346 VITI ISLANDS. 
These compact basalts pass into veszcular varieties, in which elon- 
gate vesicles are generally contained in a base otherwise compact, and 
not scoriaceous throughout, like many lavas. Occasionally we see 
fragments in which the vesicles are thickly disseminated. Some of 
the vesicular basalts have the cavities filled with geodes of quartz, 
chalcedony, and different zeolites; they have an amygdaloidal cha- 
racter, without, however, becoming true amyedaloids. 
The basalts pass into trachytes, of a light grayish, grayish-yellow or 
grayish-blue colour; but I have not observed these rocks “in situ.” 
The only other variety of igneous rock meriting distinct notice is 
pumice, which is found in very well-characterized masses, and has 
some light shade of colour, generally grayish-white or a tinge of 
grayish-blue. It floats readily, and may be collected from the shores 
of most of the islands, where it has been thrown up by the sea. 
The conglomerates consist of the above materials, thrown together 
in angular or partially-rounded fragments, and imbedded in an earthy 
base of the same origin. ‘The imbedded masses are of all sizes, to six 
or eight feet in diameter, and often the coarse and fine are piled on 
one another without any regularity. ‘The coarse conglomerates in 
some places pass gradually into a basaltic sandstone consisting of 
fine grains of very uniform texture. A still finer variety of compact 
structure resembles an argillaceous rock, and might be mistaken 
from hand specimens. <A remarkable deposit of tufa and pumice-con- 
glomerate occurs at Mali Point, on the north side of Vanua Lebu. 
The rock varies from a coarse aggregate of fragments of pumice 
and decomposing trachyte, on the one hand to a fine, almost impal- 
pable argillaceous deposit, and on the other, either slowly or by 
abrupt transitions, to a very coarse conglomerate, consisting of angular 
masses of compact and imperfectly vesicular basalt. This pumice- 
conglomerate and tufa has a white or straw-yellow colour, and pre- 
sents a clean, neat appearance. It is quite soft, and the fragments 
composing it are fragile, and apparently half decomposed. Many of 
them are compact, but look not unlike yellowish cheese, and are 
scarcely of greater hardness. 
Much of the coarse conglomerate in the Mali cliff has a very re- 
markable aspect: it consists of large angular masses of the black basalt, 
with the interstices filled in with this ight straw-coloured tufaceous 
material. The tufa and conglomerate are very irregularly intermin- 
gled, and are remarkable in forming concurrent and not alternate 
layers. 
