301 ANNUAL OF SCIENTIFIC DISCOVERY. 



droppings of fowl, reacts on the bone phosphate of lime, to eliminate acid 

 salts of phosphoric acid, and these cement other portions, or decompose 

 shells, which are composed of carbonate of lime and animal tissues. The 

 felspar-like granules are generally compact, colored portions of converted 

 shells, having a crystalline form, and there are aggregates of ferruginous and 

 aluminous phosphates, arising from the same kind of action on ferruginous 

 matter, which, in the form of a fine clay, or volcanic ash, has been brought 

 within, the sphere of the action of the acid phosphates. The cavities some- 

 times present minute crystalline facets of phosphate of lime crystals, while 

 the capillary channels and pores, which give the trachyte-like character, are 

 really the passages through Avhich the carbonic acid and other gases escaped, 

 during the transformation of the organic matter, precisely as they occur in 

 basalt and trap, where igneous action has been supposed to have been in- 

 fluential. 



This rock is covered more or less by Atlantic guano rock, presenting the 

 variety which consists of compact, light-colored phosphate of lime, contain- 

 ing about twenty parts in one hundred of carbonate of lime, and in some 

 parts is a consolidated shell-bank ; the recent shells and coral fragments 

 being visible. Where, through time and favorable ' exposure, the bone 

 remains have thoroughly decomposed the shells, hand specimens would be 

 mistaken for the flesh-colored, massive phosphate of lime of New Jersey. 

 These more or less well-cemented and altered rocks are also connected with 

 still more recent deposits, retaining even the odorous animal remains of oily 

 acids ; and the whole formation, above that of the trachytic form of rock, 

 contains the remains of infusoria. 



Thus a small island of the Atlantic, lying about eighteen degrees north of 

 the equator, presents us with an epitomized succession of rock strata, formed 

 from materials which, once endowed with life, have served to nourish other 

 living systems, and then given rise to chemical changes, resulting in the 

 production of various mineral solids which remain. 



The trachyte-like rock forming the basis rock of this island, theoretically, 

 may have received its geological and chemical characters in ocean water. 

 A subsidence of the land, after its surface had been deeply covered with 

 organic remains, would allow of that aqueous action of decomposition and 

 cementation which we notice, and the subsequent desiccation would explain 

 the natural divisions by rents. The formation of silicates of iron, mangan- 

 ese, and allumina from phosphates of lime, is a mineralizing process which 

 can take place in ocean water by infiltration, volcanic ashes, or divided ma- 

 terials of plastic rocks being present, as analysis shows them to be. The 

 rock is hydrous, losing nearly ten per cent, of its weight by ignition, or 



TVater with a little organic matter, 10.00 



Bone Tbospbate of Lime, 8520 



Carbonate of Lime, 3.00 



Oxides Iron, Manganese and Alumina, 5.22 



Silicic Acid and Sand, 1.78 



105.20 



