USA > Illinois > Atlas of the State of Illinois, to which are added various general maps, history, statistics and illustrations > Part 17
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STATE GEOLOGY.
Above the quarry roek of this group, and forming its upper division, we find a bed of blue or asb-colored calcarco-argilla- ceous shale, which contains a great variety of geodes, the cavi- ties of which aro lined with beautiful crystals of quartz, mam- millary chalcedony, crystals of calcite, dolomite, zinc-blende, iron pyrites and arragonite. These geodes furnish beautiful cabinet specimens of the crystalized minerals abovo named, and have heen widely distributed among the mineralogists of this country. Locally this upper division becomes cadcareous, and forms thin hedded limestones that contain the same fossils as the heds below. At the top of this formation, a bed of hy. draulic limestone occurs in Jersey and Monroe Counties, about six feet in thickness, which has been successfully worked for the manufacturo of cement. On the eastern borders of the Illinois coal field, in Crawford County, Indiana, tbis group con- sists mainly of argillaceous and sandy shales, the latter passing into saudstone. Its outerop in Illinois is mainly around the western borders of the coal field, from Henderson County on the north to Jackson County on tbo southwest, and it also ap- pears in Hardin County, on tho Ohio River, on the extreme southern horder of the State.
ST. LOUIS GROUP .- This group is quite variable in its litb- ological characters, being partly a fine-grained or semi-orystal- line, even-bedded, bluish gray limestone, and partly concretion- ary, as in the vicinity of Alton. North of the mouth of the Illinois River, however, the lower portion is everywhere more or less magnesian, and locally hecomes argillaceons and shaly, as at Warsaw, where this division consists of alternate beds of blue argillaceous shales, and coarse-grained magnesian linie- stones, while the upper part is a fine, compact, bluisb gray con- cretionary and brecciated limestone, that is so pure a carbonate of lime as to be everywhere used along its line of outerop for the manufacture of quicklime. In the extreme southern por- tion of the State, the limestones of this group become highly bituminous, and are dark blue or nearly black in color, and wben fine grained they receive a fine polish and make a very good black marble. At other localities in the same region, the rock is light gray, and contains some massive beds of oolitic limestone. This is the case near Rose Clare in Hardin County, where the oobitic beds are well exposed in the bluffs of the Ohio River. There are two species of fossil corals, that may bo considered as characteristic of this horizou, wherever this rock is exposed, from Iowa to Alabama, the Lithostrotion canadense and L. prolifera. In the vicinity of Alton and St. Louis, this limestone contains a large echinoid, or fossil sea urchin, which has been called Melouites multipora, the name being suggested by its resemblance to a melon. That it be- longs to the animal rather than to the vegetable kingdom may be readily seen, however, from the calcareous structure of the plates of which the body is composed, and their general analogy of structure with the living forms of this peculiar group of animals. In the vicinity of Warsaw, the shaly por- tion of this group is filled with delicate forms of bryozouns, a low group of the order mollusca, among which is the peculiar screw-shaped fossd known as the Archimedes. Just above these shales, there is a bed of massive magnesian limestone, which is sometimes arenaceous, and affords a very durable ma- terial for the construction of culverts and bridgo ahutments, where resistance to the combined action of frost and moisture is required. This bed has furnished the rock from the Sonora quarries, in Hancock County, used for the foundation of the now State House at Springfield. On the western borders of the State, this limestone generally lies immediately below the coal messures, and hence its outcrop is a reliable guide in deter- mining the boundary of the coal deposits.
In Hardin County, this limestono is traversed by veins of fluor spar, carrying galena and zinc blende. Lead mining was commenced here as esrly as 1842, and has been prosecuted at intervals ever since. The veins afford a large amount of fluor spar, and when this finds a ready market, the mines can be worked with profit. This is the only formation in the State that appears to be traversed by true metallic veins.
CHESTER GROUP .- This group, although it attains an ag- gregate thickness greater than that of all the other divisions of the Lower Carboniferous series, is only found in the southern portion of the State, and thins out so rapidly to the northward that at Alton the group is represented by only about twenty fect of strata, though in the counties of Randolph and Jack- son, not more than a hundred miles to the southward, it is fully eight hundred feet in thickness. It consists of hard, gray crystalline and argillaceous limestones, alternating with
sandy and argillaccous shales and sandstones, which locally re- placo each other. It is the " Pentremital limestone" of Owen and others, and also the " Archimedes limestone," in part, of Swallow and Shumard. These names were applied to it by some of the early observers, because the Pentremite and Arcbi- medes were among the most common forms of organic life that it- contained, but as tbesc genera are not restricted to this group, but are also found in other divisions of the Lower Carboniferous series, these names have become obsolete. In the shales of this group we find a tbin seam of coal, varying from one to six inches or more in thickness, which is, so far as is known, the carlicst evidence of the existence of true coal forming condi- tions in the paleozoic formations of the Mississippi Valley. A few species of a true Carboniferous flora are also found in the arenaceous shales and sandstones of this group, and are the carliest traces of land plants that have been found in this State. They occur hoth in Randolph and Pope Counties, and belong for the most part to the following species : Megaphytum protu- berans, Stigmaria reticulata, S. minor, S. stellatta, Knorrhia imbricata, and an undetermined species of Lepidodendron.
Commencing on the Ohio River in Hardin County, tbis group outcrops in a narrow belt from five to twelve miles in breadth, around the southwest border of the coal-field, as far north as the southern line of St. Clair County, beyond which it has only been seen in thin isolated outliers. It is character- ized by several species of Pentremites, among which P. godoni, P. pyriformis and P. sulcatus are the most common. These are associated with three or four species of Agassizocriuus, a genus uuknown in any of the lower divisions, aud also with several species of Zeacrinus and Poteriocrinus, peculiar to this horizon. It bas afforded the two most gigantic species of Cephalopoda known in the Carboniferous system, the Nautilus spectabilis and Orthoceras nobile. The former is about two feet in diameter, and, though incomplete, the largest specimen found weighs ahont one hundred and sixty pounds. The Or- thoceras was at least seven or eight feet in length when per- fect, though only ahout eighteen inches in length of the shell has been preserved. This fragment is about nine inchies in diameter at one extremity, and six at the other. The most common shells of this group are Athyris ambigua, A. Royissii, Spirifer bisulcata, Spirifer Leidyi, Spiriferini octoplicata, Myalina angulata, Schizodus Chesterensis, and a Piuna, closely resembling, if not identical with P. flabelliformis of European authors. Associated with these are a few species of fossil corals and bryozoans, among the most common of which are Zaph- rentis spinulosa, Archimedes Swallovana, and seveml species of Lyropora. The teeth and spines of a few species of fossil fishes have been found in this group, but these remains are by no means as numerous in this horizon as in some of the lower divisions of the Carboniferous system. Good building stone is obtained botb from the limestones and sandstones of this group.
CARBONIFEROUS SYSTEM-UPPER.
This division of the Carboniferous system includes the Con- glomerate, or " Mill Stone Grit" of European authors, and the truc coal measures. Its aggregate thickness may be estimated at about twelve hundred feet in the southern portion of the State, but it gmdually diminishes to the northward, and in the vicinity of La Salle it scarcely exceeds four or five hundred feet in thickness.
CONOLOMERATE .- This name has been used in the Geologi- cal Survey of Illinois to designate a thick hed of sandstone that lies at the base of the coal measures, and appears to have resulted from the culmination of the arenaceous sedimentary accumulations so conspicuous in the formation of the Chester group of the Lower Carboniferous series. It consists of mas- sive quartzose sandstone, sometimes nearly white, but more frequently stained red or hrown hy the ferruginous matter which it contains, and is frequently composed in part of round- ed quartz pebbles, from the size of a pea to several incbes in diameter. Sometimes these pebbles constitute the greater por- tion of the rock, but more frequently they are hut sparsely scattered through it, or are entirely wanting. When highly ferruginous, it weathers quite unevenly, and the oxide of iron cements the sand into a hard erust on the surface of the rock, which successfully resists the denuding influences of the atmos- phere, and the rock forms towering cliffs on the stream along its outerop. Where the quartz pebhles are of large size and abundant, the finor material is frequently disintegrated from
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STATE GEOLOGY.
around them on the exposed surfaces, leaving them projecting | few fishes have also been obtained from it iu this State, though from the surface like half embedded eannon balls. Sometimes it passes locally into thin bedded sandstone and shale, with one or more seamus of coal, and henee in the coloring of tho map it is not separated from the coal measures. Its thickness is variable. In the southern portion of the State it is often seen from one hundred and fifty to two hundred feet, or more, in thickness; while in the northern portion it seldom exceeds a thickness of twenty-five feet, and is frequently wauting altogether. It has afforded a few species of fossil plants, belonging to the following genera: Stigmaria, Sigillaria and Lepidodendron, and of species identical with those of the coal measures. No animal remains bave yet been obtained from it.
COAL MEASURES .- Tbis term has generally been used by American geologists, to designate the formation in which our principal coal deposits are found, and in this State it attains an aggregato thickness of at least a thousand feet, and covers nearly three-quarters of its entire area. It is by far the mnost important formation of stratified rocks to be found in the State, whether cousidered in relation to the extent of surface which it oceupics, or the value of the mineral deposits which it con- tains. The strata are horizontal in their position, the dip or inclination being seldom more than from six to ten feet to the mile. Its boundaries may he readily seen by referring to the accompanying map, and there is no considerable area probably within this boundary, that does not coutain valuable deposits of coal. Over a considerable portion of the central part of the State, however, no thick heds of coal havo yet been found, for the reason that they are only to be reached by a shaft from four to six hundred feet or more in depth, and the expense of putting a coal mine in successful operation where the eoal lies so far below the surface has deterred capitalists in this region from engaging extensively in coal mining, as an individual enterprise ; but this difficulty is being overcome by the forma- tion of joint stock companies for the development of the coal. ' At the present time, our coal mines are for the most part restricted to the regions bordering on the outerop of tho eoal seamus, whero they may be worked by tunneling into the seam along the outerop, or are to be reached by shafts carried down from one to three hundred feet below tho surface. The prinei- pal seams are all in the lower part of the measures, and are consequently most accessible on the outer borders of the coal field, where they outerop, or may be found not very far below the surface.
This formation is made up of sandstones, shales, eitber sandy, argillaceous or bituminous, thin beds of limestone, with coal and its associated fire elays. Seven workable heds of coal have been found in the lower part of the measures, which have an average thickness of from two to five feet, and in the upper measures, there are probably as many more of less im- portance, ranging in thickness from six inches to two feet. It was suggested by some of the early geologists, who partially examined portions of the Illinois eoal field, that it was not con- tinuous, but was broken up by disturbing influences into isolated basins. This opinion, however, is entirely without foundation in fact, aud we find the strata of the coul formation continuous over the whole area of tho coal field. This area embraces fully 37,000 square mães, heing three times as great as the coal area of either Ohio or Pennsylvania, and the averago thickness of the seven workable beds which it contains would form a stratum twenty feet in thickness.
The fire clays on which tbo coal seams usually rest probably represent the ancient soil, which sustained the growth of trees and plants of which the coal is formed. These elays, if pure, are valuable for the manufacture of fire brick, drain tile and common pottery, and may be profitably worked in connection with the coal seams. The covering or roof of the eoal is most frequently a bituminous shale, though it is sometimes a lime- stone, an argillaceous shale or sandstone. Iron in some form oceurs almost everywhere in the coal measures, sometimes in nodules or regular seams of the carbonato, which is its most common form in shales, or as a sulphuret forming yellow or silvery white erystals in the coal. In this form, it greatly depreciates the value of tho coal, when it cannot be readily separated from it in mining. The metamorphio conditions that prevailed in a portion of Pennsylvania, to produce the anthracito of that region, did not extend to the Illinois eoal field, and our coals are entirely of the bituminous varieties.
Marine shells, corals and crinoiden abound in the limestones and calcareous and bituminous shales of this formation, and a | valley.
these remains are comparatively rare. The most remarkable fossil of this kind which has yet been found in this State is a spiue of a huge fish belonging to the genus Edestus. This was obtained from Coal No. 6 (Belleville seam) at one of the mines near Belleville, in St. Clair County. It is about one foot in length, nearly three inches in breadth, and one an'l a quar- ter inelies in thickness. and is set on one side with serrated tooth-like projections, composed of solid enamel, which led Prof. Leidy to describe a similar spine as a portion of the jaw with the teeth remaining. This unique fossil, wbieb probably belonged to an animal nearly twenty feet in length, has been figured aud deseribed for the fourth volume of the Geological Survey of Illinois. Of the Lower Carboniferous species of fossil shells, we find the following in the coal measures : Pro- ductus punctatus, P. semireticulatus, and Athyris Royissii, and in the Chester group we find a Chonetes, scarcely to be distin- guished from the C. grunulifera of the coal measures, but with theso few exceptions, the speeies from the upper and lower divisions of the Carboniferous system are generally distinet. Fossil plants are quite abundant in this formation, especially in the shales above Coals Nos. 2 and 5. About ono bundred and fifty species of fossil plants have been already determined from the coal measures of Illinois, and this interesting field of scientific researeb is by no means exhausted. The sbales above Coal No. 2 have afforded the greatest variety of plants, mostly ferns, preserved in uodules of irou ore, and with these we find a few species of fishes, several insects, and one reptile, the only specimen of this order yet found in the State. For the most part, the fossil animals of the coal measures are as decidedly marine, with the exception of the insects and reptile above mentioned, as those of the Lower Carboniferous limestones. The shale beds also near Morris, where the remains of air- breathing animals bave been found, wero no doubt of marine origin, as two or three species of marine shells have been found in them, but this loeality is on the extreme northern verge of the eoal field, and the remains of these air-breathing animals were washed into the adjoining sea or bay, where they were buried and preserved in the constantly accumulating sediments.
The coal resources of this State are just beginning to be developed, and we shall soon realize to some extent the value of the coal deposits hidden beneath the surface of our broad prairies. No other State or country on the face of the globe, with the same area of territory, can com- pare with Illinois in the extent and value of its deposits of fossil fuel.
TERTIARY SYSTEM.
This system is only represented in the southern part of the State, where certain deposits of stratified sands, shales and conglomerate are found, which appear to mark the northern boundary of the great Tertiary formation of the Gulf States. Its outerop appears to be restricted to the counties of Alex- ander, Pulaski, Massae and Pope, and occupies but a very limited area upon the map. In the vicinity of Santa Fe, in Alexander County, it contains some good potter's clays, and also a thiu bed of lignite, whieb has led to some delusivo ex- pectations of the existence of a valuable coal deposit in the vicinity of its outcrop. This lignite bed, however, is value- less for fuel purposes. Siliceous wood is quite common in these beds in Pulaski County, and the casts of a few species of marine sbells are found in the green sandy sbales of this forma- tion, hut they are generally too imperfeet for specifie determina- tion. Although we now find no well marked Tertiary beds north of the counties above named, there is, nevertheless, very good reason for believing that beds of this age were deposited in the valley of the Mississippi, much to the northward of any known outerop, and, possibly, still exist beneath the alluvial deposits of the river valley. Three or four species of sharks' teeth, of undoubted Tertiary age, and in a perfect state of preservation, have been found hy the writer in tho vicinity of the Lower Rapids of the Mississippi, and one of them from a locality nearly forty miles north of the rapids, in the valley of Skunk River in Iowa. These probably camo from some still existing outliers of tho Tertiary formation, which was originally continuous for at least three bundred miles up the valley of the Mississippi, above the mouth of the Ohio, and may still be found beneath the alluvial deposits of this great
QUATERNARY SYSTEM.
This system embraces all the superficial material, including sands, clays, gravel and soil, which oversprends the older forma- tions in all portions of the State, and consequently is the most universally distributed, aud most accessible of them all. It is also of primary importance economically considered, because it gives origin to the soil, from which our all-important agrieul- tural resources are derived. This system may be properly separated into four divisions, viz .: Post-tertiary sands and elays, drift elay and gravel, Loess and Alluvium. The post-tertiary sands occupy the lowest position in the series, and consist of beds of stratified yellow sand and blue elay of variable thiek- ness, overlaid by a black, or chocolate-colored, loamy soil, con- taining leaves, branches and trunks of trees in a good state of preservation. In the southern part of the State, in the counties of Washington, Perry and the adjacent region, there is below the drift a bed of what seems to have been a blue mud, such as would accumulate in the bottom of a muddy pond. This also contains a large amount of vegetable matter partially decom- posed, emitting a very fetid odor when brought to the surface, from the decomposed animal and vegetable matter. At Bloom- ington in McLean County, at Coatshurg in Adams County, and at various other localities in the State, this ancient soil and the underlying beds of elay and sand have been penetrated in sinking shafts for coal, and in digging wells, which leads to the conclusion that they extend over a large portion of the State. Several fresh water and land shells were found in the quick- sand of this formation at Bloomington, but the only one that was sufficiently well preserved for determination proved to be a Helicina occulata, which is also found in the Loess, and living at the present time.
Above these stratified sand aud elays, and the ancient soil which overlies them, we find the truc Drift deposits, consisting of blue, yellow or brown elays, containing gravel and houlders of various sizes, some of them several feet in diameter, the water-worn fragments of rocks, many of which have been trans- ported from the northern shores of the great lakes. This drift accumulation varies in thickness from twenty to one hundred and twenty feet or more, and is sometimes overlaid by beds of stratified gravel, or, as it is sometimes termed, " modified drift." The true Drift presents but faint traces of stratification, except where it has been subjected to the subsequent action of waves, or water currents, whichi have sifted out the finer materials and arranged the gravel and boulders in a more or less regu- larly stratified position. At Vandalia, in the bluffs of the Okaw, there is a good exposure of this formation, showing both the stratified and unstratified deposits above mentioned. The unstratified drift-clays constitute the lower portion of the bluff, extending to the height of thirty-five or forty feet above the bed of the river at low water, and are succeeded by about the same thickness of gravel and sand, presenting distinct lines of stratification.
These accumulations are probably due to the combined action of water currents and moving ice, and the general direction of the currents appear to bave been to the southward, though the evidenees of the existence of counter currents are by no means wanting. Quartzgeodes, unmistakably derived from the Keokuk group, have been found at various points, far to the northward of any outerop of that formation, and the writer observed a large block of Burlington Limestone, of more than a ton's weight, in the drift deposits near Decatur, Illinois, that prob- ably did not come from the north, as there is no known outerop . of that limestone in that direction, and was most probably transported to its final resting-place by some northeastern eur- rent. Nevertheless tbe great body of drift material has come from the northiward, and ineludes the water-worn fragments of all the formations that are known to ontcrop in that direction for a distance of several hundred miles.
The subsoil, over a large portion of the central and northern divisions of the State, is predicated upon tho drift deposits, but it differs from them essentially in its character, and probably owes its origin to other and more recent eauses than the drift agencies. It is generally composed of fine brown clay, which differs in its appearance from the elays of the Drift, and pre- sents essentially the same characters, whether overlying these clays or tho sandy marls of the Loess. Hence we may infer that its origin is due to some eause, subsequent in its action to tho accumulation of these deposits, and uniform in its effects over formations essentially different in their constituent mate- rials. Prof. Lesquereux has given a very satisfactory explana- tion of the origin of this brown olay, as well as the soil above
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it, in a chapter on the "origin and formation of the prairies," in the first volumo of the Report on the Illinois Survey, as fol- lows : " It is evident that the black soil of their surface (the prairies), as well as the clayey subsoil, whatever the thickness of these strata way he, have been formed in place by the ageney aud growth of a peculiar vegetation. In stagnant water, whenever water is low enough to admit the transmission of light and air in sufficient quantity to sustain vegetable life, the bottom is first invaded by confervæ, and especially by Characez, and a peculiar kind of floating moss ( Hypnum aduncum). These plants contain in their tissue a great pro- portion of lime, allumina, silica, and even of oxide of iron, the elements of elay. When exposed to atmospheric influence, the Characex become covered with an effloresenee of scarcely ear- bonized or pure iron. Morcover, this vegetation of the low, stagnant waters feeds a prodigious quantity of' small mollusks aud infusoria, whose shells and detritus greatly add to the de- posits. The final result of the decomposition of the whole matter is that fine olay of the subsoil of the prairies, which is indeed truly impalpable, when dried and pulverized and un- mixed with sand." In other words, the surface of the prairie region was originally covered with shallow ponds and marshes, that produced a peculiar growth of vegetation, from the decom- position of which, in conjunction with the animal remains that also abounded in then, the soil and subsoil of our prairies were formed. This seems to be a satisfactory explanation of the origin of the subsoil of our prairie region, aud shows the reason of its preserving sueh a uniform character over wide areas, and why it is so little affected by the changes in the character of tho un- derlying formations. The prairie soil only differs from the subsoil by the addition of partly carhonized vegetable matter, that from year to year accumulates upon the surface from the annual growth and decay of its luxuriant flora, which imparts to it its peculiar black color. Where the surface is rolling or broken by streams, this partially earbouized vegetable matter washes dowu and accumulates in the valleys, leaving the soil but slightly colored and scarcely distinguishable from the suh- soil below. In age this deposit would seem te correspond most nearly with the Alluvium.
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