120 Papers from the Marine Biological Laboratory at Tortugas. 



REPORT ON EXAMINATION OF MATERIAL FROM THE SEA-BOTTOM 

 BETWEEN MIAMI AND KEY WEST. 



By George Charlton Matson. 



"The accompanying table gives the results of physical and micro- 

 scopic examination of the sea-bottom materials obtained among the 

 Florida keys. The physical examination was made by passing the ma- 

 terial through standard sieves having respectively 20, 40, 80, 100, and 

 200 meshes to the inch. The percentage of each sample remaining upon 

 the different sieves and the percentage which passed through the 200- 

 mesh sieve were determined by weight. Before sifting, the material 

 was carefully ground in a mortar to separate the grains which were aggre- 

 gated, care being exercised to avoid crushing the individual grains. In 

 this work considerable difficulty was experienced with the finer-grained 

 specimens because the grains adhered to each other with such tenacity 

 that it was hard to separate without pulverizing them. 



"After grinding, a sample was taken for sifting. In order to have 

 the results of the examination of the different specimens comparable, 

 samples of as nearly uniform size as possible were used; the weight of the 

 samples being fixed at 13 grams. In dealing with samples so small, it was 

 necessary to use an accurate balance, because an error of one-tenth of a 

 gram would amount to nearly i per cent. For this reason a chemical 

 balance was used, and the weights were determined to thousandths of a 

 gram. The percentage of the material of different sizes was computed 

 from the weights. 



"The microscopic study included an examination of each sample 

 after sifting. This examination was made by mounting the material in 

 water and studying it with a petrographic microscope. It was found that 

 the coarse material consisted largely of shells and shell fragments and 

 that amorphous lime carbonate formed a large percentage of most of the 

 samples which passed through the 40-mesh sieve. A few specimens 

 were composed of almost pure quartz sand and this material was found 

 in smaller quantities in specimens from nearly all of the localities. 



' ' Calcite and aragonite in the form of small fragments were present 

 in many specimens and in two cases spherules of chalcedony were ob- 

 served. Some of the specimens contained oval grains of carbonate of 

 lime which may possibly have an oolitic structure, though such slides 

 as we now have show nothing but aggregated calcite in a finely divided 

 state. 



" Sponge spicules and diatoms were noted in many cases and they 

 are probably to be found in all cases where there is amorphous carbonate 

 of lime, but they were seldom detected without first dissolving the lime 

 in acid. After treatment with acid there was a gelatinous residue which 

 blackened on exposure to the air. It is doubtless organic matter of some 

 sort." (For a list of the localities by numbers see p. 115 ; see map, plate 

 2, on which the localities are platted.) 



