USA > Iowa > Chickasaw County > History of Chickasaw and Howard counties, Iowa, Volume I > Part 7
USA > Iowa > Howard County > History of Chickasaw and Howard counties, Iowa, Volume I > Part 7
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Thin-bedded, coarse-grained, magnesian limestone like that in the upper part of the Croft quarry is exposed in the banks and bottom of a small branch of Crane Creek, in the northeast quarter of section 33, Saratoga Township. At one point a small quarry has been opened, but the stone comes out in pieces too small to be very serviceable.
The Devonian beds show very little dip in any direction. The inclination corresponds very nearly to the general slope of the surface toward the south- west. Chester is fifty feet higher than Elma. The distance between the two points is about sixteen miles. The same beds are exposed at both places. The dip from one point to the other, which is along a line very nearly at right angles to the strike, is but little more than three feet to the mile. Cresco is 118 feet higher than Elma. The inclination of the surface between the two points-about seven feet to the mile-is greater than the dip of the strata, and hence it is that the Elma horizon is lower than the horizon of the quarry stone at Cresco. The limestones at Cresco are the highest, stratigraphically, occurring in the county.
The general section of the Howard County Devonian may be arranged in the following divisions :
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Feet
5. The quarry beds at Cresco, Vernon Springs, the Jones quarry in section 24, Chester Township, and the quarry on high ground in the southeast quarter of section 14, Forest City Township
50 4. Non-dolomitic beds at the base of the Salisbury quarry and exposed at a few other points, as in section 18, Forest City Township, carrying Orthis, Gypidula and Atrypa, like forms found in the quarries at Independence.
8
3. Beds varying in character, some of the layers white, fine- grained, lithographic, in some places rich in stromatoporoid corals
I5 2. Coarse-grained, dolomitic beds in the northeastern part of the county, less dolomitic at Elma and southwest, the ยท horizon of Favosites, Acervularia and Pentamerella, the quarry beds at Elma and the country southwest. 15
I. Productella beds, soft, buff-colored, vesicular dolomite, with casts of fossils, quarried in massive blocks at Foreston, the real equivalent of the quarry stone beds at Independ- ence 40
PLEISTOCENE SYSTEM
KANSAN STAGE
Kansan Till. The oldest drift sheet positively recognized in Howard County is the Kansan. In boring deep farm wells on the prairies, partially decayed logs and other remnants of buried forests are found at various depths ranging to 250 feet ; but the evidence of a definite forest, peat or soil horizon between two distinct bodies of glacial detritus is not clear. There is as yet no certainty that the sub-Aftonian of pre-Kansan till is present in the area we are considering, although it is very probable that it exists in the parts of the county covered with deep drift, in Oak Dale, Jamestown, Afton and Howard townships, and in the southern parts of Paris and New Oregon. The Kansan till, overlain by a thin deposit of Iowan loess, is the surficial drift in a comparatively small area in the northeastern corner of the county, and over the larger area southwest of the loess margin it is present beneath the much later drift sheet, the Iowan. The physical characteristics of the two areas and the position of the boundary line between them have been previously discussed under the head of Topography. In the Loess-Kansan area the weathered ferruginous ferretto zone of the Kansan is seen along roadsides and in many other places, wherever rainwash has cut through the overlying loess. At the brick yard in Cresco the yellow Iowan, free from limestone pebbles, is used in brick making, but some of the excavations have gone down to the unweathered blue clay of the Kansan. A deep railway cut 11/2 miles south of Elma reveals the Kansan drift in its unweathered phase. A few rods north of a wagon bridge which here spans the cut, the section shows :
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Feet
3. Yellow, unweathered Iowan till. 6
2. Old peaty soil developed in the intervals between the Kansan and the Iowan stages of glaciation. 2
I. Blue unweathered Kansan to bottom of the cut. I5
There is here no ferretto zone at the surface of the Kansan; the organic material of the peaty soil bed was capable of more than counterbalancing any effects of oxidation which might have taken place before the Kansan surface was covered and protected from further change by the deposition of the Iowan drift. One-fourth of a mile south of the bridge there are a number of lenses of gray sand included in the blue Kansan clay, some of which are three feet in thickness and fifty feet in length. Though the hill in which the cut is made is one of the highest of the region, it shows none of the characteristics of a paha, that unique and interesting type of land forms so common at corresponding distances from the Iowan margin in Delaware, Jones, Linn and Cedar counties. When first seen from a distance it was confidently believed that it would prove to be a loess-covered pahoid ridge, but in the place of loess it is covered with a thin sheet of Iowan till and its surface is liberally sprinkled with large Iowan bowlders. The fresh Kansan till is here, as everywhere else in Iowa, a blue clay crowded with small pebbles, many of which are limestone. Greenstones are also common. Granites are relatively scarce, and none are as large as the third and fourth rate granites of the Iowan, even when first class bowlders are made to include everything above twelve feet in diameter. The earth taken out is piled on the west side of the Elma cut and covers an area of considerable width. In the few years of its exposure to the air, rains have concentrated the pebbles in a sheet over the surface, by washing away the fine clay in which the pebbles were imbedded. The dump, therefore, now corresponds in a small way to the initial stages of the condition which existed over hundreds of square miles in southwestern Iowa, before the loess was laid down. A sheet of residual gravel, sometimes fully six inches in thickness, conforming to the surface of the erosional hills and valleys, is widely distributed on weathered Kansan under- neath the loess, in all the southwestern counties of the state. The fact is dis- cussed and illustrated in the report on Page County. The dump near Elma affords an interesting and concrete illustration of the manner in which these residual gravels were developed.
Wherever there are exposures of the pre-Iowan surface of the Kansan drift. undisturbed by the later glaciation, the materials are found to be very much altered by weathering. The iron-bearing constituents of all fine flour and other minute particles derived from wear of crystalline rocks, are completely oxidized, and as a result the normal blue of the unaltered clay is changed to deep reds and browns. The fresh Kansan is always rich in limestone flour and small limestone pebbles. In the weathered zone all the calcareous material, except the larger pieces of limestone, have been dissolved and leached out by descending ground waters. Many of the small granite bowlders have crumbled into minute fragments which are distributed among the other loose materials near the sur- face, others are ready to fall to pieces under the application of the slightest force.
Buchanan Gravels. Beds of old weather-stained gravels resting on Kansan.
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and overlain by Iowan drift, were first recognized as a distinct Pleistocene- deposit in Buchanan County, Iowa. Later investigations show these gravels to be extensively developed all over the northeastern part of the state. Howard County has its share, and they are known to be present in adjacent parts of Minnesota. On one side of the Loess-Kansan border they are generally cov- ered with lowan drift, on the other side, as is strikingly illustrated around Colesburg in Delaware County, they are overlain by loess. The gravels occur- principally in two situations. They are either on the high plateaus and ridges, or they are in the river valleys; and there are very marked differences between. the upland and the valley deposits. The upland gravels are distinguished by the presence of coarser and less perfectly assorted materials. Cobbles and bowlders of all sizes up to ten or twelve inches in diameter, are found indifferently mixed with pebbles and fine sand, and many of the larger erratics show glacial' planing and striation on one or more sides. While the gravels have all the characteristics of deposits made in flowing water, it is certain that the planed and' striated cobbles have not been rolled or transported very far. The valley gravels, on the other hand, are quite uniform as to the size of the pebbles. It is seldom that any of the material exceeds three-fourths of an inch in diameter. The usual size is about half an inch, and the great body of the valley phase is composed of well rounded, polished, silicious pebbles. Cross bedding is more common in the tipland, than in the valley gravels.
A very typical example of the upland phase of the Buchanan gravels occurs in the large gravel pit in the southwest quarter of section 27, Vernon Springs Town- ship, about midway between Cresco and Vernon Springs. The material is very rusty from the complete alteration and oxidation of the iron bearing constituents of a large proportion of the crystalline pebbles. In places the amount of iron present is sufficient to cement the gravel into a firm conglomerate. The granites, embracing small bowlders up to eight or ten inches in diameter, are decayed and fall to pieces, when taken from their surroundings. Every feature of the deposit indicates age. The gravel at this point has been used extensively for road material. The pit is fully fifteen feet in depth, but it does not show the whole thickness of the deposit. The location is near the edge of an area of thin lowan drift. There is practically no stripping, nothing above the deposit but a bed of humus-stained, gravelly soil. In the adjacent parts of section 34 and in section 35 there are esker- like knobs of Buchanan gravels which have not been worked.
A feature of the landscape which should probably have been described under the. head of Topography, is a conspicuous esker of Buchanan gravel which stands out prominently near the center of the southwest quarter of section 27. Albion Town- ship. It is located inside the Iowan area and is surrounded by a thin sheet of Iowan drift. but the Loess-Kansan margin is less than one-fourth of a mile away. The attenuated edge of the Iowan glaciers probably overflowed it, for it has no loess such as mantles all surfaces in the neighborhood which were not covered by the Towan ice. In general the forms assumed by deposits of these gravels suggest that they had their origin in trains or sheets of outwash from the margin of the melting Kansan ice. Occurrences of such deposits illustrating the upland phase of the gravels are numerous. It may be sufficient to mention as typical examples, the beds seen along the western edge of section 7. Vernon Springs Township, and those in' sections 31 and 32 of Howard Center Township.
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The valley phase of the Buchanan gravels is much more extensively developed than the upland phase. Every stream valley that served as a drainage course when the Kansan ice was melting, is bordered throughout its whole length with trains and terraces of ferruginous gravel in which the pebbles are comparatively small and of uniform size. The terrace on the south side of the river at Florenceville and that on which the Village of New Oregon is located have already been mentioned. For some miles above Chester there is a wide, well marked, continuous terrace occupying an area of several hundred acres. The great beds of valley gravels about Le Roy, Minn., which the Chicago, Milwaukee & St. Paul Railway has used so extensively for ballasting its line, are but part of the enormous gravel trains which floods from the melting Kansan ice strewed continuously along the valley of the Upper Iowa. The same valley gravels are found the whole length of Crane Creek and along the branches of the Wapsipinicon, in the southwestern part of the county. In the southeast quarter of section I, northern part of New Oregon Township, there is a terrace of the valley gravels, some parts of which are cemented into a firm conglomerate. Cementation is not uncommon in other localities.
Genesis of the Gravel. The Kansan ice was thick, and it melted rapidly, especially when the shrinking margin was gradually retreating through northern Towa. Large floods of water, capable of transporting great loads of material, flowed outward over the surface which had but a short time previously been vacated by the waning ice. Heavy bodies of the ice must have lingered in the lowlands and valleys long after the hill tops were laid bare, and the re-entrant sinuses in the ice margin, corresponding in position to the higher lands, were drainage channels accommodating torrential streams which were hemmed in by banks of ice. These streams carried material of all grades of fineness up to cobbles and bowlders several inches in diameter. Some of the larger bowlders found in the deposits may have been floated by detached blocks of ice. The heavy material was not carried far, however. With the glacial markings uneffaced in some cases, it was dropped on the accumulating bars of sand and gravel which the overloaded streams deposited before their exit from the ice canyons. Such imperfectly assorted accumulations, now found on the higher grounds, constitute the upland phase of the Buchanan gravels.
As soon as the upland streams emerged from their ice canyons, the waters sought the lower levels and gathered in the unobstructed valleys beyond the ends of the ice lobes. Before they reached the valleys the heavier material had all been deposited : only the smaller, well rounded and easily transported pebbles were carried. and it is of these that the valley phase is made up. The upland gravels were laid down near the most northerly points of the ice margin. not far from where the streams originated. The valley gravels give evidence of having been transported farther, and they may have been deposited at distances of several miles from the southern extremities of the lobes of ice which occupied the lower grounds.
IOWAN STAGE
Iowan Till. Fully nineteen-twentieths of the area of Howard County is cov- ered with Fowan drift. Where this drift is present in sufficient force to disguise
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the pre-Iowan topography, the region is a plain modified by only slight relief. No loess is present, but large granite bowlders are prominent features of the landscape. The fresh Iowan till is yellow in color and carries quite a large amount of lime carbonate even at the surface. Among the pebbles limestones and greenstones are rare. The bowlders are coarse-grained and light colored, and it is a surprising fact that in all northeastern Iowa approximately three- fourths of the entire bulk of the Iowan erratics represent but one type of granite, which might all have come from a single locality. Iowan bowlders are large and numerous as compared with bowlders in the Kansan drift, but the variety and number of rock species are far greater in the Kansan than in the Iowan.
Over parts of Howard County lying southwest of the Loess-Kansan boundary, the Iowan drift is thin or even absent. As would be expected, the thin spots are near the margin where the ice became attenuated and the movement approximated zero. The load of glacial detritus carried by the Iowan glaciers seems to have been very unequally distributed, and there must have been places where it was altogether wanting. Quite a large area of thin Iowan, or no Iowan, occurs along the Turkey River from section 31, Vernon Springs Township, to section I of New Oregon. The original topography developed in the old rock surface by preglacial erosion is but imperfectly masked by all the Pleistocene deposits. The tops and slopes of the hills are covered with loose fragments of the magnesian Devonian limestone. The small amount of drift present is of the weathered Kansan type, and yet the surface is strewn with Iowan bowlders. A typical area of thin Iowan, where knobs and tors of Devonian limestone project through the drift, is found in section 14, Forest City Township. Bowl- ders seem to be the only element of the Iowan drift ever deposited in the locality. Along Crane Creek and the branches of the Wapsipinicon the later drift is so thin that the Buchanan gravels come practically to the surface in many places, and the same thing is true of the valley of the Upper Iowa above Chester. Taking the Iowan area as a whole, the distribution of the bowlders seems unaccountably irregular. There are some belts and patches,-as near the center of Jamestown Township and in the southern sections of Howard Center,-where the rounded blocks of northern granite are liberally sprinkled over the surface, and again there are areas of miles in extent in which scarcely a trace of a bowlder can be discovered.
Iowan Loess. The fine, yellow, pebbleless clay called loess forms a mantle of approximately uniform thickness over that portion of the surface of the old eroded Kansan drift which lies outside of the Iowan margin. All that part of the county upon which the Iowan ice advanced, up to the edge and terminus of the glaciers, is free from loess. The loess is fresh and young as compared with the weathered, leached and otherwise altered drift upon which it rests. In this part of the state, it seems very clear, the loess is of the same age as the Iowan till, and was derived from it by some process of transportation outward from the terminal border of the Iowan glaciers. In Mitchell County, as well as in many other counties in Iowa, there are thin deposits of a loess that is younger than the Iowan, probably of the age of the Wisconsin drift. Near Peoria, Ill., Wisconsin loess is as strongly developed as is the Iowan in Howard County. Loess may, indeed, have been formed during any age of the Pleistocene.
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Along the Missouri River the process of loess deposition seems to be still active. Wherever found, and to whatever age it may belong, it is wholly unlike drift or alluvium,-unlike any glacial, aqueo-glacial, or aqueous deposit known. The origin of the loess of the Mississippi and Missouri valleys has long remained a puzzle to careful and thoughtful geologists. On account of its unique structure, peculiar distribution and fossil contents, the trend of opinion among the best informed students of loess problems is, today, toward the view that it is an aeolian deposit, that winds have been the active agents in its transportation and deposition.
ALLUVIUM
In Howard County alluvial deposits are very meager. If the Turkey River between Vernon Springs and the east line of the county be left out of considera- tion, it may be said that throughout the Iowan area the stream valleys in their present aspects and relations are young. There are here no true valleys of erosion, no flood plains, no notable deposits of river silt. Along the Upper Iowa, or Oneota River, east of Foreston, the valley is old, it is well widened out in places, and there are occasional narrow fringes of alluvial plains between the stream and the bluffs. The same is true, but to a more limited extent, of the old part of the Turkey River Valley east of Vernon Springs.
THICKNESS OF THE PLEISTOCENE DEPOSITS
The sheets of drift and other Pleistocene deposits vary greatly as to thickness. There are two areas where the indurated rocks come near to the surface. One is northeast of a line drawn from Chester to the middle of the eastern boundary of New Oregon Township; the other is at Elma and in the country south and west of that locality. All the quarries and rock exposures are in these two areas. At all the quarries the stripping consists largely of disintegrated limestone. Not infrequently the overlying soil, as at the Salisbury quarry, fails to attain the di- mensions of a distinct layer. So far as data could be collected, the Pleistocene reaches its greatest thickness in Jamestown Township and in the territory imme- diately around it. Well drillers report that limestone has been struck at '200 feet in the southern part of Oak Dale Township, but some wells end in drift at a depth of 300 feet. The well of John P. Thelen in Jamestown Township found water in gravel at 252 feet from the surface. Near the center of section 30, Jamestown Township, a well in process of boring was down 130 feet and still in blue clay. "Chips of an old rotten log" were reported from a well in the northern part of Jamestown, at a depth of 250 feet. The Pleistocene clays are therefore known to range in thickness from practically zero in the northeastern part of the county, to more than three hundred feet in Jamestown and contiguous parts of adjacent townships.
SOILS
The soils of Howard County rank with the best to be found in Iowa. There are (I) loess soils which are limited to the small Kansan area in the northeast corner of the county. Where the surface slopes are comparatively gentle, there Vol.I-5
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are no better soils than those developed on the loess. The loess is a fine, porous, calcareous clay, free from sand on the one hand and bowlders on the other. In many respects it makes an ideal soil. It absorbs and retains moisture well. The roots of plants easily penetrate it to great depths. Where the surface is rela- tively level, a very fine, fertile, brownish, easily tilled loam develops on its sur- face. On the steeper slopes, however, the loess erodes easily, the vegetable loam is washed away as fast as it accumulates, and steep-sided gullies are cut by surface drainage. A hard, stiff, intractable soil usually results from the fact that surface erosion continually exposes fresh loess which has not been modified by the growth and decay of plants, by burrowing animals, by frosts or other mellowing agencies. Fortunately, in the county, the area where soils of the quality last described occur, are small. The farms of the Loess-Kansan area give every evidence of generous production. The porosity and depth of the loess render it capable of successful cultivation in times of drought, such as prevailed in 1901, or during periods of excessive rainfall, as in 1902.
(2) 'There are some small areas of rich, mellow, alluvial soil in the valley of the Upper Iowa River, between Foreston and the eastern border of the county, and a small number of acres of the same type of soil occur in the valley of the Turkey, east of Vernon Springs. Above Chester on the Upper Iowa, at New Oregon on the Turkey, and at many points along the streams draining the southwestern part of the county, the Buchanan gravels come near enough to the surface to produce (3) a gravelly and sandy soil. Buchanan gravels play an important part as subsoils over extensive areas along the branches of the Wapsipinicon in southwestern Howard, giving perfect underdrainage to the surface loams. The typical characteristics of these areas are well illustrated in the level plain from one to two miles west of Elma.
(4) By far the most important of the soil types occurring in Howard County is that which is developed on the Iowan drift. The area in which this type is found is many times larger than that of any other type, and its fertility, ease of cultivation, and lasting qualities set it far above any other. The atmosphere, the rains and frosts of the changing seasons, the growth and decay of plants, the work of the burrowing gophers and ants and earth-worms, have all combined to produce a deep, rich, black, warm soil of ideal quality ; and this soil is spread over a surface so level and unbroken that farm machinery of every kind can be operated on it to the very highest advantage.
UNCONFORMITIES
Some interesting examples of unconformities are furnished by the geological formations of this part of Iowa. The first and most important is that between the Devonian and the Maquoketa shales. The overlap of the Devonian referred to at the beginning of this report was a true transgression of the sea upon an eroded surface. The contact of the Devonian with the Ordovician is seen in only a few sections, and these are of limited extent ; but the relative altitudes of the two formations at a number of points indicate that the Devonian was deposited on an uneven floor. One or two concrete illustrations will show the nature of the evidence on which conclusions are based. One-fourth of a mile south of the center of section 8, Albion Township, magnesian limestone contain-
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ing remains of 'fishes and Devonian brachiopods, occurs at a much lower level than that at which undoubted Maquoketa is found along the north line of the same section. At the bridge over the Turkey River near the northeast corner of section 12, New Oregon Township, the Devonian beds are continued down to the level of the water in the stream, while less than half a mile east of the county line Maquoketa shales rise fully twenty feet above the water. Further- more the phase of the Maquoketa seen in the outcrop referred to is not that which belongs at the top of the formation. The difference in the relative alti- tudes of the river and the Ordovician strata at the bridge and at the springs a short distance below, cannot be accounted for by either the fall of the stream or the dip of the shales, but by irregularities in the surface on which the Devonian was laid down. Along the east line of section 13, Vernon Springs Township, on the hill slope forming the south side of the Valley of Silver Creek, the Devonian occurs well up toward the top of the slope, and gives place to buff or ash colored Maquoketa about twenty-five feet above the bottom of the valley. On the north side of the valley Devonian rocks in place are exposed less than ten feet above the small flood plain. How much lower the Devonian may go is not known, for at this point there is no Maquoketa in sight. The other unconformities need only be mentioned without giving specific illustrations. The Kansan drift is unconformable on the rock surface upon which it rests; and the loess and lowan drift are spread unconformably upon the old eroded sur- face of the Kansan.
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