i. ARCH.EAN TIME. 



Synonymy. — Primitivgebirge, Urgebirge, Lehmann, 1756, Werner. Urformation. Ur- 

 gneissformation. Azoic Rocks, Murchison and De Verneuil, 1845, Bussia in the Urals, i. 

 10. Fundamental Gneiss, Lewisian Gneiss, and later, Laurentian Gneiss, after Logan, 

 Murchison. Mona Series, De La Beclie, Geol. 06s., p. xxxii, 1851, for crystalline rocks of 

 Anglesea, etc. Azoique, D'Orbigny, Fal. et Geol., 1851. Azoic System, J. D. Wliitney, Bcp. 

 of Foster and Whitney, Geol. Lake Superior Land District, Part ii., pp. 8-35, 1851, the 

 system comprising rocks north of Lake Superior, others south of the lake, also others in 

 the Adirondacks, etc. Laurentian and Huronian, Logan, 1852, 1854. Azoic (following 

 "Whitney, with Logan's subdivisions), first edition of tliis Geology, 1863. Archaean, 

 D., Amer. Jour. Sc, viii. 213, 1874, and second edition Geology, 1875. Eozoic, J. W. 

 Dawson, 1875. Crystallophyllian, Belg. Geologists of the Internat. Congr. Geol., 1885. 



Archaean time commences geologically with the earth as a solid globe, or 

 one having at least a solid exterior ; for only the conditions of such a globe 

 are within reach of geological investigation. By following the lead of ascer- 

 tained law in physics and chemistry, and the suggestions of astronomy, and 

 also such analogies as are afforded by later geological history, some probable 

 conclusions may be drawn with reference to earlier time. But this is not the 

 place for their discussion, except so far as to state the principal steps of 

 progress. The following is a general view of the natural subdivisions of 

 Archaean time. 



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 teon. 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 (amounting 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 sub- 

 stances (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 dis- 

 turbance and orographic work was begun ; when " statical meta- 

 morphism" or that dependent on heat of a statical source, — the 

 earth's mass and the vapors about it, — began. 



2. The OcEAJifio 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 



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