22 
THE OCEAN WORLD. 
In Jakes without any outlet, as the Dead Sea, and the Lake of 
Ural, the degree of saltness has considerably augmented. Numerous 
experiments have proved that the water of the Dead Sea is six times 
salter than that of the ocean. MM. Boutron and O’Henry analysed, 
in April, 1850, after the rainy season, some water of the Dead Sea, 
taken at about two leagues from the mouth of the Jordan ; its density 
was then 1’10. 
The saltness of sea water makes it more fitted to carry ships, 
because its density is increased by the salts which are dissolved in it. 
Besides this, these salts contribute to prevent what is called the 
corruption of water, caused by decomposition of the organic matter 
contained in it. 
By the table representing the composition of the water of the 
ocean and of that of the Mediterranean, we see that salts of lime and 
potassium, as well as iodine and silicium, are only found in infinitely 
small quantities. Nevertheless, the lime and silicium contained in the 
sea water are of very great importance, for these quantities, which 
appear to us so small in the table of a chemical analysis, become 
enormous in the entire extent of the ocean. The marine plants take in 
the lime, the silicium, the potassa, and the iodides which are dissolved 
in the sea water ; these mineral substances enter into their textures. 
It is from the carbonate of lime and silicium that the marine animals 
form their solid covering, their shell or carapace. The infusoria make 
use of the lime, silicium, and potassa for the same purpose. It is by 
the life and habits of the polypi that we explain these Coral Islands 
found in the sea, the existence of which has been a subject of much 
astonishment, and ought, therefore, to find a place in this chapter. 
The Pacific and Indian Oceans are studded with islands in a state 
of formation, which owe their origin to the polypi and corallines. 
These zoophytes extract from the sea water the lime and silicium 
which are found there in the state of soluble salts. In order to grow 
and develope, they must be continually under water. They are con- 
stantly producing calcareous deposits ; these deposits rise rapidly, and 
at last reach the surface of the water. Then the seaweed and rubbish 
of all kinds that the sea carries along with it, arrested by these 
emerged masses, cover them with a layer of fertile soil which is soon 
covered with vegetation, as the birds and the w'aves bring seeds thither. 
The Coral Islands of the Pacific are formed in this way. 
