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

 ™,,vV. +V.o /li'ot-inrf. ic A-7 nani-iral milfs flip ramrf in denth is onlv frorr 



275 



although the distance is 67 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. 1 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 

 MgC0 3 , the lowest percentage in any specimen so far considered. The 

 percentage of CaC0 3 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, 22§ sea miles from Gun Cay, between Gun Cay Light and 

 Northwest Passage. 



Foraminifera (few): 



Orbiculina adunca, few. Polystomella stnatopunctata, one. 



Orbiculina compressa, one. Two or three Quinquelocuhna 



Quinqueloculina reticulata, one. and Trilocuhna. 



Verneuilina affixa, one. 



No. 72. Great Bahama Bank, 305 sea miles from Gun Cay. 



Foraminifera: . . 



Orbiculina adunca, few. Planispinma exigua, one. 



Quinqueloculina reticulata, few. Clavulina angulans, one. 



Peneroplis pertusus, few; Verneuilina affixa, few. 



Peneroplis pertusus var. discoideus, few. Few Quinqueloculina and Tri- 

 Articulina sagra, one. culina. 



No. 73. Great Bahama Bank, 38^ sea miles from Gun Cay. 



Foraminifera: 



Orbiculina adunca, few. Planispinma 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. 



