4 INTROUICTJON. 



In following a cross section from tlie emerged coral reef called 

 the Florida Keys, the so-called Hawk Channel is first crossed, limited 

 ontside hy the living coral reef Its greatest depth is seldom more 

 than six or se\en fathoms, generally mnch less towards its northern 

 extremity ; it is often interru^jted h_y shoals and so-called linah of live 

 coral, and its hottom consists of calcareons mud from decomposed 

 corals and corallines. Next comes tiie reef rising nearlv to low- 

 water mark, hut hy no means continuous. It extends from Cape 

 Florida soutli and west to a short distance heyond Key West, and 

 seems to he slowly increasing in that direction. 



Although the deep blue color of the water after j^assing the reef 

 seems to indicate a very abrujit slope, there is in no part of it 

 anything to compare with the sudden deepening on the edge of 

 the coral reets of the Pacific Ocean, or even of the Bahamas or 

 the coast of Cuba. The distance fi'om the reef to the hundred- 

 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 liie. 



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 locky lioor, without great iu(M|ualities ; this formation obtains 

 its greatest lireadth. of about eighteen luiles, a little to the east of 

 Sombrero Liglit. and tapei-s oif to tiu' west, where it ends in about 

 the same longitude as the end of tju' reef; towards the east and north 

 it approaches nearer the reef, and ends gradually between Carysfort 

 Reef and Ca])e Florida. This Itottoiu, wiiicli is called " Pourtales' 

 Plateau," in Professor Agassi/'s report, is \er\- rich in deep-sea corals, 

 the greater number of those desei'ibed in tliese pages having been 

 dredged on tliis ground. 



Outside of the i-ocky bottom tlie (Jlohigeriua luud prevails and fills 

 the trough of tlic chainiel.* 



On tlie ('uha sliore the l)ottom is rocky and the slope very abrujit, 

 particularly for tlie lirst lour or live hundred fathoms. Along the Salt 

 Key and IJaliama Banks, the slo])e is also exceedingly abrupt, but the 

 underlying rock is often covere(I with mud. 



Each of these regions named has its peculiar coral fauna, as will 

 be shown afterwards. 



The dredgings began with a lew casts in 1S67 off Sand Key, Florida, 

 and ofl' Chorrera, a small harlior three or four miles west of Havana, 

 the landing-point of one of the Florida and Cuba telegraph caliles. 

 The next year lines of souudiugs and dredgings were run across the 

 St. Nicholas iiiid Saiitareii Chniiuels. from the Salt Key Bank to 



* See Bulletin of the Mii.seum of Coinparative Zoiiio^y, Xos. G, 7, and 13; also Pi'tvrinaim's 

 Geog. Mittbeiluiigen, IS 70, Ileft XI. 



