4 INTRODUCTION. 



In following a cross section from the emerged coral red' called 

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

 outside by the living coral reef. Its greatest depth is seldom more 

 than six or seven fathoms, generally much less towards its northern 

 extremity; it is often interrupted by shoals and so-called heads of live 

 coral, and its bottom consists of calcareous mud from decomposed 

 corals and corallines. Next comes the reef, rising nearly to low- 

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

 Florida south and west to a short distance beyond Key West, and 

 seems to he 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 

 anything 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 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 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; towards the east and north 

 it approaches nearer the reef, and ends gradually between Carysfort 

 Reef anil Cape Florida. This bottom, which is called " Pourtales' 

 Plateau," in Professor Agassiz's report, is very rich in deep-sea corals, 

 the greater number of those described in these pages having been 

 dredged on this ground. 



Outside of the rocky bottom the Globigerina mud prevails 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. 



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

 be shown afterwards. 



The dredgings began with a few casts in 1867 off Sand Ke} T , Florida, 

 and off Chorrera, a small harbor three or four miles west of Havana, 

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

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

 St. Nicholas and Sautaren Channels, from the Salt Key Bank to 



* See Bulletin of the Museum of Comparative Zoology, Nos. 6, 7, and 13; also Petermann'a 

 Geocr. Mittheilungen, 1870, Heft XI. 



