Bible Encyclopedias
Devonian System

Groups.

Formations.

Probable

European

Equivalent.

Chautauquan.

Chembing beds with Catskill

as a local facies.

Famennien.

Portage beds (Naples, Ithaca

and Oneonta shales as local

Senecan.

facies).

Genesee shales.

Tully limestone.

Frasnien.

Erian.

Hamilton shale.

Marcellus shale.

Givetien.

'

Onondaga (Corniferous)

Ulsterian.

limestone.

Schoharie grit.

Eifelien.

Esopus grit (Caudagalli grit).

Oriskanian.

Oriskany sandstone.

Coblentzien.

I Kingston beds.

Helderbergian

Becraft limestone.

New Scotland beds.

Gedinnien.

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 shales and sandstones with a freshwater and brackish fauna.

Although the correlation of the strata has only advanced a 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 Colorado, Utah, Nevada, Wyoming, Montana, California and Arizona; Devonian rocks occur between the Sierras and the Rocky Mountains, in the Arbuckle Mountains of Oklahoma and in Texas. In the western interior limestones predominate; 6000 ft. of limestone are found at Eureka, Nevada, beneath 2000 ft. of shale. On the Pacific coast metamorphism of the rocks is common, and 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 Mackenzie river and the Canadian Rockies, whence they stretch out into 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, Africa, Australia, &c. - In South America the Devonian is well developed; in Argentina, Bolivia, Brazil, Peru and the Falkland Islands, the palaeontological 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 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 Victoria, New South Wales and Queensland; an Upper division has also been observed. In New Zealand the Devonian is well exposed in the Reefton mining field; and it has been suggested that much of the highly metamorphosed rock may belong to this system.

Stratigraphy of the Old Red Sandstone Facies. The Old Red Sandstone of Britain, according to Sir Archibald Geikie, " consists of two subdivisions, the lower of which passes down conformably into the Upper Silurian deposits, the upper shading off in the same manner into the base of the Carboniferous system, while they are separated from each other by an unconformability." The Old Red strata appear to have been deposited in a number of elongated lakes or lagoons, approximately parallel to one another, with a general alignment in a N.E.-S.W. direction. To these areas of deposit Sir A. 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 Highlands and the southern uplands lay " Lake Caledonia." Here the lower division is made up of some 20,000 ft. of shallow-water deposits, reddish-brown, yellow and grey sandstones and conglomerates, with occasional " cornstones," and thin limestones. The grey flagstones with shales are almost confined to Forfarshire, and are known as the " Arbroath flags." Interbedded volcanic rocks, andesites, dacites, diabases, with agglomerates and tuffs constitute an important feature, and attain a thickness of 6000 ft. in the Pentland and Ochil hills. A line of old volcanic vents may be traced in a direction roughly parallel to the trend of the great central valley. On the northern side of the Highlands was Lake Orcadie," presumably much larger than the foregoing lake, though its boundaries are not determinable. It lay over Moray Firth and the east of Ross and Sutherland, and extended from Caithness to the Orkney Islands and S. Shetlands. It may even have stretched across to Norway,where similar rocks are found in Sognef j ord and Dalsfjord, and may have had communications with some parts of northern Russia. Very characteristic of this area are the Caithness flags, dark grey and bituminous, which, with the red sandstones and conglomerates at their base, probably attain a thickness of 16,000 ft. The somewhat peculiar fauna of this series led Murchison to class the flags as Middle Devonian. In the Shetland Islands contemporaneous volcanic rocks have been observed. Over the west of Argyllshire 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 Shropshire and South Wales by a great series of red rocks, shales, sandstones and marls, some 10,000 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. Interbedded lavas and tuffs are found in the island of Hoy. An interesting feature of this series is the occurrence of great crowds of fossil fishes in some localities, notably at Dura Den in Fife. In the north of England this series rests unconformably upon the Lower Old Red and the Silurian.

Flanking the Silurian high ground of Cumberland and Westmorland, and also in the Lammermuir hills and in Flint and 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 Ireland the lower division appears to be represented by the Dingle beds and Glengariff grits, while the Kerry rocks and the Kiltorcan beds of 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. Doubtless at all times there were regions of the 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 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 life of this period bears a distinct 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 w 0 a brachiopod. The tabulate corals were represented by Favosites, Michelinia, Pleurodictyum, Fistulipora, Pachypora and others. Heliolites and Plasmopora 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 foraminifera.

In the Devonian period the brachiopods reached the climax of their development: they compose three-quarters of the known fauna, and more than I too 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 productids ( Productella, Chonetes, Strophalosia ) were increasing. The strophomenids were still flourishing, represented by the genera Leptaena, Stropheodonta, Kayserella, and others. The ancient Lingula, along with Crania and Orbiculoidea, occur among the inarticulate forms. Another long-lived and wide-ranging species is Atrypa reticularis. The athyrids were very numerous(Athyris, 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 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 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 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, Calccocrinus and Eleuthrocrinus. The cystideans were falling off ( Proteocystis, Tiaracrinus ), but blastoids 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 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 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 mark the Lower and Upper Devonian respectively, while the genus Dalmania (Odontochile ) was represented by species with an almost world-wide range. The Ostracod Entomis (Cypridina ) was extremely abundant in places - Cypridinen-Schiefer - 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.

Insects appear well developed, including both orthopterous and neuropterous forms, in the New Brunswick rocks. Mr Scudder believed he had obtained a specimen of Orthoptera in which a stridulating organ was present. A species of Ephemera, allied to the modern may-fly, had a spread of wing extending to 5 in. In the Scottish Old Red Sandstone myriapods, Kampecaris andA rchidesmus, have been described; they are somewhat simpler than more recent forms, each segment being separate, and supplied with only one pair of walking legs. Spiders and scorpions also lived upon the 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 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 waters. Foremost in interest are the curious ostracoderms, a remarkable group of creatures possessing many of the 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 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 lung-fishes; and it is of extreme interest to note that a few of these curious forms still survive in the 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 faculty of moving the head in a vertical plane. These comprise the wide-ranging Coccosteus with Homosteus 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 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. Mesacanthus, Diplacanthus, Climatius, Cheiracanthus are characteristic genera. The crossopterygians, ganoids with a scaly 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 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 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 Professor 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 plants. In some regions so abundant are the vegetable remains that in places they form thin seams of veritable 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 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 stem and two kinds of sporangia in sessile sporocarps.

Physical Conditions, &c. - Perhaps the most striking fact that is brought out by a study of the Devonian rocks and their fossils is the gradual transgression of the sea over the land, which took place quietly in every 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. Kayser has pointed out the probability of a Eurasian sea province extending through Europe towards the east, across north and central Asia towards 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 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. Barrois has indicated the existence of three zones of deposition: (i) A northern, Old Red, region, including Great Britain, Scandinavia, European Russia and Spitzbergen; here the land was close at 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 access to wide areas, only to be driven off again, during pauses in the relative subsidence of the land, when the continued 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 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 borne in mind that the abovementioned 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 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 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 disjunctus and others. The fauna of the Calceola shales can be traced from western Europe to Armenia and 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 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 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 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-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 veins of tin, lead, copper, iron are exploited, as in Cornwall, Devon, the Harz; in New Zealand, gold veins occur. 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 gas of western Pennsylvania and south-western New York. In Ontario the middle division is oil-bearing. Black phosphates are worked in central Tennessee, and in England the marls of the " Old Red " are employed for brick-making.

REFERENCES. - The literature of the Devonian rocks and fossils is very extensive; important papers have been contributed by the following geologists: J. Barrande, C. Barrois, F. Beclard, E. W. Benecke, L. Beushausen, A. Champernowne, J. M. Clarke, Sir J. W. Dawson, A. Denckmann, J. S. Diller, E. Dupont, F. Frech, J. Fournet, Sir A. Geikie, G. Gurich, R. Hoernes, E. Kayser, C. and M. Koch, A. von Koenen, Hugh Miller, D. P. Oehlert, C. S. Prosser, P. de Rouville, C. Schuchert, T. Tschernyschew, E. O. Ulrich, W. A. E. Ussher, P. N. Wenjukoff, G. F. Whidborne, J. F. Whiteaves and H. S. Williams. Sedgwick and Murchison's original description appeared in the Trans. Geol. Soc. (2nd series, vol. v., 1839). Good general accounts will be found in Sir A. Geikie's Text-Book of Geology (vol. ii., 4th ed., 1903), in E. Kayser's Lehrbuch der Geologie (vol. ii., 2nd ed., 1902), and, for North America, in Chamberlin and Salisbury's Geology (vol. ii., 1906). See the Index to the Geological Magazine (1864-1903), and in subsequent annual volumes; Geological Literature added to the Geological Society's Library (London), annually since 1893; and the Neues Jahrbuch fiir Min., Geologie and Paldontologie (Stuttgart, 2 annual volumes). The U.S. Geological Survey publishes at intervals a Bibliography and Index of North American Geology, &c., and this (e.g. Bulletin 301, the Bibliog. and Index for 1901-1905) contains numerous references for the Devonian system in North America. (J. A. H.)

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