"THE VOYAGE OF THE BEAGLE" - читать интересную книгу автора (Darwin Charles)

he knows as living only in South America. The dust falls
in such quantities as to dirty everything on board, and to
hurt people's eyes; vessels even have run on shore owing to
the obscurity of the atmosphere. 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. Within historical times, no signs
of volcanic activity have, I believe, been manifested in any
part of St. Jago. Even the form of a crater can but rarely
be discovered on the summits of the many red cindery hills;
yet the more recent streams can be distinguished on the
coast, forming lines of cliffs of less height, but stretching
out in advance of those belonging to an older series: the
height of the cliffs thus affording a rude measure of the age
of the streams.

During our stay, I observed the habits of some marine
animals. A large Aplysia is very common. This sea-slug
is about five inches long; and is of a dirty yellowish colour
veined with purple. On each side of the lower surface, or
foot, there is a broad membrane, which appears sometimes
to act as a ventilator, in causing a current of water to flow
over the dorsal branchiae or lungs. It feeds on the delicate