ST. PAUL'S ROCKS.

This small island is situated in the Atlantic Ocean, nearly one degree
north of the equator, and 540 miles distant from South America, in 29
degrees 15 minutes west longitude. Its highest point is scarcely fifty feet
above the level of the sea; its outline is irregular, and its entire
circumference barely three-quarters of a mile. This little point of rock
rises abruptly out of the ocean; and, except on its western side, soundings
were not obtained, even at the short distance of a quarter of a mile from
its shore. It is not of volcanic origin; and this circumstance, which is
the most remarkable point in its history (as will hereafter be referred
to), properly ought to exclude it from the present volume. It is composed
of rocks, unlike any which I have met with, and which I cannot characterise
by any name, and must therefore describe.

The simplest, and one of the most abundant kinds, is a very compact, heavy,
greenish-black rock, having an angular, irregular fracture, with some
points just hard enough to scratch glass, and infusible. This variety
passes into others of paler green tints, less hard, but with a more
crystalline fracture, and translucent on their edges; and these are fusible
into a green enamel. Several other varieties are chiefly characterised by
containing innumerable threads of dark-green serpentine, and by having
calcareous matter in their interstices. These rocks have an obscure,
concretionary structure, and are full of variously coloured angular pseudo
fragments. These angular pseudo fragments consist of the first-described
dark green rock, of a brown softer kind, of serpentine, and of a yellowish
harsh stone, which, perhaps, is related to serpentine rock. There are other
vesicular, calcareo-ferruginous, soft stones. There is no distinct
stratification, but parts are imperfectly laminated; and the whole abounds