It Has Often Fallen On
Ships When Several Hundred, And Even More Than A Thousand
Miles From The Coast Of Africa, And At Points Sixteen Hundred
Miles Distant In A North And South Direction.
In some
dust which was collected on a vessel three hundred miles
from the land, I was much surprised to find particles of
stone above the thousandth of an inch square, mixed with
finer matter.
After this fact one need not be surprised
at the diffusion of the far lighter and smaller sporules of
cryptogamic plants.
The geology of this island is the most interesting part of
its natural history. On entering the harbour, a perfectly
horizontal white band, in the face of the sea cliff, may be seen
running for some miles along the coast, and at the height of
about forty-five feet above the water. Upon examination
this white stratum is found to consist of calcareous matter
with numerous shells embedded, most or all of which now
exist on the neighbouring coast. It rests on ancient volcanic
rocks, and has been covered by a stream of basalt, which
must have entered the sea when the white shelly bed was
lying at the bottom. It is interesting to trace the changes
produced by the heat of the overlying lava, on the friable
mass, which in parts has been converted into a crystalline
limestone, and in other parts into a compact spotted stone
Where the lime has been caught up by the scoriaceous fragments
of the lower surface of the stream, it is converted into
groups of beautifully radiated fibres resembling arragonite.
The beds of lava rise in successive gently-sloping plains,
towards the interior, whence the deluges of melted stone
have originally proceeded.
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