THE CARBONIFEROUS LIMESTONE OP SOUTH-WEST GOWER 47 
following series : a grey limestone, 30 feet in thick- 
ness, (6) with Productus ' giganteus ’ at the top only ; but 
crowded with Lithostrotion Martini and Syringo'pora sp. ; 
a blue limestone, (7) 25 feet thick, in which. Productus ah. 
Cora appears, with a vein containing Seminula amhigua 
(mut. Sg) and Seminula aff. ficoidea. 
The rock now gradually becomes oolitic, (8) and Productus 
ah. Cora is the characteristic fossil ; Lithostrotion Martini and 
Syringopora are still fairly common, and a few specimens 
of Carcinophyllum 0 occur. Corals, however, are not 
nearly so abundant as in the upper beds. 
Towards the base Aihyris planosulcata, Productus fim- 
hriatus and Seminula occur, with occasional masses of 
Alveolites. 
The oolitic character of the limestone is maintained 
through about 200 feet of rock, save where it is broken by 
bands of black calcareous sandstone. (9) Three of these 
blac^ bands appear, each from 3-4 feet in thickness, and 
contain the same fossils as the limestone. The oolitic rock 
ceases abruptly, and gives place to beds of blue and grey 
limestone, (10) the first 70 feet of which contain merely a few 
specimens of Lithostrotion Martini d^nd Syringopora. Pro- 
ductus ah. Cora, as far as I can determine, does not extend 
below the oolitic series. The succeeding 30 feet of lime- 
stone are interstratified with bands of black sandstone 
similar to those of the oolitic bed. The fossils are broken 
and badly preserved, and consist of Lithostrotion Martini 
and Productus (sp.), with Lithostrotion affine sparingly in 
the lowest layer. At Porteynon Head this bed, which is 
the last of sub-zone Sg, is at the base of the cliff, between 
high and low water mark. 
Sub-zone S^. 
A huge fault, running north and south, brings the under- 
lying beds into view on the cliff at Overton, where a fine 
