Manual of physical geography

Front matter

Class (V „B 5 _.

Book

Copyright If

Preface

The exercises in this " Manual " have, for the most part, grown out of the author's class-room experiences. There is presented a variety of exercises, some of them advanced in character, that will cover the topics capable of laboratory illustration usually presented in a course in physical geography. For such classes as cannot use the entire " Manual," the author suggests a selected list of exercises which are starred (*). Most of the exercises can be used in a different order from that given by omitting the references to other exercises.

Some of the exercises and their order of presentation may require explanation. Considerable attention is given to elementary principles of mathematical geography. Many students of this phase of the science seem to have a vocabulary rather than an understanding of it. For example, rather few students know precisely why it is colder in winter than in summer, or why the seasons change. The author would urge thorough drill in these elementary principles and in the elementary facts of insolation. Climate is treated early vi PREFACE

in the course in order that a foundation may be laid for intelligent weather observations throughout the year. Especial attention is given to the cyclone, since it is the main climatic factor in the United States. If the teacher prefers to postpone the consideration of climate until later in the course, it can be done without inconvenience.

In presenting land forms due to normal erosion, the author has been most successful in grouping them according to their structure. Looked at in this way, the different types of mountains, for example, are produced by erosion acting upon different structures. Constructive imagination is brought out and a valuable discipline is secured.- The author is aware that this plan leads into structural geology farther than many teachers care to go. The questions are therefore arranged so that the facts of structure can be omitted and the topographic facts studied by themselves. The topics of soils and harbors are introduced because they are geographic factors so important that every student should know of them.

It is the author's conviction that physical geography should lead up to, and should include a study of, the United States. To this end a series of exercises has been provided in Chapter XVIII to present important typical regions. Further reasons for these exercises

PREFACE vii

are that the preceding principles may be reviewed and that the student may gain facility in studying large areas. Few sciences offer better opportunities than physical geography for studying large units and grouping their various phenomena.

Wherever possible for the sake of economy, the same quadrangles have been used in different exercises. For those who wish to show the same features on different quadrangles, the United States Geological Survey has issued a useful pamphlet, " Topographic Maps of the United States showing Physiographic Types," which will be sent on application.

Most of the climatic tables have been taken from Hann's ' Cl Lehrbuch der Meteorologie," second edition, from " Climatology of the United States " by Alfred J. Henry, and from various tables published by the Smithsonian Institution. Many suggestions have been derived from " Climate " by Professor R. DeC. Ward and from the same author's " Handbook of Meteorology," from which the method in Exercise 27 is taken.

The thanks of the author are due to various Weather Bureau officials who have kindly furnished data ; to Dr. J. A. Bonsteel, of the United States Soil Survey, who read the manuscript of the chapter on Soils ; to Professor C. F. Marbut, of the University of Missouri, who has aided in many ways. The author is especially

Vlll PREFACE

indebted to Professor George D. Hubbard, of the Ohio State University, who read the manuscript and made many valuable suggestions.

FREDERICK V. EMERSON.

Columbia, Missouri,

CHAPTER I The Earth as a Planet PAGE

1. The Form of the Earth 1

*2. The Earth's Axis 3

Parts I, II, and III . . . . 3

3. Length of Day and Night 5

4. Longitude and Time . . . 7

5. To ascertain the Noon Hour 8

6. Longitude 8

7. To ascertain the Local Latitude 9

8. Revolution of the Earth 10

Chapter II

*9. Diurnal Insolation 12

*10. Insolation at Various Latitudes 13

11. Insolation, Length of Day, and Temperature in Norway . 15

*12. Maxima of Temperature due to Insolation .... 16

*13. Continental and Marine Average Annual Temperatures . . 16

*14. Hourly Temperatures 17

1.5. Temperatures on the East and West Shores of the Atlantic . 18

*16. Temperature and Altitude .19

CHAPTER III Moisture of the Atmosphere

*17. Capacity and Temperature .20

*18. Observations of Relative Humidity 20

X CONTENTS

PAGE

*19. Diurnal Relative Humidity 23

20. Absolute Humidity and Relative Humidity in Continental

and in Marine Climates 24

21. Climate during August, 1896 25

*22. Equatorial Rainfall 26

*23. Tropical Rainfall 26

24. Monsoonal Type of Rainfall 27

Chapter IV

*25. General Map Study of a Cyclone

*26. Construction of a Weather Map

*27. Wind Directions in Cyclones and Anticyclones

*28. Isotherms in Cyclones and Anticyclones .

*29. State of Sky in Cyclones and Anticyclones

30. Inference of a Cyclone or an Anticyclone from Wind Direction

31. Inference of Cyclones and Anticyclones from Isotherms .

32. Conditions in Different Parts of Cyclones and Anticyclones

33. Cyclones and Anticyclones in Summer and in Winter *34. Cyclone Paths

Chapter V

*35. A Land and Sea Breeze 43

36. A Chinook Wind 44

*37. Observation of a Rain Storm 45

38. The Dew-point .46

*39. Observations on Dew Deposition ...... 46

40. Study of a Fog .47

•41. Cloud Study 47

*42. Observations of Frost Conditions 48

43. Map Study of Frost Conditions 49

*44. Local Forecasting . .50

45. Trade Winds and Sailing Routes 51

*46. Local Study 53

CONTENTS xi

CHAPTER VI Common Minerals and Rocks PAGE

*47. Common Minerals 54

*48. Common Rocks 55

*49. Field Study of a Rock Outcrop 59

Chapter VII

*50. Construction of a Contour Map 60

Chapter VIII

*51. Field Study of Weathering 66

*52. Field Study of Stream Work . . 67

53. Weathering and Corrasion Curves 72

*54. Map Study of Streams and Stream Valleys .... 74

55. Reversed Stream Tributaries 76

*56. Braided (Anastomosing) Streams 77

*57. Flood Plains 78

*58. A Graded River 79

59. Mississippi Delta 80

60. Alluvial Fans 82

61. River Deposits. Bars 85

62. Flood Plain Meanders .85

63. River Terraces 87

64. Stream Capture 88

65. Youthful Topography and Drainage 91

*Parts I, *II, III, IV, *V 91

66. Mature Rivers and Valleys 95 xii CONTENTS

PAGE

*67. Early Mature Topography . . ' . . . . .97

*68. Mature Topography and Drainage 98

69. A Region in Old Age 99

70. A Stream in Old Age 99

71. A Region in Old Age, recently Revived 100

*72. Review. The Cycle of Erosion 100

*73. A Peneplain recently Elevated 101

74. A Rejuvenated or Revived River 101

75. Incised (Intrenched) Meanders 103

76. A Superimposed Stream . . . . . . . . 104

*77. Drowned Stream Valleys . . . . . . .105

78. Field Study of Consequent, Insequent, and Subsequent Streams 106

79. Map Study of Consequent, Insequent, and Subsequent Streams

and their Associated Valley Patterns . . . . . 107

*80. Study of a Canon 109

*81. Study of a Waterfall 110

Chapter IX

Land Forms in Various Rock Structures. Stratified and Homogeneous Rocks

*82. Hills and Valleys in Stratified Rocks of Varying Strength

83. Mountains of Circumerosion (Circumdenudation)

84. Mountains in Youth (Circumerosion)

85. Mountains of Circumerosion in Maturity . *86. Escarpments

87. Escarpment and Outliers ....

88. A Maturely Dissected Mountainous Divide Part I ; Part II

113 114 115

116 116 117 118 118

CHAPTER X Land Forms in Folded and Tilted Rocks

*89. Young Anticlinal Mountain and Synclinal Valleys . . 121 90. An Anticlinal Mountain (Unsymmetrically Folded) . . 122

Xlll

PAGE

91. An Anticlinal Valley 123

*92. An Eroded Anticline with Monoclinal Ridges . . . 124

93. Synclinal Mountains 126

*94. Eroded Synclines ; Monoclinal Ridges 127

95. A Syncline with Pitching Axis 128

96. Land Forms resulting from the Erosion of a Pitching Anti-

cline 130

97. Stream Adjustment in Folded Structure .... 132 *98. Stream Capture in Folded Rocks 134

99. The Effect of a Change in Dip upon the Width of Outcrop . 135

Part I ; Part II 135

100. Peneplains 136

*101. Stage of Erosion in Topography developed on Folded Rocks 138 102. Monoclinal Shifting .... . . . .138

104. A Cuesta 141

CHAPTER XI Land Forms due to Faulting and Volcanism

105. Fault Scarps

*PartI; Part II ....

*106. Block Mountain and Rift Valley .

107. Review of Forms due to Folding and to

*108. A Volcanic Mountain

*109. A Dissected Volcanic Mountain

110. Laccolithic Mountains

*111. A Volcanic Neck ....

112. Topography due to a Dike

*113. Lava Cones and Cinder Cones.

*114. A Sill

Faulting

Chapter XII

*115. Alpine or Mountain Glaciers 116. Cirques ....

152 152

XIV CONTENTS

PAGE

*117. U-shaped and Hanging Lateral Valleys 154

*118. Marginal Moraines . . . ■ ■ 155

*119. Comparison of Ground Moraine and Marginal Moraine . 157 120. Comparison of Mountains modified by Mountain Glaciation

and by Continental Glaciation 157

*121. A Comparison of Mountains affected by Glacial Erosion and

by Subaerial Erosion 158

*123. A Glacially Diverted Stream 160

*124. Drumlins 161

125. Comparison of Glacial Erosion and Glacial Deposition . .162

126. Sand Plains and Ice-contact Slopes 162

127. General Exercise .163

128. General Review 165

*129. A Comparison of Driftless, New Drift, and Older Drift Areas 166

CHAPTER XIII Lakes

*130. An Ox-bow Lake 170

*131. Lakes and Swamps on a Flood Plain 170

132. Delta Lakes . .170

133. Lakes in Rock Basins 171

•134. An Ice-blocked Valley 171

*135. Morainic Lakes 171

136. An Extinct Glacial Lake 172

137. A Crater Lake 173

138. Consequent and Solution Lakes 175

139. Lakes due to Faulting 175

140. A Nearly Drained Lake . 176

*141. Lakes as Filters 176

Chapter XIV

*142. The Floor of the Atlantic . 177

*143. The Continental Shelf 178

XV

PAGE

*144. Daily Tides 178

*145. Daily High Tides . .179

146. Tides on a Smooth and an Indented Coast .... 180

147. Lagging of the Tides 181

148. Tidal Currents 182

*149. Oceanic and Coastal Tides . . . . . . .182

*150. Ocean Currents 183

151. An Atoll 184

*152. Coral Reefs 185

Chapter XV

*153. Comparison of Subaerial and Submarine Topography . . 187

154. A Young Coast 188

*155. Off-shore Bars 189

156. Sea Cliffs and Wing Spits 191

157. Tied Islands 194

158. Shore Lines of Extinct Lakes 195

*159. A Risen Coast 197

160. A Young Risen Coast with a Narrow Coastal Plain . . 198

161. Elevated Wave-cut Terraces and Cliffs 198

162. A Tidal Delta 199

163. General Exercise 200

CHAPTER XVI Harbors

*164. Introduction

*165. A Drowned Valley Harbor

*166. A River Harbor

*167. A Moraine Harbor .

*168. A Bar Harbor

*169. San Francisco Harbor

170. A Coral Reef Harbor ♦Part I ; Part II

XVI

PAGE

*171. A Fiord Harbor ... 210

174. A Spit Harbor 211

175. A Tied Island Harbor . . 212

Chapter XVII

*176. Soils along an Aggrading River

*177. Soils on Alluvial Fans ....

178. Valley Soils due to Wash from the Uplands

*179. Soils on River Terraces ....

*180. Soils on Lake Shores and Bottoms .

181. Soils in a Region of Ridges

182. Soils in Central Florida ....

183. Soils on Ground Moraine and Drumlins . *184. Soils on a Moraine and Outwash Plain .

213 214

CHAPTER XVIII Studies op Typical Areas

*185. A Youthful Plain ; The Red River Valley . . . .220

*186. Mature and Old Plains, Kansas 223

*187. The Ontario Plain and the Alleghany Plateau, New York . 224 *188. The Coastal Plain, Piedmont Plateau, and Highlands in New

Jersey . 228

189. The Coastal Plain, Piedmont Plateau, Blue Ridge, Great

Valley, Ridge Belt, and Alleghany Plateau in Maryland,

Virginia, and West Virginia 232

*190. The Piedmont Plateau, Blue Ridge, Appalachian Valley,

Cumbei'land Plateau, and Nashville Basin .... 237

191. A Portion of the Ridge Belt and the Great Valley in Penn-

sylvania ' . . 244

192. The Coastal Plain in Florida 246

*193. The Lower Mississippi Valley . . ; . . .248

XV11

*194. Southern New England. Connecticut

195. The Black Hills and the Great Plains .

*196. The Eastern Margin of the Rocky Mountains and the Adjacent Great Plains .....

*197. The Eastern Border of the Great Basin .

*198. The Plateau of Arizona and the Grand Canon

*199. The Western Great Basin and the Sierras

*200. The Sierras in California

201. The Northern Cascade Mountains and the Columbia Plateau

Appendix . . .

PAGE

249 252

255 256 261 264 266 271

" Effective power in action is the true end of education."

— Eliot.

Chapter I

THE EARTH AS A PLANET 1. FORM OF THE EARTH

* Part I. — One of the best ways by which the form of the earth has been determined is the measurement of degrees of latitude on different parts of the earth's surface. If the earth were a perfect sphere, would the degrees of latitude be equal in all parts of the earth ?

If the earth were a spheroid as in Figure 1, what part of the spheroid would be a portion of a large circle ? Why ?

Of a small circle ? Why ?

In what part of Figure 1

would the latitude degrees be longest ? Why ? Shortest ? Why ?

Part II. — Make a graph illustrating the length of latitude degrees as given in the table. A graph is a line drawn to illustrate a table of facts. Upon your coordinate paper allow the heavy vertical lines to represent every ten degrees of latitude. Allow each lighter horizontal line to represent j^-q of a mile. Take the lowest corner to represent the lowest value in your table as a starting point. In this table this lowest value represents the length of the latitude degree at the equator. The length for 5° latitude is 68.71, and the point representing this value is at the intersection of the 5° line and the line representing 68.71 miles. Finish the location of points for each value, connect the points, and you have the graph.

Length of Degrees of Latitude at Various Latitudes

Latitude

Latitude

Latitude

68.704

68.935

69.281

68.710

68.993

69.324

68.725

69.054

69.360

68.751

69.115

69.386

68.786

69.175

69.402

68.829

69.230

69.407

68.879

Is the graph a straight line ? Does the graph indicate constant or changing values ? Plot on same sheet a graph, assuming that the degrees are 68.70 miles long the world over. Is this a straight line ? Why ? Plot on the same sheet a graph, assuming that the latitude degrees increase j±^ of a mile for each 5° of latitude.

THE EARTH AS A PLANET

Is it a straight line ? Why ? Compare your three graphs as to straightness and direction. Does your graph of latitude degrees show increasing or decreasing values ? Where is the greatest increase ? Where the least ? What does this show about the curvature of the earth ? Where is the curvature greatest, at the equator or at 50° ? At 20° or at 60° ?

•2. THE EFFECTS OF THE INCLINATION OF THE EARTH'S AXIS

Part I. — To find the effect of the inclination of the earth's axis to the plane of the orbit, an apparatus

Fig. 2.

shown in Figure 2 x will be useful. The horizontal wire represents the rays of the sun. First keeping the

1 See Appendix.

axis vertical and parallel to its first position, move the earth in a circle, also moving the wire. Does the wire always point to the same latitude on the globe ? How much of the earth is illuminated ? Pass a cord or rubber band around the globe, dividing the illuminated and non-illuminated portions. Placing the globe so that the wire points to the equator, move the earth in a circle. Are the hemispheres equally illuminated ? Change the inclination of the axis to about 23J°. Move the globe in a circle as before. Do the rays point always to the same latitude ? If not, through how great a range of latitude are the rays vertical ? Are the hemispheres equally illuminated at all times ? At any times ? Change the inclination of the axis to 10° ; 50° ; 90°. Compare in all respects with your previous results.

Part II. — Move the globe in a circle, but do not keep the axis parallel to its first position. How do your results compare with those in Part I ?

Part III. — Referring to Parts I and II, what area of the globe receives direct rays of the sun at some time of the year ? How wide is this area ? How much beyond the poles does the circle of illumination extend ? (The circle of illumination divides the lighted from the dark parts of the earth.) What is the tropical zone ? What is its width ? What determines its limits ? What is the width of the polar zones ? What determines their limits?

THE EARTH AS A PLANET 5

3. LENGTH OF DAY AND NIGHT

The reason for the varying length of day and night is often not thoroughly understood. Do not leave the topic until you can demonstrate it.

Take a globe and apparatus as in Exercise 2. How much of the earth is illuminated ? Can it ever be more ? Less? The boundary of the illuminated part is called the circle of illumination. Is it a great circle (i.e. does it always bisect the earth) ? Place the globe in its position at equinox. Does the circle of illumination bisect the equator ? The other parallels ? What, therefore, is the length of day and night over the globe ? Place the globe in the position of the June solstice. Is the equator bisected by the circle of illumination ? Is the Tropic of Cancer ? The Tropic of Capricorn ? Are days and nights equal at the equator ? Why ? At the Tropic of Capricorn ? Why ? At the Tropic of Cancer ? Why ? Are days and nights always equal at the equator ? Why ? When only are they equal at other places ?

Taking a given point, say your home city or some other city, follow it through the illuminated and non-illuminated portions of the earth at the June solstice. Does it pass for the greater distance through the illuminated or non-illuminated portions ? Follow the same study for the December solstice.

It will now be apparent that unequal length of day and night is due to the unequal division of the northern and southern hemispheres by the circle of illumination. That is, when the days are long, these hemispheres pass through a smaller shadow than when the days are short. The principle can be well shown by the ajDparatus shown in Figure 3. Take a globe (a slated globe is preferable)

Jt ^ and compass. With one .leg

of the compass on the equator and the compass opening equal to the radius of the globe, the circle described will pass through the poles. This circle will represent the circle of illumination with the sun at its center. What time of the year is represented ? Moving the FlG - 3 - leg of the compass north or

south of the equator in the same way as the sun's vertical rays move, the circle of illumination can be shown for various positions of the sun. With this in mind demonstrate the following problems : —

When the vertical rays are 5° north of the equator, what is the location of the circle of illumination near the North Pole ? Near the South Pole ? What is the position of the circle of illumination when the vertical rays are 20° north of the equator ? When they are 23 J° south of the equator ?

THE EARTH AS A PLANET 7

From the following table plot graphs showing the length of day for 60° north and 60° south. (Use the length of day in minutes for plotting.) Why are the graphs pointed in opposite directions ? Plot on another sheet of paper the graphs for 30° north and 30° south. (Use the same scale for each.) In which set of graphs is the greatest length of day shown ? Why ? The least ? Why ? Which graphs show the greatest range of length of day ? Why ?

Table showing the Duration op Direct Sunlight on the Fifteenth of each Month for Latitude : 60° North, 60° South, 30° North, and 30° South

60° North

60° South

30° North

30° South hr. m.

m.

hr. m.

m.

hr.

m. m.

hr. m. m.

6 19

17 41

16 616

13 44 824

8 51

15 9

58 658

13 2 782

11 30

12 30

50 710

12 10 730

14 18

9 42

45 765

11 15 675

May

16 50

7 10

31 811

10 29 629

June

18 26

5 34

55 835

10 5 605

July

17 46

6 14

46 826

10 14 614

15 27

8 33

7 787

10 53 653

12 43

11 17

14 734

11 46 706

21 681

12 39 759

7 17

16 43

31 631

13 29 809

5 35

18 25

5 605

13 55 835

4. LONGITUDE AND TIME

How long does it take the earth to make one rotation f Through how many degrees does the earth turn to make one rotation ? Through how many degrees does it rotate in an hour ? In a minute ? In a second ? What is the difference in time between two places 45° of longitude apart ? What is the difference in time between two places 65° apart ? 90° apart ?

If two places have a difference in time of 2 hours, how many degrees of longitude are they apart ? How many if they have a difference in time of 3 hours 30 minutes ? Of 6 hours 45 minutes ? What is the difference in solar time between New York (74°) and San Francisco (122° 29') ? New York and Chicago (87° 36') ? Between New York and your own or nearest city ?

5. TO ASCERTAIN THE NOON HOUR

From a south window hang a plumb line. Measure its shadow at different hours of the day and record their lengths. Plot these lengths. How do the shadows behave as noon is approached ? As noon is receded from ? Why is this so ? What shadow, the longest or the shortest, represents noon ? Why ? (A perpendicular post will answer the same purpose as the

plumb line.)

6. LONGITUDE

Arredono, Fla., and Nome, Alaska, Quadrangles. What are the latitudes of the Florida and Alaska maps ? What difference in latitudes ? What is the scale of the maps? What is the length (in miles) of five minutes of

THE EARTH AS A PLANET 9

longitude on the Florida map ? What therefore is the length of a degree here ? What is the length of a degree on the Alaska map ? What is the reason for this change in length ? What is the length of a degree of longitude at the poles ? You will note that the Alaska map is narrower at the top than at the bottom. Why is this ? Do the Florida maps show as much narrowing ? Why ? Draw to illustrate.

7. TO ASCERTAIN THE LOCAL LATITUDE

Using the same apparatus as in Exercise 5, find the length of the shadow. This should preferably be done at one of the equinoxes. Measure ^ A

the shadow BC (Figure 4) at noon.

The angle ABC represents the altitude of the sun. This angle can readily be b" obtained by trigonometry, or by con- fig.4.

struction as follows : Construct the right-angle triangle ABC to scale. Then the angle ABC can be measured with a protractor. The use of this angle will best be seen from a few problems. At the equator the sun at this time will be directly overhead. Angle ABC is 90°, and the complement of this is 0° or the latitude. In latitude 5° from the equator the angle ABC will be 95°. Applying the same reasoning, what is your latitude as determined from angle ABC1 Compare this with your latitude as determined by more careful work. The local latitude can as easily be obtained at the solstices by adding or subtracting 23^°. If the angle ABC or the sun's altitude is 50° at the equinox, what is the latitude ? If it is 50° at the June solstice, what is the latitude ? What is the latitude if the sun's altitude is 50° at the December solstice ?

8. REVOLUTION OF THE EARTH

* Part I. Path of the Earth. — From the following table plot a graph of the earth's distance from the sun.

Table showing the Earth's Distance from the Sun on the Fifteenth of Each Month (Derived for 1908)

Distance

Distance

Distance

January February March April

May June July

September October November December

When is the earth nearest (perihelion) ? When farthest (aphelion) ? Is the change from perihelion to aphelion sudden or abrupt ? Does the graph show the earth's path to be a circle or an ellipse ? If it were a circle, how would your graph appear ? What is the average distance of the sun ? (Find from your graph, not from computation.) What is the range of distances ? (Find from your graph.) Preserve your graph. It will be needed later.

THE EABTH AS A PLANET

Part II. — From the following table plot the average daily velocities of the earth for the year.

Table showing for Each Month the Total Distance in Miles Traveled by the Earth in its Orbit and its Average Daily Velocity (Calculated for 1908)

Miles pek

Average

Daily Velocity

Miles per Month

Average

Daily Velocity

May

June

July

Are the velocities equal? How would your graph look if they were ? When is the velocity greatest ? When least ? Compare your graph with that of Part I. Do their maxima and minima come at about the same time ? Why ?

How are the monthly velocity and distance from the sun related ? When do the velocities change most suddenly ? Why ? At what parts of the year are the velocities least changing ? Why ? How does your graph show at a glance the rapid and the slow changes ?

What is the total length of the earth's path ? In what month is it longest ? In what, shortest ? How does its length from March to September, inclusive, compare with the rest of the year ?