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CARBONIFEROUS SYSTEM

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Originally appearing in Volume V05, Page 313 of the 1911 Encyclopedia Britannica.
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CARBONIFEROUS See also:

SYSTEM , in See also:geology, the whole of the See also:great See also:series of stratified rocks and associated volcanic rocks which occur above the Devonian or Old Red See also:Sandstone and below the See also:Permian or Triassic systems, belonging to the Carboniferous See also:period. The name was first applied by W. D. See also:Conybeare in 1821 to the See also:coal-bearing strata of See also:England and See also:Wales, including the related grits and limestones immediately beneath them. The See also:term is a relic of that See also:early period in the See also:history of stratigraphy when each See also:group of strata was supposed to be distinguished by some See also:peculiar lithological See also:character. In this See also:case the carbonaceous beds—coal-seams—naturally appealed most strongly to the See also:imagination, and the name is a See also:good one, not-withstanding the fact that coal-seams occupy but a small fraction of the See also:total thickness of the Carboniferous system; and although subsequent investigations have demonstrated the existence of coal in other See also:geological formations, in none of these does it See also:play so prominent a See also:part. The stratified rocks of this system include marine limestones, shales and sandstones; estuarine, lagoonal and fresh-See also:water shales, sandstones and marls with beds of coal, oil-bearing rocks, See also:gypsum and See also:salt. In many parts of the See also:world there is no See also:sharp See also:line of demarcation between the Devonian and the Carboniferous rocks; neither can the fossil faunas and floras be clearly separated at any well-defined line; this is true in See also:Britain, See also:Belgium, See also:Russia, See also:Westphalia and parts of See also:North See also:America. Again, at the See also:summit of the Carboniferous series, both the rocks and their fossil contents See also:merge gradually into those of the succeeding Permian system, as in Russia, Bohemia, the See also:Saar region and See also:Texas. This has led certain geologists to classify the Devonian, Carboniferous and Permian into one See also:grand system; E. See also:Renevier in 1874 proposed to include these three into a single " Carbonique " system, later he retained only the two latter See also:groups. There seems to be sufficient See also:reason, however, to maintain each of these groups as a See also:separate system and limit the term Carboniferous (earboniferien) in the manner indicated above.

At the same See also:

time it must be remembered that there is in See also:India, See also:South See also:Africa, the Urals, in See also:Australasia and parts of North America an important series of rocks, with a " Permo-Carboniferous " See also:fauna, which constitutes a passage formation between the Carboniferous, sense stricto, and See also:Jurassic rocks. Stratigraphy.—No assemblage of stratified rocks has received such careful and detailed examination as the Carboniferous system; consequently our knowledge of the stratigraphical sequence in isolated See also:local areas, where the coals have been exploited, is very full. In See also:Europe, the system is very completely See also:developed in the See also:British Isles, where was made the first successful See also:attempt at a See also:classification of its various members, although at a somewhat earlier date See also:Omalius d'Halloy had recognized a terrain bituminifere or coal-bearing series in the Belgian region. The See also:area within which the Carboniferous rocks of Britain occur is sufficiently extensive to contain more than one type of the system, and thus to See also:cast much See also:light on the varied See also:geographical conditions under which these rocks were accumulated. In prosecuting the study of this part of British geology it is soon discovered, and it is essential to See also:bear in mind, that, during the Carboniferous period, the See also:land whence the See also:chief supplies of sediment were derived See also:rose mainly to the north and north-See also:west, as it seems to have done from very early geological time. While therefore the centre and south of England See also:lay under clear water of moderate See also:depth, the north of the See also:country and the south of See also:Scotland were covered by shallow water, which was continually receiving See also:sand and mud from the adjacent See also:northern land. Hence See also:vertical sections of the Carboniferous formations of Britain differ greatly according to the districts in which they are taken. The Coal-See also:Measures and Millstone Grit are usually grouped together in the Upper Carboniferous, the Carboniferous See also:Limestone series constituting the See also:Lower Carboniferous. In addition to the above broad subdivisions, See also:Murchison and See also:Sedgwick, when working upon the rocks of See also:Devonshire and See also:Cornwall, recognized, with the assistance of W. See also:Lonsdale, another phase of sedimentation. This comprised dark shales, with grits and thin limestones and thin, impure coals, locally called " See also:culm " (q.v.). These geologists appropriated the term " culm " for the whole of this tacies in the west of England, and subsequently traced the same type on the See also:European See also:continent, where it is widely developed in the western centre.

Besides the considerable exposed area of Carboniferous rocks in Great Britain, there is as much or more that is covered by younger formations; this is true particularly of the eastern See also:

side of England and the south-eastern counties, where the coal-measures have already been found at See also:Dover. From England, Carboniferous rocks can be followed across northern and central See also:France, into See also:Germany, Bohemia, the See also:Alps, See also:Italy and See also:Spain. In Russia this system occupies some 30,000 sq. m., and it extends northward at least as far as Spitzbergen. Carboniferous rocks are See also:present in North and South Africa, and in India and Australasia ; in See also:China they See also:cover thousands of square See also:miles, and inthe See also:United States and British North America they occupy no less than 2oo,000 sq. m. ; they are known also in South America. The subjoined table expresses the typical subdivisions which can be recognized, with modifications, in the United See also:Kingdom. Upper: Red and See also:grey sandstones, marls and See also:clays with occasional breccias, thin coals and limestones with Spirorbis, workable coals in the South Wales, Coal See also:Bristol, See also:Somerset and See also:Forest of See also:Dean coalfields. Measures. See also:Middle: Sandstones, marls, shales and the most important of the British coals. Lower: Flaggy hard sandstones (ganister), shales and thin coal seams. Grits (coarse and See also:fine), shales, thin coal seams and occasional thin limestones. The fossil See also:plants connect this group with the coal-measures; the marine fossils have, to some extent, a Carboniferous limestone aspect.

Upper See also:

black shales with thin limestones (Pendleside group) connecting this series with the Millstone grit above. The thick, See also:main or scaur limestone (See also:mountain See also:lime- See also:stone) of the centre and south of England, Wales and Carboniferous See also:Ireland, which splits up in the See also:Yorkshire dales Limestone (Yoredale group) into a See also:succession of stout limestone Series. beds between beds of sandstone and shale, and becomes increasingly detrital in character as it is traced northwards. Lower limestone shales of the south and centre of England with marine fossils, and the Calciferous Sandstone group of Scotland with marine, estuarine and terrestrial fossils. (See BERNICIAN, TUEDIAN and See also:AVONIAN.) At an early period, owing to the immense commercial importance of the coal seams, it became the practice to distinguish a " productive " (flotzfiihrend, terrain houiller) and an "unproductive," barren (flotzleerer) Lower Carboniferous; these two groups correspond in North America to the " Carboniferous " and " Sub-Carboniferous " respectively, or, as they are now sometimes styled, the " Pennsylvanian " and " Mississippian." But it was soon discovered that the " productive " beds were not regularly restricted to the upper or younger See also:division, and, as E. See also:Kayser points out, the real See also:state of the See also:matter is more accurately represented by the subjoined See also:tabular See also:scheme. See also:Continental Type of Marine Type of See also:Deposit. Formation. Upper Upper Productive Carboni- Younger Carboniferous Carboni- ferous limestone and the Fusu- ferous lina limestone of Russia and Western North America Lower Lower Productive Carboni- See also:Calm Lower Carboni- Carboni- ferous (in part) ferous lime- ferous stone series While the continental type of deposit, with its coal beds, was the earliest to be formed in certain areas, and the marine series came on later, in other regions this See also:order was reversed. It should be observed, however, that the repeated intercalation of marine deposits within the continental series and the frequent occurrence of thin coaly layers in the marine series makes any hard and fast distinction of this See also:kind impossible. The so-called " unproductive " or barren strata, that is, those without workable coals, are not always limestones; quite as often they are shales, red sandstones and red marls. In subdividing the strata of the Carboniferous system and correlating the See also:major divisions in different areas, just as in other great systems, use has to be made of the fossil contents of the rocks; stratigraphical See also:units, based on lithology, are useless for this purpose. The groups of organisms utilized for zoning and correlation by different workers include brachiopods, pelecypods, cephalopods, See also:corals, fishes and plants; and the results of the comparison of the faunas and floras of different areas where Carboniferous rocks occur are generalized in the table below.

The relative value of any group of animals or plants for the correlation of distant areas must vary greatly with the varying conditions of sedimentation and with the precise See also:

definition of the zonal See also:species and with many other factors. It is found that the sub-divisions in this system demanded by palaeobotanists do not always coincide with those acknowledged by palaeozoologists; nevertheless there is See also:general agreernent as to the main divisional lines. Breaks in the Stratigraphic Sequence.—The sequence of Carboniferous strata is not everywhere one of unbroken continuity. From central France eastward towards the Carpathians only later portions of the system are found. These generally See also:rest upon crystalline rocks, but in places they contain See also:evidence of the denuded surfaces of Lower Carboniferous, as in the See also:basin of See also:Charleroi, where the See also:equivalent of &Att. n. or absent. roxsibro See also:diet,batlon of Land & Sen.- ad«. ---- Yo''See also:nye!' lmtermed,See also:ate stores ore not sr...) S W." Millstone Grit. the Millstone Grit contains fragments of chert which can only have come from the See also:waste of the earlier limestones. This unconformity is generally found about the same See also:horizon in the continental Culm areas, and it occurs again in the western part of the See also:English Culm. In the eastern border of the Rhenish Schiefergebirge the Permian rests unconformably upon Lower Carboniferous rocks. In the Tabular Statement of the See also:Principal Subdivisions of the Carboniferous United States, in See also:Missouri, See also:Pennsylvania, West See also:Virginia, See also:Kentucky, See also:Ohio and elsewhere, there is an unconformable junction between the Lower and Upper Carboniferous, representing an See also:interval of time during which the lower member was strongly eroded; it has even been proposed to regard the Mississippian (Lower Carboniferous) as a distinct geological period, mainly on See also:account of this break in the succession. Thickness of Carboniferous Rocks.—The great variety of conditions under which the sediments and limestones were formed naturally produced corresponding inequalities in the thickness.

In the See also:

Eurasian land area the greatest thickness of Carboniferous rocks is in the west; in North America it is in the See also:east. In Britain the Carboniferous limestone series is 2000-3500 ft. thick; in the Ural mountains it is over 4500 ft.; the Culm in See also:Moravia is credited with the enormous thickness of over 42,000 ft. The Upper Carboniferous in See also:Lancashire is from t2,000 to 13,000 ft.; elsewhere in Britain it is thinner. In western Germany this portion attains a thickness of Io,000 ft. In Pennsylvania the sandstone and shale, at its maximum, reaches 4400 ft., but even within the limits of the state this formation has thinned out to no more than 300 ft. in places. In See also:Colorado the Lower Carboniferous is only 400-500 ft. thick; while the limestones of the See also:Mississippi basin amount to 1500 ft. and in Virginia are 2000 ft. thick. See also:Life of the Carboniferous Period.—We have seen that in the Carboniferous rocks there are two phases of sedimentation, the one marine, the other continental; corresponding with these there are two distinct faunal facies. (1) Fauna of the Marine Strata.—Numerically, the most important inhabitants of the clear Carboniferous seas were the crinoids, corals, See also:Foraminifera and brachiopods. Each of these groups contributed at one See also:place or another towards the upbuilding of great masses of limestone. For the first time in the See also:earth's history we find Foraminifera taking a prominent part in the marine faunas; the genus Fusulina was abundant in what is now Russia, China, See also:Japan, North America; Valvulina had a wide range, as also had Endothyra and Archaediscus; Saccammina is a See also:form well known in Britain and Belgium, and many others have been described ; some Carboniferous genera are still extant. See also:Radiolaria are found in cherts in the Culm of Devonshire and Cornwall, in Russia, Germany and elsewhere. See also:Sponges are represented by spicules and See also:anchor See also:ropes.

Corals, both See also:

reef-builders and others, flourished in the clearer See also:waters; rugose forms are represented by Amplexoid, Zaphrentid and Cyathophyllid types, and by Lithostrotion and Phillipsastraea; See also:common tabulate forms are Chaetetes, Chladochonus, Michelinia, &c. Amongst the echinoderms crinoids were the most numerous individually, dense submarine thickets of the See also:long-stemmed kinds appear to have flourished in many places where•their remains consolidated into thick beds of See also:rock; prominent genera are Cyathocrinus, Woodocrinus, Actinocrinus; See also:sea-urchins, Archaeocidaris, Palaeechinus, &c., were present; while the curious See also:extinct Blastoids, which included the groups of Pentremitidae and Codasteridae, attained their maximum development. Annelids (Spirorbis, Serpulites, &c.) are common fossils on certain horizons. The B ozoa were also abundantinsomeregions(Polypora, See also:Fenestella), including the remarkable form known as See also:Archimedes. Brachiopods occupied an important place; most typical were the Productids, some of which reached a great See also:size and had very thick shells. Other common genera are Spirifer, Chonetes, Athyris, Rhynchonellids and Terebratulids, Discina and Crania. Somespecies had an almost world-wide range with only See also:minor See also:variations; such are Productus semireticulatus, P. cora, P. pustulosus; Orthotetes (Streptorhynchus) crenistria, Dielasma hastata, and many others. Pelecypods among the true See also:mollusca were increasing in See also:numbers and importance (Aviculopecten, Posidonomya) ; Nucula, Carboni-cola, Edmondia. Conocardium, Modiola, Gasteropods also were numerous (Murchisonia, Euomphalus, Naticopsis). The Pteropods were well represented by Conularia and See also:Bellerophon. Amongst the Cephalopods, the most striking feature is the rise and development of the Goniatites (Glyphioceras, Gastrioceras, &c.); straight-shelled forms still lived on in some variety (Orthoceras, Actinoceras), along with numerous nautiloids. See also:Trilobites during this period sank to a very subordinate position, but Ostracods (Cythere, Kirkbya, Beyrichia) were abundant.

Many See also:

fish inhabited the Carboniferous seas and most of these were Elasmobranchs, sharks with crushing See also:pavement See also:teeth (Psammodus), adapted for grinding the shells of brachiopods, crustaceans, &c. Other sharks had piercing teeth (Cladoselache and Cladodus) ; some, the petalodonts, had peculiar See also:cycloid cutting teeth. The Arthrodirans, so prominent during the Devonian period, disappeared before the See also:close of the Carboniferous. Most of the sharks lived in the sea continuously, but the ganoids frequenting the coastal waters appear to have migrated inland. About 700 species of Carboniferous fish have been described largely from teeth, spines and dermal ossicles. (2) See also:Flora and Fauna of the Lagoonal or Continental Facies.–The strata deposited during this period are the earliest in which the remains of plants take a prominent place. The fossil plants which are found in the upper beds of the preceding Devonian system are so closely related to those in the Lower Carboniferous, that from a palaeobotanical standpoint the two form one indivisible period. In the Lower Carboniferous the flora was composed of six great groups of plants, viz. the Equisetales (See also:Horse-tails), the Lycopodiales (See also:Club mosses), the Filicales (Ferns) and Cycadofilices, the Sphenophyllales and Cordaitales. These six groups were the dominant types throughout the period, but during Upper Carboniferous time three other groups arose, the Coniferales, the See also:Cycadophyta, and the See also:Ginkgoales (of which Ginkgo biloba is the only See also:modern representative). See also:Algae and See also:fungi also were present, but there were no flowering plants. The true ferns, including See also:tree ferns with a height of upwards of 6o ft., were associated with many plants possessing a See also:fern-like See also:habit (Cycadofilices) and others whose See also:affinities have not yet been definitely determined. The fronds of some of these Carboniferous ferns are almost identical with those of living species.

Probably many of the ferns were epiphytic. Pecopteris, Cyclopteris, Neuropteris, Alethopteris, Sphenopteris are common genera; Megaphyton and Caulopteris were tree ferns. Our modern diminutive " horse-tails " with scaly leaves were represented in the Carboniferous period by gigantic calamites, often with a See also:

diameter of 1 to 2 ft. and a height of 50 to 90 ft. The Carboniferous forerunners of the tiny club-See also:moss were then great trees with dichotomously branching stems and crowded linear leaves, such as Lepidodendron (with its See also:fruit See also:cone called Lepidostrobus), Halonia, Lepidophloios and Sigillaria, the largest plants of the period, with trunks sometimes 5 ft. in diameter and too ft. high. The roots of several of these forms are known as Stigmaria. Sphenophyllum was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods. Cordaites, a tall plant (20-30 ft.) with See also:yucca-like leaves, was related to the cycads and conifers; the catkin-like inflorescence, which See also:bore See also:yew-like berries, is called Cardiocarpus. Many large trees which have been looked upon as conifers on account of their See also:wood structure may perhaps belong more properly to the Cordaitales. True coniferous trees (Walchia) do appear at the See also:top of the coal measures. The animals preserved in the continental type of Carboniferous deposit naturally differ markedly from the fossil remains of the purely marine portions of the system. The inhabitants of the waters of this geographical phase include mollusca, which are supposed to have lived in brackish or fresh water, such as Anthracomya, Naiadites, Carbonicola, and many forms of See also:Crustacea, e.g. (Bairdia Carbonia), phyllopods (Estheria), phyllocarids (Acanthocaris, Dithyrocaris), schizopods (A nthrapalaemon), Eurypterids (Eurypterus, Glyploscorpius).

Fishes were abundant, many of the smaller ganoids are beautifully preserved in an entire See also:

condition, other larger forms are represented by fin spines, teeth and bones; Ctenodus, Uronemus, Acanthodes, Cheirodus, Gyracanthus are characteristic genera. Frequently a temporary return of marine conditions permitted the entombment of such salt water genera as Lingula, Orbiculoidea, Productus in the thin beds known as " marine bands." Remains of See also:air-breathing See also:insects, myriapods and arachnids show that these forms of life were both well developed and individually numerous. Among the insects we find the See also:Orthoptera, See also:Neuroptera, See also:Hemiptera and See also:Coleoptera represented; cockroaches were particu• See also:lady abundant; crickets, beetles, locusts, walking-stick insects, mayflies and bugs a;e found, but there were neither flies, moths, butterflies nor bees, which is no more than we should expect from System. o II . America. Predominant ° V . plant Types. N European Developmentis= a x o r f-. Ouralien and Stephanien a Ferns and // \\ ss Annularias (marine type) (continental type) [ a Moscovien and Westphalien Sigillarias // \\ and (marine type) (continental type) Calamites 2 0).v Dinantien and Culm a Lycopods o o II II o. u a (marine pelagic, (marine littoral) a. 3 a including See also:con- en o a ° tinental de- y v posits in some U. areas) the conditions of plant life. Many insects, &c., have been obtained from the coalfields of Saarbruck and See also:Commentry, and from the hollow trunks of fossil trees in Nova See also:Scotia.

Certain British coal-See also:

fields have yielded good specimens: Archaeoptilus, from the See also:Derby-See also:shire coalfield, had a spread of wing extending to more than 14 in.; some specimens (Brodia) still exhibit traces of brilliant wing See also:colours. In the Nova Scotian tree trunks land snails (Archaeozonites, Dendropupa) have been found. In the later Carboniferous rocks the earliest amphibians make their See also:appearance in considerable numbers; they were all Stegocephalians (Labyrinthodonts) with long bodies, a See also:head covered with bony plates and weak or undeveloped limbs. The largest were about 7 or 8 ft. long, the smallest only a few inches. Some were probably fluviatile in habit (Loxomma,Anthracosaurus,Ophiderpeton) ; others may have been terrestrial (Dendrerpeton, Hylerpeton). Certain footprints in the coal measures of See also:Kansas have been supposed to belong to lacertilian or dinosaurian forms. The See also:Physical Conditions during the Period.—In western Europe the See also:advent of the Carboniferous period was accompanied by the See also:production of a series of synclines which permitted the formation of organic limestones, See also:free from the sediments which generally characterized the concluding phases of the preceding Devonian deposition. The old land area still existed to the north, but doubtless much reduced in height; against this land, detrital deposits still continued to be formed, as in Scotland; while over central Ireland and central and northern England the clearer waters of the sea furnished a suitable See also:home for countless corals, brachiopods and foraminifera and great beds of sea lilies; sponges flourished in many parts of the sea, and their remains contributed largely to the formation of the beds of chert. This clearer water extended from Ireland across north-central England and through South Wales and Somerset into Belgium and Westphalia; but a narrow See also:ridge of elevated older rocks ran across the centre of England towards Belgium at this time. Traced eastward into north Germany, Thuringia and See also:Silesia, the limestones pass into the detrital culm formations, which owe their existence to a See also:southern uplifted See also:massif, the See also:complement of the synclines already mentioned. Sediments approaching to the culm type, with similar flora and fauna, were deposited in synclinal hollows in parts of France and Spain. Thus western Europe in early Carboniferous time was occupied by a series of constricted, gulf-like seas; and on account of the steady progress of intermittent warping movements of the crust, we find that the areas of clearer water, in which the limestone-See also:building organisms could exist, were repeatedly able to spread, thus forming those thin limestones found interbedded with shale and sandstone which occur typically in the Yoredale See also:district of Yorkshire and in the region to the north, and also in the culm deposits of central Europe.

The spread of these limestones was repeatedly checked by the steady influx of detritus from the land during the pauses in movements of depression. Looking eastward, towards central and northern Russia, we find a wider and much more open sea; but the continental type of deposit prevailed in the northern portion, and here, as in Scotland, we find coal-beds amongst the sediments (See also:

Moscow basin). Farther south in the Donetz basin the coals only appear at the close of the Lower Carboniferous. In North America, the crustal movements at the beginning of the period are less evident than in Europe, but a marked See also:parallelism exists; for in the east, in the Appalachian See also:tract, we find detrital sediments prevailing, while the open sea, with great deposits of lime-stone, lay out towards the west in the direction of that similar open sea which lay towards the east of Europe and extended through See also:Asia. The close of the early Carboniferous period was marked by an See also:augmentation of the orogenic movements. The gentler synclines and anticlines of the earlier part of the period became accentuated, giving rise to pronounced mountain ridges, right across Europe. This See also:movement commenced in the central and western part of the continent and continued throughout the whole Carboniferous period. The mountains then formed have been called the " Palaeozoic Alps " by E. Kayser, the " Hercynian Mountains " by M. See also:Bertrand. The most western range extended from Ireland through Wales and the south of England to the central See also:plateau of France; this was the " Armorican range " of E. See also:Suess.

The eastern part of the See also:

chain passed from South France through the See also:Vosges, the Black Forest, Thuringia, Harz, the See also:Fichtelgebirge, Bohemia, the Sudetes, and possibly farther east; this constitutes the " Varischen Alps " of Suess. The sea had gained somewhat at the beginning of the Carboniferous period in western Europe, but the effect of these movements, combined with the rapid formation of detrital deposits from the rising land areas, was to drive the sea steadily from the north towards the south, until the open sea (with limestones) was relegated to what is now the Mediterranean and to Russia and thence eastward. Similar events were meanwhile happening in North America, for the seas were steadily filled with sediments which drove them from the north-east towards the south-west, and doubtless those movements which at the close of this period uplifted the Appalachian mountains were already operative in the same direction. The folding of the Ural mountains began in the earlier part of this period and was continued, after its close, into the Permian; and there are traces of uplifts in central Asia and See also:Armenia. None of these movements appears to have affected the southern hemisphere. The See also:net result of the orogenic movements was, that at the close of the period there existed a great northern continental See also:mass, embracing Europe, North Asia and North America; and a great southern continental mass, including South America, Africa, See also:Australia and India. Between these land masses lay a great Mediterranean sea—the " Tethys " of Suess. The conditions under which the beds of coal were formed will be found described under that head; it will be sufficient to See also:notice here that some coal seams were undoubtedly formed by See also:jungle or swamp-like growths on the site of the deposit, and it is equally true that others were formed by the transport and deposition of See also:vegetable detritus. The main point to observe in this connexion is that large tracts of land in many parts of the world were at a See also:critical level as regards the sea, a condition highly favourable to frequent extensive incursions of marine waters over the See also:low-lying areas in a period of extreme crustal instability. Vulcanicity.—In intimate relationship with the mountain-building orogenic crustal movements was the prevalence of volcanic activity during the earlier part of this period. In the Lower Carboniferous rocks of Scotland intercalated volcanic rocks are strikingly abundant, and now form an important feature in the geology of the southern portion of that country. Of these rocks See also:Sir See also:Archibald See also:Geikie says: Two great phases or types of volcanic See also:action during Carboniferous time may be recognized—0) Plateaus, where the volcanic materials discharged copiously from many scattered openings now form broad tablelands or ranges of hills, sometimes many hundreds of square miles in extent and 1500 ft. or more in thickness; (2) Puys, where the ejections were often confined to the See also:discharge of a small amount of fragmentary materials from a single See also:independent vent." The plateau type was most extensively developed during the formation of the Calciferous Sandstone; the See also:puy type was of somewhat later date.

Basic lavas, with andesites, trachytes, tuffs and agglomerates are the most common Scottish rocks of this period. Similar eruptions, but on a much smaller See also:

scale, took place in other parts of Great Britain. Granites, porphyries and porphyrites belonging to this period occur in the Saxon See also:Erzgebirge, the Harz, Thtiringerwald, Vosges, See also:Brittany, Cornwall and See also:Christiania. Porphyrites and tuffs are known in the See also:French Carboniferous. In China, at the close of the period, there were enormous eruptions of melaphyre, porphyrite and See also:quartz-See also:porphyry. In North America, the principal region of volcanic activity lay in the west; great thicknesses of igneous rocks occur in the Lower Carboniferous rocks of British See also:Columbia, and from the middle of the period until near its close volcanoes were active from See also:Alaska to See also:California. Igneous rocks of this period are found also in Australasia. See also:Climate.—That the vegetation during this period was unusually exuberant there can be no doubt, and that a general uniformity of See also:climatic conditions prevailed is shown not only by the wide See also:distribution of coal measures, but by the uniformity of plant types over the whole earth. It is well, however, to guard against an over-estimation of this exuberance; it must be See also:borne in mind that the physiographic conditions were peculiarly favourable to the preservation of plant remains, conditions that do not appear to have obtained so completely in any other period. The climate, we may assume from the distribution of land and water, was generally moist, and it was probably mild if not warm; conditions favourable to the growth of certain types of plants. But there is no good evidence for an excess of See also:carbon dioxide in the atmosphere—an See also:assumption founded on the luxuriance of the vegetation, coupled with the fact that vulcanicity was active and wide-ranging. Carbon dioxide may have been present in the air in greater abundance in earlier periods than it is at present, but there is no reason to suppose that the percentage was appreciably higher in the Carboniferous period than it is now.

The occurrence of red deposits in western Australia, Scotland, the Ural mountains, in See also:

Michigan, See also:Montana and Nova Scotia, &c., associated in some instances with the formation of gypsum and salt, clearly points to the existence of areas of excessive evaporation, such as are found in land-locked waters in regions where something like See also:desert conditions prevail. The xerophytic structures found in some of the plants might seem to corroborate this vjew; but similar structures are assumed by many plants when dwelling in brackish marshes and morasses. The abundance of corals in some of the Carboniferous seas and possibly also the large size of some of the Productids and foraminifera may be taken as evidence of warm or temperate waters. In spite of the bulk of the evidence being in favour of geniality of climate, it is necessary to observe that certain deposits have been recognized as glacial; in the culm of the See also:Frankenwald, in the coal basins of central France, and in central England, certain conglomeratic beds have been assigned, somewhat doubtfully, to this origin. They have also been regarded as the result of torrential action. Glacial deposits certainly do exist in the Permo-carboniferous formations, which are described under that head, but in the true Carboniferous system glaciation may be taken as not proven. The See also:foreign boulders of See also:granite, See also:gneiss, &c., found in the coal-measures of some districts, are quite as likely to have been dropped by rafts of vegetation as to have been carried by floating icebergs. Economic Products.—Foremost among the useful products of the Carboniferous rocks is the coal (q.v.) itself; but associated with the coal seams in Great Britain, North America and elsewhere, are very important beds of ironstone, See also:fire-See also:clay, terra-See also:cotta clay, and occasionally oil shale and See also:alum shale. Oil and See also:gas are of importance in the Lower Carboniferous Pocono sandstone of West Virginia and in the See also:Berea grit of Ohio, where brine also occurs. In the Carboniferous Limestone series, the purer kinds of limestone are used for the manufacture of lime, See also:bleaching See also:powder and similar products, also as a See also:flux in the smelting of See also:iron; some of the less pure varieties are used in making See also:cement. The beds of chert are utilized in the pottery See also:industry, and some of the harder and more crystalline limestones are beautiful See also:marbles, capable of taking a high See also:polish. The sandstones are used for building, and for millstones and grind-stones.

Within the Carboniferous rocks, but due to the action of various agencies long after their deposition, are important ore formations; such are the Rio Tinto ores of Spain, the See also:

lead and See also:zinc ores and some See also:haematite of the Pennine and Mendip hills and other British localities, and many ore regions in the United States. REFEitENCES..—For a good general account of the Carboniferous system, see A. Geikie, See also:Text See also:Book of Geology, vol. ii. (4th ed., 1903) ; and for the See also:American development see T. C. Chamberlin and R. D. See also:Salisbury, Geology, vol. ii. (1906). These two See also:works give abundant references to the literature of the subject. See also, See also:Recent Additions to Geological Literature, published annually by the Geological Society of See also:London since 1893 ; and Neues Jahrbuch See also:fur Mineralogie (See also:Stuttgart). (J.

A.

End of Article: CARBONIFEROUS SYSTEM

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