T1IK c.MMJONM-KKOUS SYSTEM _':<:{ 



l Modiola (cf. lata), and the higher beds containing Productus 

 bassus, and near the top an abundance of Cleistopora geometrica, 

 a small compound coral of Miclu-linioid aspect. 



The Zaphrentis zone consists of encrinital limestones charac- 

 terised in the lower part by an abundance of Spirifer clathratus, 

 and in the upper part by Zaphrentis Konincki. 



The Syringothyris zone consists largely of dolomitic and 

 oolitic limestones in which Cominia cylindrica, Michelinia cf. mega- 

 stoma, and Spirifer (Syringothyris) cuspidatus are common and 

 characteristic fossils. Caninia patula marks a lower, and Cyatho- 

 jihyllum (sp. <f>) an upper sub-zone. 



The Seminula zone consists of limestones with shale-partings in 

 the lower part, and beds of pisolitic limestone in the upper. The 

 index fossil is the Athyrid Seminula ficoides, but Productus 

 corrugato-hemisphericus is common, as also are massive and dendroid 

 Lithostrotions and Carcinophyllum. 



The Dibunophyllum zone consists of limestones, shale*, and 

 occasional grits. It is characterised by the abundance of highly 

 developed corals : Dibunophyllum (simple in the lower and 

 advanced in the upper sub-zone ; Lithostrotion irregulare, Cyatho- 

 phyllum Murchisoni are common forms ; Lonsdaleia floriformis and 

 Cyathophyllum regium mark the upper sub-zone. 



At Wick war, near the northern end of the Bristol coalfield, the 

 limestone series is reduced to 1670 feet, and farther north, in the 

 Forest of Dean area, it is less than 600 feet. In the last-mentioned 

 area the highest limestones are of Seminula age, and are succeeded 

 conformably by sands and quartz-pebble conglomerates that have 

 been referred to the " Millstone grit " although they are of con- 

 siderably earlier age than the base of the typical Millstone grit of 

 the Midlands and Yorkshire. 



In South Wales, at the eastern end of the coalfield, the Avonian 

 Series, with shales at base and summit, is about 1000 feet thick 

 near Cardiff and Newport, but thins northward to less than 500. 

 (The series is, however, incomplete at the top as Millstone grit lies 

 unconformably upon Seminula, and Lower Dibunophyllum Beds.) 

 \\fstward, near Rhymney, and in the Gower Peninsula, the Avonian 

 attains a thickness of 3000 feet. Tin-re the black shales and 

 limestones 2 above the Dibunophyllum limestone (see Fig. 77) 

 yield a peculiar fauna, including the Goniatites Glyphioceras bi- 

 lingue, G. spirale, and G. reticulatum. These are characteristic 

 species of the Pendleside Beds of Lancashire and North Stafford, 

 and belong to a zone or sub-zone which lies between the Dibuno- 

 phyllum zone of the Bristol area and the typical Millstone grit 

 of the Dovedale country. 



