246 CARNEGIE INSTITUTION OF WASHINGTON. 



the potential future combinations that are significant. For example, 

 an\' rock likel)' to arise from the residual sands, earths, and clays by 

 any probable raetamorphism, or even by remelting, would have a 

 lower specific gravity than the original average rock, or than any 

 rock likely to be developed from the alkalies and alkaline earths 

 removed by the leaching process in connection with the original 

 rock. The leaching of the land material had, therefore, a permanent 

 effect on its specific gravity — an effect not eliminated by any probable 

 change resulting from its burial under late accumulations. The 

 segments built up by accretion on the land were hence lighter than 

 the segments built up under the waters, and the difference increased 

 as the segments grew in thickness. 



It follows from the greater weight of the water- covered segments 

 that the compression beneath them, as they became more and more 

 weighted with incoming material, was greater than the compression 

 beneath the land segments, and hence the water-covered areas were 

 depressed relatively more than the land areas. The waters drawn in 

 upon the depressed segments augmented the depressing effects due 

 to difference in specific gravity. 



It is not necessary to suppose that there was at the outset a gen- 

 eral or continuous covering of certain large areas by water and a 

 general and continuous prevalence of land in other regions, but 

 merely that over certain portions of the globe water areas were more 

 abundant than over other areas. Where water predominated it may 

 at first have taken the form of numerous small bodies. Such areas 

 of prevalent water would, on the average, become heavier than other 

 areas, and hence, acting more or less as units, would become more 

 depressed. This excess of depression would extend the water-covered 

 areas, draw water away from the areas less depressed, and this water 

 would add its weight to the previous excess, and so by progressive 

 and cumulative action develop the great water areas and differentiate 

 them from the chief land areas. The tendency would always be 

 toward the more complete unification of the land and water areas 

 respectively. 



So long as the earth continued to grow appreciably by accession, 

 the water areas should continue to grow larger and deeper and the 

 land areas narrower and higher, so far as this one process is con- 

 cerned. The wash from the land tended to build its borders out 

 into the water basins and other influences modified the results, but 

 the deepening and spreading of the water basins is believed to have 

 been a markedly dominant process during the earth's growth. After 



