106 GEOLOGY. 



atmosphere should combine to give to the pit-forming effects extraor- 

 dinary magnitude, such, perhaps, as the moon exhibits (Vol. I, pp. 597- 

 598). 



Volcanic action not necessarily antecedent to the atmosphere. — It is 

 not necessary to the hypothesis to suppose that volcanic action was 

 an essential preliminary to the acquisition of an atmosphere, nor that 

 it came into function before the earth acquired an atmosphere, for 

 the initial atmosphere may have been supplied from external sources. 

 The apparent vigor and the wide prevalence of volcanic action on the 

 moon, if its pitted surface means vulcanism, as well as the glassy material 

 found in meteorites, whose origin is referred preferably to small, atmos- 

 phereless bodies, favors the view that the internal gases were given 

 forth abundantly before the earth grew to a mass sufficient to hold 

 them. If this were true, an ample source of atmospheric supply was 

 ready and waiting when the earth first acquired sufficient gravity to 

 clothe itself with a gaseous envelope. 



V. The Initial Hydrospheric Stage. 



The origin of the ocean. — -When the increasing water-vapor of the 

 growing atmosphere reached the point of saturation, it took the liquid 

 form and became a contribution to the hydrosphere. Probably con- 

 densation had occurred within the fragmental zone long before the 

 external atmosphere reached saturation. The hydrosphere, there- 

 fore, probably had its birth underground, and so long as the fragmental 

 zone retained its highly porous condition, it was what its name implies, 

 a veritable sphere or spheroidal layer. As the water increased it 

 rose to the surface, and doubtless first appeared in the innumerable 

 pits resulting from the previous volcanic action, and in the depressions 

 resulting from other deforming agencies. Its surface deployment is, 

 therefore, pictured as a growth from innumerable lakelets, scattered 

 with unknown promiscuousness over the face of the young planet, into 

 more and more enlarged and confluent bodies, until at length they 

 developed into the vast, irregular oceans of to-day. This evolution is 

 of fundamental geologic importance, for it involves the origin of the 

 ocean basins and of the continental platforms, and these constitute 

 at once the grand topographic features of the globe, the great integers 

 of deformation, and the controlling physical factors in the evolution 



