FLORIDA REEFS AND KEYS. 211 



and Crocus reef, also with ten feet ; another between Crocus 

 reef and Alligator reef, with two fathoms ; another between 

 Alligator reef and Tennessee reef, with two fathoms and a 

 half; and a sixth to the west of Tennessee reef varying in 

 depth from two and a half to three fathoms." 



Through the labors of Mr. de Pourtales, in connection 

 with the soundings by the Coast Survey, interesting facts 

 have been brought to light respecting the sea between the 

 Florida reefs and the opposite shores or reefs along the Ba- 

 hamas and Cuba, called the Straits of Florida. A few par- 

 agraphs on these straits by Mr. de Pourtales, are cited from 

 his memoir referred to on page 204. The places described will 

 be found on the map at the close of this volume. 



" In transverse sections of the channel, the greatest depth 

 is nearest its southern or eastern shore, and in a longitudinal 

 section the depth diminishes in passing toward the north, 

 finding its minimum in the narrowest part between Cape. 

 Florida and the Bemini Islands, after which it increases 

 again. In a transverse section between Key West and Ha- 

 vana, the greatest depth is 853 fathoms ; between Sombrero 

 Light and Elbow or Double-Headed Shot Key, on the Salt 

 Key Bank, 500 fathoms ; between Carysfort reef and Orange 

 Key, on the Great Bahama Bank, 475 fathoms ; and between 

 Cape Florida and the Bemini Islands, 370 fathoms. In fol- 

 lowing a cross section from the emerged coral reef 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 

 toward its northern extremity; it is often interrupted by 

 shoals, and so-called heads of live coral, and its bottom con- 

 sists of calcareous mud from decomposed corals and corallines. 

 Next comes the reef, rising nearly to low-water mark, but by 



