USA > Illinois > Atlas of the State of Illinois, to which are added various general maps, history, statistics and illustrations > Part 16
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SILURIAN SYSTEM-UPPER.
NIAGARA GROUP .- Tbis formation in Northern Illinois eon- sists of buff, gray and brown magnesian limestones, sometimes evenly bedded, as at Joliet and Athens, and at other points concretionary or hrecciated, as at Bridgeport and Port Byron. In the vicinity of Chicago, the upper part of this formation is highly bituminous, and the cells and pockets in the roek when freshly quarried are filled with petroleum. Attempts were made during the oil excitement, a few years since, to develop a. supposed oil deposit here, but it was found on boring that only the upper thirty fcet of tbe limestone presented this oil bearing character, while below that horizon the roek was entirely free from bituminous matter.
Tbe quarries at Joliet and Athens, in Will County, and at Grafton, in Jersey County, have long been celebrated for their fine building stone aud flagging stones, which are in some re- speets superior to any other to he found in the State. The rock is very evenly bedded, the strata varying in thick ness from two inches to two feet or more, and breaking so evenly, that dimension stone or flags of any desirable form or size ean be readily obtained. The rock is of a light gray color, which changes to buff on exposure, euts casily when freshly quarried, and hardens slightly by exposure. In Piko County, near Pleas- ant Hill, tbis formation is partially exposed, showing beds of huff and gray limestone, mostly in massive layers, wbich afford un excellent building stone. In Calhoun County, there are ex- tensive outcrops of this formation both in tbe Illinois and Mississippi River bluffs, where it presents the same lithological characters as at Grafton. In these evenly hedded magnesian limestones, fossils are usually quite rare, but the beds at Graf- ton present one exception to this rule. 'Tbese quarries have afforded fragments of some half dozen species of Trilobites, only one of which, bowever, is abundant. This is the common Calymene Blumenbucki, of whieb the quarrymen obtain a great many, whieli they sell to visitors for a trifling sum. They call them stone dogs, hut their resemblance to a dog is not very apparent. They oceur as perfeet ensts of the animal in lime- stone, and are associated with Orthoceras annulatum Lituites capax, &c.
The quarries at Bridgeport, near Chicago, have afforded nearly one hundred species of marine fossils, consisting of shells, corals and encrinites, but these are all costs of the or- ganio body preserved in the rock, while the calearcous portion has been dissolved away. Many of these are exceedingly inter- esting and instructive, as they exhibit aceurately in many cases the internal markings of these ancient marine forms of organio life. The rock at this locality, and at Port Byron on the Mis- sissippi, is too unovenly bedded to form a good building stone, but it furnishes an excellent material for quieklime, which is
manufactured in large quantities at both localities. In addition to the localities already eited, this formation outcrops over a great portion of the area between the northern boundary of the coal field and the northern line of the State. Its thickness in Western and Northern Illinois ranges from fifty to two bundred and fifty feet.
In Union and Alexander Counties, in the southern portion of the State, the Upper Silurian series consists mainly of tbin bedded gray or buff colored silicious and cherty limestone locally appearing argillaceous and shaly, hut for the most part execed- ingly cberty, the flinty material greatly predominating over the limestone. At the base of the group here, there is about three feet of dark gray limestone, that contains some characteristic Niagara fossils, among which is the Dalmanites Dans, which is quite abundant. The cherty mass wbich forms the middle and upper portion of the group has afforded but few fossils in Illi- nois, but at Bailey's Landing, in Missouri, we were ennhled to collect some twenty or thirty species, mostly of marine shells, which were generally identical with those from the Delthyris Shale of the New York series, which is there supposed to over- lio the Niagara beds. I douht the propriety of separating these heds, however, from the Niagara, for in Tennessee we find tbe characteristic Niagara and Delthyris Shale fossils mingled together in the same beds. At the base of this formation, there are some massive beds of mottled brown and gray lime- stone, that receives a fine polish and makes a good marble. The eherty beds of tbis group will furnish an inexhaustible supply of road material in its broken flints, which abound in the heds of all the streams that interscet its outcrop. This constitutes the hest material known for turnpike or macadamized roads, and it has also been used in the manufacture of artificial stone, for which it is said to be superior to the chalk flints of England. This formation is about two hundred and fifty feet in thickness in Southern Illinois.
DEVONIAN SYSTEM.
This system is represented in Illinois hy three well marked divisions, equivalent to the Oriskany Sandstone, the Onondaga Limestone, and tbe Hamilton and Corniferous beds of New York, the two latter not being separable in the West, and by a fourth or higher division, the Black Shale formation of Illinois, wbieh we place doubtfully iu the Devonian series. Tbese divi- sions, though comprising au aggregate tbiekness of about five hundred feet, are exposed only over a very limited area, their outerop being restricted to a few isolated exposures along the bluffs of the Illinois, the Mississippi and Roek Rivers.
CLEAR CREEK LIMESTONE .- The lower division, to whieb the name of " Clear Creek Limestone" has been given in the Illinois Reports, attains a thickness of about two hundred and fifty feet, and is only found in the extreme soutbern portion of the State. Commencing at the " Back-bone " in Jackson County, it forins the lower extremity of that ridge, and ex- tends thence southeastwardly to the southern terminus of the highlands in Alexander County, covering a narrow belt of country from two to six miles in widtb. The surface of the country over wbieh this formation outerops is broken into sharp ridges and precipitous hills, separated by deep gulebes, or narrow valleys, and the arahle land over this area is mainly confined to the valleys of the small streams. It consists of chert, or impure flint, and thin bedded silico-magnesian lime- stones, rather compaet in texture, and of buff, light gray or nearly wbite colors. It is highly silicious, and when decom- posed by atmospherie influences, it forms a fine white clay, resembling common chalk in its appearance. These clay beds are familiarly known in these counties and the adjacent region in Missouri as " Chalk banks." Some of the cherty beds are quite porous, like the common burr-stone of Europe, and some good mill-stones have been made from this material in Union County. Other portions of the mass aro close textured, and form, in part, the common flints which abound in the valleys of all the streams in this region, and which are derived alike from this formation and the underlying Upper Silurian beds, of which it is a close lithological representativo.
At the lower extremity of the "Baek-bone," where this formation first appears in Jackson County, and at Bald Rock on the Big Muddy, as well as in the nothern part of Union Coun- ty, there are massive beds of light hluisb gray and mottled crystalline limestone, which receives a fine polish and makes an elegant and durable building stone. Some of the beds on the Mississippi are streaked with pink, huff and light hlue colors,
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and, when polished, form a beautiful marhle. On Huggin's Creek, in Union County, the rock is of a delicate grayish white color, even texture and assumes the appearance of a whito marhle.
The characteristic fossils of this group, obtained from tho beds in Uniou County, which serve to identify it with the Oriskany Sandstone of New York, are the following species : Leptocalia flabellites, Leptoma nucleata, Rhyuchonella speci- osa, Palatyceras tortuosum, Rensselaria Condoni, Spirifer arctus, and Stricklandinia curta. At the exposures ou the Mississippi, the calcarcous heds abound in fossils, among which the remains of Crinoidea are abundant, consisting mainly of columns and body plates. The chalky clay to which this formation gives origin promises to hecome of considerable value for use in the mechanie arts, and the porous cherty layers, when of sufficient thickness, may he successfully used in the manufacture of hurr-stones.
ONONDAGA GROUP .- This group consists of sixty feet or more of quartzose sandstone and striped silicious shales, over- laid by ahout twenty feet of massive light gray limestone. 'The sandstone directly overlies the Clear Creek limestone usually, hut the fossils which it contains appear to ally it to the lime- stone ahove rather than that helow. They belong to the following genera: Zaphrentis, Pleurodictyum, Orthis aud Strophodonta, with fragments of a large Trilobite helonging to the genus Odontocephalus. The structure of the rock is almost identical with that of the St. Peter's Sandstone, being composed of clean white sand at some points, while at others it is slightly stained cither red or yellow hy the oxide of iron. It would he very difficult in hand specimens to distinguish these rocks from each other.
The striped silicious shales have received the local name of " Calico rock," in the vicinity of their outerop, from their vari- egated color, and have afforded no fossils at any of the localities examined. In the vicinity of their outcrop in Union County, heds of fine potter's clay occur in connection with the surface deposits, which have the same tints of color that prevail in the shale, and these may have beeu derived from their decom- position.
At the " Bake-oven " in Jackson County the lower portion of this group consists of alternate layers of quartzose sandstone with silicious limestones, the whole hecoming gradually more and more calcareous, and finally pass into the massive white limestone above. This limestone is ahout twenty feet in thickness, and occurs in evenly hedded massive strata, with a rather coarsely granular structure, and is a durable stone for heavy masonry. The most characteristic fossils of this lune- stone are Centronella hecate, Spirifer acuminatus, S. fimbri- atus, several undetermined Spirifers with very extended hinge lines, Atrypa reticularis, a Productus like P. sub-aculeatus, and a Tribolite resembling the Odontocephalus selenurus of the New York Devonian. This group has not been found in any portion of the State north of Jackson County.
HAMILTON GROUP .- The rocks comprising this group are more variable in their lithological characters thau those of either of the other divisions of the Devoniau system, and it would he quite impossible to identify the various outcrops in the State, except by the fossils which they contain. In South- ern Illinois, it is found in Union and Jackson Counties, from eighty to a hundred feet in thiekness, and contains two heds of dark hluish gray fetid limestones, separated by about twonty fect of chocolate colored, or yellowish brown, calcareous shales. The limestones are highly bituminous, and probably represent both the Hamilton and Corniferous heds of New York.
On the western horders of the State, in Jersey and Calhoun Counties, this group is represented hy a thin hed, only from six to ten feet in thickness, of hard siliceous limestone, which passes into a true quartzose sandstone at some points, and at others becomes argillaccous, as in the vicinity of Grafton, where it closely resembles a hydraulic limestone. The lower layers of the rock here are crowded with fossil corals, in a highly siliccous conditiou. They are mostly the Cystiphyllum Ameri- canum, a species common to the Hamilton heds in New York and elsewhere.
In Rock Island County, the most northern known outerop of this formation in Illinois, it consists of fine-grained, light gray and blue, or dove-colored limestone, associated with hrown cal- carcous shales. The thickness of the heds scen ahove the river level at Rock Island is about sixty feet, but on the opposite side of the river, a short distance ahove Davenport, they are found extending at least eighty feet hy measurement above the
STATE GEOLOGY.
| river bed. The rock has a concretionary structure here, and its total thickness is probably quite variablo. It forms the hed of Rock River at Camden, and a low bluff for some miles above, and is directly overlaid, in this vicinity, hy the sand- stones and shales of the coal measures. Tho rock has heen ex- tensively used in the vicinity of Rock Island as a building stone, and is also extensively manufactured into quicklime, for which purpose it is well adapted.
Fossils are abundant in this group, at almost every locality in the State where it has heen examined, and their specific identity at remote localities enables the observer to determine the equivalency of the outcrops, notwithstanding the diversity in their lithological characters. Several species of corals ahound iu this rock at nearly all the localities examined, belonging to the generu Cyathophyllum, Cystiphyllum, Zaphrentis, etc. Thero are also a few shells which are found at all the exposures of this formation, such as Strophomena demissa, Orthis Iowen- sis, Spirifer pinnatus, and Atrypa reticularis. The shells, with several species not cuumerated, are quite ahundant in the calcareous shales near Rock Island, and a small Trilobite, the Phacops rana, is also found both in the northern and southeru portions of the State. Many of the fossil corals from this for- mation receive a fine polish, and have been widely distributed over the country for cane heads and other ornamental purposes, under the name of Iowa marble, the first specimens of which were obtained near Iowa City. A few fragments of fossil fishes have been obtained from this formation, and they are the oldest remains of vertebrated animals that have been found in the State.
BLACK SHALE .- This formation we place douhtfully in the Devonian series for various reasons. First, hut a single species of fossil shell has been found in it in this State, a Lingula, which resembles the L. umbonata of Cox, a carboniferous species, far more than any one at present known from Devo- nian strata. Then again it coincides with the Lower Carbon- iferous, rather than with the Devonian in its development, for at various points in Tennessee it is associated with Lower Car- honiferous strata, and rests directly upon the Upper Silurian limestone, while there is no development of any Devonian strata below it in that region ; and finally it shades into the Lower Carhonifcrous beds so imperceptibly that, at many localities, it is impossible to define the boundary between them. Furthermore, there is no evidence that this hituminous shale, and associated heds in Illinois, are the stratigraphical equivalents of the heds in Ohio, to which the name " Black Slate" was originally applied. But a very small portion of the hed in this State presents a highly hituminous character, and by far the greater portion consists of green, blue or chocolate colored shales, in no way distinguishable from similar heds of the Kiu- derhook group, and at many localities the hituminous character is entirely wanting. Nevertheless, as it has generally heen considered to he of Devonian age hy Western geologists, and in the ahsence of conclusive evidence as to its true age, we place it provisionally in that horizon, leaving the question an open one, to he determined hy future developments.
In Union County, where it probably attains its maximum development, it ranges from fifty to seventy-five feet in thick- ness. A portion of it only, and that usually the lower portion, is a fino black lamiuated slate, that splits easily iuto thin, hut irregular laminæ, and sometimes closely resembles the hitumi- nous shales associated with the coal seams, and disseminated through the coal measures. This has led to the helief, among those not conversant with the subject, that it was a true coal- hearing deposit, and the consequence has heen that more time and moncy has been spent in looking for coal in this formation than would defray the expense of a thorough geological survey of all the counties in the State in which this slate is found. The highly hituminous portion of the mass is rich in hydro- carbon, and will yield hy distillation from fifteen to twenty per cent. of erude oil resembling petroleum. Crystals of iron pyrites are abundant in the argillaceous portions of the group at many localities, which might readily ho couverted into cop- peras or aluui, and this sometimes gives rise to alum springs. In the counties of Jersey, Calhoun and Pike, the most north- erly points where this formation appears above the surface, it varies in thickness from a few inches to about thirty fect, and is mostly an argillaceous shale, which locally hecomes partly bituminous, though it seldom shows this character to any great extout, and frequently it is entirely ahsent. In the horing for coal at Quincy, the Black Slate was said to have been reached at a depth of something more than a hundred feet. This
horing was commenced at the foot of the bluff, near the hase of the Lower Carboniferous Inuestone, and more than two hun- dred feet helow the lowest coal known in the State.
CARBONIFEROUS SYSTEM-LOWER.
This division of the Carboniferous System has heen subdi- vided in tho Illinois Geological Reports into the following groups, viz .: Kinderhook group, Burlington limestone, Keokuk group, St. Louis group and Chester group. These may he as readily distinguished from each other, hoth hy their lithological characters and their fossil contents, as the suhdivisions of the Silurian and Devonian systems. A few species of fossil shells, that have a wide stratigraphical as well as geographical range, extend through the whole scries, and, indeed, iuto the upper division of the system also, hut the greater number of the species are restricted to a single group of the series. This division of the Carhoniferous system attains its maximum de- velopment in Southern Illinois, where it reaches au aggregate of at least fourteen or fifteen hundred feet in thickness, hut thins out to the northward so rapidly that the whole disap- pears helow Rock Island, and in the vicinity of the Lower Rapids on the Mississippi, its thickness does not greatly exceed three hundred feet.
KINDERHOOK GROUP .- This gronp, which is quite variahle in its lithological characters, consists of argillaceous and saudy shales, with thin beds of compact and oolitic limestone, the whole passing locally into calcareous shales or impure limc- stones. In the extreuic southern portion of the State, it is found in Union and Hardin counties, where it consists mainly of siliceous and argillaccous shales, which have as yet afforded no fossils, hut they may he readily identified with this group by their lithological characters, and hy their stratigraphical position immediately above the Black Slate formation already described. In Monroe County, this group is represented in part hy red calcareous shales, that contain many of the characteristic fossils of this horizon, and these red shales are underlaid hy ash-colored argillaceous shales that have as yet afforded no well marked fossils. In Jersey County, we find this group forming the upper portion of the bluffs in the vicinity of Grafton, and the lower portion five miles helow, where the rock consists of thin hedded ash-colored limestone, with some massive layers of magnesian limestone with shaly partings. The lower portion contains nodules of calcite, re- sembling externally the geodes of the Kcokuk group, hut the interior portion of these is a solid mass of crystalized calcite. There are a few fossils to he obtained from the heds here exposcd, among which are Spirifer Vernonense, Athyris Prouti, Strophomena analoga, Productus semireticulatus, variety Bur- lingtonensis, and Proctus arcuatus.
In the connties of Calhoun and Pike, it is well developed, and consists for the most part of greenish and ash-colored shales, either sandy or argillaceous, with thin hands of oolitic and fine-grained limestone. The latter is of a light blue or dovo color, and weathers to a light gray. It is the so-called " Lithographie Limestone " of the Missouri Report, and is not greatly developed on the eastern shore of the Mississippi, heing seldom found more than five to ten feet in thickness, and is frequently ahsent altogether. The oölitic hed is here more properly an oulitic conglomerate, heing composed of variously colored pebbles cemented in an oölitic paste, and receives a fine polish, showing a mottled color. It is only from three to four feet in thickness. In the shalc heds we find a large "fucoid," or marine plant, quite abundant, which resembles the cauda galli of the Corniferous group of New York, and the occurrence of this forin in this group is sometimes urged as an evidence of its Devonian age, hut we find fucoids undis- tinguishable from this, high up in the coal measures of this State. Near Hamburg, the oolivie hed is shaly in its structure, and sometimes crowded with fossils, mostly of two or three species, among which the Rynchonella pustulosa is the most abundant. At Kinderhook, in Pike County, we find an exposure of thirty or forty fect of shaly sandstone forming the upper portion of this group, which contains casts of Aviculopectens, Spirifers, Orthis, Strophomena, Goniatites, etc. North of Pike County only a few feet of the upper part of this group has been found in surface outerops, hut in a horing made near Oquawka June- tion, in Henderson County, the hore was said to have passed through a thickness of one hundred and twenty feet of these shales. This whole formation is mainly a mechanical sediment, with hut a very small portion of organic matter.
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BURLINGTON LIMESTONE .- Tbis limestone differs entirely in its lithological characters from the group last deserihed, and is made up almost entirely of tho fossilized remains of organic beings, with harely enough of sedimentary material to cement tho organic matter together, Although its maximum thickness scarcely exceeds two hundred feet, it is nevertheless one of the most interesting aud important groups of the Lower Car- boniferous series. Its principal outerops are in the counties of Jersey, Greene, Scott, Calhonn, Pike, Adams, Warren and Henderson. The rock is usually a light gray, buff or brown limestone, with a coarsely granular or crystalline structure, and contains considerable cherty material either in seams or nodules. At Burlington, Iowa, where the rock was first studied, and in the adjacent region in Illinois, the upper portion is composed of light gmy crystallino limestoues, and the lower division of hrown arenaceous and magnesian beds, some of which readily decomposo by exposure, forming n brown sand or marly clay, from which the embedded fossils may be obtained in a most perfect state of preservation. Farther south, the distinctive characters of the upper and lower divisions are less marked, and in Jersey County, whero the entire thickness may bo seen in a single outcrop, as is the case at the bluff just below Jer- sey Landing, the rock is mainly a light gray cherty limestone, with local intercalations of brownish colored beds.
The most characteristic fossil shells of this limestone are the following: Spirifer Grimesi, S. plenus, S. imbrex, Enoupha- Ins latus, Productus semireticulatus, variety Burlingtoncusis, and Chonetes Illinoiseusis. Bnt hy far the most interesting group of fossils which this limestone has afforded are the Crinoideu, those beautiful " Lily Stars," of the old Carbonif- erous ocean, that swarmed in countless numbers during the ac- cumulation of tho sediments, that, in conjunction with their remains, form nearly the whole substance of this rock. Abont four hundred species of this class of marine animals have been found in this limestone, in the vicinity of Burlington alone, a number exceeding all that had previously been known from the rock formations of all ages, and from all other portions of the habitable globe. These fossils are quite as abundant in the adjacent region in Illinois as at Burlington, but these localities have been less prolific in fossils because the quarries are not so extensively worked. The teeth, spines and palate bones of a few species of cartilaginous fishes have beeu obtained from this limestone, but these remains are far less abundant in this horizon than in the group ahove. It affords some good building stone, as well as limestone, suf- ciently free from foreign material to be used in the manu- facture of quicklime.
KEOKUK GROUP .- Tbis group immediately succeeds the Bur- lington limestone in the ascending order, without any strongly defined line of separation hetween them. The lower portion of the group consists of thin bedded gray limestone, alternating with bands of chert, the limestone only differing from the Burlington rock in being of a more bluish gray color. The fossils, bowever, with the exception of a few species of shells, are entirely distinct from those in the beds below, and of all the four hundred species of Crinoidea that the Burlington limestone has afforded, not more than one or two have yet been found in the Keokuk beds. The thin hedded cherty limestone which forms the base of this group passes upward into a tolerably regularly bedded, bluish gray limestone, the quarry rock of Keokuk, in Iowa, and Nauvoo and Hamilton, in Illinois. This group has afforded some forty or fifty species of Crinoidea, but all, with one or two exceptions, entirely dis- tinet from those found in the limestone below. The most characteristic fossil shells of this group are the following : Spirifer striatus, S. Keokuk, S. linealus, S. tenui-costatus, Productus punctatus, P. semireticulatus, Hewiprouites erenis- tria, Athyris plano-sulcata and Platyceras equilatera, and with these we find a turbinated coral, Zaphrentis dalii, equally abundant. But the most interesting group of fossils which this rock affords are the remains of vertebrates. The teeth, spines and palate bones of more than fifty species of fossil fishes have been found in this group, in the vicinity of War- saw and Nauvoo alone, and the most of these have been de- scribed and figured in the second volume of the Report on the Geological Survey of Illinois. These were mostly obtained from certain zones, usually limited to a single stratum hut a few inches in thickness, where these fossils abounded, though comparatively rare in the intervening heds. Two of these zones belong to this group, and from these most of the ichthyic remains of this horizon have been obtained.
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