Tol. 67.] THE CARB0N1FEK0US SUCCESSION IN GOWEK. 489 



Typical exposures. — Threecliff Bay, east side. Pwll-clu Bay. 

 Whiteshell Point : — lower part of the zone. Longland Bay, east 

 side : — the whole zone, in sequence with those above and below. 

 Limeslade and Broadslade (Bracelet) Bays : — much of S.„ the 

 junction with D 1 at Tutt and at Mumbles Head (in both the Middle 

 Head islet and the adjacent cliff). Bishopston Valley : — several 

 exposures, including one of the same junction at the Sker. 



D = DlBUKOPRYLLUM Zone. 



The development of the upper part of this zone in Gower differs 

 in important respects from that in the Bristol and Dublin districts, 

 and has therefore been subdivided on somewhat different lines. 

 In Eastern Gower the following groups are present. Above the 

 lower part of the zone, which is a normal development of D x , 

 comes a group of limestones, connected faunally with both D x and 

 D„ and, therefore, referred to as D 12 . This forms the top of the 

 Main Limestone, and is followed by a calcareo-argillaceous group, 

 the ' Upper Limestone Shales ' of the Geological Survey, 1 which 

 probably represents part of D , but certainly extends to a higher 

 horizon and is therefore known as D 2 _ 3 . A resemblance of some of 

 its fossils to forms which are common in the Zaphrentis Zone led at 

 one time, before the D 3 -fauna of County Dublin was known, to 

 some controversy as to the systematic position of D.,_ 3 . It is now 

 clear, however, that, as Dr. AVheelton Hind maintained, 2 it occurs 

 at the top of the Yisean. 



It is succeeded by an almost purely argillaceous group, which 

 is included in the Millstone Grit by the Geological Survey and has 

 been recognized by Dr. Hind as a representative of the Pendleside 

 Series. And, though it is possible that the Pendleside Series is a 

 phasal equivalent of part of the sequence of coral-and-brachiopod 

 zones of some regions, the name Posidonomya Zone (P), already in 

 use for it, will be retained. 



D 1 = 0(f) Subzone. 



Lithological characters. — Chiefly light-grey, thickly-bedded 

 limestones, many partly dolomitized. The limestones are pre- 

 dominantly of the type, peculiar in Gower to the D-zone, charac- 

 terized by the remarkable ' pseudobrecciated ' structure which 

 has been described by Mr. Tiddeman 3 and forms the subject 

 of a separate note (p. 507). Besides much obviously subsequent 



1 The disadvantages attaching to other names, such as ' Bishopston Beds,' 

 which have been applied to this group, have been stated by Dr. Strahan in 

 the Swansea Memoir, p. 21. It may be added that, as delimited by Mr. E. B. 

 Wethered & Prof. C. Lloyd-Morgan, the ' Upper Limestone Shales ' of the 

 Avon, — for which Buckland & Conybeare originally proposed the name, — 

 include lower horizons than those of Gower. 



2 Geol. Mag. dec. 5, vol. i (1904) pp. 585-87. 



Swansea Memoir, p. 10. He observes the persistence and high horizon of 

 these rocks, and groups them together as the ' Mumbles Head Beds.' 



