BOTTOM SAMPLES, MURRAY ISLAND, THE BAHAMAS, AND FLORIDA. 275 



although the distance is d"] nautical miles, the range in depth is only from 7 to 

 12 feet. Gun and Cat Cays on the west are composed of oolite, as is Andros 

 Island on the west. This rock extends under sea, and a series of samples taken 

 at intervals across the bank shows its continuity from one side to the other. 

 The last movement of this area with reference to change in sea-level has 

 been by submergence of what was a land area, some parts of which stood 

 at least 198 feet above the sea.^ During the period of emergence the pre- 

 viously formed oolite was indurated; after its resubmergence waves have 

 broken up the rock and the bottom is now largely covered by an oolitic 

 sand, some grains of which are still embedded in a hard matrix. The 

 paucity of life on this enormous flat is as remarkable as the uniformity of 

 its depth and the continuity of one geologic formation. 



The results of a mechanical analysis of sample 71 are given on page 269 

 and are graphically shown on plate 94. The percentage of particles of silt 

 and clay size is 2.3, very nearly the same as that for Cocoanut Point and 

 Murray Island. The small proportion of material of this size is probably 

 due to currents, both wind-induced and tidal, which set across the bank, 

 as there is open water at the east end of the course indicated, and at its 

 west end there are only a few small cays. The water is also open both to 

 the north and to the south. 



The chemical analysis (see page 270) shows only 0.38 per cent of 

 MgCOs, the lowest percentage in any specimen so far considered. The 

 percentage of CaCOs is 99.49, almost pure calcium carbonate. 



It has already been stated that the material is an oolitic sand. The 

 following lists of foraminifera, by Dr. Cushman, show how rare foramini- 

 fera are at each of five stations occupied : 



No. 71. Great Bahama Bank, ii\ sea miles from Gun Cay, between Gun Cay Light and 

 Northwest Passage. 



Foraminifera (few): 



OrbicuHna adunca, few. 

 Orbiculina compressa, one. 

 Quinqueloculina reticulata, one. 

 Verneuilina affixa, one. 



Polystomella striatopunctata, one. 

 Two or three Quinqueloculina 

 and Triloculina. 



No. 72. Great Bahama Bank, 30I sea miles from Gun Cay 



Foraminifera: 



Orbiculina adunca, few. 

 Quinqueloculina reticulata, few. 

 Peneroplis pertusus, few; 

 Peneroplis pertusus var. discoideus, few. 

 Articulina sagra, one. 



Planispirinia exigua, one. 

 Clavulina angularis, one. 

 Verneuilina affixa, few. 

 Few Quinqueloculina and Tri- 

 culina. 



No. 73. Great Bahama Bank, 385 sea miles from Gun Cay. 



Foraminifera: 



Orbiculina adunca, few. Planispirinia exigua, few. 



Peneroplis pertusus var. discoideus, one. Verneuilina affixa, few. 



Quinqueloculina reticulata, few. 



'Vaughan, in Carnegie Inst. Wash. Year Book No. 13, p. 230, 1915. 



