371. The quantity of detritus brought down by the rivers, and distributed in this manner over the bottom of the sea, is so great, that several narrow seas have been thereby rendered sensibly shallower. The Baltic has been computed to decrease in depth at the rate of forty inches in a hundred years. The Yellow Sea, which is a large gulf contained between the coast of China and the peninsula of Corea, receives so much mud from the great rivers that run into it, that it takes its colour, as well as its name, from that circumstance; and the European mariners who have lately navigated it, observed, that the mud was drawn up by the ships, so as to be visible in their wake to a considerable distance.[187] Computations have been made of the time that it will require to fill up this gulf, and to withdraw it entirely from the dominion of the ocean: but the data are not sufficiently exact to afford any precise result, and are no doubt particularly defective from this cause, that much of the earth carried into the gulf by the rivers, must be carried out of it by the currents and tides, and the finer parts wafted probably to great distances in the Pacific Ocean.[188] The mere attempt, however, towards such a computation, shows how evident the progress of filling up is to every attentive observer; and, though it may not ascertain the measure, it sufficiently declares the reality of the operations, by which the waste of the present continents is made subservient to the formation of new land. [Footnote 187: Staunton's Account of the Embassy to China, vol. i. p. 448.] [Footnote 188: Perouse, in sailing along the coast of China, from Formosa to the strait between Corea and Japan, though generally fifty or sixty leagues from the land, had soundings at the depth of forty-five fathoms, and sometimes at that of twenty-two. Atlas du Voyage de la Perouse, No. 43.] 372. Sandbanks, such as abound in the German Ocean, to whatever they owe their origin, are certainly modified, and their form determined, by the tides and currents. Without the operation of these last, banks of loose sand and mud could hardly preserve their form, and remain intersected by many narrow channels. The formation of the banks on the coast of Holland, and even of the Dogger Bank itself, has been ascribed to the meeting of tides, by which a state of tranquillity is produced in the waters, and of consequence a more copious deposition of their mud. Even the great bank of Newfoundland seems to be determined in its extent by the action of the Gulf stream. In the North Sea, the current which sets out of the Baltic, has evidently determined the shape of the sandbanks opposite to the coast of Norway, and produced a circular sweep in them, of which it is impossible to mistake the cause.