4 CHEMICAL MANUEES. 



tions form phosphates of Hme, kon, and alumina. On the phosphate 

 beds so formed new layers of phosphates were deposited as soon as- 

 the carbonic acid acting as the phosphoric acid solvent had set free 

 sedimentary phosphates. When the solution percolated into 

 hollows it formed pockets. The carbonated water could even con- 

 vert already formed phosphate into a special form, for example 

 that of vitreous statfelite. Nodules w^ere formed when the rock to 

 which the phosphoric acid was combined was deficient in consistency, 

 or had lost it, for example owing to the upheaval of the deposit, 

 the different portions of which were washed and removed by water, 

 thus rounding the fragments. Nodules may a^ain be formed by 

 the fixation of phosphoric acid round a centre, for example around 

 grains of sand swimming in the solution on the impulse of a crystal! 

 growing in an appropriate solution, or organisms or even bells of 

 gas rising in the solution drawing to it particles of the same nature 

 as itself. Finally, another hypothesis of the formation of nodules 

 is that where precipitated phosphate of lime had been gradually re- 

 united into compact nuclei by water through the intervention of" 

 pebbles of silex. Apatite was the first phosphate formed by the 

 crystallization of the incandescent rocky magma. Its crystaUine 

 form is hexagonal. As it cooled slowly, the mass of liquid apatite 

 formed crystals of different sizes, from capillary needles, scarcely 

 visible, up to 12 in. in length. Their interior always assumes a. 

 lamellar structure. Apatite is found massive, w^ith this crystalline 

 structure, or even compact and massive when it is embedded in 

 basalts. But compact massive apatite always comes from crystalline 

 apatite. Pseudo-apatite is disintegrated apatite. All these forms of 

 phosphate, from the crystalline form to the amorphous, from isolated 

 nodules to rock phosphate, go back to an identical origin. Sum- 

 ming up, phosphorus existed in the beginning of things in the 

 primitive rocks. It has become more assimilable in virtue of its- 

 distribution in sedimentary and transported soils; vegetables have 

 absorbed it, then they have given it up to the animals, which have 

 condensed and accumulated it in numerous points of the globe. Let 

 us note, with Buckland, that it is astonishing that the human race 

 should, for so many centuries, have remained ignorant of the fact that 

 a considerable portion of the surface of the globe was formed by the 

 debris of the animals w^hich inhabited the ancient seas. There 

 exists, according to the same author, vast plains and enormous 

 mountains which are merely, so to speak, the charnel houses of 

 preceding generations, in which the petrified debris of extinct 

 animals and vegetables are piled up to form marvellous monuments. 

 These monuments attest the work of life and death during incalcul- 

 able periods. Cuvier, appreciating these curious natural phenomena, 

 declared that the sight of such a spectacle as that of the debris of 

 life forming almost all the soil on which our feet tread was so- 



