USA > Iowa > Henry County > The history of Henry county, Iowa, containing a history of the county, its cities, towns, &c. > Part 36
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"The concretionary limestone extends quite across the river here, forming a ripple just below the dam. There is a bed of iron ore from two and a half to three feet in thickness, which appears to thicken in a wedge-shaped form as it penetrates the hill. The ore itself is a cellular brown oxide of iron, and, if the bed thickens sufficiently to keep a furnace in operation, may prove a valua- ble acquisition to the mineral resources of the State.
" On Section 32, in Tippecanoe Township, a coal-seam has been opened, which is said to be from three to four feet in thickness ; but, at the time of my visit to the locality, the roof had fallen in, preventing any satisfactory examina- tion, either with regard to the thickness of the seam or the quality of the coal. On the south side of Cedar Creek, in the west part of Salem Township, this seam has been opened at several points near the county line, and about two miles north of Hillsboro. At Dr. Crail's bank, the coal is three and a half feet thick, and is overlaid by about four feet of bituminous slate. The coal here rests directly upon the concretionary limestone, with only a few inches of shaly clay and slate between. The vicinity of Hillsboro now furnishes nearly all the coal used in the southern part of the county. Thus it will be seen that the only coal lands in Henry County that promise anything like a profitable coal-seam are those lying west of Skunk River and Cedar Creek ; and for the benefit of those who are disposed to test the question, whether coal can be found at any particular spot, let me repeat that, by boring down from a point near the general level of the country to the limestones below, which, in Henry County, may be reached almost anywhere in less than a hundred feet from the surface, the question will be settled beyond a doubt, so far as that particular locality is concerned.
CONCRETIONARY LIMESTONE.
" This is one of the most important limestones in the county, inasmuch as it outcrops over a greater extent of surface than any other in it, and affords almost everywhere an abundant supply of building-stone, as well as an inex- haustible quantity of material for the manufacture of lime. This bed outcrops in the bluffs of Skunk River and Cedar Creek throughout the county, and on'
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HISTORY OF HENRY COUNTY.
Big Creek from the mouth to the joint where the Iowa City Road crosses it, two miles north of Mount Pleasant. It also outcrops on Crooked Creek in Scott Township, in the northeast corner of the county, and on Little Cedar Creek throughout its extent in Salem Township. Its average thickness in this county does not exceed forty feet, and in the northern part is somewhat less. The lower portion of the bed is usually more or less magnesian and quite mass- ive, affording suitable material for heavy masonry. The rock for the abutments of the railroad bridge across Skunk River was obtained from this portion of the concretionary bed, four miles below Rome. The middle portion is usually a mass of greenish gray, concretionary and brecciated limestone without regular lines of stratification, and only valuable for the manufacture of lime. The upper portion is usually a thin-bedded, light-gray limestone in regular layers from two to six inches thick, sometimes arenaceous and affording good flagging- stones.
" The most characteristic fossil of this bed is the Lithostrotion canadense, which is usually found weathered out in the beds of all the streams traversed by this rock. At Trueblood & Hyatt's mill on Cedar Creek, this coral is ex- ceedingly abundant; also on Big Creek, three miles south of Mount Pleasant. Two miles south of Mount Pleasant and one mile south of Salem, there are marly partings between the limestone strata, containing Terebratula, Rhyn- chonella, Productus and Spirifer, of species yet undetermined.
GEODE BED.
"This bed is well exposed in the vicinity of Lowell, where it attains a thickness of about thirty feet, and consists of calcareo-argillaceous shales, with geodes of quartz crystals, chalcedony, calcspar, etc. In its northern extension it thins out rapidly ; and, in the vicinity of Mount Pleasant, it is only repre- sented by a few feet of blue and yellow shaly-clay, which separates the concre- tionary limestone from the Keokuk beds below.
KEOKUK LIMESTONE.
" This limestone forms the bed of Skunk River from Lowell to Rome, and also appears again at Deedsville in the north part of the county ; it likewise crops out on Big Creek northeast of Mount Pleasant, and on Cedar Creek northwest of Salem. It consists of layers of buff-gray and bluish-gray lime- stones in strata from four to fifteen. inches in thickness, and has been quarried extensively on Big Creek northeast of Mount Pleasant, for the construction of the Insane Asylum. Not more than twenty feet in thickness was exposed in any of the quarries in this vicinity ; and it is quite probable that this, as well as the geode bed, thins out rapidly toward the north. The rock quarried in the vicinity of Mount Pleasant for the construction of the Asylum, is somewhat traversed by seams of argillaceous matter, which causes it to split on exposure to frost, and renders it unfit for heavy masonry. For this reason, great care should be taken in the selection of the material for so important a work ; and none should be used, especially where they are required to be set on edge, unless quite free from seams and of an even texture. The bluish-gray layers contain iron-pyrites, which decompose on exposure to the atmosphere, giving a dingy, copperas color to the rock ; for this reason the buff-gray layers should be pre- ferred. These beds do not afford as great a variety of fossils in this county as at points further south, but enough can be obtained to identify the beds without difficulty. At Willet's quarries I found the large Spirifer striatus, Simbrica- tus (?) Athyris lamellosa, A. Squamifera (?) Productus alternatus, together
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HISTORY OF HENRY COUNTY.
with several species of Capulus, Pleurotomaria, etc., common in the same beds at Keokuk. No trace of crinoids, other than a few joints of the columns, were seen here. At Oakland Mills on Skunk River and Trueblood & Hyatt's mill on Cedar Creek, the fossils of this bed may be obtained.
" The only outcrop of crinoidal limestone in Henry County is on Big Creek in the northwestern part of New London Township, on Sections 4, 5 and 6. Only a few feet of the rock are exposed along the bed of the creek, where two or three small quarries have been opened in it. These beds have a slight dip to the south west and soon disappear beneath the Keokuk limestone.
ECONOMICAL GEOLOGY.
" The Keokuk limestones and concretionary bed afford an abundant supply of good building-stone, which may be procured in the bluffs of Skunk River, on Big Creek, north and west of Mount Pleasant, and on Cedar and Crooked Creeks, and several smaller tributaries to Skunk River. The Keokuk lime- stone is more argillaceous here than in places further south, and some of the layers are traversed by seams of argillaceous matter which cause the rock to split where exposed to the action of frost.
"The concretionary limestone of some localities is magnesian and heavy- bedded, affording strata two feet in thickness, and well adapted to heavy ma- sonry. This character is usually restricted to the lower portion of the bed, while the upper part is commonly a light-gray or dove colored compact lime- stone, with a conchoidal fracture, and in layers from four to eight inches thick. This limestone is the only deposit in the county from which a supply of lime can be obtained, the Keokuk limestones being too argillaceous to be used for that purpose. As this bed is accessible on almost every stream in the county, it will afford an inexhaustible supply of material for the manufacture of lime.
"Thin layers of coal are found in various parts of the county, but the workable seams appear to be restricted to the west side of Cedar Creek, along the west line of the county. The coal-seam outcropping here varies from two to three feet in thickness, and is probably the same as that opened in the vicinity of Fairfield, Jefferson County. The southern part of the county is mostly supplied at the present time from the vicinity of Hillsboro. Nodules of clay and iron ore occur very generally in connection with the lower coal-seams, and are also common in the drift, derived probably from the same source. At Crawford's mill, on Skunk River, about one mile north of Rome, a bed' of ore occurs in the coal-measures. The bed at its outcrop is only two or three feet thick, but seems to thicken in a wedge-shaped form as it penetrates the hill. Good potter's clay occurs at Trueblood & Hyatt's mill, on Cedar Creek, six miles north of Salem, and also at several places in the county where outliers of coal are found.
" As an agricultural region, Henry County may be ranked among the very best in the State, having an abundant supply of timber, while the prairie lands are generally rolling and dry, and all susceptible of a high state of cultivation. Building-stone is abundant in nearly all parts of the county, costing only the labor necessary to quarry and remove it to the places where it is wanted. An abundance of water may be procured at points remote from the main water- courses, by sinking wells to the depth of from twenty to forty feet."
A FEW INFORMAL COMMENTS.
In the preceding pages, Prof. Hall speaks in technical terms of the several formations discoverable in this county. He does not, however, find it within
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the province of his thought to explain, in popular language, the nature of the more superficial strata, and a page or two may here be devoted with propriety to a less scientific, but perhaps equally readable, consideration of the subject.
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. In Henry County this deposit is estimated to be no less than from sixty to eighty feet in thickness. Strewed all over the country, on the hills, in the valleys and upon the level prairies, covering up the native rocks, to a depth oftentimes of fully three hundred feet, is found this peculiar substance. The well-diggers and the colliers in their excavations encounter it, and the quarryman has to "strip " it from the surface of the rockbed. It is not all alike; first there are a few feet of vegetable soil, created by the decay of com- paratively recent growths ; then, a. variable depth of clay or clay and sand intimately blended ; then water-worn gravel and sand, and then blue clay, rest- ing upon the country rock.
Scattered over the continent are frequently seen "lost rocks," or bowlders, 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.
What were the causes which produced such a diversity of deposit, and where did these bowlders come from ? Let us try to offer a theory, based upon the researches of scientists.
The blue clay, which lies upon the country rock, 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 numerous varieties and sizes, unassorted and unstratified ; it, 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. The cause of its formation is one of the most interesting subjects that scientific minds have investigated. The history of the glacial phenomena is the history of the deposition of the blue clay formation.
To the late Prof. Agassiz and Principal Forbes the major part of the credit of discovering the true theory of this deposit is due. These eminent savants built a hut on a living glacier in Switzerland, and studied the monster in all its bearing to the past history of the globe.
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, of a moving mass of iron, thousands of tons in weight, being dragged over a newly plowed field. The track of this immense body is marked by a level bed of compressed, pulverized earth. Transfer your imagination to a mass of ice cov- ering the entire northern hemisphere, to a point as far south as the thirty-eighth parallel (at which point the equatorial heat began to assert itself on the ice walls, and decompose them, carrying the flow of water and substances once held in place in the ice, southward). Consider this ice-cap moving toward the south at the rate of six inches, or more, a day, which motion was imparted by the hydraulic pressure from behind and within-the streams which fed the gla- cier-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-bed upon which is rested.
To illustrate this point is here given a quotation from Prof. Gunning : " 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
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lifeless solitude of snow and ice. The snow overtops the hills and levels up 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, or 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, according to the mathematical and astronomical calculations of Prof. Croll, there existed an ice-cap over America and Europe, from the pole to the thirty-eighth parallel, which made the northern hemisphere as Greenland is now, covered with a solid blanket of ice from 3,000 to 6,000 feet in thickness.
The dynamic force of such a mass of ice is inconceivable. It is fit to liken it unto the mills of the gods, which "grind slowly but exceeding fine." This monstrous ice-plane shaved off the rugged crags of mountains, as it forced its way southward, leveling up valleys and filling up ancient river-beds. 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 not more than six inches in twenty-four hours-but the slowness of movement aided in the atomization of the bed-plain. Thus was the blue clay formed. Its color is doubtless owing to the Laurentian rock of Canada. It always has the same color and composition. During the glacial period the northern portion of the continent was elevated at least one thousand feet, and perhaps two thousand, above the present level. Le Conte says : " The polar ice-cap had advanced southiward to 40° latitude, with still further south ward projections, favored by local conditions, and an arctic rigor of climate prevailed over the United States, even to 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 Conte says : " This ice-sheet moved, with slow, glacier motion, south- eastward, 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 the 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 probable time of the last glacial period was one hundred thousand years back ; then the eccentricity of the earth's orbit was very great, and the earth in aphelion (or when most distant from the sun, being about thirteen millions of miles further than in summer) in midwinter ; 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.
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 depression took place, a large portion of the Mississippi Valley was
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HISTORY OF HENRY COUNTY.
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 pointat 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 sub- stances 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 disap- peared 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. Corrobo- rating 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 undu- lating 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 exca- . vation 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 sur- face, 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 iceberg, occurred at that time, but it was a period of filling in, a period of dis- tribution 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
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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 to 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 wash-outs- 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 Champlain period. As geology has written its history on 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 yon- der. 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 pro- duced 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.
ORIGIN OF THE PRAIRIES.
Prof. Hall, in his Geological Report of lowa, says :
The subject of the origin of the prairies, or the cause of the absence of trees over so exten- sive 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 deen 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 hy 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.
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