First Book of Physical Geography

Front matter

FIRST BOOK OF PHYSICAL GEOGRAPHY Frontispiece. Granite peaks in the Yosemite. FIRST BOOK OF PHYSICAL GEOGRAPHY BY RALPH S. TARR, B.S., F.G.S.A. PROFESSOR OF DYNAMIC GEOLOGY AND PHYSICAL GEOGRAPHY AT CORNELL UNIVERSITY AUTHOR OF "ECONOMIC GEOLOGY OF THE UNITED STATES" " ELEMENTARY PHYSICAL GEOGRAPHY " " ELEMENTARY GEOLOGY," ETC. Ncto garfe THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Ltd. 1897 All rights reserved Copyright, 1S97, By THE MACMILLAN COMPANY. Noriuaotj -$nss J. S. Cushing it Co. - Berwick & Smith Norwood Mass. U.S.A.

Preface

In preparing my Elementary Physical Geography, I attempted to present the subject in such a way as to put it forward in its more modern aspect, and particularly to include the new physiography, or science of land form. An effort was made to cover the entire ground in a very elementary way ; hut at once the difficulty arose that the field was so large, that even to present the subject in an elementary manner would require a good-sized book. To avoid this there were two things possible : one to omit some parts and curtail others ; the other to com mence the consideration of some subjects with the assump tion that either the scholars knew the preliminary points, or that the teacher could explain them. Both of these methods of shortening the book were followed, but even then it grew to a size entirely too large for those schools in which the subject has a minor place.

The result has been, that although this book has met with a success wholly unexpected, many teachers who wish to give instruction in the new physical geography, are unable to make use of it. It is partly in the hope of meeting the needs of these, that I have undertaken the prep aration of this smaller book, from which still other sub jects are omitted, but in which the attempt is made to start from the beginning, and make every topic thoroughly clear, assuming no more than is absolutely necessary in a subject

PREFACE.

VIII which is based in part upon certain well-known principles of other sciences, notably physics and geology. If I have been successful in this effort, the other object that I have in mind may also be accomplished. Now, in man)* of the better schools, geography is taught first as a home study of observation, and this is followed by general geography, and this by physical geography. But the latter subject, as treated in most geographies, is entirely inade quate, and ought to be supplemented, or better still be entirely replaced, by a real study of physical geography in the upper grade of the grammar school. Since the great majority of our youth never go further than the grammar school, I believe that they ought not to be allowed to go out into life without a genuine knowledge of the main principles of air and earth sciences.

I feel this strongly, not merely because of the information which they gain, but also because of the discipline and culture which these sciences can impart. In reality, it is for the last object that I chiefly seek, for I believe that with this information and training, the stu dent, if he enters the high school, will then be able to go on with much greater profit with a more thorough study of the earth sciences, geology and physiography. Indeed, I would urge, that where the general study of physical geography as a whole can be put into the grammar schools, the high schools should take up, not a more thorough study of the same subject, on the " concentric " plan, but a fuller study of a part, or better still, several parts, like meteo rology, physiography, and geology. Although having in mind the use of this book in the high school, I would frankly say that I have no sympathy with the conditions which seem to demand it. Modern

PREFACE.

IX education should rise above fourteen-week courses, and it is better to omit physical geography, giving its place to a more thorough study of some other science, than to keep it on that plane. By peculiar merits of its own it demands fuller study. It is my hope, therefore, that where this book may be used in high schools in which conditions have made necessary a short course, it may help to create a de mand for better and fuller instruction in the subject. Much of the value of the new physical geography, — in deed I might almost say its whole value, aside from the information which it imparts, — depends upon the way in which it is taught. To assign certain pages to be memo rized, and to stop there, whether this is done in the grammar or the high school, is to fail to obtain the full results which can be gained from the study.

Simple class-room experiments ; laboratory stud)*- of specimens, maps and photographs ; observations made by students independently, and discussed in the class ; practice in grouping facts which logically lead to conclusions ; and collective study out-of doors, should take the place of much of the time-honored recitation. No specific suggestions are made here, but teachers will find some in my earlier book. No school is so unfavorably situated that opportunities for such study cannot be found in abundance ; no genuine teacher will fail to find pleasure from the results of such study; and no student will fail to gain great profit from it. Much good comes in any study when the desire is created for fuller information ; and still more benefit arises when to satisfy this desire, students are taught that there are places in which to look, and are given instruction how to find them. To make these benefits possible, I appended at the close of each chapter of my Elementary Physical

PREFACE.

X Geography, a list of books of reference selected from the best. It is not worth while to repeat these here ; but at the end of this book there are a few supplementary refer ences, chiefly to works which have appeared since the former book was published. This book follows approximately the same order as that of my Elementary Physical Geography, because I believe that this is the best. Still some will be found who prefer a different order, and there is no reason why a teacher who prefers to commence with the land ma)* not do so. As in my Elementary Physical Geography and Elementary Geology, I have introduced illustrations profusely, because it is my belief that next to nature itself, such illustrations are of most value. More can be told in the space occupied by them than in several times that much space in type, and it can be told more clearly.

Moreover, some of them can be made to serve as a basis for observation study. A considerable majority of the illustrations are original, but some are copied, and some are reproduced from photographs taken by others. To those who have kindly allowed me to use these I return especial thanks. CONTENTS Part I. Introduction

Chapter I

Condition of the Earth PAGE Form of tlie Earth 3 The Earth a Sphere 3 Longitude 4 Latitude ........... 6 The Earth an Oblate Spheroid 6 General Condition of the Earth . 7 Air 7 Ocean ............ 7 The Solid Earth 8 Surface of the Earth .......... 9 Continents and Ocean Basins 9 Mountain Irregularities ........ 12 Minor Irregularities 13 Movements of the Earth . . . . . . . ■ . .13 Rotation 13 Revolution 15 The Sun in the Heavens ......... 15 Cause of Seasons ....... ... 17

Chapter II

The Universe The Solar System 22 The Sun 22 The Planets 23 Satellites 21 The Universe 25 The Nebular Hypothesis 27 Symmetry of the Solar System 27 The Explanation 28 Facts accounted for ......... 30 Other Nebulæ 31 CONTENTS XII Part II. The Atmosphere

Chapter III

General Features of the Air PAGE Importance of the Air .... ... 32 Composition 33 i Ixygen and Nitrogen ......... 33 Carbonic Acid Gas 33 Water Vapor 35 Dust Particles .......... 38 Height of the Atmosphere -10 Changes in the Air 42

Chapter IV

Light, Electricity, and Magnetism Light Nature of Light 43 Reflection 44 Absorption 47 Selective Scattering 48 Refraction 48 The Colors of Sunrise and Sunset 49 Th.* Rainbow .51 Halos and Coronas 51 Sunlight Measurements 52 Electricity and Magnetism Lightning 52 Magnetism 53

Chapter V

Sin's Heat Nature of Heat 55 Reflection of Heat .55 Absorption of Heat . ......... 57 Radiation of Heat 57 Conduction of Heat .......... 59 Convection .59 Heat on the Land CONTENTS XIII PAGE Warming of the Ocean . . . . ... . . .61 Temperature of Highlands 02 Effect of Heat on the Air 64 Effect of Rotation 60 Effect of Revolution 67 Temperature Measurement 68

Chapter VI

Temperature or the Earth's Surface Day and Night Change 70 Daily Range .......... 70 Change with the Seasons . .71 Effect of Land and Water . .72 Irregular Changes ... ..... .73 Seasonal Temperature Change ... ... 74 Seasonal Range .......... 71 Influence of Latitude ......... 76 Influence of Altitude 77 Influence of Land and Water .77 Climatic Zones ........... 78 Isothermal Lines . ......... 70 Temperature Extremes . . . . . * . . ■ .84

Chapter VII

Winds Air Pressure ........... 85 Measurement of Air Pressure 85 Change in Air Pressure . . . . • . ■ • .88 Planetary Winds 00 Theoretical Circulation ........ 00 Trade-Wind Circulation 01 Prevailing Westerlies ......... 93 Periodical Winds ' • .95 Monsoons ........... 95 Land and Sea Breezes .97 Mountain and Valley Breezes 98 Irregular Winds 99 Velocity of the Wind 99 Measurement of Winds CONTENTS XIV

Chapter VIII

Storms PAGE Weather Changes V2 Weather Maps 102 Comparison of Weather Maps 104 Cyclonic and Anticyclonic Areas ...••■■ 107 The Lowand High-Pressure Areas 107 Origin of the Highand Low-Pressure Areas . . . .111 Explanation of the Winds 112 Explanation of the Rain ■ .113 Explanation of the Temperatures 114 Hurricanes or Tropical Cyclones ....... 116 Time and Place of Occurrence . ■•••:.* 'xxO Characteristics .......... 117 Explanation .......... 118 Storm Winds 119 Thunder Storms * .121 Tornadoes 124

Chapter IX

Moisture in the Atmosphere Vapor 126 Instruments for Measuring Vapor . 129 Dew 130 Frost 132 Fog 133 Haze 134 Mist 135 Clouds 135 Cloud Materials 135 Forms of Clouds 136 Causes of Clouds 139 Rain 140 Hail 141 Snow 141 Measurement of Rainfall ......... 144 Nature of Rainfall 144 Distribution of Rain .......... 145 Distribution of Snowfall ......... CONTENTS XV

Chapter X

Climate PAGE Meaning of the Word Climate 149 Climatic Zones 149 Climate of the Tropical Zone 150 Belt of Calms 150 The Trade-Wind Belt 152 The Indian Climate 154 Climates of the Frigid Zones 155 The South* Frigid Zone 155 Near the Arctic Circle 155 In the Higher Latitudes 15(3 CHmates pf the Temperate Zone 160 Various Types 160 United States Climates 161 Difference between United States and Europe .... 162 Variation with Altitude 163 Differences between Ocean and Land 163

Chapter XI

Distribution of Animals and Plants Zones of Life ■ . . 165 Life in the Ocean Plants 165 Animals 167 Faunas of the Coast Line (Littoral Faunas) .... 167 Animals of the Ocean Bottom (Abyssal Fauna) .... 169 Life at the Surface (Pelagic Faunas) 171 Life in Fresh Water 173 Life on the Land Plants 174 Animals 178 Distribution of Man 180 Modes of Distribution of Animals and Plants ..... 182 BaTriers to the Spread of Life CONTENTS Part III. The Ocean

Chapter XII

General Description of the Oceanpage Area of the Ocean 187 Importance of the Ocean 187 Tlie i Icean Water is Salt . 188 Temperature of the Ocean Surface 180 Life on the Bottom 191 Methods used in Studying the Ocean Bed 193 Ocean Bottom Temperatures 195 The Depth of the Sea 198 Topography of the Ocean Bottom 200 The Ocean Bed 203 Globigerina Ooze 203 Red clay 204

Chapter XIII

The Movements of the Ocean Wind Waves 205 Tin* Tides 210 Nature of the Tides 210 Causes of lides 211 Effects of the Tides 213 Ocean Currents 215 Differences in Temperature 215 Atlantic Currents 216 The Explanation 218 Effects 219 Part IY The Land

Chapter XIV

The Earth's Crust Condition of the Crust ooo Minerals of the Crust ooi Elements ooi Definition ooo CONTENTS XVII PAGE Minerals of the Crust : Quartz 222 Feldspar .223 Calcite 224 Rocks of the Crust 226 Igneous Rocks 226 Sedimentary Rocks 228 Metamorphic Rocks 231 Position of the Rocks 232 Movements of the Crust 234 Age of tbe Earth 236 Geological Ages 238

Chapter XV

The Wearing Away of the Land Entrance of Water into the Earth 240 Return of Underground Water to the Surface 212 Springs 212 Artesian Wells 243 Mineral Springs 244 Limestone Caves 246 Breaking Up of the Rocks 248 Methods Employed 248 Difference in Result 251 Effects of Weathering 254 Erosion of the Land 257 Destruction of the Land - . • • 260

Chapter XVI

River Valleys, including Waterfalls and Lakes Characteristics of River Valleys 261 The River Work 264 History of River Valleys 268 Accidents interfering with Valley Development .... 274 The River Course 278 River Deltas 283 River Floodplains 286 Waterfalls 288 Lakes CONTENTS XVIII

Chapter XVII

Glaciers and the Glacial Period PAGE Valley Glaciers 294 The Greenland Glacier 300 Icebergs 304 Glacial Period 305 Evidence of this 305 Cause of the Glacial Period 308 Glacial Deposits 309 Effects of the Glacier 310

Chapter XVIII

Sea and Lake Shores Difference between Lake and Sea Shores 313 Form of the Coast 313 Sea Cliffs 314 The Beach 317 Wave-carved Shores 320 A Sinking Coast 321 A Rising Coast 323 Marshes 323 Coral Reefs 324 Islands 326 By Construction 326 By Destruction 328 Promontories 330 Changes in Coast Line 331

Chapter XIX

Plains, Plateaus, and Mountains Plains 332 Plateaus 334 Treeless Plains 335 Mountains Nature of Mountains 335 Development of a Mountain System 337 The Destruction of Mountains 340 Other Kinds of Mountains 342 The Cause of Mountains CONTENTS XIX

Chapter XX

Volcanoes, Earthquakes, and Geysers Volcanoes PAge Birth of a Volcano 344 Vesuvius 345 Krakatoa 347 The Hawaiian Volcanoes 340 Other Volcanoes 351 Materials Erupted 351 Form of the Cone 352 Extinct Volcanoes 353 Distribution of Volcanoes 355 Cause of Volcanoes 356 Explanation of the Differences in Volcanoes 356 Earthquakes 357 Geysers ILLUSTRATIONS PHOTOGRAPHS AND DIAGRAMS FIG. PAGE 1. Ocean surface showing curvature of earth 3 2. Diagram to illustrate curvature of earth 4 3. Maps to illustrate latitude and longitude 5 4. Diagrammatic section from surface to interior of earth . . 9 5. The two hemispheres 10 0. Land and water hemispheres 11 7. Section across South America, Atlantic Ocean, and Africa . 12 8. Globe to illustrate day and night at Equinox .... 16 9. Globe illustrating conditions in northern summer ... 18 10.

Globe illustrating conditions in northern winter ... 19 11. Diagram to illustrate cause for seasons 21 12. Diagram illustrating small amount of heat reaching earth . 22 13. Relative size and distance of planets and sun .... 24 14. Craters on the moon 25 15. Diagram illustrating Nebular Hypothesis 29 16. Andromeda Nebula 31 17. Diagram illustrating density of air 40 18. Ideal section of atmosphere . . . - . . . .63 19. Daily temperature change, summer 66 20. Thermograph 69 21. Thickness of air passed through by vertical and oblique rays . 70 22. Diurnal variation of temperature 70 23. Daily temperature range for several places .... 71 24. Influence of ocean on daily temperature range .... 72 25. Daily range in desert and humid tropical lands .... 73 26. Irregularities in daily temperature range 74 27.

Temperature range for several days 74 28. Seasonal temperature range, several places . . . .75 29. Seasonal temperature range, several places .... 76 ILLUSTRATIONS XXII FIG. PAGE 30. Influence of ocean on seasonal temperature range ... 78 31. Isothermal chart for New England 83 32. Diagram showing changes of pressure 86 33. Aneroid barometer 87 34. Diagram showing general air circulation . .... 90 35. Ideal circulation of surface air, southern hemisphere . . 93 36. Monsoon of Spanish peninsula 95 37. Summer and winter monsoon, India 96 38. Effect of sea breeze on daily temperature range ... 98 39. Disturbance of wind by surface irregularities .... 99 40. Pulsation of wind 100 41. Anemometer 101 42. Weather conditions, Jan. 7, 1893 103 43. W'eather conditions, Jan. 8, 1893 104 44. Weather conditions, Jan. 9, 1893 105 45.

Paths followed by low-pressure areas, November, 1891 . . 107 46. Weather conditions, April 20, 1893 108 47. Weather conditions, Nov. 27, 1896 109 48. Weather conditions, Jan. 12, 1897 110 49. Theoretical air movement in storm 112 50. Theoretical air circulation in anticyclone 112 51. Tropical cyclone in India 116 52. Change in barometer in hurricane 117 53. Temperature change in cold wave and sirocco . . . .119 54. Influence of cyclone and anticyclone on temperature . . 120 55. Temperature change during chinook, Montana .... 121 55. 50. Photograph of distant thunder storm 122 57. Map showing location of thunder storms in cyclonic area . . 123 58. Tornado near St. Paul, Minn 125 59. Diagram showing change in relative humidity .... 128 60. Psychrometer 129 61. Upper surface of valley fog 134 62.

Clouds on cliff in the Yosemite 136 63. Cumulus clouds 137 64. Cirrus clouds 138 65. Strato-cumulus clouds 138 66. Cirro-cumulus clouds 139 67. Photograph of large hailstones 141 68. Photograph of snow flakes 142 69. Rain gauge ILLUSTRATIONS XXIII FIG. PAGE 70. Desert vegetation in the west 153 71. Midnight sun, northern Norway 150 72. Ice-covered sea in the Arctic 157 73. Land in Greenland, summer 158 74. Greenland ice sheet 159 75. Cold wave, March 13, 1888 160 76. Map showing snowfall of United States 161 77. Mangrove swamp, Bermuda 166 78. Seaweed mat, Cape Ann, Mass. 107 79. Corals, Great Barrier reef, Australia 109 80. Deep-sea fish 170 81. Deep-sea crinoid 171 82. Semi-tropical forest in Florida 174 83. Cactus in Arizona desert 175 84. Mountain peak, crest of Andes, Peru 176 85. Near timber line, Rocky Mountains 177 86.

Arctic flora in snow 178 87. A Bermuda road 182 88. Bit of Bermuda landscape 183 89. Arctic sea ice 100 90. Deep-sea sounding machine 102 91. Deep-sea dredge on ocean bottom 194 92. Temperature of ocean bottom of north Atlantic . . . 195 93. Temperature of ocean at various depths 190 94. Section from Atlantic to Gulf of Mexico 197 95. Section of ocean from New York to Bermuda .... 109 96. Section across Atlantic showing temperature and depth . . 200 97. Ocean bottom topography (Jones model) .... 201 98. Ocean bottom topography (Jones model) .... 202 99. Diagram showing approach of wave on beach .... 207 100. Diagram illustrating origin of tidal wave 210 101. Diagram showing advance of tidal wave in Atlantic . . 211 102. Diagram showing cause of spring and neap tides . . . 212 103. Diagram showing currents of eastern north Atlantic . . 217 104.

Stratification in horizontal rocks 220 105. Quartz crystal 222 106. Piece of calcite 224 107. Section of diabase enlarged by microscope .... 226 108. Diagram illustrating intrusion of granite 227 109. Consolidated pebble bed ILLUSTRATIONS XXIV FIG. PAsiE 110. Beach, Cape Ann, Mass 230 111. Coquina 231 112. Diagram of volcano in cross section 233 113. Crumpling of rock 233 114. Diagram illustrating faults 235 115. Photograph of small fault 236 116. Folded rocks 236 117. A monocline 237 118. Section of gneiss enlarged by microscope 241 119. Diagram illustrating conditions in hot springs .... 242 120. Diagram illustrating cause of hillside springs .... 242 121. Diagram illustrating artesian wells 243 122. Diagram illustrating artesian wells 244 123. Hot Springs, Yellowstone 245 124. Howe's Cave, New York 246 125.

Natural Bridge 247 126. Column in cavern 248 127. Effect of frost action on mountain top 249 128. Effect of weathering in arid lands 252 129. Butte in western Texas 253 130. Crumbling of rocks on mountain side 255 131. Decaying granite, Maryland 256 132. Diagram illustrating residual soil 257 133. Bad Lands, South Dakota 258 134. River gorge in Peruvian Andes 262 135. Rocky stream bed in Adirondacks 264 136. Enfield Gorge, Ithaca, N.Y 265 137. Diagram illustrating stream action and weathering . . . 267 138. Meandering of Missouri River ....... 268 139. Young valley, central New York 269 140. Diagram illustrating base level 270 141. Diagram illustrating development of stream valley . . . 271 142. Broad mature valley, Ithaca, N.Y 271 143. Delaware Water Gap 272 144. Cross section of Colorado River 274 145.

View in Colorado canon 274 146. Diagram illustrating Chesapeake Bay river system . . . 275 147. Drainage in mountain 279 148. Drainage on plain 279 149. Interlocking tributaries ILLUSTRATIONS XXV FIG. PAGE 150. Changing of mountain tops to valleys 281 151. River flowing in anticline 282 152. Cross section of delta 283 153. Alluvial fans in the west 285 154. Waterfall, central New York 288 155. General view of Niagara Falls 289 156. Peat bogs in Adirondacks 290 157. Snowfield in high Alps 295 158. An Alpine glacier 296 159. Crevassed surface of Muir glacier, Alaska .... 297 160. Margin of Cornell glacier, Greenland 301 161. Delta in glacier lake 302 102. Scratched glacial pebble, Greenland 302 103. Ice floating in water 303 104. Iceberg off North Greenland coast 304 165. Map of United States showing extension of ice in glacial period 305 166.

Boulder clay, Cape Ann, Mass. 306 167. Glaciated rock surface in Iowa 307 168. Terminal moraine hills, Ithaca, N.Y. 308 109. Boulder-strewn moraine, Cape Ann, Mass 309 170. Sea cliff, Bermuda 315 171. Undercut sea cliffs, Bermuda 316 172. Wave-cut cliff, Lake Superior 318 173. Bar across bay, Cape Breton, Nova Scotia .... 319 174. Bars on shore of Martha's Vineyard 320 175. Tiny wave-carved bay, Cape Ann, Mass 321 176. Depressed coast of part of Connecticut 322 177. Beach and coral reef, coast of Florida 325 178. Serpula atolls, Bermuda 327 179. Wave-cut islands, shore of Bermuda 328 180. Islands caused by sinking of Bermuda 329 181. Island joined to land by bars 330 182. Plain of Everglades, southern Florida 332 183. Diagram illustrating dissection of plain 334 184. Sections of Appalachian Mountains 330 185.

Grandfather Mountain, North Carolina 337 186. Mount Moran, Teton Mountains 339 187. Near timber line, Gallatin Mountains, Montana . . . 341 188. Pompeii and Vesuvius 347 189. Mauna Loa, Hawaiian Islands ILLUSTRATIONS XXVI FIG. PAGE 190. Crater of Kilauea 349 191. Tiny volcano, Mediterranean 350 192. Popocatapetl, Mexico 353 193. Volcanic necks, New Mexico 354 194. Distribution of Volcanoes 355 195. Effect of Japanese earthquake, 1891 .358 196. Diagram illustrating earthquake wave 359 197. Isoseismals, Charleston earthquake 360 198. Giant Geyser, Yellowstone 361 PLATES PLATE FACING PAGE Granite peaks in the Yosemite .... Frontispiece 1. Isothermal chart of the world for July 79 2. Isothermal chart of the world for January 80 3. Isothermal chart of the world for the year 81 4. Isothermal chart of the United States for July .... 82 5.

Isothermal chart of the United States for January ... 83 0. Isothermal chart of the United States for the year ... 84 7. Chart showing isobaric lines for the world 90 8. Map showing prevailing winds of the globe for July ... 92 9. Map showing prevailing winds of the globe for January . . 93 10. A West Indian hurricane 116 11. Typical winter storm 117 12. Rainfall chart of world 146 13. Rainfall chart of United States 147 14. Average temperature of sea surface 189 15. Depth of Atlantic Ocean 198 16. Chart of ocean currents 214 17. Three rock specimens (diabase, granite, and gneiss) . . . 227 18. Delta of Mississippi 283 19. Map of drowned coast, Maine 314 20. Mountain ridge in the northwest ILLUSTRATIONS XXVII ACKNOWLEDGMENT OF ILLUSTRATIONS Aside from those that are original, illustrations in this book have been obtained from the following sources.

Some of these have been more or less modified to suit the needs of the book. A very few that have been borrowed are not acknowledged because the original source is not known. I am also indebted to Mr. B. F. White and Mr. J. 0. Martin for some of the photographs. Abbe, Annual Report, Signal Service, Part 2, 1889, Figs. 18 and 39, Agassiz, Three Cruises of the Blake, Figs. 80, 81, 92, 93. Bailey, Prof. L. H. (Photographs by), 82, 177, 182. Ball, Popular Astronomy, Fig. 11. Blanford, Climates and Weather of India, etc., Figs. 37 and 51. Buchan, Challenger Reports, Atmospheric Circulation, Plates 1, 2, 3, 7, 8, and 9. Chamberlin, Third Annual Report, U. S. G. S., Fig. 165. Dutton, Sixth Annual Report, U. S. G. S., Fig. 193; same, Ninth Annual Report, Fig. 197. Davis, Series of Lantern Slides for Schools, Fig. 143.

Freiz, J. P. (Dealer in Meteorological Instruments), Baltimore, Md., Figs. 20, 33, 41, 60, 69. Gardner, J. L., 2d (Photographs by), Figs. 166 and 169. Gilbert, Second Annual Report, U. S. G. S., Fig. 153; same, Fifth Annual Report, Fig. 172. Hann, Berghaus Atlas der Meteorologie, Plate 12, modified. Harvard College Astronomical Observatory Annals, Vol. XXXI., Fig. 31. Hayden, West Indian Hurricanes, etc., Fig. 75. Haynes, F. Jay (Photographer), St. Paul, Minn., Figs. 123, 159, and 198. Hellmann, Schneekrystalle, Fig. 68. Howes, C. H. (Photographer), Ithaca, N.Y., Fig. 139. Jackson Photograph Co., Denver, Col., Figs. 62, 85, 126, 145, 155, 186, and 192. Johnston-Lavis, South Italian Volcanoes, Fig. 191. Jones, Thomas, Chicago, 111., Photograph of copyrighted globe, Figs. 97 and 98. Kent, Great Barrier Reef, Fig. 79.

Keyes, Fifteenth Annual Report, U. S. G. S., Fig. 131, Vol. III.; Iowa Geological Survey, Fig. 167. ILLUSTRATIONS XXVIII Koester (Photographs by, sold by Fredrick and Koester, St. Paul, Minn.). Printed in Am. Met. Jour., VII., 1891, Fig. 58. Langley, American Journal Science, Vol. XL VII., 1890, Fig. 40. Libbey, Prof. W., Jr. (Photographs by), Figs. 86, 189, and 190. McGillivray (Photographer), Ithaca, N.Y., Fig. 136. Murray, Challenger Reports, Final Summary, Plates 14 and 15. Nasmyth and Carpenter, The Moon, Fig. 14. New York State Weather Bureau (from records of), Figs. 19, 22, 26, 27, 32, 52, 53, 54, and 59. Notman (Photographer), Montreal, Canada, Plate 20. Sigsbee, Deep Sea Sounding and Dredging, Fig. 90. Steeruwitz, First Annual Report, Texas Geological Survey, Fig. 129. Stoddard, S. R. (Photographer), Glens Falls, N.Y., Figs. 124, 135, and 150.

Thomson, Challenger Reports (Narrative), Fig. 91. Thornton, Advanced Physiography (from a Photograph by Mr. Roberts), Fig. 16. United States Coast Survey (Maps of), Plates 18 and 19, modified. United States Geological Survey (Maps of), Figs. 138, 147, 174, and 176, modified. United States Geological Survey (Photographs by), Figs. 70, 113, 125, 185, and 187, and Frontispiece. United States Geological Survey Folios (Campbell), Fig. 184 (Hayes), Pig. 151. United States Weather Bureau (based upon maps and records of), Plates 4, 5, 6, 10, 11, and 13, and Figs. 42, 43, 44, 45, 46, 47, 48, 55, 57, and 76. Ward, Set of Cloud Slides (Riggenbach, Burnham, etc.). Figs. 56, 61, 63, 64, 65, and 66. Williston, Prof. S. W., Lawrence, Kansas (Photographs by), Figs. 128 and 133. Part I

Chapter I Condition Of The Earth

Form of the Earth : The Eartha Sphere. — Standing upon the seashore, and 1. mking* utit upon the broad expause of water, we see ships sailing along, some near at hand and some far away. Those that are near show the sails, spars, and even the hull down to the water's edge, Fig. 1. The ocean surface to show curvature of the earth. but only the sails and masts of the more distant ones are seen, and perehance one in the offing is detected only by its topmast (Fig. 1). This is because the surface of the earth, and the water upon it, is curved (Fig. 2). The vessel gradually disappears behind the curvature of the earth, just as a man disappears from sight as he passes over the crest of a hill. There are other proofs that the earth is a spherical body. I'm* instance, if we should start on one of the ships, we might pass entirely around the globe and return to the point whence we started.

Or, by travelling over land and water, we can , n go due east or due Fio. 2. west, and in time To illustrate curvature of earth. A person standfind ourselves back in*, at IS could not see an object at C unless it . rose to the level of the line AB. •>*- the starting point (see a globe). Longitude. — Should a dozen people start from as many places, such as New York. San Francisco, London, etc., and be able to go due north, their paths would all con verge toward a point at which they might eventually meet; and this point, which is so enwrapped in ice and snow that it has not yet been visited by man, is called the North Pole. Passing due south from these same places, the travellers would in time meet at a point in the south. which is called the South Pole, and this region also is inaccessible to man.1 in mapping the globe, geographers are in the habit of projecting lines in the direction of these imaginary journeys, and these all converge toward the poles.

These me rid in us. or lines of longitude, are 300 in number, and each of these is spoken of as a degree of longitude? 1 The North and South Poles are the imaginary points on the surface of the earth through which the axis of the earth emerges. This axis is that about which the earth rotates, just as a globe or an apple may be made to rotate about an axis. These are not the same as the magnetic poles toward which the compass needle points. The north magnetic pole lies to the southwest of the true North Pole, and is situated in Boothia Land, north of Hudson's Bay. - The reason for having 360° is in order that the number of miles in a degree of latitude and longitude may he nearly equal at the equator. As The distance between these varies, for they broaden out and spread apart as the distance from the poles increases (Fig. 3).