330 SAMOAN ISLANDS. 
boulders of the beach, cemented together by the coral which has been 
thrown over them by the sea. 
4. ON THE ERA OF ERUPTION IN UPOLU AND SUBSEQUENT CHANGES IN 
THE FEATURES OF THE ISLAND. 
Era of Eruptions.—One of the most remarkable features in the 
geological structure of Upolu, is the great number of large craters, 
and their linear arrangement. In consequence of this peculiarity, 
the island is a long and narrow strip of land. It has been shown that 
in the islands of these seas, we may often discover that they originated 
in the action of one or two large volcanoes, with lateral or subordinate 
points of eruption. ‘The Sandwich Islands were mostly thus formed ; 
so also the adjoining island of Savaii. But on Upolu there has been 
a crowded line of large and nearly equal vents: the majority of the 
craters in both the eastern and western districts are within three or four 
miles of one another. We do not speak of the linear arrangement as 
in itself singular, for this is usual; but that so short a line should 
contain so many distinct vents instead of a large or parent cone, with 
its subordinate craters. We may safely conclude that the longer axis 
of the island was originally the course of an extensive fissure, along 
which, after an eruption of lava, a number of active vents remained 
open. 
We have remarked upon the greater age of the central portion of 
this island, (more especially the northern side,) and the more broken 
character of the mountains, and have contrasted with these rocks, the 
twisted scoria of Sangana and other portions of the western district. 
Shall we conclude that after the ejection of the central rocks, 
there was a long interval without eruptions, in which the older 
mountains were nearly dismantled by denudation and disruptive 
forces? It is quite as probable that active vents continued open, from 
the earliest eruption in Central Upolu, through all subsequent periods 
till the latest fires were extinguished. ‘The greater extent of the 
western district and its more recent appearances of volcanic action, 
show that the fires were longer in action in this part than in the 
eastern district. The declivities in the western district are most 
broken near the central district, that is, back of Apia and farther to 
the eastward, and we may therefore infer that here the eruptions of 
the western district first declined, and the surface was earliest left to 
