to obtain some further information relative to this very remarkable
submarine ledge, which appears to surround the Island,
before entertaining the theory of a general subsidence of the
land, or indeed any theory with reference to the cause of its existence.*
The geological structure of this remarkable land has often been
curtly described in the few words, “ it is volcanic,” and the explanation
as often considered sufficient, inasmuch as the truth of such an
assertion cannot be doubted, even by the most casual observer. This
rocky pile, however, so often briefly dismissed as troublesome to
inquire into, presents not a few points, in searching out truth, well
worthy of the student’s attention. The manner of its formation,
together with the time occupied therein, and the period that has
since elapsed in bringing it to its present shape and dimensions, are
each subjects affording unusual interest in reading that page of
nature’s book which throws light upon the ancient geography of the
Southern Atlantic region.
Its isolated position, its peculiar fauna, and its Very remarkable
insular flora, together with its geological character, present
strong reasons for placing St. Helena amongst the oldest land-
now existing on the face of the globe. I t represents a very fair
type of an oceanic volcano similar to Palma of the Canaries, St.
Paul’s Island, in the Indian Ocean, and others, of which Sir Charles:
Lyell makes the following remarks —“ Every crater must almost
invariably have one side much lower than all the others, viz., that
side towards which the prevailing winds never blow, and to which,
therefore, showers of dust and scorise are rarely carried during eruptions,
There will also be one point on this windward or lowest side-
more depressed than all the rest, by which in the event of a partial
submergence the sea may enter as often as the tide rises, or as often
as the wind blows from that quarter. For the same reason that a sea
continues to keep open a single entrance into the lagoon of an atoll
or annular coral reef, it will not allow this passage into the crater to :
be stopped up, but will scour it out at low tide, or as often as the wind
changes.”f There is, in the Island of St. Helena, precisely such a
* I hope that this subject may be investigated during the present cruise of H.M.S.'
Challenger, as Mr. Gwyn Jeffreys has most kindly promised to bring it before the notice of
Professor Wyville Thomson.
t Manual of Geology, by Sir Charles Lyell, M.A., F.R.S., 1855, p. 513.