of the Sahara; in summer, they drive them to the slopes of the Atlas Mountains. In the same way flocks and herds are driven at various points into the southern edge of the Sahara in summer, which is there the rainy season. The arts of desert people are primitive and confined largely to household industries. Making leather and leather utensils from the skins of animals, pottery from clay, and blankets and rugs from wool furnished by the flocks, are typical industries. Among American Indians, the potter's art was developed best in the arid Southwest. Here water was scarce, and durable, water-tight vessels were an absolute necessity. The Navajo Indians of this region possess large flocks of sheep, and sell wool and blankets. The latter are made by the women in many artistic designs, and enjoy a wide reputation. From force of necessity, most wandering desert tribes are rob- bers. They pillage caravans and hold travelers for ransom, or exact heavy tolls in return for safe passage through the desert. They raid adjacent agricultural lands, and in some cases have levied regular tribute upon them, or have conquered and settled in them. The Sudan and Egypt have been invaded repeatedly by tribes from the Sahara. The people of deserts are excluded more or less completely from the culture of the outside world. Hence, as in mountains (p. 309), old manners and customs persist. Customs of the time of Christ still are observed in the desert of Arabia. Scattered widely in small groups, desert people develop many dialects. They are compelled to eat very sparingly of the few things available. Nothing is wasted; the Tibbus of the Sahara eat even the skins and powdered bones of their dead animals. The scanty diet and severe hardships incident to life in the desert help to produce a distinct physical type. The men are commonly thin, but wiry, and capable of great exertion. Desert nomads have great powers of observation and a remarkable sense of locality. Intellectual activity necessarily is restricted in the desert. The dull scenery and the lonely life tend to lead the mind into reverie and contemplation. The majesty of the larger deserts, their vast extent, their great dust and sand storms, and the uncertain position of man, all tend to inspire feelings of awe and reverence. It is sig- nificant that Christianity and Mohammedanism were associated close- ly in their origin and development with the arid and semi-arid regions of the Old World. 334 LIFE IN PLAINS Life in oases. In deserts, permanent settlements based on agriculture are possible only in oases, where there is water supplied by springs, artesian wells, or rivers. The source of the water supply may be outside the desert in well-watered regions, or within the desert where elevations rise high enough to compel the passing winds to give up a part of their moisture. The Nejd Plateau, in the heart of Arabia, rises to an elevation of more than 5,000 feet, and here there are fertile oases, cultivated for centuries, and extensive pastures. Even in the Sahara, there are a few mountains which receive enough rain to support trees. The streams formed on these mountain slopes disappear after descending to the desert. Some of the narrow valleys are farmed, and grazing is possible over larger areas. Some oases serve merely as headquarters for tribes which roam over the surrounding desert in search of pasturage, and of caravans which they may attack. Some support towns, most of which are small. In general, the larger towns are located on the main caravan routes, where there is better opportunity for trade (p. 335). The houses in many cases are built of stone or adobe (sun-dried clay). In many cases, oases are cultivated most carefully in order to secure the largest possible returns from the restricted area which can be watered. Vegetables, cereals, and fruits, especially dates, are grown in the oases of the Sahara and the deserts of southwestern Asia. The date palm has a trunk in some cases fifty to sixty feet high, ending in a great crown of feathery leaves (Fig. 236). Bearing trees average from 100 to 200 pounds of dates a year, though yields of 500 or 600 pounds have been known. A tree may bear fruit for a century. The date palm is adjusted perfectly to conditions in the oases of low-latitude deserts, for it requires a dry, hot climate, and a moist soil. It has been said with truth that the Arabs built their lives on the date palm. In the future, the date palm probably will have commercial value in irrigated lands along the lower Colorado River (p. 242) and about Phoenix, Arizona. Oases in deserts are in striking contrast with the barren land about them, though most of them are not such delightful gardens as they have been described. They are subject to frequent sand-storms, their water supply is small and in many cases impure, and their prod- ucts are restricted in variety and in quantity. Commerce of the desert. Where a desert lies between well- watered and populous regions, important trade may be carried on across it. Some trade is carried on also between agricultural lands and the borders of neighboring deserts, because of their contrasted resources and the desire of the desert people to supplement their TRADE IN THE DESERT 335 meager products. Timbuctoo, on the Niger River, and Damascus, in Syria, are examples of places which serve as gateways to deserts. For centuries, goods were carried in large quantities across the vast deserts of central and western Asia only by pack animals, especially the camel, and even to- day this is the case over much of the region (Fig. 235). A number of caravan routes cross the Sahara, ex- tending from oasis to oasis. The trade which originates or terminates in the Sahara is largely in dates, salt, clothing, cereals, and camels, while for centuries the through trade has included such things as ivory., gums, spices, and gold dust. Prince Henry of Portugal learned of the trans-Saharan trade while on an expedition against the Moors in north- ern Africa in 1415, and partly with the idea of diverting the trade of the Guinea Coast to his own country by water, he began the long series of explora- tions along the coast of Africa which culminated in the discovery of the all- water route to India. The use of the latter route to the East injured greatly the caravan trade across Asia. A trans-Saharan railroad is now projected. Political conditions in deserts. The hard conditions of life in deserts repeatedly have driven their inhabitants out to conquer other regions (p. 333). On the other hand, the con- quest of deserts from without always has been attended by great difficulties, and in some cases never has been accomplished. The love of freedom and the fighting ability characteristic of desert peoples, in addition to the difficulties which an invading army finds in the lack of roads, water, and food, have helped to produce this # •'■'• **1 .,**=•-•«'■■•.? '• ^gg^3r*' *^W^^' \,l ^TIP* -* 1 Fig. 236. Date Biskra, Algeria. palms loaded with fruit. 33^ LIFE IN PLAINS result. Furthermore, the scant resources of deserts have made them relatively uninviting to outside people. Life in Arctic Plains The plains which border the Arctic Ocean are known as barren lands in North America, and as tundras in Eurasia. They are cold deserts, snow-covered for some two-thirds of the year. The short sum- mers, low temperatures, and cold or frozen soil prevent agriculture, and restrict vegetation chiefly to stunted bushes, mosses, and various quick-growing, flowering plants. The few, widely scattered inhabit- ants of the tundras depend largely on their herds of reindeer and on Fig. 237. Reindeer and sledge. hunting for their living. Fishing is an important occupation during the three or four months when the streams are free from ice. A nomadic life results from the necessity of following the game and the reindeer herds, which wander half-free in search of pasturage. As in the steppes and dry deserts, this nomadic life means small, easily transported dwellings — in many cases a tent consisting of a framework of poles covered with skins — and few and simple house- hold goods. Some of the tribes move northward with their herds in the summer, and return to pass the winter in the forests which border the tundras on the south. Here the timber affords some shelter, feed is available for the reindeer, and game may be hunted for food and fur. THE NATIVES OF TROPICAL FORESTS 337 All that the camel is to the inhabitants of low-latitude deserts, the reindeer is to the men of the Arctic desert. It is indifferent to cold, and is an excellent draft animal (Fig. 237). Its milk and flesh are used for food; its bones and horns afford material for making various implements ; its tendons and sinews serve for thread; and its skin is used for shelter and clothing. The reindeer is the most desirable form of wealth on the tundra. In some places, a herd of 50 head, which will support a family of four or five, requires between 4 and 5 square miles of tundra pasturage. This means at best a very sparse population. Some years ago the United States Government imported nearly 1,300 reindeer from Siberia, for the benefit of the natives of northern Alaska. The herds have increased rapidly, and are proving of great value. In the Arctic plains life is a constant struggle for food, clothing, and shelter. There is little opportunity for trade. Situated on the outskirts of the inhabited world, the frozen deserts of the north have played a much less important part in history than the centrally- located deserts of lower latitudes. Nor does it seem likely that they can become of much importance in the future. Life in Humid Plains of Low Latitudes Near the equator, the climate of the lowlands is characterized by heavy and frequent rains, and by high, nearly uniform tempera- tures throughout the year (p. 102). As we have seen, this results in a dense, varied vegetation (Fig. 238), like the forests of the Amazon and Congo valleys. The distinctive life of humid plains in low lati- tudes is therefore that of the tropical forest, or jungle. In some of the other realms which we have considered, man has been handicapped by lack of useful vegetation. Here, the very abundance of plant life is an obstacle to progress. Response of natives to conditions in tropical forests. The dense forests of equatorial regions are occupied by sparse populations of backward natives. The high temperatures and the moisture are enervating, and steady work is difficult. The luxuriance of the natural vegetation makes the clearing of land difficult, and after it is cleared, a constant struggle is necessary to keep out the plants which are not wanted. Unused trails through the forest are overgrown quickly, and all trace of settlement soon disappears from abandoned clearings. Under these conditions, it is not strange that agriculture rarely is practiced. Throughout the world, man appears, as a rule, to have developed agriculture, or to have domesticated animals, only when the natural food supply became too small. In the equa- torial forest, the natural food supply is abundant. The natives live 338 LIFE IN PLAINS chiefly on the fish afforded by the many rivers, and such game as inhabits the forest. This is supplemented in many places by the products of certain forest plants, such as the sago palm. The large animals found in many places in the open country near the tropical forests go into the latter only a short distance. They come and go through the denser growth by paths which they keep open by frequent passing. In the heart of the forest, there are few sources of food for animals near the ground. Flowers and fruits are found in the tree tops, however, and hence animal life is represented Fig. 238. Tower.) Tropical forest and river in flood. Southern Mexico. (W. L. chiefly by flying and climbing forms, such as insects, birds, snakes, and monkeys. Many of the birds and snakes resemble the foliage in color, a fact which favors concealment. Little is needed by the inhabitants of the tropical forest in the way of clothing and shelter. Some of the lowest savages have no homes. Some of the people live in floating houses on the rivers, or in huts built on piles to escape the floods. Rivers are the most im- portant lines of travel through the forest. A little farming is done in clearings near the edges of the equatorial forests. In some cases, this consists in scarcely more than planting PYGMIES OF THE CONGO FOREST 339 crops, and leaving them to grow. Bananas, bread fruit, rice, and other things are grown in different places, chiefly by the women. Very little labor brings large returns, so that steady effort is discouraged. As in the equatorial forest generally, life is too easy; there is no spur to progress. The Pygmies who live in parts of the Congo forest are perhaps the lowest type of human beings. Most of the adults are only a little more than 4 feet tall, and many are shorter. They make no attempt at farming, but live by hunting and fishing. They kill small game with arrows and spears tipped with a poison made from certain plants, and capture even large animals in covered pitfalls which they Fig. 239. Pygmy village in the Congo forest. make in the narrow runways followed by the animals (p. 338). They catch fish in nets or baskets. They live in small, scattered groups where there are openings in the undergrowth (Fig. 239), building temporary huts consisting in many cases of flexible sticks covered with leaves, and shifting from spot to spot in quest of game. They carry on some trade with other tribes, bartering meat, skins, and plant poisons, for weapons and vegetable food. The Pygmies have no arts save those connected with their hunting and fishing, and no family ties. Commerce of tropical forests. The forests of tropical low- lands furnish products of much importance to the outside world, such as ebony, mahogany, rubber, gums, palm-oil, and copra. Trade follows the waterways, and in general those sections are most favored commercially which are situated conveniently with reference to a navigable river (p. 104). 34Q LIFE IN PLAINS The humid lowlands of the tropics are of far greater importance to man than the Arctic plains, but unfortunately the settlement and development of them by people from middle latitudes are attended with great difficulty (pp. ioo, 103-104). Questions 1. How might one prove that a given coastal plain was formerly a marginal sea-bottom? 2. By what are the characteristics (topography, fertility, etc.) of any given plain determined? 3. Why are the soils of most plains thicker and more fertile than those of plateaus and mountains? 4. (1) What great plains, now of little value to man, are likely to have greatly increased importance in the future? Why? (2) What ones are likely to continue of little significance? Why? 5. Compare and contrast the life of primitive peoples in arid deserts and rugged mountains. 6. How does the life of people in Arctic regions resemble that of desert tribes in lower latitudes? CHAPTER XIX COAST-LINES AND HARBORS Importance of coast-lines. There is great freedom of move- ment over the ocean. A ship may sail direct from one port to another thousands of miles away, or it may make a roundabout voyage, call- ing at many ports on the way. A modern steamship can carry ten to twenty train loads of freight in a single cargo, and it costs far less to operate one steamer than to run ten or twenty trains. Furthermore, trains call for the maintenance of a railway, which is very expensive. Hence the carriage of freight by rail is much more costly than by boat. Modern commerce, therefore, depends much on the ocean highway, but it owes its rapid growth in part to favorable coast-lines through which access to the sea is secured. In early days, seamanship was much influenced by the character of the coast-line. It was unsafe to go far from land, for vessels were small and there was no way of determining position accurately, or of reckoning distances. Hence seamanship developed first along the shores of quiet inland seas like the Mediterranean, or where long bays and sheltering islands invited ventures from one headland or island to another, as in Norway. Thus the first nations to become sailors, fishermen, explorers, and sea traders were influenced by the nature of their sea-coasts. With modern steamships and skillful seamen, voyages are under- taken readily to distant parts of the earth. But even the giant steam- ship needs safe anchorage in quiet waters while its cargo is being load- ed or unloaded. Some ocean commerce is carried on from places which have no harbor, but in such cases, vessels anchor off shore while the cargo is carried {lightered) from them to shore, or from shore to them, in small boats. During heavy seas lightering is impossible, and many wares cannot be handled to advantage in this way at any time. Characteristics of coast-lines and their origin. If land along a coast were to be elevated or the sea-level lowered, a portion of 34i 342 COAST-LINES AND HARBORS the sea floor would be exposed. Most of the sea floor is smooth and even. Hence the emergence of a coastal strip tends to make an even, regular shore-line (Fig. 240) fronted by shallow water. Coasts which have risen recently, relative to sea-level, are without good harbors, except where some large river, flowing across the coastal plain, offers a haven at its mouth. Commerce with such a coast is at a disadvantage. Large vessels must anchor off shore while their cargoes are lightered, unless artificial harbors have been made by Fig. 240. Map showing regular outline of a newly elevated coast. Dotted lines indicate contours; interval 25 feet. (Nome, Alaska, Special Sheet, U. S. Geol. Surv.) building breakwaters, jetties, or long quays. The east coast of India and most of the Gulf coast of Mexico present these conditions. Madras and Vera Cruz have artificial harbors because the trade from an important region justified the great expense involved in making a harbor. The submergence of a coast land having hills and valleys pro- duces a new shore-line which is irregular, the drowned valleys form- ing bays (Fig. 241). Isolated hills on the old lowlands may front the new coast as islands. The coast of Maine furnishes good examples. Such a coast-line commonly has many sheltered bays and harbors. Commerce is favored by such a coast. Most important commercial ports, such as the Atlantic ports of North America and Europe, are along depressed coasts. The chief sea fisheries, also, are connected with irregular coasts, partly because of the many convenient refuges EMBAYED COAST-LINES 343 for fishing fleets. Not infrequently, also, large bays, like Chesapeake Bay, support valuable fisheries. Where an irregular coast-line is produced by the sinking of a coastal plain, the bays may be wide (Why?), like Delaware and Chesapeake bays, but most of them are shallow, except along the line of the old river channel, and they may have marshy land along their borders. Few places on the shores of such bays are suitable for the development of a great port. Where a higher, more rugged region Fig. 241. Map showing irregular outline of a depressed coast. Dotted lines indicate contours; interval 20 feet. (Monhegan, Maine, Sheet, U. S. Geol. Surv.) is submerged, the bays are likely to be narrow and fiord-like, as in Alaska and Norway. Most of them are deep, and some are bordered by high land which rises so abruptly from the water that there is no room for a city. Where the ocean finds access to an interior valley, a long inland arm of the sea, like Puget Sound, is developed. A former mountain pass in the Coast Range, now submerged, forms the picturesque Golden Gate entrance to San Francisco harbor (Fig. 242) , and a little further sinking would change much of the central valley of California into a great sound. Changes in shore-lines. Shore-lines are subject to constant change by waves, shore and tidal currents, rivers, winds, and ice. 344 COAST-LINES AND HARBORS The effect of glaciers on shore-lines has been noted (pp. 256, 261). Much of the value of Boston harbor depends on the protection afforded by islands of glacial origin. Shore ice has little effect on coast-lines, but hinders navigation along some coasts (p. 246). Winds often make dunes on the sea shore (p. 202), and the dunes may afford the land some protection from the sea, as along the coast Fig. 242. Diagram showing arm of ocean formed by invasion of valley through a submerged sag in mountain range. San Francisco harbor. Dotted lines indi- cate bar across entrance. (U. S. Coast and Geod. Surv., Chart No. 5500.) of Holland, but they rarely change the outline of the land to any great extent. Rivers affect shore-lines little by erosion, but delta-building rivers may change them greatly (p. 241). Other things equal, delta lands grow most rapidly in the quiet waters of bays and inland seas. Thus the delta of the Mississippi (Fig. 159) extends into the Gulf as a great irregularity, with many smaller irregularities about its borders. Delta-building in bays may lessen the irregularities of the coast by filling the bays. The value of Mobile Bay as a harbor is lessened because of the sediment deposited in it, and many others, which were important ports centuries ago, are now partly or entirely filled. The WAVES AND SHORE CURRENTS 345 city of Adria, Italy, once the port for the mouth of the Po, is now fourteen miles from the coast, and the Rhone delta, building forward at the rate of 200 feet a year, has never developed an important port (p. 270). On exposed coasts, delta-building is less rapid (Why?), and pro- duces fewer irregularities. The delta of the Amazon, for example, does not project be- yond the general coast- line. Delta lands are low, marshy, and sub- ject to floods, while the bays about their borders are shallow. For these reasons del- tas are poorly suited to the development of ports, and except at the mouths of great rivers, like the Mississippi, deltas rarely become the sites of great com- mercial cities. Waves are the chief agent changing coast- lines. On irregular coasts, the general tend- ency of waves is to wear away headlands (Fig. 243) and fill bays, thus making the shore more regular. On regular coasts, their gen- eral tendency is to wear back the shore-line. Waves therefore tend to destroy harbors. In many cases serious harm to commerce is prevented only by costly structures built to protect and improve harbors. Waves are at work almost constantly on some part of every coast-line. Large waves are more powerful than small ones; hence coasts exposed to stormy seas are worn most, and those of loose material, such as gravel and sand, are cut back more than those of solid rock. The gravel, sand, and clay of the Atlantic Coastal Plain, and the glacial drift of parts of New England, are washed away more readily than the solid rocks of Maine or Norway. In deep water away from shore, the water in a wave does not move 4*£ m S§i ■ Fig. 243. Wave erosion of an exposed headland. 346 COAST- LINES AND HARBORS forward. An idea of its motion may be gained from a field of waving grain, where wave after wave crosses the field, though each moving stem is fixed to the ground. But when a wave advances into shallow water, its motion changes because the lower part of the wave drags bottom, and so is made to go more slowly. The top tends to pitch forward, making surf (Fig. 244). A somewhat similar effect may be produced in deep water when winds blow the tops of waves forward, forming whitecaps. Hence during storms, and especially in shallow Fig. 244. Surf wave at Point Buchon, California. water, there may be a distinct forward movement of the water in a wave, but generally in deep water it is only the wave motion, not the water, which travels forward. In shallow water, the water which is thrown forward against the shore runs back down the slope of the bottom as the undertow. Drownings have resulted so frequently from bathers being caught by the undertow that many bathing beaches now have regular life guards constantly on watch during bathing hours. If waves reach the shore obliquely, they produce a movement of water parallel to it. Such a movement is known as a shore or littoral current. Where a shore is exposed to winds prevailingly from one quarter, the resulting shore currents are somewhat constant in direction. Littoral currents are most important in moving the material worn from the land by waves. CLIFFS AND TERRACES 347 Fig. 245. A cliff fronted by a terrace. Outer (dotted) part of terrace built by- deposition of sediment; inner part due to wave cutting. Erosion by waves. The force of waves hurled against the shore may be very great. Surf has been thrown to heights of more than 100 feet with force enough to destroy lighthouses. The strength of waves on the coast of Great Britain is sometimes as much as three tons per square foot. Such waves are able to move masses of rock weighing several tons. During one storm more than 200 blocks of concrete, weighing 4 tons each, were swept, from the break-water at Cherbourg, France, and tossed over an em- bankment. It is clear, there- fore, that the force of waves is great enough to wear shores, even of solid rock. Where deep water is found near shore, as along most steep coasts, erosion depends on the work of the water alone. Where waves break in shallow water, pieces of rock may be hurled forward with the rushing water, and serve as powerful tools to cut away the land. In severe storms, the land is, in rare cases, driven back many feet in a few hours. The waves of lakes are never so strong as the great waves of the sea (Why?), but the storm waves of large lakes have great force, and may do much damage even in a single storm. The great force of waves on an exposed coast has led to many attempts in different countries to use wave power for industrial purposes. None of the devices yet tried has proved practicable on an important scale. One obstacle is the ex- tremely variable char- acter of the waves. Where waves erode the land they make steep slopes, or cliffs. Such cliffs are bordered by wave-cut terraces a little below the surface of the water (Fig. 245). The width of such a terrace measures roughly the advance of the water on the land by the cutting of its waves. By rise of the land, or by sinking of the sea, the terrace may become land (Fig. 246). Fig. 246. Wave-cut terraces now well above the sea, indicating relative change in level of land and sea. Seward Peninsula, Alaska. 348 COAST-LINES AND HARBORS By driving back sea cliffs, waves tend to increase the area of the sea at the expense of the land. The island of Heligoland, off the German coast, has been so worn by waves that it is less than one-twentieth as large as it was a thousand years ago. Many shoal areas off the New England coast are due to the cutting away of small islands. Deposition by waves and shore cur- rents. Material worn from the land by waves, or brought to the shore by rivers, is shifted about by waves, under- tow, and shore cur- rents, but finally comes to rest. If left at the shore-line it makes a beach (Fig. 247). If carried farther out into the water, it takes on other forms. Fine par- ticles of mud generally are carried out into deeper water, while coarser material, such as sand and gravel, make the beach. Waves may build reefs or barriers a little way out from the shore. They are formed near the line of breakers, where the incoming wave leaves much of the sediment which it is moving toward the land. The undertow may add to the reef by carrying sediment out from the shore. Some reefs are troublesome to navigation, especially where they make "a bar" at the entrance to a harbor. Waves may build the crest of a reef above water, convert- ing it into land (Fig. 248). By building dunes, the wind may then aid in raising the surface still higher. This seems to have been the origin of many low, narrow belts of sandy land parallel to coasts, with marshes and lagoons behind them. Such barriers are common in shallow water, as at many places from New York to Texas. Lagoons behind reefs provide harbors in some places, Fig. 247. Wave-cut cliff with some of the mate- rial left in the form of a beach at its base. Lake Michigan. Fig. 248. Diagram representing cross-section of a barrier beach. REEFS, SPITS, AND BARS 349 Where a shore current reaches a bay, it does not, as a rule, follow the outline of the bay, but tends to cross it in the direction in which it had been moving. Un- der such circumstances it may build an embankment or spit of gravel and sand near the entrance to the bay. Currents do not build spits above the water, but waves may build them up into land by washing material from their slopes up to their tops. After they become land, the wind may build dunes on them (Fig. 251). When spits (Fig. 249) cross bays they be- come bars. Along some coasts, as on the south side of Martha's Vineyard Is- land, such bars have closed the entrances to many bays. Reefs, spits, and the land to which they give Fig. 249. Map of harbor formed by spits; Plymouth, Mass. Broken lines show ap- proximate limits of channel. (U. S. Coast and Geod. Surv., Chart No. no.) rise, increase the irregularity of the coast-line for a time; but they represent the first step toward regularity, for, after the reefs have Fig. 250. A barrier beach with marshy tract (filled lagoon) behind it. La- sells Island, Penobscot Bay, Me. become land, the lagoons behind them are likely to be filled with sedi- ment washed down from the land or blown in by the wind (Fig. 250). 35° COAST-LINES AND HARBORS Deposits of gravel and sand may be made between a mainland and islands near it. The Rock of Gibraltar, on the coast of Spain, has been thus "tied" to the mainland. Bars and reefs may hinder the movements of vessels, especially where they tend to close the entrances of harbors. A spit which does not obstruct the entrance to a harbor is sometimes an advantage, since it breaks the force of incoming waves. Spits which form harbors have determined the location of numerous villages and cities. The harbor of Plym- outh, Mass., for example, is protected by a spit which makes a natural break- water (Fig. 249). Prov- incetown, Mass., and Erie, Penn. (Fig. 251), have har- bors made by curved spits. Harbors. Harbors vary greatly in value. A good harbor must, first of all, afford shelter from stormy seas, must be deep enough for large vessels, must be connected with the open ocean by a deep channel, and must provide room for many ships. The direction whence the storm waves come and the direction which the harbor entrance faces have much to do with its safety. A harbor with a wide, unprotected entrance, facing the south, may be a good haven on a coast where the storm waves come from the east or northeast. The harbor of Gloucester (Mass.) illus- trates this condition. The straighter and wider the channel leading into the harbor, the better, for long vessels cannot navigate safely a narrow, winding channel. This fact alone made it necessary to open a new entrance (Ambrose channel) to New York harbor. The water near the shore should be deep enough to permit vessels to reach the docks, and the shore should be suitable for landings and port facilities. A good harbor should be free from ice. A harbor may have all these qualifications and yet be of little value commercially. Thus Casco Bay, Maine, is said to be one of the finest Fig. 251. Map of harbor formed by curved spit; Erie, Penn. Dotted areas are lines of sand dunes. (Erie, Penn., Sheet, U. S. Geol. Surv.) REQUIREMENTS OF GOOD HARBORS 351 havens in the world, but Portland is one of the lesser Atlantic ports. For commercial importance (Figs. 252 and 253), a harbor must have good lines of transportation either to a large producing region, or to one which requires many wares from the outside world. Thus New York is first among Atlantic ports, not so much because of a better harbor, as because of its better connections with the interior, where many articles of commerce are produced and consumed. As a whole, the Pacific coast of the United States is less important commercially than the Atlantic coast, partly because of the broad deserts and high mountains which lie behind it (p. 401). Harbors at the mouths of large rivers are likely to have easy communication with the interior through river navigation, and the valleys are natural routes for railways. Thus important ports, like New Orleans (Figs. 252 and 253), Para, Calcutta, and Rangoon, are near the mouths of rivers which serve as highways of trade. River- mouth harbors, however, have many disadvantages. The current is a handicap for sailing vessels, which are still important in coast- wise commerce. Many large rivers, like the Mississippi, Amazon, and Ganges, have large deltas, on which the stream breaks up into distributaries, whose mouths may be blocked by deposits of silt and mud. Shallow water is common near the entrances, and this disad- vantage increases as larger vessels are built. Not infrequently the main discharge of the stream shifts from one mouth to another. In many rivers winding channels are kept open only by building jetties to direct the current. For these reasons expensive work has been undertaken in some cases, such as the building of the Eads jetties at the Southwest Pass from the Mississippi, in order to keep one mouth open and deep at all times. In other cases, the port developing in connection with a river has been located at the nearest favorable place, free from the disadvantages of the river mouth. Thus Marseilles is about 30 miles from the mouth of the Rhone, and Kurachi is some 15 miles from the mouth of the Indus. In each case, connection with the river, inland, is made by rail. Most of the important harbors of the world have been made by the submergence of river valleys. The harbors of New York, Philadelphia, San Francisco, Seattle, Liverpool, London, Ham- burg, Shanghai, and hundreds of others belong to this class. The embayed river has many advantages over such a stream as the Ama- zon, as the place for a commercial center. The entrance rarely shifts, is likely to be deep, and not infrequently tidal currents prevent its being filled by sediment. Water navigation also may be possible 352 COAST-LINES AND HARBORS Fig. 252. Diagram showing movement of exports from the United States by- coasts and leading ports, 19 10. Values are expressed in millions of dollars. Per- centages refer to proportion of total trade. Fig. 253. Diagram showing movement of imports into the United States by coasts and leading ports, 1910. Values are expressed in millions of dollars. Per- centages refer to proportion of total trade. HARBORS AND COMMERCE 353 for some distance inland. Thus boats can go from Shanghai far into the interior of China (p. 269), and Hamburg benefits from a water route which reaches the Aus- trian frontier. Many harbors on embayed coasts are af- fected by the deposition of sediment in or across their entrances (Fig. 254). The direction in which the entrance opens, with respect to the movement of shore currents, is important in this connection. Thus the embayed mouth of the Housatonic River receives the material drifted westward by the shore currents of Long Island Sound. As a result its entrance is very shallow, and the river mouth has no important port. New Haven harbor, on the other hand, is so sit- uated that the shore current is' turned away from the entrance toward deeper water. Its entrance is deep enough for the passage of good-sized vessels, and partly for this reason New Haven early became an important shipping center. On some coasts where harbors occur only at rather long intervals, jetties have been built to over- come the action of shore currents (Fig. 255). Galveston harbor has been improved in this way. Fiords are numerous along some coasts, but they are relatively unimpor T tant as sites for large ports, partly because many fiords are in high lati- tudes where commerce is not very important, and partly because of the character of the fiords themselves. Many are too deep for anchorage in the main channel, their land borders are too steep and high for the growth of a large port, and they are associated in many cases with mountains which hamper communication with the interior (Fig. 176). The quiet upper waters of fiords, however, afford good protection Fig. 254. Map of river mouth with shallow water over the bar at the entrance; Cal- casieu Pass, La. Dotted lines indicate 6 foot depth. Broken line indicates 12 foot depth. Figures give depth in feet. The channel across the bar changes with every gale, so that stran- gers are warned not to enter without a pilot. (U. S. Coast and Geod.Surv., Chart N0.202.) from storm waves, and every primitive people occupying a fiord coast early developed the sea-going habit. Lagoon harbors may be produced by the formation of barriers, or by the growth of coral reefs. ,The former are numerous along the 354 COAST-LINES AND HARBORS NANTUCKET SOUND Atlantic and Gulf coastal plains, but, except where combined with sunken coast-lines, few attain commercial value. The water off shore is rarely deep, most of the inlets are narrow and shallow, and many have such strong tidal currents as to prevent the ready passage of small craft. The inlets also may be closed by sediments deposited by waves and currents, unless protected by artificial works. The lagoon, even if deep origin- ally, or dredged to a sat- isfactory depth, tends to become shallower through the deposition of sediment. Most lands bordering la- goons are low and marshy on the mainland side, with only a low, sandy island, ex- posed to winds and waves, on the ocean side. Neither is well fitted to be the site of a great port. Galveston is the best example of a port with a lagoon harbor; large sums have been spent to develop and maintain both the harbor and the city. Lagoon harbors due to coral reefs or atolls are fairly numerous in tropical waters, especially in the South Pacific, but are of little importance, because most of them are associated with small islands, which have little commerce. The Great Barrier Reef of Australia harms rather than helps the commerce of that country. Few harbors are suited naturally to all the demands of present-day commerce. Crooked channels must be straightened, and narrow and shallow channels must be dredged. The opening of the Ambrose channel in New York harbor is an example. This new entrance to the leading Atlantic port of the United States involved the improvement of an old channel which had a depth of only 16 feet at low tide. Fig. 255. Map of harbor maintained by jetties; Nantucket, Mass. Broken lines indi- cate approximate course of channel. (U. S. Coast and Geod. Surv., Chart No. m.) IMPROVEMENT OF HARBORS 355 This depth was enough for light-draft vessels, like scows and towboats, but the need for a better entrance led to the deepening and widening of the channel so that it now has 40 feet of water at low tide, and a width of 2,000 feet for a length of seven miles. The work was done by powerful dredges at a cost of about six million dollars. In a single year more than 600 trips were made by vessels of such size that, before the opening of the new channel, they could have entered only by lightering, or by waiting for very high tide. The channel from Philadelphia to the sea must be dredged to a depth of 35 feet in order to admit the largest ocean vessels. A plan is on foot to make a new port at the eastern end of Long Island, to accommodate steamers having such a length that docking facilities are no longer convenient in the limited space along the New York water front. In many places the demands of commerce from lands bordered by regular coasts compel the spending of large sums for artificial harbors. Dover, England, has one of the greatest artificial harbors in the world. There a series of concrete breakwaters more than two miles long enclose a harbor of nearly one square mile, with a minimum depth of 40 feet. The harbor cost more than $20,000,000. Its chief value is as a base for naval vessels at a strategic point on the English coast. A breakwater nearly two miles long has been built at Hilo, Hawaii, to protect shipping from the northeast trades. Similar extensive additions have been made recently to the works at Madras, to make that port equal to the other commercial centers of India. To keep pace with the ever-increasing demands of commerce, large appropria- tions are made annually by our federal government. From the standpoint of commerce, harbor improvement is one of the most important phases of govern- ment work. Many ports once important have declined because of the changing conditions of commerce. Thus the discovery of the all-sea route to India in 1497 shifted the main scene of commerce from the Mediter- ranean to the Atlantic coast of Europe. Mediterranean ports, like Venice, declined to such an extent that they almost ceased to be factors in the handling of European commerce. The opening of the Suez Canal (1869), however, made the Mediterranean the shortest route for trade between western Europe and the Orient; it led to a great expansion in the volume of commerce between those regions, and gave a new stimulus to Mediterranean ports. A similar condition is found in the Caribbean Sea and the Gulf of Mexico. These bodies of water bear to the Atlantic and the Amer- icas a relation resembling that borne by the Mediterranean to the same ocean and the continents of the Old World. Here also a narrow isthmus blocks communication with the Pacific. The Panama Canal, however, will open this route. By shortening the distance from our Atlantic ports to most Pacific points, it will make the Carib- bean a more important highway, and lead to increase of trade be- tween the two oceans. The neighboring ports, like those along 356 COAST-LINES AND HARBORS the Gulf coast of the United States, will be stimulated by new traf- fic destined for Pacific points; they are also likely to benefit much as handling centers, on account of their position as way-stations between the populous countries of the East and West. Many Pacific ports will be benefited similarly by freer communication with the Atlantic. Questions i. Why is Holland better situated than Belgium for carrying on sea trade? 2. Why are the natives of the Malay archipelago expert boatmen? 3. Why is the location of Montreal better than a place at the entrance to the Gulf of St. Lawrence for the development of a seaport? 4. What dangers threaten vessels plying along submerged coasts? Along recently elevated coasts? 5. How would a submergence of 500 feet affect the Mississippi River system? 6. How can the direction of shore currents be determined from the outline of the coast? Explain in the case of Cape Cod. 7. Why are there few important commercial centers on the coast between Cape Henry and Cape Florida? 8. What prevents Portland, Me., from being a leading commercial center? 9. Classify the leading seaports of the United States according to the kinds of harbors which they possess. 10. Why are some harbors in tropical regions, as Manila harbor, well pro- tected at one season and not at another? 11. Which Gulf ports are likely to benefit most from the opening of the Panama Canal? Why? 12. Why would fishing villages be more likely to develop along the coast shown in Fig. 241, than along that shown in Fig. 240? 13. Suggest the probable course of shore currents along the coasts shown in Figs. 251 and 255. Which harbor is likely to be affected the more seriously by shore currents? Why? 14. Suggest reasons why New York is a great exporting and importing city, and why Galveston exports much but imports little. CHAPTER XX DISTRIBUTION AND DEVELOPMENT OF THE LEADING IN- DUSTRIES OF THE UNITED STATES Agriculture Importance of agriculture. Agriculture is the most funda- mental industry of the United States; it furnishes, directly or in- directly, most of what we eat and wear, and other needs are less important than food and clothing. More than ^3 of the wage-earners CtVSUS-/900 Fig. 256. Wage-earning population in agricultural pursuits in each state in 1900 shown by inner black circle, and by the smaller number adjacent; wage- earning population in all pursuits shown by the outer ring, and by the larger number adjacent. Numbers = thousands of wage-earners. (After Middleton Smith.) of the country are engaged in agriculture (Fig. 256). The total value of farm lands increased about }i between 1900 and 1905, and in 1910 amounted to more than $28,000,000,000. About half the farm lands, or approximately one-fourth the area of the country, is cultivated. 357 358 DISTRIBUTION OF INDUSTRIES Fig. 257 shows the relation of improved acreage to total farm acreage (including woodlots, etc.) in the different states. The total value of all farm products has increased each year for more than a decade, and reached nearly $9,000,000,000 in 19 10. a?" 2.6 I L OS l™» 12.0 \ 1.9 I 5.1 ® ' G) VV 125.8 feV 07 W /l 9.6 /.4.7 , L® UNITED STATES FARM ACREAGE 839 MILLION IMPROVED ACREAGE 414MILLI0N Fig. 257. Map showing relation of improved acreage (black circles) to total farm acreage (outer rings) in the different states in 1900. The smaller numbers adjacent to the circles = millions of acres of improved land; the larger numbers = millions of acres of farm land. (After Middleton Smith.) This was more than double the figure for 1900 (Fig. 258). In 1910, the six crops leading in value were corn, cotton, hay, wheat, oats, billions of Dollars 1434 5*789 1870 ■ I88O 1890 1900 1 1 1 1 1 1 1 1 1 Fig. 258. Diagram showing total value of farm products in the United States for the census years 1870-1910. and potatoes. The United States produces about 4 /s of the corn of the world, V5 of the cotton, J U of the oats, and Vs of the wheat. IMPORTANCE OF CORN CROP 359 The leadership of the United States in agriculture is due to (i) the extent, variety, and high average fertility of its soils; (2) the favorable climate of most sections, with range sufficient to favor the produc- tion of many crops; (3) the facilities for marketing products; (4) the energy and ability of the farming people as a whole; and (5) the activity of federal and state agencies in introducing new plants, better seeds, and scientific methods of cultivation. Leading Crops The general distribution of crops throughout the United States is controlled largely by climate (pp. 119, 121, 127, 131). Their detailed distribution is influenced also by soil, topography, transportation facilities, market conditions, and other factors. It is practicable to consider here only the leading crops. Corn. Corn is our most important crop — in total value, acreage, and amount grown. More than 300 varieties of corn are /. / ■' i. \ \ UNITED "STATES V. / 2.184 MILLION w BUSHELS I I ,0 . 1 i 1 10. I / 3 2. 1 169^^ *. •V / ' 1 • \ • f Fig. 259. Average annual production of corn in the different states (1 899-1 908). Figures in states represent production in millions of bushels. (After Middleton Smith.) known, but only a few are grown in large amount. The leading varieties thrive best where there are plentiful rains with prevailingly warm, sunny weather during the growing season, and in rich, well- drained soils. The "corn belt" is south of the "wheat belt," be- 360 DISTRIBUTION OF INDUSTRIES cause the staple varieties of corn require a higher temperature and a longer warm season. Illinois, Iowa, Nebraska, Missouri, Kansas, and Indiana are the leading corn-producing states (Fig. 259). The average yield of corn per acre is about 25 bushels. Experiments show that this can be doubled at least by the general adoption of better methods of tillage, careful selection of seed, and the use of vari- eties best suited to the places in which they are grown. During the last five years the corn crop of the United States has averaged nearly 2,700,000,000 bushels. Because of the low price of corn, compared to its bulk and weight, little is shipped to distant markets. Most of it is used where it is grown, to feed stock. Corn is used also as a breadstuff, and in the manufacture of whiskey (p. 389), glucose, and other products. Corn appears to be a native of the highlands of Mexico, whence its cultiva- tion spread northward and southward at an early date. The colonists found it cultivated more or less by many of the Indians, and in many cases they promptly began to grow it. A number of the successful English settlements of eastern United States probably would have failed but for this food plant. As settlement spread westward, corn was the staple crop of much of the frontier. It was easy to cultivate, and usually returned a relatively large yield. It was stored easily, easily prepared for food, and was nourishing both for animals and man. "The progress of our conquest of this continent would have been relatively slow had it not been for the good fortune which put this admirable food plant in the posses- sion of our people." Wheat. In the United States, wheat is the most important food plant. It probably originated and was cultivated first in Mesopotamia, but its culture spread in prehistoric times into other parts of Asia, and into Europe and North Africa. Its great value as food, the comparative ease with which it can be transported (Why?), and its power to adjust itself to new conditions, favored its wide and rapid dispersal. As a result of long cultivation and selec- tion under different conditions, there are now more than 1,000 vari- eties of wheat, adapted to rather diverse conditions. Wheats are commonly classified as spring and winter wheat, red, white, hard, and soft. In the northern interior states spring wheats chiefly are grown, for plants from seeds sown in the fall are "winter-killed"; farther south, much winter wheat is raised. In general, soft wheats, relatively rich in starch, are used in mak- ing flour, while the very hard kinds, rich in gluten, are used chiefly for the manu- facture of macaroni (p. 1 28). The last is especially true of the durum wheat grown in the western Great Plains (p. 173). Hard and soft varieties are commonly mixed in making flour. The chief white wheat district is in the Pacific coast states. ■ THE WHEAT CROP 361 Fig. 260 shows the average annual production (1899-1908) of wheat in the different states. The total wheat crop of the country in 191 1 (more than 650,000,000 bushels) was nearly UNITED STATES 640} MILLION BUSHELS Fig. 260. Average annual production of wheat in the different states (1899- 1908). Figures in states represent production in millions of bushels. (After Middleton Smith.) seven times as great as that of 1850. This increase Was due to (1) the demands of the increasing population, (2) the occupa- tion of new areas suited to wheat culture, (3) the improvement and general use of farm machinery, and (4) the improved conditions for storing, transport- ing, and milling the grain. As in the case of most other crops, the average yield per acre of wheat in the United States can be increased greatly. For the ten years 1897 to 1906, inclusive, it was 13.8 bushels; during the same time it was 32.2 bushels in the United Kingdom, 28 in Ger- many, and 19.8 in France. During recent years the exportation of Fig. 261. Map showing centers of production of corn, wheat, and oats (1 850-1 900). 362 DISTRIBUTION OF INDUSTRIES wheat from the United States has decreased, as the demands of the home market have increased. While the acreage devoted to wheat culture in the United States can be increased in the semi-arid sections, and wheat may be imported, the greater supply needed in the future must be obtained chiefly by securing larger yields where wheat is already grown. The centers of cultivation for wheat and the other leading cereals have moved steadily westward (Fig. 261). Other cereals. Oats thrive best in a moist and relatively cool climate. They do fairly well in some of the southern states, where the climate, though warm, is moist, but do not grow well where it UNITED STATES S49 MILLION BUSHCLS - Fig. 262. Average annual production of oats in the different states (1899- 1908). Figures in states represent production in millions of bushels. (After Middleton Smith.) is both warm and dry. The chief area of production is in the north- ern Interior (Fig. 262). In recent years the total oats crop of the country has averaged nearly a billion bushels. A small part of the crop is used as food for man, chiefly in the form of oatmeal ; most of it is used as feed for animals. Although barley can be grown successfully under a wider range of climatic conditions than either wheat or corn, its cultivation in the United States is confined largely to the region west of Lake Michigan (from Wisconsin to the Dakotas), and to the Pacific coast. In the order of their importance, the leading states are California, COTTON CULTURE 363 Minnesota, Wisconsin, North Dakota, Iowa, South Dakota. In the northern Interior the barley is used chiefly for the manufacture of malt liquor (p. 389), and on the Pacific coast for feed. Among the minor cereals grown in the United States for their grains or for forage are rice (Fig. 263), rye, buckwheat, kaffir corn, and millet. Hay. Hay includes various grasses and legumes which are " cured" as food for stock. The more important ones are timothy, clover, and alfalfa (p. 297). Some of the cereal grasses, like oats and barley, sometimes are grown for hay. Hay is produced in every UNITED STATES 832,607 THOUSAND POUNDS Fig. 263. Average annual production of rice in different states (1904-1908). Figures represent production in thousands of pounds. (After Middleton Smith.) state, but the chief area is in the eastern half of the country, north of the 37th parallel. Although alfalfa is cultivated chiefly in the western part of the country, it probably will become of importance in the middle states in the near future, because of its relatively large yields, its high nutritive value, and its importance in increasing the amount of nitrogen in the soil (p. 29). Cotton. The cotton of commerce is the fiber which surrounds the seeds of the cotton plant. The value of the fiber and the uses to which it is put depend on its length (y£ to 2^ inches), strength, fineness, and color. The cotton plant requires a warm, moist climate, and a relatively long season free from frost. These are the principal factors which limit the cotton-producing area of the United States to the southern part, east of the Great Plains (Fig. 264). In some other countries, the area of cotton culture may be extended. Sea- island cotton, characterized by its long, fine fiber, thrives best on cer- tain islands off the South Atlantic coast, partly because of the high 364 DISTRIBUTION OF INDUSTRIES humidity. Sea-island cotton is also grown some distance inland in southern Georgia and northern Florida. In general, the largest yields of cotton are obtained on the alluvial soils of the valley bottoms, and on the limey soils of the coastal plain (p. 171). During the last five years the total cotton crop of the country has averaged more than 12,000,000 bales. About y$ of the cotton grown in the United States is manufactured at home (p. 387) ; the rest is exported. The cultivation of cotton in the United States began in the colonial period, but increased slowly until after the invention of the cotton gin (Eli Whitney, 1792) in this country, and of spinning machinery in England. The former made easy the separation of the fiber from the seed, enabling one man to do as much as 100 s 38 \ j /* — { ,r • ■ j 2 (540 ■res Y 5 ^4ft' *• Su^**4j3«t ^^^*^\$ 2 \ ipr V 1 UNITED STATES I0.B48 THOUSAND BALES Fig. 264. Average annual production of cotton in different states (1899-1908). Figures represent production in thousands of bales. A bale is 400-500 pounds. (After Middleton Smith.) to 200 could do by hand. These things, coupled for some years with unusually high prices for cotton, caused a great increase in its production. The develop- ment of the cotton industry meant also a greatly increased demand for slaves as field hands. The work in the cotton fields was simple, requiring little skill and few tools. In these and other ways it was adapted to slave labor, and, as years passed, cotton culture and slavery became mutually dependent. They became, too, dominant factors in the economic, social, and political life of the southeastern states, and helped to separate their interests in many ways from those of the northern states. Thus, the New England cotton manufacturer (p. 387) demanded a tariff on imported goods to protect him against foreign competition; the southern cotton planter, who bought many of his supplies abroad, was injured by the tariff, and of course opposed it. The growing sectionalism between the North and South resulted in the Civil War. Other vegetable fibers. Of the several plants besides cotton which are grown for fiber, only hemp and flax are cultivated to any large extent in the United States. Indeed, the latter is cultivated VEGETABLES AND FRUITS 365 here almost entirely for its seed, from which linseed oil is obtained. In Russia and some other places, flax is produced chiefly for the inner bark fiber, from which linen cloths are made. The fiber of hemp is used to make twine, rope, bagging, etc. Although both plants can be grown under rather a wide range of conditions, the cultivation of hemp in this country is confined largely to Kentucky, and that of flax chiefly to the Dakotas, Min- nesota, and Montana. Tobacco. The United States produces about ^3 of the tobacco of the world, its crop in 191 1 being about 800,000,000 pounds. It is grown in most states east of the 97th meridian, but a few produce the bulk of the crop (Fig. 265). The quality of the product varies greatly with the conditions of soil and climate, and with the care used in selecting the seed, cultivating the plants, and curing the leaves. Many grades are produced. Vegetables and fruits. The growing of vegetables and fruits for distant markets and for food throughout the year has become an important industry mainly as a result of (1) improved transportation facilities, especially refrigerator cars, and (2) the development of the canning industry (pp. 379, 386). It is impracticable to consider here the many fruits and vegetables now grown for commercial purposes in the United States. Some have been mentioned (pp. 119, 297, 298). Potatoes rank first in value among vegetables, and apples among fruits; the cultivation of both is distributed widely. The influence of refrigerator cars on the rise of industries involving the ship- ment of perishable foodstuffs has been very great. The fruit and vegetable indus- tries of the South and the deciduous fruit industry of the far West owe their Q^\ , \ ^^K^p/Hf 7 f 52843 1 _s* 7 Jlilk C86I \ [54355 *l 1486 \ • 7 659 %}S^^r-^\ \39 L— L • \ V 43l \ UNITED STATES X } 740.356TH0USAND V POUNDS Fig. 265. Average annual production of tobacco in different states (1 900-1 908). Figures represent production in thousands of pounds. (After Mid- dleton Smith.) 366 DISTRIBUTION OF INDUSTRIES development largely to the refrigerator car. It has enabled California, though one of the states farthest from the chief city markets, to become the leading fruit- growing state (p. 297). In many places, the refrigerator car helped change various fruits and vegetables from luxuries, obtainable during a short season only, to staple articles of food available during a long season, or throughout the year. For example, New York City formerly obtained cantaloups during a few weeks only from New Jersey, Delaware, and Maryland. Now the season for them in New York lasts from early May to late October, and some of them come from the Pacific coast. Sugar plants. Sugar-cane is a tropical and sub-tropical plant, and its cultivation in the United States is confined to the Gulf States, Georgia, and South Carolina. Louisiana grows more than 9 /io of the total crop of the country. In 191 1, 690,000,000 pounds of cane- sugar were produced in the United States. The sugar-beet was brought to this country some forty years ago from central Europe, and in recent years its cultivation has spread rapidly. California, Michigan, Colorado, Utah, Idaho, and Wisconsin lead in the production of sugar-beets, but the industry has some importance in a dozen other states. In the West, sugar- beets are grown largely on irrigated lands. The production of beet-sugar in the United States increased about sixfold between 1900 and 191 1, amounting, in the latter year, to more than a billion pounds. Animal Products of Farm and Range Cattle. Cattle are raised in the United States chiefly for beef, dairy products, and hides. Fig. 266 shows that most of the milch cows are in the more densely settled eastern half of the country, and that in the eastern half, most are in the northern states. The many cities and villages of the North Atlantic and North Central States require an enormous quantity of milk, and cannot draw their daily supplies from great distances. Herds may be kept at a greater distance from market in connection with the manufacture of butter, cheese, and condensed milk (p. 386). Fig. 267 indicates the distribution of cattle other than milch cows. This map differs from the preceding one in the smaller numbers for the North Atlantic States and the greatly increased numbers in the Great Plains and western states. Large parts of the Great Plains afford the best environment for cattle in the country, and much of the land, furthermore, cannot be used for growing crops (p. 329). Extensive areas are required for grazing THE CATTLE INDUSTRY 367 large herds of cattle, and with the growth of population in the East much land so used in earlier years has been devoted to other purposes. The United States has about V7 of the world's cattle. UNITED STATES 17.987 THOUSAND MILCH COWS Fig. 266. Milch cows on farms and ranges. Average annual number in thousands (1899-1908). (After Middleton Smith.) UNITED STATES 42.650.THOUSANO CATTLE.. Fig. 267. Cattle other than milch cows on farms and ranges. Average annual number in thousands (1 899-1 908). (After Middleton Smith.) 3 68 DISTRIBUTION OF INDUSTRIES Sheep. Sheep are raised for mutton and wool. During the last fifty years a great change has occurred in their distribution. The number in most of the middle and eastern states has decreased, while in the western states it has increased greatly. At the beginning of the period, the West had less than Vio of the sheep of the country; now it has more than Yi (Fig. 268; What are the probable reasons for the change?). The annual wool clip of the United States is more UNITED STATES 52,206 THOUSAND SHEEP. Fig. 268. Sheep on farms and ranges. Average annual number in thousands (1899-1908). (After Middleton Smith.) than 300,000,000 pounds; nearly all of it is used in American fac- tories, and in addition much is imported. Swine. About 2 /s of the swine of the world are in the United States. While they are raised more or less in every state, the great swine region (Fig. 269) is the same as the leading corn-producing section (Fig. 259), for corn is the chief food for swine. Nearly half the corn crop is disposed of in this way. Horses. A comparison of Fig. 270, showing the distribution of horses in the United States, with Fig. 257, showing the improved acreage and its relation to the total farm area in the different states, indicates that the number of horses in the different states corresponds roughly to the amount of land cultivated. This is less striking in some of the southeastern states, where many mules are used to cul- SHEEP, SWINE, AND HORSES 369 tivate the land, because they can stand hard work in that climate better than horses. The total value of farm animals in the United States in 1910 was about $5,000,000,000. UNITED STATES 48.565 THOUSAND SWINE.. Fig. 269. Swine on farms and ranges. Average annual number in thousands (1899-1908). (After Middleton Smith.) UNITED STATES 16, 929 THOUSAND HORSES. Fig. 270. Horses on farms and ranges. Average annual number in thousands (1899-1908). (After Middleton Smith.) 37° DISTRIBUTION OF INDUSTRIES Poultry and eggs. Poultry and eggs are incidental products of most farms. In recent years poultry-raising has become also a specialized industry of importance, particularly in the leading corn-producing states and near some of the larger cities. The value of the poultry and eggs produced yearly in the United States is nearly $300,000,000. Forest Resources and Lumbering The forests of the United States have been a chief factor in the progress of the country. They have furnished firewood and materials for buildings, furniture, implements, utensils, vehicles, fences, paper, FOREST REGIONS OFTHE UNITED STATES The Unshaded Areas are Treeless Except Along the Streams Fig. 271. Map showing forest regions of the United States. Not all the land within the shaded areas had forests, and much has been cleared. The unshaded areas have few forest trees. (U. S. Forest Service.) posts, poles, cross-ties, ships, railroad cars, bridges, sidewalks, etc. Our dependence on the forests for material for many things is less than formerly. Thus, coal is now used extensively as fuel; brick, stone, and cement for buildings; iron and steel for ships, freight cars, bridges, etc.; wire for fences; and cement for sidewalks. Never- theless, the yearly drain upon the forests has increased rapidly. The United States is the leading wood-producing country, and it is estimated that its total annual consumption (including that de- FOREST RESOURCES AND LUMBERING 37i stroyed by forest fires) may amount to 100,000,000,000 or more board- feet. 1 The total value of the forest products in 1909 is estimated at about $1,250,000,000. Forest regions of the United States. Forests still cover about % the area of the United States. Although the present forest land is more than 3/5 the original area, the amount of good timber remaining probably is not more than half the original amount. This is very significant in view of the compara- tively short time the forests of the country have been supplying timber. Fig. 271 shows the five great forest regions of the country. (1) The Northern For- est contains both soft and hard woods, though the for- mer have been most impor- tant. The leading kinds of trees include white pine, red pine, spruce, hemlock, cedar, balsam-fir, birch, cherry, and sugar maple. (2) The Hardwood Forest contains oak, elm, hickory, cottonwood, maple, bass- wood, chestnut, ash, etc., not all of which are hard. Cottonwood and basswood, for example, are soft. (3) In the Southern Forest the yellow pine predominates, but in places suited to their growth are cypress, oak, gum, magnolia, and other hardwoods. (4) The Rocky Mountain Forest is almost entirely coniferous; leading trees are the western yellow pine, lodge-pole pine, Douglas fir, larch, spruce, and western red cedar. (5) The Pacific Forest is also 1 A board-foot is a piece of wood one foot square and one inch thick. Billions of Feet 1 2 3 4 5 Yellow Pine ) I Doug. Fir. . . Oak White Pine.. Hemlock.... Spruce Western Pine ■ Maple Cypress Yel. Poplar. . Red Gum . . . Chestnut.... Redwood. . . . Beech Birch Basswood . . . Elm Cedar Hickory .... Ash Cottonwood. . Larch Tamarack . . . Balsam Fir.. Sug. Pine . . . Tupelo White Fir... Sycamore . . . Walnut Cherry ..... Lodgep'l. Pine Allothers... 1 1 Fig. 272. Diagram showing lumber cut for 1909, by kinds of wood. (U. S. Forest Service.) 372 DISTRIBUTION OF INDUSTRIES coniferous, consisting chiefly of Douglas fir, western yellow pine, redwood, western red cedar, sugar pine, etc. Fig. 272 shows Billions of Feet 1234 Wash.. La ... Miss.. . N.C... Ark... Va..;. Tex... Wis... Ore.... Mich. . Ala. . . Minn. . Penn.. W. Va. Ga.... Tenn. . Fla.... Cal.... Me.... S. C... m^mmm Ky.... N.Y... Mo.... N.H.. Ida.... Ind.... Ohio... Mam Mass.. Hi Vt m Mont. . ■i Md.... ■1 Okla... ■ IU Conn.. Col.... ■ Iowa . . ■ N.M.. ■ Ariz. . . 1 N.J... 1 Del.... S. D... Wyo... R. I... Utah.. Kas .. 1 Fig. 273. Diagram showing lumber produc- tion by states in 1909. (U. S. Forest Service.) the lumber production for 1909, by kinds of wood. The cut of yellow pine equaled that of the four next most important kinds; white pine, long in the lead, ranked fourth. These facts reflect the recent rapid growth of lumbering in the southern and western states, and its gradual decline in the Lake states. Distribution of the lumbering industry. As would be expected from the distribution of the forests, lumbering is carried on in every state, but, as Fig. 273 shows, the production varies greatly. For many years the northeastern states, especially Maine and New York, led in lum- bering. Since 1850, the in- dustry has declined greatly in that region. The forests of the Great Lakes region were the next to be used extensively (p. 283), fur- nishing in 1880 about Vi the lumber cut of the country. Michigan and Wisconsin became, each in turn, the leading lumbering state; now they rank tenth and eighth, respectively (Fig. 273). At present, the southern states contribute most to the lumber output (Fig. 273); but the indus- try is expected to reach its climax there within a few CONSERVATION OF FOREST RESOURCES 373 years, and already the Pacific states are large producers. Indeed, Washington is now the leader. Conservation of forest resources. About 260 cubic feet of wood per capita per year are consumed in the United States. This is greater than the rate of consumption in any other country, about ten times that in France, and seven times that in Germany. Stated in another way, we are taking, on the average, 40 cubic feet of wood per acre per year from our forests. Since the average growth in the forests of the United States is not at present more than 1 2 cubic feet per acre per year, we are consuming wood more than three times as fast as it is grown in our forests. The United States cannot in the long future count on foreign sources of supply for ordinary structural timber, for other countries probably will need all they can grow. Therefore, if there is to be a permanent supply of wood in this country, we cannot long continue to use more than our forests produce. Clearly, every means of reducing the drain upon the forests, and every means of increasing their production, should be encouraged. Altogether apart from a supply of timber, the preservation of forests in many places is desirable (1) to reduce soil erosion and the resultant deposition of waste on lower lands, in stream channels, and in harbors (p. 167) ; (2) to make floods less frequent and less dangerous (p. 237); and (3) to help equalize the flow of streams important for navigation, power (p. 290), or irrigation (p. 298). The principal ways in which the forest resources of the United States should be conserved may be indicated briefly. (1) Losses from fires should be reduced (Fig. 274). The average annual loss of merchantable timber is estimated at about $50,000,000. In addition, many lives have been lost in some forest fires, and villages have been consumed, (b) Great loss is involved in the damage to young trees and seedlings, (c) After high-class timber is burned off an area, the latter may be occupied by inferior kinds of timber, (d) The humus in the soil may be consumed, reducing or destroying the fertility of the latter, (e) Erosion may increase on burned- over areas, and the flow of streams may become more uneven. Forest fires are started by sparks from locomotives, by careless campers and hunters, by careless clearing and brush burning, by lightning, and in other ways. Save those due to lightning, nearly all may be prevented. So far as its funds permit, the Forest Service maintains a patrol in the National Forests, partly with a view to detecting fires at their beginning, and fighting them while they are still small. Some state and private forests also are patrolled during the dry season. (2) Waste in logging should be reduced so far as practicable. At present it averages about 25% in the timber holdings of individuals and companies, and something less than 10% in the National Forests. In connection with logging 374 DISTRIBUTION OF INDUSTRIES operations, young trees should be protected, and seed trees should be left. (3) The wastes in sawmills and wood-using industries should be reduced. (4) Refuse wood may be used in making many things now manufactured from good timber. (5) Wherever practicable, forest areas should be kept fully stocked with rapid- growing and valuable species of trees. In this way the production of wood in existing forests may be increased greatly. (6) In many places, cut-over or burnt- over areas should be reforested. (7) Posts, poles, cross-ties, mine timbers, pilings, Fig. 274. Effects of hurricane and fire in a heavy stand of white pine on the Little Fork of St. Joe River, Cceur d'Alene National Forest, Idaho. (U. S. Forest Service.) shingles, etc., may be treated with some preservative substance, such as creosote, and thus rendered less subject to decay and to the attack of insects. Wood treated in this way lasts 10 to 18 or more years longer than wood not so treated. The general adoption of the practice of treating with preservatives wood used in the above ways would not only lessen the drain on the forests, but also give value to much inferior timber. (8) The enormous waste of forest resources caused by in- sects can be reduced greatly. (9) The wasteful methods generally followed in the turpentine industry (p. 380) should be abandoned. (10) For many purposes, other material may be substituted advantageously for wood (p. 176). (11) Recently much has been done to conquer the diseases of forest trees, and much more may be done in the future. (12) Standing timber is taxed in most states each year, I NEW ENGLAND FISHERIES 375 and this leads owners in many cases to cut all their timber and put it on the market as soon as possible. Before the principles of scientific forestry can be adopted generally, these tax laws must be reformed. The Fishing Industries Nature and general distribution. Fishing on a commercial scale is carried on from many places on the coasts of the United States, and on many inland streams and lakes. The total annual value of the products of the fisheries has exceeded $60,000,000 in recent years, the products of the coast and ocean fisheries making nearly ^ of the total. The products include not only food-fishes, but the commercial products derived from all other marine and fresh-water animals. About 2 /$ of the products are furnished by animals other than fishes, such as clams, oysters, lobsters, shrimps, sponges, whales, and fur-seals. The leading fish of commercial im- portance are salmon, cod, shad, menhaden, mackerel, squeteague (or sea trout), haddock, herring, and trout. Most marine fishing industries are favored by (1) extensive areas of shallow water off shore, to serve as feeding and breeding grounds for large numbers of fish; (2) convenient harbors affording safe havens for fishing boats; and, where the industry is dependent on the sale of fresh fish, (3) nearness to large centers of population. With present facilities for transportation and refrigeration, the last point is less important than formerly. Where poor soil, rugged surface, or rigorous climate has made farming in coastal regions unprofitable, the people have turned to the ocean for a living. They become fishermen, develop into expert sailors and navigators, and supply men for the great merchant fleets of the world. Atlantic coast fisheries. Since early colonial days, the fishing industries of the Atlantic coast have centered in New England, which had all the advantages mentioned above. Cod, haddock, mackerel, and herring are taken in largest quantities. Most of the early settlements along the eastern coast of New England had fishing fleets, and many of them depended almost entirely on the industry. For many years, cod was the leading export of New England. The better fish were taken to southern Europe, while those of poorer quality were sold in great quanti- ties in the West Indies to feed the slaves. Here salted cod was cheaper and more wholesome than meat, and would keep much longer. In early days many fishing towns were scattered along the New England coast at points where the advantages of harbors and nearness to good fishing grounds were combined, and the industry 376 DISTRIBUTION OF INDUSTRIES was carried on chiefly from small boats near land. As the supply of fish near at hand was reduced, larger vessels were built for use on the distant banks, and the industry centered in a few places having special advantages. Gloucester has the best harbor on Cape Ann, and was the first fishing port of the district to secure rail- road connection with Boston. Accordingly, the industry developed rapidly there, while it declined at less favored neighboring towns. To-day, Gloucester and Bos- ton are the most important fishing ports in the United States. The whaling industry was important in New England for many years, although insignificant now. Several things caused its rapid decline during the third quarter of the last century, especially (i) the growing scarcity of whales and (2) the dis- covery of petroleum in Pennsylvania. The oyster is the most important shell-fish. It thrives best in relatively warm waters, and in quiet, shallow estuaries and bays, such as those between Long Island Sound and Chesapeake Bay. Some 4 /s of the oysters marketed in the United States come from this part of the coast. At first the industry depended entirely on natural beds of oysters ; but as the natural supply declined, the practice grew up of " planting" young oysters, and leaving them to mature. Pacific coast fisheries. The salmon fisheries are the most important ones on the Pacific coast, but cod and halibut are caught in large numbers. The salmon industry is centered in Alaska, about the shores of Puget Sound, and on the Columbia River. Most of the fish are caught in traps and weirs during the spring or summer run, when they ascend the rivers to spawn. At such times, the waters sometimes have been so congested with salmon that the near- by canneries, working night and day, have found it difficult to handle the fish brought in. Canned salmon is the largest fish export of the United States. In Alaska, the salmon fisheries rank next to gold mining in value of output. The total value of their product since 1868 is said to be more than $130,000,000, or more than eighteen times the amount the United States paid for Alaska in 1867. The largest fur-seal herd in the world uses the cool, moist Pribilof Islands (Bering Sea) as a breeding ground, but the estimated number of animals in it was reduced from some 5,000,000 in 1867 to about 200,000 in 1905. In recent years steps have been taken to prevent the extermination of the herd, and to put the fur-sealing industry on , a permanent basis. Mining, Quarrying, etc. The principal mineral resources of the United States, together with their uses and economic significance, were noted in Chapter XIII. The mining and quarrying of these resources afford employment to FACTORS AFFECTING MINING 377 hundreds of thousands of people, and furnish raw material or fuel for many other industries. The total value of the mineral products of the United States in 19 10 was about $2,003,000,000. The accom- panying table shows the production of the leading mineral substances in that year. Quantity Value Pig Iron 27,303,567 long tons $425,115,235 Copper 1,080,159,509 pounds 137,180,257 Gold 4,657,018 troy ounces 96,269,100 Lead 372,227 short tons 32,755,976 Silver 51,137,900 troy ounces 30,854,500 Zinc 252,479 short tons 27,267,732 Aluminum 47,734,000 pounds 8,955,700 Bituminous coal 417,111,142 short tons 469,281,719 Pennsylvania anthracite 75,433,246 long tons 160,275,302 Natural gas 70,756,158 Petroleum 209,556,048 barrels 127,896,328 Clay products 170,115,974 Cement 77,785,141 barrels 68,752,092 Stone 76,5 20,584 Other structural materials 40.821,793 Gypsum 2,379,057 short tons 6,523,029 Phosphate rock 2,654,988 long tons 10,917,000 Salt 30,305,656 barrels 7,900,344 Mineral waters 62,030,125 gallons 6,357,590 Distribution of mineral industries. In general, the distribu- tion of mineral deposits (pp. 175-183) controls that of mining and quarrying, but whether or not a given mineral deposit can be worked profitably depends on several things. Chief among these are (1) its size, (2) its quality, (3) its location, (4) the cost of working it, and (5) market conditions. The relative importance of these fac- tors varies greatly with different minerals. (1) In many places minerals of value occur in quantities too small to mine. The opening and equipment of a modern mine might be justified by a small deposit of a valuable mineral, like gold or silver, but might not be warranted by a vastly larger deposit of a cheap min- eral, like iron. (2) There is much low-grade ore and coal that cannot be mined profitably in competition with better material of the same kind. For example, the United States is estimated to have more than 75 billion long tons of low-grade iron ore, not available (i. e., not workable with profit) under existing conditions, as against less than 5 billion tons which are available. (3) The importance of location 378 DISTRIBUTION OF INDUSTRIES is greatest in the case of minerals which are abundant and cheap, and least in the case of those of great value. Thus iron ore which could be mined with a small profit if near the shores of the Great Lakes, probably could not be mined if in Utah. On the other hand, gold offers great value in small bulk, and so can be transported easily. In recent years, therefore, it has attracted thousands of men to remote sections of Alaska, where most other minerals could not be mined with profit. The discovery of gold in California in 1848 brought nearly 50,000 miners there in 1849, added a new state to the Union in 1850, and gave it a population of 360,000 in i860. (4) Relatively cheap minerals are mined only where they occur in favorable posi- tions, rather near the surface; those of greater value justify deeper mines and greater expense. In classifying coal lands, the United States Geological Survey has taken a depth of 3,000 feet as the present limit for coal mining. Some of the copper mines of the Lake Superior region are more than a mile deep. (5) The output of many mines and quarries is affected greatly by the demand for the product. The total value of the mineral products of the country declined from $2,071,- 000,000 in 1907 to $1,595,000,000 in 1908, largely as a result of the business depression which began late in 1907. The influence of mining on the distribution of population and the growth of cities is discussed elsewhere (pp. 315, 330, 397, 403). Manufacturing Industries Growth of manufacturing industries. For many years, most manufacturing in the United States was done in homes. The cloth- ing, utensils, and implements used by the people were largely " home- made," as is still the case in certain regions (p. 309). There were some factories even in the colonial period, and manufactured goods were imported from other countries, especially for the wealthier people. By 1820 or 1825, the factory system was established throughout much of the country then settled. Since 1850, and especially since 1880, the manufacturing industries of the United States have grown with great and increasing rapidity (Fig. 275), until now it ranks first among manufacturing countries. The total value of manufactured products for the country amounted,in 1910, to more than $20,000,000,000. The industrial growth of the last half -century has been due to (1) the in- crease of population; (2) the improved financial condition and higher standard of living of the people; (3) the increasing supplies of raw INDUSTRIES LOCATED BY RAW MATERIALS 379 materials; (4) the improvement of transportation facilities; and (5) the growing demand abroad for American goods. The Location of Industries Many manufacturing centers specialize in a few products. Thus Brockton, Massachusetts, is the leading boot and shoe center; Grand Rapids, Michigan, is famous for its furniture; and Peoria, Illinois, leads in distilling liquors. In some cases, as in those cited, the reasons for the development of special industries in certain places are clear; in others, the causes are obscure. In general, the most ] trillions of Dollars 2 3 4 5 6 7 8 9 IO 11 12 13 14 15 16 17 18 19 20 1850 - : 1860 1870 1880 pa ■■■■■■■■■■ \m HTnTTiiiiTiTT^^ Fig. 275. Diagram showing total value of manufactured products in the United States for the census years 1850-1910. important factors influencing the location of manufacturing indus- tries are (1) distribution of raw material, (2) command of power, (3) accessibility of market, and (4) a supply of labor. Distribution of raw material. The influence of the distri- bution of raw materials in locating the industries which use them is greatest in the case of (1) perishable raw materials, and (2) raw materials that are too bulky and too cheap to be carried far to fac- tories. (1) If prepared and handled carefully, fresh fruits and vegetables may be sent long distances in refrigerator cars (p. 365). But it is impracticable to do this with the large quantities used in the canning, preserving, and allied industries. Hence these indus- ries are located, for the most part, near the places of production. Thus, canning and drying fruit and making wine are important in- dustries in California. Indeed, California furnishes about 9 /io of the dried fruit and some % of the wine made in the United States. In 3 8o DISTRIBUTION OF INDUSTRIES New Jersey and Delaware ^ of the total canned product are toma- toes. Similar influences appear in the case of many animal products. The centering of slaughtering and meat-packing in Chicago, South Omaha, and Kansas City is due partly to the losses which result from shipping live animals long distances. Butter, cheese, and con- densed milk are manufactured extensively where large quantities of milk are produced, as in New York, Wisconsin, and Iowa. (2) Among the raw materials that are too bulky or too cheap to be carried economically to distant points are many of the products of the quarries, mines, and forests. Hence the industries which use these materials are located in most cases near the sources of supply. In some cases, on the other hand, special conditions make it practi- cable to take bulky raw material to remote manufacturing plants. Thus granite from Massachusetts or marble from Vermont is shipped profitably for monumental purposes throughout the country, because when cut and polished in a local yard a single piece may have a market value of hundreds of dollars. Again, it may be feasible to take bulky raw material to distant points because of very cheap transportation, as in the case of the iron ore of the Lake Superior region (pp. 268, 282). The tendency of wood-working industries to keep close to the lumbering districts is indicated by the distribution of saw-mills, wood-pulp mills, the turpen- tine industry, charcoal burning, and, less strikingly, furniture making. The wood- pulp industry was most important originally in western Massachusetts, and later in Pennsylvania, but as the supply of pulp-wood decreased, the industry became more important elsewhere. It is now centered in Maine, northeastern New York, and Wisconsin, where spruce and hemlock, the principal woods used in the industry, are more abundant. These regions have the additional advantages of abundant water power and relatively near markets for the finished products. The manufac- ture of furniture was carried on chiefly in the East until some twenty years ago, with New York the leading center. Now Chicago stands well ahead of New York, and Grand Rapids is a close third (p. 288). This migration of the industry fol- lowed the shifting of the center of lumbering from the northeastern states to the Great Lakes region (p. 372). Recently, the growth of lumbering in the Gulf states and northwestern states (p. 372) has led to a rapid development of furniture- making in those sections. The manufacture of tar, pitch, and turpentine has long been an important industry in the South. These things are made chiefly from the "sap" of the long-leaf pine, and this is obtained, in most cases, by frequently making needlessly large cuts in the lower part of the trunk. The average period during which a given tree furnishes sap under this method is only four years, and this has caused a steady migration of the center of the turpentine industry. North Carolina led for a time, then South Carolina came to the front. From South Carolina the industry spread into Georgia, where it is beginning to decline. Now Florida leads, and the industry is spreading rapidly into Alabama and Mississippi. The For- est Service has developed new methods of obtaining the sap from smaller cuts. The INDUSTRIES LOCATED BY POWER 381 general adoption of these methods will increase greatly the life of the industry. Most ores, except iron, have relatively high values for small bulk, but as they come from the mine, they are likely to be associated with much worthless material. Hence the metallic matter in most cases is partly separated from the waste (i.e., is concentrated) at the mine. It may also be smelted (metal extracted from the ore) at the mine, but since in its concentrated form it is commonly valuable enough to bear rather heavy freight charges, it is shipped in many cases to some big smelter, where large-scale operation reduces the cost. Refining the metal may be done in turn far from the smelter. Thus, silver ore mined in Leadville, Colo- rado, may be concentrated at or near the mine, smelted in Pueblo, refined in Jersey City, and manufactured into jewelry in Providence, Rhode Island. The source of many raw materials of high value has little if any influence on the location of the industries which use them. This is determined by other factors. Many illustrations might be given. The United States produces no raw silk for the many silk mills of New York, New Jersey, and Pennsylvania. Lowell, Massachusetts, manufactures large quantities of woolen goods, although New England now raises few sheep (p. 368). Influence of power resources. Available power may be the leading factor determining the location of manufacturing plants which use raw material suited to economical transportation. Water power determined the location of many of the older manufacturing centers of New England (p. 288). Some of these places had small power resources, and depended on the local supply of raw material; such places have declined. Others have continued to grow because they had larger power resources and were so situated that, as transpor- tation facilities were improved, they could use raw materials from increasingly distant points, and could bring in coal to supplement their water power. There are said to be more than forty important manufacturing cities in southern New England that can trace their start to an early advantage in water power. Nearly all of them now use much more steam power than water power. The use of coal and steam power in manufacturing increased rapidly after 1850. The growth of railroads steadily increased the number of places which could get coal, and also made cheaper the movement of raw materials to places situated favorably with respect to supplies of coal. The advantage of large deposits of good coal has had much to do with the remarkable industrial development since 1850 in the region extending from western Pennsylvania to Illinois. The use of other mineral fuels for industrial purposes also has located certain manufactures. Thus the discovery of natural gas in western Pennsylvania, Ohio, Indiana, and West Virginia attracted many industries because of the cheap and 382 DISTRIBUTION OF INDUSTRIES excellent fuel offered. In many places the supply of natural gas failed after a few years, and as a result many factories were abandoned or moved; some of the larger ones continued to operate by bringing in coal. California is beginning to feel the benefit of the large supplies of cheap oil discovered there within the last few years. Formerly, the industrial development of the state was retarded by the fact that much fuel had to be imported at relatively heavy expense. As the supply of fuels diminishes, hydro-electric power will be used more and more in manufacturing (p. 289). But the ease of transmitting the power to considerable distances removes the need of locating the factory near the source of the water power (p. 288). Influence of nearness to market. The advantages of a nearby market, or of superior facilities for shipping goods to more distant markets, have been leading factors in determining the location of many industries. An example is afforded by the location of the leading refineries handling imported cane-sugar. Sugar is refined and molasses is manufactured to some extent in Louisiana, where cane is grown. But much cane-sugar is imported, and the largest refineries are in New York and Philadelphia, in part because of the heavy local consumption and the excellent means of distribution to out- side markets. Furthermore, by having the refineries at tidewater the cost of transporting the raw material is reduced. A more striking case is that of the manufacture of agricultural implements. The chief market for these things is in the leading farming sections. Many im- plements are very heavy and occupy much car- space, so that freight rates on them are high. For their manufacture, there is accordingly great advantage in a loca- tion near the chief market. As a result, there has been a steady westward migra- tion of the industry as the great grain districts have expanded in that direction (p. 361). In 1880, Ohio and New York were leaders in the industry; now, Illinois is far ahead of both combined, its output having increased threefold between 1880 and 1910. Influence of supply of labor. The importance of a local sup- ply of labor in determining the location of manufactures varies great- ly. It depends in part on the character of the industry, being more important in the case of industries requiring skilled labor than in others. In general, it is much less important now than formerly, for it has become increasingly easy to attract laborers to any given point where other conditions are favorable. Doubtless, too, labor will be even more mobile in the future. In the past, manufacturing in parts of the South and in California has been retarded by lack of a satisfactory supply of labor. On the other hand, the leader- ship of New York City in the ready-made clothing industry is due in part to the presence of abundant cheap labor. The supremacy of New England in the manu- facture of cotton has been maintained of late years largely through the possession of expert workers. IMPORTANCE OF URBAN INDUSTRIES 383 Other factors. In addition to the leading factors discussed above, there are various minor factors which may influence the location of manufacturing industries. Thus the advantage of an early start has located certain industries in places without superior natural advantages. In most cases this advantage is associated closely with the question of labor. The boot and shoe industry of Brockton, Lynn, and Haverhill, Massachusetts, illustrates the advantage of an early start. The industry was established in these places at an early date, and by enlisting the services of many of the people, a supply of skilled labor was developed with enough impetus to give first rank to the localities. Most of the shoe factories of these cities are run by steam power, developed from Pennsylvania coal, and most of the leather they use is tanned in other states. Clearly, their leadership rests on an insecure basis, and the business is growing fast in other cities having more fundamental advantages. In earlier years, industries frequently were established in particular places because of a supply of local capital, but now such cases are relatively few and unimportant. Broadly speaking, capital is perfectly mobile, and goes wherever other conditions are favorable. Climate may also be a direct factor in determin- ing the location of manufacturing industries, though its influence is offset easily by other considerations. Thus the climate of the northern states is more invigorat- ing than that of the southern states, and workingmen are likely to render more efficient service, on the average, in the former than in the latter. Yet because of other advantages, the manufacturing industries of the South are growing rapidly. Combined influence of various factors. While many indus- tries are located largely or wholly by one or two factors, the distri- bution of others is the result of the combined influence of most or all of the things mentioned above. Many industries, too, have been located without regard to the geographic and economic conditions involved, and not a few have failed for this reason. Further illustrations of the leading factors which influence the distribution of industries occur in the following pages, in connection with the discussion of the leading manufactures of the country. The leading manufacturing states and cities. New York, Penn- sylvania, Illinois, Massachusetts, and Ohio, in this order, are the five leading manufacturing states, while New York, Chicago, Phila- delphia, St. Louis, and Cleveland are the five most important manu- facturing cities. In 19 10, the combined value of the manufactured products of cities having a population of 10,000 or more was more than twice that of smaller cities and rural districts. The more rapid growth of urban as compared with rural population has been one of the most striking and significant things in connection with the popula- tion changes of recent years (p. 399). It has been due in large part 3§4 DISTRIBUTION OF INDUSTRIES to the rapid growth of urban industries. The factories in the territory- east of the Mississippi River and north of the Ohio and Potomac rivers employ about ^4 of all the industrial wage-earners (not workers on farms) of the country, and contribute about the same proportion of the total value of manufactured products. Leading Manufactures of the United States The Federal Census Bureau has divided the 339 classes of manu- factures that are carried on in the United States into 14 groups. These are shown in the accompanying table. MANUFACTURING INDUSTRIES OF THE UNITED {Ranked according to value of product in 1909) STATES Group Food and kindred products Iron and steel and their products Textiles Lumber and its manu- factures Chemicals and allied prod- ucts Metals and metal products, other than iron and steel Paper and printing Vehicles for land transpor- tation Leather and its finished products Liquors and beverages .... Clay, glass, and stone products Tobacco manufactures Shipbuilding Miscellaneous industries. . . United States Year Number of establish- ments Wage earners (average number) Value of products 1909 1899 55,364 41,247 4H,575 301,868 $3,937,617,891 2,199,203,442 1909 1899 17,289 14,080 1,025,044 744,o69 3,163,126,293 1,818,036,771 1909 1899 21,695 17,640 1,437,258 1,021,869 3,054,708,084 1,627,889,077 1909 1899 48,533 34,947 907,514 669,043 1,582,522,263 1,004,716,682 1909 1899 11,745 8,687 237,988 179,539 1,430,901,954 726,105,558 1909 1899 8,750 4,996 248,785 160,422 1,238,251,401 688,927,152 1909 1899 34,828 26,627 415,990 298,744 1,179,285,247 607,957,231 1909 1899 8,248 8,738 507,3H 3M,283 999,326,577 504,969,835 1909 1899 5,728 5,625 309,766 248,626 99 2 ,7I3,322 582,047,900 1909 1899 7,347 5,740 77,827 55,120 674,3H,05i 382,898,381 1909 1899 16,168 11,524 342,827 231,716 531,736,831 270,650,143 1909 1899 15,822 14,959 166,810 132,526 416,695,104 263,713,173 1909 1899 i,353 1,107 40,506 46,747 73,36o,3i5 74,532,277 1909 1899 15,621 n,597 485,845 308,191 1,397,495,537 655,279,079 1909 1899 268,491 207,514 6,615,046 4,712,763 20,672,051,870 11,406,926,701 HISTORY OF MEAT-PACKING INDUSTRY 385 Food and kindred products. The more important items in this group are slaughtering and meat-packing products; flour and grist mill products; butter, cheese, and condensed milk; canned and pre- served fruits, vegetables, and fish; and refined sugar (p. 382). The slaughtering and meat-packing industry tends to keep close to the great stock-raising areas (pp. 366-368), in order to avoid freight charges on waste material and to prevent the animals losing weight on the way to the slaughtering centers. The total value of the products of the industry in 1910 was $1,370,000,000. Grazing naturally precedes farming in the order of economic development (Why?) , and as the chief grazing area moved westward in front of the advancing agricultural zone, the slaughtering and packing industry followed. In early days, stock was driven from the pastures of the Piedmont Plateau to be killed at Philadelphia, Baltimore, and Charleston. The battle of Cowpens, in the Revolutionary War, was so called because fought about the pens of a Piedmont cattle ranch. Later, great numbers of cattle and hogs were driven to the seaboard from the settlements west of the Appalachians (p. 274). After the War of 1812, the pork-packing indus- try found its chief center in Cincinnati, where it remained until about i860 (p. 276). During this period, the business was carried on also at various other points on the Ohio canals and the Ohio, Mississippi, Illinois, Wabash, and other rivers. By 1861-1862, the center of the industry had moved from Cincinnati to Chicago, and the business had declined in many of the river towns. Greater economy in manufacture was possible in a small number of large establishments than in a large number of small ones, and Chicago, as the greatest railroad center, had unrivaled facilities for assembling the stock. It is also on the northern edge of the corn belt (Fig. 259; Why important?), and within easy reach of the great grazing lands. Chicago still leads in the industry, contributing nearly y$ of the total value of the products for the country, but the second and third centers are found on the Missouri River, at Kansas City and South Omaha, respectively. The most important thing in the recent history of this industry has been the more and more nearly com- plete use of the waste products of the slaughter houses. Among the things made from these products are soap, candles, glue, gelatine, glycerine, ammonia, knife- handles, and fertilizer. • The value of the flour and grist mill products of the United States has increased rapidly with the growth in the production of cereals, and in 1910 amounted to more than $880,000,000. Five- eighths of the value of the output of these mills is in wheat flour. Other important products are rye and buckwheat flour, corn meal, and feed for animals. All branches of the industry have expanded west- ward, following the westward movement of the centers of production of the great cereal crops (Fig. 261). Flour and grist mills are distribut- ed widely, for with the exception of a comparatively few large mills, they supply local demands only. Minnesota, New York, Kansas, 386 DISTRIBUTION OF INDUSTRIES Ohio, and Illinois are the leading flour-producing states, and Minne- apolis is the leading city (p. 288). The manufacture of dairy products in factories is a modern development. Formerly, this work was done almost entirely on the farms. In 185 1, there was only one cheese factory in the United States; in 1905, there were more than 3,600. New York, Wisconsin, Iowa, Illinois, Minnesota, and Pennsylvania are the six leading states in the industry (p. 366). The value of factory-made butter, cheese, and condensed milk exceeded $270,000,000 in 1910. The canning and preserving of foods is a comparatively new industry in the United States, having little importance before 1850. Now, the total yearly value of canned foods, exclusive of meats, is about $160,000,000. The leading states in the industry are Cali- fornia, Maryland, and New York. The conditions which determine the distribution of the industry have been given (p. 379). Iron and steel and their products. This group of manufac- tures ranks second in value of product (p. 384). It comprises 37 industries, the basic ones being the manufacture of iron and steel. Among the others are those producing structural iron work, rails, machinery, tools, hardware, tin plate (really sheets of iron coated with tin), and various small products. The iron and steel industry is carried on in some 27 states, but nearly 9/ IO of the total output comes from Pennsylvania, Ohio, Illinois, and Alabama. The successful use of hard coal as fuel gave the first great impulse to iron production, and located the iron industry in eastern Pennsylvania, with Phila- delphia the leading market. About the close of the Civil War, the center of the industry moved to Pittsburgh, where it still remains. A number of influences led to the change: (1) The hard coal of eastern Pennsylvania, because less abundant and in great demand for domestic use, cost more than the soft coal of the western part of the state. Furthermore, coke made from the latter was more efficient, ton for ton, than hard coal. (2) The Lake Superior ore was of high average grade, was mined easily, and could be brought to Lake Erie ports cheaply by lake. (3) The rapid development of the country west of the Appalachians helped to bring about the change. Although Pittsburgh did not become the center of the industry until after the Civil War, it had nail factories, foundries, and the like, before the beginning of the century. As indicated elsewhere (p. 282; Fig. 198), Lake Superior iron ore goes to Pennsylvania coal, rather than the reverse, because much more coal than ore is needed in the manufacture of steel, and because the ore, in being sent to Pittsburgh, is on the way to its final market. Various phases of the iron industry are carried on less extensively at other cities on or near the Great Lakes, especially at Chicago and Cleveland, where ore and coal can be brought together cheaply, and where market conditions are good. In the South, Birmingham, Alabama, is the leading center of the iron and THE TEXTILE INDUSTRIES 387 steel industry. In smelting iron ore it is mixed with limestone and coke, and when the mixture is heated in the furnace, the metal iron is released from the ore, and is drawn out into molds. At Birmingham, iron ore, coal, and limestone are found close together. This fortunate combination (with the Southern market) has made Birmingham an important city, and a leading factor in the industrial growth of the southern states. Textile manufactures. The industries of this group furnish the materials for nearly all our clothing and for many household articles, such as rugs and carpets, draperies, and bedding. Vegetable and animal fibers constitute the raw materials used by the 44 textile industries. The principal industries of the group are based on cotton, wool, and silk. Various products are made also from flax, hemp, and jute. The textile mills of the United States consumed in 1910 about 2,500,000,000 pounds of raw cotton, valued at more than $290,000,000. The value of the cotton manufactures was more than $620,000,000. Southern New England has led in the manufacture of cotton throughout the history of the industry in the United States, but now its leadership is threatened seriously by the South Atlantic states. New England has the advantage of a much earlier start in the industry, and of a better supply of labor (p. 382); but the southern mills are very much nearer the cotton fields. Both sections possess abundant water power. This is a minor factor in New England, but a very important one in the South. Woolen manufactures include worsted goods, suiting, blankets, carpets, felt goods, and wool hats. Much wool is imported for the mills, which consume more than 500,000,000 pounds annually. The leading manufacturing centers are in the Middle Atlantic and New England states. The silk mills of the United States are dependent entirely upon foreign coun- tries for raw material. Mulberry trees could be grown and silkworms reared in this country, but the industry requires much hand labor, and the cost of the latter in the United States prevents the production of raw silk as cheaply as it can be produced in southern Europe, Japan, and China. The leading silk-manufacturing states are New Jersey, Pennsylvania, New York, and Connecticut. Lumber and its manufactures. The logging camp and lumber mill furnish material for the 23 other branches of industry included in this group. The fundamental industries have been discussed (pp. 370-372). Among the products of the industries which use lum- ber are doors, blinds, sash, interior finish, boxes, matches, "wooden- ware," and furniture (p. 380). Great quantities of lumber are used also in building, and in certain industries included in other groups, such as shipbuilding and the manufacture of carriages and wagons. Lumber products are manufactured on a commercial scale in every state, in marked contrast with the concentration of certain of the 388 DISTRIBUTION OF INDUSTRIES other greater industries, such as the manufacture of iron and steel and textiles. Chemicals and allied products. This group contains many manufactures which serve a wide variety of purposes. Among the products are paints and varnishes, dyestuffs, bleaching materials, medicines, druggists' preparations, baking powder, glue, soap, ink, various oils, explosives, and fertilizers. Naturally, such diverse com- modities are manufactured in many different places, but more than half the products of the group as a whole come from Pennsylvania, New York, New Jersey, Ohio, and Illinois. Metals and metal products other than iron and steel. Many things are made of gold, silver, copper, lead, and zinc (pp. 181-182), such as jewelry, watches, clocks, silverware, brassware, and pins. Many of the 34 classes of industry belonging to this group are carried on extensively in the northeastern states, especially southern New England. The chief advantages enjoyed by this section in these industries are (1) an early start, and (2) the services of skilled work- ers, more numerous there than elsewhere during the early develop- ment of these industries. Paper and printing. Printing and publishing are the most important and most widely distributed industries of this group, which includes also the manufacture of wood-pulp, paper of all kinds, paper bags and boxes, etc. The principal centers of the wood-pulp industry have been noted (p. 380). The output of paper boxes has increased rapidly during recent years ; largely be- cause of the increasing cost of wood, many things are now put up in paper boxes which formerly were packed in wooden boxes. The annual per capita value of the output in the printing and publishing business is more than ten times greater than it was in 1850. This significant change reflects in part the progress made in education, the reduced cost of reading matter, and the greater facilities for its distribution, such as rural free delivery. In 1905, the value of the products of printing and publishing in six states — New York, Illinois, Pennsylvania, Massa- chusetts, Ohio, and Missouri — amounted to ^3 that for the entire country. Vehicles for land transportation. The operations of the repair shops of steam railroad companies, the manufacture of carriages and wagons, and the manufacture of steam railroad cars are the most important of the 11 industries comprising this group. In recent years the output of bicycles has declined rapidly, while that of automobiles and motorcycles has increased enormously. The value of the automobiles made in 1900 was less than $5,000,000; in 1910, about $165,000,000. In 1905, automobiles were manufactured in 17 states, with LEATHER PRODUCTS AND LIQUORS 389 Michigan, Ohio, New York, and Connecticut leading. The value of those made in Detroit is more than y^ of the total for the industry. The leadership of Detroit appears to be due to the impetus resulting from the success of the first factories established, rather than to superior natural advantages. Leather and its finished products. The basic industry in this group is tanning, while the dependent industries include the manu- facture of leather products of all kinds. Of the latter, the boot and shoe industry is most important, but large quantities of leather are used in making harnesses, saddles, trunks, bags, furniture, gloves, mittens, and belting, in binding books, and in other ways. For many years Massachusetts has been the leading shoe-manufacturing state (p. 383), but the industry is growing rapidly at various points in the middle states. In the past, the tanning industry has depended chiefly on local supplies of tannic acid, obtained usually from the bark of oak or hemlock, and as the supply of bark failed in one area, the industry developed in another. The business is now important in Pennsylvania, Michigan, and Wisconsin. Until recently, the industry was attended by an enormous waste of timber; trees were felled by thousands, from which only the bark was taken for the tanneries, the logs being left to rot in the woods. Liquors and beverages. The value of these products increased more than % between 1900 and 1910, amounting to more than $590,- 000,000 in the latter year. Illinois leads the states in making dis- tilled liquors, while Indiana, Ohio, and Kentucky follow in the order named. New York, Pennsylvania, Wisconsin, Missouri, and Illinois are the leading states in the production of malt liquors. California, New York, and Ohio lead in wine-making. Peoria, Illinois, ranks first among American cities in the manufacture of distilled liquors. It attained leadership in the liquor industry largely because of (1) its central location in the corn belt of the state; (2) its transportation facilities, which enable it to collect at low freight rates the surplus grain of the surrounding area; and (3) an abundant supply of cheap coal from nearby mines. The manu- factured product, owing to its relatively small bulk and large value, can bear the cost of transportation to distant markets. Nearness to the grain supply has also been an important factor in the manufacture of malt liquor in Milwaukee, Chicago, St. Louis, Cincinnati, and St. Paul. Clay, glass, and stone products. Some of the industries of this group have been noted sufficiently in earlier connections (pp. 175-176, 266). Clay products are used most in the building trades, and their consumption is increasing rapidly. Ohio, Pennsylvania, New Jersey, Illinois, and New York lead in clay products. Pennsyl- vania, Indiana, and Ohio lead in the manufacture of glass. 3QO DISTRIBUTION OF INDUSTRIES Deposits of quartz sand, the only raw material which enters into all kinds of glass, are widespread, but the making of glass on a large scale is fairly well localized because of the need of satisfactory fuel for the work. With good fuel, a skillful glass-maker can make fairly good glass from inferior material, but with poor fuel he cannot make good glass with the best materials. Gas is the ideal fuel in glass- making, because it is cleanest, and gives intense, uniform heat under perfect control. The leading states in the industry attained that position largely because of their supplies of natural gas. Tobacco products. These include cigars, cigarettes, chewing and smoking tobacco, and snuff. The value of the products increased from $31,000,000 in i860 to $416, 000,000 in 1910. The manufacture of cigars is distributed widely, Pennsylvania, New York, and Ohio leading. More than 4/5 of the total output of cigarettes are made in New York and Virginia. Missouri, North Carolina, Kentucky, and Virginia lead in the production of chewing and smoking tobacco. Shipbuilding. Since 1850, the value of the products of this industry has increased nearly fourfold and the capital invested twenty-one fold. The latter fact means that, as iron and steel steam- ships replaced wooden sailing vessels, much more capital was required than when ships were built of wood only. The need of greater capital helped to bring about the concentration of shipbuilding in large establishments, with the result that there were only about half as many establishments in 1905 as in 1880. New York, Pennsylvania, Virginia, New Jersey, and Massachusetts are the leading shipbuilding states on the Atlantic coast; Ohio and Michigan lead on the Great Lakes ; and California and Washington on the Pacific coast. The rapid growth in recent years of the shipbuilding industry on the Great Lakes has been due to the demand created by the enormous increase in the com- merce of the lakes (pp. 270, 282). At the same time, of course, the development of shipbuilding has favored the continued growth of lake transportation. The ship- yards at West Bay City, Michigan, and West Superior, Wisconsin, are outgrowths of the wooden shipbuilding industry. Those at or near Buffalo, Lorain, Cleveland, Toledo, Detroit, and South Chicago are located conveniently with reference to the great steel mills. Miscellaneous industries. There are 65 industries of varying importance carried on in the United States which cannot be classed properly with any of the other groups. The combined value of their products in 1910 was more than $1,400,000,000. Among the indus- tries of the group whose products are of greater value are the manu- facture of agricultural implements (p. 382); ammunition; brooms and brushes; buttons; coke (p. 386); electrical machinery, apparatus, ! QUESTIONS 391 and supplies; fur goods; ice; mattresses and spring-beds; musical instruments; photographic materials and apparatus; and rubber and elastic goods. Questions 1. (1) Explain the fact that the shores of Chesapeake Bay, Long Island, and Lake Michigan (east shore) were among the first sections to grow vegetables on a large scale for city markets. (2) Why is the business more important on the east shore of Lake Michigan than on the west shore? 2. Formerly strawberries were grown extensively in a few places only, as in parts of Maryland, New York, Ohio, and western Michigan. Now they are grown on a large scale in Florida, Tennessee, Arkansas, Missouri, and other states. (1) Explain the relatively early development of the business in the first-mentioned states. (2) What permitted its later development in the other states? 3. It is estimated that the forests of the United States (Fig. 271) contain about the following percentages of their original stand of timber: Northern Forest, 30 per cent; Hardwood Forest, 21 per cent; Southern Forest, 50 per cent; Rocky Mountain Forest, 75 per cent; Pacific Forest, 79 per cent. Why the differences? 4. What advantages have made New Jersey a great manufacturing state (6th in 1910), in spite of the fact that it has small fuel and water-power resources, and produces relatively little of the raw material used by its factories? 5. Explain the fact that in Nebraska most of the manufacturing is done in the eastern part of the state (more than 4 /s of it in two counties) , while in Iowa it is distributed rather evenly throughout the state. 6. Among the leading manufactures of Chicago are meat products, men's clothing, foundry and machine shop products, iron and steel, the products of printing and publishing houses, and railroad cars. What advantages has Chicago for carrying on each of these industries? 7. Compare and contrast the general advantages for manufacturing of (1) Massachusetts and Texas, and (2) Utah and Ohio. 8. Flour and sugar are household necessities. (1) Explain why the former is made in thousands of mills throughout the country, and the latter at compara- tively few points. (2) Will the situation with regard to sugar change in the future? Why? 9. Why does West Virginia rank low (29th) as a manufacturing state, although it mines much coal (second coal-producing state in 1910)? 10. Explain the fact that the section east of the Mississippi River and north of the Ohio and Potomac rivers contributes about $i of the total value of man- ufactured products for the United States. CHAPTER XXI DISTRIBUTION OF POPULATION; DEVELOPMENT OF CITIES Factors Affecting Density As we have seen, the distribution and density of population are influenced by many factors — such as topography, climate, soil, natural resources, transportation facilities, and the occupations of the people. The influence of these factors may be reviewed by consider- ing briefly the expansion and present distribution of population in the United States. Fig. 276 shows the distribution of population in 1790, when the first census was taken. Nearly all the people, emigrants from Europe, were still east of the Appalachian Mountains. This was due largely to the difficulty of crossing the mountain barrier, the privations, dangers, and difficulties of life in the Interior, and the desirability of being near the Atlantic Ocean or some navigable river flowing into it, for purposes of trade. Furthermore, the lands east of the mountains and along the Great Appalachian Valley had been sufficient for the needs of the settlers until a few years before (about 1775)- In New England, the population was densest toward the south and south- east. This is explained by the colder climate at the north; the rough uplands there, infertile in many places; the fact that few of the rivers served as good high- ways far into the interior (Why?); and the importance of sea-interests (fishing, shipbuilding, the carrying trade) in New England life. The influence of the Connecticut Valley and the Champlain lowland on the distribution of the frontier population is interesting. In New York , most of the people were in or near the Hudson and Mohawk valleys, which had fertile soils in many places, and afforded easy com- munication with New York City. The Adirondacks and Catskills were almost unin- habited. The sandy, forested coastal plain of southeastern New Jersey had a sparse population, while a strip of denser settlement extended across the state between Philadelphia and New York City. (Why? Compare with Figs. 278 and 281.) In the Carolinas the Piedmont Plateau, with its relatively small farms, had a denser population than parts of the Coastal Plain, with its big plantations. The influence of the Great Appalachian Valley is shown by the settled strip which extended southwest from Virginia. The settled area in southwestern Pennsyl- 392 THE UNITED STATES IN 1790 393 Under 2 inhab. to the Sq. Mile [ 2 6-18 18-45 45-90 90 and over 83" 8.r Fig. 276. Map showing distribution of population in the United States in 1790. 394 DISTRIBUTION OF POPULATION vania reflects, in part, the attractions of the Monongahela Valley and some of its tributaries. The large area of settlement in north-central Kentucky was the famous "Blue Grass Region." Here were, rich soils, salt springs (p. 183), and navigable streams. The settlers of central Tennessee were also in a region of fertile soils, and used the Cumberland River as a highway. . The rough plateau lands of eastern Tennessee, Kentucky, and West Virginia had few settlers, or none at all. After 1790 population spread rapidly toward the west (Fig. 277), especially along such highways as the Ohio River and (later) the Great Lakes (p. 281). The population map for 1820 (Fig. 278) shows strikingly the influence of geographic features. The Adiron- dack Mountains and the less accessible parts of the Appalachian Mountains and the Alleghany Plateau remained uninhabited wil- Fig. 277. Map showing the center of population in the United States at each census, 1790 to 1910. dernesses. On the other hand, most of the fertile lowlands favorably situated and available for settlement had been occupied. The most striking feature of the western frontier was the control of settlement by the larger rivers, which were the chief highways of the time (pp. 274-276). Each one (the Red, Arkansas, Missouri, Missis- sippi, and others) was bordered for some distance by a narrow settled area, while, for the most part, the tracts between were still unoccu- pied. The influence of routes from the East is illustrated by the belt of settlement extending from western New York around the southern shore of Lake Erie to Lake St. Clair. The presence of Indians explains some of the blank areas on the map within the generally settled region, as in Georgia, Alabama, central and northern Mississippi, and western Tennessee. After the removal of the Indians, these areas were settled quickly. The unsettled condition of northwestern Ohio was due partly to the "Great Black Swamp." The lower part of the Mississippi delta and some of the lands along the Gulf coast also were unoccupied because swampy. For some years, settlers avoided the prairies of the northern Interior. They were thought infertile (P- I 73)> timber must be had for buildings, fences, and fuel; they did not afford DISTRIBUTION OF PEOPLE IN 1820 395 43-0— 41 9,5 91 89 wmmmf NOTE Center of Population 78°33'W.39°5.7'N. Under 2 inhab. to the Sq. Mile \~. « ' " " I - I 6-18 « « » « "T 1 «■« '• " EZ3 45 : 90 " «' 90 and over" :z~ Fig. 278. Map showing distribution of population in the United States in 1820. 396 DISTRIBUTION OF POPULATION THE WEST IN 1880 397 enough running water for stock or mills; there was little protection from the bitter winds of winter; and the farmers did not know how to "break" and work the tough prairie sod. The gradual conquest of the prairies is one of the most interesting phases of the settlement of the region. The dense forests in the north- ern Lake region helped for years to keep farmers away from large areas. The appearance of the railroad introduced a new and powerful factor in the expansion of population. The first American railroad was built in Massachusetts in 1826. By the early 1850 's, railroads had been built across the Appalachian Mountains from the leading seaports of the Northeast. In 1853 Chicago was connected by rail with New York City. The Mississippi River was reached shortly after, and in 1869 the first railroad was completed to the Pacific. The railroads opened up vast areas for settlement which had not been available before. This was particularly true of large areas west of the Mississippi, whose settlement and development, in the absence of navigable waterways, had to await the railroad. Fig. 279 shows the present railroad web. By 1880, many parts of the West were settled (Fig. 280). Fertile soils had favored farming along the bases of some of the mountains and in many valleys, the discovery of mineral deposits had attracted thousands of prospectors and miners to various places, and the graz- ing industry supported a sparse population over wide areas. The settlements in the Black Hills (Fig. 280) were the result of the recent discovery there of gold. Most of the settlers in central and western Montana were farmers, located chiefly in the valleys of the larger streams. Besides the farmers, there were some miners. In Colorado there were farmers (1) along the east base of the Rocky Mountains, where, at many points, irrigation was possible, and (2) in some of the mountain valleys. In addition, a large mining population had been attracted by the discovery, a few years before, of rich deposits of gold, silver, and lead in the Leadville district (p. 315). In New Mexico, the Rio Grande, Rio Pecos, and upper Canadian valleys had drawn many settlers. In Utah, the agricultural settlements of the Mormons extended along the base of the Wasatch Mountains, where there were fertile and irrigable soils (p. 291). The principal agricultural settlements in Nevada were in the Humboldt Valley and along the Central Pacific Railroad. The other settlements of the state depended chiefly on mining. In California, the commercial advantages of San Francisco Bay had attracted many people, and some of the gold-producing districts were well settled. The great central valley and the more inviting valleys of the Coast Range were occupied by farmers. The lowlands west of the Cascade Mountains in Oregon and Washington were occupied for the most part, while in the drier regions east of those mountains most of the settlements were near the Columbia River and its tributaries. The remain- ing population of the West was scattered widely at military posts, mining camps, and on cattle ranches. 398 DISTRIBUTION OF POPULATION Fig. 280. Map showing distribution of population in the West in 1880. DISTRIBUTION OF PEOPLE IN 1900 399 The population map for 1900 (Fig. 281) will be understood readily in the light of the preceding discussion, and only its larger features need be noted here. The population of the eastern half of the country was seven times as great as that of the western half. The relatively sparse population of the western half was due chiefly to prevailing aridity and the great extent of mountains and plateaus. Furthermore, many of the settled areas were occupied only recently. The relation of precipitation to population is suggested by the fact that only about V30 of the people were in regions where precipitation is less than 20 inches. Similarly, the relation of altitude to popula- tion is shown by the fact that more than 95 per cent of the population lived at elevations of less than 2,000 feet. Since 1900, the population of many parts of the West has grown rapidly because of the develop- ment of irrigation, dry-farming, and mining, and the growth of com- mercial and industrial centers. The greatest densities (Fig. 281) are found in the northeastern quarter of the country. This region in- cludes much of the glaciated area, with its highly productive soils; is unrivaled in its transportation facilities (Fig. 279); possesses vast resources in timber, in iron, coal, copper, and other useful minerals; and contains most of the great commercial and industrial centers of the country. Cities Cities have increased rapidly in the United States, both in num- ber and size. In 1850, 12.5 per cent of the total population of the country lived in the 85 cities which had 8,000 or more people each; by 1900 the percentage of the population living in such cities had increased to 32.4, and the number of such cities to 517. Nearly half of the people of the country now live in villages and cities of more than 2,500 inhabitants. The increasing proportion of the population in cities has been due chiefly to the growth of urban commerce and industries (p. 383). The region with most cities is east of the Missouri River, and north of the Ohio and Potomac rivers. Here are 35 of the 50 cities which, in 1910, had a population greater than 100,000. The leading types of cities are (1) commercial cities, (2) manu- facturing cities, (3) mining cities, (4) political centers, and (5) health or pleasure resorts. Most large cities are both commercial and industrial centers, while some belong also in varying degree to one or more of the other classes. 4oo DISTRIBUTION OF POPULATION ON , CO I •3 ! CO 3 THE RISE OF COMMERCIAL CITIES 401 Commercial cities. Cities dependent chiefly on commerce grow up (1) where conditions favor the collection and distribution of commodities on a large scale, or (2) on important lines of communica- tion at points where the mode of transportation is changed. Such places are (1) seaports, (2) river ports, (3) lake ports, and (4) railroad centers. (1) The growth of seaport cities is influenced mainly by (a) their position in relation to great trade routes; (b) the size, resources, population, and accessibility of their tributary areas {hinterlands)) and (c) the character of their harbors. The ideal harbor is large enough to contain many vessels, deep enough to admit the largest ships, protected from storms, free from ice, connected with the open sea by a deep channel, and has shores of such a kind as to facilitate the building of docks and the handling of freight (p. 350). Com- mercial cities are likely to grow up at or near the mouths of navigable rivers, for the latter serve as highways into the interior, and in many cases afford good harbors. When the lower courses of rivers have deep channels, such cities may be some distance upstream, nearer the heart of the country. Thus Montreal, more than 800 miles inland, is, in effect, a seaport. San Francisco has a fine harbor (Fig. 242), but trade with countries across the Pacific has been relatively unimportant; high mountains separate it from the interior; and to the east of these mountains stretch broad deserts with sparse populations. For years Boston, Philadelphia, and Baltimore, having good harbors and local hinterlands of importance, rivaled New York City in commercial im- portance. But the Hudson-Mohawk depression gave New York the best connec- tions with the interior, and the opening of the Erie Canal (p. 286) added the Great Lakes Region to its hinterland, enabling it to leave the others behind. (2) Since water transportation preceded railway transportation, most early inland cities are located at strategic points on navigable waterways, (a) At the head of river navigation goods are trans- ferred from water to land, or vice versa, for further distribution, and hence commercial towns develop. Thus Haverhill grew up at the head of navigation on the Merrimac, Hartford on the Connecti- cut, Albany on the Hudson, Augusta on the Savannah, and St. Paul on the Mississippi, (b) River cities are found also at the junctions of large rivers, for such places are focal points for trade. Here traffic coming upstream is divided, a part going up each stream, while in many cases freight descending the tributary streams is transferred to boats operating on the main river. Pittsburgh 402 DISTRIBUTION OF POPULATION (p. 276), Cairo, St. Louis (p. 277), and Vicksburg are examples of places whose earlier growth, at least, was aided by their position near the junction of important streams, (c) A decided change in the direc- tion of a river 's course means a division of traffic and a change in the mode of carriage (Why?). Cincinnati (p. 276), Nashville, and Kansas City benefited from their positions on great bends of rivers. Kalamazoo, Michigan, and South Bend, Indiana, are types of many smaller places situated similarly, (d) Falls or rapids may give rise to a commercial city, for river freight must be unloaded, carried around the obstruction, and either reloaded or forwarded by land. The falls (rapids) of the Ohio made Louisville, those of St. Mary's River gave rise to Sault Ste. Marie, and the growth of Buffalo was aided by the falls and rapids of the Niagara. (3) All the more important cities ranged along the Great Lakes started as commercial towns — as centers of exchange and trans- fer — and their commercial activities still dominate. As noted elsewhere (p. 279), their exact location was determined in most cases by natural lines of communication leading from the shores of the lakes. Chicago became the greatest lake port because of its superior geographic advantages. (1) It is near the head of Lake Michigan, which extends farther than the other lakes into the heart of the country. (2) It is located more centrally than its rivals with reference to the richer areas of glacial soil and the areas leading in the production of corn (Fig. 259), wheat (Fig. 260), swine (Fig. 269), and cattle (Fig. 267). (3) All land traffic from the Northwest to the eastern part of the country must pass around Lake Michigan, and is therefore tributary to Chicago. The latter is accessible also by land from the south and east, from which directions many railroads have been built to Chicago to meet the traffic of the West and Northwest. Because of its strategic position, Chicago is the greatest railroad center in the world (Fig. 279). The importance of water transportation to the growth of the leading cities of the country is shown by the fact that of the 28 cities having in 1910 a population of more than 200,000, 23 are on navigable waters. Of the 23, 10 are seaports, 7 are on the Mississippi System, and 5 are on the Great Lakes. (4) All the important seaports, river ports, and lake ports of the United States are also more or less important as railroad centers. There are also a number of large cities without water transportation, like In- dianapolis, which now owe their commercial importance largely or wholly to the fact that they are at the junction of several railroad lines. The greater cities of the United States had become important INDUSTRIAL AND MINING CITIES 403 because of their natural advantages, before the appearance of rail- roads. Railroads were built to them to share in existing trade, which they later helped to increase. On the other hand, the extension of railroads throughout the country caused a multitude of small cities and villages to spring up on sites without natural advantages. Such places serve as collecting and distributing points for the surrounding country, and, if railway junctions, they derive more or less benefit from the resulting exchange and transfer of traffic. While the more important conditions which give rise to com- mercial centers have been mentioned, villages and cities may grow up at critical points on lines of communication for reasons not men- tioned above. Thus a ford or ferry on a river may locate a town. Harrisburg, Pennsylvania, developed from Harris' Ferry, where a land route toward the west crossed the Susquehanna River ; Zanesville, Lancaster, and Chillicothe, Ohio, grew up where an important early road (Zane's Trace) crossed the Muskingum, Hocking, and Scioto rivers. Again, a mountain pass upon which trade routes focus may give rise to a city. Cumberland, Maryland, has grown up in front of Wills Creek Water-Gap, important since the colonial period (p. 232). The growth of Denver has been stimulated by its relation to several of the passes in the Rocky Mountains. Manufacturing cities. Most large commercial cities are im- portant also as manufacturing centers (p. 383), for their transportation facilities make it easy to get raw materials together and to ship out the manufactured products. Labor, too, is abundant. New York, the commercial metropolis of the country, leads also in manufacturing; Chicago, the leading inland commercial city, is the second industrial center; and Philadelphia, the fourth commercial center, is third in industry. On the other hand, all industrial cities are necessarily, in varying degree, trade centers. In most cities, therefore, commercial and industrial activities are united in varying proportions determined largely by geographic conditions. The factors which control the distribution of manufacturing industries (pp. 379-383) control also the location of the cities to which those industries may give rise. Most distinctly industrial cities are located in response to (1) power resources, like many of the New England cities (p. 381), or (2) raw materials, like Birmingham, Alabama. Mining cities. Many villages and cities, especially in the West, have developed from camps about mines. As the mining industry in a given locality grew, tents gave place to buildings of 4 o 4 DISTRIBUTION OF POPULATION wood and brick, business and professional men appeared to supply the needs of the miners, and busy settlements resulted, which in many cases became cities in a few years. Scran ton (Pennsylvania), Joplin (Missouri), Deadwood (South Dakota), Cripple Creek (Colo- rado), Butte (Montana), and Placerville (California) are types of a large number of cities and towns which have grown up solely because of the wealth of adjacent mines. Many cities at which there are no mines depend largely on the mining industry. Thus Pueblo (Colorado) and Anaconda (Mon- tana) were founded chiefly for extracting metals from ores. Sacra- mento and Denver first became important as outfitting and supply stations for nearby mines. Indeed, there are few cities in the far West which have not been influenced by the mining industry. Political centers. Few cities are merely political centers, for even though founded as such, their growth is almost certain to attract commercial, if not industrial, enterprises. Washington, D. C, is a striking exception. In locating state capitals, acces- sibility for the majority of the people has been a leading considera- tion. In states having a fairly uniform distribution of population and equal facilities for travel, the capital tends toward the geographic center. Thus the capital of Illinois shifted from Kaskaskia to Van- dalia, and later to Springfield; that of Tennessee from Knoxville to Nashville; and that of Pennsylvania from Philadelphia to Harrisburg. The centrally located capitals of Ohio, Indiana, Iowa, Missouri, and South Dakota illustrate the same principle. On the other hand, where the mass of the population is in one section of the state, the capital is likely to be located there. Thus Boston, Albany, Lincoln, and Topeka, though far from the geographic centers of their respective states, are not far from the centers of population in each case. The question of accessibility was considered, among others, in choosing the site for the national capital, but with the growth of the West it has come to have a marginal location. Health and pleasure resorts. The leading cities of this type have been stimulated in their growth by geographic conditions which make them attractive to the tourist or beneficial to the invalid; most of them are ocean, mountain, or mineral spring resorts. The attraction of the ocean resorts lies partly in their facilities for boat- ing and bathing, but chiefly in the occurrence of the cool sea-breeze (p. 74) in the hot days of summer, and in the tempering effects of winds from the sea in winter. Newport and Atlantic City are exam- LOCATION OF COLONIAL CITIES 405 pies. Asheville (North Carolina) and Colorado Springs are among the best-known mountain resorts (pp. 131,317) of the United States, and Hot Springs, Arkansas, is the most prominent health resort created by " medicinal" springs (p. 211). Los Angeles and several neighboring places in southern California have become important resorts chiefly for climatic reasons. Location of early cities. At one time people were gathered in villages and cities chiefly because of the necessity for defense. For this reason many old cities are located in places affording pro- tection, as on hills and islands. Considerations of defense as well as of trade located many of the towns founded in this country during the colonial period. The site of Boston was chosen because of (1) its strength for defense, (2) its harbor, and (3) a supply of good water. Boston peninsula was connected with the mainland by a narrow isthmus, so low that for years it was under water at high tide if a strong wind blew off the bay. This favored defense toward the land. The harbor is roomy, deep, farther inland than any other north of Cape Cod, and is located centrally on the coast of Massachusetts. This favored trade, and helped to make Boston the leading town of the colony. New York was founded on Manhattan Island for safety and in the expectation that the Hudson River would, as it did, give it command of the trade of a large district. Quebec was founded to guard the St. Lawrence highway and to command the fur trade of the Interior. The river is much narrower there than at any point farther downstream (Why advantageous?); the inland location was expected to afford security from European enemies; and the "Heights of Quebec" furnished an ideal site for a fortress. Montreal was laid out on a hilly island in the St. Lawrence River, opposite the mouth of the Ottawa River. Thus it was reasonably safe from unexpected attack, and able to draw upon the trade of both valleys. Questions 1. Discuss the leading occupations of the United States as factors affecting density of population. 2. Why are there more important cities in the United States on the Atlantic coast than on the Pacific coast? 3. Compare and contrast the commercial advantages of the seaports of south- eastern and northeastern United States. 4. Why are there fewer cities on the Great Lakes in Canada than in the United States? 5. Give examples, not mentioned in the text, of cities which have profited from their positions (i) on rivers at the head of navigation, (2) at the junctions of important rivers. 6. Lexington was for years the largest community in Kentucky. Now the pop- ulation of Louisville is more than six times that of Lexington. Explain the change. 4 o6 DISTRIBUTION OF POPULATION 7. Why has Chicago derived greater commercial advantages from its location near the head of Lake Michigan, than Duluth has from its position near the head of Lake Superior? 8. Why are Vio of the cities in the United States having in 19 10 a population of more than 100,000 situated east of the Missouri River and north of the Ohio? 9. (1) Explain the relatively small population (1900) of (a) southern Florida and (b) northern Wisconsin and northern Michigan, as shown by Fig. 281. (2) Explain the distribution of population in (a) Montana, (b) the belt through southeastern Idaho and Utah, and (c) Xew Mexico. (3) Account for the areas of relatively dense and of relatively sparse population in California. (4) Cite illustrations (not involved in preceding questions) from the map. showing the influence on the distribution of population of (a) topography, (b) means of communication, and (c) natural resources. 10. (1) Why is the railroad web (Fig. 279) thickest in the northeastern quarter of the country? (2) Account for the thinness of the railroad net in northern Xew England, northern New York, and the northern Lake Region. (3) Why is the dominant direction of railroads east-west in the Great Plains? (4) Why the relatively small railroad mileage of the western half of the country? (5) Explain the distribution of railroads in California. INDEX Abrasion by sand, 201 Africa, area and population in tem- perate zone, 113; area and population in tropics, 98; general features of, 25; rivers of, 25, 269; trade with U. S., 140, 141 Agricultural implements, manufacture of, 382 Agriculture, on alluvial fans, 236; in equatorial forests, '338; in irrigated lands, 297, 298; leadership of U. S. in, 359; in oases, 334; in mountains, 311; and rainfall, 59, 76, 80, 119, 128, 129, 291; in semi-arid regions, 327; in tropical grass lands, 104; in the United States, 357-370 Air. See Atmosphere Alaska, agriculture in, 121, 137; cli- mate of, 79, 120, 136; coast of, 343; fisheries of, 376; glaciers of, 249, 250, 251; gold mining in, 3 78 ; precipitation in, 79 Aleutian Islands, 194 Alfalfa, 30, 297, 363 Alluvial cones and fans, 235, 236 Alluvial plains, 237 Alluvial terraces, 243 Alluvium, 165 Alps Mountains, 307, 317; glaciers of, 250; life on sunny vs. shady slopes, 44; stock-raising in, 314; zones of vegetation in, 313 Altitude and climate, 109, 130 Altitude and pressure, 66, in Altitude and temperature, 44, 52, 109, 130 Aluminum, 182-183, 377 Amazon River, 104, 271, 345, 351 American waterways, 271-287; im- provement of, 287 Andes Mountains, 307, 320; as climatic barrier, 77, 105, 119 Animal life, of Antarctic region, 136; of Arctic region, 137, 336; in caverns, 212; in deserts, 107, 331; in the sea, Animal life — continued 156-158; and soil formation, 164; in tropical forests, 338. See Life Animal products, 366-370 Antarctic circle, 15, 133 Antarctic region, climate of, 135; life of, 135-136 Antarctica, snow and ice of, 251 Anthracite coal, 315, 377, 386 Anticyclones, 83, 85, 89, 90, 93 Aphelion, 7 Appalachian Mountains, and early dis- tribution of population, 392, 394; and early western settlements, 274; forest reserve in, 173, 317; in history, 308; inhabitants of southern, 310; soils of, 173; structure of, 305 Apples, 365 Arabia, desert of, 331, 333, 334 Arctic circle, 15, 133 Arctic regions, climate of, 136; ice of, 136; life in, 137-138, 336 Argentina, 122, 327 Arid climate in temperate zones, 123 Arid regions of the U. S., 79, 126 Arid plains, life in, 330-336 Artesian wells, 209, 302; in oases, 334 Asia, area and population in tropics, 98; caravan trade in, 335; climatic changes in, 79; general features of, 24; monsoons of, 75, 108-109; rivers of, 269; trade with U. S.,.140, 141 Asiatic cholera, 109 Asteroids, 4 Atlantic City, 404 Atmosphere, circulation of, 72-74; com- position of, 28-29; density of, 27; functions of, 27; heating of, 39; height of, 28; impurities of, 29, 31, 32; relation to rest of earth, 27; tempera- ture of, 34; weight of, 27, 66; work of, 204 Atmospheric pressure, and altitude, 66, .hi; distribution of, 67 4Q7 408 INDEX Australia, area and population in tem- perate zone, 113; area and population in tropics, 98; climate of, 105, 106, 109, 326; droughts in, 80, 130; general features of, 24; grazing in, 327; Great Barrier Reef of, 159, 354; population of, 105, 106 Automobiles, 388 Bacteria, of air, 76; nitrogen-fixing, Baltimore, 131, 286, 385, 401 Bananas, 339 Barley, 44, 119, 121, 129, 362 Barometers, 66 Barriers, 348 Bars, 349 Base-level, 223 Base-level plain, 227 Beach, 348 Birmingham, 386, 403 Bituminous coal mined in U. S., 377 Blizzards, 90 Block mountains, 304 Bolivia, 44, 102, no, in, 131, 320 Boot ,and shoe industry, 383, 389 Borax deposits, 126 Boston, 344, 376, 401, 404, 405 Brazil, 53, 104, 271 Bread fruit, 339 Hrick, manufacture of, 266 British Isles, advantages of isolation, 20; agriculture in, 121, 361; climate of, 47, 51, 120, 123, 150; fisheries of, 157; rivers of, 246, 271 Bubonic plague, 109 Buckwheat, 363 Buffalo, 279, 282, 286, 289, 302, 390, 402 Buffaloes, 327, 328; bones used for fertilizer, 170 Building stones, 175, 377 Butte. 330, 404 Gutter, manufacture of, 380, 386 Caldera, 195 California, climate of, 77, 79, 118, 120; fruit of, 53, 119, 297, 379; gold in, 175, 181, 378; oil in, 179, 382 California Trail, 309 Camels, 107, 331, 332 Campos, 104 Canada, 15, 47, 90, 129, 130, 137, 140, 141, 214, 246, 249, 253, 358, 263, 2S0, 282, 290, 318,405 Canals, 285-287; in foreign countries, 287; influence of, 277, 286; in U. S., 285-286 Canning industries, 379, 386 Canyons, 230; and human activities, 228 Caravans, 331, 334, 335 Carbon dioxide, 29, 30-31, 161, 178; in sea-water, 144 Catskill Mountains, 306, 311, 317 Cattle, 366-367 Caverns, 212 Cement produced in U. S., 176, 377 Cereals. See Corn, Wheat, etc. Changes of level of land, 185-187, 256 Chemicals and allied products, 384, 388 Cheese, manufacture of, 380, 386 Chicago, 279, 281, 282, 302, 328, 380, 383, 385, 386, 389, 397, 402, 403 Chile, 105, 119, 121 China, 80, 109, 122, 165, 166, 242, 243, 269, 308, 312, 317, 327, 353, 387; famines in, 109; Great Wall of, 327; isolated development of, 308 Chinook winds, 90 Cincinnati, 276, 302, 389, 402 Circle of illumination, 11,12 Circulation of air, 72-74 Cities, air of, 32; on alluvial terraces, 243; commercial, 401; on deltas, 243; fogs of, 62; on Great Lakes, 279, 282, 402; increasing number and size of, 399; location of, 3, 399-405; manu- facturing, 403; about mines, 315, 403; on rivers, 239, 240, 401, 402; in tropics, no; types of, 399 Civil War, Confederate defenses along Mississippi, 239; and Great Appa- lachian Valley, 173; and Mississippi delta, 242; sectionalism leading to, 364; use of wind-gaps in, 234 Clays and clay products, 176, 266, 377, 384, 389 Cleveland, 279, 282, 302, 383, 386, 390 Cliff-dwellers, 230 Cliffs, 347 Climate, affected by altitude, 77, 79, 106, 109, 130, 334; affected by ocean currents, 150; and cereals, 59, 121, 127-128, 129; changes of, 31, 79, 254; chief factors of, 34; as factor in life of plains, 323; and manufacturing in- dustries, 383 Climates, of polar regions, 133-139; of temperate zones, 1 13-132; of tropical INDEX 409 Climates — continued regions, 98-112; of the U. S., 118, 120, 125-128, 130 Cloudiness, 64, 84 Clouds, 62-64 Coal, 176-178; carbon dioxide produced by burning of, 30, 178; conservation of, 177-178; distribution of deposits, 176-177; duration of supply in U. S., 177; and manufacturing, 381; mining of, 177, 378; river trade in, 278, 279; total amount in U. S., 177; trade on Great Lakes, 282 Coastal Plains, 21, 322; Atlantic, 171, 302, 324, 392 Coast-lines, and harbors, 341-356; char- acteristics of, 341; importance of, 341 Cod fisheries, 375 Coke, 386 Cold waves, 90 Colorado Canyon, 230 Colorado River, 279, 290; delta of, 241 Columbia River, 279, 287, 376, 397 Commerce, of American seaports, 352; of the desert, 334; difficulties of, in tropical countries, 60; of the Great Lakes, 279-285; as influenced by form of the earth, 6; of Mississippi System, 274-279; on the ocean, 140, 141, 341; and trade- winds, 107; of tropical forests, 104, 339; of U. S. with other countries, 140, 141 Commercial cities, 401 Conduction, 38 Connecticut Valley, influence on dis- tribution of population, 172, 220,392; mountains of, 199; terrace towns of, 243 Continental climate, of temperate zones, 122; in U. S., 125 Continental shelf, 19, 20 Continents, comparison of, 24-25; grouping of, 20; and ocean basins, 19; and oceans, and temperature, 50 Contour maps, 16-17 Conservation, of coal, 177-178, 289; of forest resources, 373; of ground- waters, 210; of iron, 180; of lead, 182; of mineral resources, 183; of petrole- um, 179; of soils, 168; of waters in irrigation, 294-295 Convection, 38-39 Copper, 181, 315; mines of Lake Superior region, 181, 378; produced in U. S., 181, 377 Coral reefs, 142, 158-159 Corn, climate for, 59, 80, 121, 128; distribution of, 129, 359; and frosts, 53; production of, 358, 359; uses of, 360, 368; water needed by, 32, 207 Corrasion, 217 Cotton, 170, 171, 325, 363, 358 Cotton gin, 364 Cotton manufactures, 60, 364, 382, 387 "Cow towns," 328 Crater Lake, 195 Creep, of soils, 214 Crops, of chief importance in U. S., 358, 359; grown in mountains, 313; and marine climate, 121; and rainfall, 76, 80, 119, 128, 129; and relative humid- ity, 59; rotation of, 169. See Agriculture Crustal movements, 185 Cumberland-Alleghany Plateau, soils of, i73 Cumberland Gap, 234 Cumberland National Road, 232, 308 Cycle of erosion, 227 Cyclones, 83, 85; factors in climate, 79, 85, 123; height of, 90; movements of, 85, 89; places of origin, 89; and thunder-storms, 95; tropical, 91, 106; and weather, 85, 89, 90, 93; of winter vs. summer, 89, 90 Dairy products, 380, 386 Danube River, 270 Date palm, 242, 334 Death Valley, 58, 126 Deeps, 143 Deflection of winds, 73, 84 Degrees, length of, 11 Delaware River, 273, 286, 302 Delta, of Hwang-ho, 242; of Mississippi, 241, 344, 394; of Nile, 242 Deltas, 241-243, 267, 344-345; and commerce, 344-345; floods on, 242; lakes on, 243; soil of, 242 Denver, 403, 404 Deposition, by streams, 234-243; by glacial waters, 266; by glaciers, 257- 261 ; by ground-water, 212; by waves, 348; by wind, 202 Deserts, 3, 330-336; agriculture in, 332, 334; animals of, 331; commerce of, 334; life in, 3, 107, 33o~335j plants °fi 65, 330; political conditions in, 335; of snow and ice, 136, 336 Detroit, 302, 389, 390 4io INDEX Dew, 60, 61; in tropics, 103 Diastrophism, 185, 306 Dikes, 198 Distributaries, 242, 351 Distribution of population, 392 Doldrums, 74 Dover harbor, 355 Drainage basin, 225 Drift of ocean water, 148 Drift, glacial, 165, 257 Driftless area, 253 Droughts, 80, 129; and irrigation, 291 Drowned valleys and harbors, 352 Drowning of streams, 233 Dry-farming, 65, 173, 329, 399 Dry winds, 77 Dunes, 202, 344, 348, 349 Dust of air, 32, 201 Earth, axis of, 6, 11; form of, 5, n great relief features of, 19; magnet ism of, 18; most favored of planets 5; motions of, 6-8; orbit of, 7; revolu tion of, 6-8; rotation of, 6; size of. 6 Earthquakes, 187-191; causes of, 188 destruction by, 189; distribution of 188; and movements of sea- water 148, 191 Ecuador, 47, 102, 320 Egypt, 291,333 Elbe River, 270 Electric Power. See Hydro-Electric Power England. See British Isles Equator, 6; days and nights at, 13 Equatorial calms, 74, 101, 102 Equatorial climate, 102-104; and man, 3, 103, 104 Equinoxes, 13 Erie Canal, 281, 286, 287, 308, 401 Erosion, by glaciers, 255; by ground- water, 211, 213; rate of, 218, 219; stages of, 225; by rivers, 217; by waves, 347; by wind, 201 Eskimos, 137, 138 Europe, climate of northwestern, 51-52, 120, 150; forestry in , 3 1 6-3 1 7 ; general features of, 24; glaciation in, 253; rivers of, 269-271; trade with U. S., 140, 141 Evaporation, 56-57, 58, 64-65 Fall Line, 273 Falls, 230; and rapids, and cities, 288, 402 Farm animals, value of, 369 Farm products, value of, 358 Farming. See Agriculture Faulted mountains, 304 Faulting, 188 Ferries, and cities, 403 Fertilizers, 170, 385 Figs, 242 Fiords, 256; as harbors, 353 Fishing industries, 157, 375-376; of Arctic peoples, 138, 336; of British Isles, 157; conditions favoring, 157, 375; of Labrador, 129; of New Eng- land, 172,375 Fissure eruptions, 197 Flatboats, 275 Flax, 364 Flood-plains, deposits on, 236; soils of, 241 Floods, 80, 131, 237, 242, 262 Flour and grist mill products, 288, 385 Fog, 61, 62 Fogs, about icebergs, 149; in London, 32, 62; over ocean currents, 152; in polar regions, 135 Food products, 384, 385; of the sea, 157 Forecasting of weather, 93 Forest fires, 373 Forest products, value of, 371 Forest reserves, 165, 173, 299, 316 Forest Service, 373, 380 Forests, conservation of, 373; of equa- torial regions, 103, ^37', ev il effects of removal, 317; favored by humid cli- mate, 121, 123; and irrigation, 298; in mountains, 131, 173, 175; petrified, 79; reclamation of sand areas by, 165, 204; reduce erosion, 169, 222; repel settlers, 397; of U. S., 370; and water power, 290 France, 53, 118, 120, 270, 290, 312, 317, 352,361,373 Frosts, 53, 54-55, 61, 119, 129 Fruits, in irrigated lands, 297; preserv- ing of, 379, 386; production of, in U. S., 365; production of , near water bodies, 53; shipment of perishable, 94; in sub-tropical climates, 119 Fur trade, of Great Lakes, 280; in mountains, 318 Furniture, manufacture of, 288, 380, 387 Galveston, harbor of, 354; sea-wall, 92; storm, 91 Ganges River, 242, 269, 351 ! INDEX 411 Geography, definition of, 1 ; divisions of, 1 ; relations of, 1-3 Germany, 53, 123, 176, 270, 287, 290, 312, 314, 316, 361, 373 Geysers, 210 Glacial deposits, 257; and stream courses, 264 Glacial erosion, 255 Glacial period, 252 Glacial soils, 165, 172, 173, 174, 175, 265 Glacial waters, deposits by, 266; de- posits of, and early settlements in New England, 172 Glaciers, 247-267; effect on shore-lines, 256, 261, 344; functions of, 248; movement of, 250;. types of, 249 Glass, 389, 390 Glucose, 360 Gold, 181, 377, 378; in Black Hills, 397; in California, 175, 181, 397; produc- tion in U. S., 377 Grand Canyon of the Colorado, 228 Granite, 175, 302, 380 Grazing, 173, 175, 385, 397; in arid U. S., 175; in the Great Plains, 127, 173, 328, 366; on margins of deserts, 332; in mountains, 314; in public domain, 314; in semi-arid plains, 326, 327, 328, 329 Great Britain. See British Isles Great Lakes, cities on shores of, 279, 282, 402; commerce of, 279-285; coal trade of, 282; development of steam navigation on, 281; early navigation of, 280; freight rates on, 268; grain trade of, 284; history of, 264; iron ore trade of, 282; lumber trade of, 283; navigation season on, 246; steel freighters on, 284; total shipments on, 280 Great Plains, future use of, 329, 366; history of, 327; sand dunes of, 165; soils of, 173; underground waters of, 210, 302 Greenland, glaciers of, 250; settlements in, 137; temperatures in, 136 Ground- water, 205-215; amount of, 205; conservation of, 210; courses followed by, 206; importance of, 207; movement of, 206; surface, 205; work of, 211 Guano, 121, 170 Gulf of Mexico, 85, 355 Gulf Stream, 149, 152 Gullies, destroy land, 221; growth of, 220 Gypsum, 176, 377 Hail, 95 Hammerfest, climate of, 134; harbor of, 152 Hanging valleys, 256 Harbors, 350-355; conditions deter- mining value of, 350-351, 401; on Great Lakes, 279; and ice, 247; im- provement of, 354; in rivers, 351, 352; and tides, 152, 156 Hawaiian Islands, 105, 194 Hay, 297, 363 Health resorts, 44, 118, 131, 317, 404 Heat of atmosphere, 34, 39; distributed by wind, 51; measurement of, 34-35 Hemp, 364 High-pressure belts, 69, 72, 73 Himalaya Mountains, 19, 44, 79, 311 Holland, 301 Horses, 368, 369 Hot waves, 90 Hot winds, 65 Hudson River, 153, 272, 302 Hudson Valley, early population of, 392; and growth of New York City, 401 Humid climate in temperate zone, 123, 127, 129 Humid plains of low latitudes, 337 Humid regions of U. S., 127 Humidity, 59; and air pressures, 72; and crops, 59 Humus, 160, 373 Hurricanes, 91-92, 106 Hwang-ho River, 165, 242, 269 Hydro-electric power, 231, 288, 289, 382 Ice, of polar regions, 135, 136; on rivers, 246; on seas and lakes, 246; work of, 246 Icebergs, 251; dangerous to steamships, 149 Igneous rocks, 315 Imperial Valley, 242 India, famines in, 80, 109; irrigation in, 291; lava fields of, 198; monsoons of, 75, 108; population of, 109, 311; rain- fall in, 108; rivers of, 269 Indians, check expansion of whites, 394; of Great Plains, 327, 328; of southern Appalachians, 31 1 ; of South- west, 333 Indus River, 269 412 INDEX Industries, location of, 379-383; of the u. s., 357-391 Inland waters and their uses, 268-303 Insolation, 35-37 Intermediate zones. See Temperate Zones Iron, 179-180; conservation of , 180; dis- tribution of deposits, 180; estimated supply in U. S., 179, 377; in rocks and soils, 162 Iron and steel industries, 282, 384, 386 Iron ore, importance of location, 378; of Lake Superior region, 180, 282, 315, 380, 386; movement of, 282; production of, in U. S., 179, 180 Irrigable land, area of, 293 Irrigated land, crops of, 297; popula- tion capacity of, 297; value of, 292 Irrigation, 126, 173, 175, 291-298, 329, 397; from artesian wells, 210; early practice of, in West, 291; in Egypt, 291; government projects, 295; in humid states, 298; in India, 269, 291; and National Forests, 298; in semi- arid belt of U. S., 173; in sub-tropical regions, 119; in tropical regions, 104, no Islands, from coral reefs, 158; leading types of, in ocean, 20; off glaciated coasts, 256, 261; of volcanic origin, 194 Isobaric maps, 68, 70, 71 Isobars, 67, 83; courses of , 69-72 Isothermal maps, 46, 48, 49 Isotherms, 45, 84; courses of, 50-52 Italy, 53, 118, 166, 196, 253, 290, 312, 345 Japan, 188, 312, 316, 387 Japan Current, 150, 152 Java, 98, 99, 102 Jetties of the Mississippi, 217, 352 Kaffir corn, 173, 363, Kansas City, 277, 302, 328, 380, 385, 402 Kaskaskia, 240, 404 Krakatoa, 196, 201 Labrador, 128, 129 Labrador Current, 150 Laccoliths, 198, 305 Lagoons, 348; as harbors, 348, 353 Lake Agassiz, 262; settlement of floor of, 263 Lake Bonneville, 186 Lake-breezes, 74 Lakes, on deltas, 243; glacial, 255, 261; oxbow, 239; as resorts, 264; as sources of water supply, 302 Land reduction, rate of, 218, 219 Land-breezes, 74 Lands, area and height of, 19, 20; best uses of, in North America, 174 Landslides, 189, 214; and movements of sea- water, 148 Latitude, 9; and isotherms, 50 Lava, 192; intrusions of, 198 Lava fields, of India, 198; of the North- west, 197 Lead, 182, 397; production in U. S., 182, 377 Leadville, Colo., 315, 381, 397 Leather and its products, 384, 389 Lemons, 119, 297 Life, in Antarctic regions, 135-136; in Arctic regions, 137, 336; in arid plains, 330; in deserts, 3, 107, 330- 335; in the Great Plains, 327; in humid plains of low latitudes, 337; in mountains, 309-318; in oases, 334; in plains, 324-340; in plateaus, 320; in the sea, 156-158; in semi-arid plains, 326; in the temperate zones, 116, 121, 126, 127, 128, 129; in trade- wind belts, 107; in the tropical zone, 100, 101, 103, 104, 107; in well- watered plains of middle latitudes, 324 Lightning, 95 Limestone, 175; soils from, 164, 171, 173 Liquors and beverages, 384, 389 Littoral currents, 346 Llanos, 104 Load of streams, 166, 217 Loess, 165, 173 London, air of, 32. 62; commerce helped by tides, 271; fogs of, 32, 62; harbor of, 352 Longitude, 9; and time, 10 Los Angeles, 302, 405 Louisville, 275, 277, 402; tornado, 97 Lumber and its manufactures, 384, 387 Lumber trade, of the Lakes, 283; of Mississippi System, 278 Lumbering, 76, 316, 370-373; kinds of wood cut, 371; in Lake states, 283, 372; in mountains, 316; by states, 372 Macaroni, 128 Magnetism of earth, 18 INDEX 4i3 Malaria, in tropics, 103; in U. S., 128, 301 Malaspina Glacier, 251 Manchester Ship Canal, 287 Mantle rock, 160 Manufacturing cities, 383, 403; of New- England, 288, 381 Manufacturing industries, 378-391; of desert people, ^^; factors controlling location of, 379; groups of, 384; of interior river cities, 276-277; of mountaineers, 309, 318; total value of products in U. S., 378, 379 Map projections, 15 Marble, 176, 380 Marshes, and flow of streams, 262; glacial, 173, 260; reclamation of, 171, 241, 242, 300 Marine climate, in high latitudes, 119; and crops, 121 Marl, 171, 262 Mature topography, 226 Mean annual temperature, 35 Meanders of streams, 239 Meat-packing industry, 328, 380, 385 Mediterranean climate, 118 Mercator's projection, 16 Meridians, 8, 9 Metal products, 181-182, 381, 384, 388 Meteors, 28 Mexico, 22, 44, 240, 320; trade with U. S., 140, 141 Milch cows, 366, 367 Millet, 363 Milwaukee, 282, 302, 389 Mineral fuels, 176 Mineral industries, distribution of, 377 Mineral plant foods, 169 Mineral products, 175; substitution for wood, 176; of U. S., 377 Mineral resources, conservation of, 183 Mineral springs and waters, 211, 377 Mining, 126, 311, 330, 376-378; in- fluence on distribution of people and growth of cities, 315, 330, 397, 403; in mountains, 315 Minneapolis, 288, 302, 386 Missouri River, 240, 274, 277, 302; influence on distribution of popula- tion, 394; transportation of sediment ty' J . 6 7 . Mississippi River, 240, 243, 246, 273- 279, 286, 290, 302, 352; as a bound- ary, 274; delta of, 241, 242; influence on distribution of population, 274, Mississippi River — continued 394; traffic on, 279; transportation of sediment by, 166, 217 Mohawk Valley, 272; early population of, 392 Moisture of atmosphere. 56-65 Monadnocks, 227 Monsoons, 75, 108-109; and trade on Indian Ocean, 75 Monsoon climate, 108-109 Monsoon rains, 79, 108, 109 Montreal, 401, 405 Moon, 4, 5; and tides, 147, 154-156 Moraines, 258; use of hilly, 173, 259 Mosquitoes, 103, 301 Mt. Everest, 19 Mountain climate, in middle latitudes, 130; in the tropics, 109-111 Mountaineers, industries of, 318; life of, 309 Mountains, 22, 304-319; agriculture in, 311; as barriers, 307, 311; destruction of, 306; distribution of, 23, 304; effect on precipitation, 77, 79, 106, 131, 334; as forest reserves, 316; life in, 309- 318; mining in, 315; passes in, 232, 234, 308, 403; as resorts, 131, 317, 404; settlement of, 311; stock-raising in, 314; summer capitals in, 44; sunny vs. shady slopes, 44; types of, 304; zones of vegetation in, no, 3i3 Narrows, 232 Nashville, 277, 402, 404 National Forests, 165, 173, 299, 317; grazing in, 315; lumbering in, 373; to reclaim sandy areas, 165 National Monuments, 317 National Parks, 249, 317, 318 Natural gas, 179; and location of industries, 381, 390; produced in U. S., 377; waste of, 29, 179 Natural levees, 237; and early popula- tion of Louisiana, 237 Naval stores, 325, 380 Navigable streams of U. S., 271 Navigation, 231, 268-287; affected by tides, 152; on canals, 285-287; cities on rivers at head of, 401; of Great Lakes, 279-285; improvement of, _ 287; of rivers, 268-279 Neap tides, 156 New England, early industries in, 172, 383, 388; early population of, 392; 414 INDEX New England — continued fisheries of, 158, 375; manufacture of cotton in, 364, 382; manufacturing cities of, 288, 381; mountain resorts in, 317; rivers of, 272; soils of, 172; use of water power in, 288 New Orleans, 217, 242, 243, 275, 277, New York, 380, 382, 383, 397, 403; commercial leadership of, 277, 351, 401; and Erie Canal, 286; harbor at, 35°> 35 2 > 354; location of, 405; water supply of, 302 Niagara Falls, 289 Nile River, 268, 269; delta of, 242 Nitrate deposits, 121 Nitrogen, 28, 29-30; in sea-wate_r, 144; compounds in soil, 29, 170 Nomads, 104, 326, 332, 333 North America, area and population in tropics, 98; best use of lands of, 174; commerce of, 140, 141; general fea- tures of, 25; glaciation of, 252 Northers, 90 Norway, 51, 121, 134, 137, 256, 314, 34i Oases, 334 Oats, 128, 129, 362; climate for, 121, 362; distribution of, 129, 362 Ocean areas, 20, 98, 113, 142 Ocean basins, 19; and continents, 19- 20 Ocean currents, 145, 148-152; and cli- mate, 51, 150; cold, 145, 150; equa- torial, 149, 150; and isotherms, 51; map of , 151; warm, 145, 150 Oceans, 140-159; area of, 20, 142; chief source of water vapor, 57; depth of, 19, 143; distribution of, 98, 99, 113, 114, 115, 141; exploration of, 142; ice on, 246; importance of, 140; land areas tributary to several, 23; life of, 156-158; materials of bottom, 142; topography of bottom, 143; trade on, 34i Ohio River, 220, 274, 302 Oil. See Petroleum Old topography, 226, 227 Olives, 119 Omaha, 302, 328, 380, 385 Oozes, 142 Oranges, 119, 297 Oregon Trail, 220, 309 Ores, 212, 315; mined in U. S., 377 Outwash plain, 266 Oxygen, of the air, 29, 30, 161; in sea- water, 144, 156; in soils, 169, 170 Oyster fisheries, 376 Ozone, 29 Packing industry, 328, 380, 385 Palestine, 2, 166 Panama Canal, 191, 287, 355 Paper and printing, 384, 388 Parallels, 8 Pastoral tribes, 104, 326, 327, 332 Pelee, 192, 197 Peneplains, 227 Penguins, 136 Peoria, 277, 389 Perihelion, 7 Peru, 77, no, 121 Petrified wood, 213 Petroleum, 178-179; and manufac- turing, 382; produced in U. S., 179, 377 Philadelphia, 273, 286, 302, 352, 355, 382, 383, 385, 386, 401, 403, 404 Philippines, 44 Phosphates, 1 70-1 71; produced in U. . S -' 377 Piedmont alluvial plain, 236 Piedmont glaciers, 249, 251 Piedmont Plateau, 21; early population of, 392; soils of, 173 Pig iron produced in U. S., 377 Piracy of streams, 233 Pittsburgh, 275, 276, 278, 386, 401 Plains, 21, 322-340; advantages of, 322; classes of, 322; contrasts among, 21, 323; density of population in, 323; life of, 324-340 Planets, 4, 5 Plant life, of Antarctic regions, 135; of Arctic regions, 137, 336; de- pendence on ground-water, 207; in deserts, 65, 107, 330; on mountain slopes, 107, no, 313; in the sea, 156- 158; and soil formation, 164; in the temperate zones, 119, 121, 126, 127, 128, 129, 131; in the tropical zone, 100, 101, 103, 104, 107, no; and water vapor of air, 57 Plateaus, 21, no, 319-320 Pleasure resorts, 131, 317, 404 Polar circles, 15 Polar regions, climate of, ^7, 133-138; extent of, 133 Poles, 6; magnetic, 18; seasons at, 14 INDEX 4i5 Polyps, 157, 158 Pompeii, 196 Population, center of, in census years, 394; distribution of, 208, 392-399; engaged in agriculture, 357; factors affecting density, 392; maps, 264, 281, 393, 395, 398, 400; and rainfall, 76, 399; rural vs. urban, 383, 399; of the tropics, 98, no; at various alti- tudes, no, 399 Pork-packing, 385 Portland cement, 176, 262 Porto Rico, 92 Potassium, in soil, 169, 170 Potatoes, no, 121, 365 Pottery, manufacture of, by Indians, 333 Poultry and eggs, 370 Prairies, settlement of, 173, 284, 394; soils of, 173 Precipitation, 64, 76; and altitude, 77, 90, 106, 131, 334; average on lands, 57; in California, 77, 79; and density of population, 399; factors determin- ing, 76; and evaporation, 64; on mountains, 77, 79, 131; in polar regions, 135; in trade- wind zones, 77, 105; in U. S., 77-79, 124; for the world, 78; in zones of westerlies, 77 Pressure of air, 66; and altitude, 66; distribution of, 67; effects on man, in; representation of, on maps, 67 Pygmies, 339 Pyrenees, 307; people of western val- leys, 311 Quarrying, 376 Quebec, 405 Radiation, 38 Railroads, accidents on, and fogs, 62; and cattle industry, 328; competition with waterways, 268, 278; develop- ment of, 397; freight rates, 268; and growth of cities, 402-403; problems of, in equatorial regions, 104; pro- jected across Sahara, 335; routes of, in rugged regions, 228, 309; and snowslides, 131; and standard time, 11; trans- Appalachian, 308; of the U. S., 396 Rain, 64; how disposed of, 205 Rainbow, 95 Rainfall, affected by altitude, 77, 90, 106, 131, 334; and agriculture, 59, 76, \ Rainfall — continued 80, 119, 128, 129, 291; annual, of world, 78; in the desert, 106, 108, 334; distribution of, 77-79; of marine climates, 120; of the Mississippi Basin, 79, 85; in polar regions, 135; and thunder-storms, 95; in trade- wind belts, 77, 105; in tropical zone, 101, 102, 105, 106, 108; of the U. S., 77-79,85, 124; variation in, 79; and winds, 76, 85; in zones of westerly winds, 77 Rapids, 230 Reclamation, of arid lands, 291-298; of lake lands, 262, 297, 301 ; of swamp lands, 300-301 Reclamation Service, 298 Red clay, 142 Reefs, 348; coral, 158 Refrigerator cars, 365, 379 Reindeer, 336 Rejuvenation of streams, 233 Relief features, 19 Relief maps, 15 Rhine River, 270; valley, 270, 309 Rhone River, 270, 352; valley, 309 Rice, no, 172, 339, 363 River navigation, 268-279; decline of, 278; development of, 268, 275; present traffic, 278 River system, 225 River valleys and human life, 219 Rivers, as boundaries, 240, 274; com- mercial cities on, 239, 401, 402; effect of, on salinity of sea- water, 145; effect of, on temperature of sea-water, 146; of foreign countries, 269-271; ice of, 246; and shore-lines, 344; tides in, 153; of U. S., 271-279; work of, 215-245 Rock waste, 160 Rocky Mountains, as barriers, 309; early settlements in, 397; fur trade in, 318; and precipitation, 79; soils in, 174 Russia, 2, 122, 123, 130, 246, 269, 32:, 327, 365 Rye, 44, 59, 121, 129, 363 Sahara, 59, 77, 106, 107, 202, 333, 334, 335 St. Louis, 47, 277, 302, 318, 328, 383, 389, 402; tornado at, 97 St. Pierre, 197 Salmon industry, 376 4i6 INDEX Salt, 144, 183; deposits of, 126, 144, 183; and early settlement of Interior, 183, 394; produced in U. S., 377; of sea, 144, 212 San Francisco, 47, 352, 401; earthquake at, 188, 189 Sand, abrasion by, 201; deposits of, 165, 202; for making glass, 390; as water carrier, 302 Sand bars, and navigation, 237 Sandstone, 176; soils from, 164, 171; as water bearer, 302 Satellites, 4 Saturation of air, 58 Sea. See Oceans. Sea-breezes, 74 Sea-island cotton, 363 Sea-level, changes of, 185, 186 Sea-water, composition of, 144; gases in, 144; movements of, 145, 146, 147-156, 197; temperature of, 145, 146 Seal fisheries, 137, 158, 376 Seasons, 12-15, 3 6 ~37, 4i~435 in high latitudes, 43; in low latitudes, 42, 101, 102; in middle latitudes, 41, 116 Sediment, amount carried to sea, 212, 217; how carried, 216; of the sea- bottom, 142 Semi-arid climate in temperate zone, 123, 126 Semi-arid regions, 126, 173, 326; life in, 127, 326-329 Sensible temperature, 58, 100 Shackleton expedition, 135 Shale, soils from, 164; as water bearer, 302 Sheep, 368 Shipbuilding, 172, 384, 390 Shooting stars, 28 Shore currents, 148 Shore-lines, and harbors, 341-356; mod- ification of, 343 Siberia, 47, 123, 134, 136, 137, 246 Sierra Nevada Mountains, climatic barriers, 77, 120, 311 Silk manufacture, 381, 387 Sills, 198 Silver, 181, 388, 397; production in U. S.,377 Simoons, 201 Sirocco, 90 Slates, 176 Slavery, in Alabama, 325; and cotton culture, 171, 325, 364; favored by climate of South, 2, 171 Slumping, 213 Smelting industry, 182, 381 Snoqualmie Falls, 289 Snow, 246; fields, 45, 135, 247; and temperature of air, 45; value of, 54, 76, no Snowfall and altitude, 131 Snowslides, damage by, 131 Soil, 160, 161-171; alkaline, 126, 293; of arid regions, 126, 293; classes of, 164; conservation of, 168; enrichment of, 170; evils resulting from erosion of, 167; factors determining fertility, 171; and frost, 53; human responses to, 324; importance to man, 161; making of, 161-164; plant foods in, 169-171; prevention of erosion of, 168; pro- duced from volcanic materials, 193; provinces in U. S., 1 71-175; of re- claimed swamps, 300; removal of, 166-169; waste of, 167 Solar system, 4 Solstices, 7, 13, 36, 41 ''Soo Canal," 282 South America, area and population in temperate zone, 113; area and popula- tion in tropics, 98; distribution of population in, in; general features of, 25; rivers of, .271; trade with U. S., 140, 141 South Pass, 309 Spain, 307 Spanish Trail, 228 Spits, 349 Spring tides, 155 Springs, 208, 301 St. Anthony's Falls, 288 Standard time, 11 Steamboat trade on Mississippi, centers of, 276 Steamboats, 275, 281, 284, 341; losses of, 237 Steamship routes, vary with seasons, 149 Steamships, lost at sea, 62, 94, 149 Stock-raising, in mountains, 314; in the early western settlements, 274; on the Great Plains, 327, 328, 329 Storms, 81, 83; destruction by, 91-92, 96, 97 Streams, accidents to, 233; as boun- daries, 240, 274; deposition by, 234; and distribution of population, 394; importance of, in history of U. S., 273; meanders of, 239; as sources of water supply, 302; work of, 215-24- INDEX 4i7 Submerged valleys, 143 Subsoil, 160 Sub-tropical climates, 117; crops of, 119 Sudan, 104, 107, 335 Suez Canal, 282, 355 Sugar, 366, 382 Sugar-beet, 297, 366 Sugar-cane, no, 366 Sun, apparent motion of, 14; heat of, as source of power, 106; nature of, 4; source of heat of atmosphere, 34; and tides, 147, 155-156; worship of, 108 Sunshine, and cloudiness, 64 Sunstrokes, 58, 90, 100 Swamps, reclamation of, 171, 241, 300- 301 Swine, 368, 369 Switzerland, 44, 249, 250, 290, 310, 311, 312,314, 316 Talus, 163 Tanning industry, 389 Temperate zone, northern, seasons in, 116, 122; temperature range in, 116, 122 Temperate zones, area of land in, 113; climate of, 1 13-132; extent of, 113; population of, 113, 114 Temperature, and air pressure, 67; and altitude, 44; changes and rock-split- ting, 162, 163; daily range of, 52; distribution of, 37-40; effect of snow on, 45, 54, 76; and evaporation, 58; of land and water, 40, 50; maximum, 35; minimum, 35; modified by ocean currents, i5o;inpolarregions, 133, 135, 136; range of, 47, 52, 54; representa- tion of, on maps, 45; of the sea, 145; seasonal range of, 54; in temperate zones, 115, 118, 120, 122, 125, 130; in tropical zone, 99-100, 102, 103, 105 Terraces, alluvial, 243; of drift, 266; wave-cut, 347 Terracing, for agriculture, 168, 312 Textile manufactures, 60, 384, 387 Thermometers, 34-35 Thunder-storms, 95, 102 Tidal water power, 156 Tides, 148, 152-156, 271 Till, 257 Timber-line, 131, 313 Tobacco, 170, 172, 365 Tobacco products, 384, 390 Tornadoes, 8s, 96 Trade-wind climate, 77, 105-108; and life, 107 Trade-winds and commerce, 107 Tree-line, 313 Tropical climate, 98-1 1 2 ; characteristics of, 98; and disease, 103, 104; and life, 100, 101, 103; 104, 107; types of, 101 Tropical forests, animals of, 338; com- merce of, 104, 339; life in, 3377339 Tropical regions, area of land in, 98; climate of, 98-112; extent of, 98; future of, 112; natives of, 3, 100, 103, 104, 107, no, in, 337; population of, 98, no Tropics of Cancer and Capricorn, 15 Truckee Pass, 309 Tundras, 336 Turpentine, 325, 380 Typhoid fever, 207 Undertow, 148 United States, cities of, 399-405; climates of, 118, 120, 125-128, 130; distribution of population in, 392- 399; effects of glaciation in, 258-266; exports from, 140; imports to, 141; irrigation in, 291-298; railroads of, 396; rainfall of, 124; soils in provinces of, 1 71-175; water power in, 288- 290; vaterways of, 271-287; wet lands of, 300-301 Valley system, 225 Valley trains, 266 Valleys, as centers of human activity, 219; changed by glaciers, 255; growth of, 220-224; stages in history of, 225 Vegetables, 297, 365; canning of, 379, 386 Vegetation, of Antarctic region, 135; of Arctic region, 43, 137, 336; in deserts, 65, 107, 330; on mountain slopes, 107, no, 313; of oases, 334; in the tropics, 100, 101, 103, 104, 107, itc c ' Plant Life Vehicles, manufacture of, 3S - Veins, 212, 315 Venezuela, 104 Vesuvius, iq6 Volcanic cones, 20, 143, 193-195, 305, destruction of, 194 Volcanoes, 191-197; destructiveness of, 196; distribution of, 193; number of, 193; products of, 192; in sea, 20, 143, 148, 193 4i8 INDEX Volga River, 270 Vulcanism, 191-199; causes of, 199 War of 1812, 242, 272, 286 Washington, D. C., 404 Water power, 288-290; afforded by- hanging valleys, 256; amount devel- oped, 288; distribution in U. S., 289- 290; furnished by mountain streams, 121, 248, 256, 319; furnished by tides, 156; future importance, 289; and manufacturing, 288, 381; in other countries, 290; of Ottawa Valley, 281 Water supply, 207, 301-303 Water table, 205 Water-gaps, 232 Water vapor, 29, 31-32, 161; and air pressure, 67, 72; circulation of, 57; functions of, 56; sources of, 56-57 Wave-cut terraces, 347 Waves and wave action, 148, 345, 347, 348 Weather Bureau, 53, 75, 81; value of work of, 53, 94 Weather forecasting, 81, 93 Weather maps, 81, 82, 86, 87, 88; interpretation of, 83 Weathering, 161 Wells, artesian, 209; and domestic water supply, 210, 302; and irrigation, 210; pollution of waters of, 207 West Indies, cyclones of, 91, 92 Westerly winds, rainfall in zones of , 77 Whaling industry, 107, 137, 158, 376 Wheat, no, 119, 127, 129, 360-362; climate for, 59, 121, 128; distribution of, 128, 129, 361; production of, 361 Whiskey, 360, 389 Wills Creek, narrows of, 232, 403 Wind, 72; velocity of, 75, 84, 87; work of, 201-205 Wind-zones, 73-74 Wind-gaps, 234 Winds, 72-76; causes of, 72, 74; deflec- tion of, 73, 84; and distribution of temperature, 51; easterly, 74; and evaporation, 58; hot, 65; importance of, 72; and movements of sea- water, 147; periodic, 74; planetary, 74; pre- vailing, 74; and rainfall, 76, 77; trades, 74, 101, 105; westerlies, 73 Wine, manufacture of, 379, 389 Wood-pulp, 288, 380 Wood- working industries, 380 Wool clip of U. S., 368 Woolen manufactures, 381, 387 Yang-tze River, 269 Yellow fever, 103, 128 Youthful topography, 226 Zinc, 182; produced in U. S., 182, 377 REFERENCE BOOKS The following list contains some sixty books on geography and related subjects which might well be in a high school library. If a reference library of twenty- five books were to be chosen from the list, those which are starred would be sug- gested as most suitable. If only ten books were to be chosen, those marked with two stars would be suggested. Blackwelder and Barrows: Elements of Geology. New York: American Book Co., 1911. Price, $1.40. Presents briefly the fundamental principles of geology; helpful in answer- ing questions involving the relations of physiograph}' and geology. Brigham: Commercial Geography. Boston: Ginn and Co., 1911. Price, $1.35. Discusses at length wheat, cotton, cattle industries, iron, and coal, deducing from these the principles of commercial geography. Of commercial nations the United States is treated most fully. Many good maps and diagrams. Brigham: Geographic Influences in American History. Boston: Ginn and Co., 1903. Price, $1.25. Traces in a suggestive way the effects of the larger geographic features of the United States on many leading events in its history. ** Chisholm: Handbook of Commercial Geography. New York: Longmans, Green and Co., 191 2. (Revised edition.) Price, $4.80. A great store of information about commodities of commerce and the commercial geography of all countries. Especially valuable for reference. Coman: The Industrial History of the United States. New York: The Macmillan Co., 1905. Price, $1.60. Outlines the growth and expansion of the commerce and industries of the United States. ** Davis: Physical Geography. Boston: Ginn and Co., 1898. Price, $1.25. Treats especially the life history of land forms. Excellent for discussion of coastal plains, stages of river development, and climatic control of land form-.. Day: A History of Commerce. New York: Longmans, Green and Co., 1907. Price, $1.75. Mainly historical, but traces many relations between earth features and the development of commerce since the earliest times. Dondlinger: The Book of Wheal. New York: Orange Judd Co., 191 2. Price, $2.00. An exhaustive discussion of the factors affecting the distribution of the world's wheat regions, together with all other aspects of wheat as a crop and a commodity of commerce. Dutton: Earthquakes. New York: G. P. Putnam's Sons, 1904. Price, $2.00. Detailed, scientific treatise, covering the nature of earthquakes, their causes, the phenomena associated with them, and the leading features of the earthquake regions of the world. Geikie, James: Earth Sculpture. New York: G. P. Putnam's Sons, 1898. Price, $2.00. Devoted entirely to the origin and development of land forms. Especially good for the effects of geological structure on topographic forms, and for glacial action. REFERENCE BOOKS * Geikie, Sir A.: Elementary Lessons in Physical Geography. New York: The Macmillan Co., 1900. Price, $1.10. A simple and entertaining description of the more important aspects of physical geography. Geikie, Sir A.: Scenery of Scotland. New York: The Macmillan Co., 1901. Price, $3 .25. Most interesting reading, full of information about processes of weather- ing and erosion, and particularly about features due to glaciation. Has a good chapter on the influence of physiography on the people of Scotland. *Gifford: Practical Forestry. New York: D. Appleton and Co., 1902. Price, $1.20. Simple, effective statements of the relations of forests to soils and stream flow, the factors affecting the distribution of forests, and the industrial im- portance of forests. **Herbertson: Man and his Work. New York: The Macmillan Co., 1902. Price, 60 cents. A very suggestive discussion of man's relations to his surroundings. Herbertson: Descriptive Geographies: one volume each for North America; Central and South America; Europe; Africa; Asia; Australia and Oceanica. New York: The Macmillan Co., 1902-1903. Price, 70 to 90 cents per volume. Collections of the best descriptions of typical sections of the different continents. Interesting and instructive supplementary reading. Hogarth: The Nearer East. New York: D. Appleton and Co., 1902. Price, $2. 00. A regional study of Balkan Europe, Western Asia, and Egypt; considers fully the physiography and climate of these regions, and their relations to the life of the people. *Holdich: India. New York: D. Appleton and Co., 1905. Price, $2. 50. Covers thoroughly every phase of the geography of British India. Espe- cially good for the study of life conditions in a monsoon region. *Hunt: The Cereals in America. New York: Orange Judd Co., 1908. Price, $i.75. Excellent for details concerning soil and climatic requirements of cereal crops. Johnson, E. R.: Ocean and Inland Water Transportation. New York: D. Apple- ton and Co., 1906. Price, $1.50. Discusses fully the commercial importance of inland waterways and the chief problems in their use for navigation. * Johnson, W. E.: Mathematical Geography. New York: American Book Co., 1907. Price, $1.00. A standard reference for all matters concerning the form, motions, and dimensions of the earth, and for tides and map making. Johnstone: Conditions of Life in the Sea. New York: G. P. Putnam's Sons, 1908. Price, $3.00. Describes the plants and animals of the sea, their distribution, and their uses by man. Good also for methods of exploration of the sea and the main features of the North Atlantic Ocean. * Keltie (Editor): The Statesman s Yearbook. New York: The Macmillan Co., 1863-1911. Price, $3.00. An annual publication giving current statistics for all countries. Gives also brief statements about government, education, currency, defence, etc., for most countries. *KiN(;: Fanners of Forty Centuries. Madison, Wis.: Mrs. F. H. King, 191 1. Price, $2. so. Describes agricultural systems of China and Japan, and tells much about the effects of geography on the life of the people. REFERENCE BOOKS **King: The Soil. New York: The Macmillan Co., 1907. Price, $1.50. An exhaustive, but simple, description of soil types, their formation, and characteristics. Especially good for discussion of soil moisture. **King: Irrigation and Drainage. New York: The Macmillan Co., 1909. Price, $1.50. Treats in detail the relation of water to plant growth, the soil and climatic conditions which make irrigation necessary, the effectiveness of conserving water by tillage, and the general problems of irrigation farming. Wet lands and their drainage are considered more briefly. Kirchoff: Man and Earth. New York: E. P. Dutton and Co., (n.d.p.). Price, 75 cents. A small book with many good examples of man's relations to his surround- ings, especially in Great Britain, the United States, Germany, and China. Little: The Far East. New York: D. Appleton and Co., 1905. Price, $2.00. A regional study of China and Japan along the same lines as Hogarth's "The Nearer East" (q.v.). Lyde: Man and his Markets. New York: The Macmillan Co., 1901. Price, 50 cents. Good material on many of the larger aspects of commercial geography, presented in a new way. *Mackinder: Britain and the British Seas. New York: D. Appleton and Co., 1902. Price, $2.00. A comprehensive study of every phase of the geography of the British Isles. Especially valuable for the ten chapters tracing the effects of physical conditions on the development of the four countries. Mead: Story of Gold. New York: D. Appleton and Co., 1906. Price, 75 cents. Describes the conditions of occurrence of gold, the methods of mining, the chief gold regions of the world, and the importance of gold in industry and coinage. Milham: Meteorology. New York: The Macmillan Co., 1912. Price, $4.50. Embodies the latest results of the investigation of atmospheric phenomena. Especially good on atmospheric moisture and irregular winds. ** Mill (Editor) : The International Geography. New York: D. Appleton and Co., 1905. Price, $3.50. _ A handbook giving the main geographical aspects of all countries, by seventy authors. Mill: The Realm of Nature. New York: Chas. Scribner's Sons, 1892. Price, $1.50. An elementary and stimulating treatment .of physiography from the English viewpoint. Traces the interdependence of the different aspects of nature. * Moore, W. L.: Descriptive Meteorology. New York: D. Appleton and Co., 19 10. Price, $3.00. A general text, less advanced than Milham (q.v.); especially good for methods of weather forecasting. An appendix of 45 valuable charts. *Moulton: An Introduction to Astronomy. New York: The Macmillan Co., 1906. Price, $1.60. A clear, comprehensive exposition of modern astronomy. Especially good for discussion of the evolution of the solar system, and the planetary relations of the earth. Newell: Irrigation. New York: T. Y. Crowell and Co., 1906. Price, $2.00. Describes in detail the conditions of arid United States, the supplies of water, the methods of storing and distributing water, irrigation law, the irrigated regions of the West, and the relation of irrigation to crops in the other parts of the country. REFERENCE BOOKS Partsch: Central Europe. New York: D. Appleton and Co., 1903. Price, $2.00. Deals mainly with Germany and Austria-Hungary in a manner similar to Hogarth's "The Nearer East" (q.v.). Russell: North America. New York: D. Appleton and Co., 1904. Price, $2.00. Treats in detail the coasts, topography, geology, and climate of the United States, and considers less fully the other parts of the continent. Discusses also distribution of plant and animal life. Russell: Glaciers of North America. Boston: Ginn and Co., 1897. Price, $1.75. Same type of book as Russell's "Rivers of North America" (q.v.). * Russell: Rivers of North America. New York: G. P. Putnam's Sons, 1898. Price, $2. oo. An extensive treatment of the characteristics and work of streams. Good descriptions of the main river systems of the continent. Russell: Volcanoes of North America. New York: The Macmillan Co., 1897. Price, $4.00. Same type of book as Russell's "Rivers of North America" (q.v.). Ries: Economic Geology. New York: The Macmillan Co., 1910. Price, $3.50. Explains the formation and distribution of mineral deposits. Much information about important regions of mineral production. ** Salisbury: Physiography: Briefer Course. New York: Henry Holt and Co., 1908. Price, $1.50. A general text which emphasizes physiographic processes and their effects on land forms. **Semple: Influences of Geographic Environment. New York: Henry Holt and Co., 1911. Price, $4.00. Deals mainly with human responses to geographic conditions in typical environments. Large amount of excellent material for supplementary reading. *Semple: American History in its Geographic Conditions. Boston: Houghton, Mifflin and Co., 1903. Price, $3.00. Traces the influence of geography on United States history. Enriches the study of either subject. Shaler: Aspects of 'the Earth. New York: Chas. Scribner's Sons, 1889. Price, $2.50. A popular account of some of the larger features of earth science. Very suggestive on "Caverns and Cavern Life" and on "The Origin and Nature of Soils." * Shaler: Man and the Earth. New York: Fox, Duffield and Co., 1905. Price, $1.50. States in an interesting and convincing way man's dependence on the resources of the earth, and the need for conserving them. Shaler: Nature and Man in America. New York: Chas. Scribner's Sons, 1893. Price, $1.50. Discusses the influences of environment on man's progress in civilization, and especially the effects of the physical features of North America on the set- tlement and development of the continent. Shaler: TheStory of Our Continent. Boston: Ginn and Co., 1897. Price, 75 cents. A short, simple account of the geologic development of North America, the present condition of the continent, and of some of the larger effects of geography on the people. Shaler: Sea and Land. New York: Chas. Scribner's Sons, 1894. Price, $2.50. Features of coasts and oceans, with their influences on man. Excellent for material on harbors. Smith: The Story of Iron and Steel. New York: D. Appleton and Co., 1908. Price, 75 cents. A non-technical description of the industry and its development, par- ticularly in the United States. REFERENCE BOOKS * Stanford (Publisher) : Compendium of Geography and Travel. Twelve volumes. London: Edward Stanford, 1895-1908. Price, $5.50 per volume. Volumes for each of the continents, describing their physiography, climate, resources, and something of the development of each of their countries. Surface: The Story of Sugar. New York: D. Appleton and Co., 1910. Price, $1.00. Discusses the natural conditions required for sugar cane and sugar beets, the sugar regions of the world, the processes of manufacturing sugar, and its commercial importance. Taylor: Australia: Physiographic and Economic. Oxford, Eng. : Clarendon Press, 191 1. Price, 90 cents. An excellent analysis of the natural regions of Australia and their relations to the economic development of the country. Many good maps and diagrams. Tower: The Story of Oil. New York: D. Appleton and Co., 1909. Price, $1.00. An account of the development of the petroleum industry, mainly in the United States. Discusses also commercial and industrial importance of petroleum products. ** Van Htse: Conservation of Natural Resources in the United States. New York: The Macmillan Co., 1910. Price, $2.00. Considers our resources in minerals, forests, waters, and lands; the ways in which their use now involves needless waste; and the remedies which should be adopted to check these wastes. Outlines the recent Conservation Movement. **Ward: Climate. New York: G. P. Putnam's Sons, 1908. Price, $2.00. A full description of all the important types of climate, and of their influence on various human activities. Warren: Elements of Agriculture. New York: The Macmillan Co., 1910. Price, $1.10, Discusses the conditions of plant growth, the mineral plant foods, the raising of the chief farm crops and of live stock, and the problems of farm management. *Widtsoe: Dry Farming. New York: The Macmillan Co., 1911. Price, $1.50. Explains the principles of conserving soil moisture, the water requirements of different crops, the conditions in regions of scanty rainfall, and states what can be done to reclaim these regions for agriculture. Willis: Agriculture in the Tropics. Cambridge, Eng.: Cambridge University Press, 1909. Price, $2.50. States concisely the relations of soil, climate, and labor to farming in tropical lands, with accounts of the chief tropical crops. Examples drawn mainly from Ceylon and India. GOVERNMENT PUBLICATIONS Much supplementary material may be found in government publications, some of which are noted below, with the addresses from which they may be ob- tained. Lists of government publications on different topics, as geography, may be obtained by addressing: The Superintendent of Public Documents, Washington, D. C. Bureau of the Census: Reports and Bulletins of^ the Census. These furnish statistical and other data concerning population, industries, etc., in the United States. Address: The Director, Bureau of the Census, Washington, P. c. REFERENCE BOOKS Department of Agriculture: (i) Yearbook of the Department of Agriculture. An annual publication containing detailed statistics of agriculture for the United States and general statistics for foreign countries. Also has special articles bearing on farm industries. Obtainable through local representatives in Congress. (2) List of Publications. A monthly circular giving titles of current publications of the Department, including Bulletins and Circulars of the Forestry Service, and publications of the Weather Bureau. Address : The Editor and Chief, Division of Publications, Dept. of Agriculture, Wash- ington, D. C. U. S. Geological Survey: (i) Topographic maps of many parts of the country; (2) Mineral Resources of the United States, an annual publication; (3) Annual Reports; (4) Professional Papers; (5) Bulletins; and (6) Water Supply and Irrigation Papers. Many of the above contain much supplementary material for work in geography. The Press Bulletins of the Survey are leaflets issued at frequent intervals, which contain current items of interest, especially in regard to economic aspects of the work of the Bureau. Address : The Director, U. S. Geological Survey, Washington, D. C. Department of Commerce and Labor: (i) Monthly Summary of Commerce and Finance; (2) Commerce and Navigation of the United States; and (3) Com- mercial Relations of the United States. These contain elaborate statistical data concerning the foreign commerce of the country. The last named, an annual volume, discusses our trade with each foreign country. The volume on Commerce and Navigation (annual) gives statistics by countries, com- modities, and ports of entry or shipment. Address: The Secretary, Depart- ment of Commerce and Labor, Washington, D. C. MAGAZINES The geographical magazines noted below are important helps to students and teachers of geography: Bulletin of the American Geographical Society. New York: Broadway and 156th Street. $5 per year. Geographical J our nal. London: Royal Geographical Society. 27 s. per year. Journal of Geography. Madison, Wis.: University of Wisconsin.- $1 .00 per year. National Geographic Magazine. Washington, D. C: 16th and M Streets. N. W. $2 . 50 per year. Scottish Geographic Magazine. Edinburgh: Royal Scottish Geographical Society. 18 s. per year. a P OF NORTH AMERICA tt :-i Plate PHYSICAl ^P OF NORTH AMERICA. m Plate MAP OF THE 100 Lomritudc ITED STATES. u "(fj tadisoA • IJansink® Detroit, /. ,. J^C^^'^'^Sc^ l\ \ £*£££< "He DDcsMoineJ ^t<»^R^ iSt.Joseph 3 City 1 .*7i >eoxia I ■■■/Sprin!§ewi£SS£5£- • W L I N O I SFTerre Haute 1\ /^ no i l.St. Louis •WEST \o/ . I Jefferson©^ 7^>7l / *,xifi ilEE. \ H ML^/^««Sr i City &$*> V Evansvilfte^O^WLouiA^lK.^ y i^A^Y. T MISSOURI Ojoplin © ^ARKANSAS Little Rockil O T jO I Hot Springs v<»^ j V _^|l MISSISSIPPI} } ©Nashville i 5^./ N ORTBS\ CA:t S J*&%^ T e\n n e s s gpV' xT^^ft — TT /^ Greenwich 90 PHYSICAL MAP Oi SOUTH AMERICA. PLATE III. • AMI t COMFAH< OF EUROPE. Plate IV. ■25 30 35 *? *\ ~rV 5 \*itf>*l2\ ^^"^ \ * ^CV^l 70 75 80 MlY *lw!\ >< \. GO ^M&^^^y^ Wrk ^^\ \. 55 °liig*_-— -*r~ — vvvC^ ^-o ^A \ V?j ' _J^Px »— ( \ z> \~~ j$? ^\ 5M ^\k^™^ Vridess^l^r^ \n/^ao//^* \*JL(^ L l\ £ f \^*o ~^S^M_hi lite? »»«^_Y ))// <7 /^^ ^"^^7ii ^35 ^Scs$s3a>y 1 C_T) ^k^ — " \ EXPLANATION OF COLORS Above 6000 feet 3000 to 6000 feet 1500 to 3000 feet 600 to 1500 feet Sea Level to 600 feet ^^ llliJt? Depression below Sea Level ^\(i^4^Si\i \/l23p^5\ft" Sea depths below 100 fathoms colored in darker blue -#~ "^p"" S /2j<> -* ~ SS 40 4 5 ► »«[ (► fcAKTHC'lOWSVk'S COMPARATIVE ATIAJ. .ONDC- »f KlE.'Om AM 3F ASIA Bering Strait ggS ^ PLATE V. fcAL MAP OF AFRICA. Plate VI. PHYSICAL MAI] EXPLANATION OF COLORS T Above 6000 feet | 3000 to 6000 feet 1500 to 3000 feet 600 to 1500 feet Sea Level to 600 feet B Depression below Sea Level Sea depths below 100 fathoms colored in darker blue 00 200 390 400 590 60 English Statute Miles \ :» Longitude East 140 from Hr o> mi."' Ml KLEJOHK <••• F AUSTRALIA. Plate VII. FEB 17 1913