154 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



reef is broken to form the Necker Island Passage, and opposite Virgin 

 Gorda a long narrow belt of corals extends nearly the length of the bank 

 as far as Crab Island, with from twelve to seventeen fathoms of water, 

 forming a regular wall with a belt of deeper water on the inside of from 

 twenty to thirty fathoms, and from two to five miles wide. 



Nearly all the islands of the Virgin Bank are skirted on their eastern 

 and southern faces with patches and stretches of coral heads, often form- 

 ing extensive fringing reefs. This is the case with Virgin Gorda, Tortola, 

 St. John, St. Thomas, Culebra, and the eastern end of Crab Island. 



The Virgin Islands lie on the southern edge of a vast bank of sound- 

 ings extending from Porto Rico, which rises to a height of thirty-seven 

 hundred feet, to the east of Anegada, which has an elevation of not more 

 than thirty feet. The contract between the soundings oflF the north and 

 the south face of the bank is quite marked. The southern edge of the 

 bank is not more than seven miles from the cays, while the northern 

 edge extends nearly thirty miles to the north of the islands. The gen- 

 eral depth of the bank varies from seven to thirty fathoms. Tortola 

 rises to a height of nearly thirteen hundred feet, and Virgin Gorda to a 

 little less. St. Thomas (Admiralty Charts Nos. 130, 2183, Hydrographic 

 Chart No. 1002) rises to a height of over fifteen hundred feet, and is 

 surrounded by many small islands and cays fringed with corals. 



The 500 fathom line forms an elongated bank roimd Aves or Bird 

 Island, which is the summit of a wide fold at less than one thousand 

 fathoms running nearly north and south from Saba Bank to Bird 

 Island in the direction of Venezuela to about the latitude of Bequia, 

 a bay with a minimum depth of two thousand fathoms running between 

 it and the Windward Islands to the latitude of the southern extremity 

 of Dominica. 



Aves Island (Hydrographic Chart No. 40, Admiralty Chart No. 2600) 

 IS only ten feet above the level of the sea ; it is composed of coral rock 

 skirted all round by a reef except on the west side. The islet rises 

 from a bank of considerable extent, which has not been defined by 

 soundings. 



The south shore of Po.rto Rico (Admiralty Charts Nos. 130, 2600, 

 Hydrographic Chart No. 40) is fringed with reefs about four miles ofiF 

 shore. Mona Island is formed of white perpendicular cliffs about one 

 hundred and seventy-five feet hitrh full of holes, with numbers of 

 grottos and caves. 



A part of the east coast of San Domingo (see General Charts of the 

 West Indies, Hydrographic Charts Nos. 40, 373, Admiralty Chart No. 



