302 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 



Bank with St. Croix. I found tlie connection perfect, but the ridge has 700 

 lathoms water on it near St. Croix. There is 1,000 fathoms three miles north, 

 aud 1,800 fathoms five miles south of the ridge. I ran a line from Dog Island to 

 White House Shoal, and back to Sombrero. Here 1 found a channel about 

 ten miles wide, with 1,100 fathoms. The temperature was 38° at 1,100 ; out- 

 side 37^° at 1,600, and 36?r° at 2,500. I shall run a number of lines from 

 St, Thomas to Sombrero, to be sure that this channel connects with the deep 

 Avater olf St. Thomas. I ran a line of soundings from the south end of 

 Dominica to Avis Island. The soundings were regular at 1,000 fathoms, to 

 within ten miles of Avis Island." 



The soundings made by Commander Bartlett, after I left the 

 " Blake," to determine the ridges uniting the various islands between 

 Sombrero and Trinidad, show plainly that the cold water of the Carib- 

 bean can only come in through the passage between Sombrero and 

 the Virgin Islands, which is about 1,100 fathomsj with a bottom tem- 

 perature 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 ftithoms between it and 

 Martinique ; the 500-fathom line again uniting into one large spit, as 

 a part of South America, all the islands to the south of it. Thus the 

 bulk of the water foi'ced into the Caribbean Sea has a comparatively 

 high temperature, — 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, therefore, incredible that with this huge 

 mass of water pouring into the Gulf of Mexico, there should be anything 

 like a cold current 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 " Blake " at Barbadoes, for the purpose 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 on Trinidad and adjoining parts of South 

 America. It is closely allied to the gigantic turtles of the (Jallopagos, 

 and to the fossil land turtles, of which fragments have been described 

 Viy the late Professor Wynian. These were collected by Mr. A. Juliuu 

 at Sombrero, in the phosphate bods of the island. 



Cajibeidue, May 10, 1871). 



