GEOGRAPHIC RELATIONS OF THE THREE AMERICAS 619 



thence southwest to the Pacific coast, may be taken as the northern bound- 

 ary and Eio San Juan and the southern side of Lake Nicaragua as the 

 southern boundary. 



From the northeast coast of Honduras and Nicaragua a great sub- 

 marine plateau continues, with depths of less than 1,000 fathoms, to 

 Jamaica. Above it rises numerous banks and keys and along its course 

 are Thunder Knoll, Eosalind, Seranilla, and Pedro banks between the 

 continental shore and Jamaica. 



The principal old tectonic lines of Jamaica trend northwest to south- 

 east. As these are parallel to the shore northwest of Cape Gracias a Dios 

 and to the northeast edge of Mosquito Bank, there are evidently cross- 

 tectonic, lines nearly at right angles to each other in this ridge. 



A submarine ridge extends some 45 miles from the east end of Jamaica 

 and overlaps on the south side a ridge Avhich protrudes westward from 

 the west end of Haiti. The two ridges, however, do not connect, but are 

 separated by water over 1,000 fathoms deep. The ridge representing an 

 eastward submarine continuation of Jamaica indicates a third tectonic 

 line in that island. The last mentioned line nearly parallels the Bartlett 

 Deep, which lies to the north. The submarine slopes to the southeast are 

 toward the bottom of the Caribbean basin. 



8a. Haiti (southern part), Porto Eico, and the Virgin Islands: The 

 political division of Haiti designated Sud is dominated by east and west 

 trending mountains, which parallel in direction the east and west axis of 

 Jamaica. As the maximum depth between Haiti and Porto Eico is about 

 318 fathoms, they rise from a common, not greatly submerged, bank. 

 (See statement on preceding page in regard to considering Haiti as a 

 separate province.) 



The main mountain mass of Porto Eico, the Sierra Central, the maxi- 

 mum altitude of which is 3,750 feet at El Yunque, trends east and west, 

 paralleling in direction Sud, Haiti. There is coincidence in the direction 

 of elongation of the Jamaican bank, Sud (Haiti), and Porto Eico. 



The relative truncation of the west end of Porto Eico, except the pro- 

 tuberant which forms Cabo de San Francisco, is striking and suggests 

 faulting. The declivities both to the north and south of the island are 

 great, over 4,000 fathoms in depth being reached within 40 miles of the 

 north coast, while 2,000 fathoms are attained within a shorter distance 

 from the south coast. 



A submarine bank extending from the east end of Porto Eico to Ane- 

 gada Passage is known as Virgin Bank. The depth of water between the 

 islands rising above this bank is less than 20 fathoms, which is a maxi- 

 mum for the amount of submergence they have recently (ge()k)gically 

 speaking) undergone. These islands are detached outliers of Porto Eico. 



