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THE BAHAMA ISLANDS. 217 
The rock of the Bahama Islands is, like that of the 
Florida Keys, a coral-sand rock of wind-drift origin. It is 
generally a poor building stone because of the numerous 
sand-flaws. Its weight varies from sixty-five to one hundred 
and forty-five pounds per cubic foot. In some of the basins 
or lagoon-bottoms a chalk-like deposit occurs, and nowhere so 
extensively as along the western coast of Andros Island. The 
coarser fragments of corals are never found much beyond the 
surf range of high tide. Captain Nelson says that “the south 
side of Silver Cay and the beach extending westward from 
Nassau afford rolled blocks, pebbles, and sand derived from 
the more massive corals, mixed with remains of turtles, fish, 
crustaceans, echinoderms, and mollusks. On the beach be- 
tween Clifton Point and West Bay the shells of Strombus 
gigas more especially accompany the rolled corals. At Hast 
Point the sand is derived from corallines and nullipores ; 
the finer sand being often in approximately spherical grains, 
though not so perfectly as the White Cay, and between Ex- 
uma and Long Cay. The beach near Charlotteville Pomt con- 
sists principally of Lucina Pennsylvanica in various stages of 
comminution. At Six Hills (Caicos Group) the mass of conch 
shells (Strombus gigas) is so great and sufficiently cemented 
together as to form not only rock, but an island several hun- 
dred feet in length. Along the northwest beach at Gun Cay 
a hard, coarse, stratified rock is formed of conch shells and 
others, together with coral fragments.” 
“A counterfeit odlite occurs near White Cay, Exuma, and 
elsewhere, in which the spherules have been derived appar- 
ently from the stems of corallines.” On the larger islands 
the rocky surface of the hills is very thinly and partially cov- 
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ered with “red earth”? mixed in varying proportions with 
vegetable matter. There are many large caverns in the 
