276 ANNUAL OF SCIENTIFIC DISCOVERY. 



throughout the intervening spaces is a fine deposit of carbonate of 

 lime, which adheres with considerable tenacity to the surface upon 

 which it rests. 



The surface or crust rock, though not strictly homogeneous, is com- 

 posed of particles so minute as not to be distinguished from each other. 

 It is soluble in hydrochloric acid. It contains neither silica nor sul- 

 phuric acid. Quantitative analysis showed the mass to be for the most 

 part composed of carbonate of lime, a little hydrate of lime, and a 

 small quantity of organic matter. These ingredients permitted no 

 action like that occurring in hydraulic cements, in which silica is re- 

 quired, or like that presented in the hardening of gypsum, in which 

 sulphuric acid is necessary. To one of the two remaining processes, 

 if to either, must it be ascribed and as hydrate of lime is present, it 

 cannot be exclusively assigned to a place with calcareous spring de- 

 posits. Now, how could hydrate of lime be provided from carbonate 

 of lime ? The completeness of the suit of collections provided for me 

 by Prof. Agassiz has enabled me to answer this question in such man- 

 ner as leaves, I think, little room for doubt. On the main land against 

 the keys there are depressions which are filled with water, only at 

 long and irregular intervals. This water, like that within and about 

 the keys, abounds with animal life. As the water evaporates, these 

 animals die, and fall upon and mingle with the coral mud at the bot- 

 tom. As the beds become more and more completely dry, the layer of 

 mud and animal matter hardens till it forms a mass resembling the 

 surface or crust rock. Of this soft, growing rock, specimens were col- 

 lected. Agitated with water it yielded a turbid foetid solution. Tested, 

 it betrayed the presence of hydro-sulphuric acid. After standing 

 some hours, a delicate white film was deposited upon the containing 

 vessel, at the surface of the water, which proved to be carbonate of 

 lime. 



Conceiving this soft rock to be in the condition in which the solidi- 

 fied crust was at first, the process of hardening seems of easy explana- 

 tion. The animal matter mixed with the carbonate of lime, containing 

 sulphur and nitrogen, besides carbon, hydrogen and oxygen, in the 

 progress of decay, which warmth and a small quantity of water facili- 

 tated, gave, as an early product of decomposition, hydro-sulphuric acid. 

 This, by oxidation, at the expense of the oxygen of the atmosphere, 

 became water and sulphuric acid. The sulphuric acid coming in con- 

 tact with carbonate of lime, a salt soluble in 10,000 parts of water 

 resolved it into sulphate of lime, a salt soluble in 380 parts of water. 

 The carbonic acid set free, uniting with an undecomposed atom of car- 

 bonate of lime, rendered it soluble. At a later period, the nitrogen, 

 going over into the form of ammonia, 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 

 compound in ordinary mortar. The carbonate of lime in solution from 

 the added carbonic acid, as the water is withdrawn by evaporation, 

 takes on the crystalline 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 



