species which puzzles most
visitors by its Protean appearance. Its tints are always neutral, but
they vary in depth from the lightest to the darkest shade, and are
never mixed but in juxtaposition. Dirty yellows, cloudy reds, dim
blues and purples, occur in the ground or in the round or waved
blotches or crooked veins. It has a fine grain and a dull fracture.
This variety of Africano is known by the familiar name of _Porta
Santa_, from the circumstance that the jambs and lintel of the first
Porta Santa--a Holy Door annexed by Boniface VIII. to St. Peter's in
the year 1300--were constructed of this marble. The Porta Santa, it
may be mentioned, was instituted in connection with a centenary
jubilee, but afterwards the period of formally opening it was reduced
to fifty years, and now it is shortened to twenty-five. On the
occasion of the jubilee, on Christmas Eve, the Pope knocks three times
with a silver hammer against the masonry with which it is filled up,
which is then demolished, and the Holy Door remains open for a whole
twelvemonth, and on the Christmas Eve of the succeeding year is closed
up in the same manner as before. A similar solemnity is performed by
proxy at the Lateran, the Liberian, and the Pauline Basilicas. In all
these great churches, as in St. Peter's, the jambs and Lintel of the
Holy Door are of Porta Santa marble. This beautiful material was
brought from the mountains in the neighbourhood of Jassus--a
celebrated fishing town of Caria, situated on a small island close to
the north coast of the Jassian Bay. From this circumstance it was
called by the ancient Romans _Marmor Jassense_. Near the quarries was
a sanctuary of Hestia, with a statue of the goddess, which, though
unprotected in the open air, was believed never to be touched by rain.
The marble, the most highly-prized variety of which was of a blood-red
and livid white colour, was used in Greece chiefly for internal
decoration. It was introduced in large quantity into Rome, and there
are few churches in which the relics of it that existed in older
buildings have not been adapted for ornamental purposes. Among the
larger and finer masses of Porta Santa may be enumerated two columns
and pilasters which belong to the monument of Clement IX., in the
Church of Santa Maria Maggiore, and which are remarkable for their
exceedingly fine texture and the unusual predominance of white among
the other hues; four splendid Corinthian pillars, considered the
fi