gh Alps and from the northern slope of the
Apennines meet concentrically in the recess or mountain-bay which the
two ridges enclose; every fragment which thunder breaks out of their
battlements, and every grain of dust which the summer rain washes from
their pastures, is at last laid at rest in the blue sweep of the
Lombardic plain; and that plain must have risen within its rocky
barriers as a cup fills with wine, but for two contrary influences which
continually depress, or disperse from its surface, the accumulation of
the ruins of ages.

I will not tax the reader's faith in modern science by insisting on this
singular depression of the surface of Lombardy, which appears for many
centuries to have taken place steadily and continually; the main fact
with which we have to do is the gradual transport, by the Po and its
great collateral rivers, of vast masses of the finer sediment to the
sea. The character of the Lombardic plains is most strikingly expressed
by the ancient walls of its cities, composed for the most part of large
rounded Alpine pebbles alternating with narrow courses of brick, and was
curiously illustrated in 1848 by the ramparts of these same pebbles
thrown up four or five feet high round every field, to check the
Austrian cavalry in the battle under the walls of Verona.

The finer dust among which these pebbles are dispersed is taken up by
the rivers, fed into continual strength by the Alpine snow, so that,
however pure their waters may be when they issue from the lakes at the
foot of the great chain, they become of the color and opacity of clay
before they reach the Adriatic; the sediment which they bear is at once
thrown down as they enter the sea, forming a vast belt of low land along
the eastern coast of Italy. The powerful stream of the Po of course
builds forward the fastest; on each side of it, north and south, there
is a tract of marsh, fed by more feeble streams, and less liable to
rapid change than the delta of the central river. In one of these tracts
is built Ravenna, and in the other Venice.

What circumstances directed the peculiar arrangement of this great belt
of sediment in the earliest times, it is not here the place to inquire.
It is enough for us to know that from the mouths of the Adige to those
of the Piave there stretches, at a variable distance of from three to
five miles from the actual shore, a bank of sand, divided into long
islands by narrow channels of sea. The space betwee