CHAPTER VI. 



THE BED OF THE OCEAN. 



Changes in the Distribution of Land and Water — Formation of Sub-oceanic Strata — 

 Formation of Central Oceanic Plateaux — Formation of Areas of Elevation and of 

 Areas of Depression — Formation and Transformation of Continents — Forma- 

 tion of Mountain Ranges and Submarine Ridges. 



Changes in the Distribution of Land and Water. — It 

 was mentioned in an earlier chapter that the ordinary conception 

 of the relative distribution of land and water over the surface of 

 the earth may be replaced or rather supplemented by one which 

 more adequately embodies the results of modern research, and 

 according tawhich the surface of the solid earth-crust may be 

 considered as composed of hills and hollows, areas of elevation 

 and areas of depression — the former not necessarily constituting 

 dry land, the latter not always occupied by water. It was also 

 shown how the data furnished by recent sounding operations 

 afford additional evidence of the observation — not made for the 

 first time, since it has attracted the attention of every student of 

 comparative geography — that the principal land-masses, more or 

 less combined into one great area of elevation, gravitate towards 

 the North Pole as their common centre ; while the different 

 oceanic basins, constituting one great area of depression, 

 gather round the South Pole as their centre. If this obser- 

 vation conveys any information beyond the familiar fact 

 that there is more land in the northern and more water in the 

 southern hemisphere, it means that the slow but unceasing 

 changes which take place in the distribution of land and water 

 obey a general tendency to accumulate land in the northern and 

 water in the southern hemisphere. There are numerous indica- 



