98 PROCEEDINGS OF THE ACADEMY OF 



Silica, 52.07 per cent. 



Lime, 0.37 " 



Magnesia, 0.57 " 



Water, _ 12.17 " oxygen ratio, 10.81 



Sulphuric acid trace 



Alumina, 13.03 " 6.12 



Phosphate of Iron, 3.61 " 



Phosphoric Acid, 17.41 " 9.81 



The Alumina and Phosphoric Acid seem in this to be in the form of wavellite. 

 The guano rock from the various groups of islands has very varying compo- 

 eition, as has been seen from the foregoing investigations ; it is found in layers, 

 and the surface sometimes covered with an alluvial deposit ; these layers are in 

 places highly inclined, showing that since their deposition dynamic causes have' 

 altered their original position. This same phenomenon is described as occurring 

 at the Chincha islands in the Peruvian guano, where it is found in layers two or 

 three yards in thickness. Various theories have been formed and published as 

 to the origin of the rock guano ; these are doubtless premature, as the accounts 

 as to its occurrence are founded on reports of those not accustomed to noting 

 geological phenomenon. 



Prof. C. IJ. Shepard has, with his characteristic energy, extended his mine- 

 ralogical species to various portions of this rock, which he severally describes* 

 and designates generally as Pyroguanite minerals, and entirely destitute of am- 

 monia ; but examinations made of an average sample of a cargo from Monk's 

 Island showed one-half per cent, of nitrogen. Every specimen which I have 

 examined, has on ignition given very marked evidence of burning organic matter. 

 How this can be retained in a rock subjected to the agency of heated trap is as difiB- 

 cult to reconcile, as that the composition of minerals existing with and forming 

 a part of its mass, as Prof. Shepard describes,* containing water in their 

 composition. Moreover, how can a rock subjected to the agency of heated trap 

 have as its principal basis a salt with the formula 2CaO, HO, PO5 which is the 

 formula ascribed to it by Drs. Piggot and Beckell, of Baltimore, and which 

 seems to be the proper composition of some portions, as shown by analysis of 

 Monk's Island rock (V), though in the analysis of the specimen from El Roque 

 (X) there is obtained the formula, 3CaO PO5. 



As I have already mentioned, this Guano rock from Los Monges has been called 

 a native Super-Phosphate of Lime, but no satisfactory proofs are given as to its 

 meriting such a name ; phosphoric acid being found in solution after the 

 guano is treated with water is no proof that it exists in a free state. Phosphate 

 of Lime, when recently precipitated, is soluble to a slight extent in pure water 

 (R. Phillips, Ann. Phil. 22,188). Berzelius long since discovered Phosphates 

 of Lime and Alumina in the water and deposits of hot springs at Carlsbad. f 

 That Phosphates are insoluble and must be rendered free before becoming effi- 

 cacious as fertilizers is an erroneous though a very prevalent opinion. Accord- 

 ing to BrischofJ Phosphate of Lime must be regarded as present in all water 

 running into the sea ; it has already been detected in the waters of the Dee and 

 and of the Don, and it will most likely be found in the waters of all rivers. Phos- 

 phate of Lime and Magnesia have also been found in the waters of an artesian well 

 at Wildegg, in the Canton Argan (Switzerland). Phosphote of Lime has been 

 shown to be present in sea water by Clemm^ and by Forchammer.|| According 

 to Berzelius it is the Z>i-phosphate which is found in the mineral waters,^ which 

 is readily soluble in water saturated with carbonic acid. The Basic-Phosphate 

 of Lime is also readily soluble in water containing carbonic acid ; Bischof gives 



* Am. J. Sci. 12, xxii. 96. 



f Gilbert's Annalen, Ixxiv. 136. 



j Chem and Phys. Geology, vol. 2, p. 27 (Engl. edit). 



I Journ. fiirprakt. Chemie xxxiv. 185. 



II Berzelius, Jahresbericht xxvi. 393. 

 f Gmelin, vol. iii. p. 195. 



[March, 



