540 RESULTS OF OPERATIONS. 
Lesults of Operations. 
It is now a hundred years since the commencement of the 
improvements in the Val di Chiana, and those of the Maremma 
have been in more or less continued operation for above a gen- 
eration. They have, as we have seen, produced important geo- 
graphical changes in the surface of the earth and in the flow of 
considerable rivers, and their effects have been not less conspicu- 
ous in preventing other changes, of a more or less deleterious 
character, which would infallibly have taken place if they had 
not been arrested by the improvements in question. 
The sediment washed into the marshes of the Maremma is 
not less than 12,000,000 cubic yards per annum. The escape 
of this quantity into the sea, which is now almost wholly pre- 
vented, would be sufficient to advance the coast-line fourteen 
yards per year, for a distance of forty miles, computing the 
mean depth of the sea near the shore at twelve yards. It is 
true that in this case, as well as in that of other rivers, the 
sedimentary matter would not be distributed equally along the 
shore, and much of it would be carried out into deep water, or 
perhaps transported by the currents to distant coasts. The im- 
mediate effects of the deposit in the sea, therefore, would not 
be so palpable as they appear in this numerical form, but they 
would be equally certain, and would infallibly manifest them- 
selves, first, perhaps, at some remote point, and afterwards more 
energetically at or near the outlets of the rivers which produced 
them. The elevation of the bottom of the sea would diminish 
the inclination of the beds of the rivers discharging themselves 
into it on that coast, and of course their tendency to overflow 
their banks and extend still further the domain of the marshes 
which border them would be increased in proportion. 
It has been already stated that, in order to prevent the over- 
flow of the valley of the Tiber by freely draining the Val di 
~ Chiana into it, the Papal authorities, long before the commence- 
ment of the Tuscan works, constructed strong barriers near the 
