SEDIMENT OF THE PO. 
257 
shores of the Adriatic not less than 42,760,000 cubic metres, 
or very nearly 55,000,000 cubic yards, which carries the coast 
line out into the sea at the rate of more than 200 feet in a 
year.* The depth of the annual deposit is stated at eighteen 
centimetres, or rather more than seven inches, and it would 
cover an area of not much less than ninety square miles' with 
a layer of that thickness. The Adige, also, brings every year 
to the Adriatic many million cubic yards of Alpine detritus, 
and the contributions of the Brenta from the same source are 
far from inconsiderable. The Adriatic, however, receives but 
a small proportion of the soil and rock washed away from the 
Italian slope of the Alps and the northern declivity of the 
Apennines by torrents. Nearly the whole of the debris thus 
removed from the southern face of the Alps between Monte 
Bosa and the sources of the Adda—a length of watershed not 
less than one hundred and fifty miles—is arrested by the still 
waters of the Lakes 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 Piacenza, therefore, 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sediment over a wide surface, and the water withdrawn from 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 we add to the estimated annual deposits of the Po at its 
mouth, 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 
* This change of coast line cannot he ascribed to upheaval, for a com¬ 
parison of the level of old buildings—as, for instance, the church of San 
Vitale and the tomb of Theodoric at Eavenna—with that of the sea^ tends 
to prove a depression rather than an elevation of their foundations. 
A computation by a different method makes the deposits at the mouth 
of the Po 2,123,000 metres less ; but as both of them omit the gravel and 
silt rolled, if not floated, down at ordinary and low water, we are safe in 
assuming the larger quantity .—Article last quoted , p. 174. 
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