HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 109 



general 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 preva- 

 lent 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, and 

 draw water away from areas less depressed, and this water would add 

 its weight to the previous excess; and so, by progressive and cumula- 

 tive 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-areas and water-areas respectively. 



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

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



Fig. 32a. — Diagram intended to illustrate the evolution of the ocean basins under the 

 planetesimal hypothesis. I represents an early stage in the evolution of the hydro- 

 sphere when it was largely subterranean, being held in the porous zone and only 

 appearing at the surface in the volcanic pits developed by explosive vulcanism of 

 the supposed lunar type. These are somewhat more abundant in the regions of 

 B B than in that of C. II represents a more advanced stage in which the crater 

 lakes of the regions B,B had become largely confluent, giving the interrupted water 

 areas B', B', while the region C had become the more protuberant area C", which was 

 chiefly land. Ill shows the further progress of the aggregation of the water, the 

 relatively greater depression of the oceanic basins, B" ,B" , and the protrusion of 

 the continent, C" ' . 



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

 (Fig. 32a). The wash from the land tended to build its borders out 



