GEOLOGICAL CONSTITUTION. 25 
Pitcairn’s. The Carolines constitute another archipelago of like 
extent and character; and if we include with these the Marshall 
Islands, the ‘Tarawan Islands and Depeyster’s, the number is ninety- 
four; the only high islands in the area are Ualan, Banabe or Ascen- 
sion, and Hogoleu. Between these large coral archipelagos various 
islands are scattered over the ocean, all of which, north of a line from 
the Society Islands to Samoa and Rotuma, are of coral formation. 
There is a third archipelago, Flinders, betwen New Caledonia and 
New Holland, in which the islands north of the parallel of 25°, are 
believed to be solely of coral. Coral reefs are also extensive about 
most of the high islands. 
The basaltic islands, excluding any among the Salomon Group and 
others adjoining, which are still of unascertained character, cover an 
area of 16,000 square miles. They are of all shapes, from the simple 
volcanic cone, to broken mountain heights with deep gorges and lofty 
peaks. ‘These islands indicate that this ocean has been the scene of a 
vast number of volcanoes, subaerial or submarine. And if the coral 
islands have a basaltic basement, as is probable in those parts of the 
ocean where all the other islands are basaltic, the number would be 
still larger. We may count for each island one, and for many two or 
more, so that the number, not reckoning subordinate vents, could not 
have been less than a thousand. Yet, at the present time, there are 
few in action. In Polynesia, which embraces three-fourths of the 
ocean, they are confined to four islands, Hawaii in the Hawaiian 
Group, Tafoa and Amargura in the Tongan Group,* and the north 
island of New Zealand. In Micronesia there are none excepting 
on two or three of the Northern Ladrones, Assumption, Pagon and 
Guguan, which are barely smoking. Jn Melanesia the active volca- 
nic islands are Tanna and Ambrym in the New Hebrides, Matthew’s 
Rock west of the south extremity of New Caledonia, Tinakoro in 
the Santa Cruz or Vanikoro Group, and Sesarga and perhaps others 
in the Salomon Group, besides one or two on the east coast of New 
Britain. These alone remain of the fires that have burned over this 
wide area. 
* Information has been recently received of an eruption, and extensive flow of lavas on 
the island of Amargura, one of the Friendly Group. This eruption took place on the 
9th of July, 1847. 
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