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ARENIG GROUP

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Originally appearing in Volume V02, Page 452 of the 1911 Encyclopedia Britannica.
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ARENIG See also:

GROUP , in See also:geology, the name now applied by See also:British geologists to the lowest See also:stage of the Ordovician See also:System in See also:Britain. The See also:term was first used by See also:Adam See also:Sedgwick in 1847 with reference to the " Arenig Ashes and Porphyries " in the neighbourhood of Arenig Fawr, in See also:Merioneth, See also:North See also:Wales. The See also:rock-See also:succession in the Arenig See also:district has been recognized by W. G. Fearnsides (" On the Geology of Arenig Fawr and Moel Llanfnant," Q.J.G.S. vol. lxi., 1905, pp. 6o8–64o, with maps) as follows: c,'i o S Dicranograptus—shales. U Derfel or Orthis—limestone. 0 -o ^ (unconformity) The above succession is divisible into: (I) a Iwer See also:series of gritty and calcareous sediments, the Arenig Series," as. it is now understood; -(2) a See also:middle series, mainly volcanic, with shales, the " Llandeilo Series "; and (3) the shales and See also:lime-stones of the See also:Bala or Caradoc Stage. It was to the middle series (2) that Sedgwick first applied the term " Arenig." In the typical region and in North Wales generally the Arenig series appears to be. unconformable upon the See also:Cambrian rocks; this is not the See also:case in See also:South Wales. The Arenig series is represented in North Wales by the See also:Garth grit and Ty-Obry beds, by the Shelve series of the Corndon district, the Skiddaw slates of the See also:Lake District, the Ballantrae group of See also:Ayrshire, and by the Ribband series of slates and shales in See also:Wicklow and See also:Wexford. It may be mentioned here that the " Llanvirn " Series of H. See also:Hicks was See also:equivalent to the bifidus-shales and the See also:Lower Llandeilo Series.

End of Article: ARENIG GROUP

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