8 CONTENTS 



PAGE 



Striking Effects of Ground Water ........... 69 



Swallow Holes. Caverns. Natural Bridges. Cave Deposits. Karst. 

 Landslides. 



Concretions 75 



Composition of Concretions. Time of Formation. Oolitic Limestone. 

 Geodes. 



CHAPTER IV 



THE WORK OF STREAMS 



Factors in Stream Erosion 81 



Material Carried by Streams. How the Sediment is Moved. Factors Deter- 

 mining the Velocity of Streams. Water Wear. Solution. Vertical 

 Erosion (Corrasion). Weathering and Vertical Erosion. Base Level 

 of Erosion. Effect of Load. Factors Affecting the Rate of Erosion. 

 Scour and Fill. Lateral Erosion. 



Features Due to Stream Erosion 89 



Falls and Rapids. Exceptions — Falls not the Result of Erosion. Pot- 

 holes. Canyons. Instances of Rapid Erosion. Effect of Deforesta- 

 tion on Rivers. Growth of Valleys. Valleys Formed in Ways Other 

 than by Stream Erosion. The Direction of Valleys. Basins and 

 Divides. Elevations Due to Unequal Hardness. Outliers. Rock 

 Terraces. Stream Piracy. 



The Erosion Cycle 109 



Youth. Maturity. Old Age. Effect of Elevation and Depression on 

 Streams. 



Peneplanation , 114 



The Peneplain of Southern New England. The Appalachian Peneplain. 

 The Laurentian Peneplain. Rate of the Denudation of Continents. 

 How the Load of Streams is Measured. 



Deposition 119 



Causes of Deposition. Flood Plains. Meanders. Oxbow Lakes. Natural 

 Levees. Alluvial Cones and Fans. Piedmont or Alluvial Plains. 

 Alluvial Terraces. Discontinuity of Terraces. Characteristics of 

 River Deposits. 



Deltas 130 



Growth of Deltas. Structure of Deltas. 



Deposition in Lakes by Streams and by Other Agents 133 



Mechanical Deposits. Chemical Deposits. Organic Deposits — Diatoms. 

 Marl. Peat. Playas. Salt Lakes. Alkaline Lakes. Origin of 

 Rock Salt. Extinct Lakes. 



CHAPTER V 



THE WORK OF GLACIERS 



General Considerations .141 



Distribution and Size of Glaciers. Position of the Snow Line. Formation 

 of Ice in Snow Fields. 



