CHAPTER XLVII. 



THE ARCHAEAN AND ALGONKIAN ERAS. 



ASTRONOMICAL studies lead us to suppose that our earth was 

 once a sphere of glowing gas, and that as it gradually cooled, por- 

 tions were condensed, forming a molten nucleus surrounded by 

 intensely heated gases. That as the cooling process continued, 

 the nucleus gradually increased in size and the temperature of the 

 surrounding gases diminished until the mass ceased to be lumi- 

 nous. At length a solid crust began to form over the heated in- 

 terior. It was doubtless broken up, remelted and reformed many 

 times, but at last a continuous slag-like crust became permanent. 

 From what we know of the composition of the rocks, this crust 

 was composed mainly of the silicates of aluminium, calcium, 

 potassium, sodium and magnesium, with iron manganese and 

 other substances. 



All the water of the present oceans, lakes, and rivers, all the 

 mercury, sulphur, chlorine and other volatile matters with the 

 air formed an atmosphere of dense, poisonous vapors. In time, 

 portions of these vapors condensed, covering the crust with 

 broad, shallow oceans of hot, acid water. As the earth continued 

 to cool, the interior contracted more rapidly than the solid crust, 

 and as the crust settled down with the inner mass broad, low 

 swells and wide, shallow depressions were developed . These grad- 

 ually increased in elevation and depth until the continents ap- 

 peared, and the ocean boundaries were defined. Portions of 

 these ancient continents may have been submerged from time to 

 time for many hundreds of feet, but at no time have the conti- 

 nents and oceans changed places ; their relative positions have 

 probably always been substantially the same. 



The reactions between the acid waters and the basic rocks re- 

 (348) 



