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

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.

The term "drift deposit" applies to the soil and sub-soil of the greater part of the State, and in it alone many of our wells are dug and our forests take It rests upon the stratified rocks. It is composed of clay, sand, gravel aud boulders, promiscuously intermixed, without stratification, varying in character in different parts of the State.

root.

The proportion of lime in the drift of Iowa is so great that the water of all our wells and springs is too "hard" for washing purposes; and the same substance is so prevalent in the drift clays that they are always found to have sufficient flux when used for the manufacture of brick.

One Hundred and Two River is represented in Taylor County, the valleys of which have the same general character of those just described. The country around and between the east and west forks of this stream is almost entirely prairie.

Nodaway River.-This stream is represented by east, middle and west branches. The two former rise in Adair County, the latter in Cass County. These rivers and valleys are fine examples of the small rivers and valleys of Southern Iowa. They have the general character of drift valleys, and with beautiful undulating and sloping sides. The Nodaways drain one of the finest agricultural regions in the State, the soil of which is tillable almost to their very banks. The banks and the adjacent narrow flood plains are almost everywhere composed of a rich, deep, dark loam.

Nishnabotany River. This river is represented by east and west branches, the former having its source in Anderson County, the latter in Shelby County. Both these branches, from their source to their confluence and also the main stream, from thence to the point where it enters the great flood plain of the Missouri-run through a region the surface of which is occupied by the bluff deposit. The West Nishnabotany is probably without any valuable mill sites. In the western part of Cass County, the East Nishnabotany loses its identity by becoming abruptly divided up into five or six different creeks. A few good mill sites occur here on this stream. None, however, that are thought reliable exist on either of these rivers, or on the main stream below the confluence, except, perhaps, one or two in Montgomery County. The valleys of the two branches, and the intervening upland, possess remarkable fertility.

Boyer River.-Until it enters the flood plain of the Missouri, the Boyer runs almost, if not quite, its entire course through the region occupied by the bluff deposit, and has cut its valley entirely through it along most of its passage. The only rocks exposed are the upper coal measures, near Reed's mill, in Harrison County. The exposures are slight, and are the most northerly now known in Iowa. The valley of this river has usually gently sloping sides, and an ndistinctly defined flood plain. Along the lower half of its course the adjacent upland presents a surface of the billowy character, peculiar to the bluff deposit. The source of this river is in Sac County.

Soldier River.-The east and middle branches of this stream have their source in Crawford County, and the west branch in Ida County. The whole course of this river is through the bluff deposit. It has no exposure of strata along its course.

Little Sioux River.-Under this head are included both the main and west branches of that stream, together with the Maple, which is one of its branches. The west branch and the Maple are so similar to the Soldier River that they need no separate description. The main stream has its boundary near the northern boundary of the State, and runs most of its course upon drift deposit alone, entering the region of the bluff deposit in the southern part of Cherokee County. The two principal upper branches, near their source in Dickinson and Osceola Counties, are small prairie creeks, with indistinct valleys. On entering Clay County, the valley deepens, and at their confluence has a depth of one hundred feet, which still further increases until along the boundary line between Clay and Buena Vista Counties, it reaches a depth of two hundred feet. Just as the valley enters Cherokee County, it turns to the southward and becomes much widened, with its sides gently sloping to the uplands. When the valley enters the region of the bluff deposit, it assumes the billowy appearance. No exposures of strata of any kind have been found in the valley of the Little Sioux or any of its branches.

Floyd River. This river rises upon the drift in O'Brien County, and flowing southward enters the region of the bluff deposit a little north of the center of Plymouth County. Almost from its source to its mouth it is a prairie stream, with slightly sloping valley sides, which blend gradually with the uplands. A single slight exposure of sandstone of cretaceous age occurs in the valley near Sioux City, and which is the only known exposure of rock of any kind along its whole length. Near this exposure is a mill site, but farther up the stream it is not valuable for such purposes.

Rock River. This stream passes through Lyon and Sioux Counties. It was evidently so named from the fact that considerable exposures of the red Sioux quartzite occur along the main branches of the stream in Minnesota, a few miles north of our State boundary. Within this State the main stream and its branches are drift streams, and strata are exposed. The beds and banks of the streams are usually sandy and gravelly, with occasional boulders intermixed.

Big Sioux River.-The valley of this river, from the northwest corner of the State to its mouth, possesses much the same character as all the streams of the surface deposits. At Sioux Falls, a few miles above the northwest corner of the State, the stream meets with remarkable obstructions from the presence of Sioux quartzite, which outcrops directly across the stream, and causes a fall of about sixty feet within a distance of half a mile, producing a series of cascades. For the first twenty-five miles above its mouth, the valley is very broad, with a broad, flat flood plain, with gentle slopes occasionally showing indistinctly defined terraces. These terraces and valley bottoms constitute some of the finest

agricultural land of the region. On the Iowa side of the valley the upland presents abrupt bluffs, steep as the materials of which they are composed will stand, and from one hundred to nearly two hundred feet high above the stream. At rare intervals, about fifteen miles from its mouth, the cretaceous strata are found exposed in the face of the bluffs of the Iowa side. No other strata are exposed along that part of the valley which borders our State, with the single exception of Sioux quartzite at its extreme northwestern corner. Some good mill sites may be secured along that portion of this river which borders Lyon County, but below this the fall will probably be found insufficient and the location for dams insecure.

Missouri River.-This is one of the muddiest streams on the globe, and its waters are known to be very turbid far toward its source. The chief peculiarity of this river is its broad flood plains, and its adjacent bluff deposits. Much the greater part of the flood plain of this river is upon the Iowa side, and continuous from the south boundary line of the State to Sioux City, a distance of more than one hundred miles in length, varying from three to five miles in width. This alluvial plain is estimated to contain more than half a million acres of land within the State, upward of four hundred thousand of which are now tillable.

The rivers of the eastern system of drainage have quite a different character from those of the western system. They are larger, longer and have their valleys modified to a much greater extent by the underlying strata. For the latter reason, water-power is much more abundant upon them than upon the streams of the western system.

Des Moines River.-This river has its source in Minnesota, but it enters Iowa before it has attained any size, and flows almost centrally through it from northwest to southeast, emptying into the Mississippi at the extreme southeastern corner of the State. It drains a greater area than any river within the State. The upper portion of it is divided into two branches known as the east and west forks. These unite in Humboldt County. The valleys of these branches above their confluence are drift-valleys, except a few small exposures of subcarboniferous limestone about five miles above their confluence. These exposures produce several small mill-sites. The valleys vary from a few hundred yards to half a mile in width, and are the finest agricultural lands. In the northern part of Webster County, the character of the main valley is modified by the presence of ledges and low cliffs of the subcarboniferous limestone and gypsum. From a point a little below Fort Dodge to near Amsterdam, in Marion County, the river runs all the way through and upon the lower coal-meas. ure strata. Along this part of its course the flood-plain varies from an eighth to half a mile or more in width. From Amsterdam to Ottumwa the subcarboniferous limestone appears at intervals in the valley sides. Near Ottumwa, the subcarboniferous rocks pass beneath the river again, bringing down the coal-measure strata into its bed; but they rise again from it in the extreme northwestern part