SECTION V. 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 neighborhood 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. In some places, according to the run of the currents, the land has risen into marshy islets, consolidated, some by art, and some by time, into ground firm enough to be built upon, or fruitful enough to be cultivated: in others, on the contrary, it has not reached the sea-level; so that, at the average low water, shallow lakelets glitter among its irregularly exposed fields of seaweed. In the midst of the largest of these, increased in importance by the confluence of several large river channels towards one of the openings in the sea bank, the city of Venice itself is built, on a clouded cluster of islands; the various plots of higher ground which appear to the north and south of this central cluster, have at different periods been also thickly inhabited, and now bear, according to their size, the remains of cities, villages, or isolated convents and churches, scattered among spaces of open ground, partly waste and encumbered by ruins, partly under cultivation for the supply of the metropolis.