Basin of the Atlantic. 17 



several thousand miles, will easily recall the to them familiar fact 

 that, with rare exceptions, and those chiefly occurring in the 

 vicinity of land, the result of one day's sounding gave a tolerably 

 approximate idea of the depth to be encountered on the following 

 day. The alteration of level in mid-ocean between two points 

 as much as a hundred miles apart is generally so slight that, to 

 an observer standing at the bottom of the sea, the latter would 

 appear a perfect plain. Thus the bottom of our larger oceanic 

 basins is composed of gentle undulations rising and ialling from 

 a few fathoms to two or three miles, in distances extending over 

 many hundred miles. This view accords with the experience 

 of the geologist, who finds that the bulk of the dry land consists 

 of sedimentary strata originally laid down in a horizontal, or 

 nearly horizontal, position at the bottom of the sea, and there can 

 be little doubt but that the depths of the ocean are at the 

 present time the scene of the formation of sedimentary strata 

 which some day may be converted into dry land, and contain 

 embedded in their folds traces of the animal life with which 

 they abound. 



The Basin of the Atlantic. — One of the most remarkable 

 results in connection with the exploration of the sea is the 

 discovery of several extensive submarine plateaux, which 

 interrupt what was until lately supposed to be an unbroken 

 waste of fathomless abyss. One of these plateaux traverses the 

 Atlantic Ocean in its whole length from north to south, 

 repeating in its form the S-shaped contour of the eastern and 

 western shores of this ocean (Plate 3). After attaching itself 

 by its northern end to the plateau which connects Europe and 

 Iceland, and separates the Atlantic from the Arctic basin, it 

 runs southward towards the Azores, and, gradually con- 

 tracting in width, sweeps round towards St. Paul's Rocks. 

 Reduced, comparatively speaking, to a narrow ridge, it follows 

 the line of the Equator as far as the meridian of Ascension 



