BRANNER: THE STONE REEFS OF BRAZIL. 183 
That the deep cold ocean waters dissolve lime deposits readily is dis- 
tinctly shown by the fact that deep dredging brings up little or nothing 
in the way of calcareous shells and bones, and of sharks’ teeth only the 
hard dentine, and only the hard earbones of whales, while the larger 
bones have been dissolved. The chemical process involved seems to 
be the formation of bicarbonates, and later the deposition of carbonates 
upon the liberation of carbon dioxide. 
In ordinary chemical laboratory work it is the practice to precipitate | 
carbonates from solutions by raising their temperatures. In such cases 
it is understood that a part of the carbon dioxide is driven off by the 
increase of temperature, while the lime or magnesia is precipitated as a 
carbonate, This increase of temperature is not necessarily great, — not | 
near the boiling point. Similar increase of the temperature of ocean | 
waters is produced by the waters breaking in surf or rolling upon the | 
warm sandy beaches of the tropics. The whole process results, therefore, 
in a general tendency for the carbonates to accumulate in the tropics. 
But this accumulation must take place at or near the surface of the 
waters, for the coldness and the pressure at great depths would keep the 
carbonic acid free." Only when the pressure is relieved, and the temper- | 
A ature raised near the surface, is there any opportunity for combination | 
| and for the formation of carbonates. | 
Waters carried from a cold sea into a warm опе, or from the cold 
depths to the surface and warmed suddenly, would yield up their car- 
bonic acid contents. The form of the continental shoulder of northeast 
Brazil, and the on-shore direction of the currents, favor this process. 
The accompanying map (Plate 1) gives in contours the relief of the sea 
floor along the Brazilian coast out to the one-thousand-fathom line. 
This map shows that the continental margin lies only from twenty-five 
to thirty-five miles off the shore. When the oceanic currents strike this 
steep submarine escarpment, the colder waters are swept up from the 
depths, quickly warmed at the surface, and made ready to yield up their 
carbonic acid contents. Observations upon the waters themselves bear 
out this view. 
| Waters of the Atlantic Ocean between Fernando de Noronha and Per- 
nambuco vary in temperature from 30° at five hundred fathoms to 78° | 
at the surface.” In general the surface layer of warm water is thicker | 
1 The Prince of Monaco says Dr. Jules Richard found that gases ‘are not dis- 
solved in the depths at any other pressure than they are at the surface.” Nature, 
June 30, 1898, LVIIL, р. 201. 
2 Challenger Reports. Phys. and Chem. I. pt. I., Plate 78. London, 1884. 
