12 POLYNESIAN RESEARCHES. 
the whole group of islands; in which nothing like 
primitive or secondary rock has yet been found. 
In Tahiti, and other islands of the southern clus¬ 
ter, there are basalts, whinstone dykes, and homo¬ 
geneous earthy lava, retaining all the convolutions 
which cooling lava is known to assume; there are 
also kinds of hornstone, limestone, silex, breccia, 
and other substances, which, under the action of 
fire, do not appear to have altered their original 
form. Some are found in detached fragments, 
others in large masses. 
The variety of substances found in some of the 
smaller islands is greater than that which is met 
with in Tahiti, or the Georgian cluster. In Bora- 
bora there are masses of rock, apparently com¬ 
posed of feldspar and quartz; and in Maupiti, 
besides the common vesicular lava and the basalt 
common to all the islands, a species of granite 
is found in considerable abundance, which pre¬ 
sents an anomaly as striking in the geology of 
these islands, as that furnished by the existence 
of carbonate of lime in the island of Rurutu, where 
garnets are also obtained. Hornblende and feld¬ 
spar are found in Huahine, as well as in some of 
the other islands. Ancient lava, containing oli¬ 
vine, augite, and zeolite, are also met with, together 
with pumice and cellular lava, some kinds of which, 
found in Sir Charles Sanders’ Island, are of a dark 
blue colour, and, though apparently containing a 
portion of iron, so light as to float on the water. 
Specimens of these I have by me; and a large 
one of the latter kind from Sir Charles Sanders’ 
island, is more porous than any I ever met with 
among the volcanoes of the Sandwich Islands, and 
so completely honeycomb in its structure, that it 
is difficult to account for its formation. 
