II. Geology and Topography (original) (raw)

II. Geology and Topography

History of Hamilton County Ohio
pages 12-20
transcribed by Tina Hursh

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~ pg 12 ~

Chapter II.
GEOLOGY AND TOPOGRAPHY

There was life in the valley of the Ohio untold ages before man came to gaze upon its beautiful hills and waters. Away back in the stately march of the geologic epochs, the Silurian seas here swarmed with animate existence, many of its forms so small that the aid of the microscope is needed to trace them; and some so numerous that great and valuable layers of rock are composed almost wholly of their remains. The history of the countless varieties of sentient life that so abounded here aeons on aeons ago may be read for us only in the rocks of the valley and the hills. It is otherwise unwritten, except in the books of their Creator. Industrious inquirers, working slowly and carefully through many years, have traced the forms of them, have given them names, and catalogued them. It does not fall within the province of this work to present a list of these. It may suffice for our purposes to say that the paleontological catalogue published within two or three years by Professor MICKLEBOROUGH, of the Cincinnati normal school, and Professor WETHERBY, of the University of Cincinnati, represents no vertebrate, and their presence in the rocks of Hamilton county is exceedingly rare; but from the sub-kingdoms are presented fifty-seven species of annulosa (besides seventy-eight undetermined), one hundred and forty-five of mollusca, one hundred and thirty-nine of molluscoida, sixty-three of coelenterata, and nine of protozoa, besides sixteen species representing, in a very small way, the vegetable kingdom.

The prominent topographical features of hamilton county divide the surface into two main divisions-highland and lowland.

The first division embraces all the higher table-lands of the county, which have a general elevation of two to five hundred feet above low-water at Cincinnati. Al of these areas, though often covered with superficial drift deposits, are underlain with bedded rock, which is everywhere easily accessible, and which impresses peculiar features upon the face of the districts that contain it.

To the second division are referred the valleys of the county, and not only those which hold the present rivers, but also those in which no streams of considerable size are now found, but which are due to the eroding agencies of an earlier day. Both of the classes of valleys are often filled with heavy accumulations of drift, but they agree in being destitute of bedded rock-except at the levels of the streams they contain, or, as is often the case, at considerably lower levels.

The thickness of the drift beds does not generally exceed one hundred feet, and thus it will be seen that in the Ohio valley the lowlands have a maximum elevation of one hundred feet above low-water at Cincinnati; but as we follow back the Miamis and the lesser streams, we find these beds assuming higher elevations, as the floor of the county that sustains them is gradually elevated, so that they sometimes attain, in the northern and eastern portions of the county, a height of one hundred and fifty or even two hundred feet above the same base.

In other words, the highlands of the county are the areas in which the bedded rocks remain, to an elevation of three hundred feet and more above the Ohio river, while the lowlands are those areas from which the rocks

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have been removed, at least to the existing rivers and lesser streams.

The slopes that connect these two kinds of areas are commonly precititous, as in the river-hills of Cincinnati; but sometimes the descent is broken by the imposition of drift deposits.

The valley of the Ohio, which here runs in an east and west direction, makes the southern boundary of the county, and, though deep, is comparatively narrow. Several of the north and south valleys that traverse the county are absolutely wider than the Ohio valley; and when the volumes of the streams that they contain are taken into account, the disproportion between them and the first-named valley is very great. A similar state of facts obtains through southwestern Ohio-the valleys that trend to the west of north especially having been excavated on an ampler scale than the rest, other things being equal. These facts seem to point to glacial erosion as a prominent cause in the production of the surface features ot the county, as the glaciers are known by the strae they have left to have advanced from the northwest.

An examination of the map of the county,1in the light of the facts already known, will serve to show, what an acquaintance with it abundantly confirms, that is surface has suffered a vast amount of erosion. the most interesting facts in this connection Are not the valleys which are occupied by the greater streams of to-day, but those deep and wide valleys that are at present either entirely deserted by water-courses or traversed by insignificant streams, wholly inadequate to account for the erosion of which they have availed themselves. Attention will be called to one or two instances of this sort.

The broad valley now occupied in part of Mill creek, and in part left entirely unoccupied, extends continuously from the present valley of the Great Miami at Hamilton to the Clifton hills, just north of Cincinnati, where it divides into two branches-one passing to the north and east of the city, and entering the valley of the Little Miami between Red Bank station and Plainville-while the other branch, the present valley of Mill creek, passes directly to the Ohio through the site of the city of Cincinnati.

No rocky barriers-nothing, in fact, but the same drift terraces that make the walls of its present course-shut out the Great Miami from entering the Ohio valley at the same points where the Little Miami and Mill creek now enter. Indeed, there is the best of reasons for believing that it has followed, in the pat mutations of its history, those very courses to the great valley. Mill creek has taken possession of the middle portions of this valley, but has never occupied more than one of its lower branches, that one the narrower.

The most striking examples of this erosion of an earlier day are to be found, however, on the western side of the county, and are, for the most part, to be referred to the same river whose agency has already been invoked.

There is an open cut, at least two miles wide, in the northeastern part of Crosby township, which bears due westward from the present course of the Great Miami. Near the west line of the township this old channel is deflected to the southward, and is thenceforward occupied by the Dry fork of Whitewater, until it is merged in the valley of this last-named river. That the streams which hide themselves in this great valley to-day have had next ot nothing to do with its excavation, is evident from the fact that there is not one of them whose course agrees with the direction of the valley, but all cut across it transversely. More than half of the townships of Crosby, Harrison, and Whitewater have been thus worn away and made to give bed to the rivers in the successive stages of their history. The channel above named can be confidently set down as another of the earlier courses of the Great Miami.

Still a third of these old channels, more interesting in some respects than either of the two just named, if found near Cleves, Miami township. By the reference to the map, it will be observed that the river here approaches within a mile of the Ohio; but' instead of entering the great valley at this point, it makes an abrupt detour to the west and south, and only reaches its destination after a circuit of ten miles. Its approach to the Ohio at Cleves is blocked by a ridge that is interposed, one hundred and fifty to two hundred and seventy-five feet in height. A tunnel that was carried through this ridge, in the construction of the Whitewater Valley canal, and which is at present used by the Indianapolis & Cincinnati railroad, shows it to be composed of glacial drift. the direction of this channel is in the line in which the glacier advanced, so that it existence can be quite plausibly ascribed to the great agents of denudation. Whether or not the origin of this channel can be referred to the glacial period, its closure was certainly effected there.

It tasks the imagination to account for the excavation of these broad and deep valleys by existing erosive agencies, even when they are reinforced by the important additions of glacial ice; but to agencies identical with these the work must be referred. There is no evidence, as has already been shown, of minor flexures or axes of disturbance in the Blue Limestone region, by which the strata could have been thrown into hills and valleys; but, on the contrary, the beds are found to occur in unbroken regularity, being affected only by the slight general dip, of which account has been previously given. It is scarcely necessary to say that opposite sides of valleys give every possible proof of having been originally continuous, the sections which adjacent exposures furnish being absolutely identical in their leading features.

The Cincinnati group has been found to demand for its original formation long-continued cycles of peaceful growth and deposition, and in likes manner the fashioning of its bed into the present topographical features of the country must have been in progress through such protracted ages that the historic period in comparison shrinks into insignificance.

[The correctness or necessity of the appellation, "Cincinnati group," which often occurs in the geological reports, is gravely doubted by the local geologists. In January,

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1879, a committee of ten, headed by S.A. MILLER, esp., reported to the Cincinnati Society of Natural History "that the fossils found in the strata for twenty feet or more, above low-water mark of the Ohio river, in the first ward of the city of Cincinnati, and on Crawfish creek, in the eastern part of the city, and in Taylor's creek, east of Newport, Kentucky, at an elevation of more than fifty feet above low-water mark in the Ohio river, indicate the age of the Utica Slate group of New York. A fauna is represented in these rocks that is not found above or below them. Moreover, brown shales and greenish blue shales and concretionary nodules give a lithological character to the strata which distinguishes them from the strata both above and below." Al strata containing triarthrus becki, the committee hold, are to be referred to the age of the Utica Slate group of New York. Above its range is the Hudson River group. The Trenton group is not exposed at Cincinnati nor in the Ohio valley anywhere west of the city, but is probably represented in the rocks of Ohio a few miles east of that point. The Utica group is not represented elsewhere in Ohio. All the lower Silurian rocks in southwestern Ohio belong to the Hudson River group, except the small exposure of the Utica slate in the banks of the ohio and east of the city in the immediate vicinity of the river. The committee therefore report that the name "Cincinnati group" should be dropped, "not only because it is a synonym, but because its retention can subserve no useful purpose in the science, and because it will in the future, as in the past, lead to erroneous views and fruitless discussions." Investigation, so far, they add, has not fed to any other or further sub-divisions than those formerly adopted.]

Strictly speaking, there are no hills in Hamilton county, the surface being all referable to the table-lands and to the valleys worn in them. What are called the Cincinnati hills, for example, are merely the isolated remnants of the old plateau, which have so far escaped the long-continued denudation. Indeed, the highlands of the county are all of them outliers or insulated masses, surrounded on every side by the valleys of existing rivers, along the deep excavations wrought out by these streams at an earlier date and under somewhat different geographical conditions. These islands of the higher ground vary in area between quite wide limits, some of them containing a few scores of acres, and others as many square miles.

The high ground immediately appertaining to Cincinnati furnishes a good example of these outliers. By reference to the map, the insulation of this high found will be seen to the map, the insulation of this high ground will be seen to be perfectly effected by the Little Miami valley, the Ohio valley, the Mill Creek valley, and the abandoned channel of the Great Miami, already described, on the northern and eastern sided. Very important consequences result to the city from this insulation. It follows, for instance, that there are but two natural ways of ingress to the city by lowland, or, in other words, that there are but two railroad routes possible-one by the Ohio valley and the other by the Mill Creek valley. Both of these are circuitous and in other respects unfavorable, especially as ways of approach from the east. These difficulties have led to the project of reaching the business center of the city by a tunnel from the northern valley.

The Dayton Short Line railroad encounters, near West Chester, one of these outliers in its route, which necessitates a grade of forty-five feet to the mile at this point-the highest grad, in fact, on this line (New York Central) between tidewater and the Ohio river.

Another very noticeable outlier is found a mile west of North Bend. The Ohio & Mississippi railroad skirts it on the Ohio valley side, while the Indianapolis & Cincinnati road passes to the north of it, through the old glacial channel, which had already been described.

II. Bedded Rocks, and their Economical Products.

The upper division of the Blue Limestone or the Lebanon beds has never been found in Hamilton county. The lower boundary of the Cincinnati group has not yet been definitely fixed, but enough is known to make it certain that it is not found among the surface rocks of Ohio. The approximate place in the general geological scale of the strata exposed in the hills of Cincinnati has long been known. For the last forty years, at least, they have been referred to the later divisions of Lower Silurian Lime and recognized as belonging to the Hudson or Hudson River group of the New York geologists and of the general geological scale of the country.

The Cincinnati beds proper come next in order after the Point Pleasant beds, in Clermont county, which are the lowest rocks of the series in the State. They have for their inferior limit low-water in the Ohio and for an upper boundary the highest stratum found in the Cincinnati hills. The greatest evaluation above low-water in the immediate vicinity of Cincinnati is given by the city engineer as four hundred and sixty-five feet. Abating fifteen feet for the drift covering of the surface, we can certainly find forty-five feet of bedded rock in this division, almost every foot of which lies open to study within the city limits. The only stratum, however, that admits of easy identification, lies at an elevation of four hundred and twenty-five feet above the river; and this is accordingly assumed as the upper limit of this division.

Upon differences in lithological character, with which also changes in fossil contents ally themselves, a subdivision of the cincinnati beds is possible into three groups, which may be named respectively, in ascending order, the River Quarry beds, the Middle Shales, and the Hill Quarry beds. The first of these subdivisions has a thickness of fifty feet, the second of two hundred and fifty feet, and the third on one hundred and fifty feet.

Above the highest stratum of the Cincinnati hills and the lowermost beds of the Upper Silurian age, three hundred feet of rock intervene, that belong unmistakably to the same formation, being connected with it by identity in lithological character and by a large number of common fossils. These upper beds are nowhere found within twenty miles of Cincinnati, and yet there has never been the slightest hesitation in referring them to the same series to which the rocks there exhibited belong.

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The names assigned, it will be remembered, to the three divisions recognized here, are in ascending order:
The River Quarry Beds;
The Middle, or Eden Shales;
The Hill Quarry Beds.

No explanation is necessary of the first and the last of these names. To the intervening division a name can properly be assigned, derived from the name of the park on the eastern side of the city, in the grading of which so great a display of this division is made. this division can, therefore, be styled the Eden Shales, from the Eden park.

The whole series of the Cincinnati group is composed of alternating beds of limestone and shale. the shale is more commonly known under the name of blue clay; and this designation, is not inappropriate. It is sometimes styled marl or marlite, and the use of the latter designation is also justified by its composition. the most objectionable term by which it is characterized, is soapstone, at this name is pre-occupied by a metamorphic magnesian silicate.

The limestone of the series may, in general terms, be described as an even-bedded, firm, durable, semi-crystal-line limestone, crowded for the most part with fossils through its whole extent and often bearing upon its surface the impressions of these fossils. Its color is not uniform, as the designation by which the shale series is familiarly know, "blue limestone," would seem to imply. The prevailing color, however, may be said to be grayish blue, chiefly due to the presence of protoxide of iron, which, upon exposure, is converted into a higher oxide. The weathered surfaces generally show yellowish or light gray shades, that are in marked contrast with the fresh fracture. Drab-colored courses occasionally alternate with the blue.

The limestone varies in all these respects somewhat, however, in its different divisions. The Point Pleasant beds, and the lower courses of the Cincinnati division, deviate most widely from the description already given. They are lighter in color than the upper courses and in some instances are slaty in structure, while in others they have a tendency to assume lenticular forms of concretionary origin, sometimes to such an extent as to destroy their value as building-rock. The layers are also exceptionally heavy, attaining a thickness of sixteen or eighteen inches, and are often so free from fossils as to afford no indication of the kinds of life from which they were derived.

A few feet above low-water at Cincinnati, a very fine and compact stone comes in, that is found in occasional courses for fifty to seventy-five feet. It is composed, as its weathered surfaces show, almost entirely of crinoidal columns, mostly of small size, and mainly referable ot species of heterocrinus. The courses vary in thickness from an inch to a foot. The lighter layers ring like potmetal under the blows of a hammer.

Ascending in the series, the limestone layers are very generally fossiliferous and are rarely homogeneous in structure, being disfigured, to a greater or less degree, by chambers of shale or limestone mud, from some of which cavities, certainly, fossils have been dissolved. The thickness of the courses varies generally between the limits indicated above, but a large proportion of the stone ranges between four and eight inches. Now and then, however, a layer attains a thickness of twenty inches, or even two feet. Near the upper limits of the formation the layers are thinner and less even than below, affording what quarrymen call "shelly" stone.

The composition of the limestone from the upper half of the group is quite nearly uniform, averaging about ninety per cent of carbonate of lime; but as we descended in the series the limestones grow more silicious.

The shales, clays, or marlites, which with the limestones make up the Cincinnati group, must next be characterized. they constitute a large part of the system, certainly four-fifths of it in the two lower divisions, and probably not less than three-fifths of its whole extent. The proportions of limestone and shale do not appear altogether constant, it is to be observed, at the same horizon, a larger amount of stone being found at one point than at others.

The shales, as implied in one of the names by which they are known, "blue clay," are generally blue in color, but the shade is lighter than in the limestone. In addition to the blue shales, however, drab-colored clays appear in the series at various points. As the blue shales weather into drab by the higher oxidation of the iron they contain, the conclusion is frequently drawn that the last-named variety marks merely a weathered stage of the former. But, aside from the impossibility of explaining the facts as they occur on this hypothesis, analysis disproves it, and shows that the differences in color are connected with essential differences in the composition of the belts to which they belong.

Most of the shales slake promptly on exposure to the air, and furnish the materials of a fertile soil; but there are other portions included under this general division which harden as the quarry-water escapes, and become an enduring stone if protected from the action of frost.

The shales are sometimes quite heavily charged with fossils, which generally have a firmer structure than the material that encloses them, so that the fossils, often in an admirable state of preservation, remain behind after the shales have melted away. All of the groups of animals that are represented in the limestones are found also in the shales; but from the unequal numbers that are represented here to-day, it seems evident that some sorts were able to adapt themselves to the conditions which shaly deposits imply much more easily than others.

The proportions of limestone and shale in the series we have already spoken of in a general way; but it will be profitable to give additional statements on this point. In the River Quarry beds, the lowermost portion of the Cincinnati bads proper, there are about four feet of shale to one foot of limestone, but the shales increase in force as we ascend in the series, until about one hundred feet above low-water the proportion was more than twice as great. For the two hundred feet next succeeding, that have been styled the Eden shales or Middle shales, there is seldom more than one foot of stone in ten feet of ascent.

1. Geological Survey of Ohio, vol. 1

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