12 Depth of the Ocean. 



elevation — i.e., a raised portion of the earth's surface, which 

 may be partially or entirely covered with water, and an area 

 of depression — i.e., a hollow in the same surface, which may 

 be raised above the level of the sea, and form dry land or the 

 basin of an inland sea or lake. 



If we examine the chart of the world (Plates 1 and 2) in 

 the light which has been thrown upon this question by all the 

 reliable soundings obtained up to the present, it will be found 

 that continents and islands which we have been in the habit 

 of considering as separated from each other by wide seas and 

 deep straits virtually form part of the same area of elevation ; 

 and, in a similar manner, that certain oceans and seas, which we 

 are accustomed to distinguish by separate names, form part of 

 the same area of depression. It will also appear that, with 

 the exception of the islands scattered over the face of 

 the ocean and of the Antarctic region, all the dry land at 

 present existing may be reduced to one large area of elevation, 

 gravitating towards the North Pole, as the common centre of 

 the principal land masses ; similarly, if we except the Arctic 

 region and other inland basins, all the oceans and seas compose 

 a single vast area of depression with the South Pole for 

 common centre of the larg^er accumulations of water on this 

 globe. The x^rctic region forms a distinct area of depres- 

 sion placed in the centre of the great area of elevation, 

 and the Antarctic recrion, accordino- to the evidence we at 

 present possess, is an area of elevation, surrounded on all 

 sides by the above-described great area of depression. The 

 numerous small islands that crop up in the middle of the 

 oceanic basins are generally found associated in groups, 

 and they belong to areas of elevation at tlie present time 

 submerged, that is to say, in the condition in which we know 

 the dry land to have been at an epoch more or less remote in 

 the history of our planet. 



