Now it
acts in a directly contrary manner; for the water within the lagoon
not only is not increased by currents from the outside, but is
itself blown outwards by the force of the wind. Hence it is
observed that the tide near the head of the lagoon does not rise so
high during a strong breeze as it does when it is calm. This
difference of level, although no doubt very small, has, I believe,
caused the death of those coral-groves, which under the former and
more open condition of the outer reef had attained the utmost
possible limit of upward growth.
A few miles north of Keeling there is another small atoll, the
lagoon of which is nearly filled up with coral-mud. Captain Ross
found embedded in the conglomerate on the outer coast a
well-rounded fragment of greenstone, rather larger than a man's
head: he and the men with him were so much surprised at this, that
they brought it away and preserved it as a curiosity. The
occurrence of this one stone, where every other particle of matter
is calcareous, certainly is very puzzling. The island has scarcely
ever been visited, nor is it probable that a ship had been wrecked
there. From the absence of any better explanation, I came to the
conclusion that it must have come entangled in the roots of some
large tree: when, however, I considered the great distance from the
nearest land, the combination of chances against a stone thus being
entangled, the tree washed into the sea, floated so far, then
landed safely, and the stone finally so embedded as to allow of its
discovery, I was almost afraid of imagining a means of transport
apparently so improbable.
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