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WOODBURY COUNTY

evidence of the geological horizon to which the region belongs, and it has been supplemented by the borings at Le Mars and Sioux City, and excavations in various other places, until the general character of the underlying strata may be regarded as sufficiently settled. Of several borings upon Morton's farm, near Le Mars, all of which substantially agree in their showing, it is though best to set down here the record of No. 3 upon the bluffs and No. 4 upon the Floyd bottom—placing them side by side for covenient comparison:

Boring No. 1 on Morton's and the boring on Woodward's land, nearly three miles southeast, show substantially the same results, alike in passing through the thin beds of impure lignite, and terminating in a very hard sandstone; and the same showing, so far as it goes, is made by a boring in the broken Kettle valley, some six or eight miles above its entrance to the Big Sioux valley.

The Artesian well bored at Sioux City to the depth of 2,011 feet, can not with exactness be compared with the Le Mars borings, by reason of the indefinite nomenclature used by the workmen, but, so far as can be seen, it confirms their showing, and extends our knowledge to a much greater depth. The record is subjoined:

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HISTORY OF WOODBURY AND PLYMOUTH COUNTIES

These borings, in connection with the rock exposures above referred to, seem to establish sufficiently well that this region belongs to the cretaceous horizon, and the succession from above downward is through the loess, then the drift, then the Niobrara group, then the Fort Benton group, then the Dakota group of the cretaceous rocks; and nothing below this group can be positively affirmed, although the record of the borings seems to show quite clearly that the cretaceous rocks lie directly upon the sub-carboniferous, and that the whole series of strata between the cretaceous and the sub-carboniferous, if it ever existed, was utterly removed before the cretaceous era.

Evidently the oolitic beds in the Morton borings which appear only seventy feet below the cretceous lignite, must be identified with the oolites of the upper Des Moines valley which are referred by Dr. White to the Kinderhook beds, and which lie far below the carboniferous horizon. Just where the bottom of the cretceous system is to be fixed in these borings it is difficult to say with precision, but possibly it may be tht the sandstone No. 12 in the Morton boring No. 3 is the lowest member of the Dakota group, and the gray limestone No. 7 of the Sioux City boringmay represent the oolitic beds. As to all the strata below, sufficient data have not been collected to determine their exact position. Possibly the hard sandstone No. 18 of the Morton borings may represent the Sioux Falls quartzite,

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WOODBURY COUNTY.

and it may be considered quite certain that the hard rock, No. 15, that is met in the Sioux City artesian well at the depth of 1,315 feet. is the quartzite, and below that point to the bottom the rock is quartzite or granitic. One thing may be considered sure, there are no coal: rocks exposed on the surface nor passed through in the borings, and therefore there can be no coal within these counties, unless there be some insignificant pocket outside the ground as yet examined, and there is very small probability that such is the case. It is to be hoped that no more money will be wasted in fruitless search for coal or any metallic ores. They do not exist in the cretaceous rocks or this region. In the rich alluvial soils of the bottom lands, and in the loess and drift of the uplands are mines which, worked with plow' and reaper, produce wealth with certainty and unparalleled abundance, and our people are richer by far than the possessors of mines or metal, even if they be of gold and silver.

Probably one third of the area now under consideration is alluvial, and the present surface has been formed by the direct action of the intersecting stream wearing down its channel and widening and depositing sediment along the widened valley.

The process is going on under our own eyes and needs no further consideration, nor need much be said of the character or value of the soil so produced. It is the latest product of elemental action, and its; value is well understood to depend largely on the fineness of its particles, and on the intermixture of matters that, having once passed through the processes of growth and life, are thereby better adapted to nourish and stimulate new growths. This is the deposit that always constitutes the flood plains and deltas of rivers and some of the terraces of their valleys. It is largely composed of sand and in places is of coarse material, but for the most part in this region it is very fine and silt like.

The loess or bluff formation is older than the true alluvium, and or finer material. Its origin is much the same, indeed, in this region it may be counted exactly the same; though the silt was deposited when the Missouri spread out into a wide lake after the manner of Lake Pepin on the Mississippi, only vastly larger; and so, the water being quiet, and only the finest materials held in suspension in the lake, the loess is much finer and evener in its composition. This formation spread originally over a large extent in Iowa and Nebraska, and indeed fol-

30

HISTORY OF WOODBURY AND PLYMOUTH COUNTIES.

lowed the river down as far as Missouri. Out of it the entire bed of the Missouri and of the tributaries within its limits has been excavated, so that only small tracts of the original area remain. Very little, if any, ever existed in Plymouth county, the northeastern shore of the old lake just cutting across the southwest corner of the county.

In Woodbury it extended more widely, the line of shore being drawn irregularly from the Big Sioux river southeasterly, including the bluffs that border the Missouri bottom, and extending some distance up the larger streams, reaching a point a little above Oto, on the [the] Little Sioux, and Danbury, on the Maple. The exact boundary bas never been followed. Most of this area has been denuded by the larger streams, and the material has been used to widen and deepen the great alluvial plain, but it may be seen that the beautiful and peculiar bluffs that form so picturesque a feature of the landscape, owe their strangely beautiful rounded summits, and sharp cut ridges, smooth and abruptly retreating slopes, and entire absence of rocky ledges except at their bases, to the bluff deposit which mainly makes up their mass. This deposit, in places, reaches a depth of more than 100 feet, and near Sioux City sometimes exceeds 150 feet. Its material can not be chemically distinguished from the sediment now held in suspension by the river, and as a soil it is, of course, fully equal to the alluvium, and indeed in some respects is much superior, from its superior fineness and less compactness, as it was laid down very slowly, and has never suffered pressure. It has in consequence much of a sponge-like nature, and never suffers from drouth or from excessive rains, absorbing the rain as it falls throughout its whole depth equally, and continuing to furnish moisture to the surface as long as any remains in its mass. One singular and distinguishing property of this peculiar deposit is that it stands securely with precipitous front. The Missouri bluffs have no rocky support, and yet are so steep that it is difficult for a man to climb their declivity, and in artificial excavations a front perpendicular, or nearly so, stands securely. For all practical purposes of building, the ground it composes is as secure as any other, yet it is everywhere easily excavated with the spade-alone.

It remains unchanged by atmosphere and frost, so that wells dug to great depth--100 feet or more—need no walls except to a point above the standing water, and lime kilns and potter's kilns, and even

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WOODBURY COUNTY.

stables and caves for the occupancy of man, have been successfully carved out and used without danger for years, though their sides had no support save the natural tenacity of the soil. Its composition is

and this property of remaining unchanged, when exposed to the weather, is doubtless due to a slight cementation of the particles of silica by carbonated water percolating through the mass. The cementation, however, is never sufficient to interfere with its porosity, as is shown by the fact that nowhere within it does the water ever establish currents, ,but any surplus it cannot hold always drains from the bottom, and wells dug in it yield no water until they pass its bed into the strata below.

For agriculture this is probably as valuable as any soil in the world, and is practicably inexhaustible. Corn will grow luxuriantly in soil taken from any part of its depth, even 100 feet or more below the surface. As to the real geological age of the bluff deposit there can be no doubt. It must be more recent than the drift, because it rests upon it and is not later than the beginning of the terrace epoch, because river terraces are here and there formed in it. Few fossils are found in it, and these are all recent, such as fresh-water shells and land mollusks; no true branchiate shells except unios, the rest being pulmonate gasteropods. It contains no marine remains, and is therefore not of marine origin, but is a true deposit of the Missouri; and, if it were possible to dam the river, somewhere below, to a depth of 200 or 300 feet, in the course of ages the resultant lake would be filled with precisely the same material as that of the bluffs, and if, afterward, the lower end of the basin were to sink gradually, thus draining off the waters of the lake, the great river and its side tributaries would inevitably renew all the features and conditions which we now behold. Cotemporary with the bluff deposit which we have been c0nsidering, are found in places, considerable beds of gravel and boulders, generally stratified more or less, and inclined toward the lake on whose margin they have been formed. They lie in nooks and coves of the old lake border, generally where the waves, driven by the western winds, beat most violently against the shores. They

32

HISTORY OF WOODBURY AND PLYMOUTH COUNTIES.

have been formed by the wash against the drift, the water carrying the lighter material back into the depths, while the coarser gravel and bowlders [boulders] have accumulated in very considerable, imperfectly stratified masses.

In some places, the joint action of wind, ice and water piled up the larger stones until they formed walls along the margin. Very considerable deposits of this gravel and bowlders [boulders] and sand may be seen along the Big Sioux valley, and sometimes so placed as to be confounded with the genuine drift from which they were formed.

More than one-half of the exposed area of Woodbury county, and nearly all (except the alluvium) of Plymouth county, is buried deep beneath the drift. In a few places the streams have, near their mouths, cut through to the underlying cretaceous rocks, but these areas of exposure are insignificant, and it may be generally said the whole territory is good soil, susceptible of easy and profitable cultivation.

It has been said that the bluff formation was laid down in a fresh water expansion of the river. It is likely that during the deposit of the drift in this regin, [region] this lake-like expansion was a veritable inland sea, and during a portion at least of the period, so connected with the waters of the ocean then filling the valley of the Mississippi and the lower Missouri, as to be properly counted an oceanic gulf, through which icebergs of some magnitude could pass to the ocean below. It is quite certain that during the glacial period a large portion of northwestern Iowa, including at least Woodbury, Plymouth, Sioux and Lyon counties and portions of Osceola, Cherokee and Ida, was beneath water mos11y shallow, but deep enough in places, especially along the valleys of the Little Sioux, the Floyd and Big Sioux, to float icebergs of considerable magnitude. In the earlier portion of this period it seems likely that tracts of some magnitude lay above the surface, or near enough to be acted upon by the violent torrents that poured from the neighboring icefields during the torrid summers; for in a few places there are to be found at the very bottom of the drift, streams of sand and gravel more or less stratified, and much waterworn, [water worn?] precisely similar to recent formations along rapid streams. During the middle and later portions, it is probable that the water was deep enough to prevent abrasion of the bottom, and that there were no rapid currents.

It is quite certain that the great ice sheet that covered the northern

33

WOODBURY COUNTY.

regions to such an enormous depth, never reached the borders of Plymouth county, though some thin outliers may have existed here and there within its limits. No moraines have been observed, and it is believed that none exist. The front of the great glacier that moved down from the far north seems to have split upon the head of the Coteau de Prairie near the sources of the Big Sioux, and its eastern branch crossed into Iowa with the Ocheyedan river, and thence stretched southward through O'Brien and eastern Cherokee to the neighborhood of Des Moines, and thence turned east and northeastward, so that the country between the Little and the Big Sioux rivers has no subglacial or true till, such as may be seen so extensively spread out in the hills about Spirit Lake and along the upper course of the Ocheyedan. There is here a marked absence of the commingled clay, sand, gravel and bowlders [boulders] of diverse character—in places partially stratified, but for the most part firmly compacted into hard pan, tough and resistant, often poorly fitted to support vegetation, that form so prominent a feature in the morainic tracts along the borders of the ancient ice. The true till was subglacial in its origin that is formed beneath the ice, by the forward motion of the glacier over rocks and pre-existent soil, grinding subjacent material into paste, breaking up rocky ledges, and rolling angular fragments into smoothly rounded bowlders [boulders] and pebbles, and pushing forward and compressing the mass until it was laid down in irregular ridges and hills at the terminal edge of the glacier; or more likely morainic deposits having a considerable width were laid down mainly under the thinned edge of the ice sheet, rather than at the exact margin, or under its deeper portion. It is made up of materials collected in the glacial bed, ground up and moved forward by the glacial current, and the distance from which they have been brought is generally not great. A marked characteristic of a morainic region is the frequency of small lakes, ponds and shallow bogs. The clays of this formation, compressed by the tremendous forces of the moving ice, are impervious to water, and wherever the ridges were left so as to dam up older channels, permanent lakes were formed. No better illustration of the character of primary till and moraines in general can be found than is presented by the region around the head of the Little Sioux river, and indeed the entire plateau dividing the waters of the Little Sioux from those of the Des Moines river.

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HISTORY OF WOODBURY AND PLYMOUTH COUNTIES.

As has been said, this formation has not been observed in the limit here under consideration. The upper, or englacial, and superglacial tills are quite similar to the subglacial, but are distinguished by their looseness—by the larger size and the angularity of the rock fragments, by the more sandy and porous character of the earthy base, and by the higher oxidation of the iron compounds. This is regarded as material embraced within the glacial ice, or borne upon its surface, and by its melting, let loosely down on the true till beneath. Of course it lies above the true till, and is a large constituent of terminal moraines.

It is however, often found as a thin, irregular deposit, carried forward beyond the moraines by local and temporary ice sheets not to be reckoned as true glaciers; and some small tracts of this character may be found in the northern part of Plymouth county upon the higher grounds, so overlaid by the upper or berg till that their limits can not be determined.

Almost the entire area of Plymouth county, and the larger part of Woodbury, outside of the alluvial bottoms, is covered with the berg or floe till so called, very similar in character to the true tills, but formed under water through the agency of floating ice and sluggish currents and distinguishable from them: first, by a more homogeneous clayey base; second, by a more uniform distribution of imbedded erratics; third, by occasional traces of indistinct lamination; fourth, by its distribution, and fifth, by its stratigraphical relations. It is clear that finer materials settling down from suspension in water would distribute itself with greater uniformity than is possible to clay accumulated under a moving glacier, and stones falling from floating ice would be dispersed with a general regularity, unless there were currents or other circumstances that determined concentration along certain lines or in certain areas. The rocks stand on their edges, or even on their points, as though they fell from melting floats of ice, and were received on a soft mud bottom. Where there is laminae, the lower clayey leaves may sometimes be seen flexed beneath the stone, and the upper ones curve over it, as though it had depressed the former in its fall and the latter had been subsequently formed over it. These deposits were formed in the oceanic gulf before referred to, as preceding in time the river expansion of the bluff formation, along the margin of the melting glacier. These shallow, brackish waters, inter-

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WOODBURY COUNTY.

sected with deeper channels, were the receptacles of the issuing silt-laden glacial waters and of the icebergs that floated from the glacier front, and as different portions varied in area, depth and glacier frontage, so the relative amount of coarse and fine material varied. In places the proportion of bowlders [boulders] to clay is nearly that of the true till, and in such places the distinction between the two is doubtful. The surface aspect of these deposits assists in their correct identification. Where they occupy broad areas the surface contour is of a subdued, undulating outline-of a type readily distinguished from the surface of the true till.

In confined areas, as narrow lineal valleys, they form concave sheets, the sides of which lean against the slopes, and terminate at a definite height in shoulders on either side. These deposits are much more erodible than the till proper, and have been more sharply and symmetrically channeled where the slopes in post-glacial times have permitted it. It is this deposit that gives form and character to the landscape of most of northwestern Iowa west of the [the] divide, and it is through it that the multitudinous water courses have cut their channels. It is this deposit that, re-enforced by the decaying vegetation of unnumbered centuries, has given to Woodbury and Plymouth counties a soil practically in exhaustible, and certainly unexcelled by any other region.

It, and not the alluvial bottoms, has made the best com lands known. It has in a marked degree, the power of resisting draught and excessive rain as has been spoken of in connection with the loess. It was deposited in waters comparatively quiet, and has never peen subjected to pressure, so that it has that same peculiar sponge-like capacity. Its entire depth, ranging from fifty to one hundred and fifty or more feet, must be saturated with water before any excess can appear, and then that excess flows away at the base instead of standing on the surface to the injury of vegetation. Again, as long as any water remains in it, the moisture is available for use upon the surface. In this respect it has a vast advantage over the region of the true tills farther east, where the compact clays and frequent ridges of hardpan confine the water in shallow pools or ponds upon the surface or in depressions filled with soil, and where most of the rainfall, unable to soak deep in the ground, runs off at once in the rapid streams, and much of that left behind stagnates and sours, or

36

HISTORY OF WOODBURY AND PLYMOUTH COUNTIES.

evaporates speedily to the great detriment of life, both animal and vegetable.

It is worth mentioning here that this formation, besides its great value for agriculture, has also in places, beds of the very best brick or clay known. It is believed that this clay may be found in abundance along every valley, and it is already worked to a considerable extent at Sioux City on the Floyd, at Le Mars and in the Little Sioux valley. There is no limit to the supply, and if it were desirable, almost every farmer could have his brick kiln on his own premises. There are no fossils proper in this formation.

It is not likely that life, either vegetable or animal, existed or could exist at the time when it was laid down. However, there are found occasionally, remains, mostly fragmentary, of animals that existed in the preceding time, and which have been floated hither from the tertiary or cretaceous regions farther north and west, A tooth of the elephas primigenions was found in the sand beds at Sioux City, and a tooth and vertebra of a mastodon were picked up near Mills' farm on the Big Sioux in Plymouth county, and silicified wood is quite frequent. In many places among the coarser materials may be found the characteristic shells of the adjacent chalk, but these are all foreign to the proper formation.

Below this fruitful and beautiful surface lies the cretaceous series of strata exposed in narrow limits along the Big Sioux and Missouri bluffs. These exposures have been quite carefully examined by competent geologists as to their horizon, and there is no longer any doubt that the strata are the genuine representatives in this region of the English and European chalk.

They will here be treated of only in general terms as they have never been exhaustively explored, and, if the data were at hand, the space allotted to this paper is only sufficient for a very superficial view. But first it is proper to say a few words of what is below. The cretaceous strata lie nearly horizontal, with only a slight dip to the northwest, and disappear in that direction beneath the drift. In Lyon county the Sioux Falls quartzite belonging to the Laurentian rocks, as is believed, has a considerable dip southward and westward, and it disappears beneath the drift, No one has so far observed the connection between the chalk rocks and the quartzite, nor is there anywhere between, any indications of intervening strata. It is, therefore, pre-

A. M. Hubbard (click for large size)

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