S. p. Sharpies on Dredgings from the Oulf Stream. 169 



white, contained but little organic matter and only a mere trace 

 of iron ; it was from the third dredging, May 1, 1868, in 183 

 fathoms. The mud in external characteristics resembles the 

 Atlantic ooze, but differed from that examined by Messrs. 

 Forbes and Hunter in being almost destitute of silica and ferric 

 oxide. The silica consists almost wholly of sponge spicules. 



Fe^Og, 14-'77 20-23 -31 



MgC03, 10-56 12-39 4-26 



HgO+organic, 1-46 5-89 8-15 



100-33 100-67 100-28 100-04 



The corals were examined mainly with reference to the 

 amount of phosphoric acid that they contained. Silliman's 

 analyses, made in 1846, were as good, perhaps, as the state of 

 the science allowed at that time. He seems though to have 

 overlooked one fact in his experiments that Berzelius long ago 

 pomted out, that tri-calcic phosphate is soluble to a considerable 

 extent in neutral or alkaline solutions containing organic mat- 

 ter. In order to confirm this fact I took a solution containing 

 about -01 pr. ct of glue and added to it some sodic phosphate 

 and then calcic chloride in considerable excess and afterward 

 calcic hydrate to decided alkaline reaction. The filtrate from 

 the precipitate formed was evaporated to dryness and then 

 tested with magnesium wire after Bunsen's method for phos- 

 phorus ; it gave a strong reaction. 



. 1 also took about 100 grams of Madrepora palmata, treated it 

 in the same way as Silliman did his specimens, with the excep- 

 tion that it was put into the acid in a single piece, thereby 

 avoiding any contamination fi-om the mortar. The precipitate 

 contamed a large amount of organic matter, but on testing it for 

 phosphoric acid, it was found to be almost fi-ee from it, while 

 the coral treated in fresh state gave a strong reaction. 



CaCos Ca,P,08 H,0 



No. 1, OcuHnaarbus(nda,N. Car., 

 ^^ 2, Manicina areolata, Florida, 

 ^^ 3, MiUepora alcicornis, " 

 ^^ 4, Madrepora palmata, 

 " -' "i^aHcia agaHcites, 

 ', radians. 



8, Terebratula shells, 



