64 Professor Horsford on the 



further to the decomposition of the organic matter furnishing 

 carbonic acid, which gives solubility to the pulverulent car- 

 bonate of lime. 



The exceeding fineness of the coral mud is due in part to 

 the stone plants which flourish in the waters within the reef, 

 and which admit of ready reduction to a powder of extreme 

 fineness. Of these, two species of Millepora, I., II., and one 

 of Opuntia, III., were analysed by Mr Scoville in my labo- 

 ratory. 



in. 



Organic matter, 4-45 4'45 1-26 2*58 4-18 5-72 



Carbonic "acid, 40-09 396 i 41-08 2-70 37-68 35-81 

 Sulphuric acid, 0-0056 00056 



Lime, 47-71 47-98 46-35 4680 51-81 51-36 



Magnesia, ... ... 6-23 5-90 



Water, 3*67 3-30 4-52 ... 559 5-92 



95-92 95-37 99-44 8 99-26 98-81 



The discrepancies in the analyses of the different speci- 

 mens of the same species are due to the circumstance that 

 different parts of the stone plant contain organic matter in 

 unlike proportions ; and it is very difficult to procure two 



to have furnished no inconsiderable amount of hydrate of lime for the process 

 of consolidation. 



Prof. Dana attributes the formation of this crust-rock which has been the 

 more prominent object of my investigation, to the action of simple rain-water, 

 dissolving the carbonate of lime and again depositing it upon evaporation.* 

 This would account for its occurrence in depressions of the rock, but would not 

 account for its occurrence on eminences or on abrupt slopes ; nor would it ac- 

 count for the presence of water as hydrate of lime. 



The first sentence of the second paragraph of the above criticism has been re- 

 plied to. I have ascribed no solidifying action to the animal matter in corals. 



In regard to the second : — It will not be questioned that there is a great 

 amount of organic matter in various stages of decomposition about coral reefs. 

 Bibra found organic matter in all the ten specimens of sea-water analysed by 

 him. I have, in the paper above, repeated the statement made to me by the 

 parties who collected the specimens, that the waters within the Keys abound in 

 animal life. That procured for analysis from within the Keys was found ex- 

 ceedingly offensive from the decomposition of animal matter. It yielded the 

 odour and reactions of hydrosulphuric acid, and gave a total amount of organic 

 matter of 298 per cent. 



Now, it is difficult to see how sea-water should fail to carry the animal matter 

 it holds in solution, and more or less of that it holds in suspension into the coral 

 sands, which are saturated at every high water and again drained at low tide. 

 * Am. Jour. Sci. [2], xiv. 67 and 81. 



