CORALLINES. 
181 
the Tropics, for it is only in these regions where the warmth exists, 
s o necessary to their development, that the madrepores show them- 
selves in greatest abundance. 
The great field of madreporic formations, in short, are found in 
the warm parts of the Pacific Ocean. It is from this point, as from 
a common centre, round -which are ranged the series of madreporic 
isles and islets, that it will he useful, in concluding this chapter, to 
trace their geographical distribution. We borrow the materials for 
this from Milne Edwards’s tableaux of their distribution in the 
principal seas of the world. 
It is, as we have said, only in the warm parts of the Pacific Ocean 
that the great mass of these islands are found. They give birth 
towards the south to the group of atolls known as the archipelago 
°t the Bashee Islands, the extreme limit of the region being the Isle of 
Ihic-ie. A multitude of other islands of the same nature are sparsely 
scattered over the sea, up to the east coast of Australia. There 
ai 'e enormous areas here, in which every single island is of coral for- 
mation, and is raised to the height at which the waves can throw up frag- 
ments. The Eadack group is an angular square, four hundred miles 
1( mg by two hundred and forty broad. Between this group and the 
Lew Archipelago itself, eight hundred and forty miles by four hundred 
and twenty, there are groups and single islands covering a linear space 
°f more than four thousand miles. To the north of the Equator, the 
archipelago of the Caroline Islands constitute a very considerable 
group of madreporic formation, comprehending upwards of a thousand, 
'^tending in a broad belt over nearly forty degrees of longitude. 
Hr the other hand, all along the coast of the American continent, 
l01 md the Galapagos and the Isle of Paques, we find no trace of 
The reason assigned is, that in these regions a great current 
^ cold water, flowing from the Antarctic Pole, so much lowers the 
mnperature of the sea, that the zoophytes no longer possess the re- 
gnisite vigour. 
We still meet with atolls in the Chinese Seas, and madreporic 
arrier reefs are abundant round the Marianne and Philippine Islands, 
flese marginal reefs form also an immense tract, from the Isle of 
mior, along the south coast of Sumatra, up to the island of Nicobar, 
11 nj 16 of Bengal. 
1° the west of the Indian Peninsula, the Maidive and Laccadive 
