CONTENTS. x i 



PAGE 



123; Seismographs, 128; The Determination of the Epicentruro, 130; Deter- 

 mination of the Focus — Examples, 131 ; Effect of the Moon on Earthquake-Oc- 

 currence, 132; Relation of Earthquake-Occurrence to Seasons and Atmospheric 

 Conditions, 133. 

 Section 4. Gradual Elevation and Depression or the Earth's Crust, 133 ; Ele- 

 vation or Depression during Earthquakes, 134 ; Movements not connected with 

 Earthquakes — South America, 134; Italy, 134; Scandinavia, 135; Greenland, 

 136 ; Deltas of Large Rivers, 136 ; Southern Atlantic States, 137 ; Pacific Ocean, 

 137; River-beds as Indicators of, 137. Theories of Elevation and Depression, 

 138; Babbagc's Theory, 138; HerschePs Theory, 139; General Theory, 139. 



CHAPTER IV. 

 Organic Agencies 140-161 



Section 1. Vegetable Accumulations. — Peat- Bogs and Peat-Swamps. — Descrip- 

 tion, 140 ; Composition and Properties of Peat, 140 ; Mode of Growth, 141 ; 

 Rate of Growth, 142 ; Conditions of Growth, 142 ; Alternation of Peat with 

 Sediments, 143. Drift-Timber, 143. 



Section 2. Bog-Iron Ore, 143. Conditions of Deposit and Geological Applica- 

 tion, 144. 



Section 3. Lime Accumulations — Coral Reefs and Islands. — Interest and Im- 

 portance, 145 ; Coral Polyp, 145 ; Compound Coral, or Corallum, 145 ; Coral 

 Forests, 145 ; Coral Reef, 146 ; Coral Islands, 146 ; Conditions of Coral-Growth, 

 147 ; Pacific Reefs, 147 ; Fringing Reefs, 147 ; Barrier Reefs, 148 ; Circular 

 Reefs, or Atolls, 148 ; Small Atolls and Lagoonless Islands, 149. TJieories of 

 Barrier and Circular Reefs, 150; Crater Theory, 150; Objections, 150; Dar- 

 win's Subsidence Theory, 150; Proofs, 151; Murray's Theory, 152; Area of 

 Land lost, 153 ; Amount of Vertical Subsidence, 153 ; Rate of Subsidence, 154 ; 

 Time involved, 155; Geological Application, 155; Reefs of Florida, 156; De- 

 scription of Florida, 156 ; General Process of Formation, 157 ; History of 

 Changes, 157 ; Mangrove Islands, 158 ; Florida Reefs compared with other 

 Reefs, 159 ; Differences — 1. Continuous land-making. 2. Barriers without 

 Subsidence, 160 ; Probable Agency of the Gulf Stream. 160 Shell-Deposits, 

 160; Molluscous Shells, 161; Microscopic Shells, 161. 



PART II. 



STRUCTURAL GEOLOGY. 



CHAPTER I. 

 General Form and Structtre of the Earth .... 163-170 

 1. Form of the Earth, 163. 2. Density of the Earth, 165. 3. The Crust of the 

 Earth, 166; Means of Geological Observation, 166. 4. General Surface Con- 

 figuration of the Earth, 167 ; Cause of Land-Surfaces and Sea-Bottoms, 167; 

 Laws of Continental Form, 169. Rocks, 170 ; Classes of Rocks, 170. 



CHAPTER II. 



Stratified or Sedimentary Rocks 170-201 



Section 1. Structure and Position. — Stratification, 170; Extent and Thickness, 

 171 ; Kinds of Stratified Rocks, 171 ; I. Stratified Rocks are more or less Con- 



