CHAPTER III.

THE WORK OF RUNNING WATER.

+Rain and River Erosion+ 57

_Subaërial Erosion without Valleys_ 58

_The Development of Valleys_ 63

By the growth of gullies, 63. Limits of growth, 67. The

permanent stream, 70. Other modes of valley development,

73. Structural valleys, 77. The courses of valleys, 77. The

development of tributaries, 78.

+A Cycle of Erosion. Its Stages+ 80

+General Characteristics of Topography Developed by River Erosion+ 92

+Special Features Resulting from Special Conditions of Erosion+ 92

Bad-land topography, 93. Special forms of valleys; canyons,

94.

+The Struggle for Existence Among Valleys and Streams+ 100

Piracy, 103.

+Rate of Degradation+ 105

Material in solution in river water, 107.

+Economic Considerations+ 108

+Analysis of Erosion+ 110

_Weathering._ 110

_Transportation_ 115

Transporting power and velocity, 115. How sediment is

carried, 116.

_Corrasion_ 119

Abrasion, 119. Solution, 122.

+Conditions Affecting the Rate of Erosion+ 123

_The Influence of Declivity_ 123

_The Influence of Rock_ 124

Physical constitution, 124. Chemical composition, 124.

Structure, 125.

_The Influence of Climate_ 127

+Effects of Unequal Hardness+ 132

Rapids and falls, 132. Rock terraces, 140. Narrows, 141.

Other effects on topography, 142. Adjustment of streams to

rock structures, 146.

+Influence of Joints and Folds+ 150

Joints, 150. Folds, 154.

+Effect of Changes of Level+ 161

Rise, 161. Sinking, 170. Differential movement, warping,

171.

+The Aggradational Work of Running Water+ 177

Principles involved, 177.

_The Deposits_ 181

Types, 181. Alluvial fans and cones, 181. Ill-defined

alluvium, 183. Alluvial plains, 184. Flood-plains due to

alluviation, 186. Flood-plains due to obstructions, 188.

Levees, 188. Flood-plain meanders, cut-and-fill, 190.

Scour-and-fill, 194. Materials of the flood-plain, 196.

Topography of the flood-plain, 196. Topographic adjustment of

tributaries, 197. River-lakes, 198. Deltas, 198. Delta lakes,

204.

+Stream Terraces+ 204

Due to inequalities of hardness, 204. Normal flood-plain

terraces, 205. Flood-plain terraces due to other causes, 208.

Discontinuity of terraces, 209. Termini of terraces, 210.

Geology, Vol. 1 [of 3] · 第 3 / 22 章