Rocks of the Florida Reefs. 61 



quantity of water facilitated, gave, as an early product of 

 decomposition, hydrosulphuric acid ; this, by oxidation at 

 the expense of the oxygen of the atmosphere, became water 

 and sulphuric acid. The sulphuric acid coming in contact 

 with carbonate of lime, a salt soluble in 10,600 parts of water, 

 resolved it into sulphate of lime, a salt soluble in 388 parts 

 of water. The carbonic acid set free, uniting with an unde- 

 composed atom of carbonate of lime, rendered it soluble. 

 The nitrogen going over into the form of ammonia, at a later 

 period, decomposed the sulphate of lime, forming sulphate of 

 ammonia and soluble hydrate of lime. This hydrate of lime, 

 with an atom of carbonate of lime, united to form the com- 

 pound in ordinary mortar investigated by Fuchs. The car- 

 bonate of lime in solution from the added carbonic acid, as 

 the water is withdrawn by evaporation, takes on the crystal- 

 line form, giving increased strength and solidity to the rock. 



That this explanation may serve, in however small measure, 

 for the crust rock on the land slopes of Key West and all 

 localities of a similar character, it is necessary that there be 

 animal exuviae in coral mud, or finely divided carbonate of 

 lime. Both these occur. The water about the Keys abounds 

 in animal life. 



With the influx of the tide, the slopes became overspread 

 with the water and what it contains in suspension. The 

 retreating water, at ebb tide, leaves a thin layer of the 

 animal matter, mixed always when the water is agitated 

 with the fine calcareous powder. Before the return of flood 

 tide, exposure to the atmosphere and warmth have secured 

 the succession of chemical changes enumerated above, and a 

 thin layer of rock is formed. A repetition of this process 

 makes up the numerous excessively thin layers of which this 

 rock is composed. 



On the ocean side the deposit is formed from spray, during 

 winds which drive the froth of the sea, containing, with coral 

 mud, the exuviae from the barrier of living corals upon the low 

 bluffs of the Keys.* 



* Professor Dana in a note to his last paper on Coral Keefs and Islands in 

 the July number of this Journal, p. 83, after enumerating briefly the details of 

 the above process of consolidation, remarks : — 



