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BRANNER: THE STONE REEFS OF BRAZIL. 175 
II. Deposited from the ocean water after having been derived (through 
the agency of carbon dioxide) from calcareous organic bodies in the sea. 
III. Brought down from the land by streams. 
IV. Dissolved from calcareous beach sands by fresh water streams 
entering behind them, and redeposited while passing seaward through 
these sands. 
These sources will be considered in this order. 
I. Cement from the beach sands by rain-water or spray.—The dis- 
solving of lime carbonate by rain-water from the upper layers of cal- 
careous sands, and its redeposition a little lower down, is a well-known 
phenomenon. Woodward mentions instances of blown sands having 
been hardened sufficiently by lime and iron to be used for building pur- 
poses. This hardening is especially common in warm regions where 
abundant molluscan life and coral-forming animals, calcareous Algae, 
gorgonias, and the like so often contribute largely to the beach sands. 
Aeolian sandstones and the sands upon the shores of coral islands are 
often hardened by this process. But, во far ав I can learn, and so far as 
my own observations go, the rocks whose cements are derived from their 
own beds in this fashion are so highly calcareous as to be practically 
pure limestones. 
The rocks of Bermuda are spoken of by Vetch, Nelson, Rice, Agassiz, 
Thomson, and Heilprin as newly-formed limestones. Rice says, “ The 
cement which converts all these fragmental deposits into solid rock is 
formed by the solution of the calcareous particles themselves,” ? and he 
points out that these rocks are almost exclusively limestones derived 
from shells and other calcareous fragments. 
Sir Wyville Thomson says the sand of which the white granular 
aeolian limestone is made “consists almost entirely of carbonate of lime. 
... When rain . . . falls upon the surface of the sand, it takes up a 
little lime in the form of bicarbonate, and then, as it sinks in, it loses 
the carbonic acid and itself evaporates, and it leaves the previously dis- 
solved carbonate of lime as a thin layer of cement, coating and uniting 
together the grains of sand. . . . The extreme result is a compact, 
marble-like limestone.” ® 
1 Н. B. Woodward, The geology of England and Wales, ed. 2, р. 546-547. Lon- 
don, 1887. 
The same author cites several instances of the induration of marine deposits 
(p. 550-551). 
2 Wm. North Rice, The geology of Bermuda. Bull. 25, U. S. Nat. Mus., р. 10. 
Washington, 1884. 
8 С. Wyville Thomson, The Atlantic. Vol. L, p. 291-295. New York, 1878. 
