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CULM , in See also:geology, the name applied to a See also:peculiar See also:local phase of the Carboniferous See also:system . In 1837 A . See also:Sedgwick and R . I . See also:Murchison classified into two divisions the dark shales, grits and impure limestones which occupy a large See also:area in See also:Devonshire and extend into the neighbouring counties of See also:Somerset and See also:Corn-See also:wall . These two divisions were the Upper and See also:Lower Culm See also:Measures, so named from certain impure coals, locally called " culm," I contained within the shales near See also:Bideford . Subsequently, these two geologists, when prosecuting their researches in See also:Germany and See also:Austria, applied the same name to similar rocks which contained, amongst others, Posidonomya Becheri, See also:common to the phase of sedimentation in both areas . The Culm measures of the Devonshire See also:district are folded into a broad syncline with its See also:axis See also:running See also:east and See also:west; but within this See also:major See also:fold the rocks have been subjected to much See also:compression accompanied by See also:minor folding . This circumstance, together with the apparent barrenness of the strata, has always made a correct See also:interpretation of their position and relationships a See also:matter of difficulty; and for See also:long they were regarded as an abnormal expression of the Lower Carboniferous, with the upper-most beds as doubtful equivalents of the Millstone Grit of other parts of See also:Britain . The labours of W . A . E .
Ussher and of G
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See also:Fox have resulted in the differentiation of the following subdivisions in the Devonshire Culm:—(1) Upper Culm Measures or Eggesford grits; (2) See also:Middle Culm Measures, comprising the Morchard, See also:Tiverton and Ugbrooke lithological types overlying the See also:Exeter type; (3) Lower Culm, the Posidonomya See also:limestone and shale overlying the Coddon See also: The typical Carboniferous limestone of the Franco-Belgian area changes as it is traced towards the east and See also:south into the sandy, shaly Culm phase, with the characteristic " Posidonia " (Posidonomya) See also:schists . This aspect of the Culm is found in See also:Saxony, where there are workable coals, in Bohemia, Thuringia, the See also:Fichtelgebirge, the Harz, where the beds are traversed by See also:mineral See also:veins, and in See also:Moravia and See also:Silesia . In the last-mentioned region the thickness of the Culm formation has been estimated 1 This word is possibly connected with See also:col, coal; distinguish " See also:calm," the See also:stem of a plant, See also:Lat. culmus . by D . Stur at over 45,000 ft . In the east and south of the Schiefergebirge (a See also:general See also:term for the slaty mountains of the Hundsriick and See also:Taunus range, the Westerwald and See also:part of the See also:Eifel district), the Culm shales pass upwards into a coarser See also:deposit, the " Culm-grauwacke," which attains a considerable thickness and superficial extent . Culm fossils appear in the Carnic See also:Alps, in the Balkans and parts of See also:Spain, also in Spitzbergen and part of New See also:Guinea . The most characteristic fossil is of course Posidonomya Becheri; others are Glyphioceras sphaericum, Rhodea patentissima, Asterocalamites scrobiculatus (Schloth), Lepidodendron.veltheimianum, Gastrioceras carbonarium . See E . A . N . Arber, " On the Upper Carboniferous Rocks of West See also:Devon and See also:North See also:Cornwall," Q.J.G.S. lxiii . (1907), which contains a bibliography of the English Culm; E . Holzapfel, Palaont . '4bhandl . Bd. v . Heft i . (1889) ; H . Potoni6, Abhandl. preuss. geol . Landesanst., Neue Folge, 36 (1901) ; D . Stur, " See also:Die Culm See also:Flora," Abhandl. k.k. geol . Reichsanst. viii . (See also:Vienna, 1875) . (J . A . |
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