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 . Kidwellian .Dibunophyllum- Seminula Syringothyris Clevedonian Zaphrentis 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 . ]Iii., 1906, pp . 324-380 (plates) . (J . A .