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DEVONIAN SYSTEM
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DEVONIAN See also:SYSTEM , in See also:geology, the name applied to See also:series of stratified fossiliferous and igneous rocks that were formed' during the Devonian See also:period, that is, in the See also:interval of See also:time between the See also:close of the See also:Silurian period and the beginning of the Carboniferous; it includes the marine Devonian and an estuarine Old Red See also:Sandstone series of strata. The name " Devonian " was introduced in 1829 by See also:Sir R. See also:Murchison and A. See also:Sedgwick to describe the older rocks of See also:Cornwall and See also:Devon which W. Lonsdalt had shown, from an examination of the fossils, to be intermediate between the Silurian and Carboniferous. The same two workers also carried on further researches upon the same rocks of the See also:European See also:continent, where already several others, F. See also:Roemer, H. E. See also:Beyrich, &c., were endeavouring to elucidate the See also:succession of strata in this portion of the " Transition Series." The labours of these earlier workers, including in addition to those already mentioned, the See also:brothers F. and G. von See also:Sandberger, A. See also:Dumont, J. Gosselet, E. J. A. d'See also:Archiac, E. P. de See also:Verneuil and H. von See also:Dechen, although somewhat modified by later' students, formed the See also:foundation upon which the See also:modern See also:classification of the Devonian rocks is based. Stratigraphy of the Devonian Facies. Notwithstanding the fact that it was in See also:Devonshire and Cornwall that the Devonian rocks were first distinguished, it is in central See also:Europe that the succession of strata is most clearly made out, and here, too, their See also:geological position was first indicated by the founders of the system, Sedgwick and Murchison. See also:Continental Europe.—Devonian rocks occupy a large See also:area in the centre of Europe, extending from the See also:Ardennes through the See also:south of See also:Belgium across Rhenish See also:Prussia to See also:Darmstadt. They are best known from the picturesque See also:gorges which have been cut through them by the See also:Rhine below See also:Bingen and by the Moselle below Treves. They reappear from under younger formations in See also:Brittany, in the Harz and Thuringia, and are exposed in See also:Franconia, See also:Saxony, See also:Silesia, See also:North See also:Moravia and eastern See also:Galicia. The See also:principal subdivisions of the system in the more typical areas are indicated in Table I. This threefold subdivision, with a central See also:mass of calcareous strata, is traceable westwards through Belgium (where the Calcaire de See also:Givet represents the Stringocephalus See also:limestone of the See also:Eifel) and eastwards into the Harz. The rocks reappear with See also:local petrographical modifications, but with a remarkable persistence of See also:general palaeontological characters, in Eastern Thuringia, Franconia, Saxony, Silesia, the north of Moravia and See also:East Galicia. Devonian rocks have been detected among the crumpled rocks of the Styrian See also:Alps by means of the See also:evidence of abundant See also:corals, cephalopods, gasteropods, lamellihranchs and other organic remains. Perhaps in other tracts of the Alps, as well as in the Carpathian range, similar shales, limestones and See also:dolomites, though as yet unfossiliferous, but containing ores of See also:silver, See also:lead, See also:mercury, See also:zinc, See also:cobalt and other metals, may be referable to the Devonian system. In the centre of Europe, therefore, the Devonian rocks consist of a vast thickness of dark-See also:grey sandy and shaly rocks, with occasional seams of limestone, and in particular with one thick central calcareous See also:zone. These rocks are characterized in the See also:lower zones by numerous broad-winged spirifers and by See also:peculiar See also:trilobites (Phacops, Homelonotus, &c.) which, though generically like these of the Silurian system, are specifically distinct. The central calcareous zone abounds in corals and crinoids as well as in numerous brachiopods. In the highest bands a profusion of coiled cephalopods (Clymenia) occurs in some of the limestones, while the shales are crowded with a small but characteristic ostracod crustacean (Cypridina). Here and there traces of fishes have been found, more especially in the Eifel, but seldom in such a See also:state of preservation as to See also:warrant their being assigned tq any definite See also:place in the zoological See also:scale. Subsequently, however, E, Beyrich has described from See also:Gerolstein in the Eifel an undoubted See also:species of Pterichthys, which, as it cannot be certainly identified with any known See also:form, he names P. See also:Rhenanus. A Coccosteus has been described by F. A. Roemer from the Harz, and still later one has been cited from Bicken near Herborn by V. Koenen; but, as Beyrich points out, there may be some doubt as to whether the latter is not a Pterichthys. A Ctenacanthus, seemingly undistinguishable from the C. Bohemicus of See also:Barrande's Etage G, has also been Areas in which the Earlier Deuonian,Rocha are found \ fll_V[ I Additional areas in which See also:Mid. Devonian Rocks arefound „ „ Later See also:Distribution of , }y MI pevonian Rlimitockssof L absentand d: S or unknoea/wn ; — Suggested In Earlier Deuohfan time Devonian Rocks / --= Modifications introduced about the See also:middle of Devonian time --Cater Modifications s.w.... obtained from the Lower Devonian " Nereitenschichten of Thuringia. The characteristic Holoptychius nobilissimus has been .. detected in the Psammite de Condroz, which in Belgium forms a characteristic sandy portion of the Upper Devonian rocks. These are interesting facts, as helping to See also:link the Devonian and Old Red Sandstone types together. But they are as yet too few;and unsupported to warrant any large See also:deduction as to the correlations between these types. It is in the north-east of Europe that the Devonian and Old Red Sandstone appear to be See also:united into one system, where the limestones and marine organisms of the one are interstratified with the See also:fish-bearing sandstones and shales of the other. In See also:Russia, as wasof the Silurian rocks on which they See also:rest, for they are found gradually to overlap Upper and Lower Silurian formations. The See also:chief See also:interest of the See also:Russian rocks of this See also:age lies in the fact, first signalized by Murchison and his associates, that they unite within themselves the characters of the Devonian and the Old Red Sandstone types. In some districts they consist largely of See also:lime-stones, in others of red sandstones and marls. In the former they See also:present molluscs and other marine organisms of known Devonian species; in the latter they afford remains of fishes, some of which are specifically identical with those of the Old Red Sandstone of See also:Scotland. The distribution of these two palaeontological types in Russia is traced by Murchison to the lithological characters of the Stages. Ardennes. Rhineland. Brittany and Bohemia. Harz. See also:Normandy. Famennien Limestone of Etreeungt. Cypridina slates. Slates of Rostellec. Cypridina slates. (Clymenia Psammites of Condroz Pon sandstone (See also:Sauerland). Clymenia limestone beds). (sandy series). Crumbly limestone (Kramen- and limestone of
Slates of Famenne zelkalk) with Clymenia. Altenau.
(shaly series). Neheim slates in $auerland,
and diabases, tuffs, &c., in
Dillmulde, &c.
Frasnien Slates of Matagne. See also:Adorf limestone of Waldeck Limestone of Cop- Iberg limestone and
(Intumes- Limestones, marls and and shales with Goniatites Choux and See also:green Winterberg lime-
cens beds). shale of Frasne, and (Eifel and See also:Aix) = Budes- slates of Travuliors. See also: Stringocephalus limestone, Limestones of Cha- H2 (ofBarrande) Stringocephalus shales (Stringo- ironstone of Brilon and lonnes, Montjean dark plant- with Flaser and cephalus Lahnmulde. and 1'Ecochbre. bearing shales. Knollenkalk. beds). Upper Lenne shales, crinoidal Hl. Wissenbach slates. limestone of Eifel, red See also:sand- stones of Aix. Tuffs and diabases of Brilon and Lahnmulde. Red See also:conglomerate of Aix. Eifclien Calceola slates and Calceola beds, Wissenbach Slates of Porsguen, G3 Cephalopod Calceola beds. (Calceola limestones of Couvin. slates, Lower Lenne beds, See also:greywacke of See also:Fret. limestone. Nereite slates, slates beds). Greywacke with Spir- Guntroder limestone and G2 Tentaculite of Wieda and lime- ifer cultrijugatus. See also:clay See also:slate of Lahnmulde, limestone. stones of Hasselfeld. Dillmulde, Wildungen, Grie- Gl Knollenkalk
fenstein limestone, Bailers- and mottled
See also:bach limestone. Mnenian lime-
stone.
Coblentzien. Greywacke of Hierges. Upper Coblentz slates. Limestones of Er- See also:F2 of Barrande. See also:Haupt See also:quartzite (of
Shales and conglomer- Red sandstone of Eifel, See also:Cob- See also:bray, Brulon, See also:Vire See also: Slates of St See also:Hubert and Slates of Gedinne. Slates and quartzites Fooz, slates of Mon- of Plougastel. drepuits, arkose of Weismes, conglomer- ate of F6pin. shown in the See also:great See also:work Russia and the Ural Mountains by Murchison, De Verneuil and Keyserling, rocks intermediate between the Upper Silurian and Carboniferous Limestone formations See also:cover an extent of See also:surface larger than the See also:British Islands. This wide development arises not from the thickness but from the undisturbed See also:horizontal See also:character of the strata. Like the Silurian formations described else-where, they remain to this See also:day nearly as See also:flat and unaltered as they were originally laid down. Judged by See also:mere See also:vertical See also:depth, they present but a meagre representative of the massive Devonian greywacke and limestone of See also:Germany, or of the Old Red Sandstone of See also:Britain. Yet vast though the area is over which they form the surface See also:rock, it is probably only a small portion of their See also:total extent ; for they are found turned up from under the newer formations along the flank of the Ural See also:chain. It would thus seem that they spread continuously across the whole breadth of-Russia in Europe. Though almost everywhere undisturbed, they afford evidence of some terrestrial oscillation between the time of their formation and that rocks, and consequent See also:original diversities of See also:physical conditions, rather than to See also:differences of age. Indeed cases occur where in the same See also:band of rock Devonian shells and Old Red Sandstone fishes See also:lie commingled. In the ,See also:belt of the formation which extends south-wards from See also:Archangel and the White See also:Sea, the strata consist of sands and marls, and contain only fish remains. Traced through the Baltic provinces, they are found to pass into red and green marls, See also:clays, thin limestones and sandstones, with beds of See also:gypsum. In some of the calcareous bands such fossils occur-as Orthis striatula, Spiriferina prisca, Leptaena productoides, Spirifer calcaratus, Spirorbis omphaloides and Orthoceras subfusiforme. In the higher beds Holoptychius and other well-known fishes of the Old Red Sandstone occur. Followed still farther to the south, as far as the See also:watershed between See also:Orel and See also:Voronezh, the Devonian rocks lose their red See also:colour and sandy character, and become thin-bedded yellow lime-stones, and dolomites with soft green and See also:blue marls. Traces of See also:salt deposits are indicated by occasional saline springs. It is evident that the See also:geographical conditions of the Russian area during the Devonian period must have closely resembled those, of the Rhine See also:basin and central See also:England during the Triassic period. The Russian Devonian rocks have been classified in Table II. There is an unquestionable passage of the uppermost Devonian rocks of Russia into the See also:base of the Carboniferous system. The Lower Devonian of the Harz contains a fauna which is very different from that of the Rhenish region; to this facies the name The fossil evidence clearly shows the close agreement of the Rhenish and south Devonshire areas. In north Devonshire the Devonian rocks pass upward without break into the See also:Culm. North See also:America.—In North America the Devonian rocks are extensively See also:developed; they have been studied most closely in the New See also:York region, where they are classified according to Table IV. The classification below is not capable of application over the states generally and further details are required from many of the North-See also:West Russia. Central Russia. Petchoraland. Ural Region. Red sandstone (Old Limestones with Spir- Limestones with Arca Domanik slates and Cypridina slates, Cly- Red). fifer Verneuili and oreliana limestones with Sp. menia limestones (Fa- Sp. Archiaci. Limestones with Sp. Verneuili. Verneuili and Sp. Archiaci. mennien). Limestones with Gephy- oceras intumescens and Rhynchonella cuboides (Frasnien). Dolomites Spirifer See also:Marl with Limestones and slates and limestones Spirifer Anossofi with and corals. Anossofi. with Sp. Anossofi (Giv- etien). Limestones and slates Lower sandstone (Old Red). with Pentamerus basch- kiricus (Eifelien). Absent. Limestones and slates of the Yuresan and See also:Ufa See also:rivers, slate and See also:quartz- quartz- ite, marble of Byelaya and of Bogoslovsk, phyllitic See also:schists and quartzite. " Hercynian " has been applied, and the correlation of the strata has been a source of prolonged discussion among continental geologists. A similar fauna appears in Lower Devonian of Bohemia, in Brittany (limestone of Erbray) and in the Urals. The Upper Devonian of the Harz passes up into the Culm. In the eastern Thuringian See also:Fichtelgebirge the upper See also:division is represented by Clymenia limestone and Cypridina slates with Adorf limestone, See also:diabase and Planschwitzer See also:tuff in the lower part. The middle division has diabases and tuffs at the See also:top with Tentaculite and Nereite shales and limestones below. The upper part of the Lower Devonian, the sandy shale of Steinach, rests unconformably upon Silurian rocks. In the Carnic Alps'are See also:coral See also:reef limestohes, the equivalents of the Iberg limestone, which attain an enormous thickness; these are underlain by coral limestones with fossils similar to those of the Konjeprus limestone of Bohemia; below these are shales and nodular limestones with goniatites. The Devonian rocks of See also:Poland are sandy in the lower, and more calcareous in the upper parts. They are of interest because while the upper portions agree closely with the Rhenish facies, from the top of the Coblentzien upwards, in the sandy beds near the base Old Red Sandstone fishes (Coccosteus, &c.) are found. In See also:France Devonian rocks are found well developed in Brittany, as indicated in the table, also in Normandy and See also:Maine; in the Boulonnais See also:district only the middle and upper divisions are known. In south France in the neighbourhood of Cabrii res, about See also:Montpellier and in the Montagne Noire, all three divisions are found in a highly calcareous See also:condition. Devonian rocks are recognized, though frequently much metamorphosed, on both the See also:northern and See also:southern flanks of the See also:Pyrenees; while on the See also:Spanish See also:peninsula they are extensively developed. In See also:Asturias they are no less than 3280 ft. thick, all three divisions and most of the central European subdivisions are present. In general, the Lower Devonian fossils of See also:Spain See also:bear a marked resemblance to those of Brittany. See also:Asia.—From the Ural Mountains eastward, Devonian rocks have been traced from point to point right across Asia. In the See also:Altai Mountains they are represented by limestones of Coblentzien age with a fauna possessing Hercynian features. The same features are observed in the Devonian of the Kougnetsk basin, and in See also:Turkestan. Well-developed quartzites with slates and diabases are found south of Yarkand and See also:Khotan. Middle and Upper Devonian strata are widespread in See also:China. Upper Devonian rocks are recorded from See also:Persia, and from the See also:Hindu Kush on the right See also:bank of the See also:Chitral See also:river. England.—In England the original Devonian rocks are developed in Devon and Cornwall and west See also:Somerset. In north Devonshire these rocks consist of sandstones, grits and slates, while in south Devon there are, in addition, thick beds of massive limestone, and intercalations of lavas and tuffs. The See also:interpretation of the stratigraphy in this region is a difficult See also:matter, partly on See also:account of the See also:absence of See also:good exposures with fossils, and partly through the disturbed condition of the rocks. The system has been subdivided as shown in Table III.regions where Devonian rocks have been recognized, but every-where the broad threefold division seems to obtain. In See also:Maryland the following arrangement has been adopted—(I) Helderberg= Coeymans; (2) See also:Oriskany; (3) See also:Romney=Erian; (4) Jennings= Genesee and See also:Portage; (5) See also:Hampshire =See also:Catskill in part. In the North Devon and West South Devon. Somerset. Pilton See also:group. Grits, slates See also:Ashburton slates.
and thin limestones. Livaton slates.
Baggy group. Sandstones Red and green Entomis slates
and slates. (Famennien).
Pickwell Down group. Dark Red and grey slates with
slates and grits. tuffs.
Morte slates (?). Chudleigh goniatite limestone
Petherwyn beds (Frasnien).
See also:Ilfracombe slates with len- See also:Torquay and See also:Plymouth lime-
ticles of limestone. stones and Ashprington
See also:Combe See also: Hangman grits and slates. See also:Looe beds (Cornwall).
See also:Lynton group, grits and cal- Meadfoot, Cockington and
careous slates. Warberry series of slates
See also:Foreland grits and slates. and greywackes. (Coblent-
zien and Gedinnien.)
interior the Helderbergian is missing and the system commences with (I) Oriskany, (2) See also:Onondaga, (3) See also: The Erian series is often described as the Hamilton series outside the New York district, where the See also:Marcellus shales are grouped together with the Hamilton shales, and numerous local subdivisions are included, as in See also:Ohio, See also:Kentucky and See also:Tennessee. The rocks are mostly shales or slates, but limestones predominate in the western development. In See also:Pennsylvania the Hamilton series is from 15oo ft. to 5000 ft. thick, but in the more calcareous western See also:extension it is much thinner. The Marcellus shales are bituminous in places. The Senecan series is composed of shallow-See also:water deposits; the Tully limestone, a local See also:bed in New York, thins out in places into a layer of See also:pyrites which contains a remarkable dwarfed fauna. The bituminous Genesee shales are thickest in Pennsylvania (300 ft,); 25 ft. on See also:Lake See also:Erie. The shales and sandstones of the Portage formation reach moo ft. to 1400 ft. in western New York. In the Chautauquan series the Chemung formation is not always clearly separable from the Portage beds, it is a sandstone and conglomerate See also:Groups. Formations. Probable European See also:Equivalent. Chautauquan. Chemung beds with Catskill Famennien. Senecan. as a local facies. Frasnien. Portage beds (See also:Naples, See also:Ithaca and See also:Oneonta shales as local facies). Genesee shales. Tully limestone. Erian. Hamilton shale. Givetien. Ulsterian. Marcellus shale. Eifelien. Onondaga (Corniferous) limestone. Schoharie grit. Esopus grit (Caudagalli grit). Oriskanian. Oriskany sandstone. Coblentzien. Helderbergian See also:Kingston beds. Gedi Becraft limestone. nnien. New Scotland beds. Coeymans limestone. formation which reaches its maximum thickness (8000 ft.) in Pennsylvania, but thins rapidly towards the west. In the Catskill region the Upper Devonian has an Old Red facies—red shares and sandstones with a See also:freshwater and brackish fauna. Although the correlation of the strata has only advanced a See also:short distance, there is no doubt as to the presence of undifferentiated Devonian rocks in many parts of the continent. In the Great Plains this system appears to be absent, but it is represented in See also:Colorado, See also:Utah, See also:Nevada, See also:Wyoming, See also:Montana, See also:California and See also:Arizona; Devonian rocks occur between the Sierras and the Rocky Mountains, in the Arbuckle Mountains of See also:Oklahoma and in See also:Texas. In the western interior limestones predominate; 600o ft. of limestone are found at See also:Eureka, Nevada, beneath 2000 ft. of shale. On the Pacific See also:coast See also:metamorphism of the rocks is See also:common, and See also:lava-flows and tuffs occur in them.
In Canada, besides the occurrences previously mentioned in the eastern region, Devonian strata are found in considerable force along the course of the See also:Mackenzie river and the See also:Canadian Rockies, whence they stretch out into See also:Alaska. It is probable, however, that much that is now classed as Devonian in Canada will prove on fossil evidence to be Carboniferous.
South America, See also:Africa, See also:Australia, &c.—In South America the Devonian is well developed; in See also:Argentina, See also:Bolivia, See also:Brazil, See also:Peru and the See also:Falkland Islands, the palaeontological See also:horizon is about the junction of the Lower and Middle divisions, and the fauna has affinities with the Hamilton shales of North America. Nearly allied to the South See also:American Devonian is that of South Africa, where they are represented by the Bokkeveld beds in the Cape system. In Australia we find Lower Devonian consisting of coarse littoral deposits with volcanic rocks; and a Middle division with coral limestones in See also:Victoria, New South See also:Wales and See also:Queensland; an Upper division has also been observed. In New See also:Zealand the Devonian is well exposed in the Reefton See also:mining See also: Geikie has assigned convenient distinctive names.
In Scotland the two divisions of the system are sharply separated by a pronounced unconformability which is probably indicative of a prolonged interval of erosion. In the central valley between the base of the See also:Highlands and the southern uplands See also:lay " Lake See also:Caledonia." Here the lower division is made up of some 20,000 ft. of shallow-water deposits, reddish-See also: Over the west of See also:Argyll-See also:shire lay " Lake Lorne "; here the volcanic rocks predominate, they are intercalated with shallow-water deposits. A similar set of rocks occupy the Cheviot district. The upper division of the Old Red Sandstone is represented in See also:Shropshire and South Wales by a great series of red rocks, shales, sandstones and marls, some io,000 ft. thick. They contain few fossils, and no break has yet been found in the series. In Scotland this series was deposited In basins which correspond only partially with those of the earlier period. They are well developed in central Scotland over the lowlands bordering the Moray Firth. Inter-bedded lavas and tuffs are found in the See also:island of See also:Hoy. An interesting feature of this series is the occurrence of great crowds of fossil fishes in some localities, notably at Dura Den in See also:Fife. In the north of England this series rests unconformably upon the Lower Old Red and the Silurian. Flanking the Silurian high ground of See also:Cumberland and See also:Westmorland, and also in the Lammermuir hills and in See also:Flint and See also:Anglesey, a brecciated conglomerate, presenting many of the characters of a glacial deposit in places, has often been classed with the Old Red Sandstone, but in parts, at least, it is more likely to belong to the base of the Carboniferous system. In See also:Ireland the lower division appears to be represented by the See also:Dingle beds and Glengariff grits, while the See also:Kerry rocks and the Kiltorcan beds of See also:Cork are the equivalents of the upper division. Rocks of Old Red type, both lower and upper, are found in Spitzbergen and in Bear Island. In New Brunswick and Nova Scotia the Old Red facies is extensively developed. The Gaspe sandstones have been estimated at 7036 ft. thick. In parts of western Russia Old Red Sandstone fossils are found in beds intercalated with others containing marine fauna of the Devonian facies. Devonian and Old Red Sandstone Faunas. The two types of sediment formed during this period—the marine Devonian and the lagoonal Old Red Sandstone—representing as they do two different but essentially contemporaneous phases of physical condition, are occupied by two strikingly dissimilar faunas. Doubt-less at all times there were rebions of the See also:earth that were marked off no less clearly from the normal marine conditions of which we have records; but this period is the earliest in which these See also:variations of environment are made obvious. In some respects the faunal break between the older Silurian below and the younger Carboniferous above is not strongly marked; and in certain areas a very close relationship can be shown to exist between the older Devonian and the former, and the younger Devonian and the latter. Nevertheless, taken as a whole, the See also:life of this period bears a distinct See also:stamp of individuality. The two most prominent features of the Devonian seas are presented by corals and brachiopods. The corals were abundant individually and varied in form; and they are so distinctive of the period that no Devonian species has yet been found either in the Silurian or in the Carboniferous. They built reefs, as in the present day, and contributed to the formation of limestone masses in Devonshire, on the continent of Europe and in North America. Rugose and tabulate forms prevailed; among the former the cyathophyllids (Cyathophyllum) were important, Phillipsastraea, Zaphrentis, Acervularia and the curious Calceola (sanaalina), an operculate genus which has given palaeontologists much trouble in its diagnosis, for it has been regarded as a pelecypod (hippurite) and a brachiopod. The tabulate corals were represented by Favosites, Michelinia, Pleurodictyum, Fistulipora, Pachypore and others. Heliolites and Plasmopore represent the alcyonarians. Stromatoporoids were important reef builders. A. well-known fossil is Receptaculites, a genus to which it has been difficult to assign a definite place; it has been thought to be a. sponge, it may be a calcareous alga, or a curious representative of the See also:foraminifera. In the Devonian period the brachiopods reached the See also:climax of their development : they compose three-quarters of the known fauna, and more than II00 species have been described. Changes were taking place from the beginning of the period in the relative importance of genera; several Silurian forms dropped out, and new types were coming in. A noticeable feature was the development of broad-winged shells in the genus Spirifer, other spiriferids were Ambocoelia, Uncites, Verneuilia. Orthids and pentamerids were waning in importance, while the . pproductids (Productella, Chonetes, Strophalosia) were increasing. The strophomenids were still flourishing, represented by the genera Leptaena, Stropheodonta, Kayserella, and others. The See also:ancient Lingula, along with Crania and Orbiculoidea, occur among the inarticulate forms. Another See also:long-lived and wide-ranging species is Atrypa reticularis. The athyrids were very numerous (A ihyris, Retzia, Merista,Meristella, Kayserina, &c.) ; and the rhynchonellids were well represented by Pugnax, Hypothyris, and several other genera. The important group of terebratulids appears in this system; amongst them Stringocephalus is an eminently characteristic Devonian brachiopod; others are Dielasma, Cryptonella, Rensselaeria and Oriskania. The pelecypod molluscs were represented by Pterinea, abundant in the lower members along with other large-winged forms, and by Cucullella, Buchiola and Curtonotus in the upper members of the system. Other genera are Actinodesma, Cardiola, Nucula, Megalodon, Aviculopecten, &c. Gasteropods were becoming more important, but the See also:simple capulid forms prevailed: Platyceras (Capulus), Straparollus, Pleurotomaria, Murchisonia, Macrocheilina, Euomphalus. Among the pteropods, Tentaculites was very abundant in some quarters; others were Conularia and Styliolina. In the Devonian period the cephalopods began to make a distinct advance in See also:numbers, and in development. The goniatites appear with the genera Anarcestes, Agoniatites, Tornoceras, Bactrites and others; and in the upper strata the clymenoids, forerunners of the later ammonoids, began to take definite shape. While several new nautiloids (Homaloceras, Ryticeras, &c.) made their See also:appearance several of the older genera still lived on (Orthoceras, Poterioceras, Actinoceras). Crinoids were very abundant in some parts of the Devonian sea, though they were relatively scarce in others; they include the genera Melocrinus, Haplocrinus, Cupressocrinus, Calceocrinus and Eleuthrocrinus. The cystideans were falling off (Proteocystis, Tiaracrinus), but biastoids were in the ascendant (Nucleocrinus, Codaster, &c.). Both brittle-stars, Ophiura, Palaeophiura, Eugaster, and true starfishes, Palaeaster,Aspidosoma, were present, as well as urchins (Lepidocentrus). When we turn to the crustaceans we have to See also:deal with two distinct assemblages, one purely marine, trilobitic, the other mainly lacustrine or lagoonal with a eurypteridian facies. The trilobites had already begun to decline in importance, and as happens not infrequently with degenerating races of beasts and men, they began to develop See also:strange eccentricities of ornamentation in some of their genera. A number of Silurian genera lived on into the Devonian period, and some gradually developed into new and distinctive forms; such were Proetus, Harpes, Cheirurus, Bronteus and others. Distinct species of Phacops See also:mark the Lower and Upper Devonian respectively, while the genus Dalmania (Odontochile) was represented by species with an almost See also:world-wide range. The Ostracod Entomis (Cypridina) was extremely abundant in places—Cypridinen-Schief er—while the true Cypridina was also present along with Beyrichia, Leperditia, &c. The Phyllocarids, Echinocaris, Eleuthrocaris, Tropidocaris, are common in the United States. It is in the Old Red Sandstone that the eurypterids are best preserved; foremost among these was Pterygotus; P. anglicus has been found in Scotland with a length of nearly 6 ft.; Euryptcrus, Slimonia, Stylonurus were other genera. See also:Insects appear well developed, including both orthopterous and neuropterous forms, in the New Brunswick rocks. Mr Scudder believed he had obtained a specimen of See also:Orthoptera in which a stridulating See also:organ was present. A species of Ephemera, allied to the modern may-See also:fly, had a spread of wing extending to 5 in. In the Scottish Old Red Sandstone myriapods, Kampecaris andArchidesmus, have been described; they are somewhat simpler than more See also:recent forms, each segment being See also:separate, and supplied with only one pair of walking legs. See also:Spiders and scorpions also lived upon the See also:land. The great number of fish remains in the Devonian and Old Red strata, coupled with the truly remarkable characters possessed by some of the forms, has caused the period to be described as the "age of fishes." As in the See also:case of the crustaceans, referred to above,we find one assemblage more or less peculiar to the freshwaterorbrackish conditions of the Old Red, and another characteristic of the marine Devonian; on the whole the former is the richer in variety, but there seems little doubt that quite a number of genera were capable of living in either environment, whatever may have been the real condition of the Old Red See also:waters. Foremost in interest are the curious See also:ostracoderms, a remarkable group of creatures possessing many ofthe characteristics of fishes, but more probably belonging to a distinct class of organisms, which appears to link the vertebrates with the arthropods. They had come into existence See also:late in Silurian times; but it is in the Old Red strata that their remains are most fully preserved. They were abundant in the fresh or brackish waters of Scotland, England, Wales, Russia and Canada, and are represented by such forms as Pteraspis, Cephalaspis, Cyathaspis, Tremataspis, Bothriolepis and Pterichthys. In the lower members of the Old Red series Dipterus, and in the upper members Phaneropleuron, represented the dipnoid See also:lung-fishes; and it is of extreme interest to See also:note that a few of these curious forms still survive in the See also:African Protopterus, the Australian Ceratodus and the South American Lepidosiren,—all freshwater fishes. Distantly related to the lung-fishes were the singular arthrodirans, a group possessing the unusual See also:faculty of moving the See also:head in a vertical See also:plane. These comprise the wide-ranging Coccosteus with Homosleus and Dinichthys, the largest fish of the period. The latter probably reached 20 ft. in length; it was armed with exceedingly powerful jaws provided with turtle-like beaks. Sharks were fairly prominent denizens of the sea; some were armed with cutting See also:teeth, others with crushing dental plates; and although they were on the whole marine fishes, they were evidently able to live in fresher waters, like some of their, modern representatives, for their remains, mostly teeth and large dermal spines, are found both in the Devonian and Old Red rocks. Mesacanihus, Dipiacanthus, Climatius, Cheiracanthus are characteristic genera. The crossopterygians, ganoids with a scaly See also:lobe in the centre of the fins, were represented by Holoptychius and Glyptopomus in the Upper Old Red, and by such genera asDiplopterus, Osteolepis, Gyroptychius in the lower division. The Polypterus of the See also:Nile and Calamoichthys of South Africa are the modern exemplars of this group. Cheirolepis, found in the Old Red of Scotland and Canada, is the only Devonian representative of the actinopterygian fishes. The cyclostome fishes have, so far, been discovered only in Scotland, in the tiny See also:Palaeospondylus. Amphibian remains have been found in the Devonian of Belgium; and footprints supposed to belong to a creature of the same class (Thinopus antiquus) have been described by See also:Professor See also:Marsh from the Chemung formation of Pennsylvania. Plant Life.—In the lacustrine deposits of the Old Red Sandstone we find the earliest well-defined assemblage of terrestrial See also:plants. In some regions so abundant are the See also:vegetable remains that in places they form thin seams of veritable See also:coal. These plants evidently flourished around the shores of the lakes and lagoons in which their remains were buried along with the other forms"of life. Lycopods and ferns were the predominant types; and it is important to See also:notice that both groups were already highly developed. The ferns include the genera Sphenopteris, Megalopteris, Archaeopteris, Neuropteris. Among the Lycopods are Lycopodites, Psilophyton, Lepidodendron. Modern horsetails are represented by Calamocladus, Asterocalamites, Annularia. Of great interest are the genera Cordaites, Araucarioxylon, &c., which were synthetic types, uniting in some degree the Coniferae and the Cycadofilicales. With the exception of obscure markings, aquatic plants are not so well represented as might have been expected ; Parka, a common fossil, has been regarded as a water plant with a creeping See also:stem and two kinds of sporangia in sessile sporocarps. Physical Conditions, Eirc.—Perhaps the most striking fact that is brought out by a study of the Devonian rocks and their fossils is the See also:gradual transgression of the sea over the land, which took place quietly in every See also:quarter of the globe shortly after the beginning of the period. While in most places the Lower Devonian sediments succeed the Silurian formations in a perfectly conformable manner, the Middle and Upper divisions, on account of this encroachment of the sea, rest unconformably upon the older rocks, the Lower division being unrepresented. This is true over the greater part of South America, so far as our limited knowledge goes, in much of the western side of North America, in western Russia, in Thuringia and other parts of central Europe. Of the distribution of land and sea and the position of the coast lines in Devonian times we can state nothing with precision. The known deposits all point to shallow waters of epicontinental seas; no abyssal formations have been recognized. E. See also:Kayser has pointed out the See also:probability of a See also:Eurasian sea See also:province extending through Europe towards the east, across north and central Asia towards See also:Manitoba in Canada, and an American sea province embracing the United States, South America and South Africa. At the same time there existed a great North See also:Atlantic land area caused partly by the uplift of the Caledonian range just before the beginning of the period, which stretched across north Europe to eastern Canada; on the fringe of this land the Old Red Sandstone was formed. In the European area C. See also:Barrois has indicated the existence of three zones of deposition: (i) A northern, Old Red, region, including Great Britain, Scandinavia, European Russia and See also:Spitsbergen; here the land was close at See also:hand; great brackish lagoons prevailed, which communicated more or less directly with the open sea. In European Russia, during its general advance, the sea occasionally gained See also:access to wide areas, only to be driven off again, during pauses in the relative subsidence of the land, when the continued See also:terrigenous sedimentation once more established the lagoonal conditions. These alternating phases were frequently repeated. (2) A middle region, covering Devonshire and Cornwall, the Ardennes, the northern part of the lower Rhenish mountains, and the upper Harz to the See also:Polish Mittelgebirge; here we find evidence of a shallow sea, clastic deposits and a sublittoral fauna. (3) A southern region reaching from Brittany to the south of the Rhenish mountains, lower Harz, Thuringia and Bohemia; here was a deeper sea with a more pelagic fauna. It must be See also:borne in mind that the above mentioned regions are intended to refer to the time when the extension of the Devonian sea was near its maximum. In the case of North America it has been shown that in See also:early and middle Devonian time more or less distinct faunas invaded the continent from five different centres, viz. the Helderberg, the Oriskany, the Onondaga, the southern Hamilton and the north-western Hamilton; these reached the interior approximately in the See also:order given. Towards the close of the period, when the various local faunas had mingled one with another and a more generalized life assemblage had been evolved, we find many forms with a very wide range, indicating great uniformity of conditions. Thus we find identical species of brachiopods inhabiting the Devonian seas of England, France, Belgium, Germany, Russia, southern Asia and China; such are, Hypothyris (Rhynchonella) cuboides, Spirifer disjunct us and others. The fauna of the Calceola shales can be traced from western Europe to See also:Armenia and See also:Siberia; the Stringocephalus limestones are represented in Belgium, England, the Urals and Canada; and the (Gephyroceras) intumescens shales are found in western Europe and in Manitoba. The Devonian period was one of See also:comparative quietude; no violent crustal movements seem to have taken place, and while some changes of level occurred towards its close in Great Britain, Bohemia and Russia, generally the passage from Devonian to Carboniferous conditions was quite gradual. In later periods these rocks have suffered considerable See also:movement and metamorphism, as in the Harz, Devonshire and Cornwall, and in the Belgian coalfields, where they have frequently been thrust over the younger Carboniferous rocks. Volcanic activity was fairly widespread, particularly during the middle portion of the period. In the Old Red rocks of Scotland there is a great thickness (6000 ft.) of igneous rocks, including diabases and andesitic lavas with agglomerates and tuffs. In Devonshire diabases and tuffs are found in the middle division. In west central Europe volcanic rocks are found at many horizons, the most common rocks are diabases and diabase tuffs, schalstein. Felsitic lavas and tuffs occur in the Middle Devonian of Australia. Contemporaneous igneous rocks are generally absent in the American Devonian, but in Nova Scotia and New Brunswick there appear to be some. There is little evidence as to the See also:climate of this period, but it is interesting to observe that local glacial conditions may have existed in places, as is suggested by the coarse conglomerate with striated boulders in the upper Old Red of Scotland. On the other hand, the prevalence of reef-See also:building corals points to moderately warm temperatures in the Middle Devonian seas. The economic products of Devonian rocks are of some importance: in many of the metamorphosed regions See also:veins of See also:tin, lead, See also:copper, See also:iron are exploited, as in Cornwall, Devon, the Harz; in New Zealand, See also:gold veins occur. See also:Anthracite of Devonian age is found in China and a little coal in Germany, while the Upper Devonian is the chief source of oil and See also:gas of western Pennsylvania and south-western New York. In See also:Ontario the middle division is oil-bearing. See also:Black See also:phosphates are worked in central Tennessee, and in England the marls of the " Old Red " are employed for See also:brick-making. Additional information and CommentsThere are no comments yet for this article.
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