496 MR. S. E. L. DIXON AND DR. A. VATTGHAN ON [Nov. I O, I I , 



limit of Group 2 has not been determined, but is not con- 

 spicuous lithologically, as the succeeding beds, up to the Coal- 

 Measures, are, also, largely shales. 

 Where examined. — Bishopston, north side of road- cutting : — 

 the radiolarian cherts. Barland Common : — the shales (Group 2) ; 

 the most complete section is now overgrown, but was described 

 by De la Beche 1 and has been discussed by Dr. Strahan. 2 



(2) North-Western District. 



The sequence of the Avonian rocks in North- Western Gower is 

 similar on the whole to that in Eastern Gower, and attention 

 will, therefore, be directed chiefly to the differences between the 

 two districts. The Cleistopora Zone, however, is poorly exposed 

 in the Eastern district, and is described in some detail. 



Most of the zones were examined along Burry Pill, the banks of 

 which, north and north-west of Cheriton, afford a fairly complete 

 sequence from a horizon low in the Zaphrentis Zone up to the 

 middle of D v and much of D x was, also, found well displayed in 

 Tor-gro, a range of cliffs between Burry Pill and Landimore. 

 The thicknesses, estimated from outcrop and dip, in these localities 

 are stated in Table T (facing p. 505). 



Cleistopora Zone, 3 K. — This zone, although not completely 

 exposed, especially towards the top, probably corresponds exactly 

 with the Lower Limestone Shales, the resemblance to the develop- 

 ment in those parts of the South-Western Province where this 

 relationship holds good being close. It consists in descending order 

 of:— 



Thickness in feet. 

 Probably K 2 . 4. Grey shales, with thin limestones containing 

 crinoids and brachiopods; upper part not seen; 

 total thickness probably between 250 feet and 300 



K x or K 2 . 3. Limestones, including fine-grained dark oolite ; 



at least 30 



(2. Like 4 on the whole ; with Km 150 



j 1. Modiola Phase, Km. Grrey shales with ostracodal 

 Probably K x . ■{ and oolitic limestones and a red hasrnatitic 



limestone of a-type ; quartzitic sandstone with 

 [_ modioliform lamellibranchs near the base. 



Total between 400 & 500 



The characters and thicknesses of Groups 1-3 and of 200 feet of 

 Group 4 were determined in the banks of a dingle, north-east 

 of Eairyhill House ; the total thickness of the zone was estimated 

 from its outcrop at Cheriton. 



The base of the zone, as in most parts of the South-Western 



1 Mem. Geol. Surv. vol. i (1846) pp. 133-34. 



2 Swansea Memoir, pp. 22 & 30 ; also fig. 2 (p. 23). 



3 The field-observations were made conjointly with my colleague, Mr. T. C. 

 Cantrill. I gladly take this opportunity of thanking him for encouragement 

 and advice at many stages throughout this work. 



