Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 491 



pseudobreccias, unweathered, contrasting strongly in appearance 

 with the weathered rocks on the coast. Bishopston Valley : — 

 the outcrops of the D Zone in the sides of the valley are too 

 narrow to accommodate its probable thickness, the cause of the 

 discrepancy being, doubtless, unexposed strike-faulting. 



Dl-2- 



Lithological characters. — Much as in L\, but the pseudo- 

 breccias disappear in the upper part. The following section 

 shows the sequence at Colts Hill, and also the relations to the 

 beds (D ) above : — 



D M and D 2 _ 3 — Colts Hill. 



Thickness in feet. 

 D 2 - 3 : — 'Black lias,' — thinly-bedded, black, argillaceous lime- 

 stones and shales, one of the latter a foot thick; 

 cherts. 

 D l _ 2 : — 3. Thickly-bedded, fine-grained limestones including 

 oolite ; the highest few feet dark, with black cherts, 

 the rest light grey and chertless ; pure, except for 

 some dolomite and occasional shaly partings ; about 50 

 2. Dark, shaly nodular limestone, slightly dolomitized, 



the nodules elongated 1-2 



1. Thickly - bedded, light-grey limestones, including 

 pseudobreccias, continuous with those of D l ; base 

 not determined owing to poorness of exposure, but 

 thickness probably about ... 60 



Fauna. — See pp. 549 & 551. The Productus Band at Colts Hill 

 occurs at the top of Grroup 1. Caninia cornucopias, mut. D was 

 observed in the dark limestone immediately below D 2 _ 3 . 



Thickness. — Uncertain, but not more than 120 feet (Colts Hill). 



Limit. — The change to D 2 _ 3 , which is considerable as regards 

 both fauna and rock-types, is almost abrupt, and is emphasized 

 by weathering, as may be seen at Colts Hill : D 10 remaining 

 hard limestone, but D 2 _ 3 becoming soft, clayey ' rottenstones.' 

 The change is foreshadowed in the highest few feet only of D 12 ; 

 there the fauna includes one of the corals abundant in D 2 _ 3 , 

 while the rock is dark and contains dark cherts. 



Exposures. — Pwll-du Head: top of cliff 300 to 400 yards 

 south of High Penard. Colts Hill northern quarry and an old 

 face between this and the southern quarry. 



[The ' Upper Limestone Shales ' of the Geological Survey.] 



Lithological characters. — Limestones and shales with cherts, 

 the whole known locally as ' black lias.' The limestones are 

 thin — generally less than 3 feet thick — and evenly bedded 

 (fig. 3, p. 492); almost invariably dark-grey or black, with a 

 white skin or crust of impurities where weathered ; crinoid-debris 



Q. J. G. S. No. 268. 2 m 



