It.nt L' . \KI5oNIKKHors F.IMKsToNK OF S. WALKS (.UALFI Kl-D. I2l> 



tlie Uhul)ina sixMl-heap, as in the stream-section in the Ebbw 

 \allev (Mon. 2s SW\l), tlie ci-liniestone often encloses pebbles of 

 caleiti'-nimlstone (containini^^ St-rpiila) formed bv the churninjij^-ui) 

 of c()ntemj)ontnrous ilr])()sits, an iiulication of current-ac-tit)n that is 

 in keepinir with the rolled (diaracter of the organic remains. 



2. Crinoidal limestone and oolite — K, or K,. Up}X'r 

 and major j>art of the Lower Limestone of the Geological Survev. 



General lit ho logy. — Xon-oolitic or slightly-oolitic crinoidal 

 limestone, and oolite which is, as a rule, crinoidal. In the east 

 (Ebbw valley), the development of oolite is subordinate and 

 a])parently s|Hjradic : in the west (Tatt* valley) oolite forms the 

 upj)er an<l larger part of the group. Dolomitization is frecpifut, 

 Mud (for the greater pju-t) evidently a subsequent feature. 



Thickness. — Between 40 and oU feet on the western side of 

 i lie Ebbw valley: increasing south-westwards, to UK) feet or more 

 in the Taff valley at Tongwyidais. 



Fauna. — Brachio|M)ds are seMom abundant; the chief forms 

 will be noted in the description of e.\i)osures. Fcm'sU-Ua and 

 Uhnlnhnneaon are occasionally connnon. Ostracods occur in oolitic 

 bands at the base of the grouj) in some localities. 



In the Ebbw valley, the stream-st-ction below Coed-y-Mochyn 

 (Mon. 2S SW \1) ex])oses about 12 feet of limestone at the base 

 of the u:rou]) (fig. o, ]). 127j. The rock is richly crinoidal and 

 shelly, and contains Camarotccrhin mitchfltlcanfuxia in abundance: 

 in thin section, it jiroves to be slightly oolitic, with a few (juartz- 

 grains and occasional ostracods luuX lihafHlonirson. On the hillside 

 oO yards to the north, an old (piarry (Mon. 2SSW\2) gives an 

 almost complete section of the division. The lowest beds expose<l 

 are those of the stream-section, here yielding Leptcpiut analofjn 

 and Schclhrirnclht cf. rrrn/sfria in abundance, together with 

 Si/rimiofhi/rix cf. cuspidatn, Fmrstflla, and the tisli-t^toth Drl- 

 ((hIiik (fihhini. For the rest, the beds are crinoidal, occasionally 

 oolitic limeston«'s, generally showing conspicuous current-hnni nation, 

 and extensively vein-dolomiti/ed. About W'M) yards farther north, 

 a small excavation on the hillside above Dan-y-Gniig Brickworks 

 MOWS a white oolite which lies near the to]) of the group. 



On the eastern side of the Hhynmey valley north cd' Maelien. 

 i;i>od exposures are afforded by the crags and old workings along 

 the st-arp wiiieh extends east and west of Castell Meivdytld. Here 

 the limestones have suffered very extensive dolomitization, but th** 

 pre<loniinanee of crinoidal rock, ctirivnt-lanniiated in some beds, 

 and the development of oolite-bands, are clearly .seen. 



Westwanls from the Uhymney valley, to the neighbourhood of 

 Khubina. the l>eds are seldom well exposed, although often con- 

 sj>icuous in their ettect u|)on the to}M»graphy. Whenever seen, 

 they are highly <lolomitize<l limestones, often crinoidal. but other- 

 wise j>oorly fossiliferous. and as a rule tine-grained. The tlolomiti- 

 zation in this portion (d* the outeroj) may be partly contem|M)raneous. 

 Tin- ( }roloi,ncal Survey map ( Xewport sheet ) represents the limestone 



