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BALA SERIES

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Originally appearing in Volume V03, Page 239 of the 1911 Encyclopedia Britannica.
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BALA See also:SERIES , in See also:geology, a series of dark slates and See also:sand-stones with beds of See also:limestone which occurs in the neighbourhood of Bala, Merionethshire, See also:North See also:Wales. It was first described by A. See also:Sedgwick, who considered it to be the upper See also:part of his See also:Cambrian See also:System. The series is now placed at the See also:top of the Ordovician System, above the Llandeilo beds. The Bala limestone is from 20 to 40 ft. thick, and is recognizable over most of North Wales; it is regarded as the See also:equivalent of the Coniston limestone of the See also:Lake See also:District. The series in the type See also:area consists of the Hirnant limestone, a thin inconstant See also:bed, which is separated by 1400 ft. of slates from the Bala limestone, below this are more slates and volcanic rocks. The latter are represented by large contemporaneous deposits of See also:tuff and felsitic See also:lava which in the See also:Snowdon District are several thousand feet thick. In See also:South Wales the Bala Series contains the following beds in descending See also:order:—the Trinucleus seticornis beds (See also:Slade beds, Redhill shales and Sholeshook limestone), the Robeston Wathen beds, and the Dicranograptus shales. The typical See also:graptolites are, in the upper part, Dicellograptus anceps and D. complanatus; in the See also:lower part, Pleurograptus linearis and Dicranograptus Clingani. In See also:Shropshire this series is represented by the Caradoc and Chirbury Series; in See also:southern See also:Scotland by the Hartfell and. Ardmillan Series, and by similar rocks in See also:Ireland. See CARADOC SERIES and ORDOVICIAN SYSTEM.

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