288 Blachwelder — The Geologic Role of Phosphorus. 



ing underground water containing more or less carbonic acid 

 and other solvent materials is one of the chief agents in this 

 decay. In such solutions both apatite and dahllite dissolve 

 more readily than most other common minerals, although much 

 less rapidly than the lime-carbonate minerals such as calcite. 

 The phosphate-bearing solution then circulates through the 

 rock and soils, to be disposed of eventually in several different 

 ways. 



Much of the dissolved phosphoric acid is taken up by plants, 

 whose roots penetrate the soil, and by them is incorporated in 

 the nuclear material of their cells, and particularly in their 

 seeds. Animals taking the phosphorus indirectly from the 

 plants upon which they feed use it not only in various cells 

 and tissues, but also in bones and teeth. In the vast majority 

 of cases, part of it is soon returned to the soil as a constituent 

 of urine, faeces and dead organic matter, but bacteria then 

 decompose its compounds and the phosphoric acid returns to 

 the state of solution in ground water. Only rarely, when soon 

 buried in mud, does it become fixed in land deposits in the 

 form of bones and even mineralized faeces (coprolites). On 

 the other hand, thin beds with very limited area, consisting 

 largely of bones and teeth, have been found in a few places, 

 such as Big Bone Lick in Kentucky. 



By far the greater part of the phosphorus in ground water 

 solution must either immediately or eventually go into the 

 streams and find its way to the ocean. Of the vast quantity of 

 dissolved mineral matter annually delivered to the sea by the 

 run-off, it is estimated that about # 45 per cent consists of phos- 

 phorus pentoxide. Using the best available figures for the 

 amount of water thus brought to the ocean annually, it is cal- 

 culated that if the phosphatic material in the form of solid tri- 

 calcium phosphate were loaded into standard railroad cars it 

 would fill a train stretching continuously from Boston to Seat- 

 tle and would be 7 to 12 times as great as the world's total 

 production of phosphate rock in 1911. Nevertheless, so great 

 is the volume of the oceans, and so vast the area of their floors, 

 that if all this material were deposited in solid form uniformly 

 over the bottom of the sea, it would build annually a layer less 

 than one-fifth of a millimeter thick. Of the phosphorus poured 

 into the sea, so large a proportion is utilized by living beings 

 that the net working balance dissolved in oceanic water con- 

 stantly averages less than -005 per cent, expressed as P 2 6 , or, 

 in other words, about "18 per cent of the dissolved salts. In 

 this solution, phosphorus seems to have reached the most dilute 

 state in which it exists during the course of its complex migra- 

 tions. Its subsequent transformations, now to be described, 



