244 CARNEGIE INSTITUTION OF WASHINGTON. 



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 pref- 

 erably to small atmosphereless bodies, favors the view that the inter- 

 nal 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. 



When the increasing water-vapor of the growing atmosphere 

 reached the point of saturation, it is of course assumed to have taken 

 the liquid form and became a contribution to the hydrosphere. 

 Probably condensation had occurred within the fragmental zone long 

 before the external atmosphere reached saturation. The hydro- 

 sphere, therefore, probably had its birth under ground, 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 

 accumulation went on, it is assumed to have risen 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 deplojmient is, therefore, pictured 

 as a growth from innumerable lakelets scattered with unknown pro- 

 miscuousness over the face of the 3'oung 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 of life. The 

 evolution of the ocean basins and the continental platforms under 

 this hypothesis is, however, exceedingly simple. 



With the acquisition of an atmosphere and a hydrosphere, the condi- 

 ditions for weathering were present, and all those attendant processes 

 of a gradational nature which constitute the dominant surface work 

 of to-day. 



For the present study, two features of these gradational processes 

 overshadow all others, ( i ) the leacking action of the atmospheric waters, 

 and ( 2 ) the relative protection of the water bodies. The essence of the 



