AGASSIZ: BAHAMAS. 139 



tion. It may uot be far out of the way to assume that their thickness 

 was uo greater than that of the elevated reef of the Cuban coast on the 

 opposite side of the Old Bahama Channel. 



The diiierence in the formation of the coral reefs of Florida, the Ba- 

 hamas, and Cuba is niost striking. The coast of Cuba is characterized 

 oy the elevated reef terrace which surrounds it. In the Bahamas the 

 corals are scattered over wide areas, either on the interior of the banks 

 or lining their margijis ; tljey have played no part in the building up of 

 the Bahamas. In Florida the corals have not only built up the outer 

 keys, but also the inner line of islands, and the outer reef reaches the 

 surface at many points. In the Bahamas the reefs are subsiding, in 

 Florida they are stationary, and in Cuba they have been elevated. 



HYDROGRAPHY OP THE BAHAMAS. 



Plates I.-VIII., and Plate X. Figs. 4, 5. 



This brief sketch of the Hydrography of the Bahamas, of the Wind- 

 ward Islands, and of the Caribbean, will serve to show the relation of the 

 coral reefs to the great banks upon which they are found. The Con- 

 tour Map of the Caribbean (Plate VIII.) was prepared for my Eeports 

 on the " Three Cruises of the Blake," at the Hydrographic Office, 

 through the kindness of Commander J. R. Bartlett, U. S. N., Hydrog- 

 rapher, and it is for the sake of convenient reference reproduced in 

 this Report. For the chart of the Bahamas (Plate I.) I am indebted to 

 Commander C. D. Sigsbee, U. S. N., the present Hydrographer of the 

 Navy Department. 



The sea ftice of the Bahamas indicates depths and steep slopes "fully 

 as remarkable as any yet observed in the Pacific, even among its equa- 

 torial islands," ^ and which are in great contrast to the more gentle 

 slopes oft' the Florida Reefs.^ 



The character of the slope of the bottom off" the Florida Reefs has been 

 well described by Pourtales ^ in the Introduction to his Monograph on 



1 Dana, Corals and Coral Islands, p 216. 



■■^ See Langenbeck, he. cif., p. 28. I nm surprised to find that Dr. Langrenbeck 

 questions this. A comparison of the West Indian and Equatorial Pacific Hydro- 

 graphic Charts leaves no doubt on this point. 



3 Deep-Sea Corals, by L. F. de Pourtales, 111. Cat. Mas. Comp. Zool., No. IV., 

 1871. See also Pourtales, in I'eterm. Geog. Mittheilungon, 1870, Heft XI. ; and A. 

 Agassiz, The Tortugas and Florida Reefs, Mem. Am. Acad., XI. 107, 1882. 



