The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1876-07-01
The Coral Islands.

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interesting report of a lecture delivered at
the Stevens Institute of Technology by
Professor A. Guyot, of Princeton, N. j.,
from which we extract the following
Those who are familiar with the glowing
variations Of Captain Cook and other nav
lgators will remember that the presence of
an island is recognized long before it be.
comes visible, by clouds directly above it
in the otherwise clear sky. The land alb
serbs the heat of the sun aud accumulates
1t faster than the water; soon an ascending
current Of warm air Is formed, carrying up
moisture into the colder regions of the
atmosphere, where 1t Is condensed, and
forms clouds. A similar phenomenon is
observed in our western plains, where the
sky is frequently clear early in the morn
ing, but by 10 or II o'clock enough heat
has been accumulated to cause the forma-
ton of clouds.
The islands of the Pacific are of two
kinds, called the lower and the higher.
The lower rise but 7, 10, and rarely as
high as 100 feet above the level of the
sea, while the higher islands reach an
elevation of 10000, 10000 and even 49,
900 feet. There is no transition between
them. The most remarkable are the low
er islands. The appearance is very pecu-
liar. In the first place the eye is arrested
by white beach, then comes line of
verdure, due to tropical trees; than la
goon of quiet water Of a whitish or u yel.
lowish color; then another line of verdure,
and finally, beyond all, the dark blue
waves of the ocean. The lagoon inside of
Whitsuntide Island is but few fathoms
deep; but on the outside Of the island, the
water is $4,000 feet deep. Here then We
evidently have a tower.like structure
reaching up from the bottom of the sea,
and having depression in its summit.
Some Of these lower islands are fifty miles
across, but most Of them are not so large.
In some the ring is broken at several
points, and these are designated by the
Malay word dtoR.
The island of Tahiti, the principal one
Of the Society Islands, is good example
ofthe second class or higher islands. 1t
rises 1000 to 5000 feet above the level of
thesea, has no lagoon in its centre, but a
cratr and the water around it is very
deep 1t may, in fact, be considered as
mountain rising to height of some 49,
900 feet from the bottom of the sea.
Outsideof it is double girdle of low is
lands, Oic near, which Darwin calls a
tringing reef, and one further out, to
which he gives the name of barrier reef.
On examining these reefs and the lower
Islands theil structure will be found made
up entirely Of animal remains, generation
after generation having left their homes,
consisting Of limestone, to accumulate
there. On the top we find these animals
living and growing, in all colors, shapes
and sizes. The ligher islands, on the
contrary, except tho.a near the continent
like Borneo, Sumaua, etc., are entirely
volcanic, and do not contain sandstone,
granite or gneiss, like .he mountains of
the continent.
The limestone of the Dwer Islands is
not due to sedimentary deposits from the
ocean, but is the work of tie coral animal,
the great architect of the sea. According
to Agassizs description, which is here fol-
lowed, these animals are but sac, like
the finger Of glove, only more leathery.
Around the mouth is series of tentacles
formed by prolongation of the skin.
They are all skin, in fact, and have no
special organs, yet they digest food with
tremendous rapidity, absorbing it directly
1t makes no difference if you turn them
inside out they will digest just as well us
before. You cannot kill them by dividing
them; for they live all over, like plant.
For this reason they have been called
zoophytes. If you cut one into eight
parts, each part will live and set up in
business for ITSELF Like all other ami.
mails, however, they grow out of eggs.
The eggs are formed within the skin,
which is double, and divided into cells by
partitions or septa. When mature, they
detach themselves, move about 10 the
water until they find favorable place,
and then establish new colony. They
do not contribute to the growth Of their
parent colony, which is effected in another
way.
On examining piece Of coral, it is seen
to be full of little holes, popularity sup
posed to be the places for the stomachs of
the animals; but this is not so at all the
coral animal does not form secretion
around it like the mollrsks, but inside,
between the two folds Of its skin. Coral
is, therefore, the bones aud not the skull
of the animal. As before stated, these
animals work in societies or colonies, and
their tendency is to repeat the forms pc.
culiar to each species; thus we have corals
shaped like hand, like the branches of
trees, like mushrooms, like brain, with
its convolutions. They grow and multiply
in these societies by budding or gemma-
ton. The side Of the animal begins to
bulge out, and the protuber, nee SO formed
develops into a new mouth. which soon