part 2] 



ITS STRUCTURE AND ROCK-SUCCESSION. 



147 



Y Garnedcl Quarry, and at one point on the track about 100 yards 

 north-east of the quarry an interesting calcareous bed is seen full 

 of Seterorthis alter nata, yielding in addition : — 



Leptsena rhomhoidalis Wilckens. 

 Strophomeiia (RafinesquinaJ ex- 



pansa (Sowerby). 

 Glyptocriiius hasalis M'Coy. 

 Beyrichia (Tetradella) complicata 



(M'Coy). 



Orthis (HeterorthisJ alternata var. 

 retrorsistria (Davidson). 



Orthis (DinortliisJ flabelltdiim 

 (Sowerby). 



Orthis (s.s.) calligramma Dalman. 



Plectamhonites sericea (SoAverby). 



Plectamhouites transvei'salis (Dal- 

 man). 



This bed when traced round exhibits the folding very well. 



In Y "Garnedd Quarry the relation of the Pont-y-Ceunant Ash 

 to the underljdng beds is clearly seen, the junction being re- 

 markably irregular and ' pockety.' 



Fig. 3. — Y-Ga7'nedd Qicarri/ : diagrammatic sketch illicstrating 

 the '■ pochety'' nature of the junction of tlie Pont-y-Ceunant 

 Ash with the Allt-Ddu JSIudstones. 



The Pont-y-Ceunant Ash itself contains no fossils, but the Gelli- 

 grin Calcareous Ash which overlies it is more or less fossiliferous 

 throughout, particularly so in a band about 7 feet above the base. 



The following forms are all common 



Orthis (Nicolella) actoiiiae (Sowerby). 

 Orth is fPlatystrophaJ hiforata 



(Schlotheim). 

 Orthis (DalmanellaJ elegantula 



(Dalman). 

 Orthis (Plectorthis) plicata{Sowevhj). 

 Orthis (DalmansllaJ testudinaria 



(Dalman). 

 Orthis (Harhnessella) vespertilio 



(Sowerby). 

 Triplecia (Cliftonia) spiriferoides 



(M-Coy). 

 Leptsena rhomhoidalis Wilckens. 

 Stropheodonta comtgatella (Davidson). 



Plectamhonites sericea (Sowerby). 

 Plectamhonites transversalis (Dal- 

 man). 

 Plectamhonites rhomhica (Davidson). 

 Trinucleus concentricus Eaton. 

 Trinucleus gihhifrons M'Coy. 

 Galymene planimarginata Reed. 

 Galyinene caractaci Salter. 

 Beyrichia complicata. Salter. 

 Monticitlipora lycoperdon (Say). 

 MonticuliporcL fihrosa (M'Coy). 

 Cystid-plates. 

 P7'imitia. 

 Palsearca sp. 



l2 



