[142] The
finer dust among which these pebbles are dispersed is taken up by the
rivers, fed into continual strength by the Alpine snow, so that,
however pure their waters may be when they issue from the lakes at the
foot of the great chain, they become of the colour and opacity of clay
before they reach the Adriatic; the sediment which they bear is at once
thrown down as they enter the sea, forming a vast belt of low land
along the eastern coast of Italy. The powerful stream of the Po of
course builds forward the fastest; on each side of it, north and south,
there is a tract of marsh, fed by more feeble streams, and less liable
to rapid change than the delta of the central river. In one of these
tracts is built RAVENNA, and in the other VENICE.
What circumstances directed the peculiar arrangement of this great belt
of sediment in the earliest times, it is not here the place to inquire.
It is enough for us to know that from the mouths of the Adige to those
of the Piave there stretches, at a variable distance of from three to
five miles from the actual shore, a bank of sand, divided into long
islands by narrow channels of sea. The space between this bank and the
true shore consists of the sedimentary deposits from these and other
rivers, a great plain of calcareous mud, covered, in the neighbourhood
of Venice, by the sea at high water, to the depth in most places of a
foot or a foot and a half, and nearly everywhere exposed at low tide,
but divided by an intricate network of narrow and winding channels,
from which the sea never retires.
Pages:
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210