THE ENCYCLOPÆDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE AND GENERAL INFORMATION

ELEVENTH EDITION 1911

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AVONIAN, in geology, the name proposed by Dr A. Vaughan in 1905 (Q.J.G.S. vol. lxi. p. 264) for the rocks of Lower Carboniferous age in the Avon gorge at Bristol. The Avonian stage appears to embrace precisely the same rocks and fossil-zones as the earlier designation "Dinantien" (see Carboniferous System); but its substages, being founded upon different local conditions and a different interpretation of the zonal fossils, do not correspond exactly with those of the French and Belgian geologists.

 

 

Substages.

 

Zones.

 

Substages.

Avonian

brace

Kidwellian

brace

Dibunophyllum

brace

Viséen

brace

Dinantien

Seminula

 

Clevedonian

brace

Syringothyris

Zaphrentis

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Tournaisien

Cleistopora

The upper Avonian (Kidwellian) is well developed about Kidwelly in Carmarthenshire. The lower substage (Clevedonian) is well displayed near Clevedon in Somerset.

See A. Vaughan, "The Carboniferous Limestone Series (Avonian) of the Avon Gorge," Proc. Bristol Naturalists' Soc., 4th series, vol. i. pt. 2, 1906, pp. 74-168 (many plates); and T. F. Sibley, "On the Carboniferous Limestone (Avonian) of the Mendip area (Somerset)," Q.J.G.S. vol. lxii., 1906, pp. 324-380 (plates).

(J. A. H.)


Transcriber's note: A few typographical errors have been corrected. They appear in the text like this, and the explanation will appear when the mouse pointer is moved over the marked passage. Sections in Greek will yield a transliteration when the pointer is moved over them, and words using diacritic characters in the Latin Extended Additional block, which may not display in some fonts or browsers, will display an unaccented version.

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