See also:SYSTEM In the Thuringer Wald are certain strata, presumably Cambrian since the uppermost beds contain the Euloma-
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 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 Richthofen . In South
See also:America upper Cambrian rocks have been recorded from
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 series of strata appears to be in
See also:part at least of Upper Cambrian age . 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 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:heat and pittings caused by the showers that 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 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:local warpings of the crust may have given rise to shallow lagoon or inland-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 reason to suppose that in what are now Norway and
See also:China a glacial
See also:cold prevailed early in the period . Considerable 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 side, where the three subdivisions are found in a thin series of strata (400 ft.), in which black
See also:concretion-bearing Midland and West of 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 Stocking- Olenus fauna (Euloma-Niobe Lingula flags and shales with grey (Niobe
See also:ford shales fauna) Dictyonema fauna) (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, Paradox- ides fauna Solva group Comley or
See also:Holly- Hollybush sand- Lower Stocking-
See also:stone ford shales with upper (Purley shales) Comley lime- stone Lower Cambrian, 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 top . The upper series (Olenus) has been minutely zoned by W . C . 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 .
See also:Norwegian side the Cambrian is perhaps represented by the Roros
See also:schists which 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 Province.—The Cambrian rocks in this region are nearly all soft sediments, some 600 ft. thick; they reach from the Gulf of Finland towards Lake
See also:Ladoga . At the base is the so-called " blue
See also:clay " (really greenish) with ferruginous sandstones and with a fucoidal sandstone at its
See also:summit . This 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 Belgium and the north of France, in 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 lowergroups 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: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 Pyrenees . In Spain slates and quartzites, the slates of Rivadeo, more than 9000 ft. thick, are followed by the middle Cambrian beds of La Vega, thick quart,zites with limestone, slates and iron ores . Cambrian rocks occur also in the provinces of 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 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 Scotland 2000 ft., while no farther east than Scandinavia the
See also:complete Cambrian 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:Columbia)—while over the interior of the continent it is seldom more than loon ft. thick .
Anyattempt 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 Russia to the British Isles through Scandinavia and northern Germany, and a southern one comprising France, Bohemia, the Iberian peninsula and Sardinia . It is assumed that some 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 Britain, Sweden and eastern
See also:Canada; therefore it is likely that a north
See also:Atlantic basin existed . Prof . 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 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 .
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