SEDIMENT OF THE PO. 981 
Maggiore and Como, and some smaller lacustrine reservoirs, and 
never reaches the sea. The Po is not continuously embanked 
except for the lower half of its course. Above Cremona, there- 
fore, it spreads and deposits sediment over a wide surface, and 
the water withdrawn from it for irrigation at lower points, as 
well as its inundations in the occasional ruptures of its banks, 
carry over the adjacent soil a large amount of slime. * 
If to the estimated annual deposits of the Po at its mouth, 
we add the earth and sand transported to the sea by the Adige, 
the Brenta, and other less important streams, the prodigious 
mass of detritus swept into Lago Maggiore by the Tosa, the 
Maggia, and the Ticino, into the lake of Como by the Maira 
and the Adda, into the lakes of Garda, Lugano, Iseo, and Idro, 
by their affluents,t and the yet vaster heaps of pebbles, gravel, 
and earth permanently deposited by the torrents near their 
points of eruption from mountain gorges, or spread over the 
wide plains at lower levels, we may safely assume that we have 
an aggregate of not less than ten times the quantity carried to 
the Adriatic by the Po, or 550,000,000 cubic yards of solid 
matter, abstracted every year from the Italian Alps and the 
Apennines, and removed out of their domain by the force of 
running water. ¢ 
* The quantity of sediment deposited by the Po on the plains which border 
it, before the construction of the continuous dikes and in the floods which oc- 
casionally burst through them, is vast, and the consequent elevation of those 
plains is very considerable. Ido not know that this latter point has been 
made a subject of special investigation, but vineyards, with the vines still at- 
tached to the elms which supported them, have been found two or three yards 
below the present surface at various points on the plains of Lombardy. 
{+ The Po receives about four-tenths of its waters from these lakes. See 
LOMBARDINI, Dei cangiamenti nella condizione del Po, p. 29. All the sedi- 
ment carried into the lakes by their tributaries is deposited in them, and the 
water which flows out of them is perfectly limpid. From their proximity to 
the Alps and the number of torrents which empty into them, they no doubt 
receive vastly more transported matter than is contributed to the Po by the 
six-tenths of its waters received from other sources. 
t Mengotti estimated the mass of solid matter annually ‘‘ united to the wa- 
ters of the Po” at 822,000,000 cubic métres, or nearly twenty times as much 
