of Van Buren County, and subcarboniferous strata resume and keep their place along the valley to the north of the river. From Fort Dodge to the northern part of Lee County, the strata of the lower coal measures are present in the valley. Its flood plain is frequently sandy, from the debris of the sandstone and sandy shales of the coal measures produced by their removal in the process of the formation of the valley.

The principal tributaries of the Des Moines are upon the western side. These are the Raccoon and the three rivers, viz.: South, Middle and North Rivers. The three latter have their source in the region occupied by the upper coal-measure limestone formation, flow eastward over the middle coal measures, and enter the valley of the Des Moines upon the lower coal measures. These streams, especially South and Middle Rivers, are frequently bordered by high, rocky cliffs. Raccoon River has its source upon the heavy surface deposits of the middle region of Western Iowa, and along the greater part of its course it has excavated its valley out those deposits and the middle coal measures alone. The valley of the Des Moines and its branches are destined to become the seat of extensive manufactures in consequence of the numerous mill sites of immense power, and the fact that the main valley traverses the entire length of the Iowa coal fields.

Skunk River.-This river has its source in Hamilton County, and runs almost its entire course upon the border of the outcrop of the lower coal measures, or, more properly speaking, upon the subcarboniferous limestone, just where it begins to pass beneath the coal measures by its southerly and westerly dip. Its general course is southeast. From the western part of Henry County, up as far as Story County, the broad, flat flood plain is covered with a rich deep clay soil, which, in time of long-continued rains and overflows of the river, has made the valley of Skunk River a terror to travelers from the earliest settlement of the country. There are some excellent mill sites on the lower half of this river, but they are not so numerous or valuable as on other rivers of the eastern system.

Iowa River. This river rises in Hancock County, in the midst of a broad, slightly undulating drift region. The first rock exposure is that of subcarboniferous limestone, in the southwestern corner of Franklin County. It enters the region of the Devonian strata near the southwestern corner of Benton County, and in this it continues to its confluence with the Cedar in Louisa County. Below the junction with the Cedar, and for some miles above that point, its valley is broad, and especially on the northern side, with a well marked flood plain. Its borders gradually blend with the uplands as they slope away in the distance from the river. The Iowa furnishes numerous and valuable mill sites.

Cedar River. This stream is usually understood to be a branch of the Iowa, but it ought, really, to be regarded as the main stream. It rises by numerous branches in the northern part of the State, and flows the entire length

of the State, through the region occupied by the Devonian strata and along the trend occupied by that formation.

The valley of this river, in the upper part of its course, is narrow, and the sides slope so gently as to scarcely show where the lowlands end and the uplands begin. Below the confluence with the Shell Rock, the flood plain is more distinctly marked and the valley broad and shallow. The valley of the Cedar is one of the finest regions in the State, and both the main stream and its branches afford abundant and reliable mill sites.

Wapsipinnicon River.-This river has its source near the source of the Cedar, and runs parallel and near it almost its entire course, the upper half upon the same formation-the Devonian. In the northeastern part of Linn County, it enters the region of the Niagara limestone, upon which it continues to the Mississippi. It is one hundred miles long, and yet the area of its drainage is only from twelve to twenty miles in width. Hence, its numerous mill sites are unusually secure.

Turkey River.--This river and the Upper Iowa are, in many respects, unlike other Iowa rivers. The difference is due to the great depth they have eroded their valleys and the different character of the material through which they have eroded. Turkey River rises in Howard County, and in Winnesheik County, a few miles from its source, its valley has attained a depth of more than two hundred feet, and in Fayette and Clayton Counties its depth is increased to three and four hundred feet. The summit of the uplands, bordering nearly the whole length of the valley, is capped by the Maquoketa shales. These shales are underlaid by the Galena limestone, between two and three hundred feet thick. The valley has been eroded through these, and runs upon the Trenton limestone. Thus, all the formations along and within this valley are Lower Silurian. The valley is usually narrow, and without a well-marked flood plain. Water power is abundant, but in most places inaccessible.

Upper Iowa River.—This river rises in Minnesota, just beyond the northern boundary line, and enters our State in Howard County before it has attained any considerable size. Its course is nearly eastward until it reaches the Mississippi. It rises in the region of the Devonian rocks, and flows across the outcrops, respectively, of the Niagara, Galena and Trenton limestone, the lower magnesian limestone and Potsdam sandstone, into and through all of which, except the last, it has cut its valley, which is the deepest of any in Iowa. The valley sides are, almost everywhere, high and steep, and cliffs of lower magnesian and Trenton limestone give them a wild and rugged aspect. In the lower part of the valley, the flood plain reaches a width sufficient for the location of small farms, but usually it is too narrow for such purposes. On the higher surface, however, as soon as you leave the valley you come immediately upon a cultivated country. This stream has the greatest slope per mile of any in Iowa, consequently it furnishes immense water power. In some places, where creeks come into it, the valley widens and affords good locations for farms. The town

of Decorah, in Winnesheik County, is located in one of these spots, which makes it a lovely location; and the power of the river and the small spring streams around it offer fine facilities for manufacturing. This river and its tributaries are the only trout streams in Iowa.

Mississippi River.-This river may be described, in general terms, as a broad canal cut out of the general level of the country through which the river flows. It is bordered by abrupt hills or bluffs. The bottom of the valley ranges from one to eight miles in width. The whole space between the bluffs is occupied by the river and its bottom, or flood plain only, if we except the occasional terraces or remains of ancient flood plains, which are not now reached by the highest floods of the river. The river itself is from half a mile to nearly a mile in width. There are but four points along the whole length of the State where the bluffs approach the stream on both sides. The Lower Silurian formations compose the bluffs in the northern part of the State, but they gradually disappear by a southerly dip, and the bluffs are continued successively by the Upper Silurian, Devonian, and subcarboniferous rocks, which are reached near the southeastern corner of the State.

Considered in their relation to the present general surface of the state, the relative ages of the river valley of Iowa date back only to the close of the glacial epoch; but that the Mississippi, and all the rivers of Northeastern Iowa, if no others, had at least a large part of the rocky portions of their valleys eroded by pre-glacial, or perhaps even by paleozoic rivers, can scarcely be doubted.

LAKES.

The lakes of Iowa may be properly divided into two distinct classes. The first may be called drift lakes, having had their origin in the depressions left in the surface of the drift at the close of the glacial epoch, and have rested upon the undisturbed surface of the drift deposit ever since the glaciers disappeared. The others may be properly termed fluvatile or alluvial lakes, because they have had their origin by the action of rivers while cutting their own valleys out from the surface of the drift as it existed at the close of the glacial epoch, and are now found resting upon the alluvium, as the others rest upon the drift. By the term alluvium is meant the deposit which has accumulated in the valleys of rivers by the action of their own currents. It is largely composed of sand and other coarse material, and upon that deposit are some of the best and most productive soils in the State. It is this deposit which form the flood plains and deltas of our rivers, as well as the terraces of their valleys.

The regions to which the drift lakes are principally confined are near the head waters of the principal streams of the State. We consequently find them in those regions which lie between the Cedar and Des Moines Rivers, and the Des Moines and Little Sioux. No drift lakes are found in Southern Iowa. The largest of the lakes to be found in the State are Spirit and Okoboji, in

Dickinson County; Clear Lake, in Cerro Gordo County; and Storm Lake, in Bunea Vista County.

Spirit Lake.-The width and length of this lake are about equal, and it contains about twelve square miles of surface, its northern border resting directly on the boundary of the State. It lies almost directly upon the great watershed. Its shores are mostly gravelly, and the country about it fertile.

Okoboji Lake. This body of water lies directly south of Spirit Lake, and has somewhat the shape of a horse-shoe, with its eastern projection within a few rods of Spirit Lake, where it receives the outlet of the latter. Okoboji Lake extends about five miles southward from Spirit Lake, thence about the same distance westward, and then bends northward about as far as the eastern projection. The eastern portion is narrow, but the western is larger, and in some places a hundred feet deep. The surroundings of this and Spirit Lake are very pleasant. Fish are abundant in them, and they are the resort of myriads of water fowl.

Clear Lake. This lake is situated in Cerro Gordo County, upon the watershed between the Iowa and Cedar Rivers. It is about five miles long, and two or three miles wide, and has a maximum depth of only fifteen feet. Its shores and the country around it are like that of Spirit Lake.

Storm Lake. This body of water rests upon the great water shed in Buena Vista County. It is a clear, beautiful sheet of water, containing a surface area of between four and five square miles.

The outlets of all these drift-lakes are dry during a portion of the year, except Okoboji.

Walled Lakes.-Along the water sheds of Northern Iowa great numbers of small lakes exist, varying from half a mile to a mile in diameter. One of the lakes in Wright County, and another in Sac, have each received the name of "Walled Lake," on account of the existence of embankments on their borders, which are supposed to be the work of ancient inhabitants. These embankments are from two to ten feet in height, and from five to thirty feet across. They are the result of natural causes alone, being referable to the periodic action of ice, aided, to some extent, by the force of the waves. These lakes are very shallow, and in winter freeze to the bottom, so that but little unfrozen water remains in the middle. The ice freezes fast to everything upon the bottom, and the expansive power of the water in freezing acts in all directions from the center to the circumference, and whatever was on the bottom of the lake has been thus carried to the shore, and this has been going on from year to year, from century to century, forming the embankments which have caused so much wonder.

SPRINGS.

Springs issue from all formations, and from the sides of almost every valley, but they are more numerous, and assume proportions which give rise to the name of sink-holes, along the upland borders of the Upper Iowa River, owing

to the peculiar fissured and laminated character and great thickness of the strata of the age of the Trenton limestone which underlies the whole region of the valley of that stream.

No mineral springs, properly so called, have yet been discovered in Iowa, though the water of several artesian wells is frequently found charged with soluble mineral substances.

ORIGIN OF THE PRAIRIES.

It is estimated that seven-eighths of the surface of the State was prairie when first settled. They are not confined to level surfaces, nor to any particular variety of soil, for within the State they rest upon all formations, from those of the Azoic to those of the Cretaceous age, inclusive. Whatever may have been their origin, their present existence in Iowa is not due to the influence of climate, nor the soil, nor any of the underlying formations. The real cause is the prevalence of the annual fires. If these had been prevented fifty years ago, Iowa would now be a timbered country. The encroachment of forest trees upon prairie farms as soon as the bordering woodland is protected from the annual prairie fires, is well known to farmers throughout the State.

The soil of Iowa is justly famous for its fertility, and there is probably no equal area of the earth's surface that contains so little untillable land, or whose soil has so high an average of fertility. Ninety-five per cent. of its surface is tillable land.

GEOLOGY.

The soil of Iowa may be separated into three general divisions, which not only possess different physical characters, but also differ in the mode of their origin. These are drift, bluff and alluvial, and belong respectively to the deposits bearing the same names. The drift occupies a much larger part of the surface of the State than both the others. The bluff has the next greatest area of surface, and the alluvial least.

All soil is disintegrated rock. The drift deposit of Iowa was derived, to a considerable extent, from the rocks of Minnesota; but the greater part of Iowa drift was derived from its own rocks, much of which has been transported but a short distance. In general terms the constant component element of the drift soil is that portion which was transported from the north, while the inconstant elements are those portions which were derived from the adjacent or underlying strata. For example, in Western Iowa, wherever that cretaceous formation known as the Nishnabotany sandstone exists, the soil contains more sand than elsewhere. The same may be said of the soil of some parts of the State occupied by the lower coal measures, the sandstones and sandy shales of that formation furnishing the sand.

In Northern and Northwestern Iowa, the drift contains more sand and gravel than elsewhere. This sand and gravel was, doubtless, derived from the