1. ,^^ -^^.. .^^ '%^ \, x(^' * .^•^ x^o^ •*. A •vV . " -^ '- « '? ,-i.^^ . ^, .-^' cj;-*'<- V6 -X'' o % : %^ «r^^\^= ^> ^; x<^ V W^ N^ ■^■. m \\ •/v. V^ z ■ • '^ <^'^ <<- ■f^'^ ■v/'' Pr.ATK I. Grays Peak, Rocky Mountains of Colorado ELEMENTARY PHYSICAL GEOGRAPHY WILLIAM MORRIS DAVIS Sturgis-Hoopeb Professor of Geology in Harvard University Boston, U.S.A., and London GINN & COMPANY, PUBLISHERS Cl)e ^tlbensenm levees 1902 THE LIB eeNG Two Copifc" MAY. 6 ^902 COPVRI»HT ENTRY 0LA88 CL' XXc. No, X Entered at Stationers' Hall Copyright, 1902, by WILLIAM MOKRIS DAVIS all rights reserved PEEFACE The educational progress of recent years has resulted in two profitable advances for the venerable subject of Geography. A strong feeling has been developed in favor of treating the subject as a whole more rationally than heretofore, and a wholesome desire has arisen in favor of introducing some of its scientific aspects more generally into the school course. A natural accompaniment of this progress has been a demand for text-books that shall present Physical Geography in its modern scientific development as well as in an elementary form. The present book, reduced from the author's "Physical Geography," has been prepared to meet this demand. The reduction of the earlier book to the present volume has been made chiefly by omitting the more advanced problems and by simplifying and abbreviating the treat- ment of the remainder; but the chapter on The Atmos- phere is here given a greater length than before ; and a new chapter is added on The Distribution of Plants, Animals, and Man, considered from a physiographic standpoint. Several topics of a somewhat more advanced nature than the rest of the text, and yet of too great importance to be omitted altogether, are placed in supplements to Chap- ters I, II, and III. iv rilEFACE The plan of this volume is, like that of its predecessor, to give the problems of Physical Geography a rational treatment. The object of this method is not simply to explain physiographic facts, but through explanation to increase the appreciation of the facts themselves. It is, however, not enough that physiograpliic facts should be associated with their causes ; they must also be seen in relation to their consequences if their full importance is to be realized. This relation must not be presented merely as an afterthought, in a detached chapter at the end of a book ; it must accompany the presentation of the facts themselves. As Guyot long ago said so well: "To describe, without rising to the causes, or descending^ to the consequences, is no more science than merely and simply to relate a fact of which one has been a witness." The ideas of cause and of consequence, one preceding, the other following, the physiographic fact, have therefore been held constantly in mind by the author ; they should be no less constantly remembered by the teacher and impressed upon the pupil. Yet, while the causal notion is introduced as far as possible, it must be recognized that certain facts of great importance cannot be really accounted for in an elementary book. Such facts must therefore be described rather than explained. For example, the rotation of the earth and the separation of continental masses from ocean basins are subjects of great importance ; they must be described, and their consequences deserve careful attention, but their causes involve speculative investigation of a grade that far transcends the reach of an elementary text. Again, PREFACE V the simpler phenomena of the tides must be presented ; their period may be correlated with the movement of the moon, and the moon may be thus indicated as their chief cause ; but the relation between lunar cause and tidal effect cannot be demonstrated to young pupils. A mere outline of theory, with the briefest consideration of the joint action of sun and moon, is introduced in the sup- plement to Chapter III. The general circulation of the atmosphere is also far beyond elementary explanation. The circulation may be not unreasonably asserted to depend on the differences between equatorial and polar temperatures ; but the more intelligent the pupil, the less can he be satisfied with a simple conventional origin of the prevailing westerly winds. Explanation of this complicated problem is there- fore touched upon lightly ; while emphasis is given to the elements of which the circulation consists, to the correla- tion of these elements, and to the deduction of climatic conditions from them. The deflective effect of the earth's rotation is almost universally misunderstood, because it cannot be fully explained in an elementary manner. Its quality is briefly asserted in the text, and on account of its importance a correct explanation in the simplest pos- sible form is inserted in the supplement to Chapter II ; but neither this supplement nor that on the tides should be studied by the youngest pupils. On the other hand, the forms of the lands have not as a rule been sufficiently explained in text-books on Physical Geography. Fifty years ago there was justification for the empirical treatment and even for the neglect of land vi PREFACE forms, in the ignorance of geographers concerning their origin ; but the investigations of the hi,st thirty years have thrown a flood of light on this important division of the subject, and to-day it may be treated as rationally as any other. Many problems, formerly obscure, are now seen to be essentially simple and to lie entirely within the reach of elementary treatment. It has thus become possible to extend the explanatory method, long familiar in the study of the atmosphere and the ocean, to the lands as well ; and to present plains and plateaus, mountains and volca- noes, rivers, valleys, and shore lines under a rational system. It is believed that this division of the subject is here treated in a manner more systematic and compre- hensive and at the same time more simple and reasonable than is the case in any other elementary book. It should however be carefully borne in mind that the explanation of the processes which are involved in the dissection of a plateau, for example, is not introduced merely that the past history of the plateau shall become known, but chiefly that the existing features and especially the systematic correlation of these features shall be better perceived and remembered. While the list of topics treated will, it is believed, be found exceptionally full for an elementary book, it has nevertheless been necessary to go somewhat against time- honored traditions in omitting certain subjects. Elemen- tary text-books should not present an encyclopedic richness of contents, as if to show the learning of their authors ; they should provide a well-selected body of useful infor- mation having disciplinary value, pertinent to their subject PREFACK vii and appropriate to young pupils. It has therefore been decided to follow carefully the outline of Physical Geog- raphy lately prepared for and published by the National Educational Association, and to exclude certain traditional but irrelevant topics belonging properly to Astronomy, Geology, and Biology. It has also been deemed expedient to omit certain other relatively advanced topics ; such, for example, as the distribution of atmospheric pressure, shown by charts of isobaric lines, which have been, it may be said, fashionable since the publication of Buchan's excellent charts of these elements. Important as are the facts thus shown for the more advanced study of meteorology, they have no immediate climatic importance, and their proper use involves so many advanced considerations that they are best excluded from elementary study. Agam, there is a chart of cotidal lines, purporting to show the advance of the tidal wave through the oceans, which has been repeat- edly copied since it was first published by Whewell in 1833 ; but this pleasing generalization is omitted here because it was discredited by its very author in 1835, and because it has never since then received the approval of experts in tidal investigation. The best chart of cotidal lines, that of Berghaus' Physical Atlas (reproduced in the United States Coast Survey Report for 1900, Appendix No. 7, Figure 25), leaves the open oceans blank. The method of presentation adopted is sometimes induc- tive, sometimes deductive, according to the subject in hand. The inductive method is more largely used, because young pupils are as a rule better able to leam from direct descrip- tion than from inferences based on general principles. The viii PREFACE exercises suggested for the study of weather maps, in the supplement to Chapter II, are purely mductive ; and the sev- eral chapters on the development of land forms are largely inductive. But it must not be forgotten that the simpler processes of deduction are perfectly familiar to young pupils, and may be safely employed in teaching where they are appropriate to the topic in hand. It is indeed advisable that the pupil should gain some experience in deduction as well as in induction, and Physical Geography should be recognized as presenting ample opportunity for the exercise and development of both these mental processes. The relation of rainfall to the several mem- bers of the atmospheric circulation may be instanced as appropriately deductive, because of the systematic rela- tions of these topics. The illustrations in the chapters on land forms are of two kinds. The block diagrams represent ideal types. The views of actual landscapes in woodcuts and plates serve as examples of the ideal types. The block diagrams are in several respects more comprehensive than any actual view can be. They show so large an area, from so elevated a point of view, that the relation of the parts to the whole is easily perceived; they omit numerous and frequently irrelevant details by which the pupil's attention might be distracted ; they present in the most elementary manner possible the correlation of underground structure and surface form ; and in this respect they are far supe- rior to mere geological sections, in which the land surface is represented only by a profile line which few young pupils can translate into a topographic form. Exercises in PREFACE ix drawing simple outline maps from the block diagrams are frequently suggested, in order to insure the recognition of the essential features of the type. It will also be found useful to ask the pupil to indicate the relation of a view to its type diagram, as is done in the text for Figures 71 and 73, and for Figures 141 and 142. The questions inserted in the text are intended to aid the pupil in learning his lessons ; the questions at the end of the chapters are intended for use by the teacher in tests and reviews after the lessons have been learned. If it is desired to extend the time devoted to Physical Geography by classes whose average age is somewhat above that for which tliis book may be used, all of the text, as well as the supplements to Chapters I, II, and III, may be studied in full. If it is desired to shorten the course, the supple- ments may be passed over, the number of map drawings may be decreased, and certain sections that are concerned with relatively advanced topics (for example, Sections 99, 103, 107, 124) may be omitted. The teacher will find it practically convenient to indi- cate by a brief reference in the page margin the books and map3 mentioned in the Appendix. The examples there referred to should be supplemented as far as possible by local examples observable at or near the school. Illustra- tions of many topics treated in Chapter II will be found in the ordinary observation of passing weather phenomena. Many of the activities of the lands may be illustrated by local excursions, for which the autumn is a convenient season; while examples of the land forms seen in the school neighborhood should be studied m the spring. X PREFACE Inasmuch as land forms vary greatly from place to place, no general guide can be of service in this division of the subject; but teachers are advised to make themselves familiar with their school district by frequent excursions, and to use as far as possible all the appropriate illustra- tions that they discover. The author desires to express his thanks to a number of his correspondents who have supplied photographs from which several of the plates have been copied, and also to a number of teachers and others who have accepted the fatiguing task of criticising his manuscripts and proof, particularly to Professor J. B. Woodworth of Harvard University, Mr. M. Grant Daniell of Boston, and Mrs. M. A. L. Lane of Hingham. The questions at the ends of chapters have been prepared by Mr. R. H. Cornish, of the Girls' High School, New York, whose practical acquaintance with school work insures their value. W. M. D. Harvard University, Marcli, 1902. CONTENTS CHAPTER PAGE >'' I. The Earth as a Globe 1 ^ II. The Atmosphere ....... 23 ^ III. The Ocean 90 / IV. The Lands 129 ). V. Plains and Plateaus 141 J) VI. Mountains 177 ''/ VII. Volcanoes 215 VIII. Rivers and Valleys 234 ^ IX. Deserts and Glaciers ...... 278 X. Shore Lines 304 XT. The Distribution of Plants, Animals, and Man 332 LIST OF PLATES I. Grays Peak, Rocky Mountains of Coloi'ado (photograph by W. H. Jackson) Frontispiece FACING PAGE II. A Sailing Vessel at Sea (by Neurdin) 40 III. A. Cumulus Clouds ; B. Cirrus Clouds (by Riggenbach) . 63 IV. Waterspout over Vineyard Sound, Aug. 19, 1896 (by J. N. Chamberlain) 67 V. The Bore, or Surf-Like Flood Tide, in an Estuary at the Head of the Bay of Fundy, Nova Scotia . ... 121 VI. The Great Plains (by W. D. Johnson) 159 VII. A Railroad rounding a Spur of Mt. Ouray, Colorado (by W. H. Jackson) 191 VIII. Grandfather Mountain, North Carolina (by A. Keith) . 205 IX. A Water Gap in the Allegheny Mountains (by Maryland Geological Survey) 211 X. Diuant on the Meuse, Belgium (by Neurdin) 258 XI. The Braided Channels of the River Var in the Western Alps 261 XII. Bad Lands in the Great Plains, South Dakota (by N. H. Darton) 283 XIII. A Sand Dune rippled by the Wind (by G. K. Gilbert) . 287 XIV. The Muir Glacier, Alaska (by H. F. Reid) 292 XV. A Troughlike Glaciated Valley in the Western Alps (by Neurdin) 299 XVI. A Land-Tied Island, near Genoa, Italy (by A. Noack) . 315 XVII. A Branch of Sogne Fiord, Norvray (by A. Lindahl) . . 321 XVIII. Forest in the Equatorial Rain Belt, Ceylon 348 XIX. Moab, an Irrigated Settlement in Eastern Utah (by L. M. Prindle) 361 xii LIST OF FIGURES FIG. • PAGE 1. Eclipse of the Moon 2 2. Height of Land and Depth of Sea 3 3. The Shadow of a Box, showing the Altitude of the Sun . . 8 4. Meridians and Parallels 9 5. Latitude and Longitude 9 6. Mariner's Compass 18 7. Globular Form of Earth shown by Visibility of Stars ... 20 8. Mercurial Barometer 25 9. Mirage of Part of a Schooner, formed on a Thin Layer of Air 30 10. The Comey Self-Recording Thermometer 32 11. Illustration of an Isothermal Line 33 12. Chart of Mean Annual Temperatures 34 13. Anemometer 38 14. The Planetary Circulation of the Atmosphere 40 15. Wet- Weather Streams of the Tarso Mountains, Sahara . . 42 16. Cyclonic and Anticyclonic Areas 45 17. Monthly Positions of the Earth with Respect to the Sun . . 47 18. Chart of Mean Temperatures for January 50 19. Chart of Mean Temperatures for July 50 20. Chart of Annual Range of Temperature 51 21. Diagrams of Terrestrial Winds for January and July ... 53 22. Winds of January 54 23. Winds of July 55 24. January Monsoons in Indian Ocean 57 25. July Monsoons in Indian Ocean 57 26. A Distant Thunderstorm .... 65 27. Regions of Tropical Cyclones 68 28. Chart of Mean Annual Rainfall 71 29. Annual Rainfall of the United States 73 30. Storm Tracks of the North Temperate Zone (after Loomis) 79 31. Rotation of a Disk on a Rotating Globe 85 xiii xiv LIST OF FIGURES FIG. PAGE 32. Diagram of the Sun's Midday Altitude 88 33. Diagram of Sunrise and Sunset Hours 89 34. Water and Land Hemispheres 97 35. An Ocean Steamship 98 36. Sounding Instrument and Water Bottle 99 37. Dredge 99 38. A Vessel beset by Pack Ice 103 39. An Iceberg 104 40. Globigerina (magnified 100 time;;) . 105 41. Section of Continental Shelf 108 42. Orbital Movement of Water in Waves 109 43. Surf 112 44. Chart of Ocean Surface Temperatures and Currents . . . . 115 45. Displacement of a Vessel by Currents 116 46. Drift of Floating Objects by Currents 117 47. Low Tide in a Harbor 120 48. The Tidal Wave, or Bore, in the Seine 121 49. Jellyfish fioating in Sea Water 122 50. Deep-Sea Fish, x i 123 51. Deep-Sea Crustacean, x i 123 52. Earth and Moon 125 53. Spring Tides, New Moon 125 54. Neap Tide^, First Quarter 125 55. Spring Tides, Full Moon .- 125 56. Neap Tides, Third Quarter 125 57. Variation of Tides for Two Weeks 126 58. Height of Land and Depth of Sea 132 59. A Quarry sh'owing Weathered Kock 135 60. Mountains bordering the Sea '^~ T.42 61. Sample Map of a Mountainous Coast 142 62. Narrow Coastal Plain 144 63. Sample Map of a Narrow Coastal Plain 145 64. A Narrow Coastal Plain in Scotland 146 65. Broad Coastal Plain 147 66. Coastal Plain of the Carolinas 148 67. A Truck Farm on the North Carolina Coastal Plain .... 149 08. A Belted Coastal Plain 150 69. Sample Map of Part of a Belted Coastal Plain 151 LIST OF FIGURES XV FIG. I'AGE 70. The Belted Coastal Plain of Southern New Jersey .... 153 71. An Embayed Coastal Plain 154 72. Sample Map of an Embayed Coastal Plain 155 73. A Branch of Chesapeake Bay, Maryland 157 74. Ancient Coastal Plain of Wisconsin 161 75. A Plateau in Arizona 163 76. Diagram of a Narrow Canyon 164 77. Diagram of a Widened Canyon 165 78. The Allegheny Plateau ' 168 79. Canyon of the Kanawha River in Allegheny Plateau, W. Va. 169 80. The Enchanted Mesa, New Mexico 172 81. Broken Plateaus 173 82. Hurricane Ledge, a Dissected Fault Cliff 174 83. A Mountain Peak 178 84. Block Mountains 179 85. Mountains of Southern Oregon 180 86. A Dissected Mountain Range, Utah 182 87. Diagram of the Jura, a Folded Mountain Range 184 88. Peaks of the Central Alps 186 89. An Alpine Peak of Slanting Layers 187 90. Path of an Ice Fall in the Alps 192 91. The Landslide of Airolo, Switzerland 194 92. A Landslide in the Himalayas 195 93. The Himalaya Mountains 196 94. Alluvial Fans 198 95. A Filled Valley with a Flat Floor 199 96. A Terraced Valley 200 97. Railroad shaken by an Earthquake, Northeastern India . . 202 98. Land Surface displaced by an Earthquake, Japan .... 203 99. The Piedmont Belt, Virginia 206 100. Map of the Piedmont Belt, Virginia 207 101. The Upland of New England 208 102. Valley of the Deerfield in the New England Upland ... 209 103. Diagram of the Allegheny Mountains, Pennsylvania .... 210 104. Model of Embayed Mountain.s 211 105. Vesuvius in Eruption 217 106. Monte Nuovo 218 107. Cinder Cone and Lava Flow, California 220 xvi LIST OF FIGURES FIG. PAGE 108. Deception Island, a Volcanic Caldera (plan and section) . . 221 109. The Cone of Vesuvius in tlie Caldera of Monte Somma . . 221 110. Contour Map of Crater Lake in Mt. Mazama, Oregon . 222 111. Excavations in Herculaneum 224 112. Distribution of Volcanoes and Coral Islands 226 113. Lava Flows on the Plateaus of Arizona 228 114. The Lava Plateau of Idaho, Oregon, and Washington . . . 229 115. Contour Map of Mt. Shasta, California . 230 116. Mt. Shasta 231 117. Map of the Lake Nicaragua District 232 118. Diagram of Cavern and Sink Hole 235 119. Section showing Ground Water in Rock Crevices beneath a Valley 237 120. Diagram of a Coastal Plain with Artesian Wells .... 238 121. A Geyser 240 122. A Dividing Ridge in the Mountains of Northwest England . 242 123. Niagara Falls 248 124. Diagram of Niagara River between Lakes Erie and Ontario . 251 125. Falls of the Yellowstone River 252 126. Diagram of Torrent, with Falls and Reaches 253 127. Valley of Yakima River, Washington 257 128. The Mohawk Valley 258 129. Outline Map of a Young Valley 259 130. Diagrams of a Widening Valley 260 131. A Meandering River, Vale of Kashmir, India 262 132. A Meandering River on the Plain of Hungary 263 133. Meandering Channel and Oxbow Lakes in the Flood Plain of the Mississippi ,. 264 134. The Valley of California 266 135. Torrent Fan Delta, Lake Geneva, Switzerland 267 136. The Delta of the Mississippi 268 137. Diagram of a Narrowed Spur in a Meandering Valley ... 272 138. Diagram of a Cut-Off Spur in a Meandering Valley ... 272 139. Intrenched Meanders of the Neckar 273 140. Transverse and Longitudinal Streams . . , 274 141. Transverse and Longitudinal Valleys 274 142. Water Gap of the Susquehanna above Harrisburg, Pennsyl- vania 274 LIST OF FIGURES xvii FIG. PAGE 143. The Ozark Plateau, Missouri 279 144. Glaciated Areas, Interior Basins and Ocean Deptlis . . 279 145. Floo'd in Cherry Creek, Denver, Colorado 282 146. Sand Dunes in the Sahara 287 147. Lakes Bonneville and Lahontan 289 148. Rosegg Glacier in the Alps 293 149. Viesch Glacier in the Alps 294 150. Glacial Moraines, Sierra Nevada, California 295 151. Glaciated Area of the Northern United States 296 152. Ice-Worn Rocks, Coast of Maine 297 153. Glacial Moraines, North Dakota 298 154. A Glacial Bowlder 298 155t A Drumlin, Massachusetts 299 156. A Side Valley hanging over the "Valley of the Ticino, South- ern Alps 300 157. Lake in the Adirondacks, New York 301 158. Sea Cliffs, Grand Manan, New Brunswick 305 159. Diagram of a Lowland Coa.st with Bluff and Sand Reef . . 309 160. The Sea Cliffs of Normandy (looking southwest) .... 311 161. Diagram of an Irregular Shore Line 312 162. Diagram of an Irregular Shore Line with Cliffed Headlands and Beached Bays 312 163. Diagram of a Curved Shore Line 313 164. A Cliffed Headland and a Land-Tied Island 314 165. Gibraltar 315 166. Diagram of a Group of Sea-Cut Islands 315 167. A Cliffed Coast in Alaska . 316 168. The " Old Man of Hoy " 317 169. The Coast Platform of Norway 319 170. A Delta in a Norwegian Fiord 321 171. Deltas of the Texas Coast 322 172. A Mangrove Tree 324 173. ■ A Fringing Reef 325 174. A Barrier Reef 325 175. Part of the Great Barrier Reef of Australia (as seen at low tide, looking toward the mainland) 326 176. Diagram of Part of a Barrier Reef 327 177. Diagram of Part of an Elevated Reef with a New Fringing Reef 327 xviii LIST OF FIGURES FIG. PAGE 178. Diagram of an Atoll 328 179. An Atoll, or Coral Island 329 180. Beavers * . . 341 181. Caribou 342 182. Jaguar 343 183. Kangaroo 344 184. Cassowary 347 185. Dwarfs in the Equatorial Forest . 351 186. Eskimo hunting Walrus 352 187. Gtunted Trees at the Tree Line on the Slope of Pikes Peak . 356 188. Ibex 356 189. The Yucca, a Desert Tree 360 190. El Kantara Oasis, Algerian Sahara 362 ELEMENTARY PHYSICAL GEOGRAPHY CHAPTER I THE EARTH AS A GLOBE 1. Introduction. — Physical geography treats of the various features of the earth that influence the manner in wliich man lives upon it. Hence it must consider the form of the earth as a whole, the climates of its different parts, its oceans with their waves and tides, and the forms of its lands. It is the plan of this book to describe the more important kinds of physical features on the earth, to refer them to their causes in natural processes, and to trace them to their consequences as seen in the condition of mankind. 2. The Shape of the Earth. — The people of savage races, when they think at all about the shape of the earth, gen- erally imagine it to be a great plain, varied by hills and mountains and surrounded by the sea ; for that is the appearance of the lands when seen from some high point, with mountains rising to greater heights, lowlands extend- ing to the seashore, and the ocean stretching beyond. The people of an ignorant race usually regard the place ' where they live as the center of the great earth plain. Of ELEMEXTAUY PHYSICAL GEOGRAPHY the ocean they know little ; its further parts are invisible and mysterious and are often thought of as much more dangerous than those which border the solid lands. Among the earliest observations that led to a knowledge of the true form of the earth were those made by the Greeks, The great philosopher Aristotle, who flourished about the middle of the fourth century B.C., made an ingenious use of the eclipses of the moon to determine the form of the earth. He knew that the eai'th cast a great shadow stretching away into space on the side opposite the sun; and that whenever the moon, in its movement around the earth, entered this shadow it was hidden or eclipsed, because it then no longer received the sunlight that Fig. 1. Eclipse of the Moon, show- Ordinarily makes it visible, ing the Curved Edge of the Earth's jje noted that the edge of Shadow , , , -, ■, 1 the earth s shadow on the moon is a curved line, and thus he knew that the earth must have a curved surface, such as a globe has. The moon, revolving about the earth once in twenty- eight days, is not eclipsed every time it is opposite the sun, for it usually passes a little to one side of the earth's tapering shadow. The familiar ai'gument for the globular form of the earth, based on the disappearance of the lower part of THE EARTH AS A GLOBE 3 distant vessels at sea, was not mentioned by ancient writers until about the beginning of the Christian era. 3. Size of the Earth. — The earliest recorded measure- ment of the size of the earth was made by a Greek philos- opher in the third century B.C., who found its diameter to be about 8000 miles. The knowledge thus gained by the wise men of the ancient Mediterranean countries concern- ing the size and shape of the earth was unknown to the rest of the world and was afterwards forgotten ; but it was regained about the time of Columbus. The proof of globular form by sailing around the earth, or circumnavigation, was first accomplished in the sixteenth ^$JJj;Ss<$^'yi^v:i^^;S;>^*^>^^? 10 ELEMENTARY PHYSICAL GEOGRAPHY Low latitudes are near the equator in either hemi- sphere; high latitudes, near the poles; middle latitudes, roughly midway between pole and equator in either hemi- sphere. (See page 89.) The longitude of a place is the number of degrees by which its meridian is east or west of a standard or prime meridian. The meridian of the national observatory of Great Britain at Greenwich, a suburb of London, is now very generally taken as the standard. The longitude of a place is measured from the prime meridian east or west along the equator to the meridian of the place and is counted in degrees, 180 to half a circle, or in hours, 12 to a half circle. If NACS^ Figure 5, is taken as the standard or prime meridian, the longitude of B is measured by the arc CD of the equator, or by the angle COZ>, between the local and the prime meridians.. Is B in east or west longitude? What is the latitude oi Gl What is its longitude ? Practical Exercise. A useful illustration of the manner in which maps are rnade is given by providing a number of outline maps, showing parallels and meridians (latitude and longitude lines), on which the latitudes and longitudes of a number of points are to be platted. Tlie points should be selected on the boundary of some state or country ; their positions may be taken from ah atlas and written upon a blackboard. By drawing a line through the points thus platted each pupil will have constructed a rough map of the chosen boundary. Rivers and cities may be similarly located. Land surveys, by which the boundary lines of farms and house lots are marked out, are best made with refer- ence to the local meridian, or north line. Navigators have thp: earth A8 a globe 11 daily occasion to determine their position with respect to the network of meridians and parallels, in order to follow the desired route, to avoid islands and headlands, and to reach their intended port. The boundaries of thinly settled parts of civilized nations and states are often defined by meridians and parallels, as between the western parts of the United States and Canada, as well as between many of the states themselves, and between the various parts of Canada and Australia. Thus great advantage is taken of the simple globular form and regular rotation of the earth, v 10. Relation of the Earth to the Sun. — The sun, glow- ing with extreme heat, has the enormous diameter of 866,500 miles. If the earth were placed at the sun's center, and the moon were moving around the earth at its actual distance of 240,000 miles, the sun would still reach almost 200,000 miles beyond the moon on all sides. So huge a body is a fitting center for the earth to move around. Even at the great distance of 93,000,000 miles, the brilliant sun gives abundant heat and light to the earth. This distance is so great that an express train traveling from the earth fifty miles an hour could not reach the sun in less than two centuries. The earth travels or revolves around the sun every year in a nearly circular path, called its orbit. In order to accomplish this long journey of over 600,000,000 miles, our globe rushes along at a speed of 18.5 miles a second, or over 1,500,000 miles a day. As the motion is accom- plished with perfect smoothness, and as we move with the 12 ELEMENTARY PHYSICAL GEOGRAPHY earth, we are as unconscious of this rapid movement in the annual orbit as we are of the diurnal rotation on the axis. Exercise. Lay a large sheet of paper on a table; draw a line through the middle of the sheet. Let this line represent a distance of 200,000,000 miles. On each side of the middle of the line set up a pin, so that the distance between the pins shall represent 3,000,000 miles (^3_ of the length of the line). Lay off 189,000,000 miles on this scale on a thread and knot together the ends of this length, so as to make a loop. Lay the loop over the pins, stretch it tight witli a pencil point, and thus guided draw a curve around the pins. The line tlius drawn is nearly circular and represents the true form of the earth's orbit. Take out the pins. Around one pin hole draw a circle to scale, somewhat less than 1,000,000 miles in diameter ; this will represent the sun. On the same scale the earth would be a small dot. The points where the orbit is crossed by the middle line show the greatest and least distances of the earth from the sun. AATiat are these distances? The point nearest the sun (perihelion = "near-sun") is passed on January 1 ; the farthest (aphelion = « far- sun" ) on July 1. The stars are distant suns, shining by their owti light. Most of them are much more than a million times as far from the sun as the earth is. They are so exceedingly remote that a ray of light which travels from the sun to the earth in eight minutes would be about three and a half years on the journey to us from the nearest star. Many of the stars are believed to be larger than the sun. 11. Relation of the Earth to other Planets There are a number of other bodies which, like the earth, move around the sun. Like the earth they do not shine by their own light, but only by sunlight that falls on them. TIIK EARTH AS A GLOBE 13 At night these bodies look like stars, except that they twinkle less. Their light is brighter or fainter accord- ing to their size and their distance from the sun. The telescope shows them to be of globular form, like the earth. Their movement among the stars, easily noted from month to month, shows that they revolve around the sun in the same direction that the earth does. The spots that may sometimes be seen on the sun show that it also rotates on its axis in a little less than a month, in the same direction that the planets move around it. The planets that may be easily seen without a telescope are named Mercury, Venus, Mars, Jupiter, and Saturn. ^Mercury, Venus, and Mars are smaller than the earth; Jupiter and Saturn are much larger. Mercury and Venus are nearer to the sun than the earth is ; Mars, Jupiter, and Saturn are more distant ; and two other large planets, Uranus and Neptune, are farther away than Saturn. The planets that are near the sun revolve around it in a shorter time (or "year") than those further away. The small planets, JNIercury and Venus, are believed to rotate very slowly on their axes, so that their "day" is long. The large planets, Jupiter and Saturn, rotate rapidly, so that th*eir day is about half as long as ours. The moon is a planetlike body which revolves around the earth while the earth revolves around the sun. The moon is therefore called a satellite (= a follower), because it accompanies the earth. Its diameter is about a quarter of that of the earth; its distance from the earth is about 240,000 miles. Mercury and Venus have no satellites, Mars has two very small ones, Jupiter has five, Saturn has eight. 14 ELEMENTARY PHYSICAL aEOGRAPHY It is thus found that the earth is not a solitary body, unlike all others, but that it occupies an intermediate posi- tion in a large family of similar bodies. Diagrams may be constructed to represent the relative sizes of the planets and their relative distances from the sun by means of the following table. Diameters are given in thousands of miles ; distances in millions of miles. Distance Diameter Distance Diameter Sun ..... 866. Jujiiter . . 480 85.3 Mercury . . 36 3.0 , Saturn . . . 881 70.1 Venus . . X 67 7.6 Uranus . . 1772 30.9 Earth .... 93 7.9 Neptune . . 2770 34.0 Mars .... 141 " 4.2 1 12. The Solar System. — The sun, the planets, and their satellites form a group of bodies called the solar system. The resemblances of form and motion among the planets and satellites are so numerous that it is believed that they have all had a common origin. It has been thought that these bodies, and the sun also, have been formed by the gathering together of materials that were once scattered through an enormous space, like a vast cloud or nebftla. This interesting and famous theory is called, the nebular hypothesis, but it is not successful in explaining all fea- tures of the solar system. "^ The stars resemble the sun in many ways. It is believed that each star may be accompanied by a larger or smaller family of planets ; and hence the number of earth- like bodies in the universe is probably very large. THE EARTH AS A GLOBE 15 13. Structure of the Earth. — Rocks of one kind or another are often seen at the surface of the lands; or if the sui'face is covered by soil, rocks may be found beneath the soil in wells and railroad cuts. The deepest mines and borings, reaching about a mile beneath the surface, pass through similar rocky materials. Hence it is believed that the body of the earth is composed of rock. This great globe of rock is covered with a considerable quantity of water and air lying ujson its surface and forming its oceans and its atmosphere. The oceans are not continuous all over the earth, but are gathered on the lower parts of the surface, while the higher parts rise somewhat above the oceans and form the continents. The atmosphere entirely incloses the oceans and the continents, rising far above the highest mountains. Thus the earth as a whole consists of matter in three different states, — solid, liquid, and gaseous. The liquid portion, or water, is also known as a solid when it freezes and forms ice ; and as a gas when it evaporates and mixes with the air as invisible water vapor. The solid portion, or rock, is seen as a liquid when it comes forth from vol- canoes at high temperatures as molten lava. The gaseous portion, or air, is always gaseous under natural conditions, but it may be artificially reduced to a liquid or a solid b} subjecting it to heavy pressure at extremel}^ low tempera- tures. There is a certain amount of mixture of rock, water, and air, or of the solid, liquid, and gaseous parts of the earth. Some solid substances have been dissolved by the action of water and are now found in the oceans. A small 16 ELE.MENTARY PHYSICAL GEOGRArHY amount of rock in very fine particles, or dust, is raised from barren surfaces by the wind and carried far and wide ; the finest particles remain long in the air, slowly settling but often lifted again by rising currents. Water and air penetrate all pores and crevices that they can find in the rocky sphere. Water vapor is always present in the atmosphere in small and variable proportion ; it becomes visible when chilled and condensed, forming small liquid or solid particles in cloud, rain, or snow. A small amount of air is dissolved in the oceans ; bnt for this, the fish and many other animals that live beneath the surface of the sea could not breathe. 14. Underground Temperatures. — Temperatures meas- ured in deep wells and mines show that the earth becomes warmer beneath the surface. The average increase of temperature downwards is about 1° for sixty feet. At great depths, such as twenty or a hundred miles or more, very high temperatures would be expected ; they are proved to occur by the melted lavas that rise and escape in vol- canoes. It is therefore supposed that the great interior rocky mass of the earth is hot enough to be melted, although the enormous pressure of the outer parts may prevent the expansion that would be needed to make it liquid. It may thus be forced to remain solid in spite of its high temperature. The outer and cooler part of the ^arth is often called its crust. Just as a hot ball of iron will cool when it is hung in the free air, so the earth must be slowly cooling as it moves through cold space. It is very probable that the THE EARTH AS A GLOBE 17 unevenness of the geosphere, in ocean basins, continents, and mountains, is in some way the result of a sort of set- tUng and bending of the crust, slowly caused by the long cooling of the earth. 15. Age of the Earth. — It is impossible to say what the age of the earth and the solar system is, but it certainly should be reckoned in millions and millions of years. There is every reason to believe that the sun and the planets existed for an indefinitely long period before the condition of the earth's surface was such as to allow the habitation of the planet by plants and animals. It is well proved by the prints or fossils of various plants and animals in ancient rock layers that these lower forms of life existed upon the earth for a vast length of time, millions and millions of years before man appeared. It seems entirely possible that other planets may have once been, may now be, or may yet come to be occupied by inhabitants of some kind. 16. The Earth as a Magnet. — If a magnetized bar of steel is balanced on a pivot and placed in the neighborhood of a large magnet, the direction in which the small bar points will be determined by its large neighbor. This may be tested by changing the relative positions of the two. If the small magnet is left alone, it will in most parts of the earth turn until it points about north and south. This is because the earth acts as if it were a huge magnet and so determines the direction in which smaller magnets tend to stand. The behavior of suspended bar magnets makes them very valuable in determining directions, especially in 18 ELEMENTARY PHYSICAL GEOGRAPHY cloudy weather at sea. A magnet mounted in a con- venient case is called a compass, the bar being called a needle. In the mariner's compass a card bearing the letters indicating the points of the compass lies on the needle and turns with it. The needle seldom points along a true meridian toward the pole, but somewhat to one side or the other of a meridian, in a direction that if followed will lead toward the " north magnetic pole " (about twenty degrees away from the true north pole toward Hudson bay) or toward the "south mag- netic pole " (about the same distance from the true south pole toward New Zealand). The dif- ference between true north and magnetic north at any place may be determined by com- paring the direction of the midday (or shortest) shadow cast by a vertical pole with the direction of a compass needle. Fig. (i. Mariner's Compass 17. The Aurora. — During clear nights, especially in winter time, the northern part of the sky is sometimes illuminated by an arch of whitish, greenish, or rosy light. Moving streamers of light, whitish or colored, are seen between the arch and the higher parts of the sky. This appearance is called the aurora borealis, or "northern THE EARTH AS A GLOBE 19 lights." The aurora is more frequent and brilliant in high northern latitudes than in temperate latitudes. A similar appearance in far southern latitudes is known as the aurora australis. In both cases the middle of the auroral arch is seen in the direction of the magnetic pole. From the disturbance of delicate magnets during an auroral display it is believed that the lights are due to a faint electric discharge controlled by the magnetic forces of the earth. Supplement to Chapter I 18. Proof of the Globular Form of the Earth by Observations of the Stars. — Looking upward from the earth, the sky seems like a hoUov/ shell of vast size, carrjdng the sun by day and the stars by night. The earth may be thought of as standing at the center of the great sky shell, so that an observer at any point sees only half the sky above him, the other half being hidden beneath' the earth. The lower border of the visil)le half of the sky is called the horizon, and the plane that extends outward from the observer to the sky border is called the plane of the horizon. By watching through the night tiie Greek philosophers saw the stars rising in the eastern side of the sky and descending in the western; and they concluded that the sky, carrying the stars with it, turned around the earthy once a day. It is now known that the earth turns, and not the sky. In order to understand this clearly the pupil should learn by observation something of the diurnal movement of the sun, moon, and stars across the sky and should recognize that their paths are parts of slanting circles. Perception of the essential facts is greatly aided by tlie use of a "pointer," three or four feet long, tied at one end to the top of a stake about which it may turn freely. Direct the pointer toward the sun at different hours of the day. Repeat this until the (apparent) 20 ELEMENTARY THYSICAL GEOGRAPHY movement of the sun becomes familiar. Then sweep the pointer more rapidly through its successive i^ositions. Infer the directions it would assume if the sun could be observed all night. Infer the attitude of a line, or axis, about which the pointer turns. This line must be parallel to the axis on which the earth turns. The (apparent) diurnal rotation of the stars is best shown by home observations. Direct a pointer toward a star at a convenient evening hour. Watch the star for five or ten minutes and note its change of position. The next evening begin the observation fifteen or twenty minutes earlier. How can the facts thus observed be best accounted for? The movement of -^^ ^^ * . -IT the stars as seen from dif- ferent places must next be considered. When one travels southward from B to C it is found that new groups of stars, Z, Figure 7, not visible before, come into sight over the southern horizon, while other groups, X, that had before been seen over the northern horizon are no longer visible. From this it is concluded that the plane of the horizon HJ at the new point of observation is not parallel to the plane FG at the first point, and that the surface of the earth must be convex instead of flat. Hence the earth as a whole must be a globe or sphere. Changes of this kind are easily recognized in traveling from the northern to the southern border of the United States, or farther south into Mexico or Cuba. They may be verified by correspond- ence between different schools, several hundred miles apart north and .south. What changes would be noted in traveling northward from Bto A? Fig. 7. Globular Form of Earth shown by Visibility of Stars THE EARTH AS A CxLOBE 21 QUESTIONS Sec. 1. What are the chief subjects that are taught in Physical Geograpli y ? 2. What is the view generally held by savage races as to the size and shape of the earth ? When were correct notions first gained as to the earth's shape ? How did Aristotle infer the earth's shajie ? What must be the relative iwsitions of sun, earth, and moon when i/ the moon is eclipsed? AVliy is the moon not eclipsed every month? 3. AVhen was the earth's size first determined? When and by whom was tlie earth first circumnavigated? Name some of the places then discovered. 4. Describe the general form of the earth. State the relation of its mountain heights and ocean depths to its diameter. Does the earth's form favor travel and transportation? How? 5. How are savage tribes affected by the size of the earth? In what ways have civilized nations become associated with one another? 6. What is meant by " iip " and " down " ? How is the siirface f of a quiet body of water related to the direction of gravity ? How is the position of tree trunks and house walls related to the direction of gravity ? AVhat consequences of the action of gravity are seen in men and animals ? 7. What is the belief of j^rimitive man about the position of the earth? What are the facts? What is the effect of the earth's rota- / tion on its form ? 8. What is the cause of day and night? What is the most ' natural unit of time ? What habits of man and animals result from the earth's rotation? How are the cardinal points related to the eai-th's rotation? What is the position of the sun at midday? How are midday and true north determined? Given a north and south line, how can vou determine east and west? ...... y 9. Define mei'idian line, meridian circle, poles, parallels, equator. What is latitude and how is it measured? What is meant by low, i/ 22 ELEMENTARY PHYSICAL GEOGRAPHY middle, and high latitudes ? AVhat is longitude and how is it meas- ured? State some of tlie practical uses of meridians and parallels. 10. Compare the sun's size with that of the moon's orbit. Calcu- late the time needed for an express train to reach the sun. What is the earth's orbit? What is the earth's orbital velocity? How is it found ? What are the stars ? What can be said of their distance from us ? 11. How are the planets distinguished from the stars? Which planets can be seen without a telescope ? Name the planets in order of distance from the sun. Which are larger, which smaller, than the earth ? Compare the " day " of Jupiter and of Saturn with our day ; the " year " of Venus and of Mercury with our year. State the size and distance of the moon. 12. What is the solar system? What features are possessed in ^ common by its members ? What do these common features suggest? 13. Of what is the great body of the earth believed to consist? i/ Why ? What is meant by the earth's crust ? What are the three / states of matter? Give examples of them. What are the chief divisions of the earth? 14. AVhat is known about underground temperatures? At what rate does temperature increase downward? What is the supposed condition of the earth's interior? What relation is suggested between the earth's surface form and its interior temperature? 15. What may be said of the earth's age and of life on the earth ? 16. How is a small balanced magnet affected by a large one? How will a balanced magnet stand when alone? What is a com pass ? What are the magnetic poles ? Where are they ? How far to one side of the meridian does the compass point at your school . Does it point east or west of the true meridian ? 17. Describe the aurora borealis. How is it related to the mag- netic pole ? CHAPTER II THE ATMOSPHERE 19. The Atmosphere is a light and transparent mixture of gases, known as air. It rests upon the lands and seas, forming the outermost part of the earth. It takes part in the earth's daily rotation and yearly revolution. Many processes that take place on the lands and seas depend on the atmosphere. The waves and currents of the ocean are caused by the winds ; the soil that covers so large a part of the lands results from the decay of the underlying rocks, largely through the action of moist air. Rainfall, so important in many ways, is supplied by mois- ture received from the oceans and carried about by the movements of the atmosphere. The atmosphere far overtops the highest mountains.- Meteors, or "falling stars," — small scraps of matter dash- ing toward the earth from outer space — are heated by rushing through the air at enormous speed, so that they become luminous. They are sometimes seen at heights of more than a hundred miles, showing that some air reaches that great altitude. Cloud, haze, and dust make the lower air more or less turbid and often shut out a great part of the sun's rays ; but when the air is clear it is so transparent that sunlight is strong even at the bottom of the atmosphere. 23 24 ELEMENTARY PHYSICAL GEOGRAPHY 20. Composition of Air. — Air consists of a uniform mixture of gases in which a small and variable quantity of water vapor is usually present. The chief gases are nitrogen and oxygen, which constitute about four fifths and one fifth, respectively, of the atmosphere. Fire is the result of an active combination of some burn- able substance with the oxygen of the atmosphere. The heat thus developed may produce light, or it may con- vert water into steam, and the expansive force of the steam may be used to drive engines, and many kinds of machinery. All animals and plants breathe in air and use some of its oxygen to combine with part of their substance in a very slow combustion, which produces a slight amount of heat, but no fire. Thus all forms of life, animal and vege- table, depend u^jon the oxygen of the air, as well as upon their food, to keep them alive. Carbonic dioxide, constituting less than a thousandth part of the atmosphere, is nevertheless important for the growth of plants. The carbon taken from this gas by growing plants makes a large part of their structure. 21. Pressure of the Atmosphere. — Although the air is invisible, it is attracted by the earth and exerts a pressure of about a ton to the square foot upon the surface on which it rests. The total pressure on a man's body amounts to several tons ; but this is not felt because the air within the body exerts a corresponding pressure out- ward. The air is so easily moved that little resistance is noticed when one walks through it ; but fast railroad THE ATMOSPHERE 25 ^ trains are much impeded by the resistance of the air that they have to push rapidly aside. The pressure of the atmosphere is measured by the barometer. This instrument is of two kinds. The mercurial barometer, Figure 8, consists of a glass tube, somewhat more than thirty inches long and closed at one end. It is prepared by filling the tube with, mercury, closing the open end with the finger, and inverting the tube ; the open end is then placed in a vessel of mer- cury and the finger is withdrawn. The mei cury sinks a little below the closed upper end of the tube, leaving an empty space, or vacuum above it. The mercury column must presi down on part of the mercury in the vessel just as much as the air presses on any equal part of the mercury surface. Thus the height of the mercury column, measured by a scale may be taken as a measure of the pressure o:t the atmosphere. The aneroid barometer consists of a smal' box, from which the air has been exhausted A variation in the pressure of the atmospher< causes a slight change in the shape of th( box. The change is magnified by a series Oi. delicate levers, by which an index is moved on a dial. The reading indicated on the dial Fig. 8 Mercurial Barometer then shows the pressure of the atmosphere. The ordinary changes of atmospheric pressure, such as may be seen to accompany weather changes by reading a 26 ELEMENTARY PHYSICAL GEOGRAPHY barometer from hour to hour and from day to day, are seldom more than a thirtieth or a fifteenth of the total pressure. If a barometer is carried up a lofty mountain, leaving much of the atmosphere beneath it, the pressure of the overlying atmosphere is found to be much reduced. An ascent of a thousand feet causes a lowering of about an inch in the barometric column. Thus barometers may be used to measure mountain heights. Although very light, the air supports the flight of birds and insects. The wind drives sailing vessels and wind- mills. In dry regions, where the ground is not covered with vegetation, the shape of the surface is changed by the long-continued action of the wind in drifting sand and dust from place to place. 22. Elasticity of the Air. — Air is extremely elastic, changing its volume with every change of pressure. Its lower part is compressed by the weight of the overlying parts, so that much more air is contained in a cubic foot at sea level than at a height of three miles. This is expressed by saying that the density of the lower air is greater than that of the upper air. A cubic foot of air at sea level weighs about 0.075 pound, while at three miles above sea level its weight is only about half as much, and at an altitude of a hundred miles the air must be almost imperceptible. Men and animals living on high plateaus have become accustomed to the rarity or thinness of the air around them. There are villages on the plateau of Tibet and in THE ATMOSPHERE 27 the liiglier valleys of the Andes at heights of from 12,000 to 14,000 feet, where the density of the air is hardly two thirds of that at sea level. Mountain climbino- at alti- tudes above 20,000 feet is almost impossible, from the difficulty of breathing the thin upper air. It is by slight wavelike movements in the air that sound is transmitted. So quickly is the wavelike dis- turbance passed on that sound travels a mile in five seconds. So easily is the air disturbed that a locust (cicada) may set hundreds of tons of air vibrating per- ceptibly to our nerves of hearing. When the volcano Krakatoa, between Java and Sumatra, exploded in August, 1883, sounds were heard for 2000 miles, and atmospheric waves, detected by slight changes of pressure in barom- eters, passed three times around the earth. 23. Colors of the Atmosphere. — The clear atmosphere is so transparent that the light of faint stars can pass through its whole thickness. In the daytime the sun lights up the sky so brightly that stars are not seen. The blue color of the clear sky is due to the scattering of sunlight on countless numbers of extremely minute particles, the scattered light being seen against the darkness of outer space. The red and yellow colors near the horizon at sun- rise and sunset are due to the sifting out of other colors as the sunlight passes obliquely through a great thickness of atmosphere. As the sun sinks slowly below the western horizon after a clear sunset, a pink or rosy arch of sunlit air — the twilight arch — may be seen slowly rising over the 28 P^LEMENTARY PHYSICAL GEOGRAPHY eastern horizon; the dull blue sky below the arch is dark- ened by the shadow of the earth. A similar arch and shadow may be seen sinking in the west before a clear sunrise. Thus the shadow of night may be seen follow- ing the sunlit air of one day and disappearing before the sunlight of the next. 24. Temperature of the Atmosphere. — -' The temperature of the land and sea surface and of the atmosphere is con- trolled by the rays of the sun. The temperature of the atmosphere is not much affected directly by the sun's rays, because the air is so transparent that the rays are very little taken in or absorbed by it; hence the upper air is every- where cold. The temperature of the lower air is largely controlled by the temperature of the land or sea surface on which the air rests. The sea surface absorbs the sun's rays somewhat more actively, and the land surface much more actively, than the air does ; thus they become warmer than the air. The air lying next to the heated surface is then warmed by heat that is carried or conducted from the land or sea to the air. At night, when sunshine is absent, land, sea, and air cool by radiating their own heat {giving out rays) toward outer space. Just as the air absorbs the rays of the sun very imper- fectly in the daytime, so it gives up very little of its own heat by radiating at night. The sea surface is somewhat more active than the air in cooling by radiation at night, and the land surface is much more so. Hence the lower air is cooled at night by conduction of its heat to the cooling surfaces on which it rests. In the upper air tlie diurnal THE ATMOSPHERE 29 range or the change of temperature from day to night is very small ; it is somewhat greater in the lower air on the oceans ; it is much greater in the lower air on the lands. The sun's rays fall almost vertically on every part of the earth's surface near the equator for several midday hours, and there high temperatures must prevail. The rays fall obliquely on the polar regions, so that each ray is there spread over a larger surface than in the torrid zone, and its noon effect is no greater than that of an early morning or afternoon ray near the equator ; hence low temperatures must prevail around the poles. This may be illustrated by the difference in the heating effect of sunshine on the two slopes of a road that runs north and south over a hill. Between poles and equator intermediate temperatures are maintained. High, medium, and low temperatures are thus distrib- uted in belts — hot, medium, and cold — roughly parallel to the equator; the belts are known as the torrid, tem- perate, and frigid zones. Fortunately the cold or frigid areas occupy a relatively small part of the world. Yet even in the torrid zone lofty mountains rise into air that is so cold that snow lies on their upper parts all the year round. The lower limit of the permanent snow fields is called the snow line. It is about three miles above sea level in the mid-torrid zone ; about a mile above in latitude 55° or 60° N. or S.; it descends to sea level within the frigid zone, whei'e peimanent snow may be found even on the lowlands. Heated air expands. Hence, volume for volume, hot air is lighter than cold air ; the air of the torrid zone is 30 ELEMENTARY PHYSICAL GEOGRAPHY lighter than that of the frigid zones. This fact will be found of great importance as a cause of the winds. 25. Mirage. — A curious consequence of the strong control of air temperature by that of the land or sea sur- face on which the air rests is sometimes seen in the reflec- tion of distant objects by the lower layer of air when its temperature is distinctly unlike that of the overlying air. A reflection of this kind is called a mirage (French, mean- ing "reflection"; pron. meerahzh). Its cause is as follows: Fig. y. jNIirage of Part of a Schooner, formed ou a Thin Layer of Air The surface of a level desert in a warm zone becomes very hot under unclouded summer sunshine, and the air close to the ground is heated by conduction, so that it becomes much hotter than that three or four feet higher. The upper surface of the hot air acts like a mirror and gives an inverted reflection of objects beyond it. The reflecting air surface thus imitates a water surface so well that travelers are often deceived by it and think that a lake exists where in reality there is nothing but dry sand. THE ATMOSPHERE 31 When cold air blows over a warmer sea its lower layer may be heated by conduction from the water, so as to become distinctly warmer than the air at a greater height. When warm air blows over a colder sea the lower part may be cooled by conduction. In either case the lower layer may reflect the figure of distant vessels, the reflected image being seen upside down beneath the object itself, if the lower layer of air is thin and the observer is above it ; but above the object itself, if the lower layer is thicker and the observer is within it. s The equivalent of a mirage may often be seen by look- ing close along a brick wall that is exposed to strong sun- shine in calm warm weather. Objects that are nearly in line with the wall may be seen reflected on the film of hot air next to it. 26. Thermometers. — The temperature of the air and of other bodies may be measured by the thermometer (temperature measure), consisting of a fine tube opening into a bulb at its lower end and containing mercury (or other liquid). The glass and the mercury take the tem- perature of the surrounding air. If warmed, both expand, but the liquid mercury expands more than the solid glass, and part of the mercury is therefore pushed from the bulb into the tube ; if cooled, both contract and some of the mercury is withdrawn from the tube into the bulb. Thus the height of the mercury in the tube measures relative heat and cold, or temperature. In the United States and Great Britain it is still customary to employ the Fahrenheit thermometer (F.), 32 ELEMENTARY PHYSICAL GEOGRAPHY Fig. 10 The Comey Self-Recording Thermometer marking 32° at the freezing point and 212° at the boiling ; point of water. In continental Europe the Centigrade thermometer (C.) is used, reading 0° at the freezing and 100° at the boiling point. Some thermometers are arranged so as to give a contin- uous temperature record in a curve drawn on a sheet of paper; such instruments are called self-recording ther- mometers, or thermographs, one pattern being shown in Figure 10. Others are con- trived so as to register the highest (maximum) and low- est (minimum) temperatures of the day; this is sometimes done by placing an index or short piece of fine wire inside the tube, so that it may be pushed up or down as the liquid expands or contracts. Such instruments are called maximum and minimum ther- mometers. When the thermometer is used to measure the tempera- ture of the air it should be suspended so as to be protected from direct sunshine and from rain and snow, but exposed to the wind. If placed outside of a window, the thermom- eter should be on the north side of the building, free from the wall and where warm air escaping from windows cannot affect it. It is better placed in a special shelter, away from buildings and trees. THE ATMOSPHERE 33 i^.S 1 1 27 ( ""■""i V 23 i \ 30 27. Temperature Charts and Mean Temperatures. — The distribution of temperature is indicated on charts by lines drawn through places having the same temperature. Figure 11 gives the degrees of temperature prevailing over the middle and eastern United States on a certain morning. The dotted line is drawn so as to separate all places having higher temperatures (warmer) than 40° from those having lower temperatures (colder). Similar lines may be drawn for temperatures of 10°, 20°, 30°, 50°, and 60°. Each of these lines is called an isother- mal (equal tem- perature) line, or isotherm. It is a line of uniform temperature, separating regions of higher and lower temperature. In the example here given all the states northwest of a line drawn from the southwest corner of Arkan- sas to the western end of Lake Erie have temperatures lower than 40°. All the states southeast of this line have temperatures higher than 40°. Many illustrations of this kind are afforded by the daily weather maps issued by the national Weather Bureau. What would be ysr--^S Fig. 11. Illustration of an Isothermal Line 34 ELEMENTARY PHYSICAL GEOGRAPHY the temperature of a place halfway between the isotherms of 50° and 60°? If records of temperature are kept at regular hours every day for a month, the hours being chosen so as to include the cooler as well as the warmer periods of the day, the sum of all the temperatures divided by the number of observations will give the average or mean Fig. 12. Chart of Mean Annual Temperatures temperature of the month. Similarly, if observations are kept up through a whole year, the mean temperature of the year may be determined. The mean temperatures of a place for a year usually differ by a small amount in successive years ; hence the standard mean annual tempera- ture of a place is determined by averaging the means of ten or twenty successive years. Observations of temper- ature have now been made during many years at a great THE ATMOSPHERE 36 many places, so that the distribution of temperature all over the world, except in the two frigid zones, is fairly well known. The distribution of mean annual temperatures for the year is shown by isotherms on the chart of the world, Figure 12, which is therefore called a chart of annual iso- therms. A line drawn near the earth's equator, through the middle of the belt of greatest heat, is called the heat equator, the average temperature of which is about 80°. From the heat equator the temperature decreases toward each pole at the rate of about one degree of the Fahrenheit thermometer scale to a degree of latitude. In the southern hemisphere the isotherms are nearly parallel to the latitude circles ; this is because the oceans there are so little interrupted by land. In the northern hemisphere the isotherms are much more irregular, because the oceans are here interrupted by broad continents, and the temperatures on lands and seas are often unlike in the same latitude. Exercise. AVhat parts of the lands and oceans have a mean annual temperature above 70°? above 80°? What is the general path of the isotherm of zero in the northern hemisphere ? Estimate from the chart the mean annual temperature of your home ; of Lon- don; of Cape of Good Hope. 28. „ Circulation of the Atmosphere. — Movements of the atmosphere are usually caused by differences of tempera- ture. For example, a movement of air will take place between two rooms, one warm and the other cold, if a door is opened between them. The cold air is heavier than the warm air. Cold air Mali therefore creep into the lower 36 ELEMENTARY PHYSICAL GEOGRAPHY part of the warm room, while the light warm air spreads into the upper part of the cold loom. The movement may be shown by the drift of smoke from a smoldering match. If the cold air is warmed as it enters the warm room, and the warm air is cooled as it enters the cold room, the movement will continue indefinitely, the air going roimd and round in a circuit. Such a movement is called a circulation. It is also called a convectional circulation, because heat and cold are conveyed by the movement that is excited by differences of temperature. In the same way the cold air of the polar regions, being heavier than the warm air of the torrid zone, continually tends to creep under it, thus forming convectional air cur- rents in the lower atmosphere, which we know as winds. The warm air, being slowly raised all aromid the equatorial belt, tends to overflov/ north and south toward the poles, forming convectional air currents at a great height in the atmosphere. The lower winds approaching the equator where sun- shine is strong are warmed ; thus their air is expanded and made lighter, so that it is in tuni slowly raised over the equatorial belt to form the overflow toward the poles. The upper currents, flowing toward the poles, where sun- shine is weak, are slowly cooled; hence their, air settles down to lower levels and forms the currents returning toward the equator. A permanent interchanging move- ment or circulation is thus established between the Avarmer and colder parts of the earth. It must continue as long as the sun warms the equatorial more than the polar regions. On account of the earth's rotation the air does not move tup: atmosphere 37 directly north and south, but is turned obliquely toward the east or west. (See page 85.) Changes of temperature in the circulating atmosphere are produced not only during movements toward or from the equatorial belt, Init also during the ascent or descent of the air currents. As the warm air rises the pressure of the over- lying atmospliere upon it is less and less ; the rising air therefore expands, and in so domg it is cooled ; hence even over the torrid zone the upper atmosphere is cold. On the other hand, as the descending air in higher latitudes sinks to lower levels a greater and greater amount of air rests upon it ; it is thus compressed and warmed. The descent of air from a great altitude is therefore not a cause of cold, for the air is warmed by compression as it comes down. Changes of temperature of this kind will later be seen to be of importance in producing and in dissolving rain clouds. Illustrations of such changes may be found in a small way by noting the coolness of the air that expands as it flows out of a bicycle tire when the valve is opened, and the warmth of an air pump in Avhich air has been com- pressed in order to force it into a tire. The most general movements of the atmosphere thus established on a planet like the earth may be called the planetary circulation ; the lower members of this circula- tion are the planetary winds. The surface wmds move much slower than the upper currents, on account of fric- tion mth the earth's surface. 29. Observation of Winds. — The direction of the wind is determined by a vane or arrow, turning easily on a 38 ELEMENTARY PHYSICAL GEOGRAPHY vertical axis and freely exposed, as on a spire or high pole, to the movement of the air. The wind is named after the point of the compass from which it blows. The strength of the wmd may be described as light, mod- erate, strong (twenty miles an hour), fresh gale, whole gale, hurricane (seventy-five or more miles an hour) ; or it may be determined in miles per hour by an anemo- meter (wind measure) turning on a vertical axis, as in Figure 13. Describe the arrange- ment of the cups on the arms of this instrument. Which way will the arms turn when the Mind blows ? Why ? A pointer on a small dial, connected with the axis of the turning arms by cog- wheels, indicates the move- ment of the wind in miles per hour. The surface wind on the uneven lands seldom blows in straight lines with uniform velocity. It usually rolls and whirls, now faster, now slower. Fig. 13. Anemometer 30. RainfaU. — Water is evaporated from the ocean surface, especially from its warmer parts, and the invisible vapor thus formed mixes with the air and is carried about m the Avinds. When the moist air is sufficientlv cooled THE ATMOSPHERE 39 the vapor in it is condensed into minute water drops or snow crystals, and the air becomes cloudy. If the cooling continues still further, rain or snow may fall. The vapor may thus be returned directly to the oceans, or it may fall upon the lands, whence it returns to the oceans in streams and rivers. In this way there is a circulation of water through the atmosphere, from the ocean and back again. The processes by which the air is cooled are nearly always connected with its movements. Hence the general distribution of rainfall will be referred to in the following account of the winds, while a fuller account of clouds, rain, and snow will be given farther on. 31. Planetary Winds. — The most important members of the planetary winds are the trade winds and the pre- vailing westerlies. The trade winds blow with much regularity from about latitude 28® N. and S. obliquely toward a belt of low atmos- pheric pressure around the equator, from the northeast in the northern hemisphere, and from the southeast in the southern. The prevailing westerly winds blow from a westerly source, "but usually with a slight inclination toward the pole, over the greater part of the temperate zones ; they form great spiral whirls around regions of low pressure in the high latitudes of each hemisphere. These winds are made irregular by the occurrence of many smaller whirls, about 1000 miles in diameter, which drift eastward with the general movement of the atmosphere in middle latitudes. The winds of tlie polar regions are little known. 40 ELEMENTARY PHYSICAL GEOGRAPHY Narrow belts of light variable winds and frequent calms lie between the several belts of steadier winds ; in these belts of light winds the pressure of the atmosphere is so nearly uniform that the air is not pushed steadily in any direction. All these mem- bers of the planetary circu- lation are better defined over the oceans tlian on the lands. Point out and name the several members of the planetary circula- tion in Figure 14. In what directions do their winds blow? Between what latitudes do they occur? The trade winds are so Fig. 14. The Planetary Circulation ^^ -i £ ,i of the Atmosphere ^'^l^^d from the constancy with which they follow their course, the word trade formerly having meant "steady." • They warm slowly as they approach the heat equator. Their velocity at sea is from ten to thirty miles an hour. They give fair weather, seldom interrupted by storms. When sailing vessels enter the trade-wind belt they may count upon making good headway. If sailing with the winds, extra sails ai-e often rigged out on the ends of the yards, and thus aided by a broadened stretch of canvas the vessels speed along day and night. Coasts upon wliich the trade winds blow are usually beaten with lieavy surf, so that landing is difficult, except jin well-protected harbors. This is the ease on the north- east side of the Windward islands in the Lesser Antilles. THE ATMOSPHERE 41 Lowlands over which the trade winds blow are made desert by the drying action of their warming air; for as the winds become warmer they take up any moisture that they find instead of giving up what they have. The Afri- can Sahara and the central Australian deserts are thus explained : it is entirely on account of their dryness and not because of the infertility of their soils that these regions are barren. Where the trade winds encounter mountain ranges they are forced to ascend the side on which the}^ approach (the windward side). As they rise the air expands and cools ; as the air cools some of the invisible vapor that it contains is condensed into minute drops of water ; thus the ascend- ing air becomes cloudy and rainy. The eastern slope of the Andes, about the headwaters of the Amazon, the mountains along the east coast of Brazil under the south- east trades, and the eastern slopes of the highlands of Mexico and Central America under the northeast trades thus receive a good amount of rainfall (80 to 100 inches a year). All these mountain slopes bear heavy forests. The further slope of tlie mountains, where the winds descend (the leeward side), is relatively dry and barren, because as the air descends it is compressed by the weight of the air that follows upon it; as it is compressed it is warmed, and as it warms it holds all the vapor that it has and eagerly takes up any vapor it can get from the ground over which it blows. This is especially noticeable on the western side of the Peruvian Andes, where much of the land is a desert in spite of being near the ocean. Even in the Saliara the few mountains that interrupt 42 ELEMENTARY PHYSICAL GEOGRAPHY the general surface receive a sufficient rainfall to permit tree growth ; but the streams supplied on the mountain sides wither away after descending to the desert below. The prevailing westerlies are much less regular than the trades. They may weaken to less than ten miles an hour, or strengthen to gales of sixty or more miles an hour. They often shift from their general course to take part in the drifting spiral movements indicated in the temperate lati- tudes of Figure 14. It is chiefly to these great whirllike movements that the frequent changes of weather in temper- ate latitudes are due. The area of the United States lies almost entirely within the belt of the prevailing westerlies. If the wind is observed at noon every day for a month or two, a westerly direction will be found more common than an easterly. If the drift of clouds is observed, the general movement of the atmospheric currents from the western toward the eastern side of the sky is very noticeable. Variations from these prevalent directions are generally due to the drifting spiral movements. Fig. 15. Wet-Weather Streams of the Tarso Mountains, Sahara. Locate these mountains on the chart of mean annual temperatures, Figure 12, by the latitude and longitude here given THE ATMOSPPIERK 43 The lands under the westerly winds are generally well watered if they do not lie too far from the oceans ; the con- tinental interiors are comparatively dry. Abundant rain- fall is received on the mountainous Pacific slopes of North and South America in middle latitudes, but the opposite slopes are drier. In these latitudes the western (wind- ward) slope of the mountains is heavily forested, while the eastern (leeward) slope has an open tree growth or none. The distribution of forests over the great American moun- tain system thus gives striking illustration of the relation of timber supply to winds, land forms, and rainfall. The belt of calms and light breezes in the neighborhood of the equator, between the trade winds, is called the equatorial calm belt ; that part of the belt which lies on the oceans is known to sailors as the doldrums. The air in the doldrums is moist and sultry, for the warm inflow- ing trade winds gather much water vapor as they blow over the ocean. The sky is prevailingly cloudy; rain falls every day or two, especially in the late afternoon or night. The lands are heavily forested under this warm and moist belt, and agriculture is diificult from the very luxuriance of vegetation. Sailing vessels bound across the equator are frequently becalmed for several days in the doldrums ; there they lie idle, rocking very gently to and fro in the long flat swell that sweeps across the glassy waters. They must then take advantage of every light breeze to push onward and reach the trade winds beyond. The dull sky, the sultry air, and the glassy sea make the delay all the more vexatious. 44 ELEMENTARY PHYSICAL GEOGRAPHY The rain of the doldi'ums results from the slow ascent of the warm moist air supplied by the inflowing trade winds. The lower air is raised to greater and greater height by the inflow of more air beneath from both sides ; it expands as it rises, and cools as it expands ; the vapor in the air is then condensed into cloud particles, tlie clouds become heavier and heavier and give forth plentiful rain ; the air from which the rain has fallen continues to rise and at last overflows aloft and thus supplies the upper currents that move obliquely toward the poles. Violent thundfer- storms are frequently formed in the great cloud masses of the calm belt. The ill-defined belts of light breezes and occasional calms lying between the trades and the prevailing wester- lies in each hemisphere are known as the liorse latitudes. Their light winds usually blow obliquely outward on both sides ; hence the air here must slowly descend from the upper currents to supply the ontflcrwing breezes. As the air slowly settles down it is compressed by the weight of that which rolls in on top of it ; as it is compressed it is warmed, and as it is warmed any clouds that it may have contained are dissolved ; hence clear fair weather is preva- lent in this belt. 32. Whirls of the Westerly Winds. — The irregular winds by which the prevailing westerlies are so often interrupted sometimes have an inward, sometimes an out- ward, spiraling movement, as in Figure 16. They are like great slow-turning whirls from 500 to 1000 miles in diame- ter ; they may be compared to eddies in streams of water. THE ATMOSPHERE 46 When blowing outward the air slowly descends from aloft ; the winds are light and the weather is fair, for the reasons already given for the fair weather of the horse latitudes. When blowing inward the air slowly ascends, and the weather is cloudy and wet, for the reasons given in explaining the doldrums. Here the winds may gain a stormy strength, fifty to eighty miles an hour on land and sometimes over one hun- dred rniles an hour at sea. Exercise. Locate the cen- ters of the two whirls shown in Figure 16. Describe the spiral movement of the winds with respect to the centers. Tu which whirl does the turn- ing around the center agree ^\■ith the turning of the hands of the clock? Which whirl should have low pressure? Which one fair weather? „ -,,■ r i i r^, , i ^x-^ ■ ^ Fig. K). Inward and Outward ^\ lurls Both classes of whirls travel from 500 to 1000 miles a day in an easterly direc- tion, with the general drift of the atmosphere in temperate latitudes. Changes of weather are caused by their pas- sage. The whirls may strengthen and increase in area for a time, then weaken and fade away ; their duration being from a few days to two or three weeks, and their distance of travel from 5000 to 15,000 miles or more. The direc- tion in which the whirls turn in the northern hemisphere is opposite to that in the southern ; that is, the outflowing spirals turn clockwise in the northern hemisphere, as in 46 ELEMENTARY PHYSICAL GEOGRAPHY Figure 16, and counter-clockwise in the southern hemi- sphere. How do the inflowing spirals turn in the two hemispheres ? The pressure of the atmosphere, as shown by the barom- eter, is less than usual about the central part of the stormy- inward whirls, and greater than usual in the fair-weather outward whirls. Hence they are often called low-pressure and high-pressure areas. They have also been named cyclonic and anticyclonic areas from the curving move- ment of their winds. They will be further described in the section on weather. 33. Seasons and Zones. — As the earth moves around the sun there are six months in each year (March 21 to September 22) in which the northern hemisphere is inclined somewhat toward the sun, so that it has longer days and stronger sunshine than the southern, which is at the same time inclined somewhat away from the sun, as in Figure 17. In this condition the gain of heat in the northern hemi- sphere by the absorption of the strong sunshine during the long days is greater than the loss of heat by radiation dur- ing the short nights ; hence the temperature there rises above the mean of the year. But in the southern hemi- sphere the loss of heat by radiation during the long nights is greater than the gain by absorption of weak sun- shine during the short days ; hence the temperature there falls below the mean of the year. During these months the northern may be called the sunnner hemisphere, and the southern the winter hemisphere. THE ATINIOSPHERE 47 During the other six months of the year (September 22 to March 21) the southern hemisphere is inclined toward the sun, and the northern away from it, so that the above N " Fig. 17. Monthly Positions of the Earth with Respect to the Sun conditions are reversed. The southern is then the sum- mer hemisphere, and the northern the winter hemisphere. In both hemispheres the succession of higher and lower temperatures during the year produces the change of 48 ELEMENTARY PHYSICAL GEOGRAPHY seasons. The winter months in the northern hemisphere are December, January, and February (these being the summer months of the southern hemisphere) ; the spring months are March, April, and May ; the summer months, June, July, and August ; the autumn or fall months, September, October, and November. The zones maybe defined b}^ means of Figui-e 17 as fol- lows : In the torrid zone, from 231-° N. to 231-° S.^ every point receives vertical sunshine sometime in the year ; here the days do not vary much from twelve hours in length. In the frigid zone, extending 23^° from each pole, there is at least one day in the year when the sun does not rise and another when it does not set ; here the days vary greatly in length. The temperate zones occupy the space between the torrid and the frigid zones (231° to QQ^°), north and south latitude ; here no place has ver- tical sunshine on any day, and no day passes without a sunrise and a sunset. If zones are limited by the mean annual isotherms of 70° and 30°, their borders are much more irregular than when limited by sunshine. 34. Observations of the Sun. — Records of thermometer readings during the school year should be used to show the general fall of temperature to midwinter, and the general rise from midwinter to midsummer. These changes of temperature should be connected with the changes in the apparent movement of the sun. In late December the sun rises south of east and sets south of west ; at midday it reaches but a moderate altitude above :1 THE ATMOSPHERE 49 the southern horizon ; at this time the dnration of daylight is less than twelve hours and the strength of the sunshine is reduced. In late June these conditions are all reversed. The low temperature of winter is thus seen to depend on the weak sunshine of short days, and the high temperature of summer on the strong sunshine of long days. The ris- ing temperature through spring results from the strength- ening of simshine in the lengthening days ; the falling temperature of autumn, from the weakening sunshine in the shortening days. (See Supplement.) 35. Change of Temperature with the Seasons. — An observer at any one place notes the familiar succession of the seasons during the course of the year. A better understanding of the ■ meaning of the seasons may be gained if the earth as a whole is considered, as on the above charts. It is then seen that for a time the heat equator moves a moderate distance from the geographic equator into the summer hemisphere, while the high tem- peratures of the torrid zone advance into the temperate zone, and the rigor of polar cold is somewhat lessened ; in the other hemisphere the polar cold is extreme, low tem- peratures advance over the temperate zone, and the heat on the border of the torrid zone is decreased. In the next half year the heat equator moves slowly back and crosses the geographic equator, and all these con- ditions are reversed. The year, or period in which the earth revolves around the sun and in which the change of seasons therefore take place, thus comes to be a natural measure of time. 50 ELEMENTARY PHYSICAL GEOGRAPHY 36. January and July Isotherms. — The general distri- bution of mean temperatures for January and for July is shown in charts of monthly isotherms, Figures 18 and 19, on which the following exercise may be based. Exercise. In which summer hemisphere does the heat equator stand farther from the geographic equator ? Does the heat equator stand farther from the geographic equator on the oceans or on the lands? Where do midsummer temperatures of more than 90° occur? In which hemisphere do they cover the largest area? What is the lowest mean temperature in January ? Where does it occur ? About how much difference is there between January and July temperatures in latitude 40° S. ? Where in latitude 40° N. is there a strong difference between January and July temperatures ? 37. Mean Annual Range of Temperature. — The average change of temperature with the seasons may be best studied by taking the difference between the mean temper- atures of January and July. This difference is called the mean annual range of temperature. It is shown for the dif- ferent parts of the world in Figure 20. The range is gen- erally less than 10° over the torrid oceans and less than 20° over most of the temperate oceans. On land the range increases. Places in the interior of continents have a much stronger range than those on continental borders or islands. Central Australia and the interior of the Sahara have a range of over 30°. Over most of the United States the range is from 30° to 60°. Over a belt of land from Hudson bay into Alaska the range is more than 80°. Over the greater part of Europe- Asia the range exceeds 40°. In regions of the greatest range the winters are so cold that the ground is frozen to a depth of 100 feet or more. 120 180 160 I2U 80 40 30 120 «;^»^ ~no 160 160 120 40 80 120 Fig. 18. Chart of Mean Temperatures for January Fig. 1!). Chart of Mean Temperatures for July THE ATiMOSPIlERE 61 In winter ice is so hard that the runner of a skate does not hold upon it; wood is too hard to be chopped with an ax. In summer thawing reaches onl}^ a few feet below the surface. Trees gain only a stunted growth .or are altogether wanting. Compare the annual range on the western and eastern coasts of the continents in temperate latitudes. On which Fig. 20. Chart of Annual Range of Teniperatiire coast is the range of less amount ? The difference of range is due to the prevailing westerly winds, which carry the nearly uniform conditions of the ocean on to the western coasts, and the changing conditions of the continental interior out to the eastern coast. Exercise. Wliere is the greatest annual range? What is its amount? Coiaipare the annual range of Labrador and England, of Virginia and Spain, of Japan and California. 52 - ELEMENTARY PHYSICAL GEOGRAPHY The annual changes of temperature are much more dis- tinct in the northern hemisphere, where there is much land, than in the southern, where there is much ocean. This is because the land surface changes its temperature more easily than the ocean surface, and therefore the air over the land becomes hot in summer and cold in winter. The change of seasons in the north temperate zone, especially on the lands, is much stronger than in the south temperate zone. This is because the northern continents are broad in temperate latitudes, while the southern are relatively narrow. Exercise. In Figure 20 follow the latitude circle of 40° or .50° N. around the earth. For how many degrees of longitude does it lie on the continents? How many on the oceans? Do the same for latitudes 40° or 50° S. Compare the results. Winter and summer are not very different over the great oceans of the south temperate zones, where the weather is rather uniformly chill and damp, or inclement, all the year round. This is because water is slow to change its temperature ; the ocean waters and the air over them suffer small changes of temperature during the year. In the temperate zone the summer half year is the time of plant growth, and is therefore the season of greater activity in all industries immediately connected with agri- culture. One of the most interesting consequences of the advance of spring and summer temperatures into higher latitudes is the northward passage of migratory birds, familiar to every lover of outdoor nature. The approach of winter is accompanied by the return of the birds to warmer latitudes. THE ATMOSPHERE 53 38. Terrestrial Winds. — The strength of the planetary circulation and the boundaries of its wind belts vary with the seasons. Thus modified, the winds may be called terrestrial, as belonging to the earth in particular with its winters and summers, instead of to the other planets which may not have seasons like ours. Fig. 21. Diagrams of Terrestrial Winds for January and July Figure 21 gives a general scheme of the winds for January and JuTy, without considering the irregular winds produced by the continents and their mountain ranges. The heavier lines show the stronger winds. In which month are the winds strongest in the northern hemisphere? In what season is this? Answer the same questions for the summer hemisphere. In what season are the prevailing westerlies most interrupted by spiraling winds (cyclones and anticyclones)? Examine the isotherms in the northern hemisphere for January and July, Figures 18 and 19. In which month are the lines closer together? How can you tell from this in which month there is the greatest difference of temperature between the torrid zone and the Arctic regions? In which month would you exp)ect the general 54 p:lementary physical geography circulation in the northern hemis})here to be the stronger? AVhy? Answer the same questions for the southern hemisphere. Compare the results for the two hemispheres. It is thus seen that in winter the difference of tempera- ture between the equator and high latitudes is strength- ened. As the general circulation of the atmosphere depends on this difference, the winds will generally be Fig. 22. Winds of January- stronger in winter than in summer. This is especially true of the prevailing westerlies and their spiraling cyclonic winds in the northern hemisphere ; they fre- quently become stormy in winter, while they are rela- tively light in summer. In the southern hemisphere these changes are less marked. Why so? Examine in Figure 21 the belts of light breezes and occasional calms between the trades and the westei'lies. What is the name of these belts? Compare their positions in January and July. AVhat TPIE ATMOSPHERE 55 is the name of the belt of calms and light breezes between the trade winds ? How does its position change with the seasons ? The horse latitudes and equatorial calms are much less regular in reality than they are represented in Figure 21, on account of the irregular outline and form of the lands. A better illustration of the prevailing winds for January and for July is given in Figures 22 and 23. Fig. 23. Winds of July The light and irregular winds of the horse latitudes migrate toward the equator in the winter of their hemi- sphere, and toward the pole in the summer ; these belts of migration are known as the northern and southern subtropi- cal belts (ST, Figure 21). Any country over which a sub- tropical belt is stretched will have the westerlies and their rainy storms in winter and the drying trades in summer. This is the case with southern California and the Mediter- ranean countries of southern Europe and northern Africa, as 56 ELEMENTARY PHYSICAL GEOGRAPHY well as with central Chile, southern Africa, and south- ern Australia. These countries are said to have, a sub- tropical climate. In what months will they have their rainy season? As -countries in the subtropical belts are dry in the growing season, agriculture there generally requires the aid of irrigation (watering the fields by canals led from streams or reservoirs). Like the calms of the horse latitudes, the calms and rains of the doldrums also migrate north and south dur- ing the year. The belt of winds and rainfall thus con- trolled forms the subequatorial belt (SQ, Figure 21). The migration of these three belts follows the migration of the sun. The plains of the Orinoco in Venezuela, north of the equator, receive a plentiful rainfall in July and August, but in December and January they are relatively dry. In the wet season cattle find abundant pasture on the plains, but in the dry season they are driven into the valleys. On the plains between the headwaters of the Amazon and the Parana, south of the equator, the months of wet and dry seasons are reversed from those of Venezuela. The western Sahara, between the reach of the subtropical (winter) rains on the north and the subequatorial (summer) rains on the south, gives no important river to the Atlantic along a thousand miles of coast line. The rise of the Nile in Egypt from June to September results from the northward advance of the equatorial rains over the upper part of this river basin, as in Figure 23. THE ATMOSPHERE 57 39. Monsoons. — In the belt over which the equatorial calms move north and south during the year the trade winds change their direction in the warmer and cooler half years. Winds of this kind are called monsoons. How do the winds blow in the northern half of the subequato- rial belt (S'Q, Figure 21) in January? in July? how in the southern half? What parts of the equator are crossed by the extended northeast trades in January, Fig- ure 22 ? by the ex- tended southeast trades in July, Figure 23 ? Where do these ex- tended winds cover the greatest area? Note in Figure 24 thi_^ change in the direction of the northeast trades in January as they cross the geographical equa- tor and enter the south- ern hemisphere on their way to the calm belt. What is the direction of the wind in the same part of the southern hemisphere in July? Note the corresponding change in the extended southeast trades for July in Figure 25. The reason for this change of direction as the winds cross the equator is found in the earth's rotation, on account of Fig. 24. January Monsoons in Indian Ocean Fig. 25. July Monsoons in Indian Ocean 58 ELEMENTARY PHYSICAL GEOGRAPHY which all winds in the northern hemisphere tend to turn to the right, and in the southern hemisphere to the left. On account of the irregular distribution of land and water mon- soons are not evenly developed all around the equator. The monsoons of the Indian ocean are the most remark- able of the world. In January a belt of northwest mon- soon winds is developed for about ten degrees south of the equator, as in Figure 24. In July, when the heat equator has shifted far northward to the border of Asia, a broader belt of southwest monsoon winds is developed north of the equator, as in Figure 25. The primitive sailing vessels of the Indian ocean in earlier centuries, poorly adapted for sailing against the wind, made voyages only as the monsoons favored their courses, going outward from India to Africa in one half year and returning in the next. The east coast of the Malay peninsula is beaten by heavy surf under the northeast monsoon, and then the native fish- ermen stay ashore. But under the southwest monsoon, an offshore wind, the water is comparatively smooth, and large fleets of fishing boats put out to sea with their palm-leaf sails. In what months would the events described in the two preceding paragraphs be expected ? -. 40. Winds of the Continents. — As the air over the con- tinents is warmer than that over the neighboring oceans in summer and colder in winter, the winds tend to blow inward toward continental centers in summer and outward from them in winter, THE ATMOSPHERE 59 111 the north temperate zone the cold land winds of winter tend outward toward the sea, and the far inland regions have much clear and dry weather. In summer the warm and moist sea winds tend inward toward the still warmer lands, and the interior parts of the large con- tinents then have a greater abundance of clouds and rain. The general circulation of the atmosphere is much com- plicated by this outward and inward tendency of the winds over the continents, as may be seen by comparing the winds of January and July over Asia, Figures 22 and 23, with the winds of corresponding latitudes in Figure 21. The regular belts of winds in the latter figure are much broken up, especially in the northern hemisphere. 41. Winds on Land. — The lower winds are generally not so strong or so regular on the uneven lands as on the level seas, although the upper currents over the lands still flow rapidly. In valleys the winds are much influenced by the direction of the inclosing slopes. Hence observers living in deep valleys may often determine the general direction of the winds better by watching the drift of the clouds than by noting the position of their wind vanes. The air over the lands is cooler and therefore heavier than that over the sea at night, but warmer and lighter by day. Hence around the border of the lands the wind tends to blow alternately offshore at night and onshore by day for a short distance from the coast, such winds being kno^vn as land and sea breezes. On the coasts in the torrid zone the sea breeze is wel- come, as it tempers the excessive heat of the day on land. 60 ELEMENTARY PHYSICAL GEOGRAPHY The same is true of sviramer weather in tlie temperate zone. On the coast of Peru the fishermen sail offshore in the early morning with the land breeze, and return in the afternoon with the sea breeze. 42. Daytime Winds In fair, warm weather the lower air lying on the land becomes unduly heated by day, as compared with the overlying air. The warmer lower air then rises and the cooler upper air descends, this be'ing a, small example of convectional circulation. It is like the movement of water in a kettle that is heated at the bottom. The faster-moving currents from aloft are thus brought down to the surface. Hence on lands the winds of fair weather in the daytime are commonly stronger than those of the night. This is prevailingly the case tlirough the year on torrid lands ; on the temperate lands it is common during summer weather, but is less noticed in winter. Why does no such daily change in the strength of the wind occur at sea? 43. Humidity. — The condition of the atmosphere as to the water vapor that it contains is expressed by the term humidity. When the air contains much vapor and feels damp the humidity is said to be high. W lien it con- tains little vapor and feels dry the humidity is low. The higher the temperature of the air, the greater the amount of vapor it may contain. When as much vapor is present as is possible at a given temperature the air is said to be in the state of saturation. The lower air over the ocean is usually almost saturated ; in the doldrums tlie humidity THE ATMOSPHERE 61 is always high. Far inland, in the desert regions of con- tinents, the air may contain very little vapor; here the humidity is low. Dry air is more agreeable than damp, because it allows active evaporation from the skin. Cold damp air is chilly and " penetrating." Warm damp air is sultry and "close." 44. Dew and Frost. — Dew is a deposit of moisture on the gromid, or on loose objects like leaves and sticks lying on the ground. It is formed when the ground is cooled at night by radiation ; then the air near it is chilled by conduction, and some of the water vapor in the air is changed to the liquid form. The temperature at which dew begms to be formed in cooling air is called the dew- point. Exercise. The dew-point may be determined by experiment as follows: Half fill a tin cui3 with water whose temperature is about like that of the air. Then slowly pour in ice water, stii-ring it with a thermometer. As the cup is cooled the air next to it is cooled also. As the air is cooled the vapor that it contains will more and more nearly saturate it. When the outer surface of the cup is first clouded by a deposit of moisture the air next to it has just passed the condition of saturation, and the temperature of the water gives a close indication of the dew-jjoint. If ice is added so as to make the water still colder, more and more vapor will be condensed on the cup, the air constantly being saturated with the vapor that remains in it as its temperature falls. When moisture is condensed upon the ground at tem- peratures beloAV the freezing point it forms frost. Thus frost on the gromid corresponds to snow m the air, and dew con-esponds to rain. 62 ELEMENTARY PHYSICAL GEOGRAPHY Dew and frost are in part supplied, from water vapor in the air that lies near the ground, in part by vapor that rises through the soil from its deeper and moister parts. In the daytime the vapor from the soil escapes into the warm air ; but at night, when the ground is colder at the surface than beneath,, the rising vapor is condensed.^ Dewdrops found on the blades of grass and on the livmg leaves of plants close to the ground are in large part supplied by the water that the plants bring up from the ground through the roots. In the daytime the moisture evaporates from the leaves, but at night it may collect upon them in drops. • At night, when the air is calm and clear, the ground is cooled by losing its heat to cold outer space ; the quiet lower air is then chilled, because it lies on the cooled ground, and dew (or frost) is formed. When the wind is blowing the lower air is constantly changed and none of it is much chilled; when the sky is cloudy at night the gromrd cools but little ; hence on windy or cloudy nights little or no dew (or frost) is formed. 45. Clouds, Fog, and Mist. — The different processes by Avhich water vapor is condensed ^ in the atmosphere pro- duce clouds of many different forms. It has been explained that in daytime of fair summer weather the lower air tends to rise in convectional currents. The ascending air currents 1 It should be noticed that the term condensation, when applied to vapor, refers to its change from the gaseous to the liquid (or solid) state, and not' to its compression, as vapor, into a smaller volume. Hence condensation of vapor may take place while the air with which it is mixed is expanding, provided that the expansion produces sufficient cooling to lower the tem- perature below the dew-point. Platk III. B. Cirrus Clouds rL.VTK III. A. Cuiiuilus Clouds THE ATMOSPHERE 63 expand and cool as they rise, and, if their ascent is great enough, some of their vapor is condensed, forming round- topped clouds, brilliant white in strong sunshine, as in Plate III, A ; the air within the clouds is all saturated by the vapor it still contains. The clouds are of unequal size, but have their bases at about the same height {com- monly one fourth to one half of a mile), and all drift along with the speed of the currents in which they are formed. Their rapid motion can be recognized by watch- ing their shadows pass across a field ; they nearly always drift eastward in the United States, being borne in the prevailing westerly winds of middle latitudes. Clouds of this kind are called cumulus (heap) clouds. They usually begin to form in the warming morning hours of fair weather, but dissolve and disappear in the late afternoon, when sunshine weakens, the ground cools, and convection ceases. It is usually the case that the great cyclonic storms of the westerly winds are preceded by long filmy or feathery strips of pale whitish cloud, as in Plate III, B. Clouds of this kind are formed at a height of several miles, in the air currents that flow out and forward from the upper part of the storm. They are called cirrus (curl) clouds. They con- sist of minute ice crystals, -because the moisture forming them has been condensed in the cold upper air at tempera- tures below the freezing point. Sometimes the cirrus is spread out in a thin sheet called cirro-stratus. When the sun or moon is seen through a cirro-stratus a large ring faintly colored with red on the inside is seen around the luminary. Such a ring is called a halo ; it is formed by 64 ELEMENTARY PHYSICAL GEOGRAPHY the bending (refraction) of the light in passing through the ice crystals. Halos are common and brilliant in the polar regions. In the central parts of the great whirling cyclonic storms heavy dull-gray cloud sheets of great size are formed at a moderate height above the earth's surface by the gradual cooling of the inflowing winds. Clouds of this kind, from which rain or snow falls, are called alto-nimbus and nimbus. A nimbus cloud is shown on the right side of Plate IV. As with other clouds, the air withm the nimbus is constantly saturated. These clouds often cover the area of several states at once, and they may hide the sun and stars for several days at a time, yielding- plentiful rain or snow before they drift away eastward and reveal the clear sky again in fair weather. They are especially large and heavy in winter, when the westerly winds and their storms are strongest. When the sun or moon is seen through the fragments of nimbus clouds it is often closely surrounded by a brilliant glow, called a corona. When a cloud is formed at so low a level that it rests on the ground or on the sea surface it is called fog. This is often the case when moist sea winds of mild temperature blow across a colder part of the sea or blow inland over snow-covered hills. Fog is often formed in valleys among mountains by the coolmg of the lower air at night. Fog of this kind usually disappears in the morning sunshine, but if very heavy it may not be dissolved by the short and weak sunshine of a winter day. A slight cooling of damp air may produce a faint cloudi- ness, known as mist, much less dense than fog. THE ATMOSPHERE 65 46. Thunderstorms. — When the lower air is warm and moist it is apt to rise and form great cumulus clouds from ten to fifty miles in length, whose tops may reach heights of more than a mile. When the rising movement is active and the cloud grows to great size it may often be seen to spread out at the top in a cirro-stratus film, and about the same time ram falls from its base. If the rain becoines heavy, lightning flashes occur, causing peals of thunder; hence such storms are called thunderstorms. Storms of this kind are common in the cloudy belt of the doldrums, where they usually occur in the afternoon Fig. 26. A Distant Thunderstorm and evenmg. They are also common on the lands in periods of hot summer weather. Much of the summer rain in the Mississippi valley falls from thunderstorms which drift eastward in the afternoon and night at a rate of twenty or thirty miles an hour, giving heavy rainfall for an hour or two as they pass by. "A violent blast of wind, or thunder squall, often rushes forward from beneath the front of the cloud mass, raising a cloud of dust before the rain arrives. During the growth of a thunderstorm cloud the water particles in it become charged with electricity. When the drops become large enough to fall as rain the electricity is discharged from one part of the cloud to another, or from 66 ELEMENTARY PHYSICAL GEOGRAPHY the cloud to the ground, in a great electric spark, or light- ning flash. Thunder is the sound caused by the violent agitation of the air along the flash. It may be compared to the sound caused by snapping a whip. As sound travels through the air at the rate of a mile in five seconds, the distance of a flash can be determined in miles by counting the number of seconds between the lightning and its thunder clap and dividing the number by five. The " rolling " of thunder is caused partly by the continuous arrival of the sound from different parts of a long flash, partly by the echoing from clouds or from hills and moun- tains. At night the upper clouds of distant thunderstorms are illuminated by flashes, commonly called heat lightning, too far away for the thunder to be heard. An unusually heavy and violent rain, popularly known as a cloud-burst, sometimes falls during a thunderstorm upon a small district. If on a hillside it may wash away the soil, baring the rock beneath. 47. The Rainbow. — When a thunderstorm passes east- ward in the late afternoon a rainbow is usually seen by observers on the west of it. The bow is formed by the sun- light that is turned back and bent (refracted) by the drops that are falling from the rear of the cloud. The center of the bow will be directly opposite the sun. Why will a rainbow form a half circle at sunset? Why does a rain- bow usually show less than a half circle ? A bow forming a complete circle might be seen from a balloon. 48. Tornadoes and Waterspouts. — Violent whirlwinds are occasionally formed in thunderstorms. They are seldom THE atmospherp: 67 more than a quarter of a mile in diameter ; they drift along with the thunderstorm in which they are formed, usually in an easterly direction, passing by in a minute or two. Their whirling winds are strong enough to blow down trees and overturn buildings. Violent local storms of this kind are often called cyclones, or prairie twisters, in the Mississippi valley, but the name tornado is to be preferred in order to distinguish them from the much larger and less violent cyclonic storms. When violent whirlwinds of this kind occur over a water surface a watery column is formed in their vortex ; they are then called waterspouts. Plate IV shows a water- spout over Vineyard sound, southeastern Massachusetts, as photographed on Aug, 19, 1896. A vessel overtaken by such a whirlwind may be suddenly dismasted. 49. Tropical Cyclones (Hurricanes and Typhoons) ^ — Violent storms known as tropical cyclones are occasionally developed in the doldrums when the heat equator stands farthest from the geographical equator. They appear to be, like thunderstorms, due to the inflow, ascent, and out- flow of very warm moist air. They grow to be several hundred miles in diameter, with violent winds, whirling in great spirals around a center of low barometric pressure, great cloud sheets, and heavy rains. As in the cyclonic storms of temperate latitudes, the winds of tropical cyclones turn counter-clockwise in the northern and clockwise in the southern hemisphere. As tropical cyclones increase in size, they travel slowly (one or two hundred miles a day) westward and toward the 68 ELEMENTARY PHYSICAL GEOGRAPHY temperate zone near the western border of their ocean. In a week or ten days they pass from the trade-wind belt into the prevailing westerlies. As they enter the temperate zone, still increasing in size but usually decreasing in violence, their path curves eastward, and they join the great procession of cyclonic storms of middle and higher Fig. 27. Regions of Tropical Cyclones latitudes. The chief regions of these storms are shown by dotted areas in Figure 27. In the southern hemisphere the doldrums of the Atlantic hardly pass south of the equator, on account of the large supply of cooled water that comes northward west of Africa ; hence no tropical cyclones occur on the Brazilian coast. In the western Pacific ocean the doldrums are farthest south in February and March, and at that time cyclones occur in the region of the Fiji islands. In the southern Indian ocean cyclones occur in the same months east of Madagascar. THE ATMOSPHERE * 69 I In the northern hemisphere the doldrums are farthest north in the western Atlantic and Pacific in August and Sep- tember ; cyclones occur in these months in the West Indies, where they are commonly called hurricanes, and in the region of the Philippmes, where they are known as typhoons. In the Indian ocean there are two seasons when the doldrums stand over the warm seas between the equator and Asia : one in May, as the doldrums are moving north ; one in October, when they are moving south ; hence in this ocean alone there are two seasons when tropical cyclones occur. Formerly much destruction was wrought on vessels at sea by the furious winds of tropical cyclones ; but now that the season of occurrence, the usual path, and the behavior of the winds of hurricanes have been learned, and now that vessels are built larger and stronger, losses at sea are much less serious than they were a century ago. When hurricane winds blow over islands in the torrid oceans they may cause much damage to vessels in the harbors by driving them ashore, and to settlements by destroying the houses and plantations. Cocoanut palms may thus be stripped of their leaves, after which the trees require a number of years of growth before again bearing the fruit of which so many uses are made. The great sea floods by which Galveston, Texas, was devastated in September, 1900, were caused by the winds of a tropical cyclone which brushed the surface waters from the Gulf of Mexico into the streets of the city. Similar sea floods have repeatedly occurred on the low- lands at the head of the Bay of Bengal, drowning many thousands of the people. 70 ELEMENTARY PHYSICAL GEOGRAPHY 50. Rainf alL — Rain, snow, hail, and sleet are all included under the general term rainfall. The explanation already given in Section 30 has shown how closely the amount and season of rainfall are connected with the circulation of the atmosphere. Snow occurs when the moisture of the air is condensed at temperatures below the freezing point (32°). Snow flakes ar6 six-rayed ice crystals of various patterns. Rain occurs when the moisture of the atmosphere is condensed into drops at temperatures above the freezing point, or when the snow flakes of lofty clouds descend into the warmer lower atmosphere and melt before reaching the ground. Sleet is half-melted snow. Hail is a mixture of ice and snow, usually in romided pellets, sometimes half an inch, rarely an inch, in diameter. It occurs chiefly in summer, when the ascendmg currents of lofty thunderstorms carry raindrops so far upward that they are frozen and coated with snow before they fall. Hailstorms occasionally do much damage to crops and buildings. Hail should not be confounded with the little pellets of nearly transparent ice, properly called frozen rain, caused by the fall of raindrops from a cloud whose temperature is above 32° through a lower stratum of freezing air. Hail occurs chiefly in hot summer weather ; frozen rain in winter. The amount of rain is determmed by measuring the depth of water that is collected in a cylindrical vessel having vertical sides, called a rain gauge. The gauge should be set in an open space, away from trees and THE ATMOSPHERE 71 buildings. Snow should be melted before it is measured. Eight or ten inches of snow correspond to about an inch of rainfall. An aiuiual total of eighteen, twenty, or more inches is necessary for agriculture, as over the great prairie region of the Mississippi and Ohio valleys from the 95th meridian eastward. If the annual amount is between eighteen and ten inches, agriculture requires irrigation, as on a large part of the Great plains east of the Rocky moun- tains, and over large areas m the basins of Utah and Nevada ; but scattered grass sufficient for cattle ranges may grow in such regions. If the annual total is under twelve or ten inches, there will not be water enough for irrigation, unless it is supplied by rivers that rise in a moister climate, as in parts of Arizona and southeastern California. • The distribution of the annual rainfall over the world, represented in Figure 28, shows that the greater amounts (eighty inches or more) occur m the subequatorial belt and on mountain slopes ascended by the trade winds or the pre- vailing westerlies. Most of the dry and desert regions of the world (twenty inches of rain or less) are either low- lands of the trade-wind belt, like the Sahara and central Australia, or the slopes and lowlands to the leeward of lofty momitams, as in Peru, or continental interiors crossed by the westerly \vuids, as m central Asia. Exercise. Where are the regions of heaviest rainfall ? How are these regions related to the belts of the terrestrial winds ? to coast lines? to mountain ranges? Where are the regions of light rain- fall? How are these regions related to the terrestrial winds? The heaviest rainfall in the world occurs on the southern slopes of the Himalayas, north of the Bay of 72 ELEMENTARY PHYSICAL GEOGRAPHY Bengal. Here the rainfall of a single year would meas- ure tliirty-five or forty feet in depth, and much more than half of this amount falls during the summer half year when the southerly monsoon is blowing. On the bold southwest coast of India an annual fall of over thirty feet occurs. The greater parts of western Europe and of eastern North America are fortunate in receiving a plentiful but not excessive ramfall. In the polar regions the annual snowfall, melted, would seldom exceed fifteen inches of water, and would fre- quently be less than ten. This is because cold air can- not contain much vapor, and because when cold air is cooled thete is but little vapor condensed from it. In the torrid zone the equatorial rains are heavier because warm air can contain a large quantity of vapor, and when warm air is cooled it yields an abundant condensation of moisture. 51. Rainfall of the United States. — The ramfall of the United States may be considered' under three headings : the Pacific slope, the western interior region, the "eastern region. The Pacific slope has plentiful rainfall m the north (over sixty inches), where the storms of the west- erlies are common ; but it has light rainfall in the south (under thirty inches), because here the westerlies turn southward to join the trades, and storms are infrequent. The westerly winds are stronger and stormier in winter than in summer; hence the rainfall of Washington and Oregon is heavier in the winter than in the summer THE ATMOSPHERE 73 months. The belt of westerly winds reaches farther south in winter than in summer ; hence the rainfall of southern California is almost entirely confined to the winter months, while the summers are very dry, thus illustrating the features of the subtropical belt. Fig. 29. Annual Rainfall of the United States Darkest shade, over 80 inches. Lighter vertical lines, from 40 inches to 80 inches. Horizontal lines, from 20 inches to 40 inches. Blank, from 10 inches to 20 inches. Dotted, less than 10 inches. The western interior region, from the Cascade and Sierra Nevada mountains to the 100th meridian, has moderate or plentiful rainfall on the mountains and high plateaus, be- cause the air is cooled and some of its moisture is con- densed as the westerly winds rise over these elevations. The lower lands, as in the basins of Utah and Nevada and over the Great plains that slope eastward from the 74 ELEMENTAEY PHYSICAL GEOGRAPHY Rocky mountains, have light rainfall. The winds here, already dried by losing much of their moisture m cross- ing the ranges farther west, are seldom cooled enough to form clouds and to yield rain. Hence much of this region is arid. A large part of Nevada, Utah, and Arizona is too dry to yield pasturage ; elsewhere a tliin growth of grass suffices to support cattle if they have a large area over which to range. Agriculture is seldom successful in this region without the aid of irrigation. The eastern region is not distinctly separated from the western; the rainfall gradually increases eastward, as moisture is supplied in greater quantities by south- erly winds from the Gulf of Mexico and from the Atlantic. Over most of -this great region rainfall is well distributed through the year (over forty or fifty inches) ; somewhat more falls in summer than in winter over the mid-Mississippi basin. The heaviest fall (over sixty or eighty inches) is on the states bordering the Gulf of Mexico (not including Texas), and on the mountains of North Carolina. 52. Weather Changes. -^ The term weather includes all the atmospheric conditions that an observer may feel or see, — hot or cold, clear or cloudy, dry or wet, Avindy or calm. In the torrid zone the weather is marked by regular changes from day to night ; the changes are small at sea and greater on land, and they are seldom interrupted by storms, except that afternoon thunderstorms are common in the belt of equatorial rains. In the summer season of THE ATMOSPHERE 75 temperate latitudes weather changes are usually of mod- erate amount. In winter the weather of temperate lati- tudes is largely controlled by the passage of cyclonic and anticyclonic areas, which are then numerous and large, while the control .by the change from day to night is rela- tively weak. In frigid latitudes the change of weather from day to night is always weak compared with the changes caused by the passage of the great atmospheric whirls. The relation of weather changes to the spiraling winds of the prevailing westerlies may be simply illustrated by drawing (on an appropriate scale) the winds and clouds of a cyclonic and an anticyclonic area, as in Figure 16, on tracing paper and moving the paper slowly to the right, across a map of the United States. Let the center of the cyclonic area be supposed to move, for example, in four days from Colorado past Lake Michigan and down Hie St. Lawrence river. Note the changes of wind and weather at Indianapolis, or some other place, as the spi- ralmg wind areas advance eastward. Consider the tem- perature of the regions whence the winds come in winter and summer, Figures 18 and 19, and infer the changes of weather that they will bring. In the diagram for winter weather the area of the spiraling winds should be larger than m summer ; the cloud sheet about the cyclonic center should be larger and the winds stronger. A series of cyclonic areas sometimes pass by at the rate of two in seven days, thus causing a repetition of a certain kind of weather on the same day of the week for several weeks together. 76 ELEMENTARY PHYSICAL GEOGRAPHY 53. Summer Weather in the United States. — A well- marked series of weather changes over the central and eastern United States in summer may open with fair weather and bright blue sky ; the days are warm but not oppressive ; the nights are cool and refi'eshing. Then, if a cyclonic center appears a thousand miles or so to the west, the wind changes to a southerly source, so that it comes from the warm waters of the Gulf of Mexico and the warmer land of the Southern States. The air becomes hazy and the sky pale blue ; the days are sultry and oppressive, and the nights lose their refreshing coolness; the ground is dried and parched, and vegetation suffers. The great corn crop of the Mississippi valley may profit by these high temperatures if they do not last too long, but manual labor is exhausting under the blazing sun, and sunstrokes occur in increasing numbers. Scattered thunderstorms are then reported for a day or two in the afternoon and evening. These are followed by a more extended cloudiness as the cyclonic center approaches, and general rains may fall over several states near the low- pressure center. Thunderstorms of great size are some- times formed in the moist southerly winds, occasionally giving rise to destructive tornadoes. As these local storms pass by, the cooler northwesterly winds in the rear of the low-pressure center come from the far northern plains. The clouds drift away eastward, the pressure slowly lises, the temperature falls 20° or more, and damp sultry air under heavy clouds is exchanged for fresh air with bright blue sky. Then, as the westerly winds weaken, a southerly breeze springs up and all these changes are repeated. THE ATMOSPHERE 77 54. Winter Weather in the United States. — In winter the succession of weather changes is controlled even more dis- tinctly than in summer by the passage of cyclonic and anti- cyclonic areas. A period of fine, cold, anticyclonic weather usually has a cloudless sky with light winds. The weak sun- shine of a short midwinter day cannot overcome the strong cooling by radiation durmg the long clear night, and the tem- perature at dawn sinks to a low degree. But as the anticy- clone moves eastward the pressure begins to fall. Then long filaments of lofty cirrus cloud float slowly over from the west, announcing the approach of a cyclonic center, the wind turns to a more southerly source, and the temperature slowly rises. As the cyclonic center draws near, the wind strengthens, the sky is more heavily overcast, and the temperature rises more distinctly, for the source of the winds is now over the tempered waters of the sea on the south and southeast. The rise of temperature may continue steadily through the night, so that midnight and dawn are warmer than the pre- vious noon ; for the southerly wind may be more powerful as a cause of warming than the cloudy night is as a cause of cooling. The lowering clouds let fall their rain or snow ; if rain, the snow of former storms is rapidly washed away; if snow, the drifts of former storms are deepened and the country is shrouded in white far and wide. It is under the long-lasting snow cover that the "winter wheat" of the northern prairies, sown in November, is protected from the extreme cold of the winter winds, for the snow is an excellent non-conductor. As the cyclonic center moves on, the northwesterly winds follow it and the pressure rises. The rain or snow ceases ; 78 ELEMENTARY PHYSICAL GEOGRAPHY the clouds break up and drift away to the east and reveal a brilliantly clear sky. The cold northwesterly gale that has come from the far northern plains, west of the cyclonic cen- ter, now arrives as a "cold wave." These winds may be from 30° to 50° colder than the southerly winds. A fall of temperature may thus be produced steadily through the day, so that noon is colder than the previous midnight. If the cold gale is accompanied by falling or drifting snow, it is called a blizzard, a dreaded storm on the plains and prairies. As the temperature falls, furnaces must be made hotter to keep houses warm, and destructive fires then become more frequent than usual. The cold winds may sweep far south, causing great damage to southern crops. Then, as the storm center moves eastward, the winds farther in its rear weaken; the nights become calm and the tem- perature falls to its lowest degree, and thus another spell of fine and intensely cold weather is ushered in. 55. Summer and Winter Weather in Temperate Lati- tudes. — Both in winter and summer all the changes here described as connected with areas of liigh and of low pressure are felt earlier in the west than in the east. The eastward passage of cyclonic or low-pressure areas, illustrated in Figure 30, is controlled by the prevailing eastward atmospheric currents in' middle latitudes; and the direction of the currents is determined, as has been stated, by the earth's rotation. In summer time the difference of pressure between cyclonic and anticyclonic centers in North America is relatively small (from 0.5 to 0.8 inch) ; hence the spiraling winds are tlien relatively THE ATMOSPHERE 79 light. Moreover, the southern and northern regions whence the inflowing spiral winds are then drawn have temperatures not greatly different (about 85° and 65°); hence the changes of temperature are moderate. The eastward movement of the cyclonic areas is relatively 0° 30° Fig. 30. Stonn Tracks of the North Temijerate Zone slow (500 miles a day in the United States) ; hence the weather changes are gradual. All this is changed in winter. The differences of pres- sure are doubled (from 1.0 to 1.5 inches) and the winds often gain the strength of gales ; the regions whence the southerly and northerly winds are drawn upon the Cen- tral States have very unlike temperatures (80° and 0°), 80 ELEMENTARY PHYSICAL GEOGRAPHY and the contrast between the warmth in the front and the cold in the rear of the cyclonic areas is very marked. In the winter hemisphere the general winds are quick- ened, especially in middle latitudes ; and therefore the centers of high and of low pressure drift eastward faster (800 miles a day). Besides all this, the cyclonic and anticy clonic centers are more numerous in winter than in Summer ; hence weather changes in winter are frequent as well as rapid and strong. Winter is therefore a time of stormy changes as well as of low temperatures, thus resembling the conditions of the frigid zone ; while sum- mer weather is comparatively even at a high temperature, like that of the torrid zone. 56. Ocean Storms. — The stormy areas of the westerly winds drift from North America out upon the northern Atlantic ocean, as shown in Figure 30. Gales attend their passage, especially in the winter season, when a voyage across this ocean is much rougher than in summer. The gales caused by these stgrms are usually on the southern side of the low-pressure center, and hence from a western quarter. The general course of the storm centers is north- eastward, so that a cyclonic center that passes over New England or down the St. Lawrence valley is more likely to affect the weather of Norway than that of Spam. Storms from the North Pacific ocean come upon the west- ern coast of North America; they may before breaking up pass far inland or even cross the whole breadth of the con- tinent. The storms in the prevailing westerly wuids of the southern hemisphere encounter but little land m their THE ATMOSPHERE 81 course. They are more severe in the southern wmter (June to August) than in the summer (December to Feb- ruary). South America reaches farther south than the other continents; hence vessels rounding Cape Horn must enter much farther into this stormy belt than in rounding the Cape of Good Hope, and the passage aromid Cape Horn is dreaded for this reason. 57. Cyclonic Winds. — The inflowing spiral winds of cyclonic storms are often given special names in different parts of the world, according to the kind of weather they may bring. The cold wave of our wmters, sweepmg over the central and eastern United States from the far northern plams in the rear of cyclonic centers, has already been described. In western Europe the cold wind of winter is the northeaster, because the plains of northeastern Europe supply colder air than the ocean about Iceland. It occurs when a cyclohic center follows a more southerly track than usual. The blizzard of our plains corresponds to the buran of Siberia. No special name has been given m the United States to the sultry southerly wind that frequently brings unseasonably warm weather m front of a cyclonic center. It might be called a sirocco, after the Italian name of a similar wind. In the southern hemisphere cold winds come from the south, and hot winds from the north. In southern Australia the "wuid that corresponds to the sirocco is called a brickfielder, because it bakes the fields hard and dry. 58. Weather Predictions. — Weather maps from which the general character of the weather for one or two days 82 ELEMENTARY PHYSICAL GEOGRAPHY 1 may be predicted are now prepared daily in many countries Observations of the weather made at the same hour at many different places are telegraphed to the central station, — the Weather Bureau at Washington for the United States. They are then promptly charted so that the areas of high and low pressure, the temperature, the direction and strength of the winds, the distribution of clear and cloudy sky and of rain or snow are all shown. It is known, as described on preceding pages, that cyclonic and anti- cyclonic areas with their attending weather conditions usu- ally move eastward ; it is therefore possible to foretell with considerable accuracy the weather that may be expected for a day or two in various parts of the country from the conditions shown on the weather map. Predictions thus prepared are distributed by telegraph, and published in special bulletins and in newspapers for the benefit of the public. No one has yet succeeded in making successful predic- tions of the weather regularly for definite districts several weeks or months in advance. It is true that such "long- range predictions," as they are called, are frequently pub- lished. As the weather differs in different parts of the country, predictions of hot weather over the central United States in July and of cold weather in January, or rain in March and drought in September, may be correct for one place or another, but they must be incorrect for other places. Such predictions cannot be depended upon. 59. Climate. — The general succession of weather changes through the year, averaged for many years, THE ATMOSPHERE 83 constitutes the climate of a region. The five climatic zones into which the earth is commonly divided need further subdivision in order to correspond to the many well-marked types of climate on lands and seas, on coasts and inland regions, on lowlands and highlands. The trade-wind belt at sea has the simplest climate in the world, with small daily and yearly changes of tempera- ture. The steady wind and fair weather of almost any day give a fair sample of the year. Low lands under the regular trade winds suffer greater daily and yearly changes of temperature, with light rainfall. Compare the mean annual range of temperature in the "^^sf Indies and in inner Africa, latitude 20° N., Figure 20 ; in^A^frica, Indian ocean, and Australia, latitude 20° S. ^^-"^ The subequatorial belt has^a distinct seasonal change as the clouds of the heatequator move away and give place to the dry tj:ara.e winds. The Sudan, between the desert of Sahara and the forest belt of equatorial Africa, has plentiful rainfall and active plant growth when the equatorial cloud belt moves north, bringing the wet sea- son (May to August), but it becomes parched, barren, and dusty under the trade winds of the dry season (December to March), Examine Figure 21 and state in what months you would expect rain on or near the geographical equator. At the head of the Gulf of Guinea, west equatorial Africa, I'ain is most abundant in March and October to November. In Ceylon the rainfall is greater in May and October than in the other months; at the city of Quito, Ecua- dor, in April and November. How do you explain these double rainy seasons? 84 ELEMENTARY PHYSICAL GEOGRAPHY The south temperate zone is mostly an oceanic belt. The changes of air temperature with the seasons are small, as shown in Figure 20, because the water surface warms and cools so little in summer and winter. Its winds are more stormy in winter, less stormy in summer ; never very hot or extremely cold, but for the most part chill, damp, and blustering. Islands near 50° S. are hardly habitable, not that the winters are too severe, although cloudy and wet, but that the summers are too chilling. The north temperate zone contains large areas of both land and water, and the temperatures of its various parts are therefore very unlike, as shown in Figures 18, 19, and 20. The parallel of 50° N. crosses regions whose climates are so different that they Avould hardly have been placed under a single zone had they been studied before being named ; but the name was given from the truly temper- ate climate of southern Europe, before other parts of the world were well known. Beginning in the moderate climate of the North Atlantic, Figure 20, the parallel of 50° N. enters the favorable climate of middle Europe, where the last thousand years have witnessed the greatest human progress in the arts and sciences that the world has ever known. It crosses the broad deserts of central Asia, where the scattered population is held down in barbarism chiefly by severe and unfavorable climatic conditions. The broad North Pacific has in this latitude a climate as moderate as that of the North Atlantic. Passing the tempered and moist climate of the coast belt of British Columbia, and crossing the snowy mountain ranges beyond. THE ATMOSPHERE 85 the severe interior climate of middle Canada is reached, with extremes of temperature, summer and winter, only less than those of inner Asia. As far as habitability is concerned, the middle north temperate zone contains climatic differences almost as great as those found in passing from the equator to the pole/ Compare this account of the climate of latitude 50° X. with the conditions in latitude 50° S. Supplement to Chaptek II 60. Deflection of Winds by the Earth's Rotation. — Place a marble in the center of a circular board. Set the marble in motion by striking it a light blow. It will move in a straight line along a radius from center to circumference. Now let the board be given a slow movement of rotation around a pivot at its center. The marble will now again move directly outward, but the line that it traces on the turning board will be curved so as to fall behind the radius on which it started. If the board turns to the left, the marble will be deflected to the right of its original path ; if the board turns rapidly, the deflection will be strong. In Figure 31 the circle. A, resting on the earth in a northern latitude ^ig. 31. Rotation ot a Disk on a may be taken to represent a circular Rotating Globe board or surface of great size. A north line drawn from the center of the circle meets the prolonged axis of the earth at N. "When the rotation of the earth has car- ried the cii-cle to B the same north line has a new direction, BN, 86 ELEMENTARY PHYSICAL GEOGRAPHY showing that the circle has turned somewhat to the left with respect to its own center. Hence any such circle may be taken to represent a turning surface. A body beginning to move in any direction from the point A will tend to turn to the right, because of the rotation of the circle to the left. This tendency will be strongest at the pole, because a circle there rotates with the greatest rapidity, turning completely round in twenty-four hours. The tendency is zero at the equator, because there a circle has no movement of rotation with respect to its own center. In the southern hemisphere, where the circle must turn to the right, the deflective force acts to the left. The wind is so free to move over the earth's surface that it is greatly affected by the deflective force arising from the earth's rota- tion. Hence the members of the atmospheric circulation do not flow north and south, but are always deflected to the right of these direc- tions in the northern hemisphei'e, and to the left in the southern. The lofty overflow currents are deflected so as to run from the southwest or even from the west-southwest in the northern hemi- sphere, from the northwest or west-northwest in the southern. The winds approaching the equator do not blow directly from the north and the south in the two hemispheres, but are deflected so as to blow from the northeast and southeast, forming the trade winds. The whirling winds of cyclonic storms, described on pages 45 and 67, attempt to blow toward their centers of low pressure, but on account of the earth's rotation the winds are deflected to the right in the northern hemisphere, and to the left in the southern ; thus the storms are given their whirling movement. It should be noted that winds wiU be deflected to the right or left, in whatever direction they begin to blow, east and west winds being- affected just as much as north and south winds. Ocean currents are similarly affected but to a less degree, because they move moi'e slowly than the winds. Rivers tend to tui-u to the right in the northern hemisphere and to the left in the southern; but the tendency is practically overcome by the resistance of the banks. Similarly a railroad train tends to be deflected, but is held to its track by the flanges on the wheels. THE ATMOSPHERE 8T 61. Practical Method of studying Observations of the Sun. — In studying the control of the seasons by the sun it is desirable to determine the length of the day and the midday altitude of the sun by observations about once a fortnight, or at least once a month, through the school year, with additional observations near the times of shortest and longest days or of lowest and highest midday sun. If sunrise comes at too early an hour for convenient observation, note that midday occurs at the middle of the interval between sun- rise and sunset. Midday is determined by the method explained on page 8. The time of sunset may be directly observed. The time of sunrise may then be determined by counting back as many hours and minutes before midday as sunset occurs after midday. The midday altitude of the sun may be determined as follows : Use such a box as is shown in Figure 3, and drive a pin square into one side of the box, close to its upper corner. With the pin as a cen- ter, draw an arc of a circle on the box side. Draw a horizontal and a vertical line from the pin to the arc. The arc included between the two lines will be a right angle, or 90°. Divide it into halves, divide the halves into thirds, and the thirds again into thirds. The small divisions thus found will be 5° of arc. Number the divisions from at the horizontal line to 90° at the vertical. As the sun approaches the meridian, turn the side of the box so that it is directed toward the sun. The shadow of the pin is then seen as a slanting line, and the altitude of the sun is indicated by the angle that the shadow line makes with the horizontal line. Con- tinue to turn the box after the sun, until the altitude indicated by the shadow line begins to decrease. The greatest angle thus found is the midday altitude of the sun. In Figure 32 let the horizontal scale represent the days of the year, and the vertical scale the angular altitude oi" the sun at mid- day. IMark the sun's midday altitude by dots opposite the appro- priate dates. At the close of the school year draw a curve through the dots. Draw lines parallel to the base line and touching the upper and lower points of the curves. Draw a third line midway between the last two. 88 ELEMENTARY PHYSICAL GEOGRAPHY In Figure 33 the vertical scale represents the days of the year ; the horizontal scale measures hours before and after midday. Mark dots to the right and left of the midday line and opposite to the appropriate dates, to represent the time before and after midday at ■which sunrise and sunset occur. Connect these dots by curved lines. Draw two lines that shall stand six hours on either side of the mid- day line. Now determine from Figure 32 the dates when the sun has the greatest midday altitude (or when it stands farthest north in the sky) when it has the least midday altitude (farthest south in the sky), yept. , Oct. , Nov, I Dec. , Jan. , Feb. , Mar, , Apr, ^ May , June , Fig. 32. Diagram of the Sun's Midday Altitude and the two dates when its altitude is that of the mid-horizontal line. Deterjuine from Figure 33 the date when the day is longest, when it is shortest, and the two dates when it is twelve hours long. Compare the dates thus found. If the observations are well made and the diagrams accurately constructed, the four dates should agree on the two diagrams. The dates when the days are twelve hours long, and therefore equal to the nights, are JNIarch 21 and September 22 ; these dates are called the vernal (spring) and autumnal (fall) equinox (equal- night). The date when the sun is farthest north, and when the day in the northern hemisphere is consequently longest, is June 2L This is called the summer solstice (sun-stand), because the sun, hav- ing then finished its northward movement, stops or "stands" before beginning its southward movement. Tlie day when the sun is THE ATMOSPHERE 89 farthest south, and when the day is consequently shortest in the northern hemisphere, is called the winter solstice; this date is December 21. Between what dates is the sun moving northward in the sky? Between what dates is it moving southward ? Between what dates are the days lengthening? 12 M Se|)t At the time of the equi- noxes the sun must be on the equatoi- of the sky ; for, as is shown in Figure 17, it is only then that equal days and nights occm* in all parts of the world. Hence the middle horizontal line in Figure 32 must rejire- sent the angular altitude of the sky equator where it ci'osses the meridian. The angular distance of the sun north or south of the sky equator for any day of the year may be measured by the scale at the side of the figvu-e. The greatest angular distance of the sun from the sky eqiiator gives means of determining the limits of the zones. (See page 48.) How far north of the sky equator does the sun stand at the time of the summer solstice ? How far south at the time of the winter solstice ? How many days is it north of the sky equator? How many days south ? 62. Determination of Latitude. — The sky equator passes overhead (in the zenith) to an observer at the earth's equator ; hence the sky equator will depart one degree from the zenith for every degree that Apr. M^y Jily Fig. 33. Diagram of Sunrise and Sunset Hours 90 ELEMENTARY PHYSICAL GEOGRAPHY the observer moves toward the pole. Therefore the latitude of a place must equal the angular distance of the sky equator from the zenith. Latitude may thus be determined on any day by measuring the sun's midday altitude and allowing for its distance from the sky equator, as determined by Figure 32. The altitude of the sky equa- tor subtracted from 90° is the latitude. Results that are correct within a few degrees may be obtained even by the rough obser- vations here described. If records of the kind indicated above are taken on different dates in successive years, the increasing number of dots will give better and better definition of the curves in Figures 32 and 33 ; but minute accuracy of performance is not so important as intelligent exercise in the application of principles. Examples. If the midday altitude of the sun is 50° on the 22d of September, what is the latitude of the place of observation ? What would the latitude be if the observation had been made on Decem- ber 21 ? on March 21 ? on June 21 ? 63. Exercises on Weather Maps. — Many instructive exercises may be based on the daily weather maps. Copies of these maps for school use may be obtained, under certain conditions, by addressing the Chief of the Weather Bureau, Washington, D.C. The exercises here described may be performed on the original maps, or on outline maps of the United States upon which certain weather elements are copied. It is usually best to select maps on which differences of pressure are well defined, in order to exhibit strongly marked types of weather. 64. Distribution of Pressure. — Plat upon a blank map of the United States the barometer readings taken from a weather map, and thus guided draw in lines of equal pressure, or isobars, for every tenth of an inch according to the method already explained for iso- therms. The difference of pressure between the highest and lowest readings is.often six or eight tenths of an inch or more. Shade the areas of high and low pressure, leaving the area of intermediate pres- sure (for example, from 29.9 to 30.1 inches) blank. Describe the THE ATMOSPHERE 91 distribution of pressure thus shown. Draw a similar map for the next day. Describe the change in the distribution of pressure thus found. Temperature may be similarly treated. 65. Movement of Winds in Areas of High and Low Pressure. — Select several well-defined examples of high- and low-pressure areas whote centers lie in the mid-Ohio valley, so that observations are provided on all sides of them. Plat the wind arrows (the arrow flies with the wind on weather maps), and let their length indicate wind velocity (an eighth of an inch for five or ten miles) . Draw addi- tional lines to represent inferred wind movement between the points of observation. How is the direction of the wind at any place related to the distribution of pressure about that place ? In answer- ing this question it will be well to draw, through the point consid- ered, a line at right angles to the neighboring isobars. This line shows the direction of increase or decrease of pressure. Describe the general movement of the winds (direction and velocity) with respect to a center of high pressure ; of low pressure. 66. Composite Portrait of High- and Low-Pressure Areas. — Rule a straight line through the center of a sheet of tracing paper and mark the ends of the line N and S. Lay the center of the sheet over the center of an area of low pressure and turn the N-S line so that it shall lie most nearly parallel to the adjacent meridians. Trace off the signs indicating the state of the sky (clear, fair, rain, or snow) at various stations. Do the same for several other maps that have a low-pressure center. Do the same on another tracing paper for sev- eral areas of high pressure. Compare the results as to the distribu- tion and frequency of clear, fair, and wet weather, with respect to centers of high and of low pressure. Winds may be similarly treated. 67. Progression of High- and Low-Pressure Areas. — Select a series of four or five maps on which a well-defined area of high or of low pressure is represented as occupying successive positions eastward across the country from the Rocky mountains to the Atlantic. Chart on an outline map the path of the center of the 92 ELEMENTARY PHYSICAL GEOGRAPHY area studied and determine its velocity in miles an hour and a day. Note the weather changes (pressure, temperature, wind, sky) that occur at a single station as the cyclonic or anticyclonic area passes over it. What is the general character of these changes for a cyclonic area ? for an anticyclonic area ? Compare the succession of weather changes at any place, as deter- mined from weather maps, with the weather changes observed at school during several days. How are the local weather changes related to passing areas of high or of low pressure (anticyclonic and cyclonic areas) ? QUESTIONS Sec. 19. What processes depend on the atmosphere? What is known of its height? 20. What is the composition of air? How is oxygen iisec: ? carbonic dioxide ? 21. What is the pressure of the atmosj^here on a square foot of surface ? Describe the mercurial barometer ; the aneroid barometer. How can barometers be used to measure mountain heights ? 22. How does the density of the air vary? Why? What is the weight of a cubic foot of air at sea level ? How is sound carried ? 23. How are the colors of the sky produced? What is the twi- light arch? When may it be seen? 24. How is the temperature of the air controlled? Why is the upper air cold? Consider the diurnal range of temperature in the upper and lower air. How do the processes of absorption, conduc- tion, and radiation affect the temperature of the air ? How does the form of the earth affect the distribution of temperature ? How is the weight of air affected by heat ? 25. What is a mirage? How is it produced on level deserts? on a water surface ? 26. Explain the construction of a thermometer. How do the Fahrenheit and Centigrade thermometer scales differ? What is a THE ATMOSPHERE 93 thermograph? a maximum thermometer? a minimum thermom- eter? How should a thermometer be exposed? 27. How are temperature charts constructed? What is an iso- thermal line? How are mean temperatures determined? What is the heat equator ? Describe its position. Compare the mean annual isotherms of the northern and southern hemispheres. 28. Describe the movements of the air between a hot and a cold room. What is a convectional circulation? Describe the general circulation of the atmosphere between equator and poles. What changes of temperature are caused in ascending and descending currents ? What is the planetary circulation ? 29. How are winds named? How is their strength described? What is an anemometer? 30. Describe the steps in the circulation of water through the atmosphere. How is rain caused? 31. What are the chief members of the planetary winds? Describe the trade winds. Where do they occur? AVhat is their direction? What is the relation of rainfall and deserts to the trade winds? of wet and dry mountain slopes to the trade winds? Give examples. Describe the prevailing westerlies. Where do they occur? What is their direction? How is rainfall related to these winds? What are the doldrums? the horse latitudes? Describe and explain the weather of the doldrums ; of the horse latitudes. 32. Describe the whirls of the westerly winds. Explain their weather. How fast do they travel ? Compare the whirls of the two hemispheres. Compare the atmospheric pressure at the center of the inward and outward whirls. What names are given to these whirls ? 33. Describe the movement of the earth around the sun. Com- pare the attitudes of the northern and southern hemispheres with respect to the sun in the two half years. What are the resulting variations of temperature ? What are the months of each of the four seasons in the northern hemisphere? in the southern? What are the limits of the torrid zone ? the frigid zones ? the temperate zones ? 94 ELEMENTARY PHYSICAL GEOGRAPHY 34. What are the apparent movements of the sun in December? in June ? How are the temperatures of winter and summer related to these movements? Explain the rising temperature of spring; the falling temperature of autumn. 35, 36. How may the change of seasons be described if the earth as a whole is considered ? Mention the most striking facts shown on the isothermal charts for January and for July. 37. Describe the most striking facts shown on the chart of mean annual temperature range. Compare the annual range of temperature over the northern continents and the southern oceans ; on western and eastern coasts in temperate latitudes. Why are the annual changes large in the northern hemisphere? Why small in the southern? 38. How do the terrestrial winds differ from the planetary? Explain the differences. Describe and explain the subtropical belts. Name some countries lying in a subtropical belt and describe them as to winds and rainfall. Describe and explain the subequar torial belt. Describe its migration, Figures 22, 23, on the Atlantic ocean; on the eastern Pacific ; on the Indian ocean. Give some examples of subequatorial rainf aU in South America ; in Africa. 39. What are monsoons? How are they caused ? Where do they occur, Figures 22, 23 ? Describe the monsoons of the Indian ocean. 40. 41, 42. How do the continents affect the terrestrial winds? Give examples from Asia. What are land and sea breezes? How do fair-weather winds on lands vary from night to day? Explain this variation. Why does it not occur at sea ? 43. What is humidity? How does it vary with temperature? What is saturation? Compare the feeling of damp and dry air. 44. What is the dew-point ? How may it be determined ? What are dew and frost ? Under what conditions are they produced ? 45. Describe the chief kinds of clouds : cumulus, cirrus, cirro- stratus, alto-nimbus, and nimbus. Describe a halo ; a corona. 46. 47, 48. Describe a thunderstoripi. Where and when do such storms occur? What can you say about lightning and thunder? What is a cloud-burst? a rainbow? a tornado? a waterspout? i THE ATMOSPHERE 95 49. Where and how are tropical cyclones formed? How do their winds blow ? How do these storms travel ? In what regions do they occur? In what months? Why are there two seasons of cyclones in the northern Indian ocean? Why are tropical cyclones not formed in the South Atlantic ? 50. What is meant by rainfall? Describe and explain snow ; rain ; liail ; frozen rain. How is rainfall measured ? State the relation of rainfall to agriculture. Give several examples of the relation between the terrestrial winds, Figures 22, 23, and rainfall. Figure 28. Where is the heaviest rainfall of the world ? What is its amount? its cause ? Why is the rainfall of low latitudes large, and of high latitudes small ? 51 . Describe the rainfall of the Pacific slope of the United States ; of the interior region ; of the eastern region. 52. What is meant by weather ? Describe the prevailing weather of the torrid zone ; of the temperate zones in summer ; in winter ; of frigid latitudes. Explain the effects of cyclonic and anticyclonic areas. 53. Describe a period of summer weather in the eastern United States as a cyclonic area is approaching ; after it has passed. When are sunstrokes and thunderstorms most common? 54. Describe our winter weather in front of a cyclonic area ; in the rear. When may a warming night occur? a cooling day? What is a cold wave ? a blizzard ? 55. Describe the tracks of high- and low-pressure areas in the north temperate zone. What changes of pressure do they cause in summer? in winter? How fast do they travel in summer? in winter? Compare the changes of temperature that they produce in the central part of United States in summer and in winter. 56. 57, 58. Describe the storms of the North Atlantic. What is aburan? a sirocco? a brickfielder ? How is the weather predicted? 59. W^hat is climate? Describe the climate of the trade-wind belt at sea ; of the subequatorial belt ; of the south temperate zone ; of the north temperate zone on the oceans ; on the lands. Describe the climates of latitude 50° N. ; of latitude 50° S. I CHAPTER III THE OCEAN 68. Form of the Ocean. — The ocean is a sheet of salt water, clear and blue, covering about three quarters of the earth's surface to an average depth of about two miles. It lies in broad depressions or basins between tlie conti- nents, its shallow edges lapping over the margin of the continental masses. The outline and distribution of the ocean are best studied on a globe. A vast water area, comprising the Pacific and Antarctic oceans, covers nearly half the earth. The water surface is broken only by Australia, the Antarc- tic lands, and many small islands. A short Indian arm extends from this great oceanic area into the space between Africa and Australia, and a long, relatively narrow Atlan- tic arm runs between the Old and New Worlds, ending in the gulf-like Arctic ocean around the north pole. The surface of a hemisphere whose pole is near New Zealand is nearly all water, as in Figure 34 ; while the opposite hemisphere contains all the large land areas, except Australia, the Antarctic lands, and the extremity of South America. It is not a little curious to note that near the pole of the land hemisphere stands the greatest city of the world, the capital of the empire whose colonies are more widely spread than those of any other nation. 96 THE OCEAN 97 What lands lie entirely in the land hemisphere? What oceans lie largely in the land hemisphere? Trace the course of the great circle which divides the land and water hemispheres. 69. The Ocean as a Highway. ^ — The lands are widely separated by the oceans, and navigation of the "high seas" requires great skill and is fraught with many dangers. But the oceans are a ready-made highway, where movement Fig. .34. Water and Land Hemispheres is easy and open to all comers ; the winds furnish free motive power to sailing vessels, and coal is an economical fuel for steamers. Hence ocean-going vessels are used to carry large quantities of merchandise from one part of the world to another. Before railroads were invented the two sides of the North Atlantic were in more active communication by sea than the two sides of any continent overland. Since railroads have been extensively built inland transportation has greatly in- creased ; but a great part of international commerce is still carried on across the oceans in steamships and sailing vessels. 98 ELEMENTARY PHYSICAL GEOGRAPHY 70. Exploration of the Ocean. — The earlier exploration of the ocean discovered its shore lines on the continents and" islands. Exploration in the latter part of the nineteenth century penetrated its depths and reached its bottom. Soundings are now made with much accuracy, even to depths of four miles or more. I'ine steel wire is used for Fig. 35. An Ot'eaii Steamship a line ; the sinker is a heavy iron ball that is automatically detached on touching the bottom; then the wire is rapidly reeled in by steam power. A sounding of 3000 fathoms • {one fathom equals six feet), or over three miles, can be completed in about an hour. The temperature of the deep water is taken by self- registering thermometers. They must be protected by an outer glass tube against the tremendous pressure of the THE OCEAN 99 deep water. Samples of water are obtained from various depths by the use of brass tubes, called water bottles, sent down open but automatically closed when reeling in begins. Specimens of the ocean bottom are gathered by dredges, or strong nets with an iron rim. Wire rope is needed to haul up the ton or more of material that they take in while dragging on the sea jfloor at depths of one, two, or even tliree miles. Nets are sometimes attached to the wire rope at different depths, for the purpose of catching animals that hap- pen to enter them. The best nets are closed while sinking and rising, being open only while trolling at the greatest depth that they reach. Fig. 36 Sounding Instrument and Water Bottle 71. Ocean Depths. — Soundings have shown that the ocean basins are com- paratively steeps sided and flat floored. The greatest depth yet found is 31,614 feet, in the western Pacific near the island of Guam (lat. 12° 45' N., long. 145° 45' E.). Another place of great depth, 30,930 feet, is in the Pacific, near the Fiji islands. The deepest sounding yet made in the Atlantic is 27,366 feet, or over five miles, in a local depression 100 miles north Fig. 37. Dredare L.oFC. 100 ELEMENTARY PHYSICAL GEOGRAPHY of Porto R.ico, West Indies. The Atlantic is generally less deep along its middle (9000 to 12,000 feet) than on either side (15,000 to 18,000 feet), the shallower middle part being sometimes called a ridge or swell. (See Figure 144.) 72. Composition and Density. — The ocean contains a great variety of substances in solution, for it has received everything that streams have dissolved and carried from the lands for ages past. Common salt makes three quarters of the dissolved substances. An important but much less plentiful dissolved substance is limestone, of which many sea animals make their shells or skeletons. A small quantity of atmospheric gases is foimd dis- solved in sea water, even in its deepest parts. The gases are taken in at the surface, especially when air is caught in dashing waves. It is upon the oxygen thus supplied that fish and most other marine animals depend for breath- ing; but whales and other mammals living in the ocean come to the surface for air. The mineral substances dissolved in ocean water make about three per cent of its weight ; their presence makes it a little heavier than pure water (in proportion of 1.026 to 1.000). Although water is easily moved, it can be very- little compressed. Hence, in spite of the great pressure of the upper layers of the ocean on those beneath, the ocean is unlike the atmosphere in being of nearly uniform density from top to bottom. Anything that is heavy enough to sink at the top will sink all the way to the bottom. 73. Color and Phosphorescence. — In the open ocean, far from land, the water is extraordinarily clear. It is of a THE OCEAN 101 beautiful deep blue, so strong that one would expect the color to show in a bucket ; but if some water is dij)ped up from the sea surface, it appears perfectly transparent and colorless. In cloudy weather the ocean is of a duller, more leaden hue. Near the lands the blue is lighter and turns toward a greenish shade. Opposite large rivers the water may be yellowish from suspended sediment; the Yellow sea is so named on this account. What large rivers enter it? There are many small jellylike animals that float in the ocean. Some of these have the power of emitting, when disturbed, a pale light, visible in the dark. They are found chiefly in the warmer parts of the ocean. Break- ing waves and the foam in the wake of a vessel may thus become beautifully luminous or phosphorescent at night. 74. Ocean Temperatures. — The surface layers of the ocean vary in temperature with latitude, reaching about 80° around the equator, and being reduced to 30° or 28° in the polar regions (Figure 44). The great body of the deep ocean is cold in all latitudes ; its temperature is about 30° in high latitudes and 35° or 40° in the torrid zone. When exploring vessels dredge in a torrid ocean the sediments brought up from the bottom have a tempera- ture near freezing, strangely in contrast with that of the objects on shipboard under a hot sun. The sun's rays have small effect on ocean water at depths below 100 or 150 fathoms. At greater depths the ocean must be nearly dark, with hardly perceptible dif- ference between day and night, or between winter and 102 ELEMENTARY PHYSICAL GEOGRAPHY summer. The temperature at any point in the great body of the deep ocean is therefore nearly constant. Changes of temperature in the ocean surface through the day or the year are very small, seldom more than 3° and 15°, respectively. As the temperature of the lower air is largely controlled by that of the surface on which it rests, the climate of islands in mid ocean and of conti- nental borders where the prevailing winds blow ashore is free from great changes of temperature between winter and summer. Salt water becomes heavier and heavier as it is cooled down to its freezing point, 28°. Hence the cold surface water of high latitudes sinks to great depths and creeps very slowly toward the equator; thus the low tempera- ture of the great body of the ocean is accounted for. Fresh water is unlike salt water in being densest at 39". On being warmed or cooled from this temperature it expands and becomes lighter. Hence in winter, when all the water of a lake has been cooled to 39°, further cooling affects only the surface water, which may then soon freeze. 75. Ice in the Ocean. — Ice expands a little as it freezes ; it therefore floats, about one seventh of its volume being out of water. The ice formed in the polar oceans is known as floe ice ; it may reach a thickness of from three to seven feet in a single winter. Great fields of floe ice drift with the winds and currents. They may thus be torn apart or crushed together. When two floes collide pack ice of very irregular surface is formed; it may reach a thickness of over 100 feet. THE OCEAN 103 In Greely's expedition to the Arctic regions in 1883 his boats were frequently in danger of being crushed when ice fields drifted together, closing the water passage he had been following. Smooth floe ice is easily crossed on sleds. The Eskimos make winter journeys upon it. Where packed it may be Fig. 38. A Vessel beset by Pack Ice impassable. It was on account of the roughness of ridged pack ice that Nansen had to turn back from his " dash for the pole," in latitude 86° 13' N., longitude 96° E., on April 8, 1895. When two large fields of pack ice drift together a vessel between them would be crushed, unless of great strength and shaped so as to escape by rising. Nansen's vessel, the " Fram," was especially constructed to withstand great pressure and so survived the dangers to which it was exposed. 104 ELEMENTARY PHYSICAL GEOGRAPHY Icebergs in the North Atlantic are fragments from the ends of great fields of ice (glaciers) that descend into the sea from Arctic lands, chiefly Greenland ; they are of fresh water. The tabular icebergs of the Antarctic ocean are fragments of a heavy sheet of ice around the south pole. Some of these ice blocks measure a mile or more Fig. 39. An Iceberg on a side, and 1200 to 1500 feet in thickness. Icebergs, being of fresh water, float with about one sixth or one seventh of their volume above the sea surface. Collision with an iceberg is one of the dreaded dangers of navigation in high latitudes. In the southern oceans drifting icebergs reach latitude 50°, or even 40°. In the North Atlantic they reach latitude 45°, southeast of New- foundland, but they are absent from the northwestern coast of Europe, even in latitude 70°, on account of the THE OCEAN 105 warm water there prevailing. They are wanting in the North Pacific, except in the seas of northeastern Asia. 76. The Ocean Bottom. — The greater part of the deep ocean bottom is a comparatively even plain of soft ooze. The plain rises and falls gently in broad swells, but is not Fig. 40. Globigerina (magnified 100 times) varied by hills and valleys such as occur on the lands. A large part of the deep sea bottom is covered with a fine deposit, called ooze, which consists of the minute shells, more or less decayed, of s.imple animal forms that live at or near the surface. One of these, highly magnified, is shown in Figure 40. In the deepest oceans the bottom is covered with a fine reddish clay. Nearer the shores ^ 106 ELEMENTARY PHYSICAL GEOGRAPHY the deposits become muddy with sediments derived from the land. It is by the very slow but long-continued accu- mulation of these deposits that the ocean floor has been made so smooth. " The monotony, dreariness, and desolation of the deeper parts of this submarine scenery can scarcely be realized. The most barren terrestrial districts must seem diversified when compared with the vast expanse of ooze which covers the deeper parts of the ocean." No mountain ranges with sharp peaks and ridges separated by deep passes and valleys have yet been dis- covered on the open ocean floor far from the conti'- nents ; but Cuba and some of the neighboring islands in the West Indies seem to be the crests of a mountain range whose western extension forms submarine ridges in the northern Caribbean, connecting the islands with Central America. Volcanic and coral islands rise with steep slopes from the deep ocean. Volcanic cones sometimes rise above the ocean surface, forming lofty mountains, as in the Hawaiian islands ; sometimes they are known only by soundings, their summits being below sea level. 77. Mediterraneans. — Besides the open oceans thus far considered there are several deep seas, more or less separated from the oceans by land barriers. The most important of these is the classic Mediterranean (the sea ■•' m the middle of the lands ") ; its average depth is nearly as great as that of the great oceans, but it is connected with the Atlantic only by the narrow and shallow Strait of Gibraltar. THE OCEAN 107 Other similar mediterranean seas are the Caribbean and the Mexican (deep central part of the Gulf of Mexico), adjoining the western Atlantic ; and the Japan, China, Sulu, and some smaller seas imperfectly inclosed from the western Pacific by island chains. The deep water of mediterraneans is warmer than that of the neighbor- ing oceans, whose cold bottom waters cannot enter the mclosed basins. 78. Continental Shelves The ocean often overlaps the borders of the continental masses in a comparatively shallow belt of water, at whose outer edge the depth is commonly about 600 feet; thence it rapidly sinks to the deep ocean floor. These shallow bottoms are known as continental shelves. The water on the shelf is often greenish from fine suspended sediment, unlike the clear deep blue water of the open ocean. A well-defined continental* shelf, from 50 to 100 or more miles in width, stretches along the eastern side of North America from Newfoundland to Florida, and thence around the Gulf of Mexico. The British Isles stand upon a continental shelf that borders mid-western Europe. The Malayan and Australasian islands surmount broad shelves between Asia and Australia, separated by a belt of deeper water. The gravel, sand, and clay washed from the lands into the seas are moved about by waves, currents, and tides on the continental shelves. Thus the land waste is slowly ground finer and finer, and its finest particles are gradu- ally moved outward to (peeper water. They are seldom 108 ELEMENTARY PHYSICAL GEOGRAPHY found ill dreclgings over 200 miles from shore; for the most part they are carried a less distance. In the course of years, centuries, and ages the sedi- ments thus accumulating on a continental shelf may form successive layers, each a few inches or feet in thickness, accordmg to the rate of supply. A layer of sediments of this kind is called a bed or stratum (plural, strata). Many strata laid down on the sea floor, one Continent -water lagoons with extensive marshes of reeds borders the mainland for a breadth of about five miles. Finally come the sand reefs, half a mile or more wide, inclosing the lagoons. The reefs are interrupted by inlets, connecting the lagoons with the sea. PLAINS AND PLATEAUS 153 Name the direction of the Delaware and the Schuylkill as they flow into the inner lowland ; of the Delaware in the inner lowland ; of the streams that flow down the inner slope of the cuesta and 5 10 15 20 Fig. 70. The Belted Coastal FlMn of Southern New Jersey across the marl belt ; of the streams on the outer slope of the cuesta. Which is the steeper slope of the cuesta? How is this known ? Compare the arrangement of all these streams with those shown in Figure 08. What is the average breadth of the clay belt ? of the marl belt ? of the hilly belt? of the sandy plains? of the coastal lowland? How far is it from Philadelphia to Atlantic City? 154 ELEMENTARY PHYSICAL GEOGRAPHY 100. Embayed Coastal Plains. — The region here figured does not at first sight seem to belong to the family of coastal plains. Long shallow arms of the sea enter between low hilly arms of the land. Rivers from the back country enter the heads of the long bays ; small streams from every little valley between the hills of the Fig. 71. An Embayed Coastal Plain land arms enter little bays or coves on the sides of the larger bays. This diagram represents a coastal plain which has been depressed, so that its valley floors are " drowned " beneath the sea. Before drowning, the region must have stood for a long time higher above baselevel than now, for the valleys evidently had been eroded and widely opened before the depression of the region occurred. Many side valleys had been formed, so that the uplands between the larger rivers had been dissected into branching spurs. Now the outer coastal lowland and the broad valley floors are under PLAINS AND PLATEAUS 155 water, the latter being occupied by the bays that enter far toward the oldland, while the groups of hills stand forth as ragged arms of the land. The former simple shore Hne is thus exchanged for a very irregular shore line. Draw a map of part of the em- bayed coastal plain shown in Fig- ure 71, after the style of the outline in Figure 72. Compare Figures 65 and 71. Point out the inner border of the coastal plain in each one. In what respects do the two figures agree? In what do they differ? How has the difference been pro- duced? In each one trace a river from the oldland to its mouth. What difference is noted? The relative change in the attitude of land and sea is here opposite to that inferred in the previous examples. Since the depression of the region the land heads have been more or less cut back by the waves, and the bay heads have been some- what filled by marshy deltas. But the drowning cannot have taken place long ago, as the earth counts time, for the changes in the land heads and bay heads are of moderate amount. The Atlantic coastal plain from Delaware bay to Pamlico sound presents many examples that fall under this class. Fig. 72. Sample Map of an Em- bayed Coastal Plain 156 ELEMENTARY PHYSICAL GEOGRAPHY The outer shore line is for the most part a sand reef, inclosing lagoons. Many branching bays extend inland, the largest being Chesapeake bay. Navigable arms of the sea thus alternate with dissected arms of the land. Partly drowned coastal plains exert a peculiar control over the distribution and occupation of their population. The greater part of the valley lowlands is lost, and the people must make the most of the hilly land arms that remain above sea level. The axis of each of the larger arms is generally followed by a main road, making its way from village to village among the upland farms and giv- ing forth side roads to villages on the smaller land arms or at the little bay heads. Indicate the place of such roads and villages on Figures 71 and 72. The shallow bays are valuable for fishing grounds. More important centers of population are found either near the heads of the larger bays, where the large rivers come out from the back country and reach tide water, or near the mouths of the bays where the outer sand reefs are not continuous and the ocean is easily reached. Baltimore and Norfolk are good examples of cities thus situated. The outer shore line is inhospitable; its long sand reefs offer no good landing place, and the narrow tidal inlets allow entrance only to small-sized vessels. Where would such a view as that of Figure 73 be found in Figure 71 ? In the early history of "tide-water Virginia" the numerous drowned valleys afforded easier communication between the settlements than was found overland through the forests of the coastal plain. PLAINS AND PLATEAUS 157 101. The Fall Line. — A large river whose valley is extended across a coastal plain often lias low falls or rapids near the inner margin of the plain, which determme the " head of navigation," or uppermost point that can be reached by vessels from the river mouth. A Ime drawn tlrrough the falls on successive rivers is called the fall line. Fig. 73. A Brauch oJ: Chesapeake Bay, Maryland The falls occur where the river passes from a steeper slope on the resistant rocks of the older land to a nearly level channel excavated in the weak strata of the plain. On coastal plains of a considerable breadth settlements near the mouth and at the head of navigation of the larger rivers often develop into important cities. The lower city is the seaport of the region. The upper city bears closer relation to local industries and traffic; it hes in the midst of a diversified region, with strong water power for manufacturing the varied products of rock and soil. In South Carolina, Columbia lies on the Congaree river, 158 ELEMENTARY PHYSICAL (GEOGRAPHY where it passes from the older land to the dissected plain. Charleston lies at the outer edge of the coastal lowland on the widened course of a small river where the tide comes in from the sea. The fall line along the inner margin of the Atlantic coastal plain of the United States is marked by important cities on nearly every large river that crosses it. Trenton, Philadel- phia (at the falls of the Schuylkill), Richmond, Raleigh, Camden, Columbia, and Augusta are all thus located. The origin of the forces sufficient to deform the crust of the earth and to elevate or depress a coastal plain is not well understood. It is necessary that the student of physical geography should recognize that elevation and depression have actually taken place, and should under- stand the importance ' of such movements in controlling the forms of the lands and the conditions of their inhab- itants ; but the processes that cause such movements must be left to the more advanced study of geology. Coastal plains, narrow or broad., belted or embayed, occur along parts of the border of different continents. They resemble more or less closely the examples here given. The coastal slope of Guiana and the plains of Patagonia, South America, belong in this group of forms. 102. Inland Plains. — The Great plains of the central United States slope gently forward from the Rocky moun- tains. They are formed of many layers of sands, clays, and gravels, washed from the mountains and now lying one over the other, many hundred feet in total thickness and nearly horizontal. Some of the layers were deposited PLAINS AND PLATEAUS 159 when the region was below sea level ; some were spread over the uplifted sea bottom by rivers when the region was too low to be dissected. The plains are now high enough to be more or less dissected by streams and rivers whose valleys vary in depth and width ; but the upland spaces between the val- leys often preserve a comparatively even surface over large distances. In some districts, vast areas stretching farther than the eye can reach are monotonously even and almost as uniform in soil as in surface. In other dis- tricts, valleys are deeper and closer together, and the spaces between them are made hilly by the branching ravines of side streams. Within the United States the Great plains are treeless for 500 miles east of the Rocky mountains, except on certain hills and bluffs which occasionally rise above the general level, or in the valleys which sink below it. The absence of trees is due to the dryness of the climate, and this in turn is due to the general course of the westerly winds whose moisture has been left on the mountain ranges between the plains and the Pacific. Agriculture is impossible in the drier southern parts without irrigation. Farther north in Canada the climate is moister, and the plains are forested. In still higher latitudes the surface is treeless; the warmth of summer melts only the upper part of the soil, and vegetation is low and stunted. The treeless plains possess little mineral wealth, and they have no forests to supply lumber; hence they cannot become a closely populated manufacturing region ; but they 160 ELEMENTARY PHYSICAL GEOGRAPHY have a more or less abundant growth of herbage, which once supported herds of countless buffaloes. Now that the buffaloes have been killed off, their place is taken by cattle which range over the plains, wandering back and forth over the uplands between the valleys that they visit for water. A number of railroads traverse the plains and carry, among other things, many cattle to eastern markets. The plains of western Siberia resemble the Great plains of the central United States. They slope gently away from the mountains of central Asia. They have a mod- erate altitude above sea level and preserve a generally even surface over hundreds of miles. Marshes and shal- low lakes lie in faint depressions, as if the hollows in the original surface of the plains had not yet been drained by river action. The narrow valleys are few and far between ; they can never be cut deep while the region stands low, and they have not yet been worn wide. The more northern part of these plains is treeless because the ground is frozen. The central part is forested; but south of latitude 50° to 55° the plains have a light rainfall and are again treeless ; clothed with thin grass in summer ; cold, barren, and wind swept in winter. The treeless plains have long been the home of wander- ing tribes, whose wealth is not in fixed possessions, but in herds and flocks driven from place to place for pasture. The people live in tents and move about without definite limits to their lands. On account of their wandering habits they are called nomads (wanderers). Every man is necessarily a horseman, skilled in nearly all the arts of a wandering life. PLAINS AND PLATEAUS 161 103. Belted Inland Plains. — In Wisconsin, far inland from the ocean, the northern part of the state is occupied by rugged highlands of resistant rocks. Adjoining on the south and east are plains and uplands arranged in belts, their rock layers sloping gently away from the highlands and lapping one over another like great shingles. Fragments of the highland rocks are found in the lower members of the over- lapping strata; nu- merous marine fossils, like corals and shell- fish, occur in many layers. All the lay- ers are well consoli- dated ; the firmer ones form belts of hilly uplands, between which the weaker layers are worn down to lower plains. Although the sea may now be a thousand miles away, the belts of upland and plain are easily seen to be similar to the belted coastal plains already described, while the rugged highlands are the older land from which the strata of the plains and uplands were long ago derived. This is an ancient coastal plain ; that is, a region that began its existence as a coastal plain ages ago in the earth's history, and that now stands in the interior of the Fig. 74. Ancient Coastal Plain of Wisconsin 162 ELEMENTARY PHYSICAL GEOGRAPHY . continent because successive uplifts have broadened the continental surface. Belted inland plains, similar to the example in Wiscon- sin, occur in many parts of the world, usually presenting a succession of hilly uplands and intermediate plains sim- ilar to those here described. Good examples are found in south-central England and in northeastern France. They all enjoy the advantage that comes from diversity of form and products and from the resulting variety of occu- pations that they support. 104. Plateaus. — When plains stand at a considerable height above the sea level they are called plateaus. No defi- nite limit of height can be given to separate the two classes of forms. In elevated regions the lower parts may be called plains, even though they are more than 2000 or 3000 feet above sea level; in low regions the higher parts may be called plateaus, even though not higher than 1000 or 2000 feet. Plateaus are sometimes traversed by deep and narrow valleys or canyons, branching in various directions. The canyons are cut down to a great depth by their streams because the plateau surface stands high above baselevel. Plateaus are generally built of horizontal rock layers of various kinds, whose edges are well shown in the canyon walls. In Figures 75, 76, and 77 a deep cut is imagined across the front of the view, so as to show more clearly the rock layers that crop out in the canyon walls. The broad uplands between the canyons have a comparatively even surface across which it is easy to travel, but the deep canyons are almost impassable. PLAINS AND PLATEAUS 163 The walls of the narrower canyons consist of a succession of cliffs and slopes, often too steep to be climbed. The cliffs are formed on the hard resistant layers, which are strong enough to stand with a steep face ; the slopes are formed on the weak layers, which are more easily weathered back to a slant. The slopes are covered with coarse rock waste, or talus, weathered from the cliffs above. The rock waste weathers and falls from each cliff, and rolls, washes, and creeps down each slope to the top of the cliff next below, where it falls again, shatter- ing to fragments ; at last it reaches the stream, where its finer parts are rapidly washed away. Thus the chffs and slopes wear back or retreat, and the canyon widens. As a canyon widens, a platform or bench is formed on the top of the stronger cliffs ; it is then often possible to descend into the canyon by climbing down crevices in the cliffs, from platform to platform. 164 ELEMENTARY PHYSICAL GEOGRAPHY Point out the cliffs, slopes, and platforms of the canyon walls in Figures 76 and 77. Where are the highest cliffs, the longest slopes, the broadest platforms? Which layers, shown in the front of the diagram, are resistant ? Which are weak ? The slow creeping of waste down the slopes of the valley sides is caused by very slight movements of the fragments and particles as they warm by day and cool by night, as Fig. 76. Diagram of a Narrow Canyon they are wet by rain and dried in fair weather, or as they are moved by the freezing and thawing of films of water between them. The movement is more noticeable on steep slopes, but it does not cease even on the gentler slopes. The slow downhill creeping of weathered fragments, aided by the surface washing of fine particles in wet weather, is the chief means of moving waste down from the liigh ground to the streams in the valley bottoms. As the canyon is eroded by the main river, ravines are cut in the canyon walls by streams that rise on the plateau, PLAINS AND PLATEAUS 165 The deeper the main canyon is eroded, the deeper the side ravines are worn down, and the more the plateau is dissected. Yet in the stage shown in Figure 77 the great work of wearing away the plateau is only well begun. The lofty plateaus of northern Arizona are traversed from east to west by the Grand canyon of the Colorado, from 4000 to 5000 feet deep. The dry climate of the plateau Fig. 77. Diagram of a Widened Canyon makes vegetation scanty. The region offers no temptation to settlement, however marvelous it is to the explorer. Much of it is desolate, occupied by a few Indians, who subsist by "cultivating little patches of corn, gathering seeds, eating the fruits and fleshy stalks of cactus plants, and catching a rabbit or lizard now and then; dirty, squalid, but happy, and boasting of their rocky land as the very Eden of the earth." The great elevation of this plateau pennits an unusual depth of canyon cutting. The massive strong and weak 166 ELEMENTARY PHYSICAL GEOGRAPHY strata of which the plateau is built produce strong cliffs and long talus slopes on the canyon walls. Far down in the bottom of the great trench runs the tawny Colorado, turbid with waste that is showered from the walls in rocky avalanches or swept in from side canyons by cloud-burst torrents. The water, bearing abundant waste, is stiU rasp- ing down the rocks in its falls and rapids. Deep as the canyon is, it has been cut down only by the river. There is no indication of clefts or fractures along the river course. Unlike most great rivers whose valleys serve as paths of travel, the Colorado is almost inaccessible along its canyon. Only one exploring party has successfully gone down the canyon, and their narrative is a wonderful history of scien- tific adventure. When their boats once entered the canyon, retreat was impossible against the swift current. Escape by climbing the walls was hazardous. To descend the river was easy on its smooth stretches, even though hemmed in by great chff s ; but cascades plunge over ledges where the most resistant rock layers are not yet cut through, and rocky rapids obstruct the channel where side canyons dehver heaps of bowlders to the main river. After many perils the party came out to the open lower country on the west. Plateaus interrupted by narrow canyons are, as a rule, occupied only on their upland surface. The elevation of the upland is an advantage in the torrid zone, where the high temperatures at sea level are wilhngly exchanged by civilized races for a more moderate temperature at altitudes of several thousand feet. But in the temperate zone a high plateau is at a disadvantage from the rigor of its winters, as well as from its difficulty of access. PLAINS AND PLATEAUS 167 The canyonlike valleys are obstacles to movement ; they serve as barriers (except to birds and winged seeds) between the uplands on each side. They are seldom inhabited, unless by the people of a persecuted tribe, who sometimes take refuge as "cliff dwellers" in the recesses or caves that are often excavated between cliff base and talus top. 105. Dissected Plateaus The rugged uplands that extend continuously from New York to Alabama, known as the Catskill, Allegheny, and Cumberland plateaus, may here be treated together under the second name. The whole region is occupied by mountainlike hills and spurs, built of nearly horizontal rock layers and separated by , numberless deep valleys that have been eroded by the riv- ers and their branching streams. The hilltop view gen- erally discloses a rather even sky hne, which may be taken to mark a plateau surface that once extended over the whole region, before the branching valleys were carved. The Allegheny plateau is now thoroughly dissected by its streams. It is evidently in a more advanced stage of change than a plateau that has only a few narrow canyons. The altitude of the original upland in West Virginia (roughly 2500 or 3500 feet) has been great enough to per- mit the erosion of valleys 1000 feet or more in depth; hence some of the plateau remnants fairly deserve the popular name of " mountains," locally applied to them. Many resistant sandstone layers stand out in chffs from ten to fifty feet high. As the layers are nearly horizontal, the cliffs run in bands around the spurs of the great hills, but are usually liidden by the heavy forest that 168 ELEMENTARY PHYSICAL GEOGRAPHY covers much of this region. The weak strata occupy the intervening slopes, covered with a thin stony soil and sup- porting forest trees. The hills and spurs are all very much alike, for they have been dissected by similar streams Every side valley resem- bles its neighbors; / -s'^ all the members ^^ of a local tribe of small streams / ^ Xtt . i n „ \ ••..m^-s/ ri A' ^cascade down over the same v^' J^}sn^ X-^number of f all- ^/,\/Jx making strata in their descent to the -^,V larger rivers. In contrast to the previous example, this district has nearly everywhere lost its once continuous upland surface and is now transformed into a well-dissected hill-and-valley country. A great part of the surface consists of hillside slopes. Drainage is not delayed on extensive uplands ; but at times of rain or winter thaws water is quickly shed from the hills, and the main streams rise rapidly in destructive floods. The forests retard but do not prevent the wash of waste from the steep slopes ; a great load of waste is delivered by the side streams to the rivers. Fig. 78 The Allegheny Plateau PLAINS AND PLATEAUS 169 What parts of what states are occupied by the Allegheny plateau ? Which state has the greatest part of its area in the plateau ? What cities can you name in that state ? How far is it from the Catskill mountain district to the Cumberland plateau district ? As a whole, the Allegheny plateau is so rugged that its population is small, being generally found on isolated farms Fig. 79. Canyon of Kaftawlia River in Allegheny Plateau, West Virginia upon the disconnected uplands, in villages and occasional small cities in the valleys, or gathered about mines or other industrial works. The isolated hilltop farmers can- not afford to construct and maintain good hillside roads ; it is difficult to haul upland products down bad roads to village markets or to railroad stations, and it is doubly difficult to haul supplies up .to the farms. Life on the uplands is laborious. The hillsides are generally too steep for cultivation ; if cleared, the soil is rapidly washed away. Wild animals, 170 ELEMENTARY PHYSICAL GEOGRAPHY such as deer and bear, almost exterminated from the lower country on the east and west, still find refuge here ; small game is abundant, and hunting is almost as much of an occupation to the " mountaineers " as farming. The forests supply lumber to the more thickly settled communities on the east and west. The numerous coal seams (vegetable deposits in ancient marshes, now members of the great series of horizontal strata that build the plateau) are well exposed on the sides of the deep-cut valleys, and are now extensively mined. Iron ore occurs in certain strata. Rock oil and natural gas are found by boring deep wells. It is chiefly in comiection with the industries dependent on these important products that a larger population is to-day attracted to this rough country; In the earlier history of the United States the dissected Allegheny plateau was (excepting the North Carolina mountains) the most formidable barrier between the Atlan- tic coastal plain and the open prairies of the Ohio valley. Intercourse and traffic are still so difficult in the districts of stronger relief, away from the lines of travel, that the people of the Allegheny plateau are slow in acquiring the ways of civilization. Family feuds are still maintained among the " mountaineers " of West Virginia and Ken- tucky. As the uplands decrease in height westward, and the valleys become more open toward the Ohio river, popu- lation increases ; but Pittsburg is a city of exceptional size in this region. Its growth, in early years was favored by its position with reference to the lower Ohio valley, and in later years by the great stores of mineral wealth in the surrounding country. PLAINS AND PLATEAUS 171 106. Mesas. — Broad plains of gently rolling surface, drained by streams in wide-open, flat-floored valleys, are sometimes overlooked by flat-topped " table mountains " of horizontal rock layers. Neighboring tables are of nearly uniform height, each one being capped by the same kind of cliff-making rock layers and flanked by a sloping talus. In the western United States tables of moderate height are often given the Spanish name mesa (table ; pron. may-sa) ; while the smaller mesas are known by. the French name hutte (target or landmark; pron. hewt). Mesas and buttes of this kind are all that now remain of a plateau that once spread far and wide over the region. The open space between the mesas has been produced by the widening of the valleys, so that their floors now occupy a great part of the surface. The original level of the plateau may have been much higher than the tops of the mesas, for the uppermost strata may now be com- pletely washed away. A region of this kind represents an approach to what may be called the old age of a plateau, when even the mesas will be worn away, leaving an unbroken plain. It is very unlike the youth of the plateau, when the uplands were broad plains and the valleys were narrow canyons. The plains of western New Mexico are surmounted by numerous mesas or plateau remnants. Settlement here is chiefly limited to the lower lands. The isolated mesas and buttes, rising several hundred feet above the plains, are generally uninhabited. The mesas of an old plateau are not, like the canyons of a young plateau, serious obstacles to travel ; for while 172 ELEMENTARY PHYSICAL GEOGRAPHY canyons continue for long distances and are everywhere difficult to cross, mesas are generally of moderate length, and many broad passages are opened among them. They are occasionally occupied as natural citadels by barbarous tribes. One of the most remarkable remnants of an old plateau is the so-called Enchanted mesa of western New Mexico. Fig. 80. The Enchanted Mesa, New Mexico It rises more than 400 feet above the surrounding plain, and although no longer inhabited, it was once occupied by a small tribe of Indians, who found safety on its almost inaccessible summit. Other mesas in New Mexico and Arizona are still occupied by Indians, whose compact groups of houses on the upland cannot, at a little distance, be distinguished from the rock walls of the cliffs. The Indians cultivate small patches of corn on the lower ground, but they have not ventured to build villages there for fear of attack from more warlike tribes. PLAINS AND PLATEAUS 173 In the interior of British Guiana gigantic remnants of an old plateau rise above the surrounding lower country. .Huge mesas are rimmed round' by almost inaccessible cliffs that stand above long talus slopes. One of the highest is Roraima, whose broad table is more than 2000 feet above its base. It is uninhabited, and until recently had never been ascended. Fig. 81. Broken Plateaus 107. Broken Plateaus. — The plateaus of northern Ari- zona, of which the Sheavwits already described is one, stand in a curious relation to one another. East of the Sheavwits comes the Uinkaret, presenting the same upland (diversified by volcanic cones and lava flows), and expos- ing the same succession of cliffs and talus slopes in the canyon walls; but the Uinkaret stands about 1800 feet higher than the Sheavwits. The two are separated by a high and ragged cliff, or escarpment (CA, Figure 81), known as Hurricane ledge, facing westward. 174 ELEMENTARY PHYSICAL GEOGRAPHY The section exposed in the canyon (A, Figure 81) shows that the cliff stands on the line of a great north- and-south fracture, which divides the whole mass of strata into two blocks, the eastern block (Uinkaret) being lifted nearly 2000 feet higher than the western (Sheavwits). Several other similar plateau blocks are found in this region. The displacement of the blocks is Fig. 82. Hurricane Ledge, a Dissected Fault Cliff clearly represented in the section on the right front of the diagram, Figure 81, under the letters B, B, E. The western boundary of the Sheavwits plateau {FD, Figure 81) is one of these cliffs of displacement, 2000 or 3000 feet high. It is cut by gigantic ravines, from which great volumes of rock waste are washed out. Fractures of this kind, on which adjacent blocks of land are displaced, are called faults. The cliffs that originate on the broken face of the uplifted blocks are called fault cliffs. They are in time more or less worn back by PLAINS AND PLATEAUS 175 \ weathering and by the growth of ravines, such being the present stage of Hurricane ledge ; and they may then be called dissected fault cliffs. The forces by which the plateau blocks have been broken and lifted have not been fully explained. It is probable that violent earthquakes accompanied the produc- tion of the fractures, and that the displacement of the blocks was accomplished by many small movements, each causing a moderate earthquake. QUESTIONS Sec. 96. Describe the natural processes in operation on a moun- tainous district bordering the sea. Consider the relation of such a district to habitation. Give an example. 97. Describe a narrow coastal plain. Describe its valleys and their lateral ravines. Explain their origin. What can be inferred as to the future form of such a plain ? as to its past form ? How can the origin of such a plain be accounted for? Define baselevel, and state the relation of rivers and valleys to baselevel. Describe a narrow coastal plain in Scotland ; in Oregon ; in Mexico. 98. Describe a broad coastal plain. What is meant by relief? Describe the coastal plain of the South Atlantic States as to form ; as to soil ; as to industries. Why are its soils arranged in belts ? Compare it with the narrow coastal plain of Scotland. What products are derived from it? 99. Describe a belted coastal plain. What is the origin of its form ? What is a cuesta ? Describe the course of the streams with respect to a cuesta. Describe the belted coastal plain of New Jersey. 100. Describe an embayed coastal plain as to hills, valleys, and bays. Explain its origin. How has the depression of the region affected the form of the coast line? Describe an example of this class. Describe its effects on the distribution and occupation of its population ; on the location of roads, villages, and cities. 176 ELEMENTARY PHYSICAL GEOGRAPHY 101. Where may falls be expected in rivers that cross coastal plains? What is the cause of the falls? What is the fall line? Where are cities likely to be situated on the rivers of coastal plains? What cities lie on the fall line of the Atlantic coastal plain? 102. Describe the Great plains of the central United States as to origin, form, climate, vegetation, and industries. Describe the extension of these plains into Canada as to climate and vegetation. Describe the plains of western Siberia as to form, climate, and popii- lation. Why are the valleys in these plains shallow? What is the relation between nomads and inland plains? 103. What is a belted inland plain ? Describe an example from Wisconsin. Explain its origin. Where may some other inland belted plains be found? 104. Compai-e plains and plateaus. Describe a canyon as to form and origin. Compare the form of the canyon walls as shown in the diagrams of a narrow and a widened canyon. Explain their differences. What is the relation of strong and weak rock layers to form ? Describe the movement of rock waste in a canyon. Describe the plateaus of northern Arizona. Describe the Colorado river and its canyon. Why is it difficult to follow the river? What is the value of plateaus to habitation? of canyons as barriers? 105. What is a dissected plateau? Describe the Allegheny plateau as to location, extent, altitude, and form. Describe the hillsides; the streams ; the drainage ; the industries ; the products of this plateau. What is the condition of its people? 106. Describe mesas and their surroundings. How are mesas formed? Compare a mesa and a canyon. Compare the plateaus of northern Arizona, the dissected Allegheny plateau, and the mesa district of New Mexico. Describe the Enchanted mesa ; Roraima. 107. What is meant bj^ broken plateaus? Describe the broken plateaus of northern Arizona. How are they separated? What is a fault? a fault cliff? a dissected fault cliff'? What is the relation of earthquakes to broken plateaus ? CHAPTER VI MOUNTAINS 108. Mountain Ranges. — The peaks and ridges of moun- tains are generally grouped in belts of much greater length than breadth, called mountain ranges. When several ranges are grouped together they constitute a mountain chain. Unlike plains and plateaus, in which, as has been stated in the preceding chapter, the rock layers are nearly horizontal, mountain ranges are belts of disordered structure in the earth's crust. Sometimes the strata are broken, displaced, and tilted as if gradually disturbed by some great uplifting force from beneath; sometimes the strata are bent and folded, as if slowly compressed by some irresistible crush- ing force from one side. The origin of the forces which produce mountains is not fully understood. One of the most ingenious and satisfactory theories accounts for many ranges as great disorderly folds formed in the crust of the earth, which is thoughi: to wrinkle here and there as it very grad- ually settles down on the slowly cooling and contracting interior. Streams carve deep valleys in the uneven surface pro- duced by mountain upheaval. Mountains as we see them are therefore the result of deforming forces which slowly 177 178 ELEMENTARY PHYSICAL GEOGRAPHY raise the mountain belt to great height, and of eroding forces which still more slowly wear down the uplifted belt by carving valleys in it. Fig. 83. A Mountain Peak 109. Block Mountains. — In southern Oregon and the adjoining parts of California and Nevada there are many long narrow mountain ridges, extending about north and south. Each ridge is a few miles wide, ten to forty miles MOUNTAINS 179 long, and 1000 or more feet high. The ridges are steep or cliff-like on one side, of gentler slope on the other, and are separated by flat trough-like depressions of varying breadth and depth. A general view of the country shows that the entire region was once a plain, but that it has been gradually broken into long narrow blocks, and that the blocks are tilted one way and the other, so that their uplifted edges form the mountain crests. Fig. 84. Block Mountains Which block mountain is completely shown in Figure 84 ? How does it end ? (Note : the space included in the figure is too small to show the whole length of most of the mountains ; the northern part of sonae and the southern part of others are cut off.) Describe a large block mountain ; its crest line, its cliff face, its back slope. Where could it be best ascended ? Some of the ridges still preserve the form of the tilted blocks, hardly changed by weathering ; their sloping backs are smooth; their cliff ed fronts have little talus at the *base. Others have shallow gullies worn down the back, while the cliffs are indented by ravines, and every ravine has a fanlike deposit of rock waste spread out beneath it; 180 ELEMENTARY PHYSICAL GEOGRAPHY between the fans the cliffs have a distinct talus slope at their base. Yet the mountain blocks of Oregon are, on the whole, so little worn that they must have been broken and tilted recently in the earth's history. Earthquakes are not infrequent in this region ; hence it is believed that the tilting of the blocks is still in progress from time to time ; a movement of even a few inches would suffice to cause earth tremors, while a sudden start of a foot or more would produce a violent and destructive shock for many miles around, gradually fad- ing away at greater dis- tances. There is no sign that volcanic action has any connection with the fractures and earth- quakes of this region. The drainage of the block mountains is very simple, for the streams follow the slopes produced by the tilting of the blocks. The smaller wet-weather streams flow down the slopes of the ridges. Larger streams flow along the troughs in the direction of their slant to the deepest depressions, and there form shallow lakes and marshes. The finer waste from the ridges is spread evenly over the lower parts of the troughs, concealing their rocky floor. Certain features of the region depend on its arid climate. The rainfall is light (fifteen inches or less a year), for the Sierra Nevada and Cascade ranges on the west take niost Fig. 85. Mountains of Southern Oregon MOUNTAINS ' 181 of the moisture from the Pacific winds. Few of the lakes are filled to overflowing ; they discharge their water supply by evaporation into the dry air. Most of the lakes are therefore saline, and the plains of fine waste about them are barren. In dry seasons the lakes shrink ; some of them disappear, leaving smooth floors of sun-baked clay. The bottom of the troughs elsewhere and the lower slopes of the ridges are clothed with bunch grass and sagebrush ; the ridge slopes, receiving more rainfall than the lower lands, support scattered cedars, and the higher crests bear forests of pine and spruce. Although the ridges are of moderate height, they repel the few settlers in the region, whose ranches are all found in the troughs. The thin grass supports scattered herds of cattle, and the streams suffice for a little irrigation. Thus even in these low young ridges the effect of moun- tains on climate, distribution of vegetation, and location of settlements is well shown. 110. Dissected Ranges. — In Nevada and the adjoining parts of California and Utah there are many north-and- south mountain ranges from twenty to eighty miles long, and from five to twenty miles wide. Their summits rise from 5000 to 7000 feet above the plains. Their crests are notched and uneven ; their slopes are varied by well- carved spurs between deep valleys. The troughs between the ranges contain long slopes of gravelly waste that have spread out from the valleys when the streams are flooded. As compared with the ridges of southern Oregon, these 182 ELEMENTARY PHYSICAL GEOGRAPHY ranges are larger and more dissected. They possess more of the beauty and variety of form generally found in mountains. The ranges of Nevada, like the ridges of Oregon, seem to have been formed by the uplifting of long blocks of the earth's crust: but in Nevada the blocks must have been Fig. 86. A Dissected Mountain Range, Utali larger and the uplifting greater; and the uplifting must have begun earlier than in Oregon, for the work of dis- section by streams is here much further advanced. The ranges of Nevada are thoroughly or maturely dissected. Yet, as in Oregon, occasional earthquakes show that the mountains are still growing. The higher ranges in Nevada exhibit more distinctly than the smaller ranges of Oregon the lower temperature. MOUNTAINS 183 with greater cloudiness and rainfall, that prevails on the mountains as compared with the plains between them. The rainfall on the plains is light, but storm clouds often gather round the peaks while the sun shines else- where. When the clouds dissolve, the mountains have been refreshed by rain or whitened with snow, while the plains may be as dry as before, except where the turbid flooded streams rush out from the mountain valleys. The streams generally wither away on the gravelly plains. Settlements in Nevada are therefore commonly limited to a belt around the mountain base, where the streams may irrigate fields. Some of the ranges contain valuable ores ; hence mining towns have sprung up in their valleys. 111. Folded Mountains. — The Jura mountains, along the border of France and Switzerland, occupy a belt of country where the rock layers, once horizontal, have been slowly pressed into a series of wavelike folds. The moun- tains consist of a number of parallel ranges and valleys trending about northeast and southwest. Each range con- sists of a series of rock layers bent upward like an arch; each valley is underlaid by the same series of layers bent downward like a trough. Some of the uppermost layers have been weathered off from, the crest of the arches; the edges of the harder layers remain in flanking ridges. Waste from the arches has accumulated in the troughs, flooring them with gravel and sand. The rock layers of these mountains contain sea fossils ; the layers must originally have been horizontal strata on the floor of an ancient sea. Since then they have gradually 184 ELEMENTARY PHYSICAL GEOGRAPHY been pressed and folded into their arch-and-trough struc- ture by a powerful side pressure. The drainage of the Jura mountains is, for the most part, like that of the Oregon ridges in following the slopes of the deformed surface. Short streams run down the sides of the arches, cutting ravines on the slopes, as shown in Fig. 87. Diagram of the Jura, a Folded Mountain Range the unshaded foreground of Figure 87. Larger streams gather on the trough floors and escape at one end or the other as opportunity offers. Here and there a stream cuts across an arch, wearing a deep gorge from one trough valley to the next, and exhibiting the arched structure, as in the middle ridge of Figure 87. Where are the Jura mountains? How many arches are shown in Figure 87 ? How many troughs ? What is their trend ? How manv cross valleys ? If you were traveling there, where would you go to IVIOUNTAINS 185 see the arched rock layers ? Where does the topmost layer lap over an arch ? What forms result where the topmost layer has been partly worn away ? Describe the course of some of the small streams that rise on the top of an arch. As in all mountains of diKstinct relief, the form of this range exercises a strong control over the distribution, occupation, and movement of the population. The valley floors are well settled ; villages often lie near the mouths of transverse gorges. Roads are generally limited to the lengthwise and crosswise valleys. Byways and footpaths lead to the upland fields and pastures. Little villages are sometimes found on the tops of the broader arches. The steeper slopes are generally forested. 112. Lofty Mountains. — Lofty mountain ranges, like cer- tain parts of the Rocky mountains, but better represented by the Alps, the Caucasus, and the Himalayas, exhibit a remark- able variety of peaks, ridges, ravines, and valleys. Their higher central peaks usually consist of the most resistant rocks, surrounded by slanting layers that rise in great ridges. These majestic forms' usually depend as much on the deep erosion of great valleys by streams as on their lofty uplift. Unlike the simple tilted blocks of Oregon, or the orderly folds of the Jura, the greater ranges show little or nothing of their original form. The discovery of marine fossils in the bedded rocks of high Alpine ridges toward the close of the eighteenth cen- tury was received with great astonishment by the scien- tific men of the time. The occurrence of fossils in so elevated a position was one of the first generally accepted proofs of the changes that have gone on in the past, by 186 ELEMENTARY PHYSICAL GEOGRAPHY which the present form of the earth's surface has been fashioned. But not until the nineteenth century had well advanced was it generally understood how much more the form of lofty mountains depends on processes of land sculpture than on forces of uplift. 113. Peaks and Ridges. — The height of lofty mountain summits is due in great part to the uplift that the whole Fig. 88. Peaks of the Central Alps range has suffered, but in part also to the success of the stronger rocks in resisting the attack of the weather, under which the weaker rocks have greatly wasted away. The waste that is shed from the peaks and ridges creeps and washes down into the valleys, usually leaving the loftiest summits bare and sharp. Deep valleys are eroded by the streams between the ridges, and steep ravines are worn in the slopes and spurs. Thus mountain forms are chiefly due to weathering and stream carving. MOUNTAINS 187 The bare rocky peaks and ridges, rising into the cold upper atmosphere, far above the limits of vegetation, are silent deserts. The stillness is broken only by the rush of storm winds and the roar of rock falls and snowslides. Not less barren are the snow fields and the talus slopes on the higher mountain flanks, and the slanting reservoirs of ice and snow in the upper valley heads, from which Fig. 89. An Alpine Peak of Slanting Layers slow-moving ice streams, or glaciers, creep down to the lower valleys. The lower slopes are generally forested. Many summits in the Alps are so sharp that they are called needles or horns. They rise as almost inaccessible peaks between the growing valley heads. Mt. Blanc, the highest mountain of the range (nearly 16,000 feet), is of domelike form with a heavy snowcap ; it is not yet suf- ficiently dissected by valleys to take the form of sharp ridges and peaks. 188 ELEMENTARY PHYSICAL GEOGRAPHY The Selkirk range of the Rocky mountains in Canada has steep and bare summits surmounting the long lower slopes. The slopes are covered with waste that is slowl}^ creeping and washing into the valleys, to be borne awa}'^ by the streams. Having an abundant snowfall, the range bears extensive snow fields and glaciers. In the Rocky mountains of Colorado snow is less plentiful, snow fields are small, and glaciers are wanting. Long slopes of creep- ing waste cover the mountain flanks far up toward the summits, as in Plate I ; craggy peaks of sharp form are less common than in the Selkirks or the Alps. 114. Climate of Mountains. — On extensive plains the climate — especially the temperature and rainfall — shows little variation from place to place, being nearly uniform for hundreds of miles together. On the average, one must travel from thirty to sixty miles poleward to find a differ- ence of 1° in mean annual temperature. The same differ- ence is found on mountains by an ascent of only 300 feet. Many mountains rise so high that they receive snow while rain falls on the surrounding lower lands. Lofty mountains are therefore usually clothed with snow on their higher slopes. Broad plains may have only a scanty rainfall over hun- dreds of miles together. On mountains the rainfall rapidly increases wdth elevation, although less may fall on very lofty summits than at heights of from 5000 to 10,000 feet. Not only because they are high, but also because they receive much rain and snow, high mountains are usually the sources of large rivers. I MOUNTAINS 189 The small changes of form and climate over broad plains make the conditions of life nearly the same over great areas. A great diversity of form and climate is found in mountains within small distances, and strong contrasts are crowded close together. 115. Mountains as Barriers. — High mountains serve as barriers separating the climates and the populations of their opposite sides. The windward (eastern) slope of the equa- torial Andes has a moist climate because the damp winds from the Atlantic, ascending and cooling, give forth a heavy rainfall there ; the western slope has a dry climate because the same winds, descending and warming by compression, not only give forth no more rain, but eagerly take up what- ever moisture they find on the way. The eastern slope is densely forested; the western slope is for the greater part a desert, except in valley floors watered by streams. Moist winds from the Pacific give a plentiful rainfall on the windward (westward) slopes of the Sierra Nevada and the Rocky mountains of the United States. The same winds, descending on the eastern or leeward slopes, become in winter unseasonably warm and dry, evaporating the light snow of the plains and laying bare the dry tufts of grass, greatly to the advantage of the cattle feeding there. The dry wind is called the chino ok. A similar wind occurs in the northern valleys of Switzerland, where it is called the foehn. The great popalations of India and China, representing different races, are separated by the Himalayas and other ranges in southern Asia. The two peoples are thus so 190 ELEMENTARY PHYSICAL GEOGRAPHY well held apart that neither of them has had any important influence on the other. Lofty mountain ranges thus rank with the oceans in separating the inhabitants of the lands. When low countries on opposite sides of a high range are occupied by different peoples the mountains commonly serve as a natural boundary between them. The moun- tain range as a whole may serve as a rough boundary between uncivilized nations ; but between civilized nations the crest line dividing the rivers of the opposite slopes is often accepted as a more precise boundary, as in the Pyrenees between France and Spain, where the river divide is generally adopted as the national divide. When the river divide departs from the main range that it was supposed to follow before the mountains were explored, the boundary question may give rise to dispute, as recently between Argentina and Chile, where a number of Pacific rivers rise on the pampas of Patagonia and cut through the Andes in deep gorges. The difficulty of crossing lofty ranges gives great impor- tance to the notches, or passes, in their central ridges, through which travel and traffic may go with less effort than over their peaks. The heavy snows of the winter may close the passes for -several months. In earlier cen- turies, when the passes were traversed only by paths, houses of refuge were often maintained on the summit by monks, as on the famous pass of St. Bei"nard in the Alps. It is mostly within the last hundred years that well- planned roads have been constructed over the chief passes of various mountain ranges. The roads enter the moun- tains along the larger valleys and then zigzag up the Plate VII. A Railroad rounding a Spur of Mt. Ouray, Colorado MOUNTAINS 191 steeper slopes. They are carefully laid out so as not to exceed a certain moderate grade, — about five feet in a hun- dred. Certain passes are now crossed even by railroads, the ascent from the valleys being most ingeniously made by curves and " loops." Sometimes the last part of the ascent is avoided by tunneling the ridge under the pass, it being cheaper in the long run for a railroad to bore through than to climb higher. When gold had been discovered in California and a new population was making its way there in 1849 and 1850, the mountain ranges in the western United States were so formidable a barrier to travel that many of the emigrants preferred the long voyage by sailing vessel around Cape Horn. Those who went overland suffered great hardships in crossing the mountains by rough trails, and many died on the way. Since then the mountains have been care- fully explored, the lowest passes have been found, and sev- eral railroad lines now connect the Central States with the Pacific coast. Mountains are often climbed for the exhilaration that comes from ascending them, and for the glorious view over the peaks and valleys that is gained from the summits. Clubs of mountain climbers have been formed in many countries. They publish narratives of excursions in mountainous regions. The ascent of very lofty moun- tains, above 16,000 feet in height, is made difficult by the thinness of the air so far above sea level. Fatal acci- dents sometimes occur, especially when inexperienced climbers try to make ascents of difficult peaks without well-trained guides. 192 ELEMENTARY PHYSICAL GEOGRAPHY 116. Avalanches. — The heavy snowfall of winter often overloads the snow banks on the higher slopes, and great masses of snow slide down to lower levels. Summer melt- ing and rainfall also cause slides, or avalanches (a-val, to the valley). Sometimes the snow mass glides along the sloping surface at a moderate speed. Sometimes it leaps from cliffs Fig. 90. Path of an Ice Fall in the Alps and falls with a terrible velocity to the valleys below; a violent blast of air bursts outward from beneath, overturn- ing trees hundreds of feet beyond the reach of the snow. Certain villages in Alpine valleys carefully preserve a patch of forest on the slope above them as a protection from avalanches. Roads and railways on steep mountain slopes must here and there be covered in by long snow- sheds, over which the snow may slide without blocking or injuring the road. Heavy masses of ice are occasionally detached from glaciers that end on steep slopes, forming " ice falls." MOUNTAINS 193 These are even more destructive than avalanches of snow. An ice fall over 5,000,000 cubic yards in volume broke from a glacier on the slope of a peak in the Alps in Sep- tember, 1895 (Figure 90 ; see Figure 89, from a photo- graph taken before the fall). It slid down a steep slope two and a half miles long, gathered about 1,300,000 cubic yards of rock waste on the way, and then rushed across the valley floor, dashing far up the opposite slope and falling back again, like a wave from a cliff. A bench on the path of the sliding mass caused it to leap forward, clear of the ground; then, as it fell, the air beneath was violently driven away, blowing out fragments of ice and rock and breaking down trees hundreds of yards distant (shown by arrows turned to the right. Figure 90). 117. Landslides on Mountainsides. — In deep and nar- row valleys among mountains the side slopes are sometimes cut so steep that great rock masses may be loosened from the walls and slip to the bottom, forming landslides. A landslide in the Alps in 1898 destroyed a few of the houses on the edge of the village of Airolo, near the southern entrance to the great St. Gotthard tunnel. The scar left by the falling mass is still distinctly visible high up on the mountain side ; the fallen rock, greatly shattered, spreads forward toward the stream in the valley floor. Had the slide taken a course a quarter of a mile farther south, it would have destroyed much of the village. In September, 1893, a great landslide occurred in the deep valley of one of the upper branches of the Ganges in the Himalayas. In three days 800,000,000 tons of rock 194 ELEMENTARY PHYSICAL GEOGRAPHY fell with deafening noise, darkening the air with dust, leav- ing a great bare cavity with steep walls several thousand feet high to mark its source, and building a dam nearly 1000 feet deep across the narrow valley floor. A lake gradu- ally formed on the upstream side of the dam and grew to be four milies long before it over- flowed, about a year after the slide. In the meantime the danger that the lake might burst out in a great flood being perceived by the British engi- neers in charge of the public works of India, the bridges in the lower valley were removed; safety marks were set uj) on the valley sides, 100 or 200 feet above the ordinary river level, indi- cating the height above which the flood would probably not rise ; and a telegraph line was constructed down the valley from the dam, to give prompt warning of the outburst. The flood occurred at midnight, August 26-27, 1894. In four hours about 400,000,000 cubic yards of water Fig. 91. The Landslide of Airolo, Switzerland MOUNTAINS 195 were discharged, cutting down the dam nearly 400 feet, flooding the valley to a depth of from 100 to 170 feet, and rushing forward with a velocity of 20 miles an hour. Many miles of valley road were washed away. Every Fig. 92. A Laudslide ia the Himalayas vestige of habitation was destroyed in villages along the upper Ganges ; but so well was the notice of danger given that only one man lost his life, and that because he would not heed the warning. Under a less intelligent control, thousands of people must have perished in such a catastrophe. The remains of many other landslides are found in the valleys of the Himalaj^as. 196 ELEMENTARY PHYSICAL GEOGRAPHY 118. Valleys among Mountains. — One of the strongest characteristics of thoroughly dissected, lofty mountains is the activity with which the rock waste is weathered from the peaks and cliffs, moved down the precipitous slopes, Fig. 93. The Himalaya Mountains swept by flooded torrents down steep ravines, and washed by streams along the larger valleys and out upon the adjoining lowlands. The waste seems everywhere to be streaming (as the long-lived mountains might say) down MOUNTAINS 197 from the peaks and ridges. The carving of valleys in the mountains has been accomplished by the long duration of these active processes for ages jjast. The rock waste consists of angular fragments as it falls from the cliffs and creeps down the slopes. The angles are worn off as the waste is rolled along in rapid torrents, and after traveling thus for a few miles the fragments are well rounded, becoming smaller and smaller the farther they are swept along the stream bed. The fine grains that are worn off from the angles of the larger fragments are borne along more quickly than the larger pebbles and cobbles. A torrent that receives much coarse waste from a steep- sided ravine frequently sweeps so much of it into the main valley that it cannot all be carried away by the master river. The coarser part of the waste then accumulates in a conelike form, known as an alluvial fan^ spreading with even slope from the ravine mouth into the main valley. Alluvial fans have a steep slope when formed by small torrents bearing a coarse and plentiful load. They have a fiat slope when formed by large streams with a fine- textured load. They may grow to great size, with a radius of five or ten miles, in large valleys. Large fans drive the master river against the farther side of its valley, where it undercuts the valley wall. The fan still growing, the river may be obstructed and thus required to spread over the valley floor upstream from -the fan, forming a shallow lake, while on the downstream side the river descends in rapids over the coarsest bowlders brought down by the torrent. 198 ELEMENTARY PHYSICAL GEOGRAPHY How many fans are shown in Figure 94? Where has their material come from? How has it been brought? What effect have they on the course of the main i-iver? A torrent frequently changes its course on a fan and enters the main river at a new point. Two- Ocean creek, a small stream in the Yellow- stone Park, has built a fan that forms a part of the conti- nental divide. Some- times the stream flows on an eastern radius of the fan to Atlan- tic creek (Missouri- Mississippi system), sometimes on a west- ern radius, to Pacific creek (Columbia sys- tem). Villages are often built and fields are cultivated on fans of large size. When the torrent of such a fan is turned on a new course it may flood fields and villages, causing much damage. A valley road crossing the fan is swept away where the torrent then comes upon it, while the bridge over the former channel is useless, now that the torrent has abandoned it. Fig. 94. Alluvial Fans MOUj^TAINS 199 Accidents of this sort are common in mountain regions. In 1896 a stream entering a lake in Switzerland overflowed its fan with a stony flood fed by a landslip in the head ravine. It laid waste a strip two miles long and over 300 feet wide at the forward end, covering it with a layer of stony mud ten or twelve feet thick. Houses were pushed out of place; a road and a railroad were buried. The advance of this curi- ous flood was some- times so slow that the grass on the fields in front of it was saved by hasty mowing. For a time all travel had to go by boat on the lake. The people who lived on the fan had some compensation for their losses in car- rying the thousands of visitors to and from the scene of the disaster. Sometimes the steep torrential headwaters wash so much waste from their ravines into the lower valley that the river is unable to carry along all that it receives. Some of the waste then gathers on the valley floor, gradually filling it higher and higher, as in Figure 95. Valley floors of this form are much more easily traveled upon than when the side slopes descend directly to the river bank. After mountain waste has in this way gathered in a val- ley to a considerable depth, sometimes measuring several Fig. 95. A Filled Valley with a Flat Floor 200 ELEMENTARY PHYSICAL GEOGRAPHY hundred feet, there may be a decrease in the amount of waste supplied by the headwater streams. This change will permit the river to turn part of its strength to sweep- ing away some of the waste in its bed, and thus to deepen its channel. As more and more waste is thus removed, a new valley comes to be opened in the flat valley floor, remnants of which then stand in benches or terraces above the new level of. the river, as in Figure 96. Terraced valleys of this kind are not un- common in the Rocky mountain region. Some of the inner valleys of the Hima- laya mountains have gravel terraces over Fig. t)G. A Terraced Valley 1^00 feet high. 119. Lengthwise and Crosswise Valleys. — When a river has cut down its valley floor to as moderate a slope as the load of waste that it has to carry along will allow, it may still wear away its banks, first on one side, then on the other. Thus in the course of time the river broadens the valley floor. This is especially true in a valley that is worn down along a belt of weak rocks parallel to the gen- eral trend of a mountain range, for these rocks weather and wash away at a comparatively rapid rate. The crosswise valleys, by which the rivers of the long inner valleys find outlets through inclosing ridges, are MOUNTAINS 201 often narrow and steep-walled gorges, for the ridge- making rocks are resistant and weather slowly. The floor of a crosswise or transverse valley may be hardly wider than its stream ; the walls rise steep from the water's edge, leaving little or no room for a road or path on either side. It is chiefly in the broader lengthwise valleys that mountain peoples dwell. When the outlet valleys are narrow gorges the outer world has for centuries been reached only by passes over the inclosing ridges ; but modern engineering skill has sufficed to build and cut roads and railroads through many gorges that were impassable a century ago. 120. Earthquakes of Growing Mountain Ranges. — The process of bending and breaking the rock structures within a mountain mass is certainly very slow, but it sometimes causes sudden snaps and slips of a few inches or a few feet. Tremors then spread in all directions from the seat of disturbance, diminishing in force as they advance. On reaching the earth's surface they are felt as earthquakes, producing more or less destruction. Shocks of this kind are comparatively common in and near most of the lofty mountains of the world. Earthquake tremors travel through the earth's crust with great velocit}^, — from ten to forty miles a minute ; but, as in the case of water waves, the actual movement of the quaking earth at any point may be only a few inches or a few feet a second, backward and forward. The shocks produced by earthquake waves are most violent at places 202 ELEMENTARY PHYSICAL GEOGRAPHY directly over the seat of chief disturbance. They may be very faint, causing no damage. They may be strong enough to be felt violently over hundreds of square miles, less distinctly over many thousands, and very faintly (by the aid of delicate instruments) all over the earth; Fig. 97. Railroad shaken by an Earthquake, Northeastern India One of the greatest modern earthquakes occurred at the base of the Himalaya mountains in northeastern India in 1897. It was probably caused by some under- ground movement of mountain growth. It formed sev- eral fissures, displacing the land on one side with respect to that on the other, forming a step several feet high.. The vibrations of the shock loosened rock masses and soil on steep slopes, causing many landslides, which left MOUNTAIXS 203 the hillsides bare and clogged the valleys. Thousands of forest trees and a great number of buildings in the central area were broken down by being swayed violently back and forth, although the movement was only a few inches. Streams were obstructed and turned from their courses. Fig. 98. Land Surface displaced by an Earthquake, Japan Railroad tracks on the neighboring plains were thrown out of line. A violent earthquake occurred in Japan in 1891 by Avhich a deep fissure was formed in the earth's crust, and the land on one side of it was lowered with respect to that on the other, as shown in Figure 98. Earthquakes of moderate violence are still frequent in the Alps, occurring five or ten times a year. Five cen- turies ago (1348) a violent earthquake in the eastern 204 ELEMENTARY PHYSICAL GEOGRAPHY Alps caused a great landslide by which a valley was barred across and a lake formed upstream from the slide. Countless thousands of shocks must have been produced during the long ages of mountain growth. The associa- tion of earthquakes with the young tilted-block ridges of Oregon, with the more mature mountains of Nevada, and with vigorous ranges like the Alps and the Himalayas, is a natural result of the continued disturbance or growth of the mountains. 131. Human Life in Lofty Mountains. — The people who to-day dwell in the valleys of lofty mountains are in many cases the descendants of races who formerly occupied the adjacent lower lands, from which they Avere driven by conquering invaders. Inclosed valleys among mountains serve as refuges, where pursuit is too difficult to be profitable. There the weaker race long remains unmolested, holding little intercourse with the outer world and preserving old forms of speech and old- fashioned customs. The invaders occupy the neighboring open country ; they engage in traffic with other parts of the world and advance in new ways of living. 122. Subdued Mountains. — There are certain mountain ranges of moderate height in which sharp peaks are absent and bold cliffs are rare. The slopes are of moderate steep- ness, and rock waste covers them almost from base to summit. Mountains of this kind do not reach upward into a climate very unlike that of their base ; and if not in a dry or a frigid region, they may be forest clad to the top. MOUNTAINS 205 The earthquakes that are common in mountains of active growth and the landslides that happen frequently in moun- tains where the valley sides are still steep are rare or unknown in these mountains of gentler form. Unlike those vigorous and lofty younger forms in which uplift and erosion are still active, the rounded forms of these mountains express subdued strength, as if their high peaks and ridges had been greatly worn away by the long- continued attack of the weather. They may therefore be called subdued mountains. The Blue ridge and other mountains of North Carolina are good examples of subdued mountains. No sharp peaks tower into the sky. The summits generally rise dome- like in rounded outline. Heavy forests clothe their slopes. Subdued mountains may still have so strong a relief that the people living in their valleys preserve older fashions than those of the more open lower country. This is seen in the homespun clothing and in the primitive manner of living of the North Carolina mountaineers. The mountains of Wales make another group of sub- dued forms, but more rugged than the mountains of North Carolina. Here remain some of tlie descendants of the ancient Britons who were driven from the more open lowlands of eastern and central England by Saxon and Norman invaders, 1000 or 1500 years ago. The Welsh language, therefore, represents the original language of Britain, while the English language is a compound of the speech of the invading peoples from the continent. The Scotch highlanders are clannish because the clans have long lived in secluded glens among the Highlands. 206 ELEMENTARY PHYSICAL GEOGRAPHY 123. Worn-Down Mountains. — In certain parts of the world ancient mountain ranges have been almost com- pletely worn away. Their disordered rocks, once rising in lofty peaks and ridges, arid perhaps bearing snow fields and glaciers, have been reduced to an almost plain surface, little above baselevel and everywhere open to settlement. Low- lands of this kind are called peneplains (pene, almost). Fig. 99. The Piedmout Belt, Virginia The Piedmont belt of Virginia, between the Blue ridge and the coastal plain, is in many respects an excellent example of a worn-down mountain range. It is a pene- plain, not monotonously smooth, but undulating in graceful swells between gentle depressions. The soil is deep, fine, and fertile, and the district is very generally occupied by farms. The height to which the rock masses once rose above the present surface is reasonably estimated as at least one mile ; it may have been two or three. The wearing down of these ancient mountains to the rolling plain of to-day has required an enormously long period of time. It often happens that the plain surface of a worn-down mountain range is here and there surmounted bv rounded MOUNTAINS 207 hills or low mountains, 1000 or more feet bigh, composed of the most resistant rocks of the whole region. These hills are the last remnants of the mountains that once towered over. the surface of to-day. Several hills of this kind are scattered over the Piedmont plain of Virginia, one being shown in Figure 99. Such remnant hills and Fig. 100. Map of the Piedmont Belt, Virginia mountains are often called monadnocks, after an excellent example of their class in southwestern New Hampshire. It is generally the case that old-mountain lowlands are now uplifted above the position in which they stood when worn down, so that they form plateaulike uplands. Their streams are thus revived into a new period of activity and at once proceed to trench and dissect the upland. The Piedmont belt of Virginia now stands several hun- dred feet above baselevel. ^ It is cut across by a number of active streams that flow in rocky, steep-sided valleys 208 ELEMENTARY PHYSICAL GEOGRAPHY from 100 to 300 feet below the upland plain. It must therefore be supposed that this region has been somewhat uplifted since its ancient mountains were worn down. It is in the valley sides that the tilted rock structures in the foundations of the ancient mountains are best seen. Southern New Hampshire and Vermont, central and west- ern Massachusetts, and aU of Connecticut include many uplands, above which occasional hills and low mountains Fig. 101. The Upland of New England, with Mt. Mouaduock in the Distance and a Valley in the Foreground rise, and below which numerous open valleys are worn. When an observer stands on the uplands the sky line is seen to be comparatively even. If the valleys were in imagina- tion filled up again to the level of the uplands, the worn- down peneplain of the ancient mountains of New England would be restored. The peneplain does not now stand so low as when it was worn down. It has been uplifted into a slanting position, so that it slowly rises from sea level at Long Island sound to a height of from 1400 to JLGOO feet on the northern boundary of central and western Massachusetts. The MOUNTAINS 209 valleys have been carved because the old lowland has been lifted up. They are shallow near the coast, but deep (800 to 1000 feet) in the interior, where the upland is higher above baselevel. They are comparatively narrow where the rocks are so resistant that they weather slowly, but wide open where the rocks are weaker. The chief of the wider valleys is that of the Connecticut river, a Fig. 102. Valley of the Deerfield in the New England Upland broad lowland excavated along a belt of relatively weak -sandstones. The uplands have a scattered farming population, here and there gathered in small villages. The larger valleys contain many villages and cities, and guide the chief roads and railroads. Here is gathered the more active manu- facturing and commercial population of New England. 210 ELEMENTARY PHYSICAL GEOGRAPHY 124. Old Mountain Ridges. — The Allegheny mountains I of Pennsylvania and Virginia consist of a number of nearly j parallel ridges with remarkably even crest lines, here and ^ there cut down by the notches or water gaps of streams I and rivers. The strata of these mountain belts are strongly \ Fig. 103. Diagram of the Allegheny Mountains, Pennsylvania folded, so that, if unworn, they would rise in great arches, ' as in the background of Figure 103. But it is now so long since the strata were pressed into folds that they have been worn down to a low peneplain at the level of the dotted line AB, in the fore- ground of Figure 103. The peneplain thus formed has been uplifted one or two thousand feet ; the weaker strata have been again worn down, forming open valleys and leaving the harder strata standing in relief, as MOUNTAIXS 211 even-crested ridges. The waste from the open valleys has been washed out through the notches that have been slowly cut down where the streams flowed across the harder strata. Plate IX shows one of these ridges in Maryland, with a notch cut through it by a bianch of the- Potomac river- How many notches are shown in Figure 103? 125. Embayed Mountains. — If a mountain range near a continental border is lowered, it will be partly covered by Fig. 104. Model of Embayed Mountains Compare Figures 60, 62, and 104. Compare Figures 71 and 104. the sea. The effect thus produced will be similar to that observed in the half -drowned coastal plain already described. The valley floors and mountain flanks will be submerged to a greater or less depth, and many long bays will enter between outstretching promontories and islands, as in Figure 104. Islands of this kind are called continental because of their close relation to the neighboring land. 212 ELEMENTARY PHYSICAL GEOGRAPHY The coast of British Columbia and. southern Alaska is bordered by high mountains, into whose valleys the sea now enters in long and deep passages, called fiords. Lat- eral ridges, separated from the mainland by water chan- nels or sounds, stand forth as islands. A navigable "inner passage," well protected from the rough water of the open ocean, is thus provided for steam vessels. The steep moun- tain sides, descending rapidly beneath the sea, generally offer no flat ground for settlement ; but most of the fiords now contain delta plains where streams enter their heads ; here villages find convenient sites. The coast of Maine, part of the dissected upland in the old mountain region of New England, has been partly sub- merged, so that it is entered by many long arms of the sea and fringed by many islands. Exl3ellent harbors are thus provided, and many of the people living near the coast are sailors and fishermen. QUESTIONS Sec. 108. "What is a mountain range? a mountain system? How do mountains differ from plateaus? What is the action of mountain-making forces? State a theory of their origin. How do streams affect mountain form ? To what two processes is mountain form due ? 109. Describe an example of block mountains. Where are good examples of this class found ? How has the form of these moun- tains been produced? How do the forms of several blocks vary? What can be said of the age of these mountains? Why may it be believed that these mountains are still growing? Describe the drainage of these mountains. Consider the climate of the region. Describe the places of settlement. MOUNTAIXS 213 110. Describe the dissected ranges of Nevada. Compare thein with the block mountains of Oregon. Ai-e the Nevada ranges still growing? Compare the climate of the ranges of Nevada and of Oregon. Describe the streams of the Nevada ranges. Where are settlements found among these ranges? 111. Where are the Jura mountains? AYhat is their structure? How have these mountains been produced ? How is their sti'ucture related to their form ? What changes have been produced by erosion? Describe the drainage of these mountains. Compare the side ravines and the crossing gorges. State the location of villages and roads. 112. 113. Name some lofty mountain ranges. Upon what two pro- cesses does the form of these mountains depend ? Compare the import- ance of land sculpture in these ranges and in the block mountains of Oregon. Of what do the lofty peaks and ridges consist? What becomes of the waste from them? What is the origin of the deep valleys ? Compare the domes and the horns of the Alps. Compare the Selkirk range of Canada and the Rocky mountains of Colorado. 114. Compare plains and mountains as to variation of tempera- ture ; of rainfall ; as to conditions of life. Why are the sources of large rivers often found in mountains ? 115. How do mountains act as barriers ? Compare the two slopes of the equatorial Andes as to climate and vegetation. What influence is exerted on climate by the Sierra Nevada and the Rocky mountains ? What is the chinook wind ? the foehn ? How have the Himalayas acted as barriers between nations ? How do mountain ranges serve as national boundaries ? Give examples. Explain the importance of passes. How are roads and railroads built over moun- tains? Give an illustration of mountains as an obstacle to travel. 116. 117. What are avalanches? How are they caused? How do they move ? How are villages and roads protected from them ? Describe an ice fall in the Alps. What is a landslide? Describe the landslide of Airolo in the Alps ; of the upper Ganges in the Himalayas. What disaster followed the latter landslide? How were its dangers lessened ? 214 ELEMENTARY PHYSICAL GEOGRAPHY 118. Describe the movement of rock waste in mountains. How is the form of the waste fragments changed ? What is an alluvial fan? How is it formed ? How does the form of alluvial fans vary ? How do fans affect the course of a river in front of them ? How does the course of a torrent vary on its fan ? Describe Two-Ocean creek. To what dangers are villages and roads on fans exposed ? Describe an example from Switzerland. Describe and explain a waste-filled valley. Describe and explain a terraced valley. 119. How are valleys widened? What sort of valleys are wid- ened most easily ? Describe crosswise valleys. Compare lengthwise and crosswise valleys as to occupation. 120. What is an earthquake ? How are earthquakes related to mountains? How fast do earthquake tremors travel? How much movement may they cause? Where are the shocks felt most vio- lently? How far may they be felt? How often do earthquakes occur in the Alps? Describe the great earthquake of India, 1897. What effect was produced by an earthquake in Japan in 1891 ? 121. Compare the people of mountains with those of the neigh- boring lowlands. 122. Describe subdued mountains as to height, form, rock waste, earthquakes, landslides. Describe an example of this class. What effects have these mountains on their inhabitants ? 123. What is meant by worn-down mountains ? What is a pene- plain ? Describe an example in Virginia. What is a monadnock ? Describe and explain the valleys of the Virginia Piedmont belt. Describe and explain the uplands and valleys of southern New England. How do they influence the distribution of population? 124. Describe the Allegheny ridges as to form ; as to origin ; as to drainage. What is a water ga^s ? 125. Describe the appearance of embayed mountains. What is their origin? What is a continental island? Describe the coast of southern Alaska ; the coast of Maine. CHAPTER VII VOLCANOES 126. Volcanic Eruptions. — Most of the processes of nature go on without violence. The usual movements of the winds and currents, the flow and ebb of the tides, the rise and fall of the lands, the weathering and wash- ing of rock waste are so placid that we gain confidence in the earth as a safe home to live in. But sometimes natural processes of a more violent behavior are witnessed. Hurricanes and tornadoes bring destructive winds and tor- rential rains, flashes of lightning and peals of thunder. Landslides rush down mountain sides, overwhelming the valleys below. Now and then the rocky crust beneath us quivers and trembles in earthquakes. Great waves occasionally roll in from the sea and sweep over low coastal lands. Here and there volcanoes burst forth with terrible commotion. Nature then seems frightful and destructive. Those who are overtaken by such dis- asters struggle against them, hopefully awaiting the return of the more peaceful conditions under which their habits of life have been formed, for man could not survive if he were always battling against the wilder forces of nature. Of all natural catastrophes, the explosive eruption of a great volcano is the most terrible. The air resounds 215 216 ELEMENTARY PHYSICAL GEOGRAPHY with its roaring. The sky is darkened and the sun is hidden by clouds of dust blown from the crater. The sea is burdened with floating ashes. Glowing streams of molten rock, or lava, flow down the flanks of the volcano, driving away everything that can take flight before them. Even the earth around trembles as the gases and lavas burst out from their deep sources. No wonder that igno- rant races of men have imagined struggling giants to be imprisoned under active volcanoes, nor that even the most learned are baffled when trying to account for these ter- rific displays of natural forces. But violent as a volcanic eruption may be, it weakens and in time ceases. The sky clears, the sun shines again, and nature once more goes on with her more quiet tasks. As the years pass by and a soil is formed on the weath- ered lavas, plants clothe their surface and man comes to dwell on the flanks of the volcanic mountain. The erup- tion is forgotten ; fields and villages occupy the volcanic slopes ; little remains to tell of the commotion of former times. 127. Young Volcanoes. — Volcanoes are formed by the ascent of molten lava through fractures or passages lead- ing from unknown depths beneath the earth's crust to its surface, on the land or on the sea floor. Although the lava is very hot, it is not burning or flaming. A volcano should never be described as a burning mountain. It is believed by many that the ascent of molten lava from its deep source is chiefly caused by pressures similar to those which cause movements in the earth's crust in VOLCANOES 217 mountain building, As the lava nears the surface and meets water in greater or less quantities, explosions of steam and other heated gases take a violent part in the eruptions. Fig. 105. Vesuvius iu Eruption The early growth of a volcano has occasionally been observed. The outburst is preceded and accompanied by earthquakes, which indicate the breaking of an upward pas- sage through the underground rocks, before hot lavas make their appearance at the surface. When the eruption is 218 ELEMENTARY PHYSICAL GEOGRAPHY Fig. 106. Monte Nuovo accompanied by gaseous explosions much of the lava is blown into fragments, of which the smaller are called ashes or cinders. The larger blocks and the coarser ashes accumulate in a conical heap, or volcano, frequently having remarkable regularity of form, a cup-shaped hollow or crater being kept open at the top over the vent by the outbursting gases. The finer ashes or dust may fall far away. When the eruption is less vio- lent the lava runs ^^M forth more quietly in a stream or flow, fol- lowing the slopes of the ground. Explo- sive and quiet erup- tions may alternate in irregular succession, and after many eruptions the volcano may become a lofty mountain, one or two miles high^ Monte Nuovo (new mountain) is a small volcano that was formed on the north side of the Gulf of Naples in Italy in 1538. Earthquakes occurred thereabouts for two years before the eruption, when in a week's time a cone was built up 440 feet high, half a mile in diameter at the base, and with a crater over 400 feet deep. Masses of lava " as large as an ox " were shot into the air by the bursting of great bubbles of gas or steam that ascended through the lava in the vent. Finer ashes fell over the country for several miles around. The people of the neighboring villages fled in terror from their homes. VOLCANOf:S 219 A greater eruption took place in Mexico in 1759, when the volcano JoruUo (pron. Ho-rul-yo) was built on the central plateau, burying fertile fields of sugar cane and indigo. The outburst was preceded by earthquakes; the eruption continued half a year, building six cones and pouring out extensive lava flows. The highest cone, Jorullo, rose 700 feet above the plateau. The flows retained a perceptible heat for over twenty years. Many examples might be given of marine eruptions. In 1867 a shoal was discovered among the Tonga islands of the Pacific (lat. 20° 20' S., long. 176° 20' W.), the surrounding sea floor being about 1000 fathoms deep. In 1877 smoke was seen ascending from the sea surface over the shoal. In 1885 an island had been formed two miles long and 200 feet high. At this time a terrific eruption was in progress, and the shocks of the explosions were felt on neighboring islands. As the island consisted chiefly of ashes, it has since been rapidly eroded by the waves and will soon disappear, unless new eruptions occur. Most volcanoes have not been observed in their early growth, yet, even if not now in eruption, so perfectly do they correspond in form and structure with such examples as Monte Nuovo and Jorullo that no doubt can remain as to their origin. In northern California there is a cinder cone of remark- ably perfect form. Its barren slopes of loose ashes rise 640 feet to the rim that incloses a crater 240 feet deep. A stream of lava has issued from near the base of the cone, flooding a neighboring valley with a lava field a mile wide and nearly three miles long. The surface of the field is 220 ELEMENTARY PHYSICAL GEOGRAPHY so covered with unweathered angular blocks of lava as to be almost impassable. The edge of the field is a steep and ragged slope 100 feet high. It obstructs a stream from the south, which forms Snag lake, so called from the dead trees still standing in it. On all sides the surface of the country is covered with a layer of volcanic ashes and dust, six or more feet deep near the cone, thinner and finer farther away, yet recognizable at a distance of eight miles. Fig. 107. Cinder Cone and Lava Flow, California From the size of trees growing on the ashes it is estimated that the cinder cone was built about 200 years ago. The lava flow is younger, but none of the Indians or early settlers thereabouts (1845) observed its eruption. 128. Great Volcanoes. — Many large volcanoes, whose first eruption must have occurred many thousands of years ago, are still active. After long periods of more or less complete rest they burst forth again for a short time, blowing out showers of ashes, building their cones to a height of 10,000 feet or more, and adding new lava streams to their flanks, so as to gain a diameter of ten or twenty miles or more at the base. The melted lava often breaks VOLCANOES 221 forth from the mountain side and flows down to gentler slopes on the flanks and out upon the surrounding country ; thus the cone as a whole comes .-•-—. to have a rudely bedded struc- ture of ashy and dense lavas. It sometimes happens that the upper part of a volcano is destro3'ed by a violent eruption or broken in by underground disturbance, forming a greatly enlarged crater, or caldera. Volcanoes of this form are some- times called ring mountains. Deception island, in the South Shetland group, beyond Cape Horn, is the high rim of a caldera, breached on one side by a narrow gap, which gives entrance to a quiet circular bay. Layers of ice are to be seen between beds of ashes and lava on the caldera walls. The cone of Vesu- vius has been built in TT -.nn r^x r. f^T ■ ■ ^1 n ^^ alargc caldcraof morc Fig. 109. The Cone of Vesuvius m the Caldera » of Monte Somma (looking uorth) ancient Origin. The cone buries one side of the caldera lim, the other side being known as Monte Somma. Draw a map of A'esuvms and Monte Somma, like the map of Deception island in Figure 108. Fig. 108. Deception Island, a Vol- canic Caldera (plan and section) 222 ELEMENTARY PHYSICAL GEOGRAPHY Mt. Mazama, a superb ring mountain in Oregon, eon- tains a beautiful lake in its huge caldera. This volcano must have been once several thousand feet higher than it is now, before its upper part was engulfed in the formation of the caldera. Figures 110 and 115 are maps of Mts. Mazama and Shasta, in which the mountain form is indicated by lines that cui've around the slopes at definite heights, every line following a level course, and every pair Fig. 110. Contour Map of Crater Lake iu Mt. Mazama, Oregon of lines differing in height by a fixed amount. Lines of this kind are called contour lines, and the maps are contour maps. Where the lines are open spaced, the slopes are relatively gentle ; where the lines are close together, the slopes are steep. Compare the inward and out- ward slopes of the ring of Mt. Mazama; compare the upper and lower slopes of Mt. Shasta. Determine from Figure 110 the diameter of the caldera, and the average height of its rim above sea level and above the lake surface. VOLCAXOES 223 A rough classification of volcanoes groups them as active, when they are frequently in eruption ; dormant (sleeping), when now at rest, though giving signs in hot springs and sulphurous vapors that activity may be begun again; and extinct, when they give no sign of activity. It is not possible to make certain distinction between the last two classes ; great eruptions have taken place in vol- canoes after all signs of activity had ceased. Showers of ashes as they chance to fall may bury villages, fields, and forests. The , Fig- ure 114. Fig. 114. The Lava Plateau of Idaho, Oregon, and Washington 132. Dissected Volca- noes. — Torrential streams running down the slope of volcanic cones carve ravines on their flanks. Many ravines are formed during the periods of rest in the growth of great volcanoes, only to be filled again by later eruptions of lavas and ashes. After eruptions cease the ravines deepen more and more, leaving sharp ridges between them, and at last dis- secting the cone so deeply as to leave little appearance of its original shape. Mt. Shasta, in northern California, is furrowed on all sides by gigantic ravines, but its conical form is still well preserved, Figures 115, 116. Many meadows about its 230 ELEMENTARY PHYSICAL GEOGRAPHY base mark the sites of lakes formed by laya-flow barriers but now filled and drained. The best agricultural land in the region is of this origin. Fig. 115. Contour Map of Mount Shasta, California A number of extinct and more or less dilapidated vol- canic cones surmount the plateaus of Arizona and New- Mexico, Mts. San Francisco and Taylor being among the best examples. Before the summit of Mt. Mazama was destroyed by engulfment its height was probably about equal to that VOLCANOES 231 of Mt. Shasta to-day. Ravines like those of Shasta had been worn down the slopes of Mazama; their lower courses are still seen on the outer slopes of the ring mountain, but their upper courses are lost. Many great volcanoes in various stages of activity and dissection are found in the Andes along the western side of South America. Fig. 116. Mount Shasta 133. Geographical Changes caused by Volcanoes. — The construction of large volcanoes by successive eruptions sometimes causes curious changes in the course of rivers, whose valleys are more or less blockaded by the new-built cones. A remarkable example of this kind is found in Central America, where the growth of a range of volcanoes has transformed a bay that once opened to the Pacific into a lake, known as Lake Nicaragua. The volcanoes formed so 232 ELEMENTARY PHYSICAL GEOGRAPHY effective a barrier that the lake surface is now 105 feet above sea level and its outlet flows across what used to be the continental divide and discharges into the Carib- bean sea. Since the outlet took this course it has eroded a Fig. 117. Map of the Lake Nicaragua District deep gorge across the divide, and the level of the lake is now lower than when the eastward overflow first took place. This lake would form part of the proposed interoceanic canal route across Nicaragfua. Draw a map, based oh Figure 117, to show the genera] outline of the land before the volcanic range was built. The original outline of the bay now closed by the volcanoes and their lava flows is shown by a dotted line. Describe the changes caused by the building of the volcanic range. VOLCAXOES 233 QUESTIONS Sec. 126. Give examples of the quiet processes of nature; of the violent processes. Describe the explosive eruption of a volcano. 127. How are volcanoes formed? What is the most probable cause of the ascent of lava in volcanoes ? What is the effect of steam? Describe the early growth of a volcano. Give an example from near Naples ; from Mexico ; in the Pacific. Describe the cin- der cone in California. How did its lava flow affect a neighboring stream ? Why is this volcano thought to be of recent origin ? 128. How are great volcanoes formed? What size do they attain? What is a caldera? Describe Deception island ; Vesuvius and Monte Somma ; Mt. Mazama and its caldera. How may volcanoes be classified ? What effects may be produced by showers of ashes ? by floods? How may these floods be caused? Describe some inci- dents of the eruption of Conseguina, 183.5 ; of Cotopaxi; of Galung- gung. What can you tell of Pompeii and Herculaneum? 129. Why are earthquakes often associated with volcanoes? Describe the explosion of Krakatoa. 130. How are volcanoes distributed? Compare the Atlantic and Pacific in this respect. How many active volcanoes are known? How many of these are on the continents ? Where are volcanic islands found ? What forms have they ? Where are extinct vol- canoes often found? Where is an active volcano found far inland? Give an instance of the effects of living on a remote volcanic island. 131. Describe the surface form of lava flows. Describe the lava cascades near the Colorado canyon ; the erujition and lava flood of 1783 in Iceland; the lava floods of Idaho. 132. Describe a dissected volcano. Name some examples of this class. Compare Mts. Shasta and Mazama. 133. What geographical changes may be jiroduced by volcanoes ? Describe an example of such changes in Nicaragua. 1 CHAPTER VIII RIVERS AND VALLEYS 134. Underground V/ater The water supplied by rain and snow is disposed of in part by evaporating from the surface, in part by running down the slopes of the land to the streams, and in part by sinking underground. The latter part is called underground water, or simply ground water. The proportions of these several parts vary under different conditions. The greater part of a light and long-continued rain may pass underground, especially if falling on a plain. A very heavy rain, or " cloud-burst," falling on strong slopes is largely disposed of by direct run-off, causing sudden floods. Rain, falling on a surface having a deep soil well cov- ered with vegetation (grass, bushes, or forest), will for the most part soak into the ground. On arid plains a great part of a light rain may dry off from the barren surface of the ground, but a heavy rain will run off in a flood. Loosely consolidated strata and deep rock waste take in much ground Avater. Firm rocks, such as granites, allow but little water to enter beneath the weathered waste on their surface. When the ground is frozen little water can enter it ; hence rivers rise in floods when deep snow is rapidly melted by a heavy rain. 234 RIVERS AND VALLEYS 235 Underground water is essential to the growth of plants, whose roots must reach moist earth. Where grass and trees cover the surface, much ground water taken in by their roots is discharged into the air by evaporation from their leaves. Fig. 118. Diagram of Cavern and Sink Hole 135. Caverns. — Most rocks are not soluble in water. Limestone is exceptional in this respect ; it may be slowly dissolved, especially by ground water, which gathers cer- tain acids from decomposing vege- tation as it soaks down through the soil. Caverns in limestone districts are the result of this solvent action of underground waters. The Mammoth cave of Kentucky and the Luray cavern of Virginia are famous examples of their class. Streams gathering on the surface descend to underground pas- sages by hollows, known as sink holes or swallow holes. After flowing underground for some distance such streams may issue m enlarged and turbid currents from the mouths of caverns. Where sink holes and cavern drainage prevail so much water enters the ground that surface streams are compara- tively rare. When the sink holes or the underground pas- sages become obstructed ponds and lakes are formed in the surface basins. 236 ELEMENTARY PHYSICAL GEOGRAPHY Several species of animals dwelling in the complete darkness of caverns are blind, but their senses of hearing and touch are highly developed. As the cavern enlarges, its roof may fall in more or less completely. The beautiful Natural bridge of Virginia is the remnant of a cavern roof. 136. Springs. — Very little ground water remains per- manently beneath the land surface. Sooner or later, after descending to less or greater depths, it returns to the sur- face at a lower level than where it entered, coming out in the form of springs and joining the run-off of streams. The movement of ground water is comparatively slow while percolating among the particles of rock waste or through the pores and crevices of rocks. Where a large part of the rainfall enters the ground, the volume of the streams fed by springs is less variable than where the rain- fall is mostly discharged by direct run-off during and shortly after a storm. It is for this reason that the springs and streams of a forested region usually have a comparatively constant flow ; but this rule does not apply in regions of strong relief, such as the dissected plateau of West Virginia. • When forests are cut down, the direct run-off of the rainfall is increased; then the springs are likely to run dry and the streams will vary greatly in volume between flood and drought. Ground water slowly moves from hills and slopes, descending to lower levels and accumulating beneath the lower ground. It may, therefore, be generally found near the surface in valleys, where the soil is usually damp. At RIVERS AND VALLEYS 237 the base of a slope the ground water m^j issue in a spring, -s; Figure 119, supplying a small brook. Innumerable small springs occur unnoticed in the banks of streams. Ground water stands close to the land surface in marshes, swamps, and bogs, rising or falling somewhat with changes of weather and season. In regions of sufficient rainfall and moderate relief the ground water may be reached at almost any point except on hilltops by sinking wells to a depth of from ten to forty Fig. 119. Section showing Ground Water in Rock Crevices beneath a Valley feet. The bottom of the well should be a few feet deeper than the level at which the trickling stream of ground water enters it, so as to accumulate water in sufficient volume to supply ordinary domestic needs. Ground water and spring water carry very little rock waste (unless in solution) and are generally clear and pure. For this reason wells and springs generally afford a better water supply than the surface streams that receive the wash of fields and meadows. In coastal regions ground water may flow forth as springs directly into the sea, either on a sloping beach near low-tide level, or at the bottom offshore ; here they sometimes have a current so abundant as to supply a column of fresh water that ascends through the heavier salt water to the surface. 238 ELEMENTARY PHYSICAL GEOGRAPHY 137. Artesian Wells. — In many coastal and interior plains a large part of the rainfall enters the more sandy la3^ers and follows their gentle slope deep underground, between other layers that are less open to the passage of water. If a deep well is sunk to the water-bearing stratum, the water may rise and flow out of the surface like a foun- tain. Wells of this kind are called Artesian, from Artois, a district in France where they were first bored. It is essential that the water-bearing stratum should receive its rainfall at a higher level than that of the top of the well by which it is tapped, as shown in Figure 120. Fig. 120. Diagram of a Coastal Plain with Artesian Wells In what part of the plain does tlie stratum tapped by the deeper well reach the surface? Charleston, Galveston, and many other coastal cities receive much water supply from artesian wells. In east- ern Maryland deep wells pierce strata that reach the surface and receive rainfall west of Chesapeake bay; the strata lead the water beneath the nearly water-tight layers that floor the bay, and it is still fresh when rising in the wells. Southern Wisconsin and eastern Iowa have many artesian wells, supplied by water-bearing strata that slope gently away from the older land of northern Wisconsin, RIVERS AND VALLEYS 239 138. Hot and Mineral Springs. — Ground water some- times descends deep beneath the surface with a slow supply from a large area. While deep underground the water acquires a high temperature and stands under a heavy pressure. It is shown by experiment that hot water under pressure has increased power of dissolving certain minerals. Hence the slowly percolating water takes into solution Avhat it can dissolve of the more soluble minerals dis- covered on its wa}^ such as calcite (the mineral base of limestone), salt, and certain compounds of magnesia, iron, etc. If the water then rises rather rapidly along a rock fracture, it will appear at the surface in springs, bearing an unusual amount of mineral substances in solution and often having a high temperature. Such springs are fre- quently of medicinal value. Springs of this kind are associated with disturbed rock structures such as occur in mountainous districts. Saratoga Springs, N.Y., White Sulphur Springs, W.Va., Vichy in central France, and Karlsbad ui Bohemia are examples of settlements determined chiefly or wholly by the value of their medicinal waters. Many other mineral springs occur in the Appalachian and Rocky mountains. 139. Geysers. — In certain volcanic regions the tempera- ture of the underground water may rise to or above the boiling point. Steam then issues with the water, often in a more or less explosive manner, and such steaming and spouting springs are called geysers. The geysers of Ice- land have long been famous ; those of the Yellowstone Park are now the most celebrated in the world. 240 ELEMENTARY PHYSICAL GEOGRAPHY The jet of steaming water and spray may rise for several minutes to a height of a hundred feet, with a loud roaring noise. Then all remains quiet till the next eruption, usually a number of hours later. Mineral substances that were dissolved in small quantity by the hot water underground are partly deposited near the geyser's vent as the water cools or evaporates, and thus a mound or terrace of mineral deposits is gradually formed. The terraces around the hot springs of the Yellowstone Park are of great beauty. The intermittent action of many geysers suggests that a certain period of time (an hour or more) is necessary to warm the new supply of water that enters the crevice of discharge after a previous supply has been blown out by steam. Water under pressure must be heated above the ordinary boiling point (212° F.) before it will change to steam. Hence in the deeper part of the crevice the temperature of the boiling point is higher than at the surface. When the deeper water reaches its boiling point a great part of it is quickly converted into steam, which blows the rest of the water out of the vent. Fig. 121. A Geyser RIVERS AXD VALLEYS 241 140. Mud Volcanoes. — Certain hot springs bring a con- siderable amount of fine rock waste to the surface with their steaming water. The waste is then deposited as a muddy sediment around the opening of the spring, where it forms a mound with a hollow or crater in the center. Although seldom over a few score feet in height, the resemblance of these mounds to true volcanoes has given them the name of mud volcanoes. A number of mud vol- canoes occur in the Yellowstone Park, where some of them are only a few feet high. Some of the largest known, with heights up to 400 feet, are near the lower course of the river Indus in northwest India. 141. River Systems and their Parts. — A river is a stream of water bearing the rainfall and the waste of the land from higher to lower ground and, as a rule, to the sea. A trunk stream and all the branches that join it constitute a river system. Stream is a general term, with little relation to size. Rill, rivulet, brook, and creek apply to streams of small or moderate size. River is generally applied to the trunk or to the larger branches of a river system. A river flows in a channel that is somewhat lower than the adjoining land surface. The floor of the channel is the river bed ; the sides of the channel are the liver banks. The coarser part of the waste borne by the liver is swept along the bed ; the finer part may be carried in the stream. The land from which a river gathers its water and its load of rock waste is called its basin. The crest line, or "height of 242 ELEMf:NTARY PHYSICAL GEOGRAPHY land," between the basins of neighboring streams or rivers, or between the valleys of river branches, is called a divide. m\l^u.~~ ^P:x^ Fig. 122. A Divirting Ridge in the Mountains of Northwest England Trace the divide shown in Figure 122. Note that a divide may- be much higher at one point than at another. Follow some of the simple and branching divides shown in Figures 86 and 104. RIVERS AND VALLEYS 243 The land slopes in opposite directions on the two sides of a divide. When rain falls on the adjoining slopes it will be shed into different streams; hence a divide is sometimes called a watershed or water parting. Certain crest lines in the Rocky mountains separate the basins of rivers which discharge into the Atlantic and the Pacific oceans; these crests constitute the "continental divide." Name some of the rivers that are thus divided. On smooth plains and uplands there is no well-marked height of land or ridge separating the headwaters and side streams of neighboring rivers. Such surfaces may be described as having an undivided or imperfectly divided drainage. Undivided drainage areas are often found on young plains and plateaus. Compare the foreground and background of Figure 62 in this respect. When a plain or plateau or mountain region is well dissected numerous sharply defined subdivides are devel- oped between the smaller rivers and their branches, as on the Allegheny plateau. River and stream basins in vigorous mountains are sharply divided by the crest lines of the lofty ridges between the deeply eroded valleys. A worn-down region may have indistinct divides, as on the even uplands of the Piedmont belt of Virginia, Figure 99. Nearly all these features of river systems may be illus- trated in a small way by the temporary streams on a road surface just after a fall of rain. Many interesting studies may be made of the small stream basins, divides, branches and channels, and of the manner in which the streams bear Avaste from higher to lower ground. 244 ELEMENTARY PHYSICAL GEOGRAPHY 142. Floods and Droughts The volume of a river varies with the change in the amount of rainfall over its basin. Duiing and shortly after a rain (or a thaw of snow) the surface run-off is most active ; all the rivulets are running with water and waste to the creeks, and the creeks run to the rivers. The volume of all the streams is increased at such a time, and their current is quickened. The water is then turbid with the waste that has been washed into the streams by the rivulets on the valley sides and lifted from the stream beds by the strengthened currents. As the stream volume increases, the water may rise above the banks of the channel and overflow the low ground or flood plain on either side. There some of the fine river-borne waste, or silt, will be deposited as the current slackens. When the rain stops and the surface run-off lessens and ceases the flooded streams are drained down the valleys toward the sea; their volume decreases and their surface sinks to a more ordinary level. Then the streams must depend on ground water supplied by springs at innumerable points in the stream beds. Less waste is washed into. the streams at this time, and their current may become nearly or quite clear. During a drought of several weeks or months the streams drain away much of the ground water. Then the discharge of the springs is weakened, and the streams are reduced to smaller volume. They may shrink so much as to be unable to cover all the bed of their channel, especially in the head- water branches. The streams may entirely disappear for a time, but even if lost at the surface, ground water may gen- erally be found slowly creeping through the sand and gravel of the channel bed a few feet below the surface. RIVERS AND VALLEYS 245 In regions of plentiful rainfall, like the eastern United States, the rivers may be much reduced during droughts, but they do not entirely disappear. In the drier climate of many of the Western States the streams habitually dis- appear and leave their channels dry during the long inter- vals between rain storms. 143. The Work of Rivers Frequent reference has already been made to the work of rivers in sculpturing the lands. This important subject may now be con- sidered more carefully. The higher a river lies above baselevel, the deeper may its valley in time be worn. The steeper the channel, the faster the river flows and the more and the coarser rock waste it may sweep and carry downstream. The greater the volume of a river on a given slope, the less it is retarded by friction on the bed and banks, and the faster it flows. Hence a river in flood floAVS faster than at time of low water, and the flooded current transports a greatly increased load of rock waste. Indeed, it is chiefly in time of flood that the work of a river is performed. The deepening of a valley by the erosion of rock in the river channel is accomplished chiefly by the rasping of the rock surface with the innumerable fragments and particles of rock waste that are swept over it. The more resistailt the rock, the slower it will be worn down. The particles thus worn from the rock surface make part of the load of waste borne away by the river. As the valley bottom is worn deeper and . deeper below the surrounding country, the valley sides are attacked by 246 ELEMENTARY PHYSICAL GEOGRAPHY the weather, and much waste washes and creeps down from them into the river, thus widening the valley, decreasing the steepness of its side slopes, and adding to the load of waste borne away by the stream. It is in this sense that it is said that "rivers erode their valleys." Another portion of the river load is received from the headwaters and side streams, which in turn receive it chiefly from the wash of waste down the side slopes of their valleys at times of rain or thaw. The load of waste thus gathered is not swept along in a continuous movement to the sea ; it stops many times on the way, being laid down on the bed or sides of the chan- nel when the water is low, forming bars and banks ; it is swept forward again a greater or less distance at time of flood. Rivers that are beginning their work of erosion and transportation in sculpturing a newly uplifted land may be called young. When they have worked so long that all the land slopes in their basin have been worn down low, so as to form a surface of faint relief — a peneplain — at a small altitude above sea level, the rivers may be called old. Between youth and old age, when the rivers are actively working in well-carved valleys, sweeping along the waste received from the hills or mountains that form the valley sides, they may be called middle-aged or mature. 144. Young Rivers. — The examples of land forms described in earlier chapters have shown that when a region is first raised from the sea, or when a former land surface is uplifted, tilted, or folded, the streams as RIVERS AND VALLEYS 247 a rule follow the lead of the land slopes, uniting here and there to form rivers of larger and larger size. Young rivers thus newly established proceed to cut down their channels where the slope is steep enough to give them an active current; the waste that they gather is washed along, rasping down the ledges in the river bed; but where the slope is very faint, or where rivers enter a basin holding a lake, they lay down their load of waste and build up the land surface. While rivers are still young their course is often marked by rapids and falls, not yet eroded away, and by lakes not yet filled up with sediments or drained away by the deepening of their outlet by the outflowing stream. The current of such rivers is irregular, being- very fast at rapids and falls and almost wanting in lakes. As the river grows older both the falls and the lakes dis- appear and the current becomes more uniform. The drainage of the Laurentian highlands of Canada north of the St. Lawrence river bears every mark of youth. Lakes are very numerous and of irregular form. They often have several outlets, no one stream having cut down enough faster than the others to secure all the discharge. The streams are frequently interrupted by rapids or fslls on rock ledges, in which channels are as yet cut only to moderate depth. The rivers frequently split into two or more channels, which reunite after wan- dering in independent courses for ten or twenty miles across country. These highlands are a rugged, forested, and thinly popu- lated wilderness without roads. All travel is by canoes 248 ELEMENTARY PHYSICAL GEOGRAPHY along the water courses, and the canoes have to be car- ried past every rapid and fall. The birch tree, from whose bark portable canoes are made, is here as appropriate to the needs of the inhabitants as the camel is to the dwellers in arid deserts. The St. Lawrence system, with its many lakes, falls, and rapids, is a remarkable example of very young or Fig. 123. Niagara Falls undeveloped drainage. The outlet of Lake Superior is by a river interrupted by rapids, called the Sault Sainte Marie (Soo St. Mary). The outlet of Lake Erie is Niagara, with its renowned cataract and rapids. The out- let of Lake Ontario is the St. Lawrence, with numer- ous rapids. The lakes favor navigation, but the rapids and falls obstruct it. Canals and locks have now been RIVERS AND VALLEYS 249 constructed, by which the rapids and falls are passed. Name the great lakes of the St. Lawrence system. The region of the great African lakes bears many marks of youthful drainage. The lake basins here indicate a break- ing or warping of the earth's crust, like that in southern Oregon. The inclosing plateaus are bordered by ragged cliffs, where fractures have taken place. The Nile, flowing north from Lake Victoria Nyanza, and the Shire, flowing south from Lake Nyassa, are young rivers of powerful cur- rent, descending over falls and rapids, and are very busy in the work of deepening their valleys and draining the lakes. By long-continued action the path of a river will in time be everywhere worn down or built up to such a slope that the current will be just strong enough to carry the load of waste that it receives. Such a river may be described as passing from youth to maturity. 145. Lakes may be generally taken to indicate a youth- ful drainage system, as in the examples just given. In time they will be destroyed, partly by filling with the waste that is brought by the inflowing streams, partly by the deepening of the outlet valley. Lakes should therefore be regarded as only temporary features in the long life of the river system to which they belong. The rivers may remain long after the lakes disappear. The depressions between the tilted lava blocks of south- ern Oregon hold lakes because enough time has not yet passed to enable the streams to fill and drain their basins. Lava flows obstruct streams and for a time hold back lakes. Lakes of other kinds will be described IS/tQw 250 ELEMENTARY PHYSICAL GEOGRAPHY As the current of a river decreases on entering a lake, the stream-borne waste settles ; thus deltas are formed at the inlets and the lake bottom is strewn with the finest waste or silt. Lake Geneva in Switzerland receives the Rhone at its east end ; the river is turbid with the waste that it has received from Alpine glaciers and torrents. A delta twenty miles long has been built into the lake. It has grown a mile forward since Roman times, nearly 2000 years ago. The lake bottom is a plain of fine silt. When even the finest silt has settled, the lake water becomes very clear, and the Rhone at the outlet is wonderfully transparent. Lakes act as regulators of the discharge of their outflowing rivers ; for the level of the lake changes little, whether the inflowing streams are flooded or low, and hence the outlet river has a relatively constant volume. The Ohio without lakes and the St. Lawrence with five great lakes are strongly contrasted in respect to floods. The latter has no great floods, because even a heavy rain raises the surface of the lakes gradually and only by a small amount ; hence the outflowing river cannot be greatly increased in volume. The rains of the upper Ohio basin, a hilly district, are not detained in lakes, but quickly flow down the hillsides to the streams. Floods in the Ohio valley may rise fifty or sixty feet in a few days, spreading to ten or twenty times the usual width of the river and causing great damage to villages and cities on the valley floor. RIVERS AND VALLEYS 251 146. Falls and Rapids. — When a river begins to wear its valley it rushes down any descending slope that occurs on its course. Here a gorge is cut as the rocks are rasped away by the gravel and sand in tlie rapid current. Niagara, when first taking its present course, fell over the north-facing bluff of the upland Fig. 124. Diagram of Niaaara River between Lakes Erie and Ontario that separates the basin of Lake Erie from that of Lake Ontario ; since then the river has cut back a gorge about seven miles long from the edge of the upland ; the falls now plunge into the head of the gorge. The larger or Canadian fall is now retreating three or more feet a year at its middle. The falls of the Yellowstone river occur at the head of a deep canyon cut by the river in the process of deepening 252 ELEMENTARY PHYSICAL GEOGRAPHY its course through a lava plateau. As the falls are worn back the gorge is lengthened. While a stream is engaged in deepening its valley it often flows from a harder to a softer rock structure. It will deepen the valley much more quickly in the latter than in the former, and a rapid or fall will be formed on Fig. 125. Falls of the Yellowstone River the abrupt slope between the two. Falls and rapids of this kind are numerous, especially in dissected plateaus and mountains. .It has long been the custom to build mills near falls, so that part or all of the descending water may be used to turn water wheels and thus to drive the machinery of the mills. Villages have often grown up around the mills and factories thus located. As the work of the mills increases it has frequently been necessary to add steam RIVERS AND VALLEYS 253 power to water power ; at the same time the village may grow to be a large city. In recent years it has been found possible to transform the power of falling water into an electric current, which may be carried many miles through Fig. 120. Diagram of Torrent, with Falls and Reaches How many falls are shown in Figure 126? Draw a profile along the river course and compare its slope at and between the falls. AVhy are some of the stretches between the falls longer than others ? Where are the gorges deepest ? wires and then set to work to drive machinery, to run cars, or to furnish electric light. Waterfalls in thinly populated mountains may thus in time come to be used to supply electric power to cities on the neighboring plains. 254 ELEMENTARY PHYSICAL GEOGRAPHY 147. Graded Rivers. — A river cannot wear down its course to a level, for there must be some slope down which the current, bearing its load of rock waste, may flow toward its mouth. While the slope is strong and the current is very swift the stream is called a torrent. The waste is then swept along so actively that bare rock is commonly seen in the stream bed. Torrential streams are usually clear, because they quickly sweep away the fine particles that they receive from time to time, leaving coarse cobbles and bowlders lying on their rocky channels. Such streams are still young. As time passes and the channel is eroded deeper and deeper it will be worn down more nearly level, closer and closer to baselevel. But it must always preserve a slope sufficient to give the water a velocity that will enable it to wash forward the load of waste received from the head- waters and side streams, though without either deepening or building up the bed of the channel significantly. When such a slope is attained the river is said to be graded. It has reached maturity. The current of a graded river is usually deliberate instead of torrential. Its bed and banks consist, for the most part, of deposits of rock waste ; firm ledges are seldom seen along its course. The water is usually made some- what turbid or muddy by the presence of fine waste, with which it is plentifully supplied by its tributaries and by the wash from its bed and banks. In valleys among high mountains, where an abundant supply of coarse waste is washed down from the steep valley sides, graded streams must have a slope strong RIVERS AND VALLEYS 255 enough to give them an active current ; otherwise their coarse and abundant load could not be washed forward. In lowlands where only fine-textured waste of the land is slowly washed into the streams, graded rivers have a very gentle descent. Water moves so easily that large rivers assume very faint slopes; the lower Mississippi has a descent of only two or three inches to the mile, yet it bears along a vast amount of rock waste, — 6700 million cubic feet of sus- pended silt, 750 million of silt dragged along the bottom, and 1400 million of minerals in solution every year. 148. Reaches and Rapids. — A longer time is required to wear a valley down to grade where the rocks are resist- ant than where they are weak. If a river crosses a suc^ cession of weak and strong rocks, as in Figure 126, the graded condition will be first attained on the weak rocks, and each reach of the river on the weak rocks will be graded with reference to the sill of hard rocks next down- stream or with reference to the lake or sea into which the river may flow. The sills of hard rocks then serve as local baselevels with respect to which the stretch or reach next upstream is graded. Manj^ rivers come in this way to be divided into long smooth reaches and short plunging rapids or falls. Most of the rivers of New England and of eastern Canada are in this condition. When a river system has been undisturbed for a long period of time, even the resistant rocks are worn down. Few falls then remain to interrupt the steady flow of the 256 ELEMENTARY PHYSICAL GEOGRAPHY river current, and its graded reaches become longer and longer. The side streams, following the example of the master stream, wear down the side valleys so as to join the main valley at even grade. It is in this well-established condition that many large rivers of the world are found. When a graded condition is reached in even the smaller branches of a river system the slope will be steepest in the headwater streams and least near the river mouth; thus the profile of a well-developed river is a curve of decreasing slope from head to mouth. 149. The Development of Valleys. — While a young river is deepening its valley, the valley sides are steep and the valley bottom is no wider than the river channel, as in Fig- ure 127. At such a time the valley floor offers no attraction to settlement, as it affords no level ground for roads near the river ; roads built in such a valley must perch on the side slope. If the valley is deep, like the Colorado canyon, it may act as a barrier between the uplands on either side. Floods have little room to spread in a steep-sided valley ; hence they rise rapidly on the valley walls, even thirty feet or more in a day or two. Thus confined in the valley, the flood flows rapidly and sweeps away all obstacles, gradually subsiding as its supply of water lessens. It is for this reason difficult to maintain road bridges across the streams of the Allegheny plateau. Figure 79; the great expense of building strong and high bridges can- not be borne by the scattered population. The streams are therefore commonly crossed by fording. At time of high water travel is interrupted. RIVERS AND VALLEYS 257 The continued action of the river, wearing first on one bank and then on the other, gradually widens the valley floor. At the same time the sides of the valley are Fig. 127. Valley of Yakima River, Washington worn back to gentler slopes, and the valley floor becomes more accessible. At this stage of development the valley is mucli more available for human uses than when young, narrow, and 258 ELEMENTARY PHYSICAL GEOGRAPHY steep-walled. Villages may be built and fields may be cultivated on the valley floor. Roads may follow it on each side of the river. Instead of being a trenchlike bar- rier between two highlands, the valley has now become a well-graded pathway for settlement and for trade between the upper and lower parts of the river system to which it Fig. 128. The Mohawk Valley belongs. The Mohawk valley in eastern New York, Fig- ure 128, is a good example of this kind. Another is shown in Plate X. The behavior of rivers during the advance in the devel- opment of their valleys must now be considered in greater detail. 150. The Development of Flood Plains. — In a winding stream the fastest current is displaced from the middle of the channel toward the outer bank. Such a stream RIVERS AND VALLEYS 259 therefore tends to cut more on the outer bank than on the inner bank at every turn ; hence as it cuts down it also cuts sideways. When grade is reached the valley walls will be slant- ing, but they will be steepest on the outer side of every bend, where the stream has undercut the valley wall, as in Figure 129. The valley walls will therefore be equally steep on the two sides only where the valley is straight. At each turn sloping spurs descend opposite abrupt cliffs, and the belt of country occu- pied by the turns of the river is broadet than at first. Draw a map of the district shown in Figure 130 a, following the style of Figure 129, and show where the river is undercutting the cliffs. The river is supposed to be flowing toward the front of the diagram in Figure 130. Fig. 120. Outline Map of a When a river has worn down Young Valley its valley to a gentle slope it still wears on the outer bank of every turn, because the strong 'current runs there; thus the valley floor is broad- ened. At the same time the turns tend to become smooth curves of regular form. As the outer bank of a curving channel is slowly cut away, the inner bank, where the current runs slower, is gradually filled up nearly to high- water level with rock waste from farther upstream. A curved strip of fiat valley floor is thus developed on the inner side of each curve, as in 260 ELEMENTARY PHYSICAL GEOGRAPHY Figure 130 h, first on one side and then on the other side of the river. As the valley floor is exposed to overflow at times of flood, the flat land bordering the stream is called the flood plain. Draw a map of the district in Figure 130 J. Describe the shape and position of the patches of flood plain. What difficulties would be met in making a road along the val- ley bottom ? With continued action the river consumes more and more of the spurs that enter its curved course, as in Figure 130 c, d. In time the spurs are all worn away, as in Figure 130 e. Then an open flood plain is formed on which the river freely follows such a curved course as best suits its volume. With still fur- ther action of the river the flood plain will be slowly Fig. 130. Diagrams of a Widening Valley widenedto greater breadth. The valley will then be more attractive to settlement than before, with room for villages and fields on its floor. RIVERS AND VALLEYS 261 Which side (up-valley or down- valley) of the middle spur in Figure 130 c has been worn away? Draw a map representing Figure 130 d. Describe the form of the upland in the diagrams of Figure 130. Compare the form and breadth of the flood plain in the different diagrams. Compare the slopes of the valley sides. Compare the forms of the upland spurs that enter the curves of the valley. When a river overflows, the greatest amount of silt is laid down on the flood plain near the river channel. Thus in time the plain comes to have a gentle slope away from the river on either side, as well as down the valley. If a stream has a large load of coarse rock waste, its graded flood plain must be relatively steep (a descent of from five to twenty feet or more in a mile). In this case the stream does not turn far aside from a direct course along the flood plain to form serpentine curves; but it is constantly embarrassed by the formation of bars and islands of gravel and sand, splitting its current into a braided network of channels. The Platte is a river of this kind. It gathers much waste from the weaker rocks of the Great plains and therefore requires a rather strong slope for its graded valley floor. Many rivers flowing from the Alps to the lower lands have gravel bars and islands between their braided channels, as in Plate XL 151. River Meanders. — If the waste borne by a river is of very fine texture, the flood plain will have a very gentle grade. Then the river easily turns aside from a direct course on its broadened flood plain, and in this 262 ELEMENTARY PHYSICAL GEOGRAPHY way (whatever its original path) deveh)ps a system of serpentine curves, as in Figure ISO d,e. Curves of this kind are called meanders, after the Meander, a winding river of Asia Minor. How many turns does the river make in Figure 131? The size of the meanders increases with the volume of the stream. A meadow brook may swing around curves Fig. 131. A Meandering River, Vale of Kashmir, India measuring only forty or fifty feet across. The curves of the lower Mississippi are from three to six miles across. The flatter the flood plain, the greater is the meander turn- ing. The Koros, Figure 132, on the Plain of Hungary, has its meanders remarkably developed. Meanders are slowly changed, for the river wears away the outer bank of each curve because the current runs fastest there ; the opposite side of the channel is filled RIVERS AND VALLEYS 263 in with waste where the current is slow. The Mississippi below Cairo has in the course of ages shifted its course, now eastward, now westward, an'd has thus opened a flood plain from twenty to sixty miles wide, that is, five or six times wider than its meander belt. Similar changes may be seen on a small scale in a meadow brook. In the fine silt of a broad and flat flood plain a large river changes its course easily and rapidly; it takes material from the outer bank, where its current is strong, and deposits it farther downstream on the inner bank, where the current is weaker. The necks of the flood-plain spurs be- tween adjoining meanders are often gradually narrowed and cut through by the river, the meander around the spur being then deserted for a shorter and more direct course, called a cut-off. Where are cut-offs likely to occur in Figure 132? Large rivers, like the Mississippi, exhibit all stages of this process. An abandoned meander is occupied by nearly stagnant water, more or less completely sep- arated from the new and shorter channel by deposits of silt in the ends of its arms ; in time it becomes an oxbow lake. Fig. 132. A Meandering River on the Plain of Hungary 264 ELEMENTARY PHYSICAL GEOGRAPHY Draw an outline map to show the probable path of the Mississippi when it ran through the oxbow lakes, Figure 133. How does the channel of 1896 differ from that of 1882 ? The shifting of the channel may be checked by pro- tecting the outer bank with stone or wood, but this is expensive. Rising floods may be held back by dikes or levees built on the plain a little distance from the river banks. When the levees are overtopped or breached widespread floods may result, such as occurred on the Mississippi flood plain in April, 1897, when about 13,000 square miles of the plain (two fifths of the entire area) were under Fig. 133. Meandering Channel and Oxbow ^yater. The Value of Lakes in the Flood Phiin of the Mississippi, , according to Surveys in 1882 and 1883. The ll"^® stock and CropS position of the channel according to surveys lost in this flood was in 1895 and 1896 is shown by dotted lines. ,. , , , m.i i- nnn estimated at ^15,000,- 000 ; many thousands of people were for a time driven from their homes. In March, 1890, a strong flood in the lower Mississippi broke through the levees on the left bank, forming the RIA^ERS AND VALLEYS 265 " Nita crevasse " (a break on the Nita plantation), flood- ing the plain, carrying river silt into the shallow waters of the Gulf of Mexico, and ruining the oyster beds east of the delta. 152. Alluvial Fans of Large Rivers. — When rivers flow from mountains or plateaus and enter open lowlands, where no valley walls inclose them, they may build exten- sive alluvial fans of faint slope. The Merced river of California (see M, Figure 134) offers a good illustration of this habit. The Merced gathers much waste from its steep head- waters in the Sierra Nevada. On issuing from its narrow valley at the mountain base it is free to run in any direc- tion — forward, to the right or to the left — on the broad " valley of California," a belt of low country between the Sierra and the Coast range. Here the river, flowing first in one direction, then in another, has built a fan about forty miles in radius, of gravel near the mountains, of fine silt farther forward. As the rain of this region falls chiefly in winter, it is necess'ary to irrigate the fields for summer crops. Nothing could be better adapted to the needs of irrigation than a gently sloping alluvial fan; for the river may be easily turned into various channels at the head of the fan and led forward on different courses, and thus distributed over thousands of acres. One of the largest alluvial fans in the world is that of the Hoang-Ho, in eastern China. This great river, bear- ing a heavy load of fine silt from the basins among the 266 ELEMEJiTTARY PHYSICAL GEOGRAPHY inner mountains, issues from its inclosed valley 300 miles inland from the present shore line, and at a height of about 400 feet above sea level, and then flows to the sea down the gentle slope of its extensive fan. The great fan of the Hoang-Ho is very fertile and supports one of the densest populations on the earth ; but it is subject to overflow on a vast scale, when the river suddenly changes its course from one path to another and invades fields and villages on a new course to the sea. Overflow is prevented as far as possible by dikes; but the channel has repeatedly been changed during the many cen- turies of Chinese history. The loss of life caused by these overflows is very great. Not only are many thousands of people drowned, but the crops are de- stroyed over large districts, caus- T, .o. m, ,r ,1 . ins: famines in which many more Fig. 134. The Valley of ^ , -^ California thousands perish. 153. Broad Plains formed by Rivers. — When many rivers flow forth from mountain valleys upon a neighboring lowland their adjoining fans unite in a broad plain slop- ing gently forward from the mountain base. This may be called a river-made plain. It resembles a coastal plain in RIVERS AXD VALLEYS 267 having higher land for a background, but it does not neces- sarily front upon the sea, and it is generally but little trenched by the rivers that built it. A plain of this kind often occupies the depression between two highlands or mountain ranges. The many rivers issuing from the valleys of the Sierra Nevada and the Coast range upon the "valley of Cali- fornia" have formed an extensive plain, of which the Mer- ced fan, described above, is only a part. The successive fans are very broad and flat, so that their slightly convex form can hardly be seen. The fans from the east and west meet in a flat-floored trough, Figure 134. Fig. 135. Torrent Fan Delta, Lake Geneva, Switzerland 154. Deltas. — When a river enters a lake or the sea its current is checked. The finest part of the waste may be swept away by waves and tides ; the rest accumulates at the river mouth and builds up a new land surface, called a delta, in advance of the original shore line. The fans of mountain torrents form deltas in lakes at the mountain 268 ELEMENTARY PHYSICAL GEOGRAPHY base. Small deltas are characteristic of young rivers ; the longer the progress of river growth, the larger the delta may become. The land surface of a delta is built on the same slope as that of the river flood plain farther upstream, the delta being only the forward part of the flood plain. Under water a delta slopes at a steeper angle than above water. The great fan of the Hoang-Ho may be regarded as its delta, because it has been built forward into the Yellow sea (so named from the color given by the river waste). A river frequently splits into several channels on its delta, the outgoing branches being known as dis- tributaries. These are well exhibited in the fingerlike divisions of the Mississippi on its outer delta. Figure 136, and in the many channels of the Ganges and the Brahma- putra on their deltas at the head of the Bay of Bengal. How many distributaries are shown in Figure 136 ? Great rivers may build their deltas in the face of waves and tides. At the Mackenzie delta the tidal range is three feet, at the Niger four feet, at the Hoang-Ho eight feet, at the Ganges-Brahmaputra eighteen feet. The building of deltas by small rivers is favored by the protection from SOUTH PASS g SOUTSWEST PASS Fig. 13G. The Delta of the Mississippi RIVERS AND VALLEYS 269 waves in bay heads and by the weakness or absence of tides. Where are the above-named rivers ? The absence of deltas at the embayed mouths of certain rivers is frequently not so much because the tidal currents sweep away all the river silt, as because there has not yet been time enough to build a delta since the embayments were formed by the depression of the coastal lands. The lower valleys of the Delaware, Susquehanna, Poto- mac and neighboring rivers are drowned, forming bays in the partly submerged coastal plain of the Middle Atlantic States. Whatever deltas these rivers previously built are now beneath the sea. Very little delta growth has yet taken place at the bay heads ; hence the depression of the region is relatively recent. The deltas of large rivers consist of fine-textured waste or silt, worn during the long journey from the river head- waters and weatliered during many rests in the flood plain on the way. In a favorable climate deltas are very fertile and attract a large population. The three densest popula- tions of the world (outside of large cities) are in eastern China, northeastern India, and northern Italy, all on the lower flood plains and deltas of large rivers. « 155. Mature Rivers. — When a river and its larger branches have destroyed their lakes and falls and reduced their valleys to graded slopes, when all the side valleys join the larger valleys at grade, when the larger streams have broadened their valley floors so that they can meander freely upon flood plains in curves appropriate to their volume, and when a delta is built forward at the river 270 ELEMENTARY PHYSICAL GEOGRAPHY mouth, the river system has reached the mature or full- grown stage of its development. Mature rivers accomplish the drainage of their basins and the carrying of rock waste to the sea in the most per- fect manner. No undivided uplands remain from which a great part of the rainfall may be returned to the atmos- phere by evaporation. The largest possible share of the rainfall is shed from the well-carved surface of the land and runs off in the streams with no delay in lakes or haste in falls. No hard rock ledges remain to be worn down in the valley floors. Everywhere the waste of the land is washed down the slopes to the streams and delivered in such quantity that the streams are kept working at their full capacity to transport the waste toward the sea. The valleys of mature rivers are easily followed by roads and railroads ; they are broad enough to contain cultivated fields as well as villages and cities, as in Plate X. 156. Old Rivers. — If no disturbance occurs, a maturely developed river system passes by slow degrees into a quiet old age. The hills waste away to fainter slopes and yield less and less waste to the streams. The texture of the waste becomes finer and finer. More of the waste is car- ried in solution. The extreme old age of a river system would be char- acterized by low and ill-defined divides between faint slopes leading to broad flood plains, on which the streams would meander with great freedom. An increasing share of the transported waste would be dissolved. A large amount of rainfall might be lost by evaporation on the gentle slopes. RIVERS AND VALLEYS 271 It is unusual to find an old river system. The lower trunks of large river systems often gain very gentle slopes and free-swinging meanders, but before old age is attained by all the small side branches and the headwaters move- ments of elevation or depression generall}^ occur in the earth's crust, with more or less tilting and breaking ; and in this way the rivers are made young again and set to work at new tasks. 157. Revived Rivers. — At any stage in the erosion of a region drained by a river, the river basin may be uplifted to a greater height above sea level. Then the river will at once begin to cut its valley floor deeper than it could have done before. Such rivers may be called revived. Old rivers flowing across low worn-down mountains are rare, but revived rivers flowing through gorges in uplifted lowlands of this kind are common. The rivers and their narrow valleys in the Piedmont district of Virginia are thus explained. If a meandering river is revived, it will intrench itself beneath its former flood plain ; then its new valley will be regularly curved after the pattern of its meanders. The north branch of the Susquehanna follows a deep and winding valley of this kind through the Allegheny plateau of northern Pennsylvania. The Osage has an extremely serpentine valley in the uplands of central Mis- souri. Both these rivers seem to have learned to meander when the uplands were lowlands. Since these regions were raised the rivers have cut down valleys of a meander- ing pattern. The valleys are still narrow. The rivers are 272 ELEMENTARY PHYSICAL GEOGRAPHY enlarging their curves by cutting away the outer bank; here the river is bordered by steep bluffs. Strips of flood plain are beginning to form on the inside of the river curves where the banks are low and flat. Draw a map of the district shown in Figure 137. Describe the form and arrangement of the patches of flood plain. AMiere are the valley sides steep ? Where are their slopes gentler ? Fig. 137. Diagram of a Narrowed Spur in a Meauderiug Valley It sometimes happens that a revived meandering river, eroding its outer bank, may wear through the neck of the naiTowest upland spurs that enter its trenched course ; it will then desert a round- about course for a more direct one, Figures 137, 138. Rapids will occur for a time at the cut-off. Draw two maps of the dis- trict shown in Figure 138, one showing the path of the river Fig. ir>8. just before the cut-off was made, one just afterwards. Compare the first of these maps with the one drawn from Figure 137. Diagram of Cut-Olf Spur in a Meandering Valley The village of Lauffen (Rapids) on the river Neckar in southern Germany gains water power from rajiids formed at a recent cutroff. The former course of the river is seen in a meadow beautifully curved around an isolated hill, RIVERS AND VALLEYS the cut-off end of an upland spur, Figure 139. cut-off spur is seen near the village of Hofen. 273 Another 158. Water Gaps. — Many rivers cross the hard-rock ridges of the Allegheny- mountains of Pennsyl- vania in sharp notches, called water gaps. For example, the Delaware river gathers many branches from the open valleys of northeastern Pennsylvania and es- capes by a deep, narrow notch, called the Dela- ware Avater gap, in Kitta- tinny mountain, at the northwestern corner of New Jersey. Such cases are ex- plained as follows. Once the whole region stood lower than noAV and a lowland spread far and wide at about the level of what are the ridge crests to-day. With the elevation of the region all the revived rivers begin to wear down their valleys. Where a trunk river cuts down its new valley across the belt of hard rock that is to make the mountain ridge, the valley remains narrow for a very long time ; but elsewhere the valleys of the trunk and Fig. 139. Intrenched Meanders of the Neckar 274 elp:mentary physical geography Fig. 140. Transverse and Longitudinal Streams branch streams widen rapidly in the weaker rocks, and in time all the hills of the weak- rock belts are worn away, leaving a low- land on each side of the hard-rock ridge, through which the water gap has been cut, as in Figure 141. This explanation applies to the Susque- hanna, cutting gaps in the Allegheny ridges, Figure 142, and to the stream that has cut a deep passage in one of the Alle- gheny ridges in Maryland, shown in Plate IX. Fig. 141. TransTerse and Longitudinal Valleys Fig. 142. Water Gap of the Susquehanna above Harrisburg, Peunsylvania Where must one stand in Figure lil to gain a view like that of Figure 142? How many water gaps are shown in Figure 103? RIVERS AND VALLEYS 275 QUESTIONS Sec. 134. How is the rainfall of a region disposed of ? What is ground water ? Under what conditions will much of the rainfall be evaporated into the air? discharged by streams? absorbed by the ground ? What is the run-oif ? Of what value is gi-ound water ? 135. How are caverns generally formed? What is a sink hole? What effect have sink holes on surface streams ? Describe an under- ground stream. Describe the animals of caverns. What is the origin of the Natural bridge of Virginia? 136. What is a spring? Upon what does the variation of stream volume depend? Under what conditions is the variation small? Describe the movement of ground water. Where is it found at a small depth ? To what depth should wells be dug or bored ? Why is spring water purer than stream water ? 137. What is an Artesian well ? How is its water supplied ? Name some districts where such wells are common. What is the relation of certain Artesian wells in eastern jNfaryland to Chesapeake bay? 138. Explain hot springs. Why are they commonly charged with mineral salts ? Of what value are they ? Name some examples. 139. 140. What is a geyser? Where are the most famous gey- sers ? Describe and explain the action of geysers ; of mud volcanoes. 141. Define river, river system, river basin, divide, channel, bed, banks. What is meant by a continental divide? by undivided drainage? by subdivides? What features of a river system have you seen illustrated in a small way? 142. Describe a river flood. Where is the river-borne waste laid down ? How is a river supplied after a flood subsides ? How does a drought affect ground water? springs? streams? Compare the streams of the rainy and of the drier parts of the United States. 143. GiA'e some examples of the work of rivers from earlier chap- ters. Upon what does the depth to which a valley may be cut depend? How do slope and volume affect the velocity of a stream and its load of sediment ? Why does a river carry more sediment at 276 ELEMENTARY PHYSICAL GEOGRAPHY time of flood ? How is erosion performed by rivers ? What is the source of tlie rock waste borue by rivers V In what sense is it said that "rivers erode their valleys"? Under what conditions may a river be called young? old? mature? 144. How is the course of a young river determined? What work is done by young rivers ? What are the characteristics of young rivers? Describe the St. Lawrence system; the drainage of the Laurentian highlands ; that of the region of the great African lakes. What changes occur as a river passes from youth to maturity ? 145. How are lakes converted into rivers? Illustrate by Lake Geneva. In what part of the life of a river system are lakes most common ? How do lakes affect the transparency and the steadiness of flow of their outflowing streams? Compare the Ohio and the St. Lawrence as to floods. 146. Where are falls and rapids formed in young rivers ? How are gorges formed ? Illustrate by the gorge of the Niagara ; by the Yel- lowstone canyon. How do differences in rock structure determine the 'occurrence of falls or rapids ? What uses are made of waterfalls ? 147. Describe a torrent. What determines the least slope to which a river can wear down its course ? Describe a graded river. Where have gi'aded streams a relatively strong slope? Why? Where have they a very faint slope ? Why ? State the slope and the load of the lower Mississippi. 148. Where are graded reaches first developed in a river ? "Where do rapids siu'vive longest? What is a local baselevel? In what condition are the rivers of New England? What other region has similar rivers? Describe a river that has long been undisturbed. Describe the stream slopes in a well-graded river system. How do its branches join its trunk? AVhy are they thus related? 149. Describe the valley -of a young river. What disadvantages does it present to occupation? How do floods act in such valleys? Illustrate from the Allegheny plateau. How is a valley floor wid- ened ? What changes do the valley sides suffer ? What advantages are presented by a widened vaUey ? RIVERS AXD VALLEYS -277 150. Describe the action of a winding stream. Describe its val- ley when grade is reached. What changes occur after grade is reached ? Compare the outer and inner sides of river curves. Where and in what pattern is the flood plain first developed ? Describe the later changes in the valley spurs ; in the flood plain. Where is the most silt laid down during a flood ? How does this affect the form of a flood plain ? How does a heavy load of waste affect the behavior of a river ? Give an example. 151. How does a light load affect the course of a river and the slope of its flood plain ? What are meanders ? What is the deriva- tion of this term? On what does the size of meanders depend? How does their form vary ? How has the cou.rse of the Mississippi changed? How have these changes affected its flood plain? What is an oxbow lake ? Describe an example. How is the shifting of a river channel checked ? How are flooded rivers restrained ? Describe the effects of the Mississippi flood of 1897. Describe the Nita crevasse. 152. 153. Describe the fan of the Merced river. Why is irriga- tion needed here? How -is it favored? Describe the fan of the Hoang-Ho, and its relation to the people of China. Describe a river- made plain. Give an illustration from California. . 154. How are deltas formed ? W^hat is the relation of a delta to a flood plain ? What are distributaries ? Describe some examples. What is the relation of deltas to tides ? Give examples. Why are deltas wanting at certain river mouths ? Give examples. What is the relation of large deltas to population ? 155, 156. What are the features of mature rivers ? Describe the work of mature rivers ; the change from a mature to an old river ; an old river system.^ Why is it unusual to find old rivers? 157. What is a revived river ? Describe the rivers of the Pied- mont belt in Virginia. Describe the valley of a revived meandering river. Give two examples. What changes may happen in such valleys? Illustrate by the Neckar. 158. What is a water gap ? Give an example. Explain it. What is the origin of the lowland upstream from a water gap ? CHAPTER IX DESERTS AND GLACIERS 159. Land Forms dependent on Climate. — In regions of ordinary climate the snow of winter melts in the spring, and the droughts of summer are not severe enough to make the surface barren by preventing plant growth. The form of such regions is determined largely by the action of streams and rivers, whose work goes on steadily along branches and trunk so that, in the course of ages, the land surface is dissected and a mature system of branch- ing valleys is carved. Many examples of regions of this kind have been giv-en in the descriptions of plains and plateaus, momitains and volcanoes. An excellent illustration of a well-dissected upland is found in the Ozark plateau of southern Missouri. The once even plateau has been transformed into a succession of rounded hills and spurs of graceful form, separated by a multitude of branching valleys. The maturely dissected sur- face has much less strength of relief than the plateau of West Virginia ; its slopes are usually of moderate steepness ; it is a fertile agricultural district. Villages are generally on the uplands, for most of the valleys are as yet too narrow to attract settlement. Many other examples might be named in which well-established branching valley systems testify to the long duration of an ordinary or normal climate. 278 DESERTS AND GLACIERS 279 In certain other parts of the world the clhnate is so dry that vegetation is scanty or wanting, and the surface is left barren and desolate. Here streams flow only at rare inter- vals, the rivers frequently fail to reach the ocean, and the wind becomes an important means of moving land waste. In still other parts of the world the mean annual tem- perature is so low that the snowfall is not all melted away Fig. 143. The Ozark Plateau, Missouri in the warm season. The snow thus gathers from year to year, and, as it thickens, the under part is slowly com- pacted into ice. The ice has become thick enough to behave like a viscous body and to creep slowly down the slope of the land until it enters a warmer climate, where it melts away. Such moving sheets or streams of ice are called glaciers. Regions thus covered with ice and snow are even more barren than arid deserts. The removal of rock waste is there chiefly performed by ice instead of by rain and rivers. 280 ELEMENTARY PHYSICAL GEOGRAPHY 160. Deserts. — It has been explained in the paragraphs on rainfall that the arid deserts of the world occur under the drying trade winds, on the slopes and lowlands to the leeward of high mountain ranges, or in inclosed continental interiors. (See page 71.) The interior basins of Nevada and Utah, inclosed from moist winds by the ranges of the Pacific slope, fall under the third class, although they are less arid than many parts of the Sahara. All of these deserts are hot in summer, but they may be cool or cold in winter. They should therefore be thought of as prevailingly dry regions which may be hot or cold according to the season of the year. The deserts of cen- tral Asia have a mean January temperature of only 10° or 20° F. Rain seldom falls, and the dry air parches the dusty, sandy, or stony ground, so that plant life in deserts is scanty, though it is rarely altogether absent. Rock waste is plentifully exposed on open spaces between the scat- tered desert plants, instead of being covered by a close growth of grass, bushes, or trees, as in regions of more favorable climate. Deserts are of all forms, — mountains, j)lateaus, and plains ; but desert plains are the most extensive. The desolate gray forms of desert mountains, like the ranges of northwest Mexico (Sonora) and of northern Chile (Atacama), are much less picturesque than mountains with snowy summits and forested flanks in a moister climate ; but the wet-weather torrents of desert moun- tains have furrowed them with deep ravines like those of forested mountains. desp:rts axd glaciers 281 161. Streams of Dry Climates. — When a light rain occurs in a region of dry climate much of the water returns to the atmosphere by evaporation, a large part of the remamder sinks into the thirsty soil, and the run-off by streams is small. Much of the ground water evaporates underground and passes out from the soil as vapor, instead of coming out in springs. When a heavy rain occurs, as occasionally happens, water is supplied faster than it can soak into the ground, surface rills form everywhere, and the streams are quickly flooded; but the floods soon run away, leaving the channels empty and dry again. The streams of dry regions are, therefore, very variable in volume ; active for a while after a rain, almost or quite disappearing in the long dry seasons ; advancing far down their lower courses when in flood, then dwindling and withering away and leaving their lower channels dry. In the Sahara dry water courses, known as wadies, are commonly used for roads, as their gorges frequently offer graded ways through rocky uplands. Death by drown- ing would nowhere be so little expected as in a desert; but it sometimes happens that a caravan, following a wady through an upland, meets a down-rushing flood, and before the travelers can climb the steep walls of the gorge they may be overwhelmed and drowned. In parts of the Rocky mountain region, of generally dry climate, heavy rains occasionally fall in summer. Then for a few hours the dry channels are flooded with a rushing turbid stream, which sweeps away the waste that has been washed in by lighter rains. Camping parties, pitching their tents too near a channel that is almost 282 ELEMENTARY PHYSICAL GEOGRAPHY dry in the afternoon, may be overwhelmed by a rushing flood at night. Opposite the mouths of canyons, streams of coarse waste, including bowlders weighing many tons, are spread forward by floods from cloud-bursts in the moun- tains,; — "immense, sudden, deluging rainstorms, which at rare and exceptional moments discharge their waters into Fig. 145. Flood in Cherry Creek, Denver, Colorado one of these mountain gorges. On such occasions bowlders six or eight feet in diameter are swept down the canyon in a fearful rush, and are sometimes carried out on the . . . slope for half a mile." Figure 145 illustrates a sudden flood in Cherry creek, where it passes through the city of Denver, Colorado. The channel of the creek was dry half an hour before this raging torrent appeared. DESERTS AND GLACIERS 283 Streams that are supplied by springs in arid uplands and mountains frequently diminish in volume, partly by evaporation, partly by sinking into the ground, as they advance over desert lowlands. They may wither away and disappear entirely from the surface ; but their flow is usually continued as ground water for some distance beyond their visible end. Their load of waste is spread on the surface before them in the form of an alluvial fan. Many such streams are known around the mountains of Utah and Nevada. The depressions between the ranges are floored with fans and plains of waste that has been washed from the mountain ravines in time of flood. 162. Bad Lands. — Arid regions of weak, fine-textured strata are often minutely carved by the wet-weather rills and rivulets bordering their chief valleys. This would not happen in a moister climate, for there the abundant plant growth would protect the surface and prevent the active run-off of the wet-weather rills ; but in an arid region, where plants are few or wanting, every little wet-weather rill erodes its own little ravine in the barren surface. Western Nebraska offers many examples of uplands that have been elaborately dissected in this way. Plate XII exhibits the delicately carved sides of a young valley in an even upland. Sharply carved forms of this kind are known as lad lands because of the difficulty of crossing them. 163. Interior Basins and Salt Lakes. — The larger rivers of interior regions do not entirely wither away in their chan- nels, but continue until they reach a depression or basin be- tween the uplands. There the waters spread out, forming a 284 ELEMENTARY PHYSICAL GEOGRAPHY lake. Evaporation from -the lake surface discharges as much water into the air as is received from the inflowing streams. In regions of more abundant rainfall the streams from a moderate drainage area suffice to fill lake basins to over- flowing. The Great lakes of the St. Lawrence system gather their water from a comparatively small area around each basin, yet they are always full, up to the outlet notch in their rim. In desert regions rainfall is so scanty and evaporation is so active that the streams from a large drainage area may form only a shallow lake, occupying a small fraction of its drainage area. Lakes of the latter kind are usually salt, for all the saline substances gathered in small quantity by their rivers accu- mulate in the lake and may in time constitute a fifth or even a third, by weight, of the lake contents. Great Salt lake of Utah, with about eighteen per cent of salt, is of this kind. It lies on the lowest part of the waste plain that has been built up in the depression among several mountain ranges. Its waters are so dense that a man's body will not sink beneath the surface. The Dead sea, with twenty-four per cent of salt, is one of the most famous salt lakes, occupying a long narrow depression in Palestine. Lake Van, in eastern Turkey, containing thirty- three per cent of salt, is the densest water body known. Interior basins, from which no rivers escape to the sea, receive the waste that the slopes of the inclosing moun- tains lose. The floors of the basins are in this way built up and smoothed. By the wearing down of the moun- tains and the filling of the basins the relief of the region as a whole is decreased. (See Figure 144.) DESERTS AND GLACIERS 285 The level of the Dead sea is almost 1300 feet below that of the Mediterranean, and the bottom of the trough occupied by this sea is about 1300 feet deeper still. Ravines in the border of the uplifted plateaus lead down to stony fans that are advancing into the sea. The great depth of the water and the moderate exten- sion of the fans show that the basin contains much less waste now than it will in the future. A great part of Persia consists of large basins inclosed by mountains and wdthout outlet to the sea. Long waste slopes stretch forward five or ten miles wdth a descent of 1000 or 2000 feet, stony near the mountain flanks, and gradually becoming finer textured and more neai'ly level farther away. The central depressions are deserts of drifting sands, with occasional salt lakes. The popu- lation gathers around the margins of the basins where the dwindling streams are still running, avoiding the rugged and barren mountains on the one hand, and the unin- habitable central plains on the other. Central Asia repeats the same conditions on a still larger scale. The basin of Eastern Turkestan includes in its central part many low ranges that have been half buried with Avaste from the higher inclosing mountains. Many rivers flowing from the mountain rim wither on their way toward the chief central depression ; only the largest river (Tarim) reaches it, there spreading out in the marshy Lake Lob. The chief settlements are near the border of the basin, where the larger rivers come out from the mountains and where their waters can be used for irrisration. 286 ELEMENTARY PHYSICAL GEOGRAPHY 164. Wind Action in Deserts. — Where the land surface is covered with vegetation, the wind has little effect on the form of the ground. In arid regions where vegetation is scanty or wanting the wind becomes a powerful agent of change. The difference of wind action on a dusty road and on a grassy field may be taken to illustrate the con- trast between wind action in regions of dry and of wet climate. Wind storms in deserts raise the finest dust high into the air, drift along the sand at the bottom of the current, and rasp the unmoved stones and ledges with the drifted sand. Even in calm weather whirlv/inds are of daily occur- rence in deserts during the hot season. They are formed by the whirling ascent of air that has been heated by the action of sunshine on the dry bare ground. Before the whirl begins the existence of the overheated layer of sur- face air is often indicated by a mirage. Whirlwinds may raise dust more than a thousand feet into the air and drift it long distances before it settles. When violent winds blow, like the squalls which often precede thunderstorms in a moister climate, heavy clouds of sand and dust are raised from the desert surface, dark- ening the sky, and almost suffocating the traveler over- taken by them. Vessels in the Atlantic west of the Sahara sometimes have their sails reddened with dust brought by the trade wind from the Sahara. Rain in southern Europe is occa- sionally reddened with dust brought by storm winds from the same source. It has been estimated that, during four DESERTS AND GLACIERS 287 days of such winds in March, 1901, nearly 2,000,000 tons of dust from the Sahara fell on central Europe ; the greater part reached the ground south of the Alps, but some of the dust was observed as far north as the Baltic sea. East of the deserts of central Asia extensive deposits of wind-borne dust have been formed; they constitute some of the most fertile districts in the Chinese empire. Desert mountains and uplands are so well exposed to strong winds that the finer particles of rock waste are Fig. 146. Sand Dunes in the Sahara blown from them, leaving their surface rocky and ston)\ The finer particles settle chiefly in the depressions where the winds are less violent; here the surface is sandy or dusty. 165. Sand Dunes. — When the rocks of a desert are of a kind, like granite, that affords sand on weathering, the wind may blow the sand grains into drifts or dunes. Dunes sometimes grow to a height of from 500 to 600 feet. Their surface may be delicately rippled, as in Plate XIII. In a region of relatively steady winds the sand is blown up the windward slope and carried over the crest; hence the dune may slowly advance, gradually 288 ELEMENTARY PHYSICAL GEOGRAPHY changing its place and form. Dunes of drifting sand are usually more barren than other parts of a desert. A group of dunes sometimes advances across a dry val- ley, concealing its form for several miles. When rain falls the stream from the upper part of the valley disappears as it enters the loose sand of the dunes. Sand dunes occur also on low coasts where the winds frequently blow landward across a sandy beach. The dunes then form a belt of hills a little inland from the beach, as will be again referred to under shore forms. 166. Dry Regions, formerly Moist. — • In some regions now arid, marks of a former moist climate are found. Certain basins now almost without water have been filled with great lakes, even to overflowing; the former shore lines of the lakes are marked by clift's, beaches, and deltas, and an outlet is sometimes traceable in a trench across the lowest pass in the inclosing highlands. The basin of Great Salt lake in northwestern Utah in prehistoric times contained a much larger lake, to which the name of an explorer, Bonneville, has been given. Its shore lines are still plainly recorded on the mountain sides nearly 1000 feet above the desert plain ai-ound the present lake ; the foreground of Figure 86 shows an extensive beach of this lake. The channel of an outlet leads northward across a pass to the basin of Snake river ; hence the former lake must have been fresh. The change from the moister climate of Lake Bonneville time to the drier climate of to-day has caused the almost complete disappearance of the lake waters, revealing the sediments of the lake floor in DESERTS AND GLACIERS 289 an arid plain. The ancient lake deltas are now trenched by the streams that built tliem. Another extensive lake (Lahontan) of very irregular outline and several smaller lakes once occupied the now desert basins of western Nevada. m -^ Fig. 147. Lakes Bonneville and Lahontan Compare the area of Lake Bonneville and that of Great Salt lake (fine and coarse dots, Figure 147). How long is Lake Bonneville from north to south? How long is Great Salt lake from northwest to southeast? (Scale of figure, 200 miles to an inch.) The causes of climatic changes of this kind are little understood, but their geograpliical consequences are of great importance. Extensive lakes among forest-clad slopes have been replaced by desert plains between arid mountains. 290 ELEMENTARY PHYSICAL GEOGRAPHY 167. Salinas. — Certain basins that formerly contained salt lakes have now been more or less completely dried out, leaving marshy or dry plains of salt, known as salinas, in the central depressions, avoided by all plant and animal hfe. The Bolivian table-land, a lofty waste-filled basin lying between two great ranges of the Andes, holds Lake Titi- caca in its northern part at an altitude of 12,500 feet. The outflowing stream runs 100 miles southeast to a marshy sahna, fifty miles long. The water not evaporated here flows southwest and is lost in a broad salina of daz- zling white surface. Somewhat farther south is a more extensive salina, 4000 square miles in area, a white and level plain covered with a layer of salt about four feet thick, impassable when wet, but firm in the dry season. Salt lakes and salinas yield common salt and other min- erals of commercial value. Great Salt lake is estimated to contain 400,000,000 tons of salt. These products would be of greater utility if they did not so generally occur in thinly populated desert regions. 168. Ice Sheets and Ice Streams. — In the polar regions the temperature even in the lower atmosphere is so low that snow and ice cover much of the land all the year round, even close to sea level, cloaking the ground with ice sheets. In the temperate and torrid zones it is only on mountains that the temperature is low enough for snow to be more abundant than rain, so that snow fields are formed on the higher slopes and ice streams in the upper valleys. DESERTS AND GLACIERS 291 During winter in the northern United States there are frequent examples of the formation of small short-lived ice sheets, after a succession of snowstorms with prevalent cold weather and occasional thaws. Such an ice sheet is not thick enough to move ; but if it should grow year after year to a thickness of 1000 or more feet, it would slowly move outward from the region of greatest height and thickness to lower ground in a milder climate. This is because ice is not perfectly solid ; it moves toward its unsupported border very much as a thick mass of paste would move, but much more slowly. 169. Antarctic Ice Cap. — A few explorers of the far southern ocean have discovered a great ice sheet ending in cliffs that rise from 100 to 180 feet above the sea. No land was seen back from the top of the cliffs. Although as yet known only on one side of the south pole, the ice sheet is thought to form a polar ice cap, per- haps 1000 miles in diameter. There may be some land on which the cap rests ; but it is believed that much of it lies on the sea bottom. It must tend to thicken from snow supply over its desert plateaulike center ; but it slowly creeps toward the free seaward margin, where great tables of ice break off and float away as icebergs. As far as this desolate region has been explored it is uninhabited. 170. The Greenland Ice Sheet. — Greenland is covered by a heavy sheet of ice, measuring about 1500 miles north and south and from 300 to 600 east and west. It has a slightly convex surface and probably rises to a height of 9000 feet in the central part. The ice sheet 3onceals 292 ELEMENTARY PHYSICAL GEOGRAPHY the hills and mountains except near the margin, where the sheet is thinner ; here occasional rocky summits rise above the surface like islands in a frozen sea. Some of the Greenland glaciers (arms of the ice sheet descending toward or into the sea) are from ten to fifty miles broad. Their forward movement is from twenty to fifty feet a day. Many icebergs are formed of great fragments broken from their front. The interior of the ice sheet is a monotonous desert of snow and ice, now melting and becoming almost impassable, now freezing over or receiving a new layer of snow. The only inhabitants of this great cold desert are a minute worm and a simple microscopic plant that some- times gives a red color to snow. The Eskimos of Green- land live on the narrow belt of land between the ice sheet and the shore. j 171. Alpine Glaciers. — Glaciers of the Alpine type flow ' slowly down in streamlike tongues from snow basins in the valley heads between lofty peaks and ridges. j The end of a glacier, melting as the ice descends to a ' milder climate than that of its gathering ground, often reaches below the tree line. Glaciers of this kind occur in the Alps, the Caucasus and Himalaya mountains of the Old World, and in the mountains of Canada, Alaska, and Patagonia in the New World. In Alaska many of the glaciers descend to the sea. The front of the Muir glacier, Plate XIV, breaks off in cliffs 200 feet high. A glacier moves faster along the middle surface line than at its sides or bottom, thus resembling a river. The DESERTS AND GLACIERS 293 movement of Alpine glaciers is on the average from 100 to 600 feet a year. Glaciers press heavily on their beds, dragging rock waste beneath them and scouring the bed-rock clean and smooth. Loose grains and fragments of rock, dragged along by the ice, scratch and groove the smoothed rock surface. The rock waste thus scoured from the ice floor, as well as that torn from projecting ledges and that received - in rock slides and ava- lanches from sur- mounting slopes, is dragged or car- ried along by the ice and laid down around its lower margin or at its end, or washed away by the stream that issues from beneath the ice. Great bowlders may be carried on the ice. The ridge of rock waste that is ordinarily formed around the end of a glacier is called a terminal moraine ; one is shown in Figure 148. Note the moraine that trails down on the Rosegg glacier from a rocky spur between two of its upper snow basins. It is called a medial moraine. Why does it not follow the middle of the glacier? Fig. 148. Rosegg Glacier in the Alps 294 ELEMENTARY PHYSICAL GEOGRAPHY Describe the medial moraine of the Viesch (pron. feesK) gla- cier, Figure 149. From^ how many snow basins is this glacier supplied ? Large glaciers are sometimes so heavily covered with moraines near their lower end that a plant-bearing soil is formed upon them. Pas- turage is found for the flocks of the mountaineers in the Himalayas on cer- tain grass-covered mo- raines overlying the ice. Some Alaskan glaciers bear large forests on the moraines near their ends. Water received from side streams and supplied from melting ice gathers beneath a glacier and issues from an ice cave at its end. The water is usually whitened by fine Fig. 149. Viesch Glacier in tlie Alps "rock flour" beneath the ice. ^round 172. The Work of Ancient Glaciers and Ice Sheets. — Cer- tain parts of the world show the marks of ancient glacial action, although the climate there to-day does not allow snow to remain on the ground through the summer. Ancient glaciers occupied certain valleys in the Rocky mountains of Colorado and in the Sierra Nevada of Califor- nia. Great glaciers descending from the high Sierra into the DESERTS AND GLACIERS 295 desert lowland in eastern California built strong moraines forward from the mountain base at the mouth of the valley. Compare the glacier that once occupied the valley in Figure loO with the Rosegg glacier, Figure 148. Around the border of the Alps the lower land near the out- let of the chief valleys is often inclosed for ten or twenty miles from the mountains by a belt of hilly morainic ridges. The ancient glaciers that descended southeast from Mt, Blanc to the river- made plain of the Po built a huge terminal moraine, whose ridges rise from 1000 to 1500 feet above the plain and inclose a great amphi- theater. The most ex- tensive ice sheets of the glacial period were those that spread outward from the highlands of Canada across the basins of the Great lakes upon the northern part of the United States, and from the highlands of Scandinavia across the Baltic upon northern Germany. (See Figure 144.) The highlands of eastern Canada, — the Laurentian high- lands, — whence the ice sheets moved out to the surround- ing regions, show much bare rock, clean scoured or covered Fig. 150. Glacial Moraines, Sierra Nevada, California 296 ELEMENTARY PHYSICAL GEOGRAPHY by a thin, stony, infertile soil. The hollows between the rounded rocky hills were often deepened by the ice, so that they now hold lakes or swamps, large and small. Besides many such lakes in rock basins, others are held behind barriers of rock waste or drift that was left irregularly over the surface when the ice melted away. Fig. 151. Glaciated Area of the Northern United States /' Much of the rock waste that has been swept from Canada by ice action is now found spread out in smooth plains, forming the fertile prairies south of the Great lakes. Rock waste that has thus been dragged along by ice action or washed along under or in front of the ice by streams is known by the general name of glacial drift. The Scandinavian highlands and the lowlands of north- ern Germany exhibit the same relation to ancient glaciation that has just been described for the Laurentian highlands of Canada and the states bordering the Great lakes. The highlands are left with scanty soil and much bare rock; DEtSERTS AND GLACIERS 297 the lowlands are sheeted over with drift, much of which is fertile farming country. The highlands remain in great part a wilderness, although scattered farms and small villages are found in the valleys. The lowland plain has a large agricultural population and many busy cities. X Among the most characteristic results of ancient glacial action are the rounded shapes of scoured ledges, Figure 152, and the irregular surface of the moraines, Figure 153. Fig. 152. Ice-Worn Rocks, Coast of Maine Terminal moraines of stones, gravel, and sand are strongly developed in the states south of the Great lakes. They form belts of hills commonly from three to ten miles wide ; the hills are from fifty to two hundred feet high. The moraines are sometimes very uneven, with so many stony mounds and marshy hollows as to present a formidable barrier to travel. One may easily lose his way on such an undulating surface, where the hills are all much alike and where no conspicuous land- marks serve as guides. 298 ELEMENTARY PHYSICAL GEOGRAPHY Morainic hills are frequently dotted over with large rocks or bowlders, large and small, brought from some Fig. 153. Glacial Moraines, North Dakota more or less distant ledges by the ice; the bowlders are frequently unlike the rock on which the moraine lies. Fig. 154. A Glacial Bowlder Glacial bowlders are so plentiful in some parts of New England as to make the land there almost worthless. DESERTS AND GLACIERS 299 173. Drumlins. — In some districts the rock waste has been gathered beneath the ice sheet in arched, oval hills called drumlins, commonly half a mile or more long and from 100 to 200 feet high, easily recognized when once known. They may be compared to sand bars in rivers or to sand dunes under the wind. Fig. 155. A Drumlin, Massachusetts 174. Valleys, Lakes, and Waterfalls in Regions of Ancient Glaciers. — Some of the ancient glaciers of mountain regions were very massive, from 2000 to 5000 feet thick, and moved with relative rapidity down channels of rapid descent ; here glacial erosion was most intense. The channels thus occu- pied are now seen as broad troughlike valleys with steep walls, deepened from 500 to 1000 feet or more beneath the side valleys that once joined them at even grade. The streams from the side valleys plunge down the rocky walls of the deepened main valley, forming fine waterfalls. Dis- cordant side valleys of this kind are called hanging valleys. Many hanging valleys are found in the Alps and in the mountains of Norway and Alaska; in the latter regions 300 ELEMENTARY PHYSICAL GEOGRAPHY the deepened main valley is usually occupied b}- an arm of the sea, called a fiord. (See page 320.) ^ The rivers of a region that has been overridden by an ice sheet are often greatly disordered. At one place a Fig. 156. A Side Valley hanging over the Valley of the Ticiuo, Southern Alps valley floor may be scoured out, producing a rock basin. Lakes occupying such basins have been mentioned as com- mon in the rocky highlands of eastern Canada. At another place the irregular distribution of rock waste or drift may DESKRTS AXL> GLACIERS 301 turn a stream to a new course, where it is now seen cut- ting a steep-walled gorge with many rapids and falls. A lake is often formed upstream from the drift barrier. x The Adirondacks resemble the Black mountains of North Carolina in being dissected, subdued mountains, but the northern group possesses numerous lakes and gorges Fig. 157. Lake iu the Adirondacks, New York (" chasms ") wliich are wanting in the southern group. These peculiarities result from glacial action, which the Adiron- dacks suffered in common Avith the other northern parts of the country, but which the southern mountains escaped. When a river is displaced by barriers of glacial drift it must carve a new channel. Before the time of the ice action the river may have had a well-graded course ; now its flow is interrupted by falls and rocky rapids. Hence the displaced streams of glaciated regions supply much water power for mills and factories. 302 ELEMENTARY PHYSICAL GEOGRAPHY Many rapids and falls of this kind occur in the streams of the northern United States and Canada. It must be con- cluded that the streams have not yet had time to establish graded courses since the ice melted away, and therefore that the ice sheet covered the country not long ago, as streams measure time, even though it was thousands of years ago, as time is counted by man. The Merrimac is a famous river of this kind. Its falls at Manchester, Lowell, and Lawrence have determined the growth of great manufacturing cities. Rochester, Grand Rapids, Minneapolis, and many other important cities have grown up at the side of falls on rivers that have been turned from their former channels by glacial drift. QUESTIONS Sec. 159. What is meant by an ordinary climate ? How are land forms carved in regions of ordinary climate ? What are the condi- tions of a land surface in an arid climate ? in a cold climate ? 160. How are arid deserts related to the wind system ? Consider their climate as to heat, cold, and dryness. Describe their surface as to vegetation and rock waste. What are the forms of deserts? 161. How is rainfall disposed of in a dry climate ? Describe the streams of dry regions. What is a wady? What danger attends the use of a wady as a roadway ? Describe the floods of the di-ier parts of the Rocky mountain region. Describe a flood at Denver. How may streams end in desert lowlands? What becomes of their load of waste ? Where is their flow continued ? 162. 163. Under what conditions are bad lands formed? Describe their form. Where do they occur ? What becomes of the larger rivers of interior basins? What is the i-elation of inflow and evaporation in lakes without outlets ? in lakes with outlets ? Com- pare the lake area with the drainage area in the two cases. Why DESERTS AND GLACIERS 303 are lakes without outlets usually salt ? Describe Great Salt lake ; the Dead sea. How is the form of interior basins changed ? Describe the basin of the Dead sea ; the basins of Persia ; of central Asia. 164, 165. Compare wind action on plant-covered and on barren surfaces. Describe the action of whirlwinds in arid regions ; of violent winds. How far is dust carried by the wind? "Where do deposits of wind-borne dust occur ? Describe sand dunes as to origin, height, form, movement. Describe the dunes of coasts. 166, 167. Describe the ancient shore lines of the Great Salt lake basin. AVhat do they prove ? Describe another similar example in Nevada. How do the two differ? What is the present condition of these two basins? What are salinas? Describe an example. 168, 169, 170. Where do ice sheets occur? When may a short- lived ice sheet be seen ? Describe the movement of an ice sheet. What is known and what is supposed about the Antarctic ice cap? Describe the Greenland ice sheet. How are glaciers and icebergs related to this ice sheet ? Where do the Eskimos of Greenland live ? 171. Describe a glacier of the Alpine type. Where do such glaciers occur ? How does a glacier move ? AMiat work does it perform? Describe a terminal moraine ; a medial moraine. State the relation of vegetation to certain moraines. 172, 173. How has the occurrence of ancient glaciers been discov- ered? Where have such glaciers existed? AVhat remains have they left? Where did the most extensive ancient ice sheets occur? What effect was produced by the North American ice sheet in eastern Can- ada? in the northeastern United States? What is glacial drift? Describe the effects of the ancient ice sheet of northwestern Europe. Describe the terminal moraines south of the Great lakes. What are glacial bowlders ? Where are they plentiful ? What are drumlins ? 174. What are hanging valleys? Explain them. Where do they occur? What effect have ancient ice sheets had on drainage? Describe the drainage of the Laurentian highlands. Compare the Adirondacks and the Black mountains. • What effect have displaced streams on industries ? Name some examples. CHAPTER X SHORE LINES 175. The Border of the Lands — Next to the prospect gained from a lofty mountain, the view of the sea from the border of a highland is the most inspiring sight that the earth offers. To the traveler from an inland country it is as if the shore line marked the beginning of a new kind of world. There is the mystery of the distant horizon, far beyond which strange lands are hid- den. There is the unceasing movement of the waves as they roll upon the beach, and of the tides as they slowly rise and fall; and the thought comes that thus the ocean has been rolling in waves, rising and falling in tides, ever since the lands and the waters were divided. With the sight of the vast ocean comes the thought of unend- ing time. While the surface of the land has been for ages attacked by rain and rivers, the border of the land lias been attacked by the sea. The sun warms the air in the torrid zone, and thus the general circulation of the atmosphere is established. The winds beat on the ocean and form waves, and the waves run ashore and dash in surf upon the lands. The border of the land is worn back under so constant an attack, and the waste taken from it by the surf, as well as that washed into the sea 304 SHORE LINES 305 by livers, is slowly carried away into deeper water by the waves, the currents, and the tides. In time the area of the land would be greatly reduced by the invasion of the sea, were it not for upheavals of the earth's crust by which the land is now and then, here and there, renewed. / ?;._ i 1 RH ^B^^ISk'^w' ' H H mm B ^^^^^ m ^^^ Fig. 158. Sea Cliffs, Grand Manan, New Brunswick 176. The Work of the Sea on the Shore. — Where the border or coast of the land dips under the sea the water lies against it and marks the shore line. The waves and other agents work upon the shore and produce changes in its form. Hence the outline of any shore line depends, in the first place, on the form that the land had when its present attitude with respect to the sea was taken, and in the second place on the changes afterward made by the shore processes. 306 ELEMENTARY PHYSICAL GEOGRAPHY The agitation of sea water in waves is greatest at the sea surface and gradually decreases downward; but the large waves cause some slight disturbance even at depths of several hundred feet. The movement of water iu waves is not steadily forward in the direction in which the waves travel, but repeatedly 'to and fro over small distances. The larger the waves and the shallower the water, the greater effect their agitation has on the bottom. Fragments of rock, large and small, are thus moved back and forth according to their size and to the strength of the waves. The fragments wear each other as well as the rocky ledges on which they are rolled and thrown. Thus the edge of the land is worn back by the sea, the shallower parts of the sea are slowly deepened, and the waste is slowly removed to deeper water offshore. Little work of this kind is done in calm or fair weather; but during storms the processes of grinding and transporta- tion are actively at work, shaping the shore line and the shallow sea bottom. The currents of shore waters are chiefly of tidal origin, but they are also sometimes parts of the general circulation of the ocean. Except in narrow channels, they are seldom strong enough, unaided, to move the waste that is strewn over the bottom ; but when the waste is jostled by waves it slowly shifts along in the direction of the current. If deep water reaches close to the land, the waves spend most of their strength close to the shore line, breaking vio- lently on the headlands, whence they sweep loose material out to the deeper bottom ; there it rests in comparative quiet. Bare rock is abundantly exposed on shores of this kind. SHORE LINES 307 If the land descends slowly under the sea, the shore is fronted by shoal water ; then much of the strength of the waves is spent on the shelving bottom before they reach the shore line. Rock waste is so slowly removed from a shore line of this kind that beaches of gravel and sand are commonly strewn along it ; the waters offshore become somewhat turbid during storms with fine waste raised by strong waves from the shallow bottom. 177. Different Kinds of Shore Lines. — Two kinds of shore lines have already been described. In one the sea lies upon a smooth coastal plain that was once a sea bot- tom (page 144) ; in the other it lies on the flanks of a depressed mountain range (page 211). These two kinds are the types for many other examples. Shore lines of the first kind are smooth and simple, and are bordered by shallow water. Shore lines of the second kind are irregular and are generally bordered by deep water. Those of the first kind border lowlands of weak strata ; they have few good harbors and hence they do not offer good opportunity for traffic between land and sea. Those of the second kind generally have rocky headlands and islands inclosing protected bays, where harbors are numerous and trading settlements are favored. 178. Shore Lines of the First Kind. — The low plain of Buenos Aires dips gently beneath the sea, whose waters are shallow for many miles off the simple shore line. Large vessels cannot approach close to the land, except where an artificial harbor has been dredged out, 308 ELEMENTARY PHYSICAL GEOGRAPHY When storm winds blow from the sea they sweep the water upon the low coast and cause destructive sea floods ; dikes are built along certain parts of the shore to keep the waters off. The waves along the shallow shores of lowlands beat up the bottom sands and in time build offshore sand reefs inclosing narrow lagoons. The movement of currents along the sand reef forms a beach, straight or gently curved on its seaward side. On-shore winds blow sand from the beach and build sand hills or dunes of irregular form, sometimes fifty or one hundred feet high, on the reef. Flood and ebb tidal currents maintain passages, called inlets, through the reef, as at X>, Figure 159. Sediments are brought into the lagoons by streams from the land, and, with the aid of salt-water plants, the shallow lagoons are gradually filled and converted into salt marshes at high-tide level. Sand reefs, lagoons, and marshes are plentiful along the Atlantic and Gulf coast of the United States. A sand reef is slowly worn back by the action of the surf on its beach. The dune sands are slowly blown back into tlie narrowing lagoon or upon the lagoon marsh. At last the lagoon and its marsh disappear, and the mainland is directly attacked and cut back in a low bluff. The retreat of the sand reefs may be more rapid on one stretch of the shore than on another ; thus one part, CA, Fig- ure 159, may have a bluff cut in the mainland, while 'another part, AB, is still fronted by reef and lagoon. The coast of New Jersey is fronted by long sand reefs inclosing lagoons and tide marshes. Farther north at SHORE LINES 309 Long Branch, a noted seaside resort, the land is abeady cut back in a low bluff. Severe storms cut away the base of the bluff, sometimes undermining the houses that are built too close to it. The low coast of the middle Netherlands has retreated two miles or more in historic times. A belt of dunes, half a mile or more wide, lies inland from the smooth Fig. 159. Diagram of a Lowland Coast with Bluff and Saud Reef Draw an outline map illustrating the features of Figure 159. Draw another map representing an earlier stage in the development of this shore, line, when the whole length of shore was fronted by a reef and before any bluff had been cut. Draw a third outline show- ing a later stage, when the retreat is great enough to produce a bluff nearly all along the shore line, leaving only a small part fronted with sand reef and marsh-filled lagoon. harborless beach. The chief ports are on the lower courses of rivers, whose channels are broadened by the flow and ebb of the tides. The Romans built a castle back of the dunes, near the mouth of the Rhine. In 1520 the dunes had blown inland, grain by grain, and the sea had cut the shore back close to the castle. In 1G94 the castle stood in the sea. 310 ELEMENTARY PHYSICAL GEOGRAPHY about half a mile from land. In 1752 it disappeared, destroyed by the waves. In 1460 a church that had been built inside the dunes in the Dutch village of Scheveningen (near The Hague) was reached by the sea. A new church was then built about a mile inland, at the east end of the village. In 1574, the outer part of the village having been gradu- ally consumed by the waves, new houses had been built east of the church, so that it stood in the middle of the village. In a later century the new church again stood close to the shore, the village having moved beyond it. In southwestern France the west winds, sweepmg in from the Bay of Biscay, have formed a belt of dunes two or three miles wide. Formerly the sand was drifted far- ther and farther inland with every westerly gale. Fields and villages were invaded and buried by the advancing drifts. Now most of the dunes have been planted with a kind of pine tree that thrives in a sandy soil ; the wind is lifted from the sand by the trees, and the sand drifts have ceased advancing. The pine forests yield much resin. 179. Sea Cliffs. — As the margin of a plain is cut back by the sea, the shore bluff increases in length and height, until it may deserve the name of cliff. The cliff face weathers ; fragments, large and small, fall from it to the beach below, where they are moved about and ground to pieces by the waves. The fine particles are drifted off- shore to deeper water. Thus longer and longer stretches of the shore become harborless, and traffic between land and sea is greatly hampered. SHORE LTXES 311 In northwestern France the upland plain of Normandy- fronts the sea in a vertical sea cliff, 200 or 300 feet high, with gently curving shore line for many miles. A large part of the plain must have been consumed by the sea in the development of the cliff. Cliffs of Xormandy (looking southwest) 180. Shore Lines of the Second Kind. — These shore lines are more varied than those thus far described. When an uneven land surface is depressed and partly covered by the sea, numerous ridges and hills stand forth as promon- tories and continental islands, valleys are entered by arms of the sea, and protected harbors are plentiful. The irreg- ular coast of Maine offers many illustrations of this kind. Its relief is of moderate measure. The waves beat furiously on the exposed headlands of irregular coasts during storms. Angular rock fragments, 312 ELEMENTARY PHYSICAL GEOGRAPHY Fig. 161. Diagram of an Irregular Shore Line weathered from the rocky coast, are swept about by the dashing waves and are in time rounded to cobbles and pebbles, and worn down to sand. These fragments bat- ter the shore and erode the margin of the land, gradually forming a cliff that rises above sea level and a bench that is partly bare at low tide. Isolated rock columns or stacks stand for a time on the rock bench. At high tide the waves roll across the bench and sometimes excavate sea caves, fifty or more feet in length, at the base of the cliff. Fingal's cave, on the island of Staffa, west of Scotland, and many other less famous caves have thus been eroded by the waves. As the wave-cut bench broadens and the cliffs increase in height, some of the rock waste is swept alongshore from the headlands into the little coves and bays, forming Fig. 1()2. Diagram of an Irregular Shore Line with Cliffed Headlands and Beached Bays SHORE LINES 313 beaches on the more protected parts of the coast line. Such beaches present a smooth curve, concave to the sea ; here the surf breaks in even rollers, quite unlike the dashing and fretting waves on the ragged headlands. Dj-aw maj)s of selected parts of the coast shown, in Figures 161 and 162, on a somewhat larger scale than that of the figures, and thus illustrate the change from the original to the later outline. The cobbles and pebbles thrown up on the beaches dur- ing storms may form a wall five or ten feet above high tide. A pond or swamp is often %^ ~^^^^^.W^^^ .^" :-- ; <^^M^M/k!L inclosed behind tlie wall beach in the valley that had previ- ously opened into the bay. The New Eng- land coast has numerous beaches of this kind between its rocky headlands. Compare the coast forms in Figures 161, 162, and 163. Where has the sea gained on the land ? the land on the sea ? The promontory of Brittany in western France, beaten by heavy waves and swept by strong tides, is in about the stage of development represented by Figure 162. The headlands are dangerous on accomit of the rocky reefs that rise to half-tide height on the rock bench that fronts the ragged cliffs. The small bays are partly filled with curved beaches of cobbles, pebbles, and sand. Fig. 163. Diaa:raiii of a Curved Shore Line 314 ELEMENTARY PHYSICAL GEOGRAPHY As time passes, headlands are cut farther back, so that the cliffs become higher and longer. The bays are more and more filled with beaches and cobbles, gravel and sand, and with deltas formed by streams entering the bay heads. Thus the outline of the shore becomes more regularly curved than it was at first, and convex lines of cliffs alternate with concave stretches of beach. Fine examples of shores in this stage are found in parts of southwestern England. The cliffed headlands Fig. 164. A Cliffed Heacllaud and a Land-Tied Island are guarded by lighthouses ; settlements are usually found in the river mouths of the beached bays. The coast of western Italy and the northern coast of California offer many examples of this kind. 181. Land-Tied and Sea-Cut Islands. — Irregular coasts, formed by the depression of a mountainous region, are often originally fronted by islands. Such islands not infre- quently come to be attached to the mainland by the back- ward growth of sand reefs that are supplied with waste from the outer cliffs. Compare the two headlands of SHORE LINES 315 Figure 1 64 in this respect. A land of Italy is shown in Plate XYI. The fortified Rock of Gibraltar, belonging to Great Britain, was originally an island, but is now tied to the mainland of Spain by a broad sand reef. Part of the reef is "neutral ground," occu- pied by neither Spain nor Great Britain. If the coast is of unequal strength along its front, the rate of sea cutting may vary from place to place, and thus parts of the coast may in time be cut off from the mainland and form islands, as in Figure 166. Many islands in the bay of Panama are thus formed. They are remnants tied island on the coast Europa Poinf Fig. 165. Gibraltar Fig. IGO. Diagram of a Group of Sea-Cut Islands 316 ELEMENTARY PHYSICAL GEOGRAPHY of the mainland whose extent has been much reduced by the attack of the sea. The width of the isthmus of Panama has thus been lessened and the length of the pro- posed interoceanic canal across it has been correspondingly- shortened. Fig. 167. A Cliffed Coast iu Alaska 182. Cliffed Coasts. — Coasts that have been long exposed to strong waves and tides may have been cut so far back that no part of the original outline remains. In such cases a nearly continuous cliff, sometimes of great height, fronts the shore, as in Figure 167. Traffic between SHORE LINES 317 land and sea is practically impossible on such a coast. A vessel wrecked on the ragged bench beneath the cliffs can receive little succor while stormy weather lasts. The Orkney and Shetland islands, north of Scotland, have lost much of their former area by the attack of the sea. The head- lands are cut off by lofty cliffs, some of which are nearly 1000 feet high. An isolated stack, known as the "Old Man of Hoy," rises 600 feet above the sea. 183. Elevated Shore Lines. — When the devel- opment of shore lines is interrupt- ed by a change in the level of the land, the work of cliff cutting and bay filling must be begun again at a new level, in much the same way as before. If the land rises, the former shore line may be found at a greater or less distance inland from the new shore line. This has already been referred to in the descrip- tion of coastal plains. Fig. 168. The " Old Man of Hoy " 318 ELEMENTARY PHYSICAL GEOGRAPHY An elevated shore line, marked chiefly by rocky cliffs and benches with occasional beaches, may be traced along a great part of the western coast of Scotland at a height of from twenty to twenty-five feet above the sea level of to-day. The narrow coastal plain that slopes forward from the old shore line to the new one is pictured in Figure 64. This elevated shore line forms a convenient bench along v/hich roads may be laid near the base of the slopes that ascend to the highland summits. Old sea caves, roughly walled in, sometimes serve as stables for the seaside farmers. A low bluff, seeming to be a former shore line, has been traced on the coastal plain of Virginia and North Carolina, a short distance inland from the present shore line. Lines of ancient sea cliffs at several different levels break the coastal slopes of Cuba and form steps in the broad plains of eastern Patagonia. The western coast of Norway is bordered for much of its length by a belt of lowland and islands, sometimes as much as from three to ten miles wide, from whose inner margin an old sea cliff rises to the highlands (Figure 169). The lowland is a broad rock bench or platform, cut by the sea when the land stood about 300 feet lower than now. A large part of the population of western Norway dwells on this ancient sea floor. The former sea cliff, at the inner margin of the jDlat- form, is from 500 to 1000 feet high. A number of rocky hills stand on the platform, representing uncon- sumed islands of the former shore. The withdrawal of lake waters by a change of climate (page 288) has an effect on the condition of shore lines SHORE LINES 319 similar to that produced by an elevation of the land with respect to the sea. The cliffs and beaches that contour around the slopes of the mountains of Utah, where the waves of Lake Bonneville once beat, in many ways resemble the elevated shore lines of western Scotland, Well-defined ancient shore lines, consisting of cliffs and beaches, are found in the region of the Great lakes. The Fig. 169. The Coast Platform of Norway shore lines are found to converge toward depressions in the height of land to the south of the lakes, and well-defined channels are there discovered. This indicates the former existence of lakes much larger and deeper than those of to-day, Avith outlets southwestward to the MississipjDi system, instead of northeastward by the St. Lawrence. These facts are explained by supposing that the melting ice sheet of the glacial period obstructed the St. Lawrence valley, so that the lake waters had to rise 320 ELEMENTARY PHYSICAL GEOGRAPHY high enough to overflow southwestward. Many of the beaches are so distinct that they are used as naturally graded roadways. The outlet of the expanded Lake Erie ran past the site of Fort Wayne, Indiana, to the Wabash river. The outlet of the expanded Lake Michigan led past the site of Chicago to the Illinois river; this channel is now followed by the artificial drainage canal by which some of the water of Lake Michigan is again led along the line of ancient outlet. 184. Fiords. — The valleys in the highlands of Norway have been deepened by the heavy and strong-moving glaciers that once filled them. Since the glaciers disappeared the sea has entered the deep channels that the ice scoured out, forming long, narrow, and deep embayments, called fiords^ often deeper at the middle than near the mouth. Their depth has probably been increased by a depression of the region, by which the border of the ice-scoured lowland has been converted into a swarm of islands. The rock walls of the fiords are so steep that few set- tlements can be made along them, except at their heads or where deltas are built by side streams that cascade from the hanging valleys (see page 299) of the high- lands. Roads can seldom follow the shore lines ; hence communication is chiefly by water. An irregular coast of this kind has often favored the development of maritime arts. Its outlying islands tempt exploration ; its protected bays afford safe harborage even for small boats. The people occupying the coastal lands become expert sailors and fishermen. SHORE LINES 321 The numerous bays of southern Scandinavia were known as viks to the people who occupied them 1000 years ago, and the inhabitants were therefore called vikings, or bay people. They became bold marauders, invading the more southern coasts of western Europe, by whose people the Fig. 170. A Delta in a Norwesriau Fiord vikings were called Northmen. Normandy is to this day named after these early sea kings. They were the first European people to venture far out upon the ocean, and thus almost 1000 years ago they discovered Greenland and otlier parts of the western world. The west coast of Patagonia (southern Chile) resembles that of Norway in the possession of deep fiords among bold mountains. The Canoe Indians dwell here, — a 322 ELEMENTARY PHYSICAL GEOGRAPHY primitive people who find the steep slopes of the land so inhospitable that they live almost entirely in open canoes on the water. A small fire is kept burning on a few sods in the canoes, so that it may be carried from place to place. These Indians have no fixed habita- tions and make little use of the land, except when they build temporary shelters of tree branches, roughly thatched, in one cove or another where they stop for a time to gather shellfish. The mountainous coast of Alaska is varied by numer- ous fiords, into some of which great glaciers descend from snowy ranges in the background. As in Norway, much of the coast is so steep as to be unfit for settlement. Hanging valleys frequently open on the walls of the fiords, 500 or more feet above sea level. 185. Delta Shore Lines. — Rivers tend to build their deltas forward, and thus oppose the destructive action of the sea. The Mississippi discharges a great quantity of land waste into the Gulf of Mexico. The waters of the gulf are relatively shallow, and the tides are weak. Here the outline of the delta seems to be governed entirely by the action of the great river (Figure 136). The several distributaries of the Mississippi build low and slender banks of mud on each side of their channels faster than the waves can wear them away ; hence the delta has several fingerlike projections into the sea. In order to increase the depth of water in one of the channels, or "passes," jetties (dikes of wood and stone) have been built forward beyond the end of the delta fingers, thus SHORE LINES 323 increasing the current and forcing it to~scour the channel to a depth sufficient for seagoing vessels to enter on their Avay to New Orleans. The Rio Grande, a large river, but much smaller than the Mississippi, delivers land waste to the gulf in greater quantity than the waves and currents can altogether remove ; hence its delta is built forward (Figure 171). But the waves are strong enough to smooth the out- line of the delta; hence it has a gently convex curve without fingerlike projec- tions. The Brazos and Col- orado rivers, about midway between the Mississippi and the Rio Grande, also cause a slight forward bowing of the Texas coast. Fig. 171. Deltas of the Texas Coast 186. Effect of Climate on Shore Lines. — Shore lines, like land forms, are affected by climate ; not only by differences between regions of onshore and offshore winds, where waves and currents are stronger or weaker, but even more by differences of temperature. Iif^olar seas the land is often bordered by a fringe of ice called the ice foot. During the winter the ice foot usually remains attached to the land, unless broken by strong tides ; in summer it may loosen and float away. 324 ELEMENTARY PHYSICAL GEOGRAPHY It is often used as a longshore roadway for sled travel by Eskimos and Arctic explorers. In warm seas the shores that are not exposed to strong surf may be invaded by certain kinds of trees, forming a network so dense as to make landing difficult. The mangrove is the most important tree of this kind. It grows freely in shallow sea water on low and muddy shores, and protects the land from the waves. Muddy sedi- ments accumulate in the quiet water among the trees, and thus the land gains on the sea. Shores all overgrown with Fig. 172. Mangrove Tree mangrove SWamps are dismal as com- pared with the clean shell-strewn beaches of sand and pebbles beaten by trade-wind surf. 187. Coral Reefs. ^ The shallow waters of continental borders or mid-ocean islands in the warmer seas are commonly occupied by coral reefs, composed of the limy framework of coral animals. Living corals are found chiefly on the outer side of the reef, where they grow in the shallow water much in the same way that a thicket of small bushes grows' on the land. They take SHORE LINES 325 the limestone needed for their skeletons from solution in the sea water. When reef-building corals first take possession of the shallow waters on a shoal or near a shore line, their growth extends upward from the shallow bottom and Fig. 173. A Fringing Reef outward into the surf. Blocks and branches are detached from the bot- tom by severe storms and rolled about by the waves ; the larger fragments are thrown together, forming a beach a little above sea level ; the finer particles are carried toward deep water and strewn over the sloping bottom. The reef thus broadens, and if near the land, it forms a fringe close along the shore line. At this stage it is called a fringing reef. Strips of fringing reef are found on the equatorial coast of eastern Africa, along parts of the Brazilian coast, at various points on the coast of Cuba and elsewhere in the West Indies, and border- ing many islands in the Pacific, as the Hawaiian and other groups. The Galapagos islands in the eastern Pacific, close to the equator, are free from reefs, because of the low tem- perature of the water brought there by the strong Peruvian current. (See Figure 112.) Draw maps of the islands and reefs shown in Figures 173 and 174. Compare the two. Fig. 174. A Barrier Reef 326 ELEMENTARY PHYSICAL GEOGRAPHY Fig. 175. Part of the Great Barrier Reef of Aiistralia (as seen at low tide, looking toward tlie mainland) 188. Barrier Reefs. — A fringing reef broadens by the outward growth of the corals, and the submarine slope is built forward by the supply of coral fragments. At the same time water supplied by rain, by streams from the land, SilOKK LINES 327 Fig. 176. Diagram of Part of a Barrier Reef and especially by the surf that rolls over the reef, slowly dLs- solves and washes away the inner part of the reef where liv- ing corals are few or wanting. Thus the reef may come to be separated from the land by a shallow lagoon a mile or more wide ; and in this way a fringing reef may change to a barrier reef. The Great Barrier reef stretches along the north- east coast of Australia for about 1000 miles, the largest reef in the world. It is usually from twenty to fifty miles from the mainland, mostly beneath sea level, interrupted by numerous inlets, and bearing a few low islets. The sea outside descends rapidly to great depths ; the water inside is shallow (from ten to forty fathoms). 189. Effects of Eleva- T, .„„ ^. r^.-^, , tion. — If a slow uplift Fig. 177. Diagram of Part of an Elevated '■ Reef with a New Fringing Reef OCCUrS, COrals will con- tinue to grow on the outer face of the reef, but the body of the reef may be raised above sea level, forming a terracelike bench above the new shore line, outside of which new fringing reefs grow. Compare Figures lit) and 177. 328 ELEMENTARY PHYSICAL GEOGRAPHY An uplifted reef, forming a bench at a height of about thirty feet, with a breadtli of a mile or less, borders much of the northern coast of Cuba. The sea has worn a low cliff in the front of the bench ; from the cliff top one may look down upon the new fringing reef now growing in the sea. The loose texture of uplifted reefs allows them to be worn down again with relative rapidity. While the uplifted reef is thus wasting away, the fringing reef may be growing outward vigorously and changing to a barrier reef. The uplifted reef will be in part dissolved by the solvent action of rain water ; and it may, after elevation ceases, be reduced below sea level. A shallow body of water, or lagoon, will thus be formed within the new barrier reef. 190. Atolls. — If the central island within a barrier or fringing reef is worn away or is lost by slow submergence as the reef grows upward and outward, the reef may make an irregular ring around an oval lagoon and the ring may slowly increase in size by the outward growth of the reef, while the lagoon is deepened by the dissolving action of its waters. Such a ring island is called an atoll. Many islands of this kind are known in the Pacific ocean. Fig. 178. Diagram of an Atoll Compare the reefs shown in Figures 173, 174, and 178. SHORE LINES 329 Although one of the most wonderful objects in nature, a lonely atoll affords little opportunity for human devel- opment. The natives of such islands lead easy and indo- lent lives, but their progress toward better conditions than those of savagery is hindered by the small variety in their surroundings and by their distance from lands of more varied form and products. Fig. 179. An Atoll, or Coral Island The small height of atolls subjects them to the danger of being overwhelmed by earthquake waves. Hurricanes sometimes come upon them, unobstructed from the open sea, sweeping violent surf far up the beaches ; the storm winds break down the cocoanut palms on which the natives depend largely for food and for the materials for many of their simple arts. Atolls have no streams, but fresh water supplied by rains may be found not far below the surface. The thin soil has little variety of mineral 380 ELEMENTARY PHYSICAL GEOGRAPHY matter, but floating pumice (frothy lava) is often cast ashore from distant volcanic eruptions, and some of the islanders have learned to gather and pulverize it to use as a fertilizer for their little fields. Floating logs from other lands sometimes drift upon the atolls, and their roots occasionally carry stones of firmer texture than coral rock (for example, fragments of dense lava from a volcanic island) ; rude whetstones, pestles, and mortars are made from these chance supplies. Although birds are plentiful, there were no mammals on coral islands until rats and mice came ashore from vessels; a few domestic quadrupeds have occasionally been imported by foreign residents. QUESTIONS Sec. 175. What is the origin of the forces by which the ocean works on the lands? How is the work done? What becomes of the material worn away? Why are the lands not completely worn away? 176, 177. Upon what two conditions does the outline of any shore line depend ? Describe the movement of waves and their action on the lands. How are shore cm-rents caused? How do waves aid the work of currents? Compare the work of the sea in deep and in shallow shore waters. Describe the shore line of a young coastal plain ; of a depressed mountain range. Contrast them as to harbors, settle- ment, and trade. 178. Describe the shore of the coastal plain of Buenos Aires. What effects are here caused by storm winds? by waves? What are the origin and torm of sand reefs? What are inlets? lagoons? salt marshes ? How are the sand reefs and lagoons changed by the action of surf ? Describe the coast of New Jersey ; of the Nether- lands ; of southwestern France. SHORE LINES 331 179. What is the origin of sea cliffs ? How are they worn back ? Describe the cliffed coast of northwestern France. 180. "What are the features of a shore line of the second class? How and on what parts of these shores do waves form cliffs? stacks? caves? beaches? What are wall beaches and where are they common? Describe the coast of Brittany. Describe the shore forms of later development. Where are they found? 181. 182. What are land-tied islands? Describe an example. AVhat are sea-cut islands? Describe some examples. Describe a cliffed coast. AYhat is the relation of such a coast to human occu- pation ? Describe an example. AVhat is the " Old Man of Hoy " ? 183. AA'hat changes in the shore line result from a change in the level of the land? Describe the elevated shore line of western Scot- land; of North Carolina. Where are other examples found ? Describe the western coast of Norway. Under what conditions were certain abandoned shore lines formed in Utah ? around the Great lakes ? 184. What are fiords? Explain their origin. Where do they occur? How do they affect settlements? How does an irregular shore line affect the maritime ai'ts ? Give an example from Scandi- navia. Describe the Canoe Indians. What is the relation of hang- ing valleys to fiords ? 185. How do rivers tend to opjiose the action of the sea? Describe the delta of the Mississippi ; of the Rio Grande. 186. How does climate affect shore lines? What is the ice foot? Describe a mangrove swamp. Where is such a swamp formed ? 187. 188. What are coral reefs ? Where are they found ? (See Figure 112.) How are they formed? What is a fringing reef? Where are fringing reefs found ? Why are no reefs found on the Galapagos islands? What is a barrier reef? How is it formed? Describe the Great Barrier reef of Australia. 189, 190. Describe an uplifted reef. What changes may such a reef undergo^ What is an atoll? In what ways may atolls be formed? What opportunity do atolls afford for human develop- ment? To what danger are atolls exposed? CHAPTER XI THE DISTRIBUTION OF PLANTS, ANIMALS, AND MAN 191. Geographical Aid in Human Progress. — The study of physical geography, or physiography, gives a knowl- edge of the features of the earth, so that we may better understand the relation of man and nature. This rela- tion is of great importance, because the progress of man- kind from the savage toward the civilized state has been largely made by taking advantage of favorable geograph- ical conditions and by learning to make greater and better use of the products and forces of the earth. The winds blew over the lands and waters, carrying rain and causing waves and currents, for thousands of years while man was an ignorant savage. When he invented sailboats and windmills a new use was made of the winds, and man profited greatly by his inventions. Streams had been wearing down the falls and rapids in their valleys and spreading rock waste over their flood plains during all the long existence of the continents. When man cultivated food-bearing plants on the flood plains and built flour mills by the waterfalls, he gained much from making new and good use of these natural forms and forces. The magnetic forces of the earth have always been capa- ble of directing a compass needle, but they were not used 332 THE DISTRIBUTION OF ORGANIC FORMS 333 until man discovered liow a balanced magnetized needle would behave. Coal and iron ore lay untouched in the earth's crust for millions of years ; now the nations that make the fullest use of these invaluable resources have become the leaders of the world. Reference has frequently been made on the earlier pages of this book to the effects of geographical surroundings on the growth and distribution of plants and animals and on man's way of living. The present chapter reviews these effects and gives new examples of them. 192. Life on the Earth. — The earth is known to have been occupied for ages past by various kinds of plants and animals, for their fossil remains are found in many rock layers of ancient origin. During all these ages living forms have tended to spread over as large a region as possible, just as they do now. Barriers of different kinds limit the spreading of organic forms. Land plants and animals are stopped by the sea, unless they can travel by water or air. Sea animals are stopped by the lands. Those forms that need a warm climate do not spread into regions of cold climate. Grazing animals that need abundant grass are stopped by deserts and by forested mountains. Plants growing from heavy seeds, like nuts, spread slowly from the parent plant. Plants growing from light seeds, especially from such as are carried by tlie wind, like the seeds of the dandelion, the thistle, and the fireweed, are very rapidly distributed. The dande- lion is found on the northern lands all around the earth. 334 ELEMENTARY PHYSICAL GEOGRAPHY Certain kinds of sea animals, like mussels, barnacles, and corals, spend most of their life attached or rooted to the sea bottom, living on food that is brought "to them by the moving waves and currents. This reminds one of the dependence of rooted land plants on the mov- ing air for most of their sustenance. But the young forms of these fixed animals are free to float about, and are then carried far and wide by the currents of the sea, just as light seeds are carried by the winds. Most animals can move from place to place. They have fins for swimming, legs for walking, or wings for flying. As they wander about in search of food, they come in time to be distributed over all parts of the earth accessible and favorable to them. This is as true for the ancient history of life on the earth as it is for the life of to-day. Birds of strong flight are widely distributed. Walking birds and quadrupeds are more narrowly limited. The ostrich of Africa, the emu of Australia, and the rhea of South America are each confined to one of the southern continents. The albatross, a large sea bird, whose skill in flying without flapping its wings is very remarkable, is found all around the great southern oceans. Occasional examples of some fifty kinds of North American birds are found in western Europe ; but no stragglers from Europe are found in North America. This is because the prevailing westerly winds blow from North America toward Europe. The course of the winds is determined by the direction of the earth's rotation, and thus the rotation of the earth has an influence on animal distribution. THE DISTKIBUTIOX OF ORGANIC FORMS 335 193. Geographical Factors in the Struggle for Existence. — The number of plants and animals in a given region is usually about as great as can be supported there. Where food is plenty the number of individuals is large ; this is usually the case in the shallow borders of the seas and on the lands of the temperate and torrid zones. The luxuriant plant growth of the forests under the equa- torial rains illustrates this rule. Where food is scarce, as in very dry and in very cold regions, the number of individuals is small; and some of the cold, snow-covered deserts are almost uninhabited, as in central Greenland. Man frequently causes great changes in the numbers of plants and animals, as when he cuts down the trees of a forest and plants grain in the new-cleared fields, or when he kills the wild animals of a region .and intro- duces domestic animals in their place. But apart from changes of this kind, the plants and animals of a region remain at about the same number for centuries. It is, however, well known that every kind of plant and animal tends to increase in numbers, for the seeds of plants and the offspring of animals are always more numerous than the individuals that produce them. A single grain of corn may grow to a stalk bearing several ears, each of which may bear over a hundred grains. Many thousand eggs are contained in the roe of a single salmon. If all the young plants and animals reached maturity and produced other young forms in their turn, the number of individuals would increase enormously. The reason that the number of plants and animals in a district does not greatly increase is that, in spite of 336 ELEMENTARY PHYSICAL GEOGKAPHY the production of numerous young individuals, many of them perish in the severe competition for an opportunity to live. Many seeds fail to germinate because they fall on unfit soil, or because they are eaten by animals. Many young animals are devoured by other animals. As a rule, those individuals survive which have some advantage over their fellows and are therefore more fit to succeed in the "struggle for existence." The success of these individuals is often called the "survival of the fittest"; and the survivors are said to be chosen from those which perish by "natural selection." The chances of survival in the struggle for existence are increased for those plants and animals which are best adapted to their geographical surroundings. Fish have gained a shape that enables them to move easily through the water ; this is an advantage in getting their food and in escaping from pursuit. Many of tlie smaller animals of the open ocean move slowly ; but they imitate the transparence of sea water and so make themselves almost invisible and more likely to escape their enemies. As the earth is lighted from the sky, many animals whose backs are dark have lighter colors underneath, so as to counteract the effect of shade; they are thus less easily seen and so have a better chance of approach to their prey or of escape from their enemies. Animals inhabiting deserts are usually gray or tawny, imitating the color of the bare ground. In the snow-covered Arctic regions many animals are Avhite. Some animals gain protection by living in caverns or in the crevices of talus slopes ; others burrow in fine THE DISTRIBUTION OF ORGANIC FORMS 337 rock waste or soil. Name some animals of these kinds. Some animals choose steep cliffs and high peaks for their home, so that they shall not be easily pursued. Eagles build theii' nests on inaccessible pinnacles, such as those of the spurs that separate the huge side ravines of the canyon of the Colorado in Arizona. What can you tell about the home of the Rocky mountain sheep (the bighorn) and of the chamois of the Alps ? 194. Variation of Plants and Animals. — All the many existing kinds of plant and animal life are the descendants of a smaller number of more ancient kinds. But when the ancient forms, preserved as fossils, are compared with living forms, it is found that they are not alike. Through the millions and millions of years during which the earth has been inhabited there have been slow variations in the kinds of plants and animals living on it, so that those now living differ from their remote ancestors. The forms of life to-day are, as a rule, very unlike those whose fossils are found in the oldest fossil-bearing rocks. Among the many causes which have combined to pro- duce variations in plants and animals, none have been more important than changes in their geographical sur- roundings. While part of a sea bottom is slowly raised to form a coastal plain, the kinds of animals that once occupied this part of the sea floor must seek some other home ; at the same time the plants and animals of the neighboring older land have opportunity of taking pos- session of the young plain. As lofty mountains are slowly worn down to lowland peneplains, the forms of 338 ELEMENTARY PHYSICAL GEOGRAPHY life that once occupied the higher mountains must adapt themselves to their new surroundings or perish. During the slow change of climate which caused the gradual advance and retreat of the great ice sheets that once covered eastern Canada and the northeastern United States, plants and animals were first driven away from these regions and later allowed to return to them. Changes of these kinds have repeatedly taken place in the earth's history, and it is probable that every one of them has caused some variation in the plants and animals of their regions. The plants and animals that we now find distributed over the world represent the present stage in the long series of varying forms. 195. Life in the Seas and on the Lands. — The different parts of the earth are so unlike that it is natural to find striking differences among the plants and animals which have become fitted to occupy unlike regions. No geo- graphical contrast is greater than that between the sea floors covered by the oceans and the lands covered by the air. The kinds of plants and animals that have made their home on the lands have come to differ greatly from those that have for ages lived in the oceans. Hence continents and oceans must have existed for long ages because their plants and animals are now very unlike. A remarkable difference between land and sea life results from the much greater density of water than of air. Even the largest sea plants do not need strong trunks, but are supported by the water. Many sea ani- mals are no heavier than the water they live in ; hence i THE DISTRIBUTION OF ORGANIC FORMS 339 they can float without exertion and all their strength can be given to swimming. The kinds of fish that sometimes rest on the water bottom lie upon it so lightly that they have no need of legs ; all their members are fins. Many kinds of fish and other marine forms spend their lives in the open ocean without approaching the shores or the bottom. Birds, on the other hand, are much heavier than the air through which they fly ; hence much of their strength must be used to prevent falling. Even the best flyers spend some of their time on the ground or on trees. When they alight the air gives them so little support that they need legs on which to walk about. It has been explained in earlier chapters that the deep ocean is monotonously cold, dark, and quiet, without changes of weather or seasons, and that the ocean bottom is usually a gently undulating plain covered with ooze or mud for thousands of miles together. The lands, on the other hand, are the seat of varied conditions. They pos- sess a great variety of form and material ; they experience changes from day to night, from summer to winter; they suffer many changes of weather from warm to cold, from calm to stormy, from clear to cloudy, from dry to wet. The development of the higher forms of life, such as are com- monly found on the lands, should be regarded as a conse- quence of the great variety of geographical conditions found there, in contrast to the monotony of the deep ocean, where the forms of life are of a much simpler order. Nearly all the flowering plants live on the lands. Water plants, especially those of the sea, are of a simpler kind. No plants live on the dark ocean floor, for plants cannot 340 ELEMENTARY PHYSICAL GEOGRAPHY grow without sunlight. Many animals of the sea are attached, plantlike, to the bottom. Others move slowly, like starfish and shellfish; still others float with the drifting waters, having little movement of their own, like jellyfish. Only the more highly organized, like many of the fishes, move rapidly; but nearly all land animals move about actively, walking, running, or flying. The larger and more important laAd animals (mammals and birds) are warm-blooded. Most sea animals are cold- blooded, like the lower animals of the land. The only warm-blooded animals of the sea (whales, porpoises, seals, etc.) are believed to be the descendants of ancient land ancestors, gradually modified for the marine life which they have adopted. The reason for this belief is that the sea mammals still resemble in many ways the mammals of the lands. They bear their young alive and nourish them with milk from the breast ; they must come to the surface of the sea to breathe, for unlike fish they have no gills by which they can make use of the air that is dissolved in sea water. They differ from land mammals only in ways that make them better suited for life in the sea ; their legs have been modified into flippers for swimming ; and those forms which, like the whales, live altogether in the sea no longer have fur, like the land animals of a cold climate, but are protected from the cold of sea water by a layer of fat or " blubber " under their skin. Many land animals have developed organs for the pro- duction of sound, the most remarkable sounds being the song of birds and the speech of man. The animals of the sea are, with hardly an exception, silent. THE DISTRIBUTION OF ORGANIC FORMS 341 The greater intelligence of many land animals than of sea animals should also be regarded as a result of the develop- ment of land animals amid a greater variety of geographical conditions than is found in the seas. The class of insects, almost limited to the lands, furnishes many examples of extraordinary instincts, such as those of bees and ants. Nest building by birds, house building by beavers, " hom- ing" of pigeons, and trailing (by scent) of dogs / are examples of highly v developed instincts among land animals that have no parallel among the animals of the sea. The wonderful intel- ligence of man has been developed on the lands, because only on the lands is to be found the great variety of form, climate, and products which can stimulate the development of high intelligence. It would have been as impossible for man to develop as an inhabitant of the dark and monotonous ocean tioor as it has been for civilization to arise on the frozen and lone- some lands of the Antarctic regions. Fig. 180. Beavers 196. Life on the Continents. — The arrangement of the continents has exerted a great influence on the distribution of land plants and animals. It has been stated that the north- ern continents are nearly united around the Arctic circle, and that three great extensions of this northern land belt stretch southward; Africa being most closely associated 342 ELEMENTARY THYSICAL GEOGRAPHY with the northern lands of the Old World, South America being less closely associated with North America, while Australia is cut off from Asia by the sea. It is there- fore natural to find many resemblances among plants and animals in high northern latitudes, and to find that differences among them become greater and greater as middle and low latitudes are passed and far southern lati- tudes are entered. The lichens and mosses of the frozen northern lands are similar all around the Arctic circle. The animals of the same region include the polar bear, rein- deer (called caribou in North America), lynx, musk ox, and Arctic hare, which are of the same kind on all the lands around the north frigid zone. The northern lands must therefore have once been connected, and their connection must have occurred at so late a period in the history of the earth that there has not since then been time enough for these Arctic animals to become unlike in their now some- what disconnected homes. In the lower latitudes of the northern hemisphere the plants and animals of the lands possess certain resemblances that prove their descent from a common ancestry, but they also show certain marked differences that prove the separa- tion of the continents in these latitudes for a very long period of time. \ Fig. 181. Caribou THE DISTRIBUTION OF ORGANIC FORMS 343 * The puma and jaguar of the New World are catlike animals that resemble in many ways the lion and leopard of the Old World. The resemblance is so strong that it must be believed they are descended from a common stock ; hence in some former time the Old and New Worlds must have been connected in latitudes where the ancestors of these animals could pass from one region to the other ; but this connection ceased so long ago that distinct differences have since then arisen between the two groups of catlike animals. The long separation of the Old and New Worlds is con- n. J 1 ri T J • 1 , Fig. 182. Jaguar farmed by fandmg certain plants and animals peculiar to each region. Horses, cattle, and other domestic animals, as well as tea, coffee, and wheat, originated in the Old World, while humming birds and rattlesnakes, as well as maize (corn), potatoes, and cactus plants, are peculiar to the New World. The differences among the animals of the three southern continents are strongly marked. The giraffe, hippopotamus, and many kinds of antelopes are found only in Africa ; but that continent shares with the adjacent lands of southern Asia the lion, elephant, rhinoceros, and the manlike apes. South America stands more alone : here are found mon- keys with prehensile tails, tapirs, llamas, sloths, and arma- dillos, none of which are found in the Old World. In Australia, the most isolated of the southern conti- nents, nearly all the quadrupeds belong to the peculiar 344 ELEMENTARY PHYSICAL GEOGRAPHY group of marsupials or pouched mammals, which carry the young ill a pouch on the breast of the mother. The best known marsupial is the kangaroo. Australia contains also the lowest kind of quadruped, the water mole (or duckbill), which resembles birds in laying eggs from which its young are hatched. It is not because Australia is unfitted for mammals that they are not native there. Rabbits have been carried from Europe to southern Australia, where they have become so numerous as to be a nuisance. Shecj) are now raised there in great numbers, so that Australia has become an important wool-growing Fig. 183. Kansraroo , rpii -i p * country, ihe absence oi mammals in Australia must therefore be explained by the long separation of that land from the continents on which mammals were developed. In the same way, the absence of Australian forms in other parts of the world is not due to differences of food supply or of climate, but to the long separation of the island-continent from the other lands. The eucalyptus, a large Australian tree, thrives in the mild climate of California and southern Europe. So horses and cattle, brought from Europe to the New World, have become numerous on the prairies and plains of North America, and on the llanos and pampas of South America. Potatoes, native to America, have become an important THE DISTRIBUTION OF ORGANIC FORMS 345 food supply in Europe. What can you tell about the English sparrow? 197. Races of Mankind. — It is not only in the distri- bution of the lower animals that the grouping of the con- tinents has had a controlling influence. The several races of mankind, differing in language, religion, and form of government as well as in color, originally occupied regions that correspond in a general way to the grand divisions of the lands. Hence it may be believed that the separation of the continents by the oceans, aided by certain mountain and desert barriers, has been the chief cause of the division of mankind into races. The greatest of the continents, Eurasia, contains two races. The European race, generally light colored but with some dark-skinned families, has its home in Europe, Africa north of the Sahara, and southwestern Asia. The leading nations of this race are the most advanced peoples of the world. They have developed liberal governments in which the rights of the people are considered, and have advanced greatly in the cultivation of the arts and sciences. The Asian race is found chiefly in eastern, central, and northern Asia; it is often called the Yellow race. China contains the greatest number of this race, the Chinese being separated from the Hindus of India (a branch of the European race) by the lofty mountains of the Hima- layan system. Although comparatively advanced in many arts, the Asians have acquired little knowledge of the sciences, and their governments are usually despotic. The Japanese are to-day their most advanced nation. 346 ELEMENTARY PHYSICAL GEOGRAPHY America is the home of the American or Red race ; its native inhabitants are divided into many tribes, each led by a chief. Africa, south of the Sahara, is the home of the African or Black race, governed by despotic kings or chiefs. Australasia and the peninsulas and islands of southeastern Asia include certain black and brown races. Few nations among these races have made important advances toward civilization. Within the last few centuries the means of travel over land and sea have greatly increased, and to-day the races of mankind are by no means limited to the continents named above as their homes. People of European ancestry now make the chief part of the population in North and South America, southern Africa, Australia, and New Zealand, as well as in Europe. The Chinese are not limited to China alone, but are found as merchants and laborei'S in the islands of southeastern Asia, Australia, and elsewhere. Many descendants of the African race are now living in North and South America. It should be noticed that, while the people of the Euro- pean race are now widely distributed over all parts of the world, and while Asians and Africans are found in large numbers in other lands than their homes, few of the less advanced races have entered Europe, the chief of these being members of the Asian race, the Turks in the south- east and the Finns and Lapps in the north. 198. Life on Islands. — Islands that rise from conti- nental shelves are occupied by many plants and animals similar to those of the neighboring mainland. It is inferred THE DISTRIBUTION OF ORGANIC FORMS 347 from this that the continental mass once stood higher than now and that the continental shelf was then a lowland on which the present islands rose as hills or mountains. The forms of life that were then widespread have become sepa- rated by the submergence of the lowlands and the division of the islands from the continent. Various species of cassowaries, large ostrichlike birds unable to fly or swim, are found in Australia and on the hilly islands to the north, each land area having its own species. From this it is supposed that the ancestral family of all these species occupied the region when the continental mass stood higher and the mainland and islands were connected by the low- land now under water in the con- tinental shelf. Since then it is believed that the region has been depressed and the lowland flooded by the sea, while the higher parts remain as islands separated from Australia and from each other. The differences between the various species of cassowaries must have arisen since their family was divided by the drowning of the lowlands. Many of the islands near Australia resemble that con- tinent in possessing marsupials. The islands nearer Asia have no marsupials, but possess many mammals similar to those of the mainland to which they are related. A belt of deep water divides the two groups of islands. Fig. 184 348 ELEMENTARY PHYSICAL GEOGRAPHY Islands that rise from the deep ocean floor far from the continents have no large native animals, but are occupied by such forms of animals and plants as might have reached them through the air or the water from the nearest larger land. The Azores, a group of mid-ocean volcanic islands in the North Atlantic, are so called from the hawks that were common there when the islands were discovered by voyagers from Europe. The Galapagos islands of similar origin in the Pacific west of Peru are named from the large tortoises that abound on them. 199. Climate as a Control of the Distribution of Plants and Animals. — Differences of temperature resulting from the globular form of the earth are of great importance in limiting the distribution of plants and animals. Plants like palm trees, that flourish in the torrid zone, spread into lands of higher latitudes on both sides of the equator until they reach regions where the summers are too cool for them to mature their fruit. Plants that occupy the tem- perate zones are limited to belts -on whose polar side the summer is too brief and cool and on whose equatorial side the summer is too hot for their seeds to ripen. Thus in the central United States cotton is limited to the southern states, corn flourishes best near the middle of the country from the Ohio to the lower Missouri, and wheat is pro- duced most abundantly in the northern states. In these northern latitudes there are great forests of pines and other cone-bearing trees. Still farther north, where the ground is frozen all the year round, except for a little Pr.ATi; XVIII. Forest in ilie Equatorial Kain Belt. Ceylon THE DISTRIBUTION OF ORGANIC FORMS 349 melting during the short summer, trees are wanting and vegetation is reduced to stunted and herbaceous forms, with many mosses and lichens. (See Figure 112.) The various kinds of animals are, like plants, limited to regions in which the summers are long and warm enough — but not too warm — for them to rear their young. But unlike plants, which live on mineral food derived from the soil and the air, animals subsist either on. animal or vege- table food; and flesh-eating animals, like the lion, often devour plant-eating animals, like the antelope. Thus in the end all animals depend for food directly or indirectly on plants ; hence the distribution of animals depends in part on the distribution of plants, and this in turn depends on climate. Examples of the distribution of animals according to zones of temperature are found in the limitation of the caribou, moose, and elk to the northern parts of America; of the alligator, tapir, and sloth to low latitudes; and of the rhea to far southern America. 200. Climate as a Control over the Customs of Savage Tribes. — The customs of mankind ai-e influenced in many ways by climate. Some of the climatic influences are direct, as with regard to clothing and shelter. Some influ- ences are indirect, as with regard to food supply, which in turn is affected by the distribution of plants and animals. Climatic influences are less apparent on civilized people than on savage tribes; for the former have developed world-wide commerce, and thus gather supplies from all parts of the earth; while the latter know little or nothing 350 ELEMENTARY PHYSICAL GEOGRAPHY of regions away from their own home. Two examples are given in the following paragraphs. The equatorial belt of Africa is in large part a densely- forested wilderness, because of its plentiful rainfall. Tall trees spread their branches aloft, shading the ground all the year witli their heav}^ foliage. Vines and creepers climb the trees and hang from bough to bough in great festoons, and the shady and damp ground is covered with a thick growth of bushes with stems and branches so closely interlaced that it is almost impossible to make one's way through them without cutting a passage. Even the wild animals of the forest go and come by paths that they keep open by fre- quent passing. Objects near at liand are hidden from sight; the explorer cannot tell what is ahead of him in the gloom of the forest until he is close upon it. Vegetation is here so luxuriant that it is a burden upon the people who live amid its abundant growth. Some of the savages of this great forest are Dwarfs, from three to four and a half feet in height. They wear little clothing, for the air about them is always warm. They do not try to malce clearings and to cultivate fields, but search out the more open parts of the forest and build their villages where the undergrowth is least dense. They have some trade with other tribes, but live chiefly by hunting wild game, which is plentiful. Although entirely ignorant of many simple arts practiced by peo[)le of more open countries, the Dwarfs are expert in all the ways of forest life. They can travel (i[uickly through the woods, know- ing all the paths and open places. They protect their villages from the attack of neighboring tribes by planting THE DISTlillU'JMON OF ORCANIC FORMS 351 sharpened stakes in the paths of appicKUjh. 'I'liey dig pit- falls in the narrow forest paths, covering them with sticks and leaves, and in this way capture even the larger wild animals. They prepare a poison from certain plants and b'irairie states depend. Success in warfare lias often been influenced directly or indirectly by geographical factors. The size of an army is largely the consequence of such factors as the area, form, climate, and fertility of the country to which it belongs; the strength of the less civilized nations has therefore often been measured by the number of their warriors. The character of soldiers is largely dependent on the habits of the community from which they are enlisted. Regiments of infantry recruited from among mountaineers have always been famed as fighting men, for they have learned endur- ance and courage from the severe conditions of life in their rugged homes. Regiments of cavalry recruited from dwellers on grassy plains are famous as "rough-riders," whether they are Russian Cossacks or American cowboys ; their skill and endurance as horsemen are a natural result of habits developed in an open country of large distances, where riding is as appropriate a means of going about as walking is in a mountainous district. What exami)le can you give of a people whose home favored their becoming skillful sailors, and who thereby became invaders and con- querors of other lands? (See page 321.) The fate of battle fields has been many a time determined by the arrangement of high and low ground; hence an intimate knowledge of land forms and of local geography is of great importance to military commanders. During the recent war in South Africa the Boers, having an 370 ELEMENTARY PHYSICAL GEOGUArHY accurate acquaintance with their country, often occupied the crests of hills, and thus gained advantage over the British soldiers, who had to make attack while climbing up a slope from lower ground. What can you learn about the Spartans at Thermopylse ? What can you tell of Braddock's defeat V 209. Geographical Factors favoring the Development of Great Britain. — The progress and prosperity of a nation are even more dependent in peace than in war on the advantage that its people have learned to take of their surroundings. West of continental Europe, in the latitude of Labrador, there is an island whose climate is remarkably mild, because it is on the leeward side of an ocean across which the sur- face waters and the winds move obliquely poleward from warmer latitudes. The island is therefore fertile and has long been noted for its agricultural products. The narrow strait by which it is separated from the continent has served as a natural fortification against the armies of neighboring nations ; nearly a thousand years have passed since the island has been successfully invaded. It has rich mines of coal and iron, and these natural products have been skill- fully used in promoting manufactures of the most diversi- fied kinds. It has excellent harbors, and many of its people have therefore been fishermen and sailors ; its navigators have crossed the most distant oceans and have developed a world- wide commerce. As the population of the island increased under all these favoring conditions, many of its people emigrated to the new lands discovered by its explorers THE DISTRIBUTION OF ORGANIC FOiaiS 371 and founded colonies in them; and to-day the sun never sets on the island's possessions. The empire thus established is the most widespread that the world has ever seen. 210. The United States. — A more modern instance of the dependence of prosperity on geographical elements is seen in the rapid growth, as a world power, of a young nation whose center of population now lies in a region where the winter is so severe that provision must be made for it, yet where the summer warms a fertile soil from which industry secures provision in plenty and to spare ; where open plains and great rivers made it easy for new settlers, to enter the country, and where the small relief of the surface favored the construction of the numerous rail- roads demanded by growing traffic, yet where the variety of form is sufficient to promote diversified industries; where the products of forest and mine are added to those of the farm, and where these excellent conditions are spread over so extensive an area that abundant opportunity is offered for a vast population. Yet these favoring conditions have not been in them- selves sufficient for the growth of a powerful nation. The aboriginal inhabitants of this great land were savages who did not know how to develop its riches. The entire teil'itory remained a wilderness until it was entered by the descendants of a race that had, by long occupation of another highly favored region, gained a leading position among the peoples of the Old World. But these members of the leading race of the Old World would not have left their homes for a new country, however 372 ELEMENTARY PHYSICAL GEOGRAPHY favorable its geographical features, if its government had been tyrannical and oppressive. It is therefore not local geographical factors alone that have so soon given this young nation a giant's strength, but three highly favoring conditions combined: a land well situated, of great extent, and rich in many forms of natural wealth ; numerous immigrants from the leading race of the Old World; and a liberal form of government under which the highest opportunity is open to every citizen. Let us remember that " it is excellent to have a giant's strength, but tyrannous to use it like a giant." QUESTIONS Sec. 191. How have geographical conditions affected man's prog- ress ? Illustrate this by the use that has been made of the winds ; of waterfalls ; of flood plains ; of terrestrial magnetism ; of coal and iron. Give some examples of the effects of geographical conditions on the distribution of plants ; of animals ; on man's way of living. 192. How is it known that the earth has long been inliabited? What barriers prevent the spread of organic forms? Contrast the spreading of plants having heavy and light seeds. In what way do corals and mussels resemble certain land plants? How have free- moving animals been distributed ? Contrast the distribution of walking and of flying birds. How is the rotation of the earth shown to be a factor in the distribution of certain birds ? 193. How is the number of plants or animals in a region limited? How does man sometimes cause a change in these numbers? Why do plants and animals tend to increase in number? Why does their number not increase ? Explain the phrases " struggle for existence " ; " survival of the fittest " ; " natural selection." Upon what does the chance of sm-vival depend? Illustrate by examples from sea animals. What effects follow from the illumination of THE DISTRIBUTION OF ORGANIC FORMS 373 the earth from the sky? Give some examples of protection gained by living in out-of-the-way places. 194. Compare ancient and modern plants and animals. How have variations in plants and animals been caused? Illustrate by changes in a coastal plain ; in mountains ; in climate. 195. Name one of the strongest contrasts of geographical con- ditions. What proof can be given of the great age of the continents and oceans ? What consequences follow from the greater density of water than of air ? Contrast the conditions of the sea bottom with those of the lands. State some results of these contrasted conditions. What can you tell about the warm-blooded animals of the sea? ^Vhy are they believed to be descended from land animals ? Give examples of the remarkable instincts of certain land animals. 196. How are the several continents arranged ? Over what region are similar land plants and animals found ? Name some examples. Name some of the animals and plants of the lower northern lati- tudes in the Old and in the New Worlds. What is inferred from their differences ? Name some of the animals of the three southern continents. Why are mammals not found in Australia ? Name some animals and plants native to one part of the woi'ld and thriving in another part. 197. How has mankind been divided into races? In what ways do the races differ ? Describe the races of Eurasia ; of America ; of Africa ; of Australia. How are the races now distributed ? 198. What forms of life are found on continental islands ? What is inferred from this? How have these islands been separated from the mainland ? Illustrate by the cassowaries ; by mammals and marsupials on the islands between Asia and Australia. What forms are found on oceanic islands? What is the origin of the names Azores and Galapagos? 199. How does climate control the distribution of plants? Illus- trate by the palm (see Figure 112), by cotton, corn, and wheat. What is the vegetation of the northern treeless belt? How does climate control the distribution of animals ? Give examples. How does the 374 ELEMENTARY PHYSICAL GEOGRAPHY distribution of plants control that of animals? Give examples froiri North and South America. 200. Name some direct and some indirect effects of climate on man. Why are climatic influences more apparent on savage tribes than on civilized peoples? Describe the conditions prevailing in the forests of equatorial Africa. Describe the life of the Dwarfs of these forests. Explain the relation between their life and their environment. Do the same for Greenland and the Eskimos. What general truth do these examples illustrate ? 201. Give an example of the effects of the change of seasons on plants in the torrid zone ; in the north temperate zone. What are annxial plants? Name several ways in which animals survive the winter. How does the oblique position of the earth's axis affect the life of plants and animals ? How does change of season affect man's way of living ? Give examples from the Caspian steppes ; from Algeria. Of what advantage has winter been in the development of civilization? 202. How does climate vary on mountains ? Desci'ibe the changes of vegetation seen on ascending a mountain. AV'hat is the tree line? the snow line? What are Alpine plants? In what lowland region are the plants of high mountains found? What may be learned from the distribution of the ibex? Give a similar example from the mountains of New England. 203 . How have mountain valleys been used by defeated peoples ? Give an example from the Pyrenees ; from the Caucasus. Why is life more difficult in mountains than on plains ? Name some of the customs of mountaineers. 204. Mention some of the features of desert vegetation. What is the effect of rain in a desert ? Describe the conditions of gi-owth of desert plants. What can you say of desert animals ? 205. Describe the inhabitants of deserts ; the conditions of life in the Sahara ; the Indians of the Sonoran region. 206. What are oases? What controls their location ? Why are deserts barren? Describe the oasis of Siwa. Describe the Nile THE DISTRIBUTION OF ORGANIC FORMS 375 valley. To what are its floods due ? Of what value are they ? How is their value to be increased? 207. Where are the simplest examples of the relation of man and nature found? Why are civilized people less dependent than savages on natural conditions? How have civilized people been affected by geographical conditions? Give examples. What are anchor draggers? Show that savages are dependent on immediate surroundings and on individual work. Show that civilized people are often dependent on distant su^jplies and on the work of many men in many trades. 208. What geographical factors have affected the historical "levelopment of North America? How were the boundaries of the smaller northeastern states determined? Show that the character of soldiers and their success in warfare are dependent on geographical conditions. 209. 210. Describe the geographical factors that have favored the development of Great Britain. What favorable factors are found in the United States? What other factors have contributed to our national growth ? APPENDIX EEFEKEXCES FOR SUPPLEMENTARY READING The titles in the following list have been selected with especial refei-ence to their accessibility in public libraries. Mention is made of the publications of the U. S. Geological Survey because of their great A^alue to the geographer as well as of their wide distribution. Numbers preceding certain refei'ences indicate the page of this book to which the articles cited pertain. GENERAL REFERENCES Gannett, The United States, Stanford's Compendium of Geography, Edward Stanford, 1898. The International Geography. D. Appleton & Co., 1899. Annual Reports, Bulletins, Monographs, and Geological Folios of the U. S. Geological Survey. Some of the more geographical essays are referred to below (abbrev., G. S. Ann. Rep., etc.). The following geographical periodicals contain much material serviceable in teaching : National Geographic Magazine, Washington, D. C. (abbrev., N. G. M.). Bulletin of the American Geographical Society. New York (B. A. G. S.). Journal of School Geography, Lancaster, Pa. (-F. S. G.). Bulletin of the American Bureau of Geography, ^Vinona, Minn. (B. A. B. G.). (The two preceding periodicals are united, since .January, 1902, under the title, The Journal of Geography .) Geographical Journal, London (G. J.). Scottish Geographical Magazine, Edinburgh (S. G. M.). 377 378 ELEMENTARY PHYSICAL GEOGRAPHY Platt, The, Better Books in School Geography, J. S. G., II, '98, 181. (All the books mentioned in the above article would be found serviceable in school libraries.) Mill, Hints to Teachers and Students on the Choice of Geographical Books. Longmans, Green & Co. Davis, The Equipment of a Geographical Laboratory. J. S. G., II, '98, 170. Cornish, Laboratory Work in Elementary Physiogi-aphy, J. S. G., I, '97, 172, 204. National Geographic Monographs, American Book Co., 1895 (N. G. Mon.). Preliminary Report of Committee on Physical Geography of N. E. A. ; J. S. G., II, '98, 248. CHAPTER L THE EARTH AS A GLOBE Young, Astronomy. Ginn & Company, 1888. Todd, Astronomy. American Book Co., 1897. ScHOTT, The Earth's Shape and Size, N. G. M., XII, '01, 36. CHAPTER II. THE ATMOSPHERE Waldo, Elementary Meteorology. American Book Co., 1896. Davis, Elementary Meteorology. Ginn & Company, 1894. Jameson, Elementary Meteorology, J. S. G., II, '98, 2. Greely, American Weather. Dodd, M- a 1 & Co., 1888. Ward, Practical Exercises in Elementary Meteorology. Ginn & Company, 1899. Ward, Equipment of a INIeteorological Laboratory. J. S. G., Ill, '99, 241. Bartholomew, Physical Atlas, Vol. TTI, Meteorology. Lippincott. PAGE 63. Illustrated Cloud Forms, U. S. Hydrographic Office, Washing- ton, D.C. 67. Gakkiott. West Indian Hurricanes, X. G. M., X, '99, 17, 343 ; XI, '00, 384. APPENDIX 379 PAGE 72. (treely, Rainfall Types of the United States, N. G. M., Y, '93, 45. 72. Harrington, Rainfall of the United States, U. S. Weather Bureau, Bulletin C, 1894. 72. fxANNETT, Redwood Forest of the Pacific Coast, N. G. M., X, '99, 145. 84. Davis, The Temperate Zones, J. S. G., I, '97, 139. 84. Ward, Climatic Control of Occupations in Chile, J. S. G., I, '97, 289. 87. Davis, Practical Exercises in Geography, N. G. M., XI, '00, 62. CHAPTER III. THE OCEAN Thomson, The Depths of the Sea. Macmillan & Co., 1874. Thomson, The Voyage of the Challenger : The Atlantic. Macmillan & Co., 1877. SiGSBEE, Deep Sea Sounding and Dredging, Washington, 1880. Tanner, Deep Sea Exploration, U. S. Fish Commission,Washington. Agassiz, Three Cruises of the Blake, Cambridge, 1888. Monthly Pilot Charts of the North Atlantic and the North Pacific Oceans, U. S. Hydrographic Office, Washington. Semple, The Atlantic and Pacific Oceans, J. S. G., Ill, '99, 121, 172. PAGE 109. Davis, AVaves and Tides, J. S. G., II, '98, 122. 113, Scidmore, Earthquake Wave, Japan, N. G. M., YII, '95, 285. 114. Davis, Winds and Ocean Currents, S. G. M., XIII, '97, 55, and J. S. G., II, '98, 16. 118. PiLLSBURY, The Gulf Stream, Ann. Rep. U. S. Coast Survey, 1890. 119. Tide Tables, published annually by I'. S. Coast Survey. 121. Jefferson, Atlantic Estuarine Tides, N. G. M., IX, '98, 400 ; also 497. 380 ELEMENTARY PHYSICAL GEOGRAPHY CHAPTER IV. THE LANDS Shaler, Aspects of the Earth. Charles Scribner's Sons, 1889. J. Geikie, Earth Sculpture. G. P. Putnam's Sons. Text-books on Elementary Geology, by Dana, Geikie, Leconte, Scott, Tarr, and Brigham. Shaler, Origin and Nature of Soils, G. S. 12th Ann. Rep., Pt. I, 219. Patterson, Work of the Water Giant, J. S. G., Ill, '99, 5. CHAPTER V. PLAINS AND PLATEAUS PAGE 142. Davis, Description of the Harvard Geographical Models, pub- lished by the Boston Society of Natural History, Berkeley Street, Boston. Figures 60, 62, and 104 are taken from these models. 148. Glenn, South Carolina, J. S. G., II, '98, 9, 85. 149. Cobb, North Carolina, J. S. G., I, '97, 256, 300. 156. Abbe, Maryland, B. A. B. G., I, '00, 151, 242. 156. McGee, Chesapeake Bay, G. S. 7th Ann. Rep., 548. 157. McGee (Fall Line), G. S. 12th Ann. Rep., 360. 158. Hatcher, Patagonia, N. G. M., XL '00, 41. 158. Johnson, High Plains, N. G. M., IX, '98, 493 ; G. S. 21st Ann. Rep., 601. 159. Fenneman, Climate of the Great Plains, J. S. G., Ill, '99, 1, 46. 161. Collie, Physiography of Wisconsin, B. A. B. G., II, '01, 270. 166. Powell, Exploration of the Colorado River of the West, Washington, 1875. See pp. 98-102, 130, 131. 166. Powell, Canyons of the Colorado. Flood & Vincent, Mead- ville, Pa. 166. DuTTON, Colorado Canyon, G. S. 2d Ann. Rep., 40; G. S. Monogr. II. 168. Campbell and Mendenhall (Plateau of West Virginia), G. S. 17th Ann. Rep., 480. 168. Roosevelt, Winning of the West, I, 101 ; III, 13. G. P. Put- nam's Sons, 1894. APPENDIX 381 PAGE 168. Semple, Influence of the Appalachian Barrier upon Colonial History, J. S. G., I, '97, 3:3. 172. Hodge, The Enchanted Mesa, N. G. M., VIII, '97, 273. CHAPTER VI. MOUNTAINS 178. Russell, Southern Oregon, G. 8. 4th Ann. Rep., 435. 181. Russell, Mountains of Nevada, G. S. Monogr. XI, 38. 185. Fay, Canadian Alps, J. S. G., I, '97, 160. 185. WiLLCOX, Canadian Rockies, J. S. G., I, '97, 293 ; also N. G. M., X, '99, 113. 197. Lubbock, Scenery of Switzerland. Macniillan & Co., 1896 (p. 124). 201. Milne, Earthquakes. D. Appleton & Co., 1883. 205. Willis, Round about Asheville, N.C., N. G. M., I, '89, 291. 205. A. Geikie, Scenery of Scotland, 2d ed. (chapters on High- lands). Macmillan & Co., 1887. 205. Herbertson, Geography of Scotland, J. S. G., II, '98, 161. 206. McGee, Geographical History of the Piedmont Plateau, N. G. M., YII, '96, 261. 206. Keith, Piedmont Plateau, G. S. 14th Ann. Rep., 366. 208. Davis, Southern New England, N. G. Mon. 208. Davis, Geographical Illustrations (Southern New England), published by Harvard University, Cambridge, Mass. 210. Willis, Northern Appalachians, N. G. i\Ion. See also B. A. B. G., I, '00, 342-355. 210. Hayes, Southern Appalachians, N. G. Mon. 210. Hayes, Physiography of the Chattanooga District, G. S. 19th Ann. Rep., Pt. II, 1. 210. Davis, Rivers and Valleys of Pennsylvania, N. G. M., I, 183. CHAPTER VII. VOLCANOES Russell, Volcanoes of North America. Macmillan, 1897. Dana, Characteristics of Volcanoes. Dodd, Mead & Co., 1890. 382 ELEMENTARY PHYSICAL GEOGRAPHY JuDD, Volcanoes. D. Appleton & Co., 1881. Dodge, Volcanoes, J. S. G., I, '97, 179 ; IV, '00, 350. PAGE 218. Lyell, Principles of Geology (Monte Nuovo, I, 607; JoruUo, I, 58.5). -D. Appleton & Co., 1872. 219. DiLLER, A Late Volcanic Eruption in Northern California, G. S. Bull. No. 79. 221. Phillips, Vesuvius. Macmillan & Co., 1869. 221. Milne, Earthquakes. D. Appleton & Co., 1883. 222. Diller, Crater Lake, N. G. M., VIII, 33. 222. Diller, Crater Lake, J. S. G., I, '97, 266. 226. Moore, The Active Volcanoes North of Kivu (Central Africa), G. J., XVIT, '01, 11. 227. DuTTON (Lava Flows), G. S. Monogr. II. 227. DuTTON, Hawaiian Volcanoes, G. S. 4th Ann. Rep., 81. 229. Diller, Mt. Shasta, N. G. Mon. See also B. A. B. G., I, '00, 260. 231. Hayes, Physiography of the Nicaragua Canal Route, N. G. M., X, '99, 233. CHAPTER VIII. RIVERS AND VALLEYS Russell, Rivers of North America. G. P. Putnam's Sons, 1898. PAGE 235. Hovey, Celebrated American Caverns. Clarke, Cincinnati. 235. Hovey, Mammoth Cave, J. S. G., I, '97, 133. 236. Walcott, Natural Bridge of Virginia, N. G. M., V, '93, 59. 238. Chamberlin, Artesian AVells, G. S. 5th Ann. Rep., 125. 239. Weed, Hot Springs, G. S. 9th Ann. Rep., 613. 247. Bell, The Labrador Peninsula, S. G. M., XI, 335. 251. Gilbert, Niagara, N. G. Mon. 260. Davis, Seine, Meuse, and Moselle, N. G. M., VII, '97, 189, 228. 264. Gannett, The Flood of April, 1897, in the Lower Mississippi, S. G. M., XIII, '97, 419. 266. Fairbanks, Physiography of California, B. A. B. G., IT, '01, 232, 329. APPENDIX 383 CHAPTER IX. DESERTS AND GLACIERS I'AGE i'78. Marbut, Missouri, J. S. G., I, '97, 110, 1-14. 280. Platt, The Sahara, J. S. G., IV, '00, 255. 282. King, Geological Survey, 40th Parallel, AVashington, I, 400, 484 ; II, 470. 282. McGek, Seriland, N. G. M., VII, '97, 125. 284. Russp:ll, Past and Present Lakes of Nevada, N. G. Mon. 286. Davis, A Temporary Sahara, J. S. G., IV, '00, 171. 288. Gilbert, Lake Bonneville, G. S. 2d Ann. Rep., 169. 288. Gilbert, Lake Bonneville, G. S. Monogr. I. 289. Russell, Lake Lahontan, G. S. 3d Ann. Rep., 195. 290. Holder, A Remarkable Salt Deposit, N. G. M., XII, '01, 391. 290. Russell, Glaciers of North America. Ginn & Company, 1897. 290. Shaler and Davis, Glaciers. Houghton, Mifflin & Co., 1881. 290. Tyndall, Forms of Water. D. Appleton & Co., 1872. 290. J. Geikie, Great Ice Age, 3d ed. D. Appleton & Co., 1895. 290. Wright, Ice Age in North America. D. Appleton & Co., 1890. 291. Arctowski, Exploration of Antarctic Lands, G. J., XVII, '01, 50. 291. Nansen, First Crossing of Greenland, 1890. Longmans, Green & Co., 1890. 291. Peary, Northward over the Great Ice. Frederick A. Stokes Co., 1898. 292. Russell, Glaciers of Alaska, G. S. 13th Ann. Rep., 7. 292. Russell, Mt. St. Elias, Alaska, N. G. M., Ill, 53. 292. Reid, Muir Glacier, Alaska, N. G. M., IV, 19. 292. Reid, Glacier Bay and its Glaciers, G. S. 16th Ann. Rep., Pt. I, 415. 292. Russell, Existing Glaciers of the United States, G. S. 5th Ann. Rep., 303. 295. Russell, Mono Lake Region, G. S. 8th Ann. Rep., Pt. I, 321. 295. Bell, The Labrador Peninsula, S. G. M., XI, 335. 295. A. Geikie, Scenery of Scotland, 2d ed. (chapters on Glacial Action). Macmillan & Co., 1887. 384 ELEMENTARY PHYSICAL GEOGRAPHY PAGE 295. Russell, Geography of the Laiirentian Basin, B. A. G. S., XXX, '98, 226. 296. McGee, Drift Plains of Iowa, G. S. 11th Ann. Rep., 393. 296. Taylor, Studies in Indiana Geography, Terre Haute, 1897. (" Short History of the Great Lakes.") 296. Gilbert, Modification of Great Lakes by Earth Movement, N. G. M., YIII, 233. 297. Chamjberlin, Rock Scorings, G. S. 7th Ann. Rep., 155. 297. Chamberlin, Terminal Moraines, G. S. 3d Ann. Rep., 295, 297. Todd, Terminal Moraines in Dakota, G. S. Bull. No. IM, 16. 297. Dryer, Studies in Indiana Geography, Terre Haute, 1897. The Morainic Lakes of Indiana. 297. Leverett, The Illinois Glacial Lobe, G. S. Mon., XXXVIIL 299. Upham, Glacial Lake Agassiz, G. S. Monogr. XXV. 300. Gannett, Lake Chelan, N. G. M., IX, '98, 417. 300. Tarr, Lakes and Swamps of New York, B. A. G. S., XXXI, '99, 1. CHAPTER X. SHORE LINES 304. Shaler, Sea and Land. Charles Scribner's Sons, 1894. 308. Shaler, Seacoast Swamps of Eastern United States, G. S. 6th Ann. Rep., 93. 308. Shaler, Beaches and Tidal Marshes, N. G. Mon. 310. Gilbert, Features of Lake Shoi'es, G. S. 5th Ann. Rep., 76. 311. Shaler, Natural History of Harbors, G. S. 13th Ann. Rep., 93. 317. A. Geikie, Scenery of Scotland, 2d ed. (chapter on Shore Features). Macmillan & Co., 1887. 324. Darwin, Coral Reefs. D. Appleton & Co., 1889. 324. Dana, Corals and Coral Islands. Dodd, Mead & Co., 1890. 324. A. Agassiz, Letter in Am. Journ. Science, Feb., 1898. APPENDIX 385 CHAPTER XI. DISTRIBUTION OF PLANTS, ANIMALS, AND MAN PAGE 333. Hkilpkin, Distribution of Animals. D. Appleton & Co., 1886. 333. Beddard, Zoogeography. University Press, Cambridge, 1895. 333. MacMillan, Geographical Distribution of Plants, J. S. G., April, '97. 345. BuiNTON, Races and Peoples. 346. Wallace, Island Life. Macmillan & Co., 1891. 347. Wallace, Travels in the INIalay Archipelago. Macmillan * & Co., 9th ed. 348. Merriam, Geographical Distribution of Terrestrial Animals and Plants, N. G. M., VI, 229. 355. Gannett, The Timber Line, B. A. G. S., XXXI, '99, 118. 363. Jenxings-Bramley, A Journey to Siwa, G. J., X, '97, 597. 386 ELEMENTARY PHYSICAL GEOGRAPHY REFEEEXCES FOR MAPS The following list of map sheets, selected chiefly from those pub- lished by the U. S. Geological Survey and the U. S. Coast and Geo- detic Survey, will be found of service in illustrating various examples of land forms referred to in Chapters V to X. Complete lists of maps published by these Surveys can be had, free of charge, on application. The sheets here named might be supplemented by many others in illustration of special localities. Some account of the cost and of the method of ordering and using the maps is given in the Journal of School GeogTaphy, September, 1897, and October, 1898. Coast Sur- vey maps are here marked " C. S." The others, unless specially des- ignated, are published by the Geological Survey. Numbers preceding tlie names indicate the pages of this book to which the maps refer. CHAPTER V. PLAINS AND PLATEAUS I'AGE 1.52. Relief Map of New Jersey, published by the State Geological Survey, Trenton, N.J. ; price, 25 cents. 154. Nomini, Md. 159. Topographic Atlas of the United States, folio 1, Physiogi-aphic Types, Pis. I-III. 164. Mt. Trumbull, Diamond Creek, Ariz. 168. Kanawha Falls, Nicholas, W. Va. 172. Watrous, Corazon, N.M.; Abilene, Brownwood, Tex. 174. Mt. Trumbull, Kaibab, Echo Cliffs, Ariz. CHAPTER VI. MOUNTAINS 181. Disaster, Nev. ; Altm-as, Cal. 186. Platte Canyon, Huerfano Park, Col. 204. Asheville, Mt. Mitchell, Pisgah, N.C. 207. Atlanta, Ga. (Stone mountain is a fine example of a monad- nock on the uplands of Georgia.) APPENDIX 387 PAGE 208. Chesterfield, Granville, Mass.; "Winsted, Derby, Bridgeport, Conn. 210. Harrisburg, Hunimelstown, Lykens, Pa. 211. C. S. No. 710. CHAPTER VII. VOLCANOES 222. Crater Lake (special sheet), Oregon. 230. Shasta, Cal. ; San Francisco Mountain, Ariz. CHAPTER VIII. RIVERS AND VALLEYS 247. Citra, Fla. 251. Niagara Falls (special map). 256. Mesa de Maya, Col. 261. Donaldsonville, La. 264. 8-Sheet Map of the Alluvial Valley of the Mississippi River, published by the Mississippi River Commission, St. Louis, Mo. 264. Preliminary Maps of the Mississippi River, published by the Mississippi River Commission, St. Louis, Mo. Edition of 1900. 268. C. S. No. 194, Mississippi Delta. 271. Versailles, Tuscumbia, Mo. 273. Delaware Water Gap, Pa. ; Harpers Feriy, Va. CHAPTER IX. DESERTS AND GLACIERS 281. Disaster, Granite Range, Long Valley, Nev. 299. Oconomowoc, Sun Prairie, "Wis. 301. Elizabethtown, Mt. Marcy, N.Y. 302. Rochester, N.Y. ; Minneapolis, Minn. 388 ELEMENTARY PHYSICAL GEOGRAPHY CHAPTER X. SHORE LINES PAGE 308. C. S. Nos. 121, 122, 123 (New Jersey coast). 311. C. S.Nos. 103, 104, 105 (Maine coast). 313. C. S. Nos. 108, 109 (Massachusetts coast). 316. C. S. No. 674 (California coast). 322. C. S. Nos. 8100, 706 (Alaska coast). 323. C. S. No. 21 (Texas coa.st). INDEX Adirondacks, 301. Africa, 55, 325, 343, 346, 350. Agriuulture, 43, 52, 169, 2-30, 297, 330, 354, 364, 370, 371. and irrigation, 56, 71, 159, 362. and soil, 150, 206, 269, 278, 287, 296, 363. Air, 15, 23, 24, see Atmosphere. Alabama, 167. Ala.ska, 119, 212, 292, 299, 316. Allegheny mountains, 210, 273. plateau, 167, 243, 256, 271. Alluvial fans, see Fans. Alps, 185, 192, 203, 261, 299. ■ glaciers of, 292, 295. Amazon, 41, 56, 121. Andes, 27, 41, 189, 190, 231. Anemometer, 38. Animals, in caves, 236. and climate, 335. • on deserts, 360. distribution, 332, 348. on islands, 330, 346. on mountains, 26, 169, 355. -in ocean, 100, 105, 122, 124, 338. Antarctic ocean, 96, 104, 116. regions, 96, 129, 291. Anticyclones, 46, 75, 77, 78, 80. Aphelion, 12. Appalachian mountains, 239, 369. Arctic ocean, 96, 116, 130. regions, 103, 336, 342. Argentina, 139, 190. Arid regions, 180, 280, see Deserts. Aristotle, 2. Arizona, climate, 71, 74. plateaus, 165, 172. volcanoes, 226, 230. Artesian wells, 238. Asia, 129, 343, -345, 346. Atlantic ocean, 80, 84, 96, 100, 104, 115, 130, 226, 367. Atmosphere, 23. circulation, 35, 40, 59, 304. color, 27, 76, 225. composition, 24. convection, 36, 60, 63. currents, 36, 62, 67. density, 26, 27. ■ elasticity, 26. height, 15, 23. humidity, 60. pressure, 24, 90. properties, 15, 23, 29. saturation, 61, 63, 64. • weight, 26. Atolls, 328. see Reefs. Augusta, 158. Aurora, 18. Australasia, 131, 346. 389 390 ELEMENTARY PHYSICAL GEOGRAPHY Australia, 50, 56, 71, 130, 343, 346. Avalanches, 192. Azores, 348. Bad lands, 283. Baltimore, 156. Banks, 109. Barometer, 25. Barriers, 167, 170, 189, 256, 333. Baselevel, 145, 255. Basin, interior, 283, 288. river, 241. rock, 296, 300, see Lakes. waste-filled, 284, see Waste. Basques, 357. Bays, 119, 121, 156, 211, 314. Beach, 112, 307, 308, 313, 320. Beavers, 341. Bench, 200, 312, 327. Bengal, Bay of, 69, 72, 268. Bering Strait, 130. Birds, 52, 334, 339, 341, 354. Black mountains, 301. Blizzard, 78, 81. Blue Ridge, 205. Bluff, 308, see Cliff. Boers, 369. Bolivia, 290. Bore, 121. Boundaries, 11, 190, 368. BoAvlders, 298. Brahmaputra, 268. Brazil, 41, 68, 325, 366. Brickfielders, 81. Bristol channel, 121. British Columbia, 84, 212. British Isles, 107, 119, 370. Buenos Aires, 307. Buffaloes, 160. Buran, 81. Butte, 171. Cairo, 263, 363. Caldera, 221. California, climate, 55, 71, 73. coast, 143, 314. ■ fans, 267. moraines, 295. mountains, 178, 181. valley, 265, 266. volcanoes, 219. Calms, 43, 44, 54, 56, 57. Camden, 158. Camel, 248, 360. Canada, 85, 133, 255, 292, 295, 300, 302. Canals, 232, 248, 320. Canoes, 248, 322, 352. Canyons, 162, 164, 166, 282. Cape Cod, 138. Cape Horn, 81, 118, 191. Cape of Good Hope, 81, 118. Carbon, 24. Carbonic dioxide, 24. Cardinal points, 7. Caribbean sea, 106. Caribou, 342. Cascade mountains, 73. Cassowary, 347. Catskill mountains, 167. Caucasus, 185, 292. Caverns, 235. Central America, 106, 226, 231. Ceylon, 83. Charleston, 158, 238. Chesapeake bay, 156, 238, 368. Chicago, 369. Chile, 56, 190, 280. INDEX 391 China, 189, 269, 287, 345. Chinese, 345, 346. Chinook wind, 189. Cinder cone, 219. Circles, 9. Cirrus, 63. Cities, 156, 157, 158, 209, 253, 270, 297, 302, 368. Civilization, 4, 84, 139, 170, 332, 345, 355, 364, 370, 371. Clay, 139, 152, 366. Cleopatra's Needle, 135. Cliff dwellers, 167. Cliffs, 163, 166, 167, 171, 173, 174. sea, 305, 310, 314, 316, 318. Climate, 56, 59, 82, 102, 135. and animals, 348, 354. and land forms, 278, 283. and man, 84, 349. and plants, 83, 348, 353. and shore lines, 323. changes of, 288, 318, 338. dry, 135, 159, 180, 281, 359, 362. glacial, 290. of lands, 83, 133, 284. of mountains, 71, 183, 188, 189, 353. — of oceans, 52, 83, 84, 102. of plains, 71, 188, 189. of plateaus, 165. Cloudbursts, 66, 166, 234, 282. Clouds, 37, 39, 44, 62. Coal, 139, 170, 366. Coastal plains, 143, 147, 158. ancient, 161. Atlantic, 148, 155, 158, 170. belted, 150. embayed, 154. Coasts, 107, 141, 211, 288, 304, 305, 308, 316, 325, -368. Cold wave, 78, 81. Colorado, 188, 226, 282, 294. Colorado canyon and river, 165, 166, 337. Columbia, 157, 158. Columbia river, 198, 229. Commerce, 5, 97, 349, 364, 370. Compass, 18. Condensation of vapor, 16, 39, 62. Conduction, 28, 31, 61. Cones, 219, 220, see Volcanoes. Connecticut, 208, 368. Connecticut river, 209. Conseguina, 223. Continental divide, 198, 232, 243. Continental shelf, 107, 133. Continents, 58, 129, 132, 341, 345. Contours, 222. Convection, 36, 60. Coral reefs, see Keefs. Corn, 76, 343, 348. Corona, 64. Cotopaxi, 223. Cotton, 148, 149, 348. Crater, 218, 221. Cuba, 106, 318, 325, 328, 366. Cuesta, 153. Cumberland plateau, 167. Cumulus, 63. Currents, 114, 116, 118, 119, 120, 122, 306, 308. Cj'clones, 46, 63, 67, 75, 80, 81. Day and night, 7, 13, 28, 48. Dead sea, 284, 285. Deception island, 221. Deerfield river, 209. 392 ELEMENTARY PHYSICAL GEOGRAPHY Degrees, 9, 10. Delaware, 368. Delaware bay and river, 152, 155, 269, 273, 368. Deltas, 138, 212, 267, 269, 321, 322. in lakes, 250, 267, 289. Denudation, 137, see Erosion. Denver, 282. Deposition of waste, 108, 137, 265, 267, 283, 287. Deserts, 30, 41, 71, 133, 278, 280, 286, 288, 359. Dew, 61, 62. Dikes, 132, 266, 308, 322. Distributaries, 268, 322. Distribution of life, 332. Divides, 190, 198, 242, 243. Doldrums, 43, 44, 56, 60, 65, 67, 68. Drainage, 168, 180, 2-34, 243, 248, 270,-284. Drift, glacial, 296, 300, 302. • of ocean, 116, 117. Drought, 76, 236, 244, 359. Drumlins, 299. Dunes, 136, 287, 308, 309. Dust, 286, 287. Dwarfs, 350. Earth, 1, 332. age, 17. area, 129. astronomic relations, 11, 12, 14, 46. attraction, 5, 17, 24. axis, 6, 354. crust, 16, 132, 137, 177. interior, 15, 16. proofs of shape, 2, 3, 19. revolution, 11, 46, 48, 49, 87. Earth, rotation, 6, 7, 19, 36, 57, 85. shape and size, 1, 3, 4, 6. structure, 15. Earthquakes,175, 180, 182, 201, 217, 218, 224. Earthquake waves, 113, 114. Eclipse, 2. Ecuador, 223. Eddies, 115, 117. Egypt, 135, 363. Electricity, 19, 65, 253. Enchanted mesa, 172. England, 1.39, 162, 242, 314. Equator, 9, 29, 36, 102. heat, 35, 40, 49, 67, 83. sky, 89. Equatorial calms, 43, 57. rains, 54, 56, 72, 74, 83. Equinox, 88. Erosion, 137, 185, 245, 308, 311. glacial, 294, 299, 320. Eruptions, 219, 223, 225, 227, 231. Escarpment, 173. Eskimos, 103, 292, 324, 352. Estuaries, 121. Eurasia, 50, 129, 345, 356. Europe, 55, 72, 81, 84, 104, 129, 345, 346. Exercises, 4, 8, 10, 12, 35, 42, 45, 50, 51, 53, 61, 75, 83, 85, 87, 90, 115, 259, 260, 261, 264. Fall line, 157, 158. Falls, 157, 247, 248, 251, 299, 302. Famines, 266. Fans, 179, 197, 265, 267, 268, 283. Faults, 174. Fertilizers, 150, 152, 330. Fiji islands, 68, 99. INDEX 393 Fingal's cave, 312. Fiords, 212, 320, 322. Fire, 24. Fish, 16, 100, 335, 336, 339. Fisheries, 109, 124, 156, 212, 320. Floe ice, 102, 117. Flood plains, 258, 261, 264, 268, 270, 363. Floods, 194, 244, 250, 256, 264, 266, 281, 282. and lakes, 194, 250. sea, 69, 308. Foehn wind. 189. Fog, 64. Forests, 149, 159, 168, 170, 348. effects of, 236, 310, 350. on mountains, 41, 43, 187, 189. 192. 204, 205, 355. Fort Wayne, 320. Fossils, 108, 133, 161, 183, 185, 338, 337. France, 310, 311, 313. Frigid zone, 29, 75, 80. Frost, 61, 62, 135. Fundy, Bay of, 121. Galapagos, 119, 325, 348. Gales, 38, 80. Galung-gung, 223. Galveston, 69, 238. Ganges, 195, 268. Gases, 15, 23, 24, 100, 216, 218. Geology, 158. Geosphere, 17. Germany, 272, 295. Geysers, 239. Gibraltar, 106, 315. Glacial period, 295, 319. Glacier, 104, 188, 278, 292, 294, 322. Glacier, Alpine, 187, 250, 292, 295. ancient, 294, 299. continental, 290, 295. . — Laurentian, 295. Scandinavian, 296. valley, 292, 294. Glens, 205. Globigerina, 105. Gloucester, 109. Gold, 139, 191. Gorges, 184, 201, 251, 301. Grand canyon, 165. Grand Kapids, 302. Granite, 234. Gravity, 5, 24, 358. Grazing, 56, 71, 74, 160, 181, 294, 354, 359. Great Barrier reef, 327. Great Britain. 370. Great lakes, 248. 284, 295, 319. Great plain.s, 71, 73, 158, 366. Greek philosophers, 3, 19. Greely, 103. Greenland, 104, 291, 321, 335, 351. Greenvyich, meridian of, 10. Ground water, 234, 236, 239, 283, 362. Guam, 99. Guiana, 118, 158, 173. Gulf Stream, 116, 118 Hail, 70. Halo, 63. Harbors, 40, 119, 120, 143, 147, 152, 212, 307, 311, 320, 368. Harrisburg, 274. Hawaiian islands, 106, 325. Headlands, 311, 314. 317. Heat, 24, 28, 30, 46. 394 ELEMENTARY PHYSICAL GEOGRAPHY Height of land, 241, 319. Hell Gate, 122. Hemispheres, 9, 46, 52, 53, 54, 96. Herculaneum, 224. Highlands of Scotland, 205, 318. - Himalayas, 71, 185, 189, 193, 200, 202, 294. History and nature, 170, 205, 321, 357, 361, 367. Hoang-Ho, 265, 268. Horizon, 19. Horse latitudes, 44, 45, 55. Hot springs, 239. Hudson bay, 50. Hudson river, 368. Humboldt current, 118. Humidity, 60. Hungary, 262. Hurricane ledge, 173, 175. Hurricanes, 67, 69, 112. Ibex, 356. Ice, 15, 63, 102, 117, 279, 291, 323. falls, 192. sheets, 290, 291, 294, 319. See Glaciers. Icebergs, 104, 291, 292. Iceland, 226, 227, 239. Idaho, 229. Illinois, 320. India, 72, 189, 194, 269. Indiana, 320. Indian ocean, 58, 68, 69, 96, 115, 226. Indians, 172, 321, 361. Inlets, 152, 308. Instinct, 341. Intelligence, 341. Iowa, 238. Ireland, 116. Iron ore, 139, 170, 366. Irrigation, 56, 71, 159, 265, 362. Islands, 50, 131, 314, 320, 346, 370. continental, 211, 212, 311. coral, 106, 325, 328, 330. oceanic, 106, 131. volcanic, 106, 219, 225, 226, 348. Isobars, 91. Isothermal lines, 33, 35, 48, 50, 53. Italy, 225, 269, 314. Jaguar, 343. Japan, 114, 203, 225, 345. Java, 223. Jetties, 322. Jorullo, 219. Jura, 183, 184. Kanawha river, 169. Kangaroo, 344. Katahdin, Mt., 357. Kentucky, 170, 235. Kittatinny Mountain, 273. Krakatoa, 27, 113, 225. Labrador, 51, 119, 370. Lagoons, 308, 328. Lake Bonneville, 288, 319. Crater, 222. -Erie, 248, 251, 320. Geneva, 250, 207. Great Salt, 284, 288, 290. Lahontan, 289. Lob, 285. Michigan, 320. Nicaragua, 231. Nyassa, 249. INDEX 395 Lake Ontario, 248, 251. — - Superior, 248, 366. Titicaca, 290. Van, 284. Victoria Nyanza, 249. Lakes, 160, 230, 235, 247, 240, 263, 284, ^89, 319. African, 249. glacial, 296, 300. in mountains, 197. -salt, 181, 283. sliore lines, 133, 288, 318. temperature, 102. volcanic, 222, 228, 249. Land and sea breezes, 59. Land hemisiDhere, 96, 129, 341. Lands, 129. — - altitude, 4, 131, 132. area, 129. distribution, 130. features, 133, 141, 177, 256. life on, 338. products, 138. surface, 26, 133, 134, 136. winds on, 59. Land sculpture, 186, see Waste. Landslides, 138, 193, 202. Language, 4, 205, 226, 357. Latitude, 8, 10, 54, 89, 342. Laurentian highlands, 247, 295. Lava, 15, 16, 216, 225, 330. — - flows, 219, 227, 230, 249. — - plateaus, 227, 228, 229. Lawrence, 302. Ledges, 135, 247, 286, 306. Levees, 264. Life, 17, 24, 122, 332. Light, 24, 27, 64, 66, 124. Limestone, 139, 235. Llanos, 344, 353. London, 96. Long Branch, 309. Long Island sound, 208. Longitude, 8. Lowell, 302. Luray cavern, 235. Magellan, 3. Magnetic poles, 18, 19. Magnetism, terrestrial, 17, 332. Maine, 212, 297, Sll', 357. Malay peninsula, 58, 366. Mammals, 340. Mammoth, 134. ISIammoth cave, 235. Man, 1, 189, 204, 345. and nature, 332, see Nature. civilized, 364, see Civilization. ■ in deserts, 360. in mountains, 204, 205, 357. savage, 329, 349, 365, 371, warfare, 369. Manchester, 302. Mangrove, 324. Manufactures, 139, 157, 159, 209, 252, 301, 364, 370, 371. Maps, 386. Marshes, 152, 160, 170, 308. Marsupials, 344. 347. Maryland, 211, 238, 274, 368. Massachusetts, 132, 208, 299. Meander belt, 263. Meanders, 261, 271, 273. Mediterranean, 106, 226. Merced river, 265. Meridians, 8, 9, 10, 11. Merrimac, 302. Mesa, 171, 172. 396 ELEMENTARY PHYSICAL GEOGRAPHY Meteors, 23. Mexico, 41, 146, 226, 280. Gulf of, 74, 107, 118, 322. Mining, 139, 170, 183, 3.33. Minneapolis, 302. Minnesota, 366. Mirage, 30, 286. Mississippi river and valley, 65, 67, 71, 74, 76, 138, 255, 262, 264, 319. delta, 268, 322. flood plain, 264. meanders, 262, 263, 264. Missouri, 271, 278. river, 198. Mist, 64. Mohawk, 258. Monadnock, 207. \ Monsoons, 57, 58, 72. Monte Nuovo, 218. Months, 47, 48, 50. Moon, 2, 13, 124. V Moraines, 293, 295, 297. Mountains, 43, 133, 177. ■" air on, 26, 29. block, 178. buried, 285. climate of, 188. dissected, 181, 196, 301. ■ effects of, 170, 180, 185, 189, 356, 357, 369. embayed, 211. folded, 183, 210. growing, 201, 204. lofty, 27, 185, 188, 196, 204, 355. old, 196, 206, 210. subdued, 204, 301. worn-down, 206. young, 180, 204, 205. Mt. Blanc, 187, 295. Mt. Mazama, 222, 230. Mud volcanoes, 241. Nansen, 103, 117. Narragansett bay, 368. Natural bridge, 236. Nature and man, 170, 204, 205, 321, 332, .357, 361, 364, 367. Navigation, 10, 18, 40, 43, 58, 69, 81, 97, 104, 116, 118, 120, 248, 370. river, 157, 365. Nebraska, 283. Nebular hypothesis, 14. Neckar river, 272. Netherlands, 132, 309, 310. Nevada, 73, 178, 181, 204, 280, 283. New England, 80, 109, 209, 212, 255, 298, 31.3. Newfoundland, 104, 109, 119. New Hampshire, 207, 357. New Jersey, 112, 132, 152, 308, 366, 368. New Mexico, 171, 172, 230. New Orleans, 323. Newton, 6. New York, 239, 258, 301, 360, 368. city, 122, 369. New Zealand, 90, 131. Niagara, 138, 248, 251. Nile, 56, 249, 363. Nimbus, 64. Nitrogen, 24. Nomads, 160. Noon, 7, 8, 88. Norfolk, 156. Normandy, 311, 321. Nortli America, 43, 72, 78, 80, 107, 344, 346. INDEX 397 North Carolina, 74, 148, 150, 205, 318. North Dakota, 298. Northern lights, 18. Northmen, 321. North pole, 9, 18, 36. North Star, 6. Norway, 119, 226, 299, 318, 320. Oases, 361. Occupations, 52, 157, 162, 169, 170, 185, 209, 258, 358, 364, 365, 366, 370, 371. Ocean, 90, 304. action, 107, 112, 121, 305. air, 60, 100. bottom, 98, 105, 123. color, 100. composition, 100. currents, 114, 116, 118. density, 100. depth, 96, 90, 131. distribution, 15. 96, 129, 130. explorations, 3, 98, 103. form, 96. life in? 100, 105, 122, 338. phosphoi'escence, 100, 124. storms, 80. temperature, 28, 98, 101, 107. waves, 109, 111, 113. Ohio, 168, 170. Ohio river and valley, 71, 170, 250. Ooze, 105. Oregon, 146, 178, 182, 204, 229, 249. 0.sage river, 271. Ox-bow lake, 263. Oxygen, 24. Ozark plateau, 278. Pacific ocean, 68, 80, 84, 96, 99, 105, 115, 119, 226, 328. Pacific slope, 43, 72. Pamlico sound, 155. Pampas, 190, 344, 366. Panama, 315, 316. Parallels, 9, 10. Parana, 56. Pass, 190. Patagonia, 190, 292, 318, 321. Peaks, 178, 185, 186, 191, 356. Peneplain, 206, 208, 210, 246. Pennsylvania, 210, 271, 273, 360, 368. Pei'ihelion, 12. Persia, 285. Peru, 60, 71, 359. Peruvian current, 118, 325. Philadelphia, 158. Philippine islands, 3, 69. Piedmont belt, 149, 206, 243, 271. Pikes peak, 356. Pittsburg, 170. Plains, 141, 158, 161, 369. coastal, 143, 147, 150, 154, 269, 307, 318. glacial, 296. river-made, 266, see Flood plains. Planetary circulation, 37, 40. Planetary winds, 39. Planets, 12, 13, 14, 17, 19. distance and diameter, 14. Plants, 24, 52, 83, 235, 341, 346, 353. distribution, 332, 337, 348. in oceans, 123, 124, 338. on deserts, 359, 362. on mountains, 355. 398 ELEMENTARY PHYSICAL GEOGRAPHY Plants on plateaus, 165. Plateaus, 162, 165, 171, 173. ■ dissected, 167, 278. Platforms, 163, 318. Platte river, 261. Po, 295. Polar regions, 29, 64, 72, 75, 290. Poles, 9, 18, 29. Pompeii, 223. Population, 169, 170, 189, 370, 371. of mountains, 201, 204, 357. of river-made plains, 258, 260, 269, 270, 363. See Settlements. Porto Rico, 100. Ports, 147, 157, 309, see Harbors. Potomac river, 211, 269, 368. Prairies, 71, 170, 296, 366. Prevailing westerly winds, see Winds. Prime meridian, 10. Problems, 9, 10, 35, 50, 90. Products, 138. Promontories, 211, 311, 313. Pyrenees, 190, 357. Race, tidal, 122. Races of men, 189, 204, 205, 345. Radiation, 28, 46, 61. Railroads, 97, 160, 191, 201, 371. Rainbow, 66. Rainfall, 38, 44, 65, 70, 72, 2.34. and trade winds, 41, 44, 55. and westerly winds, 43, 55, 159. distribution of, 41 , 43, 56, 59, 71, 72, 180, 183, 188, 280. 3-59. equatorial, 56, 72, 74, 83. subequatorial, 56, 353. Rainfall, subtropical, 55, 56, 354. Rain gauge, 70. Raleigh, 158. Rapids, 166, 247, 251, 255. Reaches, 255. Reefs, coral, 324, 326, 327. sand, 152, 156, 308, 313, 314. Refraction, 64, 66. Reindeer, 342. Relief, 147, 185, 210, 284. Rhine, 309. Rhode Island, 368. Rhone, 250. Richmond, 158. Ridges, 185, 186, 190. Rio Grande, 323. Rivers, 241, 245, 261, 265, 269, 302. graded, 254. mature, 246, 254, 269. old, 246, 270. revived, 271. withering, 281, 283, 285. young, 246, 257, 271. Roads, 143, 1-56, 169, 185, 190, 209, 247, 256, 2-58, 3^8, .320. Rochester, 302. Rock basins, 296, 300. Rock waste, see Waste. Rocks, 15, 108, 134, 1.36, 138, 235. Rocky mountains, 71, 74, 185, 188, 200, 2.39, 243, 281, 294. Roraima, 173. Rotation of earth, 6, 7, 36, 57, 85. Sahara, 41, 42, 50, 56, 71, 83, 280, 286, 354, ,361, 362. Salinas, 290. Salt, 290, see Lakes. \ INDEX 399 Sand, 286, 308, 310. reefs, see Reefs. Sandstone, 107, 209. San Francisco, 369. Saratoga Springs, 239. Sargassum, 123. Satellites, 13. Saturation, 60. Sault Ste. Marie, 248. Savannahs, 148. Scandinavia, 296, 321. Schuylkill, 153, 158. Scotland, 145, 205, 317, 318. Seas, 106. Seasons, 46, 49, 50, 56, 76, 77, 78, 83, 353. Seaweed, 123. Sediment, 101, 100, 108, 121, 148. Seine, 121. Selkirk mountains, 188. Settlements on coasts, 143, 156, 212, 314, 318, 320, 368. deserts, 285, 361, 363. • ^ mountains, 181, 183, 185, 216. plains, 146, 159, 206, 297. plateaus, 165, 166, 171, 278. rivers, 209, 252, 258, 302, 363. See Population. Shasta, Mt., 222, 229, 231. Sheavwits plateau, 173, 174. Ships, 4, 40, 69, 98, 103, 120, 212. Shir6 river, 249. Shore lines, 132, 155, 304, 307, 311, 317, 323. of deltas, 322. of lakes, 133, 288, 318. Siberia, 81, 134, 160. Sierra Nevada, 73, 189, 295. Silt, 255, 263, 265, 269. Sink holes, 235. Sirocco, 81. Sky, 19, 27, 62, 76, 78, 89. Snake river, 229, 288. Snow, 70, 77, 187, 190, 192, 290. line, 29, 355. Soil, 23, 135, 148, 152, 158, 296, 362. Solar system, 14, 17. Solstice, 88. Sound, 27, 66, 340. Sounding, 98. Sounds, 212. South America, 343, 344, 346, 366. South Carolina, 148, 157. Spain, 139. Springs, 236, 239, 361. St. Bernard pass, 190. St. Gotthard, 193. St. Helena, 112. St. Lawrence, 80, 247, 248, 250, 284, 319. Stacks, 312, 317. Stars, 12, 19. Steppes, 354. Storms, 64, 65, 66, 67, 79, 80. Streams, 235, 236, 241, 281. Subequatorial belts, 55, 56, 71, 83, 353. Subtropical belts, 55, 56, 73. Sudan, 83. Sulu sea, 107. Sun, 7, 11, 14, 46, 48, 87, 125. Sunrise and sunset, 7, 27, 89, 225. Surf, 40, 58, 111, 304, 313. Susquehanna, 269, 271, 274, 368, Svanetian.s, 357. Swamps, 150, 296, 313, 324. Sweden, 132. 400 ELEMENTARY PHYSICAL GEOGRAPHY Swell, 111. Switzerland, 189, 199, see Alps. Turks, 346. Typhoons, 67, 69. Table mountains, 171. Talus, 163, 166, 178, 180. Tarim river, 285. Temperate zone, 59, 75, 78, 80, 84. Temperature of atmosphere, 28, 32, 34, 37, 46, 49, 61. and currents, 118. charts, 33. mean annual, 33, 34, 50. of earth, 16, 134. of lakes, 102. of oceans, 28, 98, 101, 118. Terraces, 200. Texas, 74, 323. Thermograph, 32. Thermometer, 31, 32. Thunderstorms, 44, 65. Tiber, 138. Tibet, 26, 226. Tides, 119, 122, 126, 268, 304. cause of, 120, 124. Time, 7, 11, 46, 49. Tin, 366. Tonga Islands, 219. Tornadoes, QQ. Torrents, 197, 253, 254, 280. Torrid zone, 29. 48, 59, 60, 74, 80. Trade winds, 39, 40, 55, 57, 71. Transportation of waste, 137, 164, 168, 188, 196, 246, 270. Tree line, 355. Trenton, 158. Tributaries, 168, 254. Tunnels, 191, 193. Turkestan, 285. XJinkaret plateau, 173. United States, 158, 170, 191, 338, 371. boundaries, 11, 368. ■ coasts, 148, 158, 368. development, 371. glacial action in, 295, 296, 302. products, 76, 139, 348, 371. rainfall, 72. weather, 75, 76, 77, 82, 291. winds, 42, 63, 79, 81. See Rivers, Lakes, Plains, etc. Utah, 71, 73, 181, 280, 283, 319. Valleys, 136, 209, 256, 259, 270. crosswise, 200. drowned, 154, 156,269, .368. filled, 199. hanging, 299, 300, 322. ■ in mountains, 185, 196, 358. in plains, 143, 145, 154, 159. in plateaus, 162. lengthwise, 200. terraced, 200. Vapor, 38, 41, 60, 62. Variation of plants and animals, 337, 338. Vegetation, 43, 159, 181, 187, 235, 350, 353, 355, 359. Venezuela, 56, 353. Vera Cruz, 147. Vermont, 208. Vesuvius, 221, 223. Vikings, 321. Vineyard sound, 67. INDEX 401 Virginia, 156, 206, 210, 318, 368. Volcanoes, 16, 106, 113, 133, 215, 216, 220, 223, 226, 229, 231. Wadies, 281. Wales, 205, Washington, 72, 229, 366. Waste of the land, 134, 136, 163, 245, 254. and climate, 135, 323. deposition of, 108, 137, 265, 267, 283, 287. glacial, 279, 293, 296. in basins, 284, 209. in valleys, 183, 197, 199, 284. on shores, 107, 112, 141, 304. transportation of, 137, 164, 168, 188, 196, 246, 270. Water, 15, 38, 96, 102, 136, 234. circulation of, 39. hemisphere, 96, 129. power, 252, 301, 302. Waterfalls, see Falls. Water gaps, 210, 273. Watershed, see Divide. Waterspouts, (H^. Water vapor, see Vapor, Rainfall. Waves, 109, 111, 304, 306, 308, 311, 316. earthquake, 113. Weather, 42, 59, 74, 76, 77, 78. bureau, 82, 90. maps, 33, 81, 90. prediction, 81. Weathering, 1.34, 163, 183, 186, 200, 205. 206, 209, 312. Wells, 237, 238. We.st Indies, 69, 106, 133, 325. West Virginia, 167, 170, 236, 278. Wheat, 77, 348. Whirlwinds, 66. 286. White mountains, 357. White Sulphur Springs, 239. Winds, 36, 37, 39, 79, 85, 91, 189. and currents, 115. and denudation, 136, 286. anticyclonic, 46, 75, 78, 80. cyclonic, 46, 63, 67, 75, 78, 80, 81. daytime, 60. land and sea breezes, 59. of continents, 58. planetary, 37, 39. prevailing westerly, 39, 42, 44, 51, 54, 63, 72, 75, 80, 334. terrestrial, 53, 76, 77, 79. trade, 39, 40, 44, 55, 57, 71. velocity, 38. westerly, see prevailing wes- terly. whirls, 39, 40, 42, 44. Windward islands, 40. Wisconsin, 161, 238. World, Old and New, 130, 343, 367, 371. Yakima river, 257. Yellow .sea, 101, 268. Yellowstone park, 198, 239, 240. Yellowstone river, 251. Yucca, 360. Zenith, 89. Zones, 29, 46, 48, 52, 348. PLATE A. PLATE B. PLATE C M. E UNITED STATES. scale' of miles. 50 100 200 300 400 500 600 Kev West „ _ , . i<^!i^Wi?"Sr^^ j'it'S'nlle City \ e "West 92 from Greenwich 87 Phila/lelpliia Itj 4 TfEW ENGLAND and Ceost of, middle AHuDtic States'. (Oo.Enlarged Scale.) SCALE OF MILES-. 25 50 100 150 200 PLATE D 1 i PLATE E. I PI, ATE F. i 1 ( PliATE G. L'ongitule Kast from Greenwicn~ >^|^3^2:^^r, .0^ tR\^J s ftc>.e.-> ^ jT^i^ -."I's. I KyJX ' V-s. \ -^ vC \ .5K ^L^qlL- — ^S-^c'^ -W. X-^s ^x'^^^*^^^^^ ■j-j- — """^'^^kiJ^ n\ % I-^^'^>\J ^i \ ^S. > ^ "O ^ ^ Shaag >al \? A '». ^^ N C ^^'*^\,/ .«^"«.'^. ■^fh.' A-' V '^. ■^. '*' x" N^^ -^^^ -.^C'^ LIBRARY OF CONGRESS 029 708 026 A