16 CUBA AND PORTO KICO 



Islands. More than half the Cuban seaboard, the various 

 groups of the Bahamas, the eastern members of the Lesser 

 Antilles, and the Bermudas are largely of coralline origin. 



The muddy deposits in the central parts of the Gulf and 

 of the Caribbean Sea are derived chiefly from the remains 

 of pteropods. In other places the shells of foraminifers 

 make up the bottom. It is only around the interior mar- 

 gin of the Gulf of Mexico that silicious sands and other 

 land debris brought down by rivers constitute the beach 

 material with which we are familiar in the United States ; 

 and, great as this is in quantity, it seems insignificant in 

 comparison with the vast amount of limestone which the 

 lower forms of life are creating through organic agencies, 

 and which, as we shall see, is the rock-making material of 

 all the non-volcanic islands of the West Indies, and one 

 of the conspicuous features which give them individuality 

 of color, soil, and landscape. 



The American Mediterranean finds a number of outlets 

 across the submerged bridge separating its abysses from 

 those of the Atlantic. Shipping may glide eastward out 

 of the Caribbean into the Atlantic between any of the 

 Windward Islands, but to go northward toward the United 

 States it must beat through one of four widely separated 

 gateways, which are of great strategic importance. These 

 are the Anegada, Mona, and Windward passages and the 

 Yucatan Channel. The Anegada Passage is the most east- 

 ern, threading its way between the region where the eastern 

 Virgin Islands of the Antillean group meet those of the 

 Windward chain. Through this passage there went for 

 many years all the European ships passing into and out of 

 the Caribbean Sea, making St. Thomas the commercial 

 capital of the West Indies. The Mona Passage separates 

 the island of Porto Rico from that of Santo Domingo, and, 

 being out of the lines of travel, is less frequented than the 

 others. The Windward Passage, between Santo Domingo 

 and Cuba, and its continuation as the Jamaican Channel 

 between the western cape of Santo Domingo and Jamaica, 



