Limestone and Shale. -The formations which underlie this area consist almost exclusively of shale and limestone arranged in nearly horizontal beds. Sandstone is almost totally wanting. Beds of limestone and of shale alternate at frequent intervals, but the total thickness of the shale greatly exceeds that of the limestone. The limestone consists of beds from an inch in thickness to more than a foot, though beds thicker than eight or ten inches are very rare. Two beds of limestone are rarely found in contact. Generally they are separated by beds of shale. This intervening shale may be as thin as paper or there may be five or ten feet of shale practically free from limestone.
One of the most striking features of the rocks of this area is the vast number of fossils, especially in the limestone. It is difficult for the people of southwestern Ohio and north-central Kentucky to realize that most of the people of the world have never seen a fossil in the rock. Here it is very rare to find a large piece of limestone without them.
Impurities and Gradation. - While in general the limestone is easily distinguished from the shale, it is far from pure. Its impurities may be from a sixth to a fourth of the entire mass. These impurities are of the same material as the shale. If they were deposited alone without the limy material they would have made shale. In similar manner the shales of this region contain calcite (carbonate of calcium); it may be as much as five or ten per cent. In occasional masses this is very much increased and in such rare cases the distinction between limestone and shale is hard to make. Certain shales are also locally arenaceous (sandy) and grade into pure sandstone, very sparingly found in the area.
Structure.-The strata in this area are not quite horizontal. They dip slightly in all directions from a point about seventy-five miles south of Cincinnati in Jessamine County, Kentucky, not far from High Bridge. In this area the steepest dip is toward the north, generally less than six feet in a mile, but there is also a dip toward the west from Cincinnati. There are local dips toward the east but these do not continue far. On the whole the westward dip exceeds the eastward, throughout this area. None of these dips are sufficiently large to be observed in a single exposure. They are determined by noting the heights at which the same formation crops out at different places.
The dips within this area are also apparent on the geologic map (Fig. 3). There it is seen that the oldest and lowest formations come to the surface near Cincinnati and that in journeying east, west, or north from that place, other formations successively younger and younger appear. As the general level of the country is not far from uniform, this arrangement of formations on the geologic map means that the rocks are slightly inclined. They are, in fact, exposed like shingles on a roof. (Compare figures 22 and 25).
Total Thickness.-The vertical distance between the lowest point in this area (where Ohio River leaves it) and the highest (near the northwest corner) is about 530 feet. If, therefore, all beds were exactly horizontal, the total thickness of all the beds exposed would be just 530 feet. The fact that the beds are not quite horizontal but dip in a northerly direction makes the thickness of exposed beds somewhat greater.
A more important factor in computations of thickness arises from the fact that the nine formations exposed in this area vary in thickness from place to place and probably no two of them have their greatest thickness in the same locality. If the maximum thickness of all the formations be added together, the sum would be about 800 feet.
Division Into Formations.-As stated above these 800 feet are divided into nine formations. Some of these are sufficiently distinguished from their neighbors in physical appearance so that they may be recognized without expert knowledge. For example, the limestone quarry beds may thus be distinguished from the shale beds from which brick is made, but even in such cases it is generally hard to locate the exact line of separation. Subdivisions made by this criterion alone would have little value because the divisions recognized at one place could not be identified at any considerable distance. The formations used by geologists in this region are based largely on fossils.
Local Variation.-While the formations in this area are not boldly distinguished from their neighbors above and below, it is also true that the same formation has not the same character or appearance from top to bottom. The color, or the proportion of limestone to shale, may be different at different levels in the same formation.
When traced from one locality to another within short distances, the general character of each formation remains the same, but the exact order in which its limestones and shales occur, and even the proportion of limestone to shale, may vary from place to place. This change from place to place corresponds to what is observed in sediments now being laid down in the shallow sea. It is sand at one place, mud at another, and limy ooze at another, all perhaps burying the same species of shells. In a few years or a few hundred years the character of sediments being laid down in the different localities may be exchanged.
Epicontinental Seas.-The general conditions of the seas in which our bed rocks were deposited are plainly revealed by the rocks themselves. The sea was shallow. Central North America (or any, other continent) never was sea in the same sense that the Central Atlantic is sea, that is, it never was ocean basin. It was always a platform separated from the deep ocean basin by relatively steep slopes. Instead of thinking of the Mississippi Valley as having once been ocean basin, it is a truer conception to think of the ocean basins as somewhat "more than full" so that their waters submerged the lower parts of the continents. Central United States was sometimes a low plain like the Gulf States at present, and sometimes a submerged plain like the banks of Newfoundland or the very shallow Hudson Bay or North Sea (Fig. 27). Such seas are called epicontinental (that is, "on the continent"), and are not parts of the deep sea like the Gulf of Mexico or the Mediterranean.
Evidences of Shallow Water.-This relation of the water to the land is plainly shown in the rocks of the Cincinnati region. Some of the limestone beds are locally ripple-marked, indicating a depth of water so small that its waves acted with vigor on the bottom. All the forms of life were those which inhabit the shallow waters of the continental shelf. There are no deep sea forms among the fossils. Some of them, like the trilobites, had good eyes, indicating that they lived in the light. Nearly all of the light of the sun's rays is lost at a depth of 600 feet and most of it at 300 feet. Many shells are broken up as if by the dashing of waves, and it is largely these shell fragments which have been swept up into roughly parallel rows and ridges two or three feet apart, making the large size ripple marks. mentioned above. At places this debris of shells constitutes a sheet with a flat base but rippled surface above. Elsewhere the sheet was so thin or the wave action on the bottom so strong that all the material was disposed in roughly parallel rows or crests several feet apart, the intervening trough being swept clean (Fig. 19).
Evidences of Low Land.-If it is plain that the waters were generally shallow, it is equally plain that the land which furnished the sediment was generally low. High land would have involved swift streams and these would have carried sand and gravel, becoming later sandstone and conglomerate. The rivers carried only mud, like the sluggish rivers of our Gulf Coastal Plain. Moreover, high lands would have afforded, at least locally, steep cliffs along the shore, and these would have yielded fragments, at first-angular, making breccia if consolidated, or later rounded by the waves making gravel and, when consolidated, conglomerate.
That the sea was warm is indicated by the extremely varied and abundant life.
Local Rising and Sinking.-Not only were the seas shallow and the land low, but there were almost constantly slight upward or downward movements of the land. To the eye all these formations are horizontal, but when a section of one locality is critically compared with that of another some miles distant, it is often seen that certain beds or members are present in the one and absent from the other. This means that during the time of their deposit, there was sea where they are now found and land where they are absent, or, if there was sea and deposit at both places, one of the localities was later raised above the sea level and the deposit eroded away. In either case crustal movements are indicated. If the rocks of the central Ohio Valley be considered in sufficiently small units or "members," it will be seen that many of them occupy only a part of the region, no two members covering exactly the same area. Moreover, each may be thick at one place and thin at another. Instead of one widespread uniform sea covering the whole region from the beginning of sedimentation to its close, the sea for a part of the time must be thought of as a bay, or several bays, separated by low peninsulas and islands, the whole surface constantly warping, shifting the bays now here now there, making them large or small or absent according to the amount of elevation. There is nothing unusual about such behavior of the earth's crust. Similar movements are at present affecting the edges of the United States and perhaps the center also, though it is not so readily apparent there as it is along the coast.
Table of Formations.-The several formations in the area here described are listed in Table II, from the youngest at the top to the oldest at the bottom. Their subdivisions (members) and groupings are likewise shown. It will be observed that some of the familiar names applied to rocks in this region are names of members, not of formations. Such is the case with the Fairmount limestone, in which most of our quarries are opened. Likewise, some names in popular use are group names, for example, the Eden shales.
The formations of the Richmond group at the top of the column, and especially those of Trenton age at the bottom, are much less abundantly represented in this area than those of the Maysville and Eden. All the groups mentioned below are known throughout this part of the United States as the Cincinnatian series, indicating that they are best known and have been most thoroughly studied in this vicinity.
General Description.-The lowest and oldest beds which come to the surface in this area belong to the Cynthiana formation of Trenton age. In Ohio the name Trenton is popularly associated with oil and gas, generally from great depths. The beds here exposed are continuous with the deeply buried oil and gas bearing formation in other parts of the State, but here they are brought to the surface by the Cincinnati anticline. Even at this place they would not reach the surface were it not for the deep valley which the Ohio has cut. If the deposits made by water and ice in our great valleys were removed, the Ohio, Miami, and Little Miami would all be found running on beds and between banks of Trenton strata.
The Trenton is commonly thought of as a limestone and much of it is; but its upper beds, fifty feet or more, the only portion exposed in this area, contain much more shale than limestone. Beneath the beds here exposed is solid limestone which is at places sixty feet in thickness (the so-called Point Pleasant limestone). In drilling wells it is encountered at levels not much below that of the Ohio channel. The driller knows by the behavior of his tools that he has reached solid limestone without shale. This he calls the Trenton, but in scientific usage the name has never been so restricted. These deeper limestone beds come to the surface and are quarried near Point Pleasant on the Ohio River about twenty-five miles above Cincinnati. The best exposure of rocks of Trenton age in this area is in the south bank of the Ohio at West Covington for a stretch of a mile eastward from the Cincinnati Southern Railway bridge. Here they form the rocky bank to a height of fifty-three feet above low water. In general the proportion of limestone to shale increases with the height above the river, the first fifteen to twenty feet being almost exclusively shale.
Several of the limestone beds in the upper part of this exposure are noteworthy because composed in large part of broken shells, as if dashed to pieces by waves on or near shore. Large undulations or ripples on the upper surface of these beds are formed by the sweeping up of these shell fragments into ridges by the waves on a shallow bottom.
Fragmental Limestone at Top.-The topmost bed of the formation contains these features with still another. Incorporated within it are balls or fragments of clayey rock, evidently derived from the wasting of a lower bed. With these are large irregular slabs of limestone, some of them two feet in diameter, evidently derived from the breaking up of an older bed. These slabs have been but little worn by the water. When brought into their present place they were embedded in a matrix of broken shells and crinoid stems, largely the latter. All the features indicate that an old sea bottom had become dry land and that when the. land again sank the readvancing waves broke up and redeposited the topmost beds of the old formation. Perhaps the new deposit thus made belongs more properly to the epoch of the overlying group (the Eden), but it has become customary to class it with the similar limestone below and to ignore its age relations with the soft shale above.
Break in the Record of Life.-The example here described is one of the best, but by no means the only example in the area, of beds which indicate that deposition was interrupted by emergence and then renewed by submergence. In all such cases the time during which the area was dry land was left without a record in the rocks. Not only that, but erosion was meantime destroying the last records made. During such intervals the evolution of marine animals was continuing in the seas elsewhere. When submergence again occurred, the later forms of life came in and were incorporated as fossils in the new sediments immediately above the antiquated forms in the beds just below the unconformity. In this particular case the gap in the record is small, but it separates the beds of Trenton age from the Eden and the Mohawkian series from the Cincinnatian. Ninety per cent of the species in the highest beds of the Cynthiana failed to reappear in the lowest beds of the Eden.
Dips.-From West Covington the top of this formation dips westward, falling forty feet in the next eight miles. West of that are no outcrops because of alluvium and debris from the bluffs. Within five miles eastward from West Covington the top of the formation sinks almost to the river level. From this lowest point (opposite Dayton, Kentucky) the formation again rises as the Ohio is ascended, until, at New Palestine, where the Ohio enters the Cincinnati quadrangle, its upper surface is nearly 100 feet above the river. It appears therefore that the formation rises toward both the south and east, but there are also minor lines of folding.
Less satisfactory exposures than the one at West Covington may be seen at the mouth of the Licking (west side) and at various other points on the Ohio and Licking.
The Eden group, consisting largely of shales, takes its name from Eden Park in Cincinnati, overlooking Ohio River. In the steep bluffs leading down from this park to the river these shales are well exposed. In scientific usage the Eden shales are divided into two formations of very unequal volume, the Utica below and the Latonia above. The lower one, while small at this place, is full of scientific interest, and is the local representative of what is elsewhere a very important formation.
How the Epoch Was Inaugurated.-It will be remembered that the. topmost beds of the Cynthiana formation consist largely of limestone,
whose ripple marks and broken shells afford sufficient evidence that the deposit was made in very shallow water. Presumably this shallow water was very near the shore. It was shown previously that limestone can be formed near shore only when the land is very low and yielding little sediment to its streams and thus to the sea. This was no doubt the condition of the land near the close of Trenton time. That epoch was brought to a close in this vicinity by the rise of the shallow bottom above the level of the sea. A land epoch then followed, after which renewed submergence introduced the Utica epoch. The first deposit on the bottom of the Utica sea was the fragmental limestone described above as commonly classed with the Cynthiana. It can scarcely be said to have been formed after submergence, but rather during submergence by the waves which beat upon the slowly receding shore. At places this wave-and-current work altered the limestone so little that it can scarcely be said to be destroyed and redeposited. Its fragments are Cynthiana fragments, and its fossils are Trenton fossils, simply broken up and rearranged by the waves of the Utica sea. When any one spot had been actually submerged, the nearness to shore and the turbidity of the water was such that mud was deposited on the bottom. This mud became the Utica shale. It is generally less distinctly blue than the shales of the higher formations. It inclines more toward yellowish, brownish, or greenish-gray shades.
Thickness and Geographic Relations.-At West Covington the Utica shale is only nine feet thick. Westward from that point it becomes still thinner, and disappears or "pinches out" before Andersons Ferry is reached. This indicates that land lay west of that point, while an arm of the sea on the east was receiving sediment from this and other shores. Eastward and farther from shore the sea came in sooner and was deeper. The formation thickens in that direction to twenty-four feet at New Richmond. Here it is about one-half limestone.
Going south to central Kentucky, the formation pinches out as it does to the west, but northeastward it thickens greatly, becoming 300 feet in northeastern Ohio, and passing into the great formation known as the Utica shale in New York. Through all this distance many of its fossils are identical. It is evident that in the continual warping and waving of the earth's crust, causing an ever changing pattern of low land and shallow water, the Utica sea reached this region in the form of a bay which gradually expanded southwestward from New York. In that region to the northeast, the submergence began much earlier, and the sediments (likewise shales) are very thick, but the submergence reached this region so late that there was time for but little sediment.
Other good exposures are at New Richmond (twenty-four feet), in the bank of Ohio River one-half mile below Brent, Ky. (fifteen and one-half feet), and near the mouth of Three-Mile Creek south of Newport.
Character.- Resting on the Utica shale, or on lower formations where that is absent, are more than 200 feet of shale with very subordinate amounts of limestone. This is the
Latonia shale, so named from Latonia, Ky., at the southern edge of the city of Covington.
As compared with the Utica shale below, the Latonia shale is more distinctly blue, often intensely so where fresh. It weathers into a greenish yellow or drab. All the shales of the formation are soft and calcareous; some beds are highly calcareous, almost marly. In others the carbonate of lime has aggregated into ellipsoidal concretions, having the texture and color of very dense blue argillaceous limestone. This feature is well shown on West Fork Creek west of Cumminsville.
Proportion of Limestone.-While the Latonia is essentially a shale formation, it contains here and there a bed of limestone.
Of the limestone layers interspersed, most are coarse textured, crystalline, and fossiliferous, but a minority are of a dense granular variety and lacking in fossils. The layman readily sees at different levels differences in the amount of limestone interbedded with the shale. It is greatest in the upper portion and least in the middle. Near the top, limestone beds reaching a maximum thickness of ten inches may at places constitute as much as one-third of the entire mass. A number of such layers, in close proximity may even make a strong ledge two or three feet thick. In the 100 feet nearest the middle of the formation not more than one-sixth to one-tenth is limestone. Locally there may be found sections of twenty to thirty feet with less than a foot of limestone. The lower fifty feet have a larger proportion of limestone, but nowhere enough to cause this formation to be mistaken for others when judged by physical character alone.
Thickness and Geographic Relations.-The Latonia formation is thicker north of Cincinnati (maximum 230 feet) than to the south. It thins to 180 feet on the southern border of the Cincinnati quadrangle and gives out entirely in parts of central Kentucky, presumably because land existed there throughout the Eden epoch. But it is known that the sea in this region was not entirely cut off by land to the South, because the fauna shows that there was free communication.
Topographic Relations of Outcrop. - All the great valleys in the southern half of this area, and to the south far into Kentucky, cut down into or through the Eden shales, but the adjacent uplands are capped by the stronger limestone formations which overlie the shales. (See Fig. 29) This structural condition has helped to make the beautiful steep bluff slopes which distinguish this area. Without the strong capping of the uplands, the hills near the rivers would have been cut to lower altitudes and gentler slopes. Without the weak shales beneath, the bluffs would be less steep, because the effects of sapping would be absent. Actual exposures of the shale are not numerous, for it is easily weathered and a thin soil formed. The general steepness of the slopes, however, prevents the accumulation of a thick soil. These features are less noticeable in the northern part of the area because of the effects of repeated and recent glaciation. It should also be remembered that the formations dip north while the valleys slope south; hence in going north the limestone on the hills comes nearer and nearer to the valley floor. North of Sharonville in Mill Creek Valley, and Venice in the Miami Valley, the shales lie entirely below the level of the alluvium. Even there, however, sapping was active when the streams ran at lower levels before the valleys were partly filled by glacial outwash.
Good Exposures Located. - The best available section of the Eden is in the steep bluff one mile west of Bromley, Ky., and opposite Sedamsville. Here it is more or less exposed from an altitude of sixty feet to 280 feet above low water. In the north bluff of the Ohio, seven miles above the mouth of the Little Miami, is a small stream with steep gradient, in whose rocky bed the lower two-thirds of the Latonia formation are well exposed. The upper two-thirds are exposed by the grading of Elberon and Columbia avenues, Cincinnati. The grading of McMicken Avenue below the Bellevue incline has similarly exposed the upper portion. The same can be well seen from the stairway leading down from Mt. Adams on the south side. In the bed of West Fork Creek west of Cumminsville, the upper two-thirds of the Latonia are well exposed.
Falls and Rapids.-The thick beds of soft shale, interrupted by strong beds or ledges of limestone, offer ideal conditions for small waterfalls of the Niagara type. There are many of these along the small streams descending the steep valley sides. Where the stream has a sufficient gradient each individual fall may cover the entire vertical distance between two limestone beds. This is well illustrated on West Fork, from one to three miles west of Cumminsville. (Plate II-A.)
Soil Cover.-Near the Ohio, especially where the drainage is young because of recent changes, are many steep slopes, crossing almost the full thickness of the Eden shales. These slopes are covered with a thin soil strewn with limestone fragments from the Latonia and higher formations. This is typically illustrated on Dry Creek and its branches south of Andersons Ferry.
On the slopes of Mill Creek Valley, and on other steep slopes near Cincinnati, the underlying Eden shales may be detected by many yellowish drab spots, only partly or poorly covered with vegetation. The color is characteristic of the weathered shales before an admixture of humus has made a true soil.
Above the Eden shales, and much exposed in the hillsides near Cincinnati, are about 200 feet of alternating limestone and shale known as the Maysville group. The name is taken from Maysville, Ky., on the Ohio River about seventy miles above Cincinnati, where the beds are typically represented. In southwestern Ohio this group was early called the "Hill Quarry beds" in distinction from the "River Quarry beds" or Cynthiana, the local representative of the Trenton.
General Character.-As indicated by the old name, this group is characterized by its limestone beds suitable for quarry rock. The aggregate thickness of these is by no means equal to that of the interbedded shales, but they afford the chief quarries of the region. The shales are soft and calcareous like those of the Eden, and generally blue, though sometimes less blue and more yellowish than those of the Eden. The limestones are blue, generally coarse textured, crystalline, and highly fossiliferous. Individual beds are from two to ten or more inches in thickness, three to six inches being common.
Some of the beds, especially in the lower part of the group, are sandy near the southern border of the area. This sandiness becomes more
prominent where the beds are weathered (often to a reddish color). An occasional bed may almost be called sandstone. This sandy character becomes more marked toward the south. In central Kentucky the lower part of this group (Mount Hope member) becomes a part of the Garrard sandstone.
Differences in character at different levels within the Maysville group are evident to the casual observer. These differences have to do largely with the proportion of limestone to shale, but to some extent also with color and other characteristics. Technically it is divided into two formations, the Fairview below and the McMillan above. These divisions are based on fossils but serve fairly well for descriptive
purposes.
Of the 120 feet of limestone and shale which compose the Fairview at Cincinnati, the uppermost fifty feet have more limestone than shale, perhaps twice as much. The remaining seventy feet have these proportions about reversed. Roughly these parts correspond to the Fairmount limestone member above (in which the quarries occur), and the Mount Hope shale member below; but only roughly, for the separation of these members is on faunal, not on physical grounds, and the dividing line is drawn about, thirty feet below the base of the closely crowded limestones. The topmost seventy to eighty-five feet (in this area) are assigned to the Fairmount, and the lower fifty (where the member is thickest) to the Mount Hope member.
The Basal Limestone.-At the base of the Mount Hope member, marking the contact between Eden and Maysville groups, is an exceptionally heavy bed of limestone, probably the thickest bed in the Cincinnatian series. Locally its thickness is more than a foot. It is one of the few beds in the region which can be readily recognized by its fossils without expert knowledge. Its surface is everywhere partly or wholly covered with shells of an easily recognized brachiopod,
Thickness and Geographic Relations. - The Fairview formation (and indeed the whole Maysville group) thins toward the west and to some extent toward the north. At the southeast corner of this area in the bluffs of the Ohio, its thickness is 120 to 125 feet. On the Miami River west of Cincinnati it is only 100 feet. Twenty miles farther west in Indiana it is but seventy to seventy-five feet, and the whole, Cincinnatian series is believed to pinch out before reaching Illinois. The lower beds pinch out first, indicating that the sea in which this group was deposited began by submergence on the east side and advanced westward by progressive sinking, but Illinois remained above water. The whole Cincinnati area may have been dry land for a time between the Eden and Maysville epochs.
Topographic Relations of Outcrop.-In the southern part of the a the Fairview formation generally outcrops in the steep bluffs. On the uplands it is generally covered by other beds, and generally the exact brow or shoulder of the hill, when such a shoulder is well marked, is caused by a higher formation. In most localities near Cincinnati the horizon of the Fairmount is easily located, not only by the topographic features here described but by the numerous quarries which have been opened in it.
Going northward along the great valleys, not only are quarries less numerous, but, as the limestone approaches the valley floor, the sapping, due to the weakness of the underlying Eden shales, becomes less and less prominent, and the bluffs are less abrupt except where recently undercut by streams. Hence, in the vicinity of Hamilton the outcrops of the several formations are not reflected in the topography to the same extent as near Cincinnati. Toward the north also, the Fairview in the uplands becomes more and more deeply covered by later formations.
Good Exposures Located.-Good sections of the formations may be studied in the steep bluff one mile west of Bromley, Ky., also along Clifton Ave., Cincinnati, below the Bellevue Incline, and in the quarries bordering Mill Creek Valley on both sides. The quarries west of the Miami River at Hamilton are in the same formation as those at Cincinnati. The Mount Hope member is perhaps best studied in the slope of the bluff known by that name southeast of Price Hill. Its thickness here is not over forty feet, having decreased from fifty on the Licking River. In the gorge of the West Fork of Mill Creek, one and one-half miles southwest of Glendale, the whole Mount Hope member is well shown, being but sixteen feet thick at that place.
Bellevue Limestone Member.-Those who are familiar with the quarries in the Fairmount formation will have observed just above most of them a strong ledge of rock fifteen or twenty feet thick, which generally stands out in a distinct angle or shoulder in the natural slope of the hill. This ledge is the Bellevue, the basal member of the McMillan formation. Its strength and prominence are due chiefly to its large proportion of limestone, but despite this fact it is not used as quarry rock. Its layers are irregular and thinner than those below. The lower three-fourths of the Bellevue is almost a solid mass of bryozoa. Many of these resemble branching corals and are frequently mistaken for them. At the top there is generally a bed often several feet thick, consisting almost wholly of single valves of a thin shelled brachiopod.
As an indication of the exceeding abundance of marine life during the time that the Cincinnatian rocks were being deposited, these beds have no superior. The sea was necessarily shallow, light, and warm, and food was abundant. That it was also clear is indicated by the fact that there was very little sediment except the hard parts of the animals themselves. The conditions were similar to what may now be found on parts of the continental shelf near Florida where the dredge brings up nothing but broken shells. In some such localities the abundance of life is said to exceed that of any tropical jungle. A fact of equal interest in the Bellevue beds is the sudden change from a colony of bryozoans to one of brachiopods. The exact reasons for such changes are not explained but they are not uncommon. Something in the temperature, the character of the water, the food supply, or the presence of enemies which fed on such animals, may have caused the change; or the mere migration of one type may have been sufficient to displace the other.
Fragments of the Bellevue beds are found frequently in the refuse of the quarries. Its technical name Bellevue is taken from the former Bellevue hotel which stood at the top of the incline used by the Clifton-Elm cars. At this point, within the bend of Clifton Avenue, these beds stand out boldly, and make the brow of the hill. Its association with the quarries, its peculiar physical character and its habit of forming the brow of steep slopes have made it one of the best known members of the Cincinnatian series.
Corryville Shale Member.-The forty or fifty feet of beds next above the Bellevue attract much less attention. Their limestone beds are relatively few and thin. Shale constitutes the larger part of this member, hence it wears down readily into gentle slopes which become covered with vegetation. The name Corryville is taken from that part of Cincinnati which lies east of Burnet Woods Park. In that part of the city it covers the Bellevue on most of the hills and uplands.
Mount Auburn Concretionary Shale Member.-Still higher on the hilltops are remnants of another member, well known to youthful collectors of fossils. It is the Mount Auburn member, generally not more than twenty feet thick and consisting mainly of blue shales. But in these shales are irregular beds and nodules of limestone, causing exposed surfaces to be rough and scraggy, the individual beds being poorly distinguished. It is in these beds that the well known massive brachiopod
General Character.-The foregoing descriptions complete the list of formations exposed in the immediate vicinity of Cincinnati, except for the ridge extending north from Westwood. Those who know the hillsides and streams a little farther north in the vicinity of Lebanon or of Oxford have encountered certain familiar forms which are unknown in the quarries and streams near Cincinnati or even Hamilton. Among these the most familiar are probably the large solitary corals having about the shape and size of "calves' horns." The presence of these indicates a higher group of rocks known as the Richmond. This higher group has been almost completely stripped by erosion from the vicinity of Cincinnati, but outcrops in a broad band thirty to fifty miles from that center where the uplift was less. Its lower formations cover considerable areas in the Hamilton and Mason quadrangles. The group as a whole is fairly well represented in the northwest corner near Oxford where it caps the higher uplands. The name of the group is taken from Richmond, Ind., where it is well exposed, and has been thoroughly studied. Where well developed it is about 300 feet thick.
Most of the Richmond is even-bedded, with clean cut alternations of limestone and shale, in this respect strongly resembling the Maysville. The limestone beds vary in thickness from two to ten inches (generally less than six inches) and comprise less than half of the whole mass, perhaps not more than one-fourth. On the whole the color of its limestones is less blue and more gray or dove colored than that of the Maysville. But these physical distinctions are relatively unimportant and not sufficiently uniform to be trustworthy for purposes of identification. The real and essential distinction is in the fossils. These show that the sea was inhabited by a very different fauna during the Richmond epoch from that which lived in the previous epochs The advent of corals is only one of the many changes.
Formations.-The lowest formation in the Richmond group is the Arnheim shale. It rests on the Mount Auburn and is about eighty feet thick. It consists largely of dark bluish shale with a subordinate amount of blue limestone. In part it is even-bedded like most of the lower formations, but it has other portions, especially near the top, which look like the Mount Auburn. In these the limestone occurs in rough irregular beds, or nodules with scraggy masses of indurated clay, strongly contrasted with the regular bedding above and below.
The next fifty feet of the Richmond is called Waynesville shale. To a casual view it is not unlike most of the other formations but at many places its gray or dove colored limestone, associated with strikingly blue or greenish-blue shales, gives something of distinction to its appearance. Its shales are sometimes highly calcareous or marly. It is well exposed near Oxford. Above the Waynesville are thirty-five feet of beds, known as the Liberty limestone, which differ little from the Waynesville except in fossils, though the limestone layers are more abundant and bluer. All that lies above the Liberty in this area is included in the Whitewater formation. The physical characteristics of this are not unlike those of the Mount Auburn beds of the Maysville. It lacks the clean-cut even bedding of the formations immediately below it. Both its limestones and shales have a rough concretionary or nodular appearance. While blue in places, the color is more generally brownish or yellowish. Much of the limestone is very impure.
