GLACIAL PERIOD

That the surface of Iowa, and, in fact, the whole of North America north of the thirty-eighth parallel, is covered by a material known as drift, has become a popular opinion. Strewed all over the country, on the hills and in the valleys and on the level prairies, covering up the native rocks to a depth of from twenty to three hundred feet, is found this peculiar deposit. The well-diggers and the colliers, in their excavations, encounter it, and the quarryman has to strip it from the surface of this rock bed. It is not all alike; first there are a few feet of surface soil, created by recent vegetable deposits; then a variable depth of clay, or clay and sand intimately blended; then water-worn gravel and sand, and then blue clay, resting upon the country rock.

Scattered over the continent are frequently seen "lost rocks," or bowlders [boulders], of various sizes and of different varieties, some of granite, others of gneiss or trap, and occasionally some of limestone. These bowlders are also frequently found in excavating the earth.

The blue clay which lies upon the country rocks, or the original formation, is the oldest of the drift deposits. It consists of a heterogeneous mixture of dark blue clay, sand, gravel, pebbles and irregular-shaped stones and bowlders, of various kinds and sizes, unassorted and unstratified, and therefore could not have been deposited in water. Sometimes an occasional piece of stone-coal and fragments of wood are found in it. This blue clay is bowlder or glacier clay. From whence it came and how formed is one of the most interesting subjects that scientific minds have investigated. The history of glacial phenomena is the history of the deposition of the blue clay formation.

Too much credit cannot be given to the late lamented Prof. Agassiz and Principal Forbes for their discovery of the laws regulating glacial action. These eminent savants built a hut on a living glacier, in Switzerland, and studied it in all its relations to the past history of the globe.

Prof. Gunning says: "The area of Greenland is nearly eight hundred thousand square miles; and all this, save the narrow strip which faces an ice-choked sea, on the west, is a lifeless solitude of snow and ice. The snow overtops the hills and levels up all the valleys, so that, as far as the eye can reach, there is nothing but one vast, dreary, level expanse of white. Over all broods the silence of death. Life, there is none. Motion, there seems to be none—none save of the wind, which sweeps now and then, in the wrath of a polar storm, from the sea over the 'ice-sea,' and rolls its cap of snow into great billows, and dashes it up into clouds of spray. But motion there is; activities we shall see there are, on a scale of grandeur commensurate with the vast desolation itself."

Let the mind go back in the history of our earth, one hundred thousand years, when, Prof. Croll, from mathematical deductions, infers the existence of a snow cap, covering the whole of North America and Europe, form the thirty-eighth parallel to the north pole; then, in imagination, see the larger portion of North America, as you see Greenland now, covered with an "ice

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mantle" 3,000 to 6,000 feet thick. A glacier is a frozen river, having motion as a stream of water has, but bound in gigantic bands by the cold atmosphere. Conceive, if you please, a moving block of iron, thousands of tons in weight, dragged over a plowed field. The track of this monster is marked by a level bed of compressed, pulverized earth. Transfer your imagination to a mass of ice covering the entire northern hemisphere, or at least to the thirty-eighth parallel (at which point the equatorial heat began to assert itself on the ice-walls, and decompose them, carrying the debris of the glacier, in solution, southward), moving half a foot or more a day, because of the hydraulic pressure from behind and within—the streams which flowed into it—and you can then have some faint idea of the incalculable force of a glacier, and the action of the ice-mass on the plastic earth.

The dynamic power of such a continental mass of ice is inconceivable. It is fit to be called one of the giant mills of the gods, which are represented "to grind slowly, but exceedingly fine." It was a monstrous ice-plane, shaving off the rugged crags of mountains, leveling up valleys and filling up ancient riverbeds. Its under surface was thickly set with rock-bowlders, which, with its ponderous weight, ground the underlying rocks to powder. This pulverized rock was washed from beneath the glacier by the overflowing waters which constantly gushed forth, and settled on far-off plains as alluvial sand and clay. The motion of the glacier was slow, perhaps six inches in twenty-four hours. This was the giant mill that ground out the blue clay—the glacier clay—that overlies the native formations of the entire country. It doubtless owes its dark blue color to the Lauentian and trap rocks of Canada. Well-diggers are familiar with it and it is nearly always the same in color and composition. Geologists are now unanimous in the opinion that during the glacial epoch the whole northern portion of the continent was elevated one thousand to two thousand feet above the present level.

Le Conte says: "The polar ice-cap had advanced southward to 40° latitude, with still further southward projections, favored by local conditions, and an Arctic rigor of climate prevailed over the United States, even to the shores of the Gulf. At the end of this epoch an opposite or downward movement of land surface over the same region commenced and continued until a depression of five hundred or one thousand feet below the present level was attained.

Le Cont says: "This ice sheet moved, with slow, glacier motion, southeastward, southward and southwestward, over New England, New York, Ohio, Illinois, Iowa, etc., regardless of smaller valleys, glaciating the whole surface and gouging out lakes in its course. Northward, the ice-sheet probably extended to the pole; it was an extension of the polar ice-cap."

It is not within the province of this sketch to go into details and give the problematic causes of this glacier period. The causes were mainly astronomical. Mr. Croll has calculated the form of the earth's orbit a million years back and a million years forward. The probably time of the last glacial period was 100,000 years back; then the eccentricity of the earth's orbit was very great, and the earth in aphelion (or when most distant form the sun, being about thirteen millions of miles further than in summer) in mid winter; then the winters were about thirty days longer than now. In summer, the earth would be correspondingly nearer the sun, and would receive an excess of heat, thus giving the earth in the northern hemisphere short, hot summers and long, cold winters.

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The subsidence referred to above forms the beginning of

THE DRIFT PERIOD

Now let us see how the drift was deposited on the bowlder clay. When the continental depressions took place, a large portion of the Mississippi Valley was submerged. Le Conte says: "It was a time of inland seas. * * * * * Another result, or at least a concomitant, was a moderation of the climate, a melting of the glaciers, and a retreat of the margin of the ice-cap northward. It was, therefore, a time of flooded lakes and rivers. Lastly, over these inland seas and great lakes, loosened masses of ice floated in the form of icebergs. It was, therefore, a time of iceberg action."

For a time the ideas upon the subject of glacial and iceberg action were confused, until Prof. Agassiz practically demonstrated the difference, on the glacier in Switzerland. The iceberg period followed that of the glacier. The depression of the continent, from 1,000 to 2,000 feet, created a sea-bed. This was filled by the melting of the glacier. Meanwhile, the water supply on the glacier continued, but the moderated climate prevented the formation of the ice-cap. As a result, the hydraulic pressure from behind forced the glacier, or frozen stream, into the sea. The buoyancy of the water counteracted on the specific gravity of the glacier, and, when the ice had projected beyond a point at which it could resist the upward pressure of the sea-water, great masses of it were broken off. These masses floated away, and are known as icebergs.

The glacier was frozen to the bottom of its river-bed, congealing in its embrace rocks, gravel, sand and whatever substances lay thereon. These substances were held firmly during the progress of the iceberg, after its liberation from the parent glacier, until it had floated into warmer waters. Then began a gradual dripping of the freight of the berg, until finally the ice itself disappeared in the mild waters of a tropic ocean.

The opinion prevails among geologists that the glacier motion was from the east of north, but that the Champlain flow was from the northwest. Corroborating this hypothesis is the marked difference in color of the bowlder clay and the Upper Drift deposit. If the glacier motion was from the north, or east of north, it did not produce the beds of our present rivers. Glaciation, or the process of leveling the earth's surface by the pressure of moving glaciers, only wore off and smoothed down the surface of the country, leaving it a vast undulating plain of dark blue mud, a heterogeneous mass of clay, sand, gravel and bowlders. The old river courses and valleys were completely obliterated. That the great beds of alluvium which cover up the blue clay were deposited in water, is clearly proven by its stratification, which can be observed in almost any excavation where a hill or bluff has been cut through in constructing railroads or mills, or where brick clay has been procured.

But let us see how the Champlain or Drift period was produced.

A continental subsidence came on and large inland lakes were formed. The climate became modified; the glaciers melted more rapidly; vast icebergs broke loose from the mountain-like glaciers and floated over the land, carrying rocks and clay and debris with them, and as they melted, strewed them over the surface, sometimes grounding and excavating basins for future lakes and ponds. Thus, year after year and age after age, did the muddy waters and freighted icebergs flow over the country, the former depositing our present alluvial drift, the latter dropping here and there the bowlders and debris that we now find scattered over the country. No erosion or wearing away, save from a stranded ice-

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berg, occurred at that time, but it was a period of filling in, a period of distribution over the submerged land, of powdered rocks, sand and clay, and an occasional bowlder. But when the continent emerged from the abyss, and the waters flowed off, and the higher undulations of the land appeared, then the erosive action of winds and waves and storms and currents took place. The waters, as they flowed toward the sea and Gulf, produced their inevitable channels.

There was much of the drift carried into the streams and borne away in the floods of the sea. Then was the stranded bowlder, by wind and wave, stripped of its soft, alluvial bed, left high and dry on the surface of the hereafter prairie. Then were the gravelly knolls that are found in some parts of the State robbed of every fine sediment, and the gravel and stones left to tell the story of the floods. Then were the great valleys washed out; then did the annual washouts all along the water-courses—rapidly at first, but more slowly in after ages—eat away the drift accumulations and form the hills. The hilly districts generally lie contiguous to the streams. Back from these water courses the land is usually undulating prairie, showing but little erosion.

The country contiguous to the Des Moines River and its tributaries bears, in many localities, unmistakable evidences of the action of the retiring waters of the Champlain period. As geology has written its history in the rocks, so the latest action of the waters has left its legible records in the drifts—it made tracks, and by its tracks we can see where it was and what it did.

When two currents of water flow together, charged with sediment, where the currents meet there will occur an eddy, the eddy-water will throw down its load of floating mud and build up a bar. In the valley of every creek in this locality, may be found many of those silted-up banks and promontories, the deposits of the waters during the later Champlain period.

If our readers will but notice the action of any swollen creek, they will at once perceive how the prairie streams have silted or thrown up the hillocks so frequently met with. Notice the little brook that meets the larger creek yonder. At the mouth of the brook is a firmer bit of ground in the slough, upon which the horseman, at an early day, safely crossed the miry ford. That firm ground was formed by the heavy sediment of the brook. The two streams produced an eddy on meeting, and the waters were delayed an instant. Some of the sand brought down stream sank during this pause, and a hillock in embryo was made.

Years from this time, the course of that stream will be changed because of an impeding elevation of land, and that elevated land will be cultivated, with rich returns. So the surface of the prairies was formed into irregular hills and dales.

BOWLDERS

are frequently found scattered over the surface of the country, and very commonly in ravines or sloughs, because, when denudation was taking place by the agency of the subsiding waters, they invariably moved down hill when the earth was washed from under them. This readily accounts for their being usually found in ravines.

ECONOMIC GEOLOGY

Timber.— Jefferson County is well supplied with timber. Most of the kinds peculiar to the West are abundant, among which may be mentioned red, black, white, burr and jack oak, white and black walnut, hard and soft maple, ash, hickory, elm, hone locust, cottonwood, cherry and birch.

W. T. Burgess - Fairfield (click on image for full size. (Page 389)

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Coal.— There is an inexhaustible supply of bituminous stone coal of as good quality as can be found in the West. Several coal-mines are extensively worked, and their products shipped by the Burlington & Missouri River (C., B., & Q.) to Mount Pleasant, Burlington and other points. The coal is found in three principal seams, cropping out at different points. The lower seam is that which is most principally worked, the upper has nowhere been found thick enough to work, except about two miles west of Fairfield, where it is about three feet in thickness. One mile and a half directly south, at Read's Mill, this seam diminishes to a thickness of but two inches. At this point the second or middle seam is six inches, and the third or lower, is three feet and three inches thick. The coal found in the vicinity of Fairfield is much sought after for mechanical purposes, because of the small proportion of the sulphuret of iron.

Penn Township is the principal coal center, within which township several banks are worked with profit. The mines at Coalport are also in successful and profitable operation. [A more comprehensive reference to the operations of these several coal-banks will be found in a history of the industrial interests of the county.] Coal has been discovered in all the townships of the county but Walnut.

Building Stone.—It is stated in the State Geological Report, of Prof. James Hall, that Jefferson County is not well equipped with good building-stone, her main resource being the sandstone of the coal-measures, which are not very reliable when exposed to atmospheric agencies, etc. Since that report was made (1858), the Burlington & Missouri Railroad Company have used, for heavy masonry, stone obtained in this county, and it is found that it is reliable when exposed to air. The abutments of the railroad bridge over Big Cedar are constructed from stone obtained in the immediate vicinity in 1859, and seem to have increased in solidity by atmospheric exposure. The same may be remarked of the stone used in the construction of the Court House, which has not crumbled away after an exposure of nearly thirty years to the atmosphere, besides supporting heavy brick superstructure. A portion of the stone used for the Court House was quarried in Walnut Township, in the northeast corner of the county. The rest was obtained in other localities in this county, but all have proved alike durable.

Quicklime.—The concretionary limestone is the main source for the manufacture of quicklime, and no better article for that purpose need be desired that that afforded by the different quarries in the eastern part of the county, on Brush Creek, Walnut Creek, and nearly all the smaller tributaries of Skunk River.

Fire-Clay.—Beds of fire-clay are found in various parts of the county in connection with the coal-seams. Near Bush Creek, on the northeast quarter of Section 36, in Lockridge, there is a bed of this material about fifteen feet in thickness. It rests on concretionary limestone, with a few inches of iron ore between. The lower part of the bed is somewhat slaty in texture, but the upper part is of excellent quality.

Sand.—A good grade of sand for building purposes is found along the breaks of the streams where the sandbeds of the deposit have been exposed by the action of the water.

Soil.—There is a variety of soil and surface. Portions along Skunk River and Big Cedar are somewhat broken and uneven in surface, but the soil is pro-

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ductive and especially adapted to the raising of wheat. The northwest part has a larger proportion of prairie, nearly all of which has been brought up to a high state of cultivation. Corn, wheat, rye and oats are the principal crops. Most kinds of vegetables are produced in great abundance an perfection. For meadows, the farmers sow clover and timothy; but blue grass and the various other kinds of grasses do well. Fruits do well. Apples, grapes and strawberries especially, grow to great perfection and seldom fail. Several parties have made the raising of grapes for the manufacture of wine a special feature of their industry. The Catawba has been the favorite wine-grape. The Clinton, Concord, Delaware and Hartford Prolific do well. Cherries, plums, gooseberries, currants and other varieties of small fruits yield abundantly with proper attention.

ORIGIN OF THE PRAIRIES

Prof. Hall, in his Geological Report of Iowa, says:

The subject of the prairies, or the cause of the absence of trees over so extensive a region, is one which has often been discussed, and in regard to which diametrically opposite opinions are entertained.

The idea is very extensively entertained throughout the West, that the prairies were once covered with timber; but that it has been been destroyed by the fires which the Indians have been in the habit of starting in the dry grass, and which swept a vast extent of surface every Autumn. A few considerations will show that the theory is entirely untenable.

In the first place, the prairies have been in existence at least as far back as we have any knowledge of the country, since the first explorers of the West describe them just as they now are. There may be limited areas once covered with woods and now bare; but, in general, the prairie region occupies the same surface which it did when first visited by the white man.

But, again, prairies are limited to a peculiar region—one marked by certain characteristic topographical and geological features, and they are, by no means, distributed around wherever the Indians have roamed and used fire. Had frequent occurrence of fires in the woods been the means of removing the timber and covering the soil with a dense growth of grass, there is no reason why prairies should not exist in the Eastern and Middle States, as well as in the Western. The whole northern portion of the United States was once inhabited by tribes differing but little from each other in their manner of living.

Again, were the prairies formerly covered by forest trees, we should probably now find some remains of them buried beneath the soil, or other indications of their having existed. Such is not the case, for the occurrence of fragments of wood beneath the prairie surface is quite rare. And when they are found, it is in such position as to show that they had been removed to some distance from the place of their growth.

It has been maintained by some that the want of sufficient moisture in the air or soil was the cause of the absence of forests in the Northwest; and it is indeed true that the prairie region does continue westward, and become merged in the arid plains which extend along the base of the Rock Mountains, where the extreme dryness is undoubtedly the principal obstacle to the growth of anything but a few shrubs peculiarly adapted to the conditions of climate and soil which prevail in that region. This, however, cannot be the case in the region of the Mississippi and near Lake Michigan, where the prairies occupy so large a surface, since the results of meteorological observations show no lack of moisture in that district, the annual precipitation being fully equal to what it is in the well-wooded country farther east in the same latitude. Besides, the growth of forest trees is rich and abundant all through the prairie region under certain conditions of soil and position, showing that their range is not limited by any general climatological cause.

Taking into consideration all the circumstances under which the peculiar vegetation of the prairie occurs, we are disposed to consider the nature of the soil as the prime cause of the absence of forests, and the predominance of grasses over the widely-extended region. And although chemical composition may not be without influence in bringing about this result, which is a subject for further investigation, and one worthy of careful examination, yet we conceive that the extreme fineness of the particles of which the prairie soil is composed is probably the principal reason why it is better adapted to the growth of its peculiar vegetation than to the development of forests.

It cannot fail to strike the careful observer that where the prairies occupy the surface, the soil and superficial material have been so finely comminuted as to be almost in a state of an impalpable powder. This is due, partially, to the peculiar nature of the underlying rocks and the facility with which they undergo complete decomposition, and partly to the mechanical causes which have acted during and since the accumulation of the sedimentary matter from the prairie soil.

If we go to the thickly-wooded regions, like those of the northern peninsula of Michigan, and examine those portions of the surface which have not been invaded by the forest, we shall observe that the beds of ancient lakes which have been filled up by the slowest possible accumulation of detrital matter and are now perfectly dry, remain as natural prairies and are not trespassed upon by the surrounding woods. We can conceive of no other reason for this than the extreme fineness of the soil which occupies these basins, and which is the natural result of the slow and quiet mode in which they have been filled up. The sides of these depressions, which were lakes, slope very gradually upward, and being covered with a thick growth of vegetation, the material brought into them must have been thus caused. Consequently, when the former lake has become entirely filled up and raised above the level of overflow, we find it covered with a most luxuriant crop of grass, forming the natural meadows from which the first settlers are supplied with their first stock of fodder.

Applying these facts to the case of the prairies of larger dimensions farther south, we infer, on what seems to be reasonable grounds, that the whole region now occupied by the prairies of the Northwest was once an immense lake, in whose basin sediment of almost impalpable fineness gradually accumulated; that this basin was drained by the elevation of the whole region, but, at first, so slowly that the finer particles of the deposit were not washed away, but allowed to remain where they were originally deposited.

After the more elevated portions of the former basin had been laid bare, the drainage becoming concentrated into comparatively narrow channels, the current thus produced, aided, perhaps, by a more rapid rise of the region, acquired sufficient velocity to wear down through the finer material on the surface, wash away a portion of it altogether, and mix the rest so effectually with the underlying drift materials, or with abraded fragments of the rocks in places as to give rise to a different character of soil in the valleys from that of the elevated land. The valley soil being much less homogeneous in composition and containing a larger proportion of course materials than that of the uplands, seems to have been adapted to the growth of forest vegetation; and in consequence of this we find such localities covered with an abundant growth of timber.

Wherever there has been a variation from the usual conditions of soil, on the prairie or in the river bottom, there is a corresponding change in the character of the vegetation. Thus on the prairie we sometimes meet with ridges of coarse material, apparently deposits of drift, on which, from some local cause, there never has been an accumulation of fine sediment. In such localities we invariably find a growth of timber. This is the origin of the groves scattered over the prairies, for whose isolated position and peculiar circumstances of growth we are unable to account in any other way.

The condition of things in the river valleys themselves seems to add to the plausibility of this theory. In the district which we have more particularly examined, we have found that where rivers have worn deep and comparatively narrow valleys, bordered by precipitous bluffs, there is almost always a growth of forest; but where the valley widens out, the bluffs become less conspicuous, indicating a less rapid erosion and currents of diminished strength; there decomposition takes place under circumstances favorable to the accumulation of prairie soil, and the result has been the formation of the bottom prairie, which becomes so important a feature of the valleys of the Mississippi and Missouri below the limits of Iowa. Where these bottom prairies have become, by any change in the course of the river currents, covered with coarser materials, a growth of forest trees may be observed springing up, and indicating by their rapid development a congenial soil.

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