146 MR. F. DIXEY AXD PROF. T. F. SIBLT OX THE [vol. IxXlii, 



Brachiopods : — 

 Papilionaceous Chonetes. 

 Productus comigato-hemisphericus 



Vaughan. 

 Productus ?iemispliericus J. de C. 



Sowerby. 



Schellirienella cf. a-enisiria (Phillips). 

 Cyrtina carbonaria M'Coy. 

 Seminula ficoides Vaughan. 

 Athyi'is cf. expansa Davidson, non 



(Phillips). 



On the whole, corals and brachiopods are not abundant, much of 

 the Seminula Oolite being poor in macroscopic organisms. But 

 beds crowded with Seminula, Productus^ or Chonetes are fairh' 

 frequent. LitJiostrotion martini is seldom abundant. Carcino- 

 phyllum vaughani may occur commonly at any level in the zone. 

 JS^ematopliyllum minus is only found near the base, while Alveo- 

 lites septosits and a large form of Productus liemispliericus become 

 abundant near the top. 



Following are notes on the best exposures of the S., beds, 

 taken in order from west to east : — 



Many exposures of beds in the upper part of S.^ occur in the outcrop from 

 E-uthin to Llanharry : among them are the foUo'wing : — 



Old Quarries (Glam. 41 NW \ 2), immediately east of the Roman Camp, 

 south of Eutbin. 



Old Quarries near Gelligarn Castle, in Coed Breigam. about a mile east 

 of Ruthin. 



Exposures immediately south and east of Llanharry village : — 



Quarry (Glam. 41 NE \ 5), 300 yards south, a little west, of St. Illtyd's 

 Church. 



Old Quarry (Glar.^ 41 NE \ 4), 300 yards east of St. Illtyds Church. 



Quarry (Glam. 41 NE A2), at the roadside east of the village, and 500 yards 

 west of Llanharry Station. 



Old Quarry (Glam. 41 NE A 3), 230 yards south-south-east of St. lUtyd's 

 Church. 



All the exposures specified above, except the last-named, exhibit the highly - 

 variable beds of the Modiola phase. The last-named exposure shows a 

 crinoidal oolite with abundant brachiojDods, which may lie either within, or 

 just below, the Modiola phase. 



In the same district, the following are the chief exposiu-es of the Semimda 

 Oolite :— 



At Craig-yr-Eos, on the southern side of Mynydd Ruthin : a level near the 

 top of the Semitiula Oolite, 



Old Quarries lying south and east of Argoed-isaf, a mile and a quarter 

 south-west of Lianharrj- : horizons rather low in the Semimda Oolite. 



The Llanharrj' Limestone Companj^'s Quarry (Glam. 41 NE A 1), east of 

 Llanharry. and 500 yards south-west of Llanharry Station. This gives an 

 extensive section. The rocks are oolites and oolitic limestones, poorly fossili- 

 ferous on the whole. Some bands of calcite-mudstone are developed. 



Old Quarry (Glam. 41 NE A 6), on the west side of the road. 300 yards south- 

 west of the last-named quarry : thickly -bedded, grey, crinoidal oolite which 

 must lie very near the base of S ,. Fossils are abimdant. Some bands are 

 crowded Avith ProdHct}i.'< corrjif/ato-hemisphericKS or Semiiuda jicoides, and 

 both Cyrtina carbonaria and Carcinophylhim vaiiciltani (?J occui* commonly. 

 Nematophyllum minus has been found at this locality only. 



Between the exposures near Llanharry, just described, and the ground 

 north of Creigiau, a distance of 4 miles, the only good exposure of beds in 

 the Main Semimda Zone is that afforded by the Bute Quarries (Glam. 42 NW 

 A 3). half a mile north-east of Miskin. These quarries lie in the Semimda 

 Oolite. They expose thickly-bedded grey oolite, with a small development of 



