44 THE CARBONIFEROUS LIMESTONE OF SOUTH-WEST GOWER 
found at Porteynon Bay, consist of a series of red shales, ( 2 )^ 
with seams of yellow and purple sandstones, the entire 
thickness of which is about 40 ft. Below this, and conform- 
able to it, a limestone bed (3)^ is reached, 250 ft. in thick- 
ness, with bands of chert, lenticules of calcareous sand- 
stone, and veins of calcite. Through the greater part of 
this, fossils are few in number, save in a few pockets con- 
taining badly preserved specimens of Lithostrotion and 
Productus ; but towards the base fine examples of Pro- 
ductus, cf. giganteus, Lithostrotion Portlocki, L. junceum, L. 
irregulare, and L. Martini (mut.) occur. 
Sub-zone D^. 
This commences with a series, 60 feet in thickness, of loose 
rubbly limestone, (4)^ lying immediately below the coral bed 
just described. It appears to be a^bsolutely unfossiliferous, 
and is followed by 30 feet of alternating bands of compact 
limestone and bright red shale. (5) These are very rich in 
fossils, particularly corals : Cyaihofhyllum Murchisoni is 
abundant, and Dibunophyllum 0, Campophyllum sp , Syrin- 
gopora sp., Lithostrotion Martini, Productus 'giganteus' and 
Productus hemisphericus are also found commonly. The 
Bryozoa, which are such a characteristic feature in the 
shale beds, at a much lower horizon (S J, do not appear 
in these, which are the basement beds of sub-zone 
SEMINULA ZONE. 
Sub-zone 83 . 
The upper beds of the succeeding sub-zone (Sg) 
are well exposed on Porteynon Head, and in the Overton 
Gorge, a mile, to the northward, and consist of the 
1 Vide Section A on page 45. 
2 Ihid. 
3 Ihid. 
