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 irregular 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 Porto 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 cañon 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 cation, 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- 
ing the existence of a ridge running 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- 
