GEOLOGY. 271 



28 seconds. Drift of ship, 3 miles. Lost two 32-pound shot and 5,500 

 fathoms of line. 



" May 10. Latitude 31 01' North ; longitude 44 31' West ; tem- 

 perature of the air 68, water 68. Got bottom with (2,300) twenty- 

 three hundred fathoms of line out. Time of running out, 1 hour 04 

 minutes 3 5 seconds." 



CORAL REEFS OF FLORIDA. 



AT the American Association, Cincinnati, Prof. Agassiz presented 

 the results of an exploration of the coral reefs of Florida, made under 

 the auspices of the U. S. Coast Survey, with a view of investigating 

 the character of the coast and the structure of its extensive range of 

 corals. 



In describing these reefs, Prof. Agassiz remarked, in the outset, that 

 they differed entirely from the coral reefs of other seas, which have 

 been so ably described by Mr. Darwin, in the British explorations under 

 Capt. Fitzroy, and by Mr. Dana, in the United States Exploring Expe- 

 dition, under command of Capt. Wilkes. In order to point out the 

 peculiar characteristics of the reefs of Florida, it would be necessary to 

 speak of the reefs of other regions, and particularly those of the Pacific. 

 These are divided into three classes ; viz., the Fringing Reef, the Bar- 

 rier Reef, and Atolls or Lagoons islands. The characters of each of 

 these divisions fully justify such a classification. But in the case of 

 the Florida reef, the coral formations extend in several parallel ridges 

 between the main land of Florida and the Gulf Stream, in a west- 

 erly course ; diverging more and more from the main land, until, 

 near Cape Sable, they are forty miles distant ; stretching like a broad 

 ami into the Gulf of Mexico, and extending in a southerly direction 

 into the rapid current of the Gulf Stream. The Pacific Ocean 

 reefs, on the contrary, grow in the open sea, and differ essentially 

 in character from those of Florida. The principal reef of living corals 

 in Florida occurs between the main keys and the rapid sea current 

 which runs between Cuba and the islands encircling the main land of 

 Florida ; but other coral deposits, of a peculiar nature, are found to 

 exist around, upon, and between the keys of the main land. The com- 

 bined action of the tides and currents produces eddies, in which fine 

 sand, and even mud, is deposited around the reefs. These materials, 

 Prof. Agassiz considers to be minute fragments, or an impalpable 

 powder, held in suspension by the water, which is rendered milky 

 white by their presence. At a short distance beyond, the water be- 

 comes clear. 



The three classes of coral reefs, distinguishable elsewhere, are, first, 

 the " fringing reefs ;" secondly, the " barrier reefs," which form rising 

 walls at some distance from the main land, between which and the 

 land a broad and safe channel frequently exists ; and, thirdly, the 

 " lagoons," or islands, which present circular walls, sometimes contin- 

 uous, and sometimes broken up. The lagoons often constitute acces- 

 sible and safe harbors. These encircling reefs are formed in a similar 

 manner to the barrier reefs, by the growth of coral from an unknown 



