BOTTOM SAMPLES, MURRAY ISLAND, THE BAHAMAS, AND FLORIDA. 255 



more, Si0 2 and (Al, Fe) 2 3 were rejected as being probably extraneous impur- 

 ities, very variable and generally very small in amount. The value used for 

 the composition of the algae as given in the preceding table is an approx- 

 imate mean of the composition of Corallinaceae and Halimeda. 



The following tables give the essential portions of the results obtained: 



'Compound grains (4) regarded as proportionate mixture of other materials present and therefore ignored. 



'Assume same chemical composition as other calcareous algae. 



'Estimated. 'Ignore. SiOj and (Al, Fe^Oj are not being calculated in the chemical composition. 



