June 28, 1873.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
1035 
from the parallels of latitude ; for while in some places 
they are separated from the equator by 30° of latitude, in 
other places they are strongly pressed towards it by the 
influence of the cold currents from the poles. 
The extent of the coral formations within this area has, 
ever since the seas began to be explored, struck the navi¬ 
gator with astonishment. Along the western coast of 
New Caledonia is a reef of 400 miles in length, and along 
the north-east coast of Australia is one of more than 1200 
miles; while it is to the labours of the reef-building polypes 
that almost all the beautiful islands which stud the tropi¬ 
cal portion of the Pacific, and many of those in the Indian 
Ocean, are mainly due. 
The speaker then drew a picture of the aspect of the 
ocean, and of the most striking members of its fauna in 
the region of coral reefs. He directed especial attention 
to the most superficial zone of the tropical ocean—that 
zone where sea and air and heat and light combine and 
concentrate the conditions of intensest animality, amid 
which becomes developed a most beautiful and marvellous 
fauna ; where Medusae and Siphonophores wander at their 
own wild will, propelled through the clear waters by the 
pulsations of crystal bell or of broad, many-coloured disc, 
or in vast fleets are floating over the sea with sail extended 
to the breeze ; where Pteropods flit on wings through the 
water like butterflies through the air; where Beroes 
catch the sunlight on their sides and flash it back in all 
the brightest hues of the rainbow ; where Salpae play in 
long undulating chains of crystal, and Pyrosoma, no less 
clear and crystal-like by day, becomes a cylinder of fire 
by night. What exuberance of life ! What intensity of 
happiness ! What unnumbered hosts basking beneath the 
tropic sky, or breaking the mirror of the sea with their 
gambols, or yielding to the impulse of the gentle trade- 
wind, or lighting up at night with phosphorescent gleam 
the dark waters of the deep ! 
Now, the coral-builders share with these bright and 
active hosts the prolific surface zone of the ocean. But 
their area is also a deeper one, and for many a fathom 
downwards their flower-like discs and banks of living 
coral may be traced by the sounding-lead and the dredge. 
This extension downwards, however, is not unlimited. 
The ocean varies with its depth in its physical characters 
and in the conditions of life which it presents, and the 
coral-builders find the conditions suited to their welfare 
within a limited and definite range. This range never 
extends beyond a depth of from 20 to 30 fathoms, so that 
no living reef-building coral is ever found at a greater 
depth than this. 
Within the upper portions of this area the coral fauna 
may be witnessed in all the perfection of its highest de¬ 
velopment and life; for there the sea is transparent as the 
purest beryl, and down fathoms deep below the boat the 
eye can penetrate through the liquid crystal to where the 
coral bank spreads around, and a scene of marvellous 
beauty becomes revealed. For there beneath the sea is a 
garden : carnations, and asters, and anemones, and gor¬ 
geous cactus-flowers seem there to expand their glowing 
petals ; flexile shrubs root themselves in the crevices of 
the rocks, and envelop their branches in bright clusters of 
flowers, like the mezereon bush in the month of March. 
What profusion of forms ! what richness of colouring ! 
crimson, and golden, and purple, and emerald-green, and 
snowy white,—no garden of the upper air can surpass 
that garden of the sea in loveliness. But, stranger than 
all, every petal is replete with sense; every flower and 
every shrub is an animated being ;—touch it, and it 
shrinks ; feed it, and it digests ; it rejoices in the warm 
sunlight, and feels happy in the caress of the ocean tide. 
Now the animated flowers of that wonderful sea-garden 
spend no life of idleness—day after day, night after night, 
they are at their work ! they are the builders of coral, the 
architects of islands, the ceaseless labourers by whose un¬ 
tiring energy have been rescued from the ocean thousands 
of miles of habitable land. 
Having thus examined the workers, and become ac¬ 
quainted with their home, the speaker proceeded to con¬ 
sider the nature of their works, and this subject would be 
best treated under the following heads :— 
1. The forms and structure of the reefs. 
2. The mode of their construction. 
3. Their relations to man. 
The Forms and Structure of Coral Reefs .—Coral forma¬ 
tions have been divided into three classes : the Atoll, or 
Lagoon Island, the Barrier Reef, and the Fringing Reef. 
The Atoll is the type of the Coral Island. It presents 
the appearance of a circular or irregularly-formed ring of 
coral rising out of the bosom of the ocean, generally 
clothed with a rich tropical vegetation of cocoanut palms, 
pandanus, and pisonia, surrounded by a wreath of white 
foam where the sea breaks upon its outer margin, and 
having a lagoon or lake of still water in the interior. 
The ring of coral is usually discontinuous in one or 
more places, and through the channels thus formed ships 
can generally sail into the calm central lagoon, which will 
then afford them, no matter how rough may be the ex¬ 
ternal sea, a safe and commodious harbour. 
It is scarcely possible to conceive of anything more 
lovely than one of these Lagoon Islands, with its graceful 
palm-trees and its groves of pisonia, the still, quiet lake 
within, the restless landless ocean without, and the glow¬ 
ing sky of the tropics stretching over all,—where 
“Droops the heavy blossomed bower; hangs the 
heavy fruited tree; 
Summer isles of Eden lying in dark purple spheres 
of sea.” 
Some of the small uninhabited Atolls especially seem 
almost as if they had been the work of enchantment. 
Even the wild creatures which dwell there appear to 
realize the wonders of the fairy tale, and make us almost 
believe that they lie under the spell of a magician. The 
United States’ explorers assure us that in some of these 
islands the birds were so little alarmed at the presence of 
man, that they allowed themselves to be taken off the 
branches of the trees as if they had been their flowers. 
When the Atoll is examined more minutely, it is found 
that the depth of the central lagoon may be about ten ox- 
twenty fathoms ; a pure coral sand or fine white coral 
mud covers its bottom; the flexible and shrub-like species 
of coral root themselves in its sides, and millions of strange 
creatures nestle in their branches, or creep over the coral 
rock, or dart through the waters of the lagoon. 
On the outer side of the ring of coral things are very 
different. The reef here usually extends outwards for 
some distance as a flat platform, with but a slight depth 
of water over it; the depth then suddenly increases, and 
immediately afterwards the sounding-lead sinks into the 
fathomless ocean where no bottom can be felt. One of 
the most remarkable features in an Atoll is thus the e.v- 
traordinarily rapid rate at which its outer side sinks into 
the ocean; and this fact must especially be noted, for it 
will aid us in our attempts to explain the formation of the 
island. , . , 
When masses of the coral of which the reef is composed 
are brought up from various depths between the surface 
and twenty or thirty fathoms below it, these fragments 
are generally found to be alive. From much greater 
depths, however, the sounding-lead will continue to hi ing 
up fragments of coral which it has detached from t ie 
sides of the reef ; but whatever fragments are brought 
up from greater depths than at most thirty fathoms axe 
invariably found to be dead. This fact is in accordance 
with what has been already said regarding the limited 
rano-e in depth at which the coral animal can live ; and it 
is another very important one, which must be also kept 
in mind as necessary in enabling us to understand the 
mode of formation of the island. 
If a correct idea of the nature of an Atoll be now con¬ 
veyed, there will be no difficulty in understanding the 
two remaining classes of coral formations. 
