THE STATE OF IOWA.

GEOGRAPHICAL SITUATION.

The State of Iowa has an outline figure nearly approaching that of a rectangular parallelogram, the northern and southern boundaries being nearly due east and west lines, and its eastern and western boundaries determined by southerly flowing rivers-the Mississippi on the east, and the Missouri, together with its tributary, the Big Sioux, on the west. The northern boundary is upon the parallel of forty-three degrees thirty minutes, and the southern is approximately upon that of forty degrees and thirty-six minutes. The distance from the northern to the southern boundary, excluding the small prominent angle at the southeast corner, is a little more than two hundred miles. Owing to the irregularity of the river boundaries, however, the number of square miles does not reach that of the multiple of these numbers; but according to a report of the Secretary of the Treasury to the United States Senate, March 12, 1863, the State of Iowa contains 35,228,200 acres, or 55,044 square miles. When it is understood that all this vast extent of surface, except that which is occupied by our rivers, lakes and peat beds of the northern counties, is susceptible of the highest cultivation, some idea may be formed of the immense agricultural resources of the State. Iowa is nearly as large as England, and twice as large as Scotland; but when we consider the relative area of surface which may be made to yield to the wants of man, those countries of the Old World will bear no comparison with Iowa.

TOPOGRAPHY.

No complete topographical survey of the State of Iowa has yet been made. Therefore all the knowledge we have yet upon the subject has been obtained from incidental observations of geological corps, from barometrical observations by authority of the General Government, and levelings done by railroad engineer corps within the State.

Taking into view the facts that the highest point in the State is but a little more than twelve hundred feet above the lowest point, that these two points are nearly three hundred miles apart, and that the whole State is traversed by

gently flowing rivers, it will be seen that in reality the State of Iowa rests wholly within, and comprises a part of, a vast plain, with no mountain or hill ranges within its borders.

A clearer idea of the great uniformity of the surface of the State may be obtained from a statement of the general slopes in feet per mile, from point to point, in straight lines across it:

From the N. E. corner to the S. E. corner of the State.........1 foot 1 inch per mile.
From the N. E. corner to Spirit Lake......

From the N. W. corner to Spirit Lake..............

...5 feet 5 inches per mile.
..5 feet 0 inches per mile.

From the N. W. corner to the S. W. corner of the State......2 feet 0 inches per mile.
From the S. W. corner to the highest ridge between the two

..........

great rivers (in Ringgold County).............
..4 feet 1 inch per mile
From the dividing ridge in the S. E. corner of the State......5 feet 7 inches per mile.
From the highest point in the State (near Spirit Lake) to the

lowest point in the State (at the mouth of Des Moines
River)

........4 feet 0 inches per mile.

It will be seen, therefore, that there is a good degree of propriety in regarding the whole State as a part of a great plain, the lowest point of which within its borders, the southeast corner of the State, is only 444 feet above the level of the sea. The average height of the whole State above the level of the sea is not far from eight hundred feet, although it is more than a thousand miles inland from the nearest sea coast. These remarks are, of course, to be understood as applying to the surface of the State as a whole. When we come to consider its surface feature in detail, we find a great diversity of surface by the formation of valleys out of the general level, which have been evolved by the action of streams during the unnumbered years of the terrace epoch.

It is in the northeastern part of the State that the river valleys are deepest; consequently the country there has the greatest diversity of surface, and its physical features are most strongly marked.

DRAINAGE SYSTEM.

The Mississippi and Missouri Rivers form the eastern and western boundaries of the State, and receive the eastern and western drainage of it.

The eastern drainage system comprises not far from two-thirds of the entire surface of the State. The great watershed which divides these two systems is formed by the highest land between those rivers along the whole length of a line running southward from a point on the northern boundary line of the State near Spirit Lake, in Dickinson County, to a nearly central point in the northern part of Adair County.

From the last named point, this highest ridge of land, between the two great rivers, continues southward, without change of character, through Ringgold County into the State of Missouri; but southward from that point, in Adair County, it is no longer the great watershed. From that point, another and lower ridge bears off more nearly southeastward, through the counties of Madison, Clarke, Lucas and Appanoose, and becomes itself the great watershed.

RIVERS.

All streams that rise in Iowa rise upon the incoherent surface deposits, occupying at first only slight depressions in the surface, and scarcely perceptible. These successively coalesce to form the streams.

The drift and bluff deposits are both so thick in Iowa that its streams not only rise upon their surface, but they also reach considerable depth into these deposits alone, in some cases to a depth of nearly two hundred feet from the general prairie level.

The majority of streams that constitute the western system of Iowa drainage run, either along the whole or a part of their course, upon that peculir deposit known as bluff deposit. Their banks are often, even of the small streams, from five to ten feet in height, quite perpendicular, so that they make the streams almost everywhere unfordable, and a great impediment to travel across the open country where there are no bridges.

The material of this deposit is of a slightly yellowish ash color, except where darkened by decaying vegetation, very fine and silicious, but not sandy, not very cohesive, and not at all plastic. It forms excellent soil, and does not bake or crack in drying, except limy concretions, which are generally distributed throughout the mass, in shape and size resembling pebbles; not a stone or pebble can be found in the whole deposit. It was called "silicious marl" by Dr. Owen, in his geological report to the General Government, and its origin referred to an accumulation of sediment in an ancient lake, which was afterward drained, when its sediment became dry land. Prof. Swallaw gives it the name of "bluff," which is here adopted; the term Lacustral would have been better. The peculiar properties of this deposit are that it will stand securely with a precipitous front two hundred feet high, and yet is easily excavated with a spade. Wells dug in it require only to be walled to a point just above the water line. Yet, compact as it is, it is very porous, so that water which falls on its surface does not remain, but percolates through it; neither does it accumulate within its mass, as it does upon the surface of and within the drift and the stratified formations.

The bluff deposit is known to occupy a region through which the Missouri runs almost centrally, and measures, as far as is known, more than two hundred miles in length and nearly one hundred miles in width. The thickest part yet known in Iowa is in Fremont County, where it reaches two hundred feet. The boundaries of this deposit in Iowa are nearly as follows: Commencing at the southeast corner of Fremont County, follow up the watershed between the East Nishnabotany and the West Tarkio Rivers to the southern boundary of Cass County; thence to the center of Audubon County; thence to Tip Top Station, on the Chicago & Northwestern Railway; thence by a broad curve westward to the northwest corner of Plymouth County.

This deposit is composed of fine sedimentary particles, similar to that which the Missouri River now deposits from its waters, and is the same which

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that river did deposit in a broad depression in the surface of the drift that formed a lake-like expansion of that river in the earliest period of the history of its valley. That lake, as shown by its deposit, which now remains, was about one hundred miles wide and more than twice as long. The water of the river was muddy then, as now, and the broad lake became filled with the sediment which the river brought down, before its valley had enough in the lower portion of its course to drain it. After the lake became filled with the sediment, the valley below became deepened by the constant erosive action of the waters, to a depth of more than sufficient to have drained the lake of its first waters; but the only effect then was to cause it to cut its valley out of the deposits its own muddy waters had formed. Thus along the valley of that river, so far as it forms the western boundary of Iowa, the bluffs which border it are composed of that sediment known as bluff deposit, forming a distinct border along the broad, level flood plain, the width of which varies from five to fifteen miles, while the original sedimentary deposit stretches far inland.

All the rivers of the western system of drainage, except the Missouri itself, are quite incomplete as rivers, in consequence of their being really only branches of other larger tributaries of that great river, or, if they empty into the Missouri direct, they have yet all the usual characteristics of Iowa rivers, from their sources to their mouths.

Chariton and Grand Rivers both rise and run for the first twenty-five miles of their courses upon the drift deposit alone. The first strata that are exposed by the deepening valleys of both these streams belong to the upper coal measures, and they both continue upon the same formation until they make their exit from the State (the former in Appanoose County, the latter in Ringgold County), near the boundary of which they have passed nearly or quite through the whole of that formation to the middle coal measures. Their valleys gradually deepen from their upper portions downward, so that within fifteen or twenty miles they have reached a depth of near a hundred and fifty feet below the general level of the adjacent high land. When the rivers have cut their valleys down through the series of limestone strata, they reach those of a clayey composition. Upon these they widen their valleys and make broad flood plains (commonly termed "bottoms "), the soil of which is stiff and clayey, except where modified by sandy washings.

A considerable breadth of woodland occupies the bottoms and valley sides along a great part of their length; but their upper branches and tributaries are mostly prairie streams.

Platte River. This river belongs mainly to Missouri. Its upper branches pass through Ringgold County, and, with the west fork of the Grand River, drain a large region of country.

Here the drift deposit reaches its maximum thickness on an east and west line across the State, and the valleys are eroded in some instances to a depth of two hundred feet, apparently, through this deposit alone.