THE BAHAMAS. 



441 



are almost unique, for their rocky walls rise at angles of 50 or even 35 degrees 

 from abysses 2,000 to 2,500 fathoms deep. The oceanic basin is everywhere 

 abruptly limited by this coralline rampart, which forms an advanced coast-line 

 of the mainland, deflecting the Atlantic currents towards the north-west ; to this 



Fig-. 213.— TONGTTE OF THE OcEAN. 



Scale 1 : 2,500.ôoo. 



West oF Greenwich 



to 16 

 Feet. 



Depths. 



16 to 3,200 

 Feet. 



60 Miles. 



general movement of the ocean stream, sweeping along the sands, living organisms 

 and other materials used by the corals in the construction of their buildings, the 

 islands and chains of reefs doubtless owe their elongated form, disposed in the 

 direction from south east to north-west. Where the current gains access through 

 open breaches it develops graceful curves in the interior of the archipelagoes, 



