SOME ILLUSTRATIVE PROBLEMS 423 



ably low, but lime, the other essential constituent of phosphate rock, is 

 abundant. If the phosphorus in a 1,000-foot column of sea-water were 

 precipitated as tricalcium phosphate a layer less than half a millimeter 

 thick would be produced. The lime in a similar column would give, if 

 sufficient P2O3 were available, a layer about 30 centimeters thick. Prac- 

 tically all of this lime could be precipitated rapidly from sea-water as 

 phosphate if the sea-water were mingled with such highly phosphatic 

 waters as were previously mentioned. If the phosphatic waters contained 

 high sulphate, mixtures of calcium phosphate and calcium sulphate would 

 be expected. 



Many other problems involving chemical factors, some of them of long- 

 standing interest, might be reviewed, but they would only further illus- 

 trate how necessary it is that tlie problems of sedimentary rocks be at- 

 tacked from many directions. 



