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: 
. _ 248 Prof. Horsford on the Rocks of the Florida Reefs. 
. : : a 
. deposits. Now, how could hydrate of lime be provided from 
‘ carbonate of lime? 
~ ‘The completeness of the suite of collections provided for me by 
Prof. Agassiz, has enabled me to answer this question in such a 
-manner 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 t 
‘water evaporates, these animals die, and fall upon and mingle 
with the coral mud at the bottom. 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 collected. Agitated 
with water, it yielded a turbid, fetid solution. Tested with acetate 
of lead, it betrayed the presence of hydrosulphuric 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. ‘T'est-paper showed the liquid to be alkaline. 
The addition of soda solution set athmonia free, and the addition 
of chlorid of barium and hydrochloric acid showed the. presence 
of sulphuric acid. 
Conceiving this soft rock to be in the condition in which the 
solidified crust was at first, the process of hardening seemed of 
easy explanation. ; 
_ The animal matter mixed with the carbonate of lime, contain- 
ing sulphur and nitrogen, besides carbon, hydrogen and oxygen, 
in the progress of decay, which warmth and a small quantity of 
water facilitated, gave, as an early product of decomposition, 
hydrosulphurit acid; this, by oxydation 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 cid set free, 
uniting with an undecomposed 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, a sul- 
phate 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 carbonate 
of lime in solution from the added carbonic acid, as the water > — 
withdrawn by evaporation, takes on the crystalline form, gE 
increased strength and solidity to the rock. for 
That this explanation may serve, in however small measure, of 
_ the crust rock on the land slopes of Key West and all reenee” 
_ asimilar character, it is necessary that there be animal exuvi@ ™ 
‘coral mud, or finely divided carbonate of lime. Both these occur 
The water about the Keys aboundsinanimal life. = 
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