SEDIMENT OF THE PO. 
259 
stones of freshly cleared forest ground are most easily removed. 
Many of the Alpine valleys west of the Ticino—that of the 
Dora Baltea for instance—were nearly stripped of their forests 
in the days of the Roman empire, others in the Middle Ages, 
and, of course, there must have been, at different periods before 
the year 1200, epochs when the erosion and transportation of 
solid matter from the Alps and the Apennines were as great as 
since the year 1600. 
Upon the whole, we shall not greatly err if we assume 
that, for a period of not less than two thousand years, the 
walls of the basin of the Po—the Italian slope of the Alps, 
and the northern and northeastern declivities of the Apen¬ 
nines—have annually sent down into the Adriatic, the lakes, 
and the plains, not less than 150,000,000 cubic yards of earth 
and disintegrated rock. We have, then, an aggregate of 
300,000,000,000 cubic yards of such material, which, allowing 
to the mountain surface in question an area of 50,000,000,000 
square yards, would cover the whole to the depth of six yards.* 
There are very large portions of this area, where, as we know 
from ancient remains—roads, bridges, and the like—from 
other direct testimony, and from geological considerations, 
very little degradation has taken place within twenty cen¬ 
turies, and hence the quantity to be assigned to localities 
where the destructive causes have been most active is in¬ 
creased in proportion. 
If this vast mass of pulverized rock and earth were restored 
to the localities from which it was derived, it certainly would 
not obliterate valleys and gorges hollowed out by great geo¬ 
logical causes, but it would reduce the length and diminish 
the depth of ravines of later formation, modify the inclination 
of their walls, reclothe with earth many bare mountain ridges, 
* The total superficies of the basin of the Po, down to Ponte Lagoscuro 
[Ferrara]—a point where it has received all its affluents—is 6,988,200 hec¬ 
tares, that is, 4,105,600 in mountain lands, 2,832,600 in plain lands — 
Dumont, Travaux Publics , etc., p. 272. 
These latter two quantities are equal respectively to 10,145,348, and 
6,999,638 acres, or 15,852 and 10,937 square miles. 
