y in all the other
sub-Alpine lakes of the Po valley. They are being gradually filled in,
every one of them, by the aggressive mud sheet. The upper end of
Lugano, for example, has already been cut off, as the Lago del Piano,
from the main body; and the _piano_ itself, from which the little
isolated tarn takes its name, is the alluvial mud fiat of a lateral
torrent--the mud flat, in fact, which the railway from Porlezza
traverses for twenty minutes before it begins its steep and picturesque
climb by successive zigzags over the mountains to Menaggio. Similarly
the influx of the Adda at the upper end of Como has cut off the Lago di
Mezzola from the main lake, and has formed the alluvial level that
stretches so drearily all around Colico. Slowly the mud fiend
encroaches everywhere on the lakes; and if you look for him when you
go, there you can see him actually at work every spring under your very
eyes, piling up fresh banks and deltas with alarming industry, and
preparing (in a few hundred thousand years) to ruin the tourist trade
of Cadenabbia and Bellagio.

If we turn from the lakes themselves to the Lombard plain at large,
which is an immensely older and larger basin, we see traces of the same
action on a vastly greater scale. A glance at the map will show the
intelligent and ever courteous reader that the 'wandering Po'--I drop
into poetry after Goldsmith--flows much nearer the foot of the
Apennines than of the Alps in the course of its divagations, and seems
purposely to bend away from the greater range of mountains. Why is
this, since everything in nature must needs have a reason? Well, it is
because, when the mud first began to accumulate in the old Lombard bay
of the Adriatic, there was no Po at all, whether wandering or
otherwise: the big river has slowly grown up in time by the union of
the lateral torrents that pour down from either side, as the growth of
the mud flat brought them gradually together. Careful study of a good
map will show how this has happened, especially if it has the plains
and mountains distinctively tinted after the excellent German fashion.
The Ticino, the Adda, the Mincio, if you look at them close, reveal
themselves as tributaries of the Po, which once flowed separately into
the Lombard bay; the Adige, the Piave, the Tagliamento farther along
the coast, reveal themselves equally as tributaries of the future Po,
when once the great river shall have filled up with its mud the space
between