AMERICAN DREDGINGS IN THE CARIBBEAN SEA. 
365 
tween Sombrero and Trinidad, show plainly that the cold water 
of the Caribbean can only come in through the passage between 
Sombrero and the Virgin Islands, which is about 1,100 fathoms, 
with a bottom temperature of 38°, while the 500-fathom line, 
as I have said, forms a gigantic island of all the islands to the 
south of Sombrero, including Dominica, with a narrow passage 
of 1,000 fathoms between it and Martinique ; the 500-fathom 
line again uniting into a large spit, as a part of South America, 
all the islands to the south of it. Thus the bulk of the water 
forced into the Caribbean Sea has a comparatively high tempe- 
rature — an average, probably, of the temperature of the 300- 
fathom line. The cold water of the Atlantic is, however, again 
forced into the western basin of the Caribbean through the 
windward passage, and all this through the Yucatan Channel, 
between Cape San Antonio and the Yucatan Bank. It is, there- 
fore, incredible that with this huge mass of water pouring into 
the Gulf of Mexico, there should be anything like a cold cur- 
rent forcing its way up-hill into the Straits of Florida, as has been 
asserted on theoretical grounds. The channel at Gun Key can 
only discharge the surplus by having a great velocity. 
Mr. Garman, who as usual accompanied me, remained in the 
West Indies after we left the Blalce at Barbadoes, for the pur- 
pose of making collections of reptiles and fishes, with a view 
of throwing additional light on the former connections of the 
islands, as I have here attempted to trace it. One of the most 
interesting of the reptiles we collected is a gigantic land tortoise, 
found at Porto Rico, differing only in size from the land turtle 
still found in Trinidad and adjoining parts of South America. 
It is closely allied to the gigantic turtles of the Gallopagos, 
and to the fossil land turtles, of which fragments have been 
described by the late Professor Wyman. These were collected 
by Mr. A. Julien at Sombrero, in the phosphate beds of the 
island. 
