1911 Encyclopædia Britannica/Avonian

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	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Kidwellian	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Dibunophyllum	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right\}\,}$	Viséen	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$	Dinantien
				Seminula

		Clevedonian	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Syringothyris
				Zaphrentis	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	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.)

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