12 POLYNESIAN" RESEARCHES. 
of volcanic agency ; it is not less than nine or ten 
miles in ength, and, in some parts, two miles 
from the sea to the foot of the mountains: the 
whole plain is covered with a rich alluvial soil, 
frequently two or three feet deep ; beneath this, a 
layer of fine volcanic ashes and cinders extends 
to the depth of fourteen or sixteen feet; these 
ashes lie upon a stratum of solid rock, by no means 
volcanic, but evidently calcareous, and apparently 
a kind of sediment deposited by the sea, in which 
branches of white coral, bones of fish and animals, 
and several varieties of marine shells, are often 
found. A number of wells have been recently dug 
in different parts of the plain, in which, after pene¬ 
trating through the calcareous rock, sometimes 
twelve or thirteen feet, good clear water has been 
always found ; the water in all these wells is per¬ 
fectly free from any salt or brackish taste, though 
it invariably rises and falls with the tide, which 
would lead to the supposition that it is connected 
with the waters of the adjacent ocean, from which 
the wells are from 100 yards to three-quarters of a 
mile distant. The rock is always hard and com¬ 
pact near the surface, but becomes soft and porous 
as the depth increases; and it is possible that the 
water in these wells may have’ percolated through 
the cells of the rock, and by this process of filtra¬ 
tion have lost its saline qualities. The base of the 
mountains which bound the plain in the interior, 
appears to have formed the original line of coast 
on this side of the island, but probably in some 
very remote period an eruption took place from 
two broad-based truncated mountains, called by 
foreigners Diamond Hill and Punchbowl Hill, evi¬ 
dently extinguished craters ; the ashes and cinders 
then thrown out, and wafted by the trade-winds in 
