Blachwelder — The Geologic Role of Phosphorus. 291 



little pellets of excrement are incessantly falling to the sea 

 bottom. Some of the dredgings of the Valdivia expedition* 

 showed that over large areas of the sea bottom, the latter 

 material forms an appreciable part of the soft ooze, and, in 

 several places the sediments consist almost entirely of such pel- 

 lets. They have been attributed in large measure to holothu- 

 rians, ecbinoids, and marine worms. ~No chemical analysis of 

 this material is available, but it is well known that animal 

 excreta in general contain a noteworthy proportion of phos- 

 phoric acid. Although the phosphorus in the excreta of 

 nearly all animals below the Mammalia seems to exist chiefly 

 in the form of insoluble organic phosphates, bacteria are able 

 to decompose these compounds, usually with the formation of 

 ammonium phosphate which is immediately returned to the 

 oceanic solution and there doubtless exists in the ionized con- 

 dition. Under ordinary circumstances, as pointed out by Sir 

 John Murray in the Challenger Reports, f even bones, teeth 

 and shells lying upon the sea bottom gradually lose their phos- 

 phoric acid. Hence this faecal material probably does not 

 accumulate to any considerable depth. In fact, over most of 

 the ocean bottom it is destroyed about as fast as it is produced. 

 In so far as this action prevails, phosphorus cannot well become 

 a solid part of the sediments deposited on the sea floors. 



Nevertheless, we find among the rocks derived from oceanic 

 sediments in many parts of the world, beds several feet thick 

 which are rich in lime-phosphate and extend rather uniformly 

 over thousands of square miles. They contain marine fossils 

 which indicate that they have accumulated upon the sea bot- 

 tom. It is therefore evident that locally there must be condi- 

 tions which cause the fixation of the phosphoric acid among 

 the bottom sediments. Some students of these deposits have 

 ascribed them to the direct deposition of phosphatic shells, 

 bones and teeth, and others have made appeal to the agency of 

 mineral springs. Generally they have sought an explanation 

 for the abundance of the phosphorus. As the writer has already 

 shown, however, the quantity of phosphorus dissolved in sea- 

 water is always sufficient to produce in a few thousand years 

 even the thickest known phosphate beds ; and hence we need 

 only to account for the special conditions which cause it to be 

 precipitated on the sea floor. There is excellent reason to think 

 that the immediately controlling conditions are chemical or 

 biochemical, but these chemical conditions in turn depend 

 upon physiographic and climatic factors difficult to analyze and 

 estimate. The study of the latter is a task for the geologist. 



* Murray, Sir Johrj, and Philippi, E. . Wissensch. Ergebn. der deutschen 

 Tiefsee Exped., Bd. x, Lf. 4, 1905, p. 103. (Carl Chun, editor.) 

 f Loc. cit. 



