MUSEUM OF COMPARATIVE ZOOLOGY. 371 



Taken as a whole, the trough of the Gulf Stream, between Cuba 

 and Florida, as well as farther east and north, presents features in its 

 configuration widely different from the relief of any equally extensive 

 area of the dry surface of our continents. The floor of this basin is 

 gradually and slowly shelving from the Florida coast to greater and 

 greater depth, while on the Cuban side it is rapidly rising again. The 

 slope is, indeed, so rapid on the Spanish shore that, at a distance of less 

 than two miles from the abrupt shore bluffs, the depth of the trough 

 is generally from 3,000 to 4,000 feet, and here and there reaches 

 5,000 feet at a slightly greater distance. We have thus here a slope as 

 steep as that of the steepest mountain ranges of that height, and even 

 steeper ; and, what is most surprising, the great inclination of this floor 

 is not the result of uplifted and slanting beds of rock, but unmistakably 

 the effect of the abrading action of the great current upon older coral 

 formations, judging from the aspect of the shore bluffs, and their evident 

 continuity with the general slope from the water-edge down to- the 

 greatest depth reached with the plumb-line and the dredge. This dif- 

 ference in the inclination of the slopes on the American and on the 

 Cuban sides of the basin obtains for more than one hundred miles, — 

 from the Tortugas to Cape Florida, — with the peculiarity only that in 

 the direction of Salt Key Bank there rises, on the Cuban side, a low 

 ridge from the deeper part of the trough, trending nearly parallel with 

 the coast. Another remarkable feature of the edge of the jrreat 

 Florida reef consists in its having a less abrupt slope to the seaward 

 than is ascribed to all the coral reefs of the Pacific Ocean. Neverthe- 

 less, the seaward slope of the reef is really steeper than the shoreward 

 slope ; and this is, it appears, an essential element in the growth and rise 

 of all the coral reefs. 



But while the great coral reef of Florida presents this exceptional 

 character, the Bahamas and the reefs to the northeast of Cuba ex- 

 hibit very abrupt slopes, and a great depth is reached close to the 

 shores of these Banks ; so that the Bahamas resemble the coral-reefs 

 of the Pacific much more than the reefs of the coast of Florida. 



The whole group of banks and keys embraced between Double- 

 headed Shot Key, Salt Key, and Aneuilla Key is a very instructive com- 

 bination of the phenomena of building and destruction. The whole 

 group is a flat bank covered by four or five and occasionally six fath- 

 oms of water, with fine sandy bottom; evidently corals reduced to 



