But the greatest exhibition of the wonderful character of the Mississippi, and in which all its singular effects are most distinctly shown, is in its Delta. For a long succession of years the immense quantities of sediment, of which we have already spoken, had gradually precipitated upon this portion of the river until it reached the surface. Drift now lodged upon it: the decomposition of drift and the accumulation of other vegetable matter soon furnished a suitable bed for the growth of a marine vegetation, and now a vast area, a level expanse of waste land and marsh, is seen extending a great distance into the Gulf, ramified here and there by the outlets of the river. Indeed, so rapid have been these formations, that upon the testimony of history, the Mississippi River to-day is twenty-nine miles farther in the Gulf than it was in 1754. Mr. Forshey, an engineer, remarks that 'the superficial area of the true Delta formation of the Mississippi, or below Baton Rouge, where the last bluffs are found, is about fifteen thousand square miles, constituting a region of mean width seventy-five miles, and mean length two hundred miles. Probable depth of alluvion is about one fifth of a mile, by inference from the depth of the Gulf of Mexico.' In the vicinity of New Orleans, boring to a depth of two hundred feet, fossils, such as shells, bones, etc., have been found. And at thirty feet specimens of pottery and other evidences of Indian habitation have been discovered. The foundation upon which rest the alluvial formations has been found to consist of a hard blue silicious clay, closely resembling that met with in the bed of the Mississippi. The most recent of the alluvial fields of the Delta have been constituted a parish, termed Plaquemine. In 1800, according to one authority, there were but very few acres in cultivation in the entire parish. Since leveeing above, the deposit has been extremely rapid, until now we find some excellent plantations in Plaquemine. Fifty miles below New Orleans the tillable land is nearly a mile in width; below there, it becomes gradually less, until it is lost in the Gulf. Still the accumulations are going on, and it is impossible even to surmise what changes the great river may yet effect in the future geography of this section of the American continent.