212 CORALS AND CORAL ISLANDS. 



no means continuous. It extends from Cape Florida, south 

 and west, to a short distance from beyond Key West, and 

 seems to be slowly increasing in that direction. 



" Although the deep blue color of the water after passing 

 the reef seems to indicate a very abrupt slope, there is in no 

 part of it any thing to compare with the sudden deepening on 

 the edge of the coral reefs of the Pacific Ocean, or even of 

 the Bahamas or the coast of Cuba. The distance from the 

 reef to the 100-fathom line is not less than three miles, and 

 often as much as six. In this space the bottom consists 

 of calcareous mud, and is not particularly rich in animal 

 life. From ninety or a hundred fathoms to two hundred and 

 fifty or three hundred, the bottom slopes rather gently in the 

 shape of a rough rocky floor, without great inequalities ; this 

 formation obtains its greatest breadth, of about eighteen miles, 

 a little to the east of Sombrero Light, and tapers off to the 

 west, where it ends in about the same longitude as the end of 

 the reef; toward the east and north it approaches nearer the 

 reef, and ends gradually between Carysfort reef and Cape 

 Florida. This bottom, which is called ' Pourtales' Plateau ' 

 in Prof. Agassiz's report (see map), is very rich in deep-sea 

 corals, the greatest number of those described in these pages 

 [the memoir here cited from] having been dredged on this 

 ground. 



" Outside of the rocky bottom the Globigerina mud pre- 

 vails and fills the trough of the channel. 



" On the Cuba shore the bottom is rocky and the slope 

 very abrupt, particularly for the first four or five hundred 

 fathoms. Along the Salt Key and Bahama Banks, the slope 

 is also exceedingly abrupt, but the underlying rock is often 

 covered with mud." 



Prof. Agassiz observes that the rocky bottom of the Pour- 



