HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. HI 



opinion that water is present, though perhaps not in the form of definite 

 water-bodies. 



It has been inferred from the almost complete, and sometimes total, 

 disappearance of the polar white-caps in summer, and from other 

 phenomena, that the climate of Mars is phenomenally mild considering 

 its distance from the sun. This has been regarded as all the more 

 puzzling because of the scantiness of the Martian atmosphere, but it 

 is what might be expected if Mars' atmosphere is like that assigned 

 the earth when it had similar size, i.e., composed largely of the heat- 

 absorbing carbon dioxide. 



Without attempting to fix the precise stage, it is not unreasonable 

 to assume that surface-waters had begun their accumulation upon the 

 earth's exterior while yet it lay 1500 to 1800 miles below the present 

 surface. The present difference between the radii of the oceanic basins 

 and the radii of the continental platforms is scarcely three miles, on 

 the average, so that if the continental segments be assumed to be 

 in approximate hydrostatic equilibrium with the oceanic segments 

 to-day, as seems highly probable, the selective weathering process 

 brought about a difference in depression of only one mile in 500 or 

 600 miles, or about one fifth of one per cent. We appear, therefore, to 

 be laying no heavier burden upon weathering than it is competent to 

 bear. It might well be thought to do much more, but the process 

 of weathering is very slow, and as new material was constantly falling 

 in and burying the old, partial alteration was all that could take place ; 

 and besides, a part of the basic material leached from the surface was 

 redeposited beneath the ground-water of the land, and was not lost 

 to the continental segments. 



Not only is the evolution of the great abysmal basins and of the 

 continental platforms thus assigned to a very simple and inevitable 

 process, but there is therein laid the foundation for subsequent deforma- 

 tions of the abysmal and continental type. 



VI. The Initial Life Stage. 



There is no direct evidence as to the time or the method of the 

 introduction of life upon the earth. The earliest legible record of 

 life, in the form of fossils, bears evidences of great advances in evolu- 

 tion along many divergent lines. The inference is, therefore, impera- 



