part 2] STEUCTUKE, ETC. or THE BALA COIINTEY. 



155 



intervening between the two. The limestone shows up best on the 

 scarp-face, and then forms a wall-Uke mass weathering in honey- 

 comb fashion, and recalhng in many respects the less massive part 

 of the Grelli-grin Limestone as regards outward appearance. Com- 

 pared with the lower limestone, however, theKhiwlas is always, as 

 already stated, paler in colour, less pure, minutel}^ lenticular, and 

 more fragmentary, characteristics which probablj" account for its 

 rejection for burning to lime, while the Gelli-grin and other lime- 

 stones of the Calcareous Ash Series have invariabl}^ been utilized in 

 this respect. Highly calcareous mudstone-bands are intercalated 

 in the Rhiwlas Limestone, and some of these, as also the purer 

 more crystalline limestone-bands, contain phosphate-nodules which 

 vary in size, the biggest found on Creigiau Bychain being about 

 the size and shape of a blackbird's egg. 



The greatest of the sj'nclines presents a definitely ovoid outline, 

 its axis trending practically north and south, and having a gentle 

 southward pitch, the general shape of the fold being clearly indi- 

 cated b}^ the wall-like outcrop of the Ehiwlas Limestone. A 

 second minute fold occurs immediately north-east of this, in which 

 the Rhiwlas Limestone is bent upon itself at the top of a little 

 roll-over of the Calcareous Ash ; farther north-westwards another 

 almost complete syncline in the limestone is seen, and a fragment 

 of the same rock indicates its connexion with another similar 

 pitching fold still farther north-westwards. 



The Khiwlas Limestone of the greatest syncline has yielded the 



following fossils : — 



Encrinurus sexcostatus Salter. 

 AgnosUis agnostiforrais (M'Coy). 

 lUsenus davisi Salter. 

 Phacops sp. 

 Christimiia tenuicincta (M'Coy). 



Hyatella portlochlana (Davidson). 

 Plectamhonites transversalis (Dal- 



man). 

 Echinosphsevites stellulifera Salter. 

 Glyptocrinus hasalis M'Coy. 



While the Calcareous Ash immediately beneath is still more 

 richly fossiliferous, yielding : — 



Calymene caractaci Salter. 

 Chasmops conicophthalniiis (Boeck). 

 Trinucleus gihhifrons M'Coy. 

 Trimicleus excentriciis Eaton. 

 Homalonotus hisulcatus Salter. 

 Strophomena fRafinesquinaJ expansa 



(Sowerby), 

 Orthis (Nicolella) actonise (Sowerby). 

 Orthis (DalmanellaJ testudinaria 



var. 

 Triplecia fCliftoniaJ spiriferoides 



(M'Coy). 



Plectamhonites rhomhica (Davidson). 

 Plectamhonites sericea (Sowerby). 

 Plectamhonites quinquecostata 



(M'Coy). 

 Leptsena rhoinhoidalis Wilckens. 

 Glyptocrinus hasalis M'Coy. 

 Monticulipora fihrosa (M'Coy). 

 Holop)ella sp. 

 Belleroplion fOxydiscvsJ acutus 



(Sowerby). 



(vwni-yr-Aethnen, Pen-y-Dallgwm^ and Foel-y-Ddinas. 



These places together afford a good section of the highest beds 

 of the Ashgillian and overlying Silurian rocks. 



The Moel-fryn Sandstones, as already described, are very 

 monotonous pale-grey rocks, with some intercalations of mudstones 



