332 PRINCIPLES OF STRATIGRAPHY 



60 to 80 degrees Fahrenheit, the decomposition of urine mixed with 

 sea water precipitated practically all the sulphate of lime present in 

 seventeen days. The complete putrefaction after death of nine 

 small crabs in 2 liters of sea water, at temperatures varying from 

 70° to 80° F., resulted in the precipitation of all the lime salts in 

 the form of carbonates. 



One objection that has been raised against this theory of lime 

 deposition is that in the decay of organic matter carbon dioxide is 

 likewise generated, and that this would tend to keep the lime in 

 solution. This is indeed the accepted explanation for the absence 

 of calcareous deposits in the deep sea, where only red clay is 

 deposited (see beyond, Chapter X\"). Natterer emphasizes the 

 importance of the abundant ammonia resulting from the decay of 

 the organic matter on the sea bottom, and holds that this must be 

 capable of precipitating lime and magnesia from the sea as car- 

 bonates, but only when there is no free COo present. The reaction 

 of ammonium carbonate and sodium carbonate resulting from 

 organic decay (Steinmann-51 : /pp) with the calcium sulphate re- 

 sults in the precipitation of calcium carbonate, which, according to 

 Linck (33:500) is aragonite and not calcite. Magnesium carbon- 

 ates and dolomites, however, are not directly separated from sea 

 water through the reactions with ammonium and sodium carbon- 

 ates (Philippi-45 : ^ji"), but will separate after an interval of 

 time, especially if the calcium salts are first removed. Murray and 

 Irvine (36: 104) found that a mixture of sea water and urine after 

 standing several days furnished the precipitate under A of the fol- 

 lowing table, the urine decomposing and furnishing the alkaline car- 

 bonate. After filtering out this precipitate and permitting the liquid 

 to stand ten days longer the precipitate given under B was obtained. 



Water and organic matter (containing 7.38 % 



ammonia in A) 3i-8i 20.25 



Carbonate of lime 4 • 85 75-35 



Phosphate of magnesia and ammonia 51 ■ 10 



Phosphate of lime 12 . 24 



Carbonate of magnesia i . 02 



Phosphate of magnesia 3-38 



The carbonate of magnesia was precipitated only after much, 

 and perhaps nearly all, of the calcium was precipitated as carbonate 

 A considerable amount of the precipitating alkali, i. e., the am- 



