FERNANDO NORONHA; TERCEIRA; TAHITI, ETC.

FERNANDO NORONHA.--Precipitous hill of phonolite.

TERCEIRA.--Trachytic rocks: their singular decomposition by steam of high temperature.

TAHITI.--Passage from wacke into trap; singular volcanic rock with the vesicles half-filled with mesotype.

MAURITIUS.--Proofs of its recent elevation.--Structure of its more ancient mountains; similarity with St.Jago.

ST.PAUL'S ROCKS.--Not of volcanic origin.--Their singular mineralogical composition.