[»ail2 ( MtnONTFEKOUS LIMESTONE OF S.WALES COALFIKLU. 145 



is only in tlu- (tiitcroi) wvst of the Ely, however, that the overlyini^ 

 iteds of the iJilninophyllinn Zone occur. Kast of the Ely, the top 

 of S. is overstepped l)V the Millstone Grit. 



The main Scmiinila Zone maintains a constant chai-act^-r from 

 the western end of the district here deserihed as far as the river 

 TafF, except for the fact that its hasal beds have become dolomites 

 in the Taff valley. 



Litholo;j:y. — Two divisions can be recoju^nized, but tiiey pro- 

 bably pass insensibly one into the other ^ : — 



14. Mod lohi phase with much stiindard limestone. Extni- 

 ordinarily varied in details of litholoi^y. iir«<//oA/- phase deiK)sits,- 

 namely, caleite-mudstones includini^ white- weathering 'chinastone- 

 limestones' with conchoidal fracture, and limestones with pisolitic 

 and ])seud()-concretionary structures, alternate repeatedly with, and 

 )»ass into, standard limestones which are essentially oolitic, shelly, 

 and crinoidal. Bands of fairly-})ure oolite are not infrequent. 

 Pisolitic structures are abundantly (leveloi)ed : they are often, but 

 not invanably, accomi)anied l)y brecciation due to contemporaneous 

 erosion. 



13. Seiiiliti(l(( Oolite: essentially, ^rcy oolites and oolitic 

 limestones of standard ty])e, but includiui^ some very subordinate 

 Modio/(i-])hiiSL' deposits resend)linu^ those of the overlying grouj). 

 Current-bedding and the develo])ment of contemporaneous breccia- 

 tion are occasional. 



Thickness. — Between 5(K) and (lOO feet, of which the Modlnhi 

 phase forms less than 200 feet. 



Fauna. -Fossils of the standard groups, brachio}x)ds, comls, 

 and crinoids, are quite as abundant and varied in the Mntilohi 

 j)has(' as in the Scmiinihi Oolite. They are, however, notibly less 

 connnon in the calcite-nuidstones and certain other less fme-grained 

 limestones <levelope<l in the Motlinia pha.se ; in these beds. 

 Smiiinda Jiroidfx is almost the only abundant form. In the 

 J[ni//n/(i phase, the rock-types just mentioned, and al.so the ])is(>- 

 litic l)e«ls with their numerous stan<lard fossils, often contain 

 Sf'rpifhi. 



(iasteropod>. includin;jj liillfi'diifnni. Kiioinphnlns, and l^n.vo- 

 iifmii, are sometimes eomiiioii. 



C(»rali* : — 

 i4i reoh7f<«i»*'j*/<»K»/w (Fleming). K«lwiir«ls 



& Haime. 

 SiirinfjniuHUt «;f. tlistnuM FIhcIkt. 

 ^•irinijoihtnt cf. ijeninihitii (Pliillip)*). 



FiiUvunln A- Haime. 



LilliDstriitiim marfini Kdwards A 



Haiiue. 

 L iDtnut ration ( SeuM toph yl I r« m ) 



tninii.i. M'Coy. 

 ('inriiiniiliiiUuni vnnfihniii Sali'e ((.'. 9 



Vinig'him). 



' C<>mpiir«' Mr. Dixon's (U-soription of S, in the caHtorn tlistrii't of (Jower; 

 < .uwer paper, p. iSS. 



• For tlie general characteristics of the S^ Modioln phaHO, «oo E. K. L. 

 l)ixon. Gower paper, p. .'>1 t. 



