DEPARTMENT OF MARINE BIOLOGY. 



227 



Geological Investigations in the Bahamas and Southern Florida, 

 by Thomas Way land Vaughan. 



BAHAMAS. 



The study of the bottom deposits along and near the shores of Andros 

 Island was prosecuted with more refinement than in 1912. In order to reach 

 a positive opinion regarding the oolitic or non-oolitic nature of the muds off 

 the west end of South Bight, an elutriating outfit composed of sieves having 

 meshes respectively of ^V, 4V, ifV, to o> and ^^0 inch in diameter and proper 

 microscopes were taken to the field. A field examination of a bottom sample, 

 No. 177, from 2 miles west of the west end of South Bight, gave the following: 



Color: light gray, tinged bluish. Reaction to litmus: strikingly alkaline. 

 Odor: fetid, some H2S. Cobalt-nitrate test: showed presence of aragonite. 



The following is a description of the separates according to size, but the 

 percentage estimates are omitted, as accurate physical analyses of samples are 

 subsequently given : 



Description of separates from bottom sample No. 177. 



Held on ^q mesh. Tests of Orhiculina adunca. 



Held on 4*5 mesh. Quantities of soft, non-indurated as well as indurated oolite grains, the former 

 easily crushed by a touch with the point of a needle. Foraminifera present. 

 Held on gg mesh. Many perfect oolite grains; also foraminifera. 

 Held on xoo mesh. Many soft oolite grains; foraminifera; fragmental particles. 

 Held on jgg me.sh. Small oolite grains; fragmental particles and fragmental material, predomi- 

 nantly oolitic. 

 Passed j^g mesh. Quantities of small, globular bodies, minute oolites, and flocculent material. 



The separates were compared with the powder of the oolite forming Golding 

 Cay. The mud is clearly oolitic. 



The following are accurate physical analyses, made in the Bureau of Soils, 

 Department of Agriculture, of two specimens collected by Mr. Drew in 1912, 

 and of sample No. 177, all of which are oolitic. Specimen No. 87 is from a 

 depth of 6 feet, 1 mile west, and specimen No. 88 from a depth of 12 feet, 2 

 miles west of the west end of South Bight. 



Chemical analysis of bottom specimen No. 87, by W. C. Wheeler, U. S. Geological Survey. 



Per cent. 



Si02 0.28 



AI2O3 0.03 



FeaOs 0.11 



MgO 1 . 25 



CaO 52.30 



H2O ■ 3.16 



CO2 42 .45 



Total 99.58 



The calcium carbonate of the specimens comprises both aragonite and 

 calcite. 



