during the morning of February 16th, close to the island of
St. Paul. This cluster of rocks is situated in 0 ° 58' north
latitude, and 29° 15' west longitude. It is 540 miles distant
from the coast of America, and 350 from the island of Fernando
Noronha. The highest point is only fifty feet above the
level of the sea, and the entire circumference is under three-
quarters of a mile. This small point rises abruptly out of
the depths of the ocean. Its mineralogical constitution is
not simple ; in some parts, the rock is of a cherty, in others,
of a felspathic nature ; and in the latter case it contains thin
veins of serpentine, mingled with calcareous matter.
The circumstance of these rocks not being of volcanic
origin is of interest, because, with very few exceptions, the
islands situated in the midst of the great oceans are thus
constituted. As the highest pinnacles of the great mountain
ranges probably once existed as islands distant from any
continent, we are led to expect that they would frequently
consist of volcanic rocks. It becomes, therefore, a curious
point to speculate on the changes which many of the present
islands would undergo, during the lapse of the countless
ages, which would be required to elevate them into snow-
clad summits. If we take the case of Ascension, or St.
Helena, both of which have long existed in an extinct condition,
we may feel assured, before so vast a period could
elapse, during the whole of which the surface would be exposed
to constant wear and tear, that the mere nucleus or
core of the island would remain ; perhaps, every fragment of
cellular rock having been decomposed, a mass of some compact
stone, as phonolite or greenstone, would crown our new
Chimborazo.
The rocks of St. Paul appear from a distance of a brilliantly
white colour. This is partly owing to the dung of a
vast multitude of seafowl, and partly to a coating of a glossy
white substance, which is intimately united to the surface of
the rocks. This, when examined with a lens, is found to
consist of numerous exceedingly thin layers, its total thickness
being about the tenth of an inch. The surface is smooth
and glossy, and has a pearly lustre ; it is considerably harder
than calcareous spar, although it can be scratched by a knife :
under the blowpipe it decrepitates, slightly blackens, and
emits a fetid odour. It consists of phosphate of lime, mingled
with some impurities; and its origin without doubt is due
to the action of the rain or spray on the bird’s dung. I may
here mention, that I found in some hollows in the lava rocks
of Ascension considerable masses of the substance called
guano, which on the west coast of the intertropical parts of
South America occurs in great beds, some yards thick, on
the islets frequented by seafowl. According to the analysis
of Fourcroy and Vauquelin, it consists of the urates, phosphates,
and oxalates of lime, ammonia, and potash, together
with some other salts, and some fatty and earthy matter. I
believe there is no doubt of its being the richest manure which
has ever been discovered. At Ascension, close to the guano,
stalactitio or botryoidal masses of impure phosphate of lime
adhered to the basalt. The basal part of these had an earthy
texture, but the extremities were smooth and glossy, and
sufficiently hard to scratch common glass. These stalactites
appeared to have shrunk, perhaps from the removal of some
soluble matter, in the act of consolidation ; and hence they
had an irregular form. Similar stalactitic masses,* though I
am not aware that they have ever been noticed, are, I believe,
by no means of uncommon occurrence.
We only observed two kinds of birds—the booby and the
noddy. The former is a species of gannet, and the latter a
tern. Both are of a tame and stupid disposition, and are so
unaccustomed to visiters, that I could have killed any number
of them with my geological hammer. The booby lays her
eggs on the bare rock ; liut the tern makes a very simple nest
* I m ay m e n tio n t h a t I w a s sh ow n , a t A s c e n s io n , som e v e ry fine
s ta la c tite s , com p o sed o f s u lp h a te o f lim e , w h ic h h a d b e e n ta k e n o u t o f a
ca v e rn . F rom th e i r e x te r n a l a p p e a r a n c e th e y w o u ld g e n e ra lly b e m is ta k e n
fo r th e o rd in a ry c a lc a re o u s k in d . I t was in te r e s tin g to o b se rv e , in a fra c tu
r e d sp e cim en , th e d o u b le c le av ag e in te r s e c tin g w ith its e v e n p lan e s , th e
irr e g u la r lay e rs o f su ccessiv e d e p o s itio n .