THE WEST INDIAN WATEES. 



341 



of Jamaica the section thus closed has an extreme depth of over 600 fathoms. 

 Beyond the Serranilla, Bajo Nuevo, Combey, and a few other cays, the vast expanse 

 of the Caribbean waters gradually deepens eastwards to abysses of 1,000, 1,500, 

 2,000, and 2,500 fathoms ; north of the Dutch Islands on the Venezuelan coast it 

 falls even to 2,600 fathoms, but again shoals in the direction' of the Bird or Aves 

 islets. 



The islands which form the outer rampart of the Caribbean Sea rise like the 

 ruiaed piers of a bridge, between Avhich flow the currents and counter-currents of 

 the Atlantic waters. Most of the Antilles are connected by submerged sills, none 



Fig. 159. — The Pueeto Rico Abyss. 

 Scale 1 : 600,000. 



to 2.000 

 Fathoms. 



2,000 to 2,500 

 Fathoms. 



Depths. 



3,000 to 3 500 

 Fathoms. 



3,500 to 4,000 

 Fathoms. 



4,00U Fathoms 

 and upwards. 



12 Miles. 



of which exceed 500 fathoms except the passage between the Virgin Islands and 

 Sombrero, and the two channels north and south of Martinique. But the sub- 

 marine bank on which the islands rest falls rapidly towards the Atlantic, where 

 the 2,000-fathom line is scarcely anywhere more than 20 miles from the insular 

 groups. The deepest cavity yet revealed in the whole of the Atlantic occurs at a 

 point due north of Puerto Rico, where the soundings have recorded a depth of 

 4,560 fathoms. 



Catchment Basins. 



Of the two great inland basins, the Gulf is about one-sixth smaller and very 

 much shallower than the Caribbean Sea. Were its level to be suddenly lowered 



