Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 3 - By Alexander Von Humboldt And Aime Bonpland.
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I Was Surprised To See That On The East Of The Little
Cayo De Don Cristoval The High Banks Are
Only distinguished by the
milky colour of the water, like the bank of Vibora, south of Jamaica,
and many other
Banks, the existence of which I ascertained by means of
the thermometer. The bottom of the rock of Batabano is a sand composed
of coral detritus; it nourishes sea-weeds which scarcely ever appear
on the surface: the water, as I have already observed, is greenish;
and the absence of the milky tint is, no doubt, owing to the perfect
calm which pervades those regions. Whenever the agitation is
propagated to a certain depth, a very fine sand, or a mass of
calcareous particles suspended in the water, renders it troubled and
milky. There are shallows, however, which are distinguished neither by
the colour nor by the low temperature of the waters; and I believe
that phenomenon depends on the nature of a hard and rocky bottom,
destitute of sand and corals; on the form and declivity of the
shelvings; the swiftness of the currents; and the absence of the
propagation of motion towards the lower layers of the water. The cold
frequently indicated by the thermometer, at the surface of the high
banks, must be traced to the molecules of water which, owing to the
rays of heat and the nocturnal cooling, fall from the surface to the
bottom, and are stopped in their fall by the high banks; and also to
the mingling of the layers of very deep water that rise on the
shelvings of the banks as on an inclined plane, to mix with the layers
of the surface.
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