292 Blaohwelder — The Geologic Role of Phosphorus. 



In its simpler aspects, the chemistry of the marine deposition 

 of phosphates has been plausibly interpreted by a number of 

 European students of the question, even as far back as 1870. 

 The following is a modification of their views, based on modern 

 information. Tbe process and results of bacterial decomposi- 

 tion of organic matter vary according to the conditions as well 

 as the particular class of bacteria that are at work. In air and 

 aerated water, decay is generally complete, resulting in the 

 production of carbon dioxide, water, soluble nitrates, sulphates, 



Fig. 2. 



Animals *" 



OCE.h ''NIC 



soluVtion 



DLCM 



•\ \ nh, n- .V.-- - £l{"_"_t:u.-t?."'1"°' '": -— c ~-- : o 



-C~ COj / y 



VO^- 

 Ume Salt. ,' 



C 'H, 

 1 * i 



vkJ 



----WjS 



B.ll./n t<fc:,<i 



LIME PHOSPHATES 



HrOROCARBONJ 



METAL SULPHIDES 



Fig. 2. Diagram to illustrate the process and results of the decay of 

 organic matter on the sea bottom. In reality the process is much too com- 

 plex to be represented in this way. (The materials which become fixed in 

 the bottom layers are shown in capitals on the lower line. Other marine 

 sediments, such as particles of sand, mud, shells and bones, have been 

 omitted from consideration.) 



phosphates, etc. In the absence of oxygen, however, the 

 anerobic bacteria somewhat more slowly break down the 

 organic compounds and produce a different series of end pro- 

 ducts, of which the most important are various hydrocarbons, 

 nitrogen, ammonia, and hydrogen sulphide, with only so much 

 of the carbonic oxides as the available oxygen in combination 

 permits. In so far as free oxygen is present in only small 

 quantities, there should be a compromise between the two 

 processes. 



Some of the most obvious characteristics of our marine 

 phosphatic rocks show that they have been associated in origin 

 with the anerobic phase of bacterial action. Almost invariably 

 they are black in color and, owing to the fact that they con- 

 tain noteworthy quantities of hydrocarbon oils, tars and gases, 



