round part, if not round the whole, of the island; here again the same
question immediately occurs, how came these masses to hold their present
position, and whence were they erupted? The same answer, whatever it may
be, probably applies in these three cases; and in a future chapter we shall
recur to this subject.

VALLEYS NEAR THE COAST.

These are broad, very flat, and generally bounded by low cliff-formed
sides. Portions of the basaltic plain are sometimes nearly or quite
isolated by them; of which fact, the space on which the town of Praya
stands offers an instance. The great valley west of the town has its bottom
filled up to a depth of more than twenty feet by well-rounded pebbles,
which in some parts are firmly cemented together by white calcareous
matter. There can be no doubt, from the form of these valleys, that they
were scooped out by the waves of the sea, during that equable elevation of
the land, of which the horizontal calcareous deposit, with its existing
species of marine remains, gives evidence. Considering how well shells have
been preserved in this stratum, it is singular that I could not find even a
single small fragment of shell in the conglomerate at the bottom of the
valleys. The bed of pebbles in the valley west of the town is intersected
by a second valley joining it as a tributary, but even this valley appears
much too wide and flat-bottomed to have been formed by the small quantity
of water, which falls only during one short wet season; for at other times
of the year these valleys are absolutely dry.

RECENT CONGLOMERATE.

On the shores of Quail Island, I found fragments of brick, bolts of iron,
pebbles, and large fragments of basalt, united by a scanty base of impure