THE EVOLUTION OF THE EARTH 



through volcanic vents, suddenly vaporizing 

 large quantities of surface-water, and causing 

 phenomena similar to those now witnessed 

 upon Saturn and Jupiter. As the crust thick- 

 ened, these volcanic agencies were more and 

 more restrained: craters became restricted to 

 certain localities where the crust was less thick 

 than elsewhere, and earthquake waves began to 

 run, as at present, along definite lines. Those 

 well - regulated earthquake pulses which raise 

 continents and ocean-floors at the rate of a few 

 inches or feet per century now began to in- 

 crease the definite heterogeneity of the surface. 

 To the long rhythms of elevation and subsi- 

 dence thus produced have been due countless 

 differentiations in the directions of ocean-cur- 

 rents and continent-axes, in watershed, in the 

 composition of sedimentary strata, and in cli- 

 mate. And to all these may be added the met- 

 amorphosis of sedimentary rocks by volcanic 

 heat, and the seismic shoving up of strata at 

 various angles. 



All these geologic phenomena are thus seen 

 to be classifiable as differentiations and integra- 

 tions of the earth's superficial matter, caused by 

 the continuous integration of the earth's mass 

 with its attendant dissipation of molecular mo- 

 tion. We may. next note that meteorologic 

 phenomena are similarly classifiable. Before the 



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