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CULM

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Originally appearing in Volume V07, Page 618 of the 1911 Encyclopedia Britannica.
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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. J. Hinde and H. 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:Hill beds with See also:radiolaria. Ussher's subdivisions were introduced to satisfy the exigencies of See also:geological mapping, but, as he pointed out, while they are necessary in some parts of the district and convenient in others, the lithological characters upon which they are founded are variable and inconstant. More recently E. A. N. See also:Arber (1904–1907) clearly demonstrated that no palaeontological subdivision of the Upper Culm (Middle and Upper) is possible, and that these strata, on the See also:evidence of the fossil See also:plants, represent the Middle See also:Coal Measures of other parts of the See also:country. Wheelton See also:Hind has called See also:attention to the See also:probability that the Pasidonomya limestone and shale may represent the Pendleside See also:group of See also:Lancashire, See also:Derbyshire, &c. The Coddon Hill beds may belong to this or to a lower See also:horizon. Thus the See also:English Culm measures comprise an Upper Carboniferous and a Lower Carboniferous group, while in Germany, Austria and elsewhere, as it is important to See also:bear in mind, the Culm, or " See also:Kulm," See also:stage is shown by its contained fossils to belong to the lower See also:division alone.

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.

End of Article: CULM

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CULMINATION (from Lat. culmen, summit)

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