934 T. W. VAUGHAN CHEMICAL DEPOSITS OF THE SEA 



In order to make an application of the results procured from a study 

 of modern sediments to the interpretation of the conditions under which 

 the older were formed, samples must be collected and studied, and all 

 obtainable information regarding the conditions under which they were 

 deposited should be gathered. This information should include the rela- 

 tions of the deposit to land areas, the configuration of the sea-bottom, the 

 velocity and direction of winds and currents, and the depth, temperature, 

 and salinity of the water. Air temperature, rainfall, and surface run-off 

 and sediment from adjacent land areas, where there are such, should also 

 be known; and it is desirable to know the chemical composition of the 

 water discharged into the sea and that of the rocks over which or through 

 which it passes. 



Each sample should be divided into four parts, unless the quantity of 

 the material is large. One part should be preserved intact, the second 

 used for a chemical analysis, the third for a mechanical analysis and 

 petrologic study, and the fourth for a detailed list of the important organ- 

 isms entering into its composition. 



Although complete analyses of selected samples are needed, the analyses 

 usually are only partial, because of the impracticability of having an in- 

 definite amount of chemical work performed. SiOa, -FcoO^, Al^Og, CaO, 

 MgO, PsOr,, and SO3 are determined in as many samples as practicable, 

 while CaO and MgO and insoluble residue after ig-nition are determined 

 in a larger number. The ratio of MgO to CaO (or of the hypothetical 

 combinations MgCOg to CaCOg) is highly important, as will later be 

 made clear. 



Mechanical analyses have been sufficiently discussed by Mr. Shaw in 

 the immediately preceding paper. 



Chemical Deposits 



As the chemical deposit of greatest geologic importance in the shoal 

 waters of the ocean is calcium carbonate, attention will be confined to it. 

 No argument is needed to show that to understand the relative saturation 

 of the ocean with reference to CaCOg is of prime importance. Fortu- 

 nately the subject has recently been attacked by a number of investigators. 



As a part of a discussion of the formation of atoll rims, I summarized 

 the results obtained up to 1914 as follows:^ 



"(1) All the bays, sounds, and lagoons within the Florida reef and key re 

 gion are filling with sediment; (2) Drew's investigations of dentrifying bae 

 teria show that chemical precipitation of calcium carbonate is taking place ii) 

 the lagoons; (3) the chemical examination by R. B. Dole of samples of sea 



2 Wash. Acad. Sci. Jour., vol. 4, Jan. 19, 1914, pp. 27-28. 



