xi The Bed of the Oceans 193 



somewhat the form of a horse-shoe, the toe to the north. 

 The western limb rises very steeply from the depressed 

 area, and tapers southward to a point in 40 S. ; it is 

 crowned by the continent of Africa, and marked off from 

 the European portion by two small depressions forming 

 the deep basins of the Mediterranean. The eastern limb, 

 marked off from the solid mass, which is the foundation of 

 Asia, by a great series of deep depressions (the basins of 

 the seas of the Malay Archipelago), runs south-eastward as 

 a comparatively narrow ridge bearing Australia, and ends 

 at 55 S. in two great spurs from which Tasmania and 

 New Zealand rise. This limb lies exactly on the opposite 

 side of the globe to the Western World Ridge. ' 



257. The Depressed half of the Lithosphere or 

 Abysmal Area forms a hollow ring round the south polar 

 elevation, and runs northward in the form of nearly flat- 

 bottomed troughs between the steep slopes of the World 

 Ridges to the edge of the North Polar Plateau. It is ridged 

 by long gentle rises and abrupt mountain-like peaks, and 

 grooved by depressions infinitely various in size and form. 

 Distinct hollows or basins of the Abysmal Area correspond 

 to each ocean, and the slopes of the world ridges rising from 

 them usually run parallel to the shore line which bounds 

 the various oceans ( 216). The basins of the Pacific, 

 Atlantic, and Indian Oceans extend southward into the 

 Southern Ocean, which has not a separate basin of its own. 

 A typical section studied in conjunction with the map will 

 impress the general form on the student's mind, although 

 the scale of depth is necessarily exaggerated. 



258. The Atlantic Basin, extending between the eastern 

 edge of the Western and the western edge of the Eastern 

 World Ridge, is long and comparatively narrow. It is 

 deepest near the walls (Fig. 36) forming in fact two 

 long sinuous troughs separated by the Dolphin Ridge along 

 the centre, which reaches on the average to mean sphere 

 level. The Azores, St. Paul Rocks near the equator, and 

 Ascension all spring from this ridge, while the lonely islets 

 of Tristan d'Acunha mark its southern extremity. Four 

 great hollows or groups of -hollows, the floors of which 



O 



