l.V 



jartlij ( VRnoMFERors F.IMKSTONE of S. wakes COAI.riKI.I). 



Nvestoni side, in the woods wvst of Khyil-y-i; wen., and on tlie 

 eastern side, in tliu mvine vvest-soiitli-west of Ffwrwni. 



In tlie limestones, ostr.icods and Calvispha'ra (/j are sometimes 

 al.undant, erinoid-dt'l)ris and toniminifera oeeiir more siaringly, 

 and serpulids oeeur rarely. The fauna is, therefore, decidedly that 

 of a Mod I old jihiseJ 



This Modiola j)hase is inunediately overlain by the dolomites 

 with Ci/rfina carhnnaria which represent the base of S^. Its 

 zonal liorizon (S, ) is, therefore, quite definite. As far east as 

 Pen-how its base is defined by the underlyin.ii; band of crysbilline 

 dolomites; but farther east, where that band dies out, it forms 

 merely the u])])ermost part of the very thick Modiola phase of 

 C -S,*age in the Khynmi-y and Ebbw valleys. 



The best Rcctions are afPonled by (1) an old quarry (Glam. 37 NE X 1) 

 sitimted about midway between Pen-y-wann and Pen-how, north-east of 

 Rudry, and (2) the stream-bed an<l l)ank8 in the ravine (Mon. 27 SE X 2) 

 inunediately west-south-weHt of Ffwrwm, on the eastern side of the Khymney 

 valley. At the first-named locality, dolomite-nuidstones and crystalline 

 dolomites predominate over caleite-mudstonea. In the Ffwrwm ravine, 

 dolomites are subordinate to a variety of ralcite-mudstones and other fine- 

 ffraine<l limestones, while a thick band of dark-f,'rey oolite forms a conspicuouB 

 feature. 



In the Ebbw valley, the C-S, Modiola phase, apparently 

 unbroken, attains a thickness of about !i75 feet. It is succeeded 

 directlv by the shales of the Millstone (irit,- but the junction is 

 not nciw exposed. The strata. ])oorly ex])osed in the cuttin*,' (in 

 the railway east of Waun Fawr Brickworks, arc chietly dolomitc- 

 mudstones, with nuich v»'ry fine-i^rained crystalline dolomite and 

 some coarsely-crystalline dolomite. Very near the Millstone-CJnt 

 boimdury, near Buck Farm on the hillside south of the railway, 

 some sniall outcrops of smooth-textured oolitic limestone, contain- 

 in*; ostracods, siv^i^est the S, hori/.on of the ravine below Ffwrwm 

 in the Khymney valley. 



(iii) The S. beds. 



It has bci'U seen (p. Ml)) that the S^ ])eds on the eastern side of 

 the 'i'aff ^ori^c comi)rise some VM) feet of dolomites succeeded by 

 nearly -RK) feet of oolites antl ooliti(! limestones. At I*en-y-bryn, 

 a mile away to the north-east, dolomites about IT)!) feet thick 

 alone rejiresent S,. This ra])i<l apparent thinning can only be 

 exjdained by overstej. of the Millstone (Irit. Kast-north-east wards 

 from IVn-y-bryn to the Khymney valley, the dolomites of S^ 

 diminish but liradually in thickness, for they amount to UK) feet 

 at Thornhill, 00 feet or more (»n the dip-slop' of Cefn-On. and 

 j.robablv .")() feet in the Khymney valley. On the eastern side of 

 th:it valley, however, they are cut out by a shar|> tninsL,'ressi<ui of 

 the (|uart/.-eoni;lomerate at the base of the Millstone (irit. 



' See E. E. L. Dixon. Oowor iMV|>er, pp. 518-lt>. 

 - Ne>v])ort Memoir. 2nd ed. p. 21, 



Q. .1.(5.8. No. 21)0. N 



