This return of the mountain chain upon itself
causes a vast difference in the character of the distribution of its
_debris_ on its opposite sides. The rock fragments and sediment which
the torrents on the north side of the Alps bear into the plains are
distributed over a vast extent of country, and, though here and there
lodged in beds of enormous thickness, soon permit the firm substrata to
appear from underneath them; but all the torrents which descend from the
southern side of the High 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.
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