Section of Mississippi River Bluffs at Warsaw Illinois A is a very fine yellow sand and clay widely developed. B is a bluish clay and fine sand C is roundled hard bowiders from small gravel up to 400 lbs., mixed with sand D is composed of angular blocks from over a ton weight clown to small stones, mingled without order; with coarse and fine sand and clay, showing no selection or sorting. The rocks are trap, porphyry, granite gneiss or syenite, hard brecciated limestone &c. The upper carboniferous shales in vicinity exhibit local displacements

THE

AMERICAN

JOURNAL OF SCIENCE AND ARTS.

[THIRD SERIES.]

ART. L.-Valley of the Minnesota River and of the Mississippi River to the junction of the Ohio: its origin considered; by Gen. G. K. WARREN, Major of Engineers. With Diagrams A, B, C, C', D, E, F and G (making plates 11 to 18 of the volume).

Definition of the term "valley," prominent natural features and length. The valley to be considered is the part included between the high banks, commonly called bluffs. Whenever it becomes necessary in this article to refer to the whole area drained by the river, the word basin will be used to designate it.

Between these high banks the greater portion is subject to overflow at time of floods, forming what is sometimes called the flood plain; the smaller part above overflow is generally composed of alluvial terraces of sand and gravel. In some cases the distinction between the terraces and the bluffs is difficult to make.

The Mississippi River in its usually navigated parts touches only here and there at places exempt from flood-waters, and these are natural landings for steamboats and sites for towns. In course of time the convenience of the people living there makes them desirable locations for bridges. It is very rare, however, that both banks of the river are above submergence; where one bank is, the opposite one is generally low, and covered many feet deep at extreme high-water, making it difficult to construct bridges sufficiently elevated for steamboats to pass under them.

The distance along the general course of this valley from St. Louis to St. Paul is about 620 miles, but steamboatmen, by the course they take along the navigable channels, make the distance AM. JOUR. SCI.-THIRD SERIES, VOL. XVI, No. 96.-DEC., 1878.