Physiography, for high schools

Front matter

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the publisher to a library and finally to you.

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to prevent abuse by commercial parties, including placing technical restrictions on automated querying.

Preface

Several good elementary books on Physical Geography have been published in the last decade or so, and some of them have met with popular favor deservedly. Yet ideas as to what a text-book on this subject should be vary so widely that there has been some demand for a text written on lines which differ from those of any of the books now before the public. The authors of the books already pubhshed would, no doubt, differ from the writer of this as much as he differs from them, not only as to the plan which should be followed m a text-book for first or second year highschool pupils, but as to the points upon which emphasis should be laid and the objects to be attained. It is quite possible that the same book is not best for all teachers or for all pupils. The method of one book will doubtless continue to appeal to one teacher, and the method of another to another, and most teachers will probably get the best results from the book which appeals most strongly to them.

This book has been prepared with the purpose of letting the beginner into the method of the science with which the book deals, as well as with the purpose of conveying information to him. It has been prepared with the conviction that the child likes to reason and to follow reasoning, and that reasoning and following reasoning contribute more to his mental growth than the accumulation of great numbers of facts. It has been written with the conviction that the growth of the pupil is more important than facts about physical geography. To those who hold other views, this volume will not appeal.

The illustrations of the book should be regarded by the teacher as vital, and should be studied and interpreted as carefully as the tejct itself. These illustrations may well be supplemented by other

ill iv PREFACE

diagrams, photographs, lantern-slides, etc., and should be supplemented by trips to points of interest out of doors, and by such exercises in the laboratory as help (1) to develop new principles, or (2) to illustrate and enforce the principles already developed in the class-room. In the judgment of the ^Titer there is little place for laboratory work which does not contribute to these ends.

In teaching, every efficient teacher will do best, probably, to follow his own method, if he has one in which he has faith. But the author suggests that the method now much used, of talking over with the pupils the subjects as they come up, before assignments are made in the text, is, on the whole, a good one. The work of the class-room, so far as it is given to the text, should be directed toward seeing that the pupil has translated it into terms of realitii; or, to put it in another way, into terms of outdoors. On the other hand, it is a mistake to assume that any one plan should be followed always. Variations of method are often to be encouraged.

Directions for laboratory work do not appear in the text, nor is laboratory material suggested. The omission is intentional, not because laboratory work is regarded as unimportant, but because, in the author's judgment, the effect upon the pupil is best when the laboratory work is suggested by the teacher. In this case it may be adapted to each class, and developed along the lines and to the extent which the apparatus and the time available permit. It is the purpose of the author to issue shortly a booklet on this subject, to accompany this text, — a booklet intended for the teacher, not for the pupil.

A few references are given at the ends of chapters. References to the more technical papers have been omitted for the most part. Further references, if desired by the teachers, can be found in the author's Physiography, Advanced Course, and in other published books on this subject.

The illustrations have been drawn from many sources, usually acknowledged in the text.

The author desires to express his great obligations to Dr. Cowles and Mr. Adams, who have been generous enough to contTv'bute Chapter XIX.

PREFACE V

Acknowledgments are due to Mrs. J. P. Cook and Miss Evel3rn Ifata, who have read parts of the text, and who have made valuable suggestions as to its adaptation to pupils of the grades for which it is intended.

UNiYKRsnT OF Chicaoo, November, 1907.

^fTRODUCnON

Contents

PAQB 3

Part I The Lithosphere Chapter

I. Relief Features 5

II. The Work op the Atmosphere 27

III. Ground-water ........ 45

rV. The Work of Running Water .o ... 73

V. The Work of Snow and Ice 149

VI. Lakes and Shores ....... 213

VII. VULCANISM 238

VIII. Crustal Movements ....... 275

IX. Terrestrial Magnetism ...... 301

Part III The Atmosphere

XI. General Conception of the Atmosphere . . . 323

XII. Constitution of the Atmosphere ..... 327

XIII. Temperature of the Air ...... 333

XIV. The Moisture cf the Air ...... 359

XV. Atmospheric Pressire ...... 374

XVI. General Circulation of the Atmosphere . . . 386

XVII. Weather Maps 402

XVIIL Climate 440

XIX. Physiography and its Effects on Plants and Animals 462

By Henry C. Cowles and Charles C. Adams.

Part IV

XX. Ten Ocean 488

PLATES

PAO«

L A narrow coastal plain in Oregon 12

n. A mountain ridge in Pennsylvania .... 16

III. Dunes in Kansas, Indiana, and Nebraska .... 32

IV. Streams disappearing in sand, gravel, etc., Nevada 76 V. The ^feramec River, Missoim, widening its valley by lateral

VI. The flat of the Mississippi River between Wisconsin and Iowa 91

VII. Meanders of rivers; Missouri ...... 92

VIII. Youthful valleys and topography. Shore of Lake Michigan,

north of Chicago ....... 100

IX. The canyon of the Yellowstone River, Wyoming . . 101

X. Mature topography (Ky.) and old-age topography (Kan.) . 102

XI. Niagara gorge ........ 108

XII. Mountain ridges formed by the outcropping edge of a hard

layer. Near Denver, Colo. ..... 109

XIII. A piedmont alluvial plain in southern California . . 128

XIV. The alluvial plain of the Platte River in Nebraska . 129 XV. The glaciers on Glacier Peak, Washington . 180

XVI. Glaciated mountain valleys in the Bighorn Mountains, Wyoming ......... 181

XVII. An ill-drained plain in Wisconsin ..... 192

XVIII. A well-drained plain in Kansas ..... 193

XIX. Lakes along the coast of Martha's Vineyard, Mass., and on

the coastal plain of Florida ...... 214

XX. Delta at the end of Seneca Lake, New York . 215 XXI. Coast-line in California, developed chiefly by wave erosion,

and a land-tied island on the coast of Massachusetts 234

XXII. Isothermal chart for the year 348

XXIII. Isothermal chart for January ...... 350

XXIV. Isothermal chart for July 351

Introduction

Definition. Physiography deals with (1) the solid part of the earth, the lithospherey (2) the liquid part of the earth, the water or hydrosphere, and (3) the gaseous part of the earth, the air or aimosphere. The land, the water, and all animal and plant life are affected by the atmosphere, while the water is related in many w^ays to the land and to the life of the globe. As to the lithosphere, physiography has to do with its surface only, a surface which has not always had its present form. It has been shaped and re-shaped by winds, rivers, waves, and ice. Volcanic forces, too, have had their part in building it up and tearing it down, and over and over again the outer part of the earth has been warped and wrinkled. It is this ever-changing surface which concerns man and life generally; and physiography has to do chiefly with the surface of the lithosphere and with the relation of air and water to it.

Physiography and geology are closely related. The history of the earth has been written in the rocks for the student of geology, and physiography deals with the latest chapter of that history, the history of the present surface.

Physiography is also related to geography; for while geography is concerned w^ith the distribution of life and human industries, rather than with the physical relations of earth, air, and water, this distribution depends largely upon soil, climate, and natural resources. Physiography not only takes up the physical side of geography, but it also sets forth much of the latest and freshest chapter of geology, a chapter which can never be finished so long as the world continues to change.

Although the solid part of the earth, the water, and the air, seem very distinct from one another, they are in reality not so sharply separated as they seem. The larger part of the water is in the ocean, lakes, and rivers; but some of it has sunk into the soil and rocks, and a little of it is always to be found in the form of vapor, which we cannot see, in the air. So, too, a part of the atmosphere penetrates the soil and rocks of the land, and gases from it are dissolved in the water. Solid matter from the land is found in water, often making it muddy, and dust is always present in the atmosphere. In spite of this mingling, the boundaries between the lithosph^re, hydrosphere, and atmosphere are usually well defined.

Chapter I Relief Features

The surface of the earth consists of two great di\4sions, the land and the sea. The area of the sea is nearly three times that of the land, but the land is of greater interest to man, because it is his home.

The surface of the land is uneven. The lowest lands are below the level of the sea, and the highest point of land (Mt. Everest in the Himalaya Mountains) is between five and six miles above it. The unevenness, or relief j of the land surface is therefore not far from six miles. The sea bottom is also uneven, and its relief is a little greater than that of the land. Since the highest points of the 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 lUhosphere 18 almost twelve miles. If the surface of the lithosphere were even, there would be no land at all, for then the water of the ocean would cover the whole earth to the depth of about 9,000 feet.

The Great Relief Features

If the high lands of the earth were planed down, and if the material were spread over the low lands, so that all parts above the sea had the same height, the land would be a little less than half a mile above the sea. If the sea bottom were made smooth, the depth of the water everywhere would be about two and one-half miles. The continents are therefore nearly three miles higher, on the average, than the bottoms of the ocean basins. The continents and the ocean basins are the greatest relief features of the earth (Fig. 1).

About the continents as we know them, there is almost everywhere a belt of shallow water. The sea bottom below this shallow water is the continental shelf (Fig. 2), at the outer edge of which there is a steep slope down to the ocean basins. The continental

shelves really belong with the con tinents, not with the ocean basins.

These basins are more than full of water, and the overflow from them covers the lower parts of the real continents. If the areas of the continental shelves be added to the continents, the continents, or elevated parts of the lithosphere, would make up about one-third of the earth's surface, and the ocean basins the remaining two-thirds.

The ocean basins and the continents are irregular both in shape and distribution. The sunken tracts are far in excess in the southern hemisphere (Fig. 3), while the elevated areas are largely in the northern hemisphere.

The continents. The continents commonly recognized are (1) Eurasia (Europe and Asia), (2) Africa, (3) North America. (4) South America, and (5) Australia. Besides these five, Antarctica may be counted a sixth continent. Greenland, the largest remaining body of land, is regarded as an island.

The ^reat land areas are not connected, as any map of the earth or any f]:lol)e plainly shows. The sea, on the other hand, is continuous, th()u«!:h its parts bear separate names, as Atlantic, Pacific, etc. Grouping of the continents. The northern hemisphere contains more than twice as much land as the southern. If the earth be divided into two hemispheres, one with its center in England, and the other in New Zealand (Fig. 3), the first would contain about six-seventlis of all the land, and might be called the land hemisphere,

Fig. 1 . — Photograph of a relief globe, showing the North Atlantic Basin depressed notably below the continents about it. The vertical scale of the globe is exaggerated.

while the other would contain only about one-seventh of the land, and might be called the uaier 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 fourteenfifteenths 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 hun^an race.

TTTrr

Fig. 2. — 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 seen to be a continuation of the coastal plain.

Origin of relief features of the first order. The ocean basins and the continental platforms seem to have been very much as they now are, for millions of years. It is probable that the ocean basins have sunk below the continents, rather than that the continents ha\3

Fig. 3. — ^Land and water hemispheres.

been raised above the ocean basins. The reason for this belief is that the earth is cooling, and therefore shrinking, and shrinking means that the outside is getting nearer to the center. This muat

PHYSICXiRAPHY

Fig. 4. — Diagram representing the conception that the continentfl were lifted and the ocean basins Bunk by movement along definite sliding planes or fault planes. The dotted line may be taken to r3pre8ent a somewhat umform original surface, which may be looked upon as the surface before continents and ocean basins were developed. The diagram indicates that the continents have risen above this surface, while the ocean basins have sunk below it.

Fig. 5. — This diagram represents the same conception as Fig. 4, except that the movement was by bending, instead of faulting.

Fig. 6. — This diagram represents the same conception as Fig. 4, except that the continental part is represented as not having risen.

Fig. 7. — This diagram represents the same conception as Fig. 5, except that the continental segment has not risen.

Fig. 8. — This diagram represents the same conception as Fig. 6, except that both ocean basin and continental segment are represented as naving sunk below the original level, the former more than the latter.

result in a sinking of the surfac'e, though not necessarily at every point. The sinking of the depressed areas or the rise of the elevated areas may be brought about in different ways, some of which are suggested by Figs. 4 to 8.

Past changes. If the sea bottom were to sink, the ocean basins would hold more, and some of the sea-water would be drawn off the continental shelves. If the bottoms of the ocean basins were to go down 600 feet, or a little more, all the water would be drawn off the continental shelves, and they would then become land. If the continents were to sink, the waters of the sea would spread farther than now over their borders, and the area of the land would be lessened. The history of the earth teaches that the areas of the ocean and land have changed somewhat from time to time. The lower parts of the continental platforms have been drowned and made into land, over and over; but it is not known that any part of the deep ocean basins has ever been land, or that any part of the land was ever beneath a deep sea.

Relief Features of the Second Order

The more strongly marked features of the continents and the ocean basins are relief features of the second order. The continental areas are made up of plains, plateaus, and mountains. Plains are the low lands of the earth, and the plateaus and mountains are the high lands. The relations of these features are shown in Fig. 2.

Plains

Though plains are generally lower than plateaus and mountains, they cannot be defined in terms of height above the sea, for they may be but a few feet above it, or they may be hundreds or even thousands of feet above. If so high as a thousand feet, however, they are generally 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, in size, in shape of surface, in fertility, in origin, and in various other ways. Different names are given to various sorts of plains, the names being intended to turn attention to some one

PHYSICXiRAPHY feature. Important classes of large plains are coastal plains, which border the sea, and interior plains, which are far from the sea, or separated from it by high lands.

Coastal plains occur on the borders of many continents. They are wide in some cases, and narrow in others. A narrow, low plain with a nearly flat surface is shown in Fig. 9. The landward edges of coastal plains are not always so sliarply marked as in this illustration.

Plate I represents, in another way, a part of the narrow coastal plain of Oregon. Since illustrations of the sort shown in this plate

Fig. 9. — A narrow coastal plain.

will be used often in the following pages, the principles on which it is based must be understood. It is called a contour or topographic map.

ExPI,ANATIOX OF CONTOUR MaP

The topographic map shows three sorts of features. These are (1) the shape of the surface, (2) the distribution of water, and (3) the works of man.

The shape of the surface. A land surface may ho flat or uneven. If flat, it may l»e hiph or low. and if uneven, it may have little r<»licf or much. The topopraphic map .showc^ how flat or how nnigh it is.

The hoiffht of land is n'ckoncd fmm .»iea-levol. Thf heights of many points are measured exactly, and some of them are pi\en t>n the map in figures. It is tic-iircd, however, to give the elevation of all parts of the area mapped, and to show what parts are flat, and what parts have sIoi>es. Xot only this, hut if there* arc .slopes, it is important to show whether they are gentle or steej). All these things are done by lines called contour lint a. or simply cmitours. \ contour line connects points of the same elevation above sea-level. Thus the contour of 20 feet connects points which are 20 feet above sea-level, the contour of 40 feet connects points which are 40 feet above sea-level, and so on. The vertical distance between two contour lines is the contour interval. The contour interval may be 10, 50, 100, or any other number of feet. On the

Fig. 10. — Sketch and map of the same area to illustrate the representation of topography by means of contour lines. (U. S. Geol. Surv.)

maps of the United States Geological Survey, the contours are printed in brown (Plate I).

The manner in which contours express elevation, form, and grade is shown in the sketch and contour map of Fig. 10. The sketch represents a river valley between two hills. In the foreground is the sea, with a bay which is partly closed by a sand bar. On each side of the valley is a terrace. From the terrace on the right, a hill rises gradually, while from that on the left the ground ascends steeply, in a cliiJ. Contrasted with this cliff is the gentle descent of the slope at the left. In the map. each of these featurea >& %V^sy^^ by contours directly beneath its positon in the sketch. The following explanation may make clearer the manner in which contours show elevation, form, and grade:

1. We are to remember that a contour indicates a certain height above sea-level. In this illustration, the contour interval is 50 feet; therefore the contours are drawn 50, 100, 150, 200 feet, and so on, above sea-level. The 50- foot contour connects all points of the surface 50 feet above the sea, and the 100-foot contour connects all points 100 feet above the sea. In the space between any two' contours, the elevation is greater than that of the lower, and less than that of the higher. Thus the contour at 150 feet falls just below the edge of the terrace, while that at 200 feet lies above the terrace. All points on the terrace are more than 150 but less than 200 feet above the sea. The summit of the liigher hill is stated to be 670 feet above the sea, and the contour at 650 feet surrounds it. In this illustration nearly all the contours arc numbered; but on most maps this is not possible. Instead, certain contours — say every fifth one — are made lieavier and numbered (PI. I); the height of any contour not numbered may then be known by counting up or down from one that is numbered.

2. Contours show the forms of slopes. Since contours are continuous horizontal lines at a given height above the sea, they wind smoothly alK)ut smooth surfaces. They run up into ravines, and project out in passing about prominences. The relations of contour curves and angles to the form of the surface can be traced in Fig. 10.

3. Contours give some idea of the steepness of a slope. The vertical space between two contours is the same, whether they lie along a clifT or on a gentle slope; but to rise a given height on a gentle slope one must go farther tlian on a steep slope. Therefore contours are far apart on gentle slopes, and near together on steep ones.

Drainage. On the maps of the United States Goolopical Survey, watercourses are indicated by blue lines (PI. I). If the streams flow all the year, the line is drawn unbroken; but if the channel is dr>' a part of the year, the blue line is broken or dotted. Where a stream sinks and reappears at the surface, the supposed course imder the ground is shown by a broken blue line. Lakes, marshes, and other bodies of water are also sho>Mi in blue.

Culture. The works of man, such as roatls, railroads, and to\^nis, and also boundaries of to\\Tiships. counties, and states, are printed in black.

Let US now apply these princij)les to Plate I. We notice at the outset that onn inch on the map corresponds to about two miles, and that the contour interval is 100 feet.

We note at once tliat the contours are far apart at the left and close together at the ri^iht. Tliis means that tlie surface is rougher at the east, and smoother at the west. The area at the east is higher

Black lock Pf^ , ,

TawerRock \{^ l^J than that at the west, as the numbers on the contours show. The 500, 1,000, and 1,500-foot contours are heavier than the others, and are the only ones numbered. But small areas reach a height of 1,500 feet.

At the north, the first contour is nearly an inch from the coast. This shows that north of Floras Lake the land does not rise to the height of 100 feet for a distance of about two miles from the shore. South of Floras Lake, on the other hand, the 100-foot contour line is close to the shore, showing that there is a steep slope (cliff) more than 100 feet high along this part of the shore.

Cape Blanco has two contours, and is therefore more than 200 feet high. Gull Rock, Castle Rock, and Blacklock Point are more than 100 feet high. Few points reach a height of 200 feet, west of the rough land to the east. At the western border of the high land, there are steep slopes where six contours occur in the space of an eighth of an inch {}4 mile). This shows that the surface rises at least 500 feet in a quarter of a mile in some places, and this makes a steep slope. The principal wagon road of the region runs along the base of the steep slopes, while less important roads (indicated by dotted lines) branch from the main one.

Interior plains are often higher, and sometimes much higher, than coastal plains. A large part of the area between the Appalachian Mountains on the east, and the Rocky Mountains on the west, is a great interior plain. Here and there mountains, such as the Black Hills of South Dakota, and the Ouachita (pronounced Wash'- i-ta) Mountains of Arkansas and Oklahoma rise distinctly above the general level of this plain.

Extent and habitability. Plains are more extensive than plateaus or mountains, and most of the people of the earth live upon them. They are the chief places of human activity, partly because their climate is more favorable than that of higher regions, and partly because there is a greater proportion of land which is flat enough to be cultivated. Plains favor transportation and commerce, for (1) the building of roads, railways, and canals is much easier in plains than in higher and rougher regions; and (2) the streams of plains are more commonly navigable than those of mountains and plateaus. For these reasons, and also because many of the raw materials used in manufacturing are grown on plains, the larger part of the manufacturing of the world is there. It is noteworthy that the extensive plains most favored by climate and soil border the Atlantic Ocean, and, largely for this reason, these plains have been the theaters of the world's culture and trade.

In 1880, when the population of the United States was about 50,000,000,* about four-fifths of the people lived on lands less than

^s* C

Fig. 1 1 . — A plain in Wyoming. Mountains in the background.

1,000 feet above the sea, and only about ono-fiftictli lived above 2,000 feet.

Not all plains support an abundant population. Thus the northern plains of Eurasia and North America are too cold to be hospitable to varied industries, and their populations are likely to remain small.

Origin. Plains are formed in various ways. Some coastal plains are lands worn down from hiirlicr lands; others are parts of former continental shelves built up abovt^ the water by sediment laid down upon them; while still others Represent former continental shelves, from which the sea- water has b(»en drawn ofT. Some interior plains were once coastal plains. They are now inland because other ' Lat<»r data on this point are not availabk.

land has been fonned between them and the sea, so that they are no longer near the coast.

PlateaiLS

Plateaus are tracts of land so situated as to appear high from at least one side, while they have, at the same time, considerable areas at or near their summit levels. Thus if a coastal plam rises gradually from the sea to a height of 200 feet, and then rises by a steep slope

Fig. 12. — Diagram to illustrate the relations of mountain, plateau, plain, ocean basin, ocean deep, etc.

Himalajfa Mtt.

NarShan Mt$.

Fig. 13. — Section across Asia, showing plateau between the Himalayas and the Nan-Shan Mountains. ,

Shrra Mta

Fig. 14. — Section across North America, showing plateaus between the mountains in the western part.

I -y<tm _._r?rrmimir^^r^iT777r:. ^ .. _. ^ sea Leva .

Fig. 15. — Section across Africa, latitude \{f S., showing a great plateau rising directly from the ocean. Vertical scale exaggerated about fifty times.

to another tract of level land which rises 200 feet higher (Fig. 12), the upper tract would be called a plateau, not so much because of its altitude above sea-level, as because of its distinct rise above the plain along one side of it. The Piedmont Plateau, which lies between the Appalachian Mountains and the Atlantic Coastal Plain of the United States, is not very high, but it is enough higher than the Coastal 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.