504 ME. E. E. L. DIXON AND DE. A. VAT7GKAN ON [Nov. 191 1, 



Dibunophyllum Zone, 1 D. — The important feature of this 

 zone in South- Western Gower is a strong development of D 2 , a 

 subzone which is unknown in Eastern Gower though present in 

 the North-Western District. 



The facies of D T differs in no important respect from that observed 

 in Eastern Gower. An oolite, 7 feet thick, in part of the coarse 

 type usual at this horizon, lies at or near the base. Some of the 

 beds, including some pseudobreccias, 2 are dolomitized, the gastero- 

 pods showing the selective action previously mentioned. 



In D 2 are placed the highest beds of the Main Limestone. The 

 change of fauna in passing from D l to D 2 is not accompanied by 

 any lithological change, so far as known, but pseudobreccias die 

 out some distance above. The upper part of D„ consists of various 

 rock-types, including coarse oolite, coral-limestone, dark fine- 

 grained bituminous limestone with black chert, dolomite, and pale 

 limestone. Some of the latter occurs immediately below D 2 _ 3 , 

 but is as pure as any other part of the Main Limestone, except 

 for an abundance of pale chert. The change to D 2 _ 3 , faunal and 

 lithological, is as rapid as in Eastern Gower. 



D 2 _ 3 is equivalent to the Upper Limestone Shales, which are 

 similar to the beds of the same name in Eastern Gower, except that 

 they include, interbedded among the argillaceous limestones and 

 shales, a few pure, pale limestones with chert, resembling some of 

 the D 2 limestones. The correlation with D 2 _ 3 of Eastern Gower is 

 discussed on pp. 551-52. 



The top of the zone and its relations to the overlying P beds are 

 not revealed. 



The whole of D 1 and D 2 , 600 feet in all, and a thickness of at 

 least 150 feet of D 2 _ 3 , the latter folded, and much reddened by 

 Triassic infiltration, crop out on the shore of Port-Eynon Bay. 

 Belter exposures of much of D x and D 2 , with the faunas recorded 

 on pp. 548-49, are obtained in quarries in the plateau above Port- 

 Eynon Point; those in D 2 lie about a quarter of a mile south- 

 south-west of Port-Eynon church. 



Posidonomya Zone, P. — The development in this district is 

 probably the same as in other parts of Gower. Radiolarian cherts 

 are believed by Dr. Strahan 3 to crop out near Overton ; and shales, 

 grey or raddled, with the fauna enumerated on p, 552, are exposed 

 in an old ' paint-mine ' at Port Eynon described by the same author 

 (loc. cit.). Black, evenly-bedded sponge-cherts do not appear to 

 be exposed in the mine in situ; but, to judge by fragments in 

 the overlying Triassic conglomerate, they do occur in the series. 

 A single band, a few inches thick, of shale studded with crinoid- 

 ossicles and now decalcified, emphasizes the rarity of such material 

 above the Dibunophyllum Zone. 



1 First recognized in this district by Dr. Gubbin & Dr. Vaughan, Proc. 

 Bristol Nat. Soc. ser. 4, vol. i (1905) pp. 43-44 & 56. 



2 These I described in the West Gower Memoir, p. 16, as ' without dolomite.' 

 whereas some only are undolomitized. 



3 West Gower Memoir, p. 18. 



