HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 83 



the general conceptions that have been entertained by the majority 

 of geologists during the past century. 



" I. The Astral aeon, as it has been called, or that of the fluid globe having a 

 heavy vaporous envelope, containing the future water of the globe or 

 its dissociated elements, and other heavy vapors or gases. 



II. The Azoic aeon. Without life. 



1. The Lithic Era: commencing with the earth a solid globe, or at least 



solid at the surface ; the temperature at the beginning above 2500° F. ; 

 the atmosphere still containing all the water of the globe (amount- 

 ing to 200 atmospheres, according to Mallet, 1880), all the carbonic 

 acid now in limestone and that corresponding to the carbon now 

 in carbonaceous substances and organic substances (probably 50 

 atmospheres) , all the oxygen since shut up in the rocks by oxidation, 

 as well as that of the atmosphere and of organic tissues. The time 

 when lateral pressure for crustal disturbance and orographic work 

 was begun; when 'statical metamorphism,' or that dependent 

 on heat of a statical source, — the earth's mass and the vapors about 

 it, — began. 



2. The Oceanic Era: commencing with the waters condensed into an ocean 



over the earth, or in an oceanic depression, with finally some emerging 

 lands, — the temperature perhaps about 500° F., if the atmospheric 

 pressure was still 50 atmospheres. The first of tides and the beginning 

 of the retardation of the earth's rotation. Oceanic waves and currents 

 and embryo rivers begin work about the emerged and emerging lands; 

 the large excess of carbonic acid and oxygen in the air and water 

 a source of rock-destruction; before the close of the era, the forma- 

 tion of limestones and iron-carbonate by chemical methods, removing, 

 carbonic acid from the air and so commencing its purification; 

 the accumulation of sediments without immediate crystallization or 

 metamorphism, and thereby the beginning of the earth's supercrust. 

 III. The Archceozoic aeon. Life in its lowest forms in existence. 



1. The Era of the First Plants: Algae, and later of aquatic Fungi (Bacteria), 



commencing with the mean temperature of the ocean at possibly 

 150° F., since plants now live in waters up to and even above 180° F. 

 Limestones formed from vegetable secretions, and silica deposits 

 from silica secretions; iron carbonate, and perhaps iron oxides 

 formed through the aid of the carbonic acid of the atmosphere and 

 water; large sedimentary accumulations, where conditions favored, 

 thickening the supercrust. 



2. The Era of the First Animal Life: mean temperature at the beginning 



probably about 115° F., and at the end 90° F., or lower; limestones 

 and silica deposits formed from animal secretions; deposits of iron- 

 carbonate and iron-oxides continued; large sedimentary accumula- 



