USA > Iowa > Lee County > The history of Lee county, Iowa, containing a history of the county, its cities, towns, &c. > Part 11
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In this formation, fossils are abundant, so much so that, in some places, the rock is made up of a mass of shells, corals and fragments of tribolites, cemented by calcareous material into a solid rock. Some of these fossils are new to science and peculiar to Iowa.
The Galena Limestone .- This is the upper formation of the Trenton group. It seldom exceeds twelve miles in width, although it is fully one hundred and fifty miles long. The ontcrop traverses portions of the counties of Howard, Winnesheik, Allamakee, Fayette, Clayton, Dubuque and Jackson. It exhibits its greatest development in Dubuque County. It is nearly a pure dolomite, with a slight admixture of silicious matter. It is usually unfit for dressing,
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HISTORY OF THE STATE OF IOWA.
though sometimes near the top of the bed good blocks for dressing are found. This formation is the source of the lead ore of the Dubuque lead mines. The lead region proper is confined to an area of about fifteen miles square in the vicinity of Dubuque. The ore occurs in vertical fissures, which traverse the rock at regular intervals from east to west; some is found in those which have a north and south direction. The ore is mostly that known as Galena, or sul- phuret of lead, very small quantities only of the carbonate being found with it.
CINCINNATI GROUP.
Maquoketa Shales .- The surface occupied by this formation is singularly long and narrow, seldom reaching more than a mile or two in width, but more than a hundred miles in length. Its most southerly exposure is in the bluffs of the Mississippi near Bellevue, in Jackson County, and the most northerly yet recognized is in the western part of Winnesheik County. The whole formation is largely composed of bluish and brownish shales, sometimes slightly arena- ccous, sometimes calcareous, which weather into a tenacious clay upon the sur- face, and the soil derived from it is usually stiff and clayey. Its economic. value is very slight.
Several species of fossils which characterize the Cincinnati group are found in the Maquoketa shales ; but they contain a larger number that have been found anywhere else than in these shales in Iowa, and their distinct faunal char- acteristics seem to warrant the separation of the Maquoketa shales as a distinct. formation from any others of the group.
UPPER SILURIAN SYSTEM.
NIAGARA GROUP.
Niagara Limestone .- The area occupied by the Niagara limestone is nearly one hundred and sixty miles long from north to south, and forty and fifty miles . wide.
This formation is entirely a magnesian limestone, with in some places a con- siderable proportion of silicious matter in the form of chert or coarse flint. A large part of it is evenly bedded, and probably affords the best and greatest amount of quarry rock in the State. The quarries at Anamosa, LeClaire and Farley are all opened in this formation.
DEVONIAN SYSTEM. HAMILTON GROUP.
Hamilton Limestone .- The area of surface occupied by the Hamilton lime- stone and shales is fully as great as those by all the formations of both Upper and Lower Silurian age in the State. It is nearly two hundred miles long and from forty to fifty miles broad. The general trend is northwestward and south- eastward.
Although a large part of the material of this formation is practically quite worthless, yet other portions are valuable for economic purposes ; and having a
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HISTORY OF THE STATE OF IOWA.
large geographical extent in the State, is one of the most important formations, in a practical point of view. At Waverly. Bremer County, its value for the production of hydraulic lime has been practically demonstrated. The heavier and more uniform magnesian beds furnish material for bridge piers and other material requiring strength and durability.
All the Devonian strata of Iowa evidently belong to a single epoch, and re- ferable to the Hamilton, as recognized by New York geologists.
The most conspicuous and characteristic fossils of this formation are bra- chiopod, mollusks and corals. The coral Acervularia Davidsoni occurs near Iowa City, and is known as "Iowa City Marble." and " bird's-eye marble."
CARBONIFEROUS SYSTEM.
Of the three groups of formations that constitute the carboniferous system, viz., the subcarboniferous, coal measures and permian. only the first two are found in Iowa.
SUBCARBONIFEROUS GROUP.
The area of the surface occupied by this group is very large. Its eastern border passes from the northeastern part of Winnebago County, with consider- able directness in a southeasterly direction to the northern part of Washington County. Here it makes a broad and direct bend nearly eastward, striking the Mississippi River at Muscatine. The southern and western boundary is to a considerable extent the same as that which separates it from the coal field. From the southern part of Pocahontas County it passes southeast to Fort Dodge, thence to Webster City, thence to a point three or four miles northeast of El- dora, in Hardin County, thence southward to the middle of the north line of Jasper County. thence southeastward to Sigourney, in Keokuk County, thence to the northeastern corner of Jefferson County, thence sweeping a few miles eastward to the southeast corner of Van Buren County. Its area is nearly two hundred and fifty miles long, and from twenty to fifty miles wide.
The Kinderhook Beds .- The most southerly exposure of these beds is near the mouth of Skunk River, in Des Moines County. The most northerly now known is in the eastern part of Pocahontas County, more than two hundred miles distant. The principal exposures of this formation are along the bluffs which border the Mississippi and Skunk Rivers, where they form the eastern and northern boundary of Des Moines County, along English River, in Wash- ington County ; along the Iowa River, in Tama, Marshall. Hamlin and Frank- lin Counties : and along the Des Moines River, in Humboldt County.
The economic value of this formation is very considerable, particularly in the northern portion of the region it occupies. In Pocahontas and Humboldt Counties it is almost invaluable, as no other stone except a few boulders are found here. At Iowa Falls the lower division is very good for building pur- poses. In Marshall County all the limestone to be obtained comes from this formation, and the quarries near LeGrand are very valuable. At this point
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HISTORY OF THE STATE OF IOWA.
some of the layers are finely veined with peroxide of iron, and are wrought into ornamental and useful objects.
In Tama County, the oolitic member is well exposed, where it is manufac- tured into lime. It is not valuable for building, as upon exposure to atmosphere and frost, it crumbles to pieces.
The remains of fishes are the only fossils yet discovered in this formation that can be referred to the sub-kingdom VERTEBRATA; and so far as yet recog- nized, they all belong to the order selachians.
Of ARTICULATES, only two species have been recognized, both of which belong to the genus phillipsia.
The sub-kingdom MOLLUSCA is largely represented.
The RADIATA are represented by a few crinoids, usually found in a very im- perfect condition .. The sub-kingdom is also represented by corals.
The prominent feature in the life of this epoch was molluscan ; so much so in fact as to overshadow all other branches of the animal kingdom. The pre- vailing classes are : lamellibranchiates, in the more arenaceous portions ; and brachiopods, in the more calcareous portions.
No remains of vegetation have been detected in any of the strata of this formation.
The Burlington Limestone .- This formation consists of two distinct calca- reous divisions, which are separated by a series of silicious beds. Both divi- sions are eminently crinoidal.
The southerly dip of the Iowa rocks carries the Burlington limestone down, so that it is seen for the last time in this State in the valley of Skunk River, near the southern boundary of Des Moines County. The most northerly point at which it has been recognized is in the northern part of Washington County. It probably exists as far north as Marshall County.
This formation affords much valuable material for economic purposes. The upper division furnishes excellent common quarry rock.
The great abundance and variety of its fossils-crinoids-now known to be more than three hundred, have justly attracted the attention of geologists in all parts of the world.
The only remains of vertebrates discovered in this formation are those of fishes, and consist of teeth and spines ; bone of bony fishes, like those most common at the present day, are found in these rocks. On Buffington Creek, in Louisa County, is a stratum in an exposure so fully charged with these remains that it might with propriety be called bone breccia.
Remains of articulates are rare in this formation. So far as yet discovered, they are confined to two species of tribolites of the genus phillipsia.
Fossil shells are very common.
The two lowest classes of the sub-kingdom radiata are represented in the genera zaphrentis, amplexus and syringapora, while the highest class-echino- derms-are found in most extraordinary profusion.
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HISTORY OF THE STATE OF IOWA.
The Keokuk Limestone .- It is only in the four counties of Lee, Van Buren, Henry and Des Moines that this formation is to be seen.
In some localities the upper silicious portion of this formation is known as the Geode bed. It is not recognizable in the northern portion of the formation, nor in connection with it where it is exposed, about eighty miles below Keokuk.
The geodes of the Geode bed are more or less spherical masses of silex, usually hollow and lined with crystals of quartz. The outer crust is rough and unsightly, but the crystals which stud the interior are often very beautiful. They vary in size from the size of a walnut to a foot in diameter.
The economic value of this formation is very great. Large quantities of its stone have been used in the finest structures in the State, among which are the post offices at Dubuque and Des Moines. The principal quarries are along the banks of the Mississippi, from Keokuk to Nauvoo.
The only vertebrate fossils found in the formation are fishes, all belonging to the order selachians, some of which indicate that their owners reached a length of twenty-five or thirty feet.
Of the articulates, only two species of the genus phillipsia have been found in this formation.
Of the mollusks, no cephalopods have yet been recognized in this formation in this State ; gasteropods are rare ; brachiopods and polyzoans are quite abundant.
Of radiates, corals of genera zaphrentes, amplexus and aulopera are found, but crinoids are most abundant.
Of the low forms of animal life, the protozoans, a small fossil related to the sponges, is found in this formation in small numbers.
The St. Louis Limestone .- This is the uppermost of the subcarboniferous group in Iowa. The superficial area it occupies is comparatively small, because it consists of long, narrow strips, yet its exten+ is very great. It is first seen resting on the geode division of the Keokuk limestone, near Keokuk. Pro- ceeding northward, it forms a narrow border along the edge of the coal fields in Lee, Des Moines, Henry, Jefferson, Washington, Keokuk and Mahaska Counties. It is then lost sight of until it appears again in the banks of Boone River, where it again passes out of view under the coal measures until it is next seen in the banks of the Des Moines, near Fort Dodge. As it exists in Iowa, it consists of three tolerably distinct subdivisions-the magnesian, arena- ceous and calcareous.
The upper division furnishes excellent material for quicklime, and when quarries are well opened, as in the northwestern part of Van Buren County, large blocks are obtained. The sandstone, or middle division, is of little economic value. The lower or magnesian division furnishes a valuable and durable stone, exposures of which are found on Lick Creek, in Van Buren County, and on Long Creek, seven miles west of Burlington.
Of the fossils of this formation, the vertebrates are represented only by the remains of fish, belonging to the two orders, selachians and ganoids. The
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HISTORY OF THE STATE OF IOWA.
articulates are represented by one species of the trilobite, genus phillipsia, and two ostracoid, genera, cythre and beyricia. The mollusks distinguish this formation more than any other branch of the animal kingdom. Radiates are exceedingly rare, showing a marked contrast between this formation and the two preceding it.
The rocks of the subcarboniferous period have in other countries, and in other parts of our own country, furnished valuable minerals, and even coal, but in Iowa the economic value is confined to its stone alone.
The Lower Silurian, Upper Silurian and Devonian rocks of Iowa are largely composed of limestone. Magnesia also enters largely into the subcarbon- iferous group. With the completion of the St. Louis limestone, the production of the magnesian limestone seems to have ceased among the rocks of Iowa.
Although the Devonian age has been called the age of fishes, yet so far as Iowa is concerned, the rocks of no period can compare with the subcarbon- iferous in the abundance and variety of the fish remains, and, for this reason, the Burlington and Keokuk limestones will in the future become more famous among geologists, perhaps, than any other formations in North America.
It will be seen that the Chester limestone is omitted from the subcarbon- iferous group, and which completes the full geological series. It is probable the whole surface of Iowa was above the sea during the time of the formation of the Chester limestone to the southward about one hundred miles.
At the close of the epoch of the Chester limestone, the shallow seas in which the lower coal measures were formed again occupied the land, extending almost as far north as that sea had done in which the Kinderhook beds were formed, and to the northeastward its deposits extended beyond the subcarbon- iferous groups, outlines of which are found upon the next, or Devonian rock.
THE COAL-MEASURE GROUP.
The coal-measure group of Iowa is properly divided into three formations, viz., the lower, middle and upper coal measures, each having a vertical thick- ness of about two hundred feet.
A line drawn upon the map of Iowa as follows, will represent the eastern and northern boundaries of the coal fields of the State: Commencing at the southeast corner of Van Buren County, carry the line to the northeast corner of Jefferson County by a slight easterly curve through the western portions of Lee and Henry Counties. Produce this line until it reaches a point six or eight miles northward from the one last named, and then carry it northwest- ward, keeping it at about the same distance to the northward of Skunk River and its north branch that it had at first, until it reaches the southern boundary of Marshall County, a little west of its center. Then carry it to a point
128
HISTORY OF THE STATE OF IOWA.
three or four miles northeast from Eldora, in Hardin County ; thence west- ward to a point a little north of Webster City, in Hamilton County; and thence further westward to a point a little north of Fort Dodge, in Webster County.
Lower Coal Measures .- In consequence of the recedence to the southward of the borders of the middle and upper coal measures, the lower coal measures alone exist to the eastward and northward of Des Moines River. They also occupy a large area westward and southward of that river, but their southerly dip passes them below the middle coal measures at no great distance from the river.
No other formation in the whole State possesses the economic value of the lower coal measures. The clay that underlies almost every bed of coal furnishes a large amount of material for potters' use. The sandstone of these measures is usually soft and unfit, but in some places, as near Red Rock, in Marion County, blocks of large dimensions are obtained which make good building material, samples of which can be seen in the State Arsenal, at Des Moines. On the whole, that portion of the State occupied by the lower coal measures, is not well supplied with stone.
But few fossils have been found in any of the strata of the lower coal meas- ures, but such animal remains as have been found are without exception of marine origin.
Of fossil plants found in these measures, all probably belong to the class acrogens. Specimens of calamites, and several species of ferns, are found in all of the coal measures, but the genus lepidodendron seems not to have existed later than the epoch of the middle coal measures.
Middle Coal Measures .- This formation within the State of Iowa occupies a narrow belt of territory in the southern central portion of the State, embrac- ing a superficial area of about fourteen hundred square miles. The counties more or less underlaid by this formation are Guthrie, Dallas, Polk. Madison, Warren, Clarke, Lucas, Monroe, Wayne and Appanoose.
This formation is composed of alternating beds of clay. sandstone and lime- stone, the clays or shales constituting the bulk of the formation, the limestone occurring in their bands, the lithological peculiarities of which offer many con- trasts to the limestones of the upper and lower coal measures. The formation is also characterized by regular wave-like undulations, with a parallelism which indicates a widespread disturbance, though no dislocation of the strata have been discovered.
Generally speaking, few species of fossils occur in these beds. Some of the shales and sandstone have afforded a few imperfectly preserved land plants- three or four species of ferns, belonging to the genera. Some of the carbonif- erous shales afford beautiful specimens of what appear to have been sea-weeds. Radiates are represented by corals. The mollusks are most numerously repre- sented. Trilobites and ostracoids are the only remains known of articulates.
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HISTORY OF THE STATE OF IOWA.
Vertebrates are only known by the remains of salachians, or sharks, and ganoids.
Upper Coal Measures .- The area occupied by this formation in Iowa is very great, comprising thirteen whole counties, in the southwestern part of the State. It adjoins by its northern and eastern boundaries the area occupied by the middle coal measures.
The prominent lithological features of this formation are its limestones, yet it contains a considerable proportion of shales and sandstones. Although it is known by the name of upper coal measures, it contains but a single bed of coal, and that only about twenty inches in maximum thickness.
The limestone exposed in this formation furnishes good material for building as in Madison and Fremont Counties. The sandstones are quite worthless. No beds of clay for potter's use are found in the whole formation.
The fossils in this formation are much more numerous than in either the middle or lower coal measures. The vertebrates are represented by the fishes of the orders selachians and ganoids. The articulates are represented by the trilobites and ostracoids. Mollusks are represented by the classes cephalapoda, gasteropoda, lamelli, branchiata, brachiapoda and polyzoa. Radiates are more numerous than in the lower and middle coal measures. Protogoans are repre- sented in the greatest abundance, some layers of limestone being almost entirely composed of their small fusiform shells.
CRETACEOUS SYSTEM.
There being no rocks, in Iowa, of permian, triassic or jurassic age, the next strata in the geological series are of the cretaceous age. They are found in the western half of the State, and do not dip, as do all the other formations upon which they rest, to the southward and westward, but have a general dip of their own to the north of westward, which, however, is very slight. Although the actual exposures of cretaceous rocks are few in Iowa, there is reason to believe that nearly all the western half of the State was originally occupied by them ; but being very friable, they have been removed by denuda- tion, which has taken place at two separate periods. The first period was during its elevation from the cretaceous sea, and during the long tertiary age that passed between the time of that elevation and the commencement of the glacial epoch. The second period was during the glacial epoch, when the ice produced their entire removal over considerable areas.
It is difficult to indicate the exact boundaries of these rocks ; the following will approximate the outlines of the area :
From the northeast corner to the southwest corner of Kossuth County ; thence to the southeast corner of Guthrie County; thence to the southeast corner of Cass County; thence to the middle of the south boundary of Mont- gomery County ; thence to the middle of the north boundary of Pottawattamie County; thence to the middle of the south boundary of Woodbury County ;
*
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HISTORY OF THE STATE OF IOWA.
thence to Sergeant's bluffs ; up the Missouri and Big Sioux Rivers to the northwest corner of the State; eastward along the State line to the place of beginning.
All the cretaceous rocks in Iowa are a part of the same deposits farther up the Missouri River, and in reality form their eastern boundary.
Nishnabotany Sandstone .- This rock has the most easterly and southerly extent of the cretaceous deposits of Iowa, reaching the southeastern part of Guthrie County and the southern part of Montgomery County. To the north- ward, it passes beneath the Woodbury sandstones and shales, the latter passing beneath the inoceramus, or chalky, beds. This sandstone is, with few excep- tions, almost valueless for economic purposes.
The only fossils found in this formation are a few fragments of angiosper- mous leaves.
Woodbury Sandstones and Shales .- These strata rest upon the Nishna- botany sandstone, and have not been observed outside of Woodbury County, hence their name. Their principal exposure is at Sergeant's Bluffs, seven miles below Sioux City.
This rock has no value except for purposes of common masonry.
Fossil remains are rare. Detached scales of a lepidoginoid species have been detected, but no other vertebrate remains. Of remains of vegetation, leaves of salix meekii and sassafras cretaceum have been occasionally found.
Inoceramus Beds .- These beds rest upon the Woodbury sandstones and shales. They have not been observed in Iowa, except in the bluffs which border the Big Sioux River in Woodbury and Plymouth Counties. They are composed almost entirely of calcareous material, the upper portion of which is extensively used for lime. No building material is to be obtained from these beds; and the only value they possess, except lime, are the marls, which at some time may be useful on the soil of the adjacent region.
The only vertebrate remains found in the cretaceous rocks are the fishes. Those in the inoceramus beds of Iowa are two species of squoloid selachians, or cestratront, and three genera of teliosts. Molluscan remains are rare.
PEAT.
Extensive beds of peat exist in Northern Middle Iowa, which, it is esti- mated, contain the following areas :
Counties.
Acres.
Cerro Gordo
1,500
Worth
2,000
Winnebago
2,000
Hancock
1,500
Wright ..
500
Kossuth
700
Dickinson
80
Several other counties contain peat beds, but the character of the peat is inferior to that in the northern part of the State. The character of the peat
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HISTORY OF THE STATE OF IOWA.
named is equal to that of Ireland. The beds are of an average depth of four feet. It is estimated that each acre of these beds will furnish two hundred and fifty tons of dry fuel for each foot in depth. At present, owing to the sparse- ness of the population, this peat is not utilized ; but, owing to its great distance from the coal fields and the absence of timber, the time is coming when their value will be realized, and the fact demonstrated that Nature has abundantly compensated the deficiency of other fuel.
GYPSUM.
The only deposits of the sulphates of the alkaline earths of any economic value in Iowa are those of gypsum at and in the vicinity of Fort Dodge, in Webster County. All others are small and unimportant. The deposit occupies a nearly central position in Webster County, the Des Moines River running nearly centrally through it, along the valley sides of which the gypsum is seen in the form of ordinary rock cliff and ledges, and also occurring abundantly in similar positions along both sides of the valleys of the smaller streams and of the numerous ravines coming into the river valley.
The most northerly known limit of the deposit is at a point near the mouth of Lizard Creek, a tributary of the Des Moines River, and almost adjoining the town of Fort Dodge. The most southerly point at which it has been found exposed is about six miles, by way of the river, from this northerly point before mentioned. Our knowledge of the width of the area occupied by it is limited by the exposures seen in the valleys of the small streams and in the ravines which come into the valley within the distance mentioned. As one goes up these ravines and minor valleys, the gypsum becomes lost beneath the over- lying drift. There can be no doubt that the different parts of this deposit, now disconnected by the valleys and ravines having been cut through it, were orig- inally connected as a continuous deposit, and there seems to be as little reason to doubt that the gypsum still extends to considerable distance on each side of the valley of the river beneath the drift which covers the region to a depth of from twenty to sixty feet.
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