t St.
Michael's Mount is at the present day, that few would deny that if the
Mount ever was a "Hoar rock in the wood," it must have been so before the
time of which Diodorus speaks, that is, at least before the last two
thousand years. The nine apparent reasons why St. Michael's Mount cannot
be the Ictis of Diodorus, and their refutation, may be seen in Mr.
Pengelly's paper "On the Insulation of St. Michael's Mount," p. 6, seq.

Mr. Pengelly proceeded to show that the geological change which converted
the promontory into an island may be due to two causes. First, it may have
taken place in consequence of the encroachment of the sea. This would
demand a belief that at least 20,000 years ago Cornwall was inhabited by
men who spoke Cornish. Secondly, this change may have taken place by a
general subsidence of the land, and this is the opinion adopted by Mr.
Pengelly. No exact date was assigned to this subsidence, but Mr. Pengelly
finished by expressing his decided opinion that, subsequent to a period
when Cornwall was inhabited by a race speaking a Celtic language, St.
Michael's Mount was "a hoar rock in the wood," and has since become
insulated by powerful geological changes.

In a more recent paper read at the Royal Institution (April 5, 1867), Mr.
Pengelly has somewhat modified his opinion. Taking for granted that at
some time or other St. Michael's Mount was a peninsula and not yet an
island, he calculates that it must have taken 16,800 years before the
coast line could have receded from the Mount to the present cliffs. He
arrived at this result by taking the retrocession of the cliffs at ten
feet in a century, the distance between the Mount and the mainland being
at present 1,680 feet.

If, however, the severance of the Mount from the mainland was the result,
not of retrocession, but of the subsidence of the country,--a rival theory
which Mr. Pengelly still admits as possible,--the former calculation would
fail, and the only means of fixing the date of this severance would be
supplied by the remains found in the forests that were carried down by
that subsidence, and which are supposed to belong to the mammoth era. This
mammoth era, we are told, is anterior to the lake-dwellings of
Switzerland, and the kitchenmiddens of Denmark, for in neither of these
have any remains of the mammoth been discovered. The mammoth, in fact, did
not outlive the age of bronze, and before the end of that age, therefore,
St. Michael's Moun