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CAMBRIAN

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Originally appearing in Volume V05, Page 89 of the 1911 Encyclopedia Britannica.
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CAMBRIAN See also:

SYSTEM In the Thuringer Wald are certain strata, presumably Cambrian since the uppermost beds contain the Euloma-See also:Niobe See also:fauna. See also:Sardinia contains both See also:middle and upper Cambrian. The Cambrian system is represented in the See also:Salt Range of See also:India by the Neobolus or Khussack beds, which may possibly belong to the middle subdivision. The same See also:group is probably represented in Corea and the Liao-tung by the thick " Sinisian formation of F. von See also:Richthofen. In See also:South See also:America upper Cambrian rocks have been recorded from See also:north See also:Argentina. The See also:Lower Cambrian has been found at various places in South See also:Australia; and in See also:Tasmania a thick See also:series of strata appears to be in See also:part at least of Upper Cambrian See also:age. See also:General See also:Physical Conditions in the Cambrian See also:Period.—The Cambrian rocks previously described are all such as would result from deposition, in comparatively shallow seas, of the products of degradation of See also:land surf aces by the See also:ordinary agents of denudation. Evidences of shallow See also:water conditions are abundant; very frequently on the bedding surfaces of sandstones and other rocks we find cracks made by the See also:sun's See also:heat and pittings caused by the showers that See also:fell from the Cambrian See also:sky, and these records of the See also:weather of this remote period are pre-served as sharply and clearly as those made only to-See also:day on our tidal reaches. Ripple marks and current bedding further point to the shallowness of the water at the places where the rocks were made. No Cambrian rocks are such as would be formed in the abysses of the sea—although the See also:absence of well-See also:developed eyes in the See also:trilobites has led some to assume that this See also:condition was an indication that the creatures lived in abyssal depths. At the See also:close of the pre-Cambrian, many of the deposits of that period must have been elevated into regions of fairly high ground; this we may assume from the nature of the Cambrian deposits which are mainly the product of the denudation of such ground. Over the land areas thus formed, the seas in Cambrian See also:time gradually spread, laying down first the series known as Lower Cambrian, then by further encroachment on the land the wider spread Upper Cambrian deposits—in See also:Europe, the middle series is the most extensive.

Consequently, Cambrian strata are usually unconformable on older rocks. During the general advance of the See also:

sea, See also:local warpings of the crust may have given rise to shallow See also:lagoon or inland-See also:lake conditions. The See also:common occurrence of red strata has been cited in support of this view. Compared with some other periods, the Cambrian was See also:free from extensive volcanic disturbances, but in See also:Wales and in See also:Brittany the earlier portions of this period were marked by voluminous outpourings; a condition that was feebly reflected in central and See also:southern Europe. No definite conclusions can be See also:drawn from the fossils as to the See also:climatic peculiarities of the See also:earth in Cambrian times. The red rocks may in some cases suggest See also:desert conditions; and there is See also:good See also:reason to suppose that in what are now See also:Norway and See also:China a glacial See also:cold prevailed See also:early in the period. Considerable See also:variations occur in the thickness of Cambrian deposits, which may generally be explained by the greater former a barren series of conglomerates and quartzites, the latter a series of See also:grey and See also:green fissile shales 1200 ft. thick with sandstones, greywackes and conglomerates. Scandinavia.—Here the Cambrian system is only distinguished clearly on the eastern See also:side, where the three subdivisions are found in a thin series of strata (400 ft.), in which See also:black See also:concretion-bearing Midland and See also:West of See also:England. North Wales. South Wales. See also:Shropshire. See also:Malvern Hills.

See also:

Nuneaton. Upper Cambrian, Tremadoc slates Tremadoc beds Shineton shales Bronsi1 shales, Upper See also:Stocking- Olenus fauna (Euloma-Niobe Lingula flags and shales with grey (Niobe See also:ford shales fauna) Dictyonema fauna) (See also:Merivale shales) Lingula Hags Malvern black Middle Stocking- (I) Dolgelly beds shales (See also:White- ford shales, (2) Ffestiniog leaved-See also:oak (See also:Oldbury shales) beds shales) (3) Maentwrog beds Middle See also:Cam- Menevian beds Menevian beds _ See also:brian, See also:Paradox- ides fauna Solva group Comley or See also:Holly- Hollybush See also:sand- Lower Stocking- See also:bush See also:sandstone See also:stone ford shales with upper (Purley shales) Comley See also:lime- stone Lower Cambrian, See also:Harlech grits and Caerfai group Lower Comley Hollybush sand- Upper Hartshill Olenellus fauna See also:Llanberis slates See also:limestone stone with Mal- See also:quartzite. Hyo- Wrekin quartzite vern quartzite lithes shales and and conglomer- limestone See also:ate at the See also:base Middle an'tl lower Hartshill quart- zite and the quartzite of the Lickey Hills shales See also:play an important part. Limestones and shales with the Euloma-Niobe fauna come at the See also:top. The upper series (Olenus) has been minutely zoned by W. C. See also:Brogger, S. A. Tullberg and J. C. Moberg. In the middle series (Paradoxides) three thin limestone bands have been distinguished, the Fragmenten-See also:Kalk, the Exulans-Kalk and the Andrarums-Kalk.

On the See also:

Norwegian side the Cambrian is perhaps represented by the Roros See also:schists which See also:lie at the base of a See also:great series of crystal-See also:line schists, the probable See also:equivalent of Ordovician and See also:Silurian rocks. Baltic See also:Province.—The Cambrian rocks in this region are nearly all soft sediments, some 600 ft. thick; they reach from the Gulf of See also:Finland towards Lake See also:Ladoga. At the base is the so-called " See also:blue See also:clay " (really greenish) with ferruginous sandstones and with a fucoidal sandstone at its See also:summit. This See also:division is the equivalent of the Lower Cambrian. Above the fucoidal sandstone an important break appears in the system, for the Paradoxides and Olenus divisions are absent. The upper members are the " Ungulite grit " and about 20 ft. of Dictyonema shale. Cambrian rocks have been traced into See also:Siberia (See also:lat. 71 °) and on the See also:island of Vaigatch. Central Europe.—Besides the Bohemian region previously mentioned, Cambrian rocks are See also:present in See also:Belgium and the north of See also:France, in See also:Spain and the Thuringer Wald. In the See also:Ardennes the system is represented by grits and sandstones, shales, slates and See also:quartz schists, and includes also whet slates and some igneous rocks. A. See also:Dumont has arranged the whole series (Terrain ardennais) into three systems, an upper " Salmien," a middle " Revinien " and a lower " Devillien," but J.

Gosselet has subsequently proposed to unite the two lower See also:

groups in one. France.—In See also:northern France Cambrian rocks, mostly See also:purple conglomerates and red shales, See also:rest with apparent unconformability upon pre-Cambrian strata in Brittany, See also:Normandy and northern See also:Poitou. In the See also:Rennes See also:basin limestones—often dolomitic—are associated with quartzites and conglomerates; silicious limestones also occur in the See also:Sarthe region. Farther south, around the old lands of See also:Languedoc, equivalents of the two upper divisions of the Cambrian have been recorded; and the uppermost members of the system appear in See also:Herault. Patches of Cambrian rocks are found in the See also:Pyrenees. In Spain slates and quartzites, the slates of Rivadeo, more than 9000 ft. thick, are followed by the middle Cambrian beds of La See also:Vega, thick quart,zites with limestone, slates and See also:iron ores. Cambrian rocks occur also in the provinces of See also:Seville and See also:Ciudad-Real. Upper Cambrian strata have been found in upper See also:Alemtejo in See also:Portugal. In See also:Russian See also:Poland is a series of conglomerates, quartzites and shales; some of the beds yield a Paradoxides fauna. rapidity of deposition in some areas than in others. Nothing could be more striking than the difference between the thicknesses in western and eastern Europe; in Brittany the deposits are over 24,000 ft. thick, in Wales at least 12,000 ft., in western England they are only 3000 ft., and in northern See also:Scotland 2000 ft., while no farther See also:east than Scandinavia the See also:complete Cambrian See also:succession is only about 400 ft. thick. Again, in North America, the greatest thicknesses are found along the mountainous regions on the west and on the east—reaching 12,000 ft. in the latter and probably nearly 40,000 ft. in the former (in See also:British See also:Columbia)—while over the interior of the See also:continent it is seldom more than loon ft. thick.

Any See also:

attempt to picture the See also:geographical conditions of the Cambrian period must of See also:necessity be very imperfect. It was pointed out by See also:Barrande that early in Palaeozoic Europe there appeared two marine provinces—a northern one extending from See also:Russia to the British Isles through Scandinavia and northern See also:Germany, and a southern one comprising France, Bohemia, the Iberian See also:peninsula and Sardinia. It is assumed that some See also:kind of land barrier separated these two provinces. Further, there is a marked likeness between the Cambrian of western Europe and eastern America; many fossils of this period are common to See also:Britain, See also:Sweden and eastern See also:Canada; therefore it is likely that a north See also:Atlantic basin existed. Prof. See also:Kayser suggests that there was also a Pacific basin more extensive than at present; this is See also:borne out by the similarity between the Cambrian faunas of China, Siberia and Argentina. The same author postulates an See also:Arctic continent, bordering upon northern Europe, See also:Greenland and North America; an See also:African-Brazilian continent across the present south Atlantic, and a marine communication between Australia and India, where the faunas have much in common.

End of Article: CAMBRIAN

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