98 THREE CRUISES OF THE " BLAKE." 



Passing now from the Atlantic to the Caribbean (Fig\ 57), 

 we find that a very different topography characterizes the west- 

 ern and eastern parts of this sea. The natural division between 

 them is an immense submarine bank, — the extension of the 

 Honduras and Mosquito coast plateau (which is less than a hun- 

 dred fathoms) towards Jamaica, — this plateau being, as far as 

 is known, nowhere at greater depth than five hundred fathoms, 

 and forming a number of smaller banks, such as the Rosalind, 

 the Pedro, Serranilla banks, which are less than a hundred 

 fathoms in depth. The Mosquito plateau shelves very gently 

 .towards the east, and forms an ii-regular triangular plateau 

 uniting Jamaica at the five-hundred-fathom line with Hondu- 

 ras. The channel between Jamaica and San Domingo slopes 

 gradually to the thousand-fathom line from both sides. The 

 island of Jamaica forms the western extremity of a chain of 

 mountains extending along the southern coast of San Domingo, 

 but with a tongue to the northward of Navassa between it and 

 Formigas Bank and another between Formigas and Jamaica. 

 These banks, with Porta Rico and the Virgin Islands, constitute 

 the northern boundary of the Eastern Caribbean, and separate 

 it from the Atlantic, leaving only the comparatively shallow 

 Mona Passage with two hundred and sixty fathoms at its great- 

 est depth between San Domingo and Porto Rico, and the still 

 shallower passages running between the Virgin Islands across 

 the plateau, which unites them all and is formed by the hun- 

 dred-fathom line. 



There is a comparatively deep canon of about eleven hundred 

 fathoms, leading from Sombrero into a small basin of twenty- 

 four hundred fathoms in depth between Santa Cruz and St. 

 Thomas. This canon, separating the Lesser from the Greater 

 Antilles, has a bottom temperature of thirty-eight degrees, 

 plainly showing that it connects with the Atlantic, and indicat- 

 inor the existence of a ridoe runnino; between Santa Cruz and 

 Porto Rico. The " Albatross " (as reported by Commander 

 Bartlett) discovered this ridge, with nine hundred fathoms as 

 its greatest depth. The soundings of the "Albatross" further 

 developed the presence of an elevation running north and south 

 nearly parallel with the chain of the Windward Islands, reach- 



