USA > Iowa > Allamakee County > Past and present of Allamakee county, Iowa. A record of settlement, organization, progress and achievement, Vol. I > Part 8
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Clays and shales being formed of much finer material covered up and pre- served some wonderfully perfect fossil animal and plant remains. Impressions and casts of leaves are found so perfect that even the parts so minute that they can be seen only with a microscope, are just as in the original leaf, only of stone.
A large part of the stratified rocks are of limestone. Lime was dissolved from the older rocks forming the existing dry land, or formed by chemical union of their component parts and was carried in solution by the rivers to the sea. There limestone deposits that ultimately became lime rock were formed in two ways. One was by precipitation, settling the same as mud in dirty water settles to the bottom of a pail. Limestones thus formed are called tufas. The lime incrusta- tion on the inside of a tea kettle is a sample of what such rock is like. But little limestone was formed in this way.
The great body of lime rocks, often many hundreds of feet in thickness, was formed in a very different way. The sea is and has been inhabited by count- less myriads of animals of a low order, such as clams, snails, corals and micro- scopic creatures called protozoans or animalcules that formed a covering or pro- tection of lime for their soft body parts. This lime they had the power of ex- tracting from the sea water and of it forming their shells.
And the great body of limestone rocks is formed largely of the pulverized and comminuted shells of these animals when dead.
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As by far the greater bulk of such rock is formed by shells that are micro- scopic, some idea may be formed of the immense number of the minute or- ganisms producing them that existed in the old oceans, and of the immense length of time required to produce such great deposits of their dead shells.
The great mass of sedimentary or stratified rocks of the interior of North America have been but little disturbed by movements of the earth's crust, and so far as their order and position is concerned. are now much as they have always been.
As the ancient backbone of the American continent,-the "first dry land."- lay to the north, there was the shore line of the sea when sedimentary rocks first began to be formed on its bottom. This sea bottom sloped very gradually to the south and west where the deeper waters lay, so that all stratified rocks of the in- terior area or Mississippi valley, have a uniform slope or dip to the southwest. For the area under consideration it approximates eight feet to the mile.
It appears that the deeper parts of the sea have through the ages been con- tinually getting deeper, and the land had been gradually elevated, what was once sea bottom being lifted above the waters and added to the land area. This is why stratified rocks, once sea bottom, are now found far inland.
With these remarks on general geology we may now proceed to a study of the different formations exposed in our county.
The Mississippi river along the eastern border of the county has cut deeply into the limestone, shales and sandstones, forming a gorge from two to four miles wide, and the tributary streams, large and small, have eroded their valleys to the level of the flood plain of the great stream.
The high steeply rounded bluffs and hills, the castellated rocks at their tops, the escarpments and sheer precipices, the wooded crests and slopes, with the river, the islands, sloughs and lakes form scenery of great beauty. Professor Calvin has called it the Switzerland of Iowa. Except for its ruined castles, and the interest which attaches from its long occupancy by man, we doubt if the famous Rhine valley affords its equal.
For a general description of the topography we copy Norton's description in Volume XXI of the Iowa Geological Reports.
"Allamakee, the northeasternmost county of Iowa, lies almost wholly in the driftless area. The region is a deeply and intricately dissected upland, attaining an elevation of 1,300 feet above the sea level, and rising about 700 feet above the Mississippi river, which forms the eastern boundary of the county. The valleys of the streams are flat-floored and wide. The Mississippi flood plain attains a width of four miles and embraces a maze of sandy islands and braided bayous. The floor of the valley of the meandering Upper Iowa river has a general width of three-quarters of a mile, widening in its lower course to a mile and more. The valley of Yellow river is narrower but conforms to the same general type. The tributary creeks have well-opened mature preglacial valleys, and the courses of even their wet-weather affluents are graded.
"The topographic age of the region is best read in the semi-circular coves carved by the ancient stream on both sides of the valley of Upper Iowa river. These deep amphitheaters are guarded at their entrances by lofty isolated buttes, remnants of the rock spurs cut by the stream as it entrenched its curving course. No such coves and buttes are seen along the bluffs of the Mississippi. though
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the succession of strata is equally favorable to cliff recession and planation, the vast volume of water of the latter Pleistocene times having cut back any salients of the valley sides and left a wall of rock singularly continuous and even and sweeping in its curves.
"The interstream areas consist of parallel east-west ridges or uplands, whose summits, where broadest, are cut by shallow valleys into a gently rolling topog- raphy. Their dissected flanks consist of lobate ridges of sinuous crest whose steep sides are gashed by deep ravines.
The summits of the divides rise to a common level. If the valleys could be filled with the material that has been swept away by running water they would constitute a plain whose origin may be ascribed to long subaerial erosion near the level of the sea. An additional proof of the former existence of this ancient peneplain, of which the summits of the divides are the remnants, is found in the valuable limonite and hematite deposits of Iron Hill on the crest of Waukon Ridge. Such deposits are common on peneplains where the rocks have long been wasted by slow decay.
"Some evidence of a second and lower erosion plane is seen in the accordant level of the long lateral spurs that separate the valleys of the creeks tributary to Upper Iowa river. The crests of these spurs, which are capped by the Saint Peter sandstone, fall into a common plane about 1,100 feet above sea level, and thus lie distinctly below the level of the upland. Measured by the distance be- tween the escarpments of the Galena and Platteville limestones of the upland. the width of the valley floor of the Upper Iowa, developed 1, 100 feet above sea level, was about ten miles. In age the planation of this valley floor would seem to correspond with that of the similar peneplain of the second generation devel- oped at Dubuque on the weak Maquoketa shale. In each place, however, an- other explanation may be found in cliff recession under weathering. In Alla- makee county the Galena-Platteville escarpment may be supposed to have re- treated because of the weak Saint Peter sandstone on which it rests and which caps the ridges defining the 1,000-foot level ; and in Dubuque county the Niagaran escarpment may be held to have receded in a similar manner because of the un- dermining of the immediately subjacent Maquoketa shale."
The lowest and consequently the oldest rock exposed in the county is that along the foot of the bluffs from Lansing to New Albin.
A very fine outcrop can be seen just in the rear and to the north of the second business block from the river in Lansing. Here at the south end of a short, low and narrow ridge is a vertical section of sixty feet of sandy shales and clays of shades of dirty yellow, brown, red, gray, and green. These shales are quite firmly bedded in the hill, but on exposure to the atmosphere disintegrate and fall to pieces.
They have no economic value except as a surface dressing for clay roads, for which purpose they are excellent, forming a firm smooth surface. No fossils are found in this formation, which extends down to and for 700 feet below the surface of the river as shown by the record of the strata encountered in drill- ing the city artesian well.
It rests unconformably on a hard crystalline quartzite. Above the formation described lies twenty-five feet of a harder bedded rock that has been quarried to some extent for building purposes.
1
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The entire 825 feet from the quartzite to the harder quarry beds has been given the name of the Dresbach sandstone. This is the western equivalent of the old Potsdam sandstone of New York. It outcrops along the valley of the Mis- sissippi from New Albin to near Heytmans where the dip carries it below the level of the river. It also can be seen as far up the valley of the Oneota as sec- tion 6, township 99, range 5, Union City township, where there is an outcrop beside the highway in a gorge a few rods west of Mr. Regan's.
This is the rock from which the water of the flowing wells at Lansing, New Albin, and in the valley of the Oneota, comes the interstices between the sand grains forming a vast reservoir having the hard impenetrable quartzite for its bottom. In the Oneota valley artesian water will rise but a few feet above the top of this formation.
Above the quarry beds over the Dresbach is twenty feet of a formation yellow in color, described by Calvin as "horizontally laminated, fine in texture, quite dis- tinctly calcareous (formed of lime) and easily split into thin leaves along the planes of lamination." This is the St. Lawrence limestone of the Minnesota geologists, and the quarry beds below should probably be included with it under the same name. In it are found the fossil impressions of a trilobite, an ancient animal having a little resemblance to a crawfish without the claws. Also what may have been a giant sponge, three or more feet across and a foot or more high.
A fine exposure containing the characteristic fossils of this formation is found on the top of the hill of Dresbach at Lansing.
Above the St. Lawrence limestone lies another bed of sand called the Jordan sandstone. At Lansing the top of this bed lies 100 feet above the top of the exposed St. Lawrence which would make the sandstone 100 feet thick, but as the rock forming the bluff side for forty feet above the St. Lawrence ledge is concealed by a covering of loose rock and soil it is more than likely that the sandstone is not so thick, but that the St. Lawrence is thicker than the part that can be seen. Except near the top, the Jordan is a deposit of incoherent sand, in places having numerous harder, very irregular layers, that when the softer part is washed or blown away, form very curious designs and figures in relief, a common one in cliff faces being that of a giant hour glass. Occasionally these concretionary forms are very regular, taking the form of almost perfect spheres, from the size of a marble up to those having a diameter of a foot or more. Where such occur they are often found washed out in numbers and strewn along on the bottom of the drainage ravines cutting the formation.
Farther south towards the central part of the state, where the dip has carried this sand bed several hundred feet below the surface, it is one of the notable reservoirs for artesian water. But in Allamakee it is too high to afford flowing wells, though in the central, western and southern part of the county, deep wells find in it an abundance of water but not artesian.
Near the top the grains of sand are usually very coarse. The formation is barren of fossils, and has no economic value except for use in making mortar.
Above the Jordan lie beds of impure limestone alternating with sandy layers gradually changing to heavy beds of pure limestone. At places cherty or flinty strata are to be found with some quartzite. These beds, having a total thickness of around 200 feet, were given the name of Oneota limestone by Professor
CORALS FROM DECORAIL SHALES
1-Stroptelasma cornienlum. 2-Praspora. 3-Branching forms, species not de- termined. No. 1 is a true coral; Nos. 2 and 3 are Bryozoan corals,
VURLID
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Calvin because they form the conspicuous vertical cliffs and escarpments along that stream from near its mouth westward to and beyond the boundary line of the county. This was the lower Magnesian limestone of the older geologists.
The upper heavy beds afford an abundant and convenient supply of excellent building stone. Quarries have been opened in them at New Albin, Lansing, near Dorchester and in many other places.
Scattered abundantly through the rock at a horizon near the center, are very thin veins, layers and incrustations of iron ore, often beautifully crystallized, but so much diffused through the rock as to be of no commercial value. Asso- ciated with it is much crystallized calcite, a rock having the appearance of milky glass, but soft enough to scratch with the point of a knife.
Lead, too, is found in it in places. Many years ago prospectors found this ore in the hills along Mineral creek, in section 13, of Hanover township. It is said that about one hundred thousand pounds were taken out of crevices at this place. But the crevices "pinched out," and no more being found, the miners went their ways, the cabins disappeared, and all that is now known about it is but little more than a tradition.
About the year 1891, Capt. J. M. Turner, discovered on the northwest quarter of the northeast quarter of section 10, township 99, range 4, about six miles northwest of Lansing, a lead bearing north and south vertical crevice which on development proved to have a length of 1,200 feet and a maximum depth of seventy-five feet, and from which about five hundred thousand pounds of ore was mined by a local company.
The vertical sheet of mineral was about three inches in thickness, having generally, a very considerable residual product (geest) on each side between it and the body wall. The interior of the ore body was a lead sulphide, the out- side being a carbonate.
While float ore has been picked up in many different places in the northern part of the county where the Oneota outcrops, no other crevices containing it have been found. Small pieces of zinc carbonate are occasionally found. Few fossils are found in the Oneota except in the cherty layers which occur near the mid- dle of the formation. In this in places, are found some very well preserved fragmental impressions of orthocerata (chambered shellfish), and gasteropods (snails).
The crevices and seams make this a dry rock. In sections of the county immediately underlaid by it, wells usually have to be drilled entirely through it into the Jordan sandstone before finding water.
The dip of the Oneota carries it out of sight near Clayton station midway between McGregor and Guttenberg. In going by train from Waukon Junction to McGregor this dip is very noticeable in the outcrops of ledges of the massive upper strata, along the sides of the Wisconsin bluffs on the opposite side of the river. Beginning at the very tops opposite Harper's Ferry, when the Wisconsin river is reached, they have dropped to near the bases of the bluffs and disappear a few miles below the mouth of that river.
This maker of bold headlands, high precipices, and altogether rugged and picturesque scenery, is succeeded by twenty to twenty-five feet of a thin bedded red sandstone known as the New Richmond Sandstone. The layers of this for- mation, mostly one to three inches in thickness, are formed of a fairly coherent
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red sand, differing from the sand making up the beds of the Dresbach, Jordan and later St. Peter, by having each separate grain surrounded by a coating or incrustation of silica or crystallized quartz, the facets of which make it sparkle in the sunlight. Near the bottom are thicker and much harder strata. in places being beautifully ripple marked. one such locality being in an exposure by the roadside near the southeast corner of Southwest, Northwest, Section 29. Town 98, Range 3, Lafayette township. At the top it is again a close-grained quartzite. The central portion of this sand rock breaks down very easily and is usually covered by gentle slopes of clay and soil and is only seen in ditches and gullies. .A very good exposure of nearly the entire thickness can be seen in the ditch at the side of the road near the top of the llartley hill in Southeast, Southeast, Section 3. Town 99, Range 5.
The change from the Oneota limestone to the New Richmond sand is very abrupt, enough so as to lead to a suspicion of slight unconformity.
So far in the rock formations we have been describing. there is no break in the continuity. One stratum laid down on the old sea bottom was succeeded by another perhaps a little different, deposited under perhaps slightly different con- ditions, but there was no sudden and complete change indicating that deposition under certain conditions had ceased, and after a period, during which the sea bottom had probably been elevated and become dry land and its surface worn and gullied by erosion, had again sunk beneath the waves and deposition commenced anew under changed circumstances, the strata of the new sea bottom being spread continuously over the broken and worn layers of the old.
Where such a condition is shown by the rock exposures it is called an uncon- formity. There is a very decided such unconformity between the Dresbach and the quartzite on which it rests. But from there on, while the old sea over what is now Iowa was very shallow, and there must have been great areas of mud flats and low sandy islands over which the waves washed, no part was above the water for any great length of time and the formation is unbroken and con- tinuous through the Dresbach, the St. Lawrence, the Jordan, and the Oneota. . \t the close of the Oneota there may have been an elevation above the sea for a long enough period to show some of the effects of erosion, after subsidence the New Richmond being laid down on this slightly changed bottom.
The thicker. harder slabs of this rock made good building stone, but are not readily accessible except where washed down into the gullies and ditches. Such rocks are easily recognizable, two to four inches of the center being uncol- ored, while about the same thickness on both the under and upper side of the slab is stained red by oxide of iron.
Superimposed on the New Richmond is the Shakopee limestone, a lime forma- tion quite largely dolomitic, but not usually massive, having but little good quarry stone, and "not showing much tendency to form cliffs." It has an approximate thickness of fifty feet and is chiefly of interest on account of numerous "peculiar structures," at certain horizons that are supposed to be fossils of large animal formations of a very low order called cryptozoons. The very oldest animal or plant remains discovered fossil so far belong to this low order, which may be either plant or animal .- or neither.
Next in the ascending scale is the St. Peter sandstone, so called because of its outcrops being very abundant near St. Peter, Minnesota. This is simply a vast
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bed of incoherent and nearly pure sand having a very uniform thickness of from sixty to one hundred feet, extending southward and westward under Iowa, Illinois, and Southern Wisconsin and Minnesota. There is no bedding or strati- fication except in a few places where, for local reasons unknown, it has been hardened into a firm quartzite, excellent for building purposes. Usually it can be readily dug with a pick and shovel. Exposure to the atmosphere has a ten- dency to harden it so that continuous low cliffs or ledges are common where it outcrops. In places portions of the body harden into domes ten to twenty feet high, underneath which the sand seems even less coherent than usual. Where such domes are cut through by stream valleys, the softer part is often washed out, forming small caves. Such a cave is to be seen beside the public road on southeast, northeast, section 8, town 96, range 5. about one mile south of Forest Mills in Franklin township.
Contrary to the usual opinion this loose sand rock appears to be more resistant to weathering and erosion than the limestone formation beneath and the shales and limestones above. And in the northern and central parts of the county in Waterloo, Hanover, French Creek, Lansing, Center and Lafayette townships, its runs from the main divides between Paint Creek, Village Creek and the Oneota River out along the minor ridges between the numerous tributary stream valleys, in long, narrow tongues, forming a very decided step up from the peneplain or level of the top of the Oneota, of its full thickness. Usually these tongues are capped by a thin veneer of a few feet of Platteville limestone, but nowhere does the limestone approach near to the edge of the vertical scarps of the sandstone, much less over-hang it as it would do were the latter the less resistant.
The dendritic divides described above are marked features of the landscape all along the northern and eastern boundary of the St. Peter.
The dip carries it beneath the river at Guttenberg.
Except near its northeastern limit it is the source of an abundant pure water supply, furnishing artesian wells from Elkader, near its boundary, down to the south central part of the state.
At Clayton, in Clayton county, it has been mined for thirty years on a small scale, and shipped to Clinton and Milwaukee for glass and malleable iron man- ufacture. At this place there seems to be almost no impurity or coloring, what little there is being washed out in moving it by water in a trough several hundred feet, from the pit to the bins beside the railroad. At this place, in 1910, the point of contact with the Shakopee was exposed in the ravine alongside, and from what could be seen there seemed to be unconformity between the two formations.
All along the top of the St. Peter from a few inches to a foot or more, is highly impregnated with iron oxide which has cemented it into a very hard cap stratum very resistant to erosion. At places, like the pictured rocks below McGregor, the oxide seems to have been present in greater abundance and to have penetrated deeply into the formation, coloring it beautiful shades of red, brown, yellow and pink. The side of a cut about one mile northeast of Waukon on the railroad to the Iron Mine shows some fine coloring.
The St. Peter changes very abruptly at its top to a three-foot bed of blue slightly sandy shales containing imperfect fossil bryozoon corals. This is the Glenwood shale, so called because of a number of good exposures studied by Calvin in Glenwood township, Winneshiek county.
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The Glenwood shales again change quite as abruptly as their top to the Platte- ville limestone. This, at the bottom, is often massive and dolomitic for the first four to six feet. Above that it changes to thin, hard beds that break up much in weathering and that contain an abundance of fossil fragments of brachiopods (shellfish, whose shells somewhat resemble those of small clams), corals and gasteropods. These strata, in their turn, near the top of the formation, change to heavy bedded quarry stone, some of which are excellent for building purposes, while others that are solid and firm when freshly quarried crumble on exposure to the action of frost and rain. The rock wall around the courtyard at Decorah is built of this latter kind.
Some layers of these beds are in places composed entirely of comminuted fragments of fossil shells and corals, cemented together into a hard stone. At Decorah a number of years ago such layers were sawed up into slabs and polished, making beautiful "fossil marble," used for mantels, table tops and other such purposes.
The Platteville limestone has a thickness of about fifty feet. Good, partial exposures can be seen in the ravines just north of Waukon, to the west of the Ice Cave at Decorah, near Hesper, where the quarry stone beds have been worked for building purposes for years, and on Yellow river below Myron.
This is the first of the highly fossiliferous formations. Up to this horizon fossils are rare when the whole rock mass is considered, but from this point upward through the succeeding ages, animal life, judging from the fossil remains, was very abundant and of an endless variety.
Beginning with the very lowest forms of life there came into existence suc- cessively, higher and still higher forms culminating finally with man.
The Platteville changes quite abruptly so far as physical appearance is con- cerned, but without great change of fossils, and conformably, to the Decorah shales, a highly fossiliferous bed of clay, shales, and thin strata of limestone, having a thickness of twenty-five to thirty feet. There is an abundance of beau- tifully preserved, complete and unbroken fossils in this bed of shales, the great body of which is made up largely of powdered and broken fragments of corals and shells. The predominating kinds are bryozoon, corals, true corals, brachio- pods, gasteropods, lamellibranchs (clams) and trilobites.
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