136 MB. F. DIXET AND PEOF. T. F. STBLV ON THE [vol. Ixxiii, 



1. Quarry (Glam. 41 SW \ 1), on the west side of the road, 400 yards 



north of Penlline Church. 



2. Exposures (Glam. 41 SE \ 2), a little west of Coed Pen-cyrn. east 



of Llansannor. 



3. Crags (Glam. 41 SE A 3). 200 to 250 j-ards Avest of Xew Barn, east 



of Llansannor. 



4. Exj)osure (Glam. 42 XW X 14). 700 yards east of the cross-roads, 



Miskin. 



5. Old Quarry (Glam. 42 NE X 2), 100 yards east-north-east of Craig 



Channel, Pant-y-gored. 



6. Old Quarries (Glam. 42 NE X 5), 700 yards south-east of Pentyrch 



Chra-ch. 



5. Dolomites and doloiuitie limestones: Z. ^ — From 

 ^Nliskin eastwards, this is essentially a series of grey finely crystal- 

 line dolomites, Avitli numerous small nests of ealcite and dolomite. 

 Chert is developed sporadically near*the base. Crinoid-ossicles are 

 often abundant, but brachiopods are rare. Spirifer clathratus 

 and SclieUirienella of. crenistria are the only species of the latter 

 group recorded, unless the fossiUferous band of Ty-nant Quarry 

 (p. 138) is included in this division. 



The beds are poorly exposed. Two sections near Miskin, and 

 one east of Creigiau, expose the base of the group and the passage 

 into the underlying crinoidal limestones: these are (1) crags 

 (Grlam. -42 XW \l-±), representing old workings, 700 yards east of 

 the cross-roads at Miskin, (2) a small quarry midway between 

 these crags and the cross-roads, and (3) old quarries (Grlam. 42 

 XE/\5) 700 yards south-east of Pentyrch Church. Ty-nant 

 (Quarry, in the Taif valley, affords the only good exposure of the 

 upper beds of the group. A fossiliferous band in this quarry 

 should perhaps be included in this group, that is, in Z, rather than 

 in the Caninia Zone (see p. 138). 



In the drift-covered area west of Miskin, exposures are few, and 

 little is known about the group. The lower part retains its 

 dolomitic character as far west as the ground north of Ystradowen ; 

 but, farther west, dolomitization at this level seems to diminish. 

 The lower portion of a thick oolite whicli is developed north of 

 Llansannor and Penlline appears to represent the upper beds of 

 this group in the extreme west. This oolite is well seen in a 

 quarry (Glam. 41 SE X-l) at Xew Barn, 800 yards east of Llan- 

 sannor Church : it is there a dark-grey rock containing Spirifer 

 clafhratus and a few other brachiopods. 



6. Crinoidal limestones, etc. : yC,. — This division is a 

 series of thinly-bedded, richly-crinoidal, grey or black limestones, 

 with a considemble development of poorly-crinoidal argillaceous 

 bands, usually buft'-coloured. An iiTegular development of black 

 argillaceous streaks, accompanied by contemporaneous brecciation 

 and evidently due to current-action, is not uncommon. Many of 

 the crinoidal beds are very rich in brachiopods and corals, together 

 with gastero])ods and bryozoa. Xodular chert is developed 

 occasionallv, in small amount. 



