CONTENTS. xni 



PAGE 



rotation, 73. The order in which the contingencies of 

 collision come into play, 75. The collecting zones, 77. 

 Competitive nuclei and selective dominance, 78. The 

 shifting of orbits, 78. The spacing-out of the planets, 

 78. 

 Summary 81 



CHAPTER II. 



THE HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 



I. Stages Under the Common Form of the . Gaseo- Molten (La- 



placian) Hypothesis 82 



1. The Astral Eon 83 



2. The Azoic Eon 83 



(a) The Lithic era, 83. (b) The Oceanic era, 83. 



3. The Archeozoic Eon 83 



(a) The era of the first plants, 83. (b) The era of 

 the first animal life, 83. 

 Difficulties Encountered by the Gaseo-Molten Hypothesis . . 84 



1. Evidence Relative to an Original Crust 84 



The theoretical crust a universal identifiable sub- 

 stratum, 84. The limitations of pyroclastic concela- 

 ment of the crust, 85. The adverse bearing of recent 

 discoveries, 85. 



2. Atmospheric Difficulties 86 



The adverse evidence of early life, 87. Incongrui- 

 ties on the physical side, 87. 



II. A Modification of the Preceding View 88 



I. The astral eon, 90. II. The molten eon, 90. 

 III. The lithic eon, 90. IV. The primitive volcanic eon, 

 91. V. The sedimentary eon, 91. 

 III. Stages of Growth Under the Accretion (Planet esimal) Hypothesis 91 



1. The Nuclear Stage 92 



2. A Possible Atmosphereless Stage 92 



3. The Initial Atmospheric Stage 93 



The origin of the atmosphere, 93. External source 

 of supply, 94. Internal source of supply, 94. The 

 nature of the initial atmosphere, 95. Summary of avail- 

 able material, 96. The actual proportions of the atmo- 

 spheric gases determined by the earth's gravity, 96. 



4. The Initiation of Vulcanism 99 



