x CONTENTS. 



PAGE 



fications of Glaciers, 46 ; Motion of Glaciers, 48 ; Advance and Retreat — 

 Graphic Illustration, 4S ; Line of the Lower Limit of Glaciers, 49 ; General De- 

 scription, 50 ; Earth and Stones, etc., 53. Moraines, 54. Glaciers as a Geologi- 

 cal Agent, 55 ; Erosion, 55 ; Transportation, 57 ; Deposit — Balanced Stones, 57 ; 

 Material of the Terminal Moraine, 57 ; Evidences of Former Extension of Gla- 

 ciers, 58 ; Glacial Lakes, 58. Motion of Glaciers and its Laics. — Evidences of 

 Motion, 59; Laws of Glacier-Motion, 59. Theories of Glacier-Motion, 01. Vis- 

 cosity Theory of Forbes. — Statement of the Theory, 61 ; Argument, 61. Regela- 

 tion Theory of Tyndall, 63 ; Eegelation, 64 ; Application to Glaciers, 64 ; Compari- 

 son of the Two Theories, 65 ; Croll's Theory, 65 ; Thomson's Theory, 66. Struct- 

 ure of Glaciers, 66 ; Veined Structure, 66 ; Fissures, 67. Theories of Structure. 

 — Fissures, 67 ; Veined Structure, 68 ; Physical Theory of Veins, 69. Floating 

 Ice — Icebergs, 70; General Description, 71; Icebergs as a Geological Agent — 

 Erosion, 72; Deposits, 72. Shore-Ice, 72. Comparison of the Different Forms 

 of the Mechanical Agencies of Water, 73. 

 Section 4. Chemical Agencies of Water. — Subterranean Waters, Springs, etc., 

 74 ; Springs, 74 ; Artesian Wells, 75 ; Chemical Effects of Subterranean Waters, 

 76 ; Limestone Caves, 76. Chemical Deposits in Springs. — Deposits of Carbon- 

 ate of Lime, 77 ; Explanation, 77 ; Kinds of Materials, 78 ; Deposits of Iron, 79 ; 

 Deposits of Silica, 79 ; Deposits of Sulphur and Gypsum, 79. Chemical Depos- 

 its in Lakes. — Salt Lakes and Alkaline Lakes, 79 ; Conditions of Salt-Lake For- 

 mation, 80; Deposits in Salt Lakes, 81. Chemical Deposits in Seas, 82. 



CHAPTER III. 

 Igneous Agencies . . . . . . . . . 82-140 



Section 1. Interior Heat of the Earth. — Stratum of Invariable Temperature, 83 ; 

 Increasing Temperature of the Interior of the Earth, 84 ; Constitution of the 

 Earth's Interior, 84 : 1. Rate of Increase not uniform, 85 ; 2. Fusing- Point not 

 the same for all Depths, 86 ; Astronomical Reasons, 87 ; Most Probable View, 87. 



Section 2. Volcanoes. — Definition, 87 ; Size, Number, and Distribution, 88 ; Phe- 

 nomena of an Eruption, 89 ; Monticules, 90 ; Materials erupted, 90 ; Stones, 90 ; 

 Lava, 90; Liquidity of Lava, 90; Physical Conditions of Lava, 91 ; Classifica- 

 tion of Lavas, 92 ; Gas, Smoke, and Flame, 93 ; Kinds of Volcanic Cones, 93 ; 

 Mode of Formation of a Volcanic Cone, 93 ; Comparison between a Volcanic 

 Cone and an Exogenous Tree, 96 ; Estimate of the Age of Volcanoes, 97. Theory 

 of Volcanoes, 97 ; Force, 97 ; The Heat, 98 ; Internal Fluidity Theory, 98 ; Ob- 

 jections, 98; Chemical Theory, 99; Recent Theories, 100; Aqueo-igneous The- 

 ory, 100; Fisher's Theory, 100; Mechanical Theory, 100; Prestwich's Theory, 

 101. Subordinate Volcanic Phenomena, 101; General Explanation, 101. Gey- 

 sers, 101 ; Description, 101 ; Phenomena of an Eruption, 103 ; Yellowstone Gey- 

 sers, 103; Theories of Geyser-Eruption, 106; Mackenzie's Theory, 106; Bun- 

 sen's Investigations, 107; Theory of Geyser-Eruption — Principles, 108; Appli- 

 cation to Geysers, 108 ; Bunsen's Theory of Geyser-Formation, 110. 



Section 3. Earthquakes, 111; Frequency, 111; Connection with other Forms of 

 Igneous Agency, 111 ; Ultimate Cause of Earthquakes, 113; Proximate Cause, 

 114 ; Application to Earthquakes, 1 14 ; Experimental Determination of the Ve- 

 locity of the Spherical Wave, 116 ; Character of the Wave, 116 ; Explanation of 

 Earthquake-Phenomena, 117; Verticose Earthquakes, 120; Explanation, 120; 

 Minor Phenomena, 122. Earthquakes originating beneath the Ocean, 125 ; Great 

 Sea-Wave, 125; Examples of the Sea-Wave, 126. Depth of Earthquake-Focus, 



