202 THE OCEAN WORLD. 
It is, as we have said, only in the warm parts of the Indian and 
Pacific Oceans that the great mass of these islands are found. They 
give birth towards the south to the group of atolls known as the archi- 
pelago of the Bashee Islands, the extreme limit of the region being 
the Isle of Ducie. A multitude of other islands of the same nature are 
sparsely scattered over the sea, up to the east coast of Australia. There 
are enormous areas here, in which every single island is of coral forma- 
tion, and is raised to the height at which the waves can throw up 
fragments. The Radack group is a quadrilateral, 400 miles long by 
240 broad. Between this group and the Low Archipelago itself, 840 
miles by 420, there are groups and single islands covering a linear 
space of more than 4,000 miles. To the north of the Equator, the 
archipelago of the Caroline Islands constitutes a very considerable 
group of coral islands, comprehending upwards of 1,000, extending in 
a broad belt over nearly 40° of longitude. On the other hand, all 
along the coast of the American continent, round the Galapagos and 
the Isle of Paques, we find no trace of them. The reason assigned 
is, that in these regions a great current of cold water, flowing from 
the Antarctic Pole, so much lowers the temperature of the sea, that 
the corals can no longer exist. 
We still meet with atolls in the Chinese Seas, and coral barrier 
reefs are abundant round the Marianne and Philippine Islands. These 
marginal reefs form also an immense tract, from the Isle of Timor, 
along the south coast of Sumatra, up to the Island of Nicobar, in the 
Bay of Bengal. 
To the west of the Indian Peninsula, the Maldive and Laccadive 
Islands form the extremity of another group of atolls, and important 
madreporic reefs, which extend towards the south, by the Maldives 
and the Chagos Islands ; they consist of low coral formations, densely 
clothed with cocoa-nut trees. The Maldives, the most southerly 
cluster, include upwards of 1,000 islands and reefs; the Laccadives, 
seventeen in number, are of similar origin. The Saya de Malha 
Bank, towards the south-east, constitutes a further group of madreporic 
islets. Finally, the coast of the Mauritius, of Madagascar, of the 
Seychelles, and even the African continent, from the northern extremity 
of the Mozambique Channel to the bottom of the Red Sea, are 
studded with numerous reefs of the same nature. They fail, however, 
almost completely, along the coast of the Asiati¢ continent, where, 
among others, the waters of the Euphrates, the Indus, and the Ganges, 
enter the sea. The western coast of Africa, and the east coast of the 
American continent, are almost entirely destitute of great madreporic 
reefs, but they abound in the Caribbean Seas. In the Gulf of Mexico, 
