In like manner, the muddy matters form at the mouth of the Rhine, of the Meuse, and of the Scheld, those immense polders, which constitute such an essential part of the territory of Holland, and the numerous banks at the mouth of these rivers are only composed of sand and carbonate of lime. Now the rapidity of the current, long before reaching the mouth, is not sufficiently great to carry down the sands; in fact, no trace of them is perceived; these banks are therefore the production of the sea. Finally, in order to appreciate at the _maximum_ the power of the fluviatile deposit in the formation of the coasts, observations have been made upon the Yssel, that branch of the Rhine which discharges itself into the Zuyderzee. This sea has but very feeble tides, 0 _met._, 40, at ordinary high water, and very much resembles the Mediterranean, the Black Sea, and the Adriatic Gulf in this respect. A muddy Delta has also been formed at the mouth of the Yssel, of the same shape as those of the Rhone, the Po, the Nile, &c. &c. This Delta cannot be exclusively owing to the Yssel, because, although it is true that the tides of the Zuyderzee are very feeble, on the other hand the shores which surround it are of an exceedingly friable nature; now, however feeble the tides may be, they yet attack the banks, and what proves it, is, that the Hollanders are obliged to defend them. By considering the Delta of the Yssel as a fluviatile deposit solely, we shall therefore have an extreme case. Now, this Delta has a superfice of only 1500 _hectares_, while the superfice of the land in Holland, which is evidently of modern deposit, is at least 1,000,000 _hectares_. If it is observed that the Yssel only emits a fifteenth of the whole volume of the Rhine and the Meuse united, it will give 22,500 _hectares_ for the deposit of the river, against 1,000,000 deposited by the sea; which is scarcely two per cent. of what the sea has furnished in the formation of the polders of Holland. From the examination of all these facts, it evidently results, as we have said, that in seas with tides, the rivers not only do not form banks, alluvium, or deltas at their mouths, but farther, that the alluvium found in the regions of these rivers submitted to the action of the tide, is deposited by the sea. We shall now prove that these conclusions are equally true for the rivers of the Mediterranean, notwithstanding the opinion of the Italian engineers, who have considered the fluviatile origin of their deltas as demonstrated.