compacted that the
substance takes a good polish. The well-known Column of Trajan--the
first monument (_columna cochlaea_) of this description ever raised in
Rome, and far superior to the Antonine Column--is composed of
Lumachella marble from Megara. It presents, in twenty-three spiral
bands of bas-reliefs, winding round thirty-four blocks of stone, the
history of the victories of Trajan over the Dacians, and, without
reckoning horses, implements of war, and walls of cities, is said to
consist of no less than two thousand five hundred figures, each about
two feet two inches high. It is a strikingly suggestive thought, that
this majestic pillar--which produced so deep an impression upon the
minds of posterity that, according to the beautiful legend, Pope
Gregory the Great was moved to supplicate, by means of masses in
several of the Roman churches, for the liberation of him whom it
commemorated from purgatory--should be composed of the relics of
sea-shells.

"Memorial pillar! 'mid the wreck of Time,
Preserve thy charge with confidence sublime,"

said Wordsworth; but this sublime charge is committed to frail
keeping. It is itself a sepulchre of the dead; and the tragedies of
the Dacian war are inscribed upon tragedies that took place long ages
before there was any human eye to witness them. The historic
sculptures that so deeply move our pity for a conquered people, are
based upon the immemorial sculptures of creatures whose sacrifice in
whole hecatombs touches us not, because it is part of the order of the
world by which life forms the foundation of and minister to life. It
is strange how many of the grandest monuments are wrought out of the
creations of primeval molluscs. The enduring pyramids themselves are
formed of the nummulitic limestone studded with its "Pharaoh's beans,"
the exuviae of shell-fish that perished ages before the Nile had
created Egypt.

Of the breccias there is a great variety among the relics of ancient
Rome. A breccia is a rock made up of angular pebbles or fragments of
other rocks. When the pebbles are rounded the conglomerate is a
pudding-stone. Marble breccias are formed of angular pieces of highly
crystalline limestone, united together by a siliceo-calcareous cement,
containing usually an admixture of a hornblendic substance, and which
is due to a particular action of adjacent masses or veins of iron ore.
The hornblendic cement, with its iron or manganese base, produces the
varieg