Rocks of the Florida Reefs. 63 



mucilage or glue, fills up the interstices, increases the extent 

 of surface, and with it the cohesive attraction ; and still 



I. 2-3090 gr. gave 02850 gr. II. 1-4322 gr. gave 0-1550 gr. 



The hydrochloric acid solution filtered from the organic matter gave a preci- 

 pitate of oxalate of lime, which was determined as carbonate. 

 I. 0-8770 gr. gave 0-4100 gr. 

 Expressed in per cents, the above determinations give of 

 Water, expelled at 100° C. 

 I. 7-77 per cent. II. 7*66 per cent. Average, 7-72 per cent. 



Total volatile matter, 

 I. 41-17 per cent. II. 42-06 per cent. Average, 41*58 per cent. 

 The following per cents, are estimated upon the substance as dried at 100° C. 

 Sulphur existing as sulphate and soluble in diluted hydrochloric acid. 

 I. 0*65 per cent. II. 0*90 per cent. 1*26 per cent. Average, 094 per cent. 

 Sulphur in organic matter. 



1 1-45 per cent. 



Total sulphur of the above determinations, 2-39 per cent. 

 Total sulphur by oxidation of the mass, including the organic and inorganic 

 parts. 



J. 1-61 per cent. II. 1*84 per cent. Average, 172 per cent. 

 Average by the two methods, .... 2-05 per cent. 



Lime, I. .... 30*09 per cent. 



Placing side by side the results of the above determinations with the quan- 

 tities which Prof. Dana justly conceives to be inadequate to the changes 

 ascribed, we have, 



Per cent. Per cent. 



Organic matter, ..... 5' 2016 



Sulphur, 0-1 2-05 



The conditions of this soft rock, and of the surface or crust rock at the time 

 of its formation, I conceive to have been quite identical. The soft rock is the 

 residue left by spontaneous evaporation of a considerable body of sea-water 

 thrown, with its mingled coral mud and animal matter, into an inland basin, at 

 the rare juncture of favourable high wind and tide. A single layer of the 

 surface rock is the residue left by evaporation of the water mingled with coral 

 mud and animal matter, thrown up in spray from the dashing of the waves, or 

 carried up by flood-tide, and left by evaporation in the interval between the 

 two tides. This will account for its stratification, for its occurrence on emi- 

 nences as well as in depressions and along abrupt slopes, for its interstratified 

 arrangement with the coarse coral sand ; indeed, for all the phases and pecu- 

 liarities of it which are presented in the extensive suite of collections sub- 

 mitted to me. 



In addition to the changes enumerated in the above paper as resulting from 

 the decay of the animal matter, another may be mentioned. The ammonia 

 evolved in the process of decomposition, would provide hydrate of lime from 

 the sulphate present in the sea-water. This ingredient, taking the average of 

 Bibra's analysis, is to the chloride of sodium as 1 to 16, and may be conceived 



