114 CORALS AND CORAL LSLANDS. 



the Florida reefs, and the strength of the Gulf Stream in the 

 channel between the Keys and Florida, the adjoining sea- 

 bottom consists mainly of common mud, with relics of deep- 

 water life, and only sparingly of coral debris. According to 

 Mr. L. F. de Pourtales, between twelve fathoms and one 

 ■hundred, in the Florida channel, outside of the reef, coral frag- 

 ments occur, but are rare ; dead specimens of Cladocora and 

 Oculina occur to a depth of about 50 fathoms. But on the 

 other side of the channel, " along the Salt Key Bank, dead 

 corals were dredged up in 315 fathoms ; but this is at the foot 

 of a very steep slope washed by the edge of the Gulf Stream ; 

 which is much better defined here than on the Florida side." 

 The bottom, in the Florida channel, of 100 fathoms, is a rocky 

 plateau, and outside of 200 fathoms, a mud full of foraminifers, 

 Globigeriiia j?md, as it is called from the species characterising 

 it ; and yet this channel is situated beneath the Gulf Stream and 

 close by the Florida reefs. The facts seem to show that in most 

 regions the reefs contribute little calcareous matter to the deep 

 ocean. This may be otherwise over the bottom, of compara- 

 tively little depth, of a great Archipelago like that of the East 

 Indies. 



IV. INNER REEFS. 



In the still waters of the inner channels or lagoons, when 

 of large extent, we find corals growing in their greatest per- 

 fection, and the richest views are presented to the explorer of 

 coral scenery. There are many regions — in the Feejees, ex- 

 amples are common — where a remote barrier incloses as pure 

 a sea as the ocean beyond ; and the greatest agitation is only 

 such as the wind may excite on a narrow lake or channel. 

 This condition gives rise to some important peculiarities of 

 structure in the inner reefs, in which the inner margin of the 

 barrier reef participates. 



In the general appearance of the surface, the inner gene- 

 rally much resemble the outer reefs. They are nearly flat, and 

 though mostly bare of life, and much covered with coral sand, 



