Black-welder — The Geologic Role of Phosphorus. 293 



they are famous for their bad odor. In central Wyoming,* 

 phosphate rocks of this kind contain so much oily matter that 

 they are being successfully exploited for petroleum. Although 

 such phosphates contain a few fossils such as fish teeth, 

 brachiopods and larval gastropods, they are invariably devoid 

 of sessile bottom-inhabiting organisms, a fact which suggests 

 that the bottom layer of sea water lacked the oxygen necessary 

 to support life. 



The deficiency of oxygen is, therefore, the controlling 

 -'chemical condition, for it not only determines that the bacterial 

 decay shall be of the anerobic type, but also prevents animal 

 scavengers from devouring such organic matter as may fall to 

 the bottom, for no animal can be active in an oxygen-free 

 medium. Through the work of Birge and Judayf on the 

 Wisconsin lakes, and that of other students of lake phenomena, 

 it is now well understood that mechanical circulation of the 

 water is the only factor that serves to prevent this deficiency 

 of oxygen from becoming general in all waterbodies. At the 

 present time most parts of the ocean bottom are thus sup- 

 plied with enough oxygen to support their benthic faunas. It 

 is carried in by the slow convective circulation downward from 

 the polar regions and upward near the equator. In order to! 

 account for the oceanic phosphate deposits, therefore, we must 

 apparently discover those rare areas of the sea bottom where 

 this circulation is not effective. Deep inclosed gulfs or seas, 

 such as the Black Sea, to-day afford some of the conditions, 

 but not all of them. The bottom sediment of the Black Sea:}: 

 is now a lifeless mud blackened by hydrocarbons and charged 

 with hydrogen sulphide. There is, however, some condition 

 lacking, for the deposition of phosphates in the Black Sea is 

 not indicated by the dredgings thus far reported. 



Passing by this question as a room for which the key is yet 

 to be found, we may consider the manner in which phosphorus 

 comes to be fixed in the oceanic sediments under anerobic con- 

 ditions wherever they may be developed. 



As was long ago pointed out by Bonney,§ — under ordinary 

 circumstances all of the products of decay are likely to either 

 remain in solution or escape as gases rather than to be precip- 

 itated. Under special conditions, however, most of them 

 remain in solid form and others react with the sediments of 

 the bottom or with materials in solution, in such a way as to 

 form insoluble products. For example, hydrogen sulphide, in- 



* Woodruff, E. G., The Lander Oil Field, Fremont County, Wyoming, 

 Bull. U. S. Geol. Survey. No. 452, 1911. 



f Birge, E. A., and Juday, C, The Inland Lakes of Wisconsin, Bull. No. 

 22, Wis. Geol. & Nat. Hist. Survey, 1911. 



X Andrussov, N., La Mer Noire, Guide des Excursions der 7 me Congres 

 Geologique International, No. 29. 



§Bonney. T. G., Cambridgeshire Geology. 



