The Temple of Serapis at Puzzuoli, near Naples, is perhaps, of all
the structures raised by the hands of man, the one which affords most
instruction to a geologist. It has not only undergone a wonderful
succession of changes in past time, but is still undergoing changes
of condition. This edifice was exhumed in 1750 from the eastern shore
of the Bay of Baiæ, consisting partly of strata containing marine
shells with fragments of pottery and sculpture, and partly of volcanic
matter of sub-aerial origin. Various theories were proposed in the
last century to explain the perforations and attached animals observed
on the middle zone of the three erect marble columns until recently
standing; Goethe, among the rest, suggesting that a lagoon had once
existed in the vestibule of the temple, filled during a temporary
incursion of the sea with salt water, and that marine mollusca and
annelids flourished for years in this lagoon at twelve feet or more
above the sea-level.
This hypothesis was advanced at a time when almost any amount of
fluctuation in the level of the sea was thought more probable than
the slightest alteration in the level of the solid land. In 1807 the
architect Niccolini observed that the pavement of the temple was dry,
except when a violent south wind was blowing; whereas, on revisiting
the temple fifteen years later, he found the pavement covered by salt
water twice every day at high tide. From measurements made from 1822
to 1838, and thence to 1845, he inferred that the sea was gaining
annually upon the floor of the temple at the rate of about one-third
of an inch during the first period, and about three-fourths of an inch
during the second. Mr. Smith of Jordan Hill, from his visits in 1819
and 1845, found an average rise of about an inch annually, which was
in accordance with visits made by Mr. Babbage in 1828, and Professor
James Forbes in 1826 and 1843. In 1852 Signor Scaecchi, at the request
of Sir Charles Lyell, compared the depth of water on the pavement with
its level taken by him in 1839, and found that it had gained only 4½
inches in thirteen years, and was not so deep as when MM. Niccolini
and Smith measured it in 1845; from which he inferred that after 1845
the downward movement of the land had ceased, and before 1852 had been
converted into an upward movement.
Arago and others maintained that the surface on which the temple
stands has been depressed, has _remained under the sea, and has again
been elevated_. Russager, however, contends that there is nothing in
the vicinity of the temple, or in the temple itself, to justify this
bold hypothesis. Every thing leads to the belief that the temple has
remained unchanged in the position in which it was originally built;
but that the sea rose, surrounded it to a height of at least twelve
feet, and again retired; but the elevated position of the sea continued
sufficiently long to admit of the animals boring the pillars. This view
can even be proved historically; for Niccolini, in a memoir published
in 1840, gives the heights of the level of the sea in the Bay of
Naples for a period of 1900 years, and has with much acuteness proved
his assertions historically. The correctness of Russager’s opinion,
he states, can be demonstrated and reduced to figures by means of the
dates collected by Niccolini.--See _Jameson’s Journal_, No. 58.
At the present time the floor is always covered with sea-water. On the
whole, there is little doubt that the ground has sunk upwards of two
feet during the last half-century. This gradual subsidence confirms
in a remarkable manner Mr. Babbage’s conclusions--drawn from the
calcareous incrustations formed by the hot springs on the walls of the
building and from the ancient lines of the water-level at the base of
the three columns--that the original subsidence was not sudden, but
slow and by successive movements.
Sir Charles Lyell (who, in his _Principles of Geology_, has given a
detailed account of the several upfillings of the temple) considers
that when the mosaic pavement was re-constructed, the floor of the
building must have stood about twelve feet above the level of 1838 (or
about 11½ feet above the level of the sea), and that it had sunk about
nineteen feet below that level before it was elevated by the eruption
of Monte Nuovo.
We regret to add, that the columns of the temple are no longer in
the position in which they served so many years as a species of
self-registering hydrometer: the materials have been newly arranged,
and thus has been torn as it were from history a page which can never
be replaced.