Cambrian, Ordovician and Silurian beds have been recognized, the Upper Cambrian consisting of a limestone which is very rich in metalliferous ores (especially galena and calamine).
Contemporaneous volcanic rocks are associated with the Ordovician beds and with the Rhaetic sandstones in several places.
The higher steppes, as far as they are known, consist of Ordovician and Cambrian rocks, with an average elevation of 1500 to 3000 ft.
The breaking up of the old Archean foundation block began in Cambrian and Ordovician times.
Marine Ordovician rocks were deposited along the same general course.
This Silurian sea was less extensive than the Ordovician in Victoria; but it appears to have been wider in New South Wales and in Queensland.
The Ordovician and Silurian systems are widely developed, and it is most probable that, with the exception of the Archean continents of Finland and the S, the sea covered the whole of Russia.
Little is known of the early geological history of Asia beyond the fact that a large part of the continent was covered by the sea during the Cambrian and Ordovician periods.
Here the folded Archean rocks are overlaid by Cambrian and Ordovician beds, which still lie for the most part flat and undisturbed.
Besides the plant beds extensive outflows of basic lava rest directly upon the Cambrian and Ordovician strata.
In the northern unfolded region great flows of basic lava lie directly upon the Cambrian and Ordovician beds of Siberia, but are certainly in part of Tertiary age.
Undue stress is often laid on the fact that Lingula has come down to us apparently unchanged since Cambrian times, whilst Crania, and forms very closely resembling Discina and Rhynchonella, are found from the Ordovician strata onwards.
the Gasteropod Capulus, whilst most of the invertebrate classes were represented in the Ordovician by forms which do not differ from their existing representatives in any important respect.
One of the Asaphidae allied to Illaenus, from the Ordovician of East Gothland, Sweden.
- Restoration of Triarthrus Becki, Green, as determined by Beecher from specimens obtained from the Utica Slates (Ordovician), New York.
The crystalline rocks are succeeded by beds which have been referred to the Cambrian and Silurian systems. In the valley of the Trombetas, one of the northern tributaries of the Amazon, fossils have been found which indicate either the top of the Ordovician or the bottom of the Silurian.
In the Maecuru, another northern affluent, graptolites of Ordovician age have been discovered, and Silurian fossils are said to have been found in the Maraca.
In the latter range a few Ordovician fossils have been found, but in general the oldest strata which have yielded organic remains belong to the Cretaceous system.
Gneiss and granite occur; Ordovician fossils have been found in the Upper Shan States, and Carboniferous fossils in Tenasserim and near Moulmein.
The series is now placed at the top of the Ordovician System, above the Llandeilo beds.
See Caradoc Series and Ordovician System.
From the geological formation here the name Trenton is applied to the upper series of the Ordovician (or Lower Silurian) system, and, particularly, to the lowest stage of this series.
The Heteroptera can be traced back farther than any other winged insects if the fossil Protocimex silurica Moberg, from the Ordovician slates of Sweden is rightly regarded as the wing of a bug.
In 1892 the phosphates of Tennessee, derived from Ordovician limestones, came into the market.
No Cambrian rocks have as yet been discovered, but the Ordovician system is represented by the Aorere beds in the north-western part of the South Island.
Upon the folded slates and schists which constitute these inliers the Devonian rests with marked unconformity; but north of the ridge of Condroz Ordovician and Silurian beds make their appearance.
Until comparatively recent times the molluscs were considered as appearing on the limits of the Cambrian and Ordovician; but Charles D.
Recent discoveries of vertebrates are of the same significance, the most primitive fishes being traced to the Ordovician or base of the Silurian, 2 which proves that we shall discover more 2 Professor Bashford Dean doubts the fish characters of these Ordovic Rocky Mountain forms. Frech admits their fish character but considers the rocks infaulted Devonic.
Ordovician System.The succeeding Ordovician (Lower Silurian) system of rocks is closely connected with the Cambrian, geographically, stratigraphically and faunally.
The Ordovician system contains much more 9~ S~ ~ 1~
The succession of formations in that state is as follows Upper Ordovician (or J and Indiana).
Middle Ordovician (or I Trenton limestone.
Ordovician Mohawkian) -~ Black River limestone.
Lower Ordovician (or I Chazy limestone.
The oil and gas of Ohio and eastern Indiana come from the middle portion of the Ordovician system.
The fossils of the Ordovician system show that life made great progress during the, period, in numbers both of individuals and of species.
Beside the expansion of types which abounded in the Cambrian, vertebrate remains (fishes) are found in the Ordovician.
The departure of the Ordovician life from that of the Cambrian was perhaps most pronounced in the great development of the molluscs and crinoids (including cystoids), but corals were also abundant for the first time, and graptolites came into prominence.
Siluriaii System.The Silurian system is much less widely distributed than the Ordovician.
This and other corroborative facts imply a widespread emergence of land at the close of the Ordovician period.
As a result of this emergence the stratigraphic break between the Ordovician and the Silurian is one of the greatest in the whole Palaeozoic group.
Graptolites had declined notably as compared with the Ordovician, and the trilobites passed their climax before the end of the period.
As a whole, the system is more-widespread than the Silurian, though not so widespread as the Ordovician.
As in the case of the Ordovician and the Silurian, the New York section has become a standard with which the system in other parts of the country is commonly compared.
The system is well developed in the Mississippi Basin, whence its name, Its formations are much more widespread than those of any other system since the Ordovician.
In many places in the west they rest on what appear to be Ordovician beds, but without unconformity.
The explanation of the apparent conformity of the strata from the Cambrian to the Pennsylvanian in some parts of the west, with no fossils defining with certainty any horizon between the Ordovician and the Mississippian, is one of the open problems in the geology of the United States.
This epoch, indeed, is the epoch of maximum submerg,ence during the period, and the maximum since the Ordovician.
The Ordovician and Silurian are absent here, and the Devonian rests unconformably upon the Cambrian; but along the northern margin of the Palaeozoic area, Ordovician and Silurian rocks appear, and beds of similar age are also exposed farther north where the rivers have cut through the overlying Tertiary deposits.
The Cambrian, for example, is exposed at Leimitz near Hof in the Frankenwald, and the important coal-field of the Saar lies on the southern side of the Hunsruck, while Ordovician and Silurian beds have been found in several localities.
1.2.1 Archean Rocks 1.2.2 Eastern or Younger Schists 1.2.3 Torridonian Sandstone 1.2.4 Cambrian 1.2.5 Ordovician and Silurian 1.2.6 Old Red Sandstone 1.2.7 Carboniferous 1.2.8 Permian 1.2.9 Triassic 1.2.10 Jurassic 1.2.11 Cretaceous 1.2.12 Older Tertiary 1.2.13 Post-Tertiary 1.2.14 Recent
Abundant fossils (grapholites principally) in certain parts of these rocks have shown that representatives of both the Ordovician and Upper divisions are present.
The strata of this system rest upon the Pre-Cambrian, and are succeeded by the Ordovician system.
de Lapparent classifies the Cambrian as the lowest stage in the Silurian, the middle and upper stages being Ordovician and Gothlandian.
In a general survey of the life of this period, as it is revealed by the fossils, three outstanding facts are apparent: (I) the great divergence between the Cambrian fauna and that of the present day; (2) the Cambrian life assemblage differs in no marked manner from that of the succeeding Ordovician and Silurian periods; there is a certain family likeness which unites all of them; (3) the extraordinary complexity and diversity not only in the assemblage as a whole but within certain limited groups of organisms. Although in the Cambrian strata we have the oldest known fossiliferous rocks - if we leave out of account the very few and very obscure organic remains hitherto recorded from the pre-Cambrian - yet we appear to enter suddenly into the presence of a world richly peopled with a suite of organisms already far advanced in differentiation; the Cambrian fauna seems to be as far removed from what must have been the first forms of life, as the living forms of this remote period are distant from the creatures of to-day.
The Cambrian rocks of Ireland, a great series of purple and green shales, slates and grits with beds of quartzite, have not yet yielded sufficient fossil evidence to permit of a correlation with the Welsh rocks, and possibly some parts of the series may be transferred in the future to the overlying Ordovician.
On the Norwegian side the Cambrian is perhaps represented by the Roros schists which lie at the base of a great series of crystalline schists, the probable equivalent of Ordovician and Silurian rocks.
The Cambrian formation generally occurs along with the Ordovician, and consists of many divisions.
The upper divisions consist of bituminous limestones, clay-slates, alum-slate, and contain numerous species of trilobites of the genera Paradoxides, Conocoryphe, Agnostus, Sphaerophthalmus, Peltura, &c. The Ordovician formation occurs in two distinct facies - the one shaley and containing graptolites; the other calcareous, with brachiopods, trilobites, &c. The most constant of the calcareous divisions is the Orthoceras limestone, a red or grey limestone with Megalaspis and Orthoceras.
The Cambrian and Ordovician strata occur in isolated patches in Vesterbotten, Jemtland (around Storsjo), Skaraborg, Elfsborg, Orebro, Ostergotland and Kristianstad.
In the Himalaya the geological sequence, from the Ordovician to the Eocene, is almost entirely marine; there are indeed occasional breaks in the series, but during nearly the whole of this long period the Iimalayan region, or at least its northern part, must have been beneath the sea - the Central Mediterranean Sea of Neumayr or Tethys of Suess.
The oldest beds which have hitherto yielded fossils, belong to the Ordovician system, but it is highly probable that the underlying " Haimantas " of the central Himalaya are of Cambrian age.
Of the Lower Palaeozoic rocks the Ordovician appears to be the most widely-spread.
The Ordovician beds have yielded fossils in several places, Vallongo and Bussaco being amongst the best-known localities.
The Palaeozoic beds have yielded fossils of Cambrian, Ordovician, Devonian and Carboniferous age.
In southern Bolivia Cambrian and Ordovician beds form the greater part of the eastern Andes, but farther north the, Devonian and Carboniferous are extensively developed, especially in the northeastern ranges.
The rocks of the Ordovician system, though widely distributed, have not always been separated from the Silurian rocks, which they often closely resemble lithologically.
The occurrence of Ordovician rocks was first established by Dun at Tomingley, 33 m.
The fossiliferous horizon is of Upper Ordovician age.
The extent of the Ordovician will probably be increased by addition of areas, which cannot yet be separated from the Silurian.
Numerous quartz reefs occur both in the Silurian and Ordovician rocks.
The gold-quartz veins are mainly in the Ordovician and Silurian rocks; but some also occur in the Devonian, and there are impregnations of gold in tufas of Devonian age.
The central and most picturesque part of the district is formed of great masses of volcanic ashes and tuffs, with intrusions of basalts and granite, all of Ordovician (Lower Silurian) age.
Mid Wales is built up, for the most part, of Silurian or Ordovician rocks, practically free from igneous intrusions except in the south-west.
Old Red Sandstone & Devonian r (Silurian Ordovician Cambrian Metamorphic Group + +J Volcanic Rocks It Basic Intrusive Rocks 'V /1 '
We may note the pre-Cambrian lavas and tuffs of the Wrekin district in Shropshire and the somewhat later volcanic rocks of Charnwood; the porphyrites, andesites, tuffs and rhyolites of the Borrowdale volcanic centre, erupted in the Ordovician period, and the Silurian granites of the same region.
Regarding now the outcrops of bed-rock, there are exposures of Algonkian (doubtful, and at most a mere patch on Pilot Knob), Archean, Cambrian, Ordovician, Silurian, Devonian, sub-Carboniferous and Carboniferous.
Lima is situated in the centre of the great north-western oil-field (Trenton limestone of the Ordovician system) of Ohio, which was first developed in 1885; the product of the Lima district was 20,575,138 barrels in 1896, 15,877,730 barrels in 1902 and 6,748,676 barrels in 1908.
Both groups make their first appearance together near the end of the Cambrian; but while in the succeeding Ordovician and Silurian the Dendroidea are comparatively rare, the Graptoloidea become the most characteristic and, locally, the most abundant fossils of these systems.
from the Ordovician rocks of Esthonia, is in essential structure just the form demanded by comparative palaeontology to make a starting-point.
Even if the volcanic and intrusive basic rocks prove to be Ordovician (Lower Silurian), which is very doubtful, the metamorphic series of the core is clearly distinct, and appears to be " fundamental " so far as Ireland is concerned.
Following on these rocks of unknown but obviously high antiquity, we find fossiliferous Ordovician (Lower Silurian) strata near Killary harbour on the west, graduating upwards into a complete Gotlandian (Upper Silurian) system.
They are unfossiliferous, and in the absence of undoubted Cambrian, Ordovician and Silurian strata in Africa they may be regarded as of older date than any of these formations.
Some unfossiliferous conglomerates, sandstones and dolomites in South Africa and on the west coast are considered to belong to the Cambrian, Ordovician and Silurian formations, but merely from their occurrence beneath strata yielding Devonian fossils.
The oldest Palaeozoi strata are referred, from their included fossils, to the Cambrian Ordovician and Silurian systems. They range through a vas region of Andalusia, Estremadura, Castile, Salamanca, Leon arii Asr,urias, and along the flanks of the Pyrenean and Cantabria~ chain.
The Ordovician system has not been certainly identified; but probably many of the slates and quartzites.
in north-western Tasmania and of the mining field of Beaconsfield on the estuary of the Tamar, are Ordovician.
The inner or eastern ridge farther north of Argentina consists of crystalline rocks with infolded Ordovician and Cambrian beds, often overlaid unconformably by a sandstone with plant-remains (chiefly Rhaetic).
Girvanella, found in Cambrian, Ordovician and Silurian rocks, as well as in later deposits, appears to have played a part in the origination of oolitic rock-structure.
These forms, and others like them, go back to the Silurian and Ordovician; while Gyroporella, from the Permian, is another fairly characteristic Siphoneous type.
It has recently been stated, however, that the supposed Algae are in reality the megaspores of Vascular Cryptogams. Scarcely anything is known of Palaeozoic Florideae; Solenopora, ranging from the Ordovician to the Jurassic, resembles, in the structure of its thallus, with definite zones of growth, Corallinaceae such as Lithothamnion, and may probably be of the same nature.
From the Ordovician and Silurian, however, a certain number of authentic remains of Algae (among many more that are questionable) have been investigated; they are for the most part either verticillate Siphonae, or the large - possibly Laminariaceous - Algae named Nematophycus, with the problematical but perhaps allied Pachytheca.
The package becomes sandy through the Late Devonian Ordovician.
The Paleozoic Fossils of Ontario ** Ordovician and Silurian trilobites.
In the north-western Highlands masses of white quartzite, resting unconformably in Torridonian sandstone, run from Loch Eriboll to Skye, forming in places great conical hills and some L J Recent & Pleistocene F l Cretaceous Jurassic Trias Granite & Acid Intrusive Rocks' Permian Coal Measures, Carboniferous Millstone Grit Series Lower Carboniferous Old Red Sandstone & Devonian Silurian Ordovician Cambrian Scale, z:4,600.000 English Miles o xxxx xzxx xxxx Metamorphic Group Volcanic Rocks ® Basic Intrusive Rocks 'I +++ +++ ob.o times capping isolated mountains of red Torridon sandstone.
The mountain group of North Wales is the largest and loftiest; its scenery resembles that of the Scottish Highlands because of the juxtaposition of ancient Palaeozoic rocks - Cambrian and Ordovician, often altered into slate - and contemporaneous volcanic outbursts and igneous intrusions.
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