The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1884-01-12

the keys. This is carried westward by tn,
counter current and thus the flats grow
westward. No trace of Mississippi muC
has ever been found eastward of the Mis-
sissippi at more than hundred miles from
its mouth. The line of keys seemed to bt
formed from the waste of the present ex
terror reef The oldest part of the reef
from Pine Keys northward, the bay has
little by little, been filled up and trans.
formed for the most part into wide, shallow
mud fats
Westward of Pine Keys is a more recent
part of the reef, in which the keys rise
higher above the mud flats. These regions
of flats and keys terminate at line from
one to nine miles distant from the true
reef, the area on which living corals still
prosper. The Florida plateau, bearing its
mud-fats, keys and reef, dips to the south
west, and it is only on such parts as, from
the action of ocean currents, winds and
tides have attained a sufficient elevation to
allow corals to flourish, that the reef can
extend The Tortugas stand on such an
elevated area, as does also an incipient coral
reef forming still further west, at a depth
of less than twenty fathoms. Both these
areas repeat conditions which formerly ex-
isted to the eastward of them, and both
must eventually become part of the reef,
THEORY OF ALEXANDER AGAssIZ.
From the foregoing and other facts, ac-
cumulated by observation and examination,
Prof. Agassiz concludes that the present
Florida Bank, the older concentric reefs
which make up the southern part of Flor
ida; the great bank to the east of the Mos
quito coast, extending practically to Jamai-
ca; the reefs of the south coast of Cuba, and
the Yucatan Bank, have all been formed
by the gradual accumulation, upon already
existing plateaux, of materials brought by
the oceanic currents, winds and tides, and
of the remains of the animals existing in
great abundance upon these plateaux
These submarine banks are usually con-
nected with volcanic elevations In the
West India Islands great number of peaks
of volcanic origin have arisen nearly to the
surface of the sea, or above it, and have
formed the foundation of great submarine
banks. The soundings of the exploring
vessels Challenger and Tuscarora have de-
veloped number of submarine elevations,
covered by deposits of pteropods and glob-
igerina ooze, and forming extensive banks,
serving as foundations for barrier reefs and
atolls, completely hiding the volcanic SUBJ
stratum. The experiments carried on by
the Challenger and the Blake seem to prove
that there are sixteen tons of carbonate of
lime in every square mile of water hun
dred fathoms deep.
The theory of Professor Agassiz is, there
fore, that the submarine plateaux already
existing in depths where animals having
calcareous shells or envelopes live and -four
ish, especially in the track of great ocean
currents, have been built up by the debris
of these animals to level suitable for the
growth of reef-building corals, which thus
cap the elevation formed by other causes.
The action of the currents, winds and tides
clears away the animal remains from some
spots to deposit it in others, so that certain
points of the submarine plateau reach the
surface, while others remain below.
This theory will explain the reefs found
in the West Indies better than that of
Darwin and Dana, while in the Pacific and
Indian Oceans it will render clear what was
before hard to understand. Subsidence has
doubtless occurred over vast area in the
Pacific, and the gradual building up of the
reef as the land sank has resulted in the
production of an immense thickness of CO.
raj; yet there is no need to suppose that the
entire vast height from the solid ocean floor
to the summit of the atoll is formed of
coral. 1t is far more probable that the
great ocean currents have deposited their
sediment upon areas of elevation, folds and
submarine mountains that already existed,
and that these deposits have eventually
raised plateau to height at which corals
could flourish. Subsidence, whether con-
tinuous or discontinuous, if slower than
the rate at which the debris accumulated,
or the corals built, would account for the
great height of the coral-capped elevations
of the Pacific, compared with those of the
West Indies, where no such subsidence has
occurred.
The sides of the path Of a great aeeaA
current offer the most favorable condition
for the growth of animal life, since the
current brings both the food and the car
Donate of lime. Reef-building corals grow
best in localities where the current washes
away all sand and silt, and Prof Agassiz
states thati cannot be proved that the depths
to which they are practically limited are
really their bathy-metrical limit or whether
the accumulation of silt at loN. levels kills
them Other species Of corals, of solitary
habits, or at least forming colonies of no
great extent, occurs in depths of more than
1000 fathoms, but the great patches of
madrepores, clusters of porites and domes
of meandrina growing in close proximity,
offer the most favorable conditions for the
deposition of sand wherever the current
does not carry it away, While still alive
they are buried under the mass of material
passing over them. Even on calm days
Professor Agassiz states that large quanti-
ties of corals are broken off by the waves,
while after blow; water discolored from
this cause is not uncommonly met with
from six to ten miles from the reef.
By adopting Prof. Agassiz's view we can
understand why it is that in an area that is
not sinking, such as the West India Islands,
land is gradually built up behind the ele-
vated keys while in an area of subsidence
such as that in which the Pacific atolls
occur, the isolated patches which were
once built above the waves become separa
ted by channels that perpetually become
deeper and deeper.
A FEW MORE rAoTs ABOUT CORAL REEFS
Reef-building corals, of which the prin-
cipal are the branching madrepones and the
dome-like Asireas and their relatives, are
confined to waters in which the tempera
ture of the coldest winter month does moi
fall below SO degrees Fahrenheit. None
occur upon the western coasts of either the
Old World or the New, and only few
patches along the Brazilian shore, but they
are abundant in the wide area separating
the two Americas, and still more in the
Central Pacific, where there are a much
greater number of species than in Other