BOTTOM SAMPLES, MURRAY ISLAND, THE BAHAMAS, AND FLORIDA. 287 



CONCLUSIONS. 



(i) An attempt has been made to outline a method of studying calcium- 

 carbonate bottom deposits, in the hope that progress may be made toward 

 an adequate classification of such sediments. The method includes the 

 consideration of the following subjects, viz: (a) mechanical analyses; (b) 

 study of the composition of the separates of different sizes and the deter- 

 mination of the percentage composition of each separate according to the 

 origin of its constituents; {c) the chemical composition of the different con- 

 stituents; (d) the chemical composition of the entire sample; (e) the correla- 

 tion of the chemical composition of the entire sample with that of its different 

 constituents according to their percentages; (/) the conditions under which 

 the deposit is formed, viz: its relations to land areas, the configuration of 

 the bottom, winds, and currents, and the depth, temperature, and salinity 

 of the water in which formed; (g) the areal extent, and if possible the volume 

 of the deposit. 



(2) Only one class of deposits, the sands forming on the flat behind the 

 reef, is specially considered for Murray Island. The beach sand and gravel, 

 however, represent a deposit of another class. 



(3) Three classes of deposits are recognized in the shoal waters of the 

 Bahamas, viz: (a) the sands forming behind the reefs are mostly of organic 

 origin and are essentially identical with the sands from Murray Island; 

 (b) the fine-grained muds forming in South Bight and on the west side of 

 Andros Island are largely chemical precipitates, the precipitation being due 

 to bacteria, probably acting concomitantly with inorganic agencies, evapora- 

 tion and expulsion of CO2 from the sea-water by heat and by surface agitation 

 of the water; (c) the oolitic sands of the Great Bahama Bank are due to the 

 breaking up by wave-action of a previously formed oolite. Of the three classes 

 of deposits (a) is of least areal extent; the areas covered by (b) and (c) have 

 not been delimited, but together they cover an area at least 60 times as great 

 as that covered by {a). The beach sands probably constitute another class of 

 shoal-water deposit. Globigerina ooze covers the floor of the Tongue of the 

 Ocean. 



(4) Deposits similar to classes (a) and (b) of those from the Bahamas 

 occur in Florida: Class (b) (the lagoon deposits) may be subdivided into 

 grades, according to size of grain. The Tortugas Lagoon samples are coarser 

 than those in Marquesas Lagoon, and those from the latter locality are coarser 

 than the Bahaman samples from South Bight and the west side of Andros 

 Island. The beach sands represent a distinctive class of deposits. The 

 relative area occupied by the different classes has not been determined. 

 Corals, however, are subordinate agents. A deposit from an intermediate 

 depth, 60 fathoms, off Sand Key light, presents distinctive characters, as it 

 contains large bottom-living as well as pelagic foraminifera. 



