History of the city of Columbus, capital of Ohio, Volume I, Part 88

Author: Lee, Alfred Emory, 1838-; W. W. Munsell & Co
Publication date: 1892
Publisher: New York and Chicago : Munsell & Co.
Number of Pages: 1202

USA > Ohio > Franklin County > Columbus > History of the city of Columbus, capital of Ohio, Volume I > Part 88

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Edward Unton

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blocks of wood referred to above are the most common of these vegetable fossils. Excellent specimens are frequently found within the limits of the city. They sometimes occur, like the fishes already described, as the nuclei of the symmetrical concretions which abound in the shale. The wood when examined in thin sec- tions under the microscope proves exceedingly interesting. It belongs to an extinct group of coniferous trees. The rings of annual growth are clearly recog- mizable in the wood and they appear to show a division of the year even at this early time into seasons of growth and rest, as at present. Several distinct species of woods have already been described on the basis of their microscopic structure. Most of our specimens fall under Dawson's genus, Dadoxylon, but Knowlton has recently found some of them to be Auracarioxylon.

Coneretions .- The remarkable forms known as concretions; which oecur abun- dently throughout the entire shale series, have been repeatedly referred to in the preceding discussion. They are sure to attract the attention of even the least observant. They are brought as curiosities from the ravines where they are found into dooryards; they are employed as hitching blocks, or built into columns, and in all these ways they demonstrate the fact that nobody can pass them by without notice. As a rule they are symmetrical in form, the most common type being that of an oblate spheroid. When situated in the shale in situ the flattening of the spheroid is seen to be in the line of the bedding of the shale. In other words, the shorter diameter is always perpendicular to the plane of the bedding. Some- times they differ but little from the form of spheres and sometimes they are flat- tened out into discoidal shapes. In size they show a wide range, their diameters varying from five or six inches to five or six feet. In fact the extreme figures will divide or double even the ones above given, but the cases in which blocks more than six feet in diameter occur are rare. In composition they exhibit some diver- sity. They can be said in general to consist of compounds of iron and lime with which a few other substances are occasionally associated. The iron occurs largely as carbonate (siderite) but sometimes as sulphide (pyrite or marcasite). When the iron weathers, hydrated peroxide results, and this is the most common mode of the occurrence of the concretions in the surface deposits of the city. When a heavy block of stone covered an inch deep with iron rust is found in an excavation in the city, it is next to certain that a decomposing concretion is in hand. The lime exists as carbonate. Silica, barite and celestite are occasionally found in the interior of the concretions. Fluorite has also been reported. As indicated by the last sentence, the interiors of the concretious are frequently crys- talized. Calcite is the most common element here, but with it the substances named above are associated when they are present. The calcite of the concretions bas a very characteristic appearance. It is distinctly crystallized and has a dark brown or almost black color. No other known mode of its occurrence is likely to be con- founded with this. The color is due to presence of bituminous matter. The cen- ters of the concretions often show hollow spaces of a few cubic inches in dimen- sion, Sometimes a small quantity of petroleum is found here, and sometimes also asphaltic grains are associated with the crystals.

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How are these concretions formed ? What explanation can be given of their origin ? The amount of interest which these symmetrieal and unusual bodies inspire ean be measured very well by the frequency with which the questions above given are asked. One can searcely enter into a conversation upon the geology of Franklin County with any person of ordinary observation, without being interrupted after a little with questions of this character. In attempting a partial explanation of these formations, a few facts that have been already stated will be recalled. One of these faets is that the great bony plates of the fishes of the shale are often found at the centers of the concretions. Another fact is that fossil wood often has a like situation. And still another fact in the same connec- tion ean be profitably recalled, viz., the occasional occurrence of petroleum or asphalt in the central portions of the concretions. A fourth fact my be added, viz., that the black bitnminous calcite that is so frequently found at the eentres of the eoneretions is sometimes found also in fossil wood. Part of what was originally a block of wood has been converted in such a case into this black calcite, while surrounding portions of the same fragment are silieified and retain all the cell markings of the original growth. It seems safe, therefore, to conclude that all of the black calcite has this mode of origin.

In the light of these facts it is probably safe to say that all of the concretions of the shale originally had organie nuclei. This is about the same as saying that some fragment of an animal or a plant lodged in the shale by ordinary agencies is the cause of the formation of the concretion. Invariable association would carry with it the idea of cause, under these circumstanees. The question returns, how do these organic nuclei accomplish this work? The answer is by means of the organic acids to which they give rise in their decomposition, or by means of the carbonic acid into which all these organic aeids soon fall. A wide range of solvent power belongs to these organic acids. They are, however, energetic in their attacks on iron, lime and silica, for which, indeed, they are the proper solvents. All of these substanees are rendered freely soluble in their presence. According to this view the organic fragment is buried in the shale, at least a few feet deep, on the old sea floor ; decomposition goes forward and petroleum may result, on the one side, but probably, in sparing quantity ; on the other side the organie acids are set free in abundant amount and are blended with the water that surrounds the fragment. Wherever these acids are diffused,-above, below, on the right band and on the left, they dissolve the iron and lime of the shale and the silica in part, and these substances, one or all, descend, or ascend, or migrate, along these radial lines, towards the centre from which the disturbing agency proceeds. The silica is quite likely to reach and replace the wood itself, though sometimes the structure will be lost in part. As we have already seen, bituminous calcite some- times divides with the silica the space where the wood lay, but it never retains the vegetable structure.

A bone exerts a similar agency to that of the block of wood, but it does not itself suffer complete replacement as the latter does. Its organic matter is lost, but the phosphate of lime remains in great part as it was. In concretions in which the sulphide of iron is prominent, it would scem probable that the nucleus was of

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animal origin, for the reason that sulphur is found in much larger quantities in animal structures than in plants. It must be added that the organic nucleus often disappears altogether in this process, especially if it is of a vegetable matter. Its former presence is in such cases indicated by black calcite, petroleum or asphalt.

The answer to the question, how were concretions formed, is according to this view as follows : They result from the deposition around an organic nuclens, of carbonate of iron and also of silica and a few other minerals, all of which were set free from the surrounding rock by the action of the acids that were formed in the decomposition of the nucleus. This answer, it may be added, is in substantial harmony with the facts that we have lately learned as to the growth of concretions of manganese, silica and iron that are now in progress of formation on the floor of the deep seas.

Petroleum and Gas .- The Ohio black shale has always been noted as a source of weak oil and gas springs which occur along its outcrop. The formation is given to " surface indications," and during the last few years in the eager search that has gone on for these substan ces, it has raised in half a dozen states a great many hopes and expectations that it was unable to fulfill. What is the source of these bituminous substances that are found universally distributed throughout the formation wherever it occurs? In answering the question, petroleum and gas do not need to be treated separately and independently. Petroleum comes first in the order of nature and is easily decomposed into the simpler body, natural gas. When oxidized by exposure to the air it turns into maltha or tar, and finally into asphalt. The origin of petroleum in the black shale is unquestionably due to the decomposition of organie matter that was deposited in the shale contemporane- ously with its accumulation. The occasional presence of petroleum in the concre- tions of the shale has already been noticed and has been connected with the decomposition of the organic nuclei, at least as a possibility. But do we find . organic matter that suggests or offers a source for the petroleum that occurs in every foot of the shale from top to bottom of the formation ? Unquestionably we do. The five to fifteen per cent. of organic matter that colors all the darker por- tions of the shale certainly prove an abundant supply of organic matter in its formation. What was the character of this organic matter? From what source was it derived ? The microscope comes to our aid. We find many portions of the shale crowded with beautifully preserved spores of ancient sea-weeds, and this fact gives full support to Newberry's suggestion that the black shale sea was a sargasso sea ; or, in other words, a sea the surface of which was heavily mantled with marine vegetation, the decaying fragments of which found their way to the bottom and became incorporated with the silicious clay that distant rivers were bringing in.

We are sure that the petroleum of the shale is not the result of voleanic heat or of any high temperatures that have affected the formation. There are no traces of the disturbance or the mineral change that such factors would necessitate. It is certain that no high temperatures have taken part in the history. We are therefore shut up to the conclusion that organic matter can pass directly by a peculiar form of decomposition into petroleum. Nor is the art a lost one in

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Nature. Petroleum is forming now; and the last geological age is, in fact, the most prolific in its production of these bituminous substances of any in the entire scale. The organic matter of the shale passed through a series of changes of which petroleum was at least one of the products. How could it be retained and preserved in the shale ? This question can be easily answered. Clay has the property of absorbing oil. If the oil, when generated, had floated on the water, it would have been absorbed by the fine clay that was diffused through the sea and would in time have sunk with it to the seafloor in the form that we find it now, viz., a petroliferous clay. When the formation rises to the surface in the accidents of its geological history this original stock is by slow exchanges with water descending from the surface, brought out in the feeble oil springs to which reference has already been made. There is no reason to believe that the oil or gas are forming from their elements now. The world is old and there has been time enough and to spare for the full operation of all chemical forces. The black shale is not in its outerops an important source of either oil or gas in Ohio ; its ontput is always small; but in no division of our scale can the law of the formation of these substances be studied to better advantage than here.

Water Supply. - As will be inferred from statements already made, the black shale is not a generous source of underground water. It resists the entrance of surface water and no formation can be expected to give what it does not contain. The wells and springs that depend on the shale have as a rule a scanty and highly mineralized supply. They are generally rank with iron and often reek with sulphurated hydrogen. Toward the base of the formation and where the shale comes in contact with the limestone, outflows are sometimes obtained, but even here they are generally counted mineral springs.

Soils. - The soils derived from the weathering of the shales are marked by peculiar features. Where the decomposition has gone on to its furthest point, a stubborn blue clay is the residue; but generally the clay is physically lightened to a considerable extent by flakes and fragments of shale distributed through it. These soils are fairly well adapted to some varieties of forest growth, as the chest- nut, the chestnut oak and the swamp Spanish oak, and also to fruit trees and vines ; but they do not produce the firmer and more valuable woods, and the soils derived from them are on the whole poorly adapted to grass and grain.

One source of economic value in the shales remains to be named. It gives rise to clays which, if not fitted to become fertile soils, furnish an excellent basis for certain clay manufactures. These clays can be made into as good sewer pipe as the State affords, and this is the same as saying as good as can anywhere be found. They can also be burned in building brick and paving blocks to excellent advantage. The uses of the clays derived from the weathering shale are only in their infancy as yet. These clays cannot fail to become of more economical importance to the city than they are now counted.

Geological History. - In concluding this description of the shale series a few words may be devoted to its geology proper. The junction or contact of two distinct formations is always an interesting point for geological study. One chapter of the record ends and a new one begins at such lines of contact. If the

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formations differ in character to a marked degree, an equally marked change in the physical geography of the two periods is necessarily inferred. There is not a sharper contrast in the Ohio scale than that which the two great formations now described exhibit when their line of contact is found. For reasons presently to be given these exposed contacts are rare in the vicinity of Columbus. The best one known is found six miles northwest of the city, near the mouth of Slate Run in Perry Township. The limestone is here seen to be overlain sharply but com- formably by shale beds. The boundary is as distinct as a chalk line on a black- board. There is no appearance of a lost interval, such as an croded surface of the limestone would show, but nevertheless the change in the character of the deposits is abrupt. On the boundary the drill would show eight hundred feet of fossiliferous limestone beds with scarcely a single interruption. These beds belong to four distinct formations, each of which is characterized by its own forms of life. In other words, each of these divisions comprised in its own time what we called a creation, as orderly and tranquil in its progress as our own. Above the boundary, oecur a few feet, not more than three or four at most, of impure and flinty limestone, and then the shale begins with all its characteristics fully shown at the start. Its microscopic fossils, its fossil wood and its concretions are all found in their most characteristic state within ten feet of the base; and from this point upward the formation rises without important change for three hundred or three thousand feet, according to the locality at which the section is measured. Below the boundary, the rocks consist of carbonate of lime more or less pure, and they contain in great abundance marine fossils of all the usual types of the time which they represent. Above the boundary, silicious shales, blackened by organic matter and containing a searely recognizable amount of carbonate of lime, com- pose the beds, and in them not a single trace of the life that swarms below is found The beds of limestone show many indications of origin in shallow water. The shale gives no hint of an adjacent shore line in its wide extent.

What inferences are we warranted in drawing from these facts as to the con- ditions under which the shale was formed ? We have almost everything to learn as to the history, but one or two points can be counted settled. 1. The shale was formed in a period of widespread depression of seafloors previously shallow and of some previously existing land areas. The seafloor sunk to the southward and south westward especially, submerging large areas that had previously become dry land. There was also a deep and long continued depression over New York and Pennsylvania. 2. This deepening sea drowned out abruptly the abundant life that had preceded it and thus put an end to limestone growth over these sub- merged areas. 3. The fine sand and clay that constitute the bulk of the formation were derived from shores to the eastward. The materials grow coarser and thicker in that direction. 4. This sea was covered far and wide with an abun- dant marine vegetation, the fragments and products of which supplied the organie matter to the formation. From the same source the petroleum that the shales contain is undoubtedly derived.

Over the site of Columbus the shale originally extended, no doubt, in its full thickness and perhaps several hundred feet higher than the present surface ; but

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it is easily eroded material, and atmospheric agencies would be sure to waste, fur- row and degrade it at a rapid rate, wherever it was exposed. In the course of ages it was largely removed from all the central districts of the city, but in the high land from Fifth Avenue north ward it is still found as an outcropping rock.

Driftbeds .- The two formations now described, viz., the Devonian limestone and the Ohio shale, are the only two rock formations, as this term is ordinarily used, that take a direct part in the surface geology of Columbus; but, as has been already shown, neither of them comes to the surface in any large way. To assign to them onetenth of the area of the city would be generous. What then consti- tutes the remaining ninetenths of the surface ? Everyone is ready with an answer. The city is built upon beds of clay, sand and gravel variously distributed. Excel- lent sections of these beds are shown in excavations for buildings, for sewers, for wells and the like, throughout the city.

Boulder Clay .- In the northeastern quadrant of our area, as well as in many other similar districts, a dark blue, compact and stony clay forms a universal man- tle. This clay is in a large way impervious, but generally the uppermost ten to fifteen feet carry a moderate supply of water. It becomes yellow by weathering. It bears no marks of having been originally deposited in water. It is unstratified and without order. Beds of sand and gravel are also distributed irregularly through it. One of the most striking features of the clay is the occurrence in it of innumerable boulders, small and great. The largest of them show surfaces of thirty or forty square feet and weigh many tons. They are largely granitic in character and are strikingly unlike any rocks that occur in the geological scale of Ohio. The nearest locality where such rocks are found in place is the region north of the Great Lakes. The north shore of Lake Superior is composed of rock masses of precisely the same character as the boulders here described. In the central and eastern parts of the city, they are especially abundant. Excavations for the foundations of dwellings near the intersection of Broad Street and Par- sons Avenne, for example, are sure to reveal the presence of several large boulders to every square rod of surface.

These granite blocks are further characterized, in many instances, by peculiar markings. They bear evidence of having been rubbed and scored in a peculiar way. They are often covered with parallel markings or striations on one or on several sides. These markings extend down even to the smallest fragments of these lost roeks. Most striking exhibitions of this action can be observed wherever deep excavations are made in this formation in the parts of the city that have here been indicated. These beds of boulder clay constitute by far the largest section of the surface deposits of which we are treating. Con- siderable portions of them were originally swampy in character.

Next to these clay deposits in amount must be named the beds of stratified sand and gravel which occur, in particular, in the central and western portions of the city. They constitute the warmest and kindest soils and the most desirable building sites of the region, and were therefore the first to be occupied in the build- ing of the city. Water is always found in them in abundance at a moderate depth

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and they also afford effective natural drainage. They have something of a terrace- like structure.

The river valleys proper constitute the remaining section of these drift deposits, but they require no special description. Collectively these several formations are known as the drift, or they are sometimes divided into the glacial drift and the modified or stratified drift. How thick are these drift beds within the city limits ? Unless we have given special attention to the facts, we are scarcely prepared for the answer that must be made. The average depth of the drift bed within the city limits is little if any less than one hundred feet. The drill must descend on the average thus far to reach the underlying shale. How came these deposits here, or in other words, what is the history of the drift? The answer is one of the most startling and paradoxical that the science of geology is compelled to make to any of the questions that come within its purview. The drift owes its origin to a descent of polar ice on a vast scale from the region which it now ocenpies, as far south as the fortieth parallel. The northeastern portion of the North American Continent, at the same time with many other northern regions of the globe, was transformed for thousands and tens of thousands of years into the condition in which Greenland is today. It was overrun by an enormous sheet of ice, a conti- nental glacier, that has its nearest counterpart in the great Greenland glaciers of the present, and in the still thicker and more extensive ice sheet under which the Antarctic continent lies buried.

Of many elements in the history of the invasion of northern ice we can make ourselves certain. At the date of the glacial epoch, Ohio had been for a long series of ages a part of the dry land of the continent. It was raised from beneath the sea, as we have already seen, where its beds were all originally formed, at the end of the second great division of the earth's history ; and for millions of years there- after it stood exposed to the abrading agencies of the atmosphere. Rains fell upon its weathered and softened surface for untold centuries and the streams that carried this falling water away, wore by slow degrees their channels deep into limestone, shale and sandstone. Each of the river systems of the State carved its drainage basin into a vast ramification of valleys, shallow and deep, and the few remnants of the original plain were left as the hills and highlands of the State. Over this deeply buried surface the northern ice was gradually extended. It found all portions of this rocky floor covered with the products of its own weath- ering in the shape of soils and broken rocks. All this loose material and much more beside was pushed on by and beneath the advancing ice. By this means the valleys were gradually filled and the entire surface of the State that was thus overrun was restored to its original monotony. The vegetable and animal life that were previously established here were necessarily displaced and driven to the open lands to the southward. Of the forests that covered the surface at this time we have abundant representatives in the fragments of wood that are buried in the boulder elay. Hundreds of specimens of this preglacial wood have been exhumed in the various excavations that have been made within the city limits. The wood thus preserved is in most if not all cases red cedar. When exposed to the air, after its long burial, it usually falls to pieces; but if left nndisturbed in the clay

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there is no reason to believe that it would not last for thousands of years longer with but slight change.

The striation and polishing of the fragments of rock contained in the glacial drift have been already touched upon in a preceding paragraph. To this must be added that the rocky floor of the country has itself suffered a like abrasion. Large surfaces of the rock in places are worn and polished in a remarkable way. These phenomena are unequivocal and indubitable proofs of the agency of land ice. They occur only under the advance of a glacier, and no more distinctive markings are left by any known geological agent than those that are now described. Furthermore, there is no portion of the country that contains more abundant representatives of the first of these effects than Central Ohio. The rock inscriptions are, however, rarely found just here, largely on account of the heavy covering of the deposits already named. The boulder clay, or till, as the forma- tion is called in Great Britain, is therefore beyond question a product and a proof of land ice in all the areas in which it is found. The seams of sand and gravel that occur in the boulder clay in irregular beds stand for occasional melting that went on in the glacier and around it, in its various stages of advance and recession.

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History of the city of Columbus, capital of Ohio, Volume I, Part 88

Author: Lee, Alfred Emory, 1838-; W. W. Munsell & Co Publication date: 1892 Publisher: New York and Chicago : Munsell & Co. Number of Pages: 1202

Author: Lee, Alfred Emory, 1838-; W. W. Munsell & Co
Publication date: 1892
Publisher: New York and Chicago : Munsell & Co.
Number of Pages: 1202