20 BRITISH AVONIAN CONODONT FAUNAS 
of the section. In the lower portion of the section fossils are rare, ostracods, gastro- 
pods and algae being the most common ; brachiopods and bivalves are generally 
rare. Ascending the sequence, fine grained compact limestones become more 
prominent, their upper bedding surfaces being covered with brachiopods and 
crinoids. The upper part of the Lower Cleistopora Beds is an alternating sequence of 
claystones and thin limestones, which has a banded appearance. Occasional more 
massive limestone bands, about one foot thick, are also interbedded. 
The highest beds of the shallow-water phase consist of seven distinct beds, 
separated by thin shale partings. The lower six beds range from 11 inches to 23 feet 
in thickness and are crinoidal limestones, which have been stained by haematite. 
The uppermost bed (the Bryozoa Bed) is a massive, limestone bed, eight feet thick, 
crowded with crinoids, bryozoa and small gastropods. 
The Upper Clezstopora Zone consists at the base of sandy fossiliferous limestones 
with interbedded calcareous shales. Near the base is a “ gritty’ six inch bed of 
crinoidal limestone, the Palate Bed, which contains bryozoa, palatal teeth and 
coprolites. Thinly bedded limestones, and alternating shales follow. The upper- 
most beds of the K Zone consist of blue-grey calcarenite beds, up to one and a half 
feet thick, and alternating brown silty shales. 
Horizon 8 consists of thinly bedded, coarse crinoidal limestone, with thin shale 
layers developed between the more massive limestone bands. The beds of the main 
Z Zone are blue-grey fossiliferous massive limestones, with some alternating, thinly- 
bedded limestones and a few shale partings. The limestones approach a “ petit 
granit ’’ in character. 
The Laminosa Dolomites were probably originally identical to the Z Beds in 
lithology, but subsequent dolomitisation has resulted in these beds weathering to a 
brownish colour, which contrasts strongly with the blue-grey limestones of the 
Zaphrentis Zone beneath and with the white oolites of the Caninia Zone above. 
The Caninia Oolite is a pinkish-grey, white-weathering, current-bedded, fine 
grained oolite with uniformly rounded grains. It is succeeded by a series of current- 
bedded, marly limestones, dolomitic limestones, occasional oolitic bands and blue, 
grey, yellow, green or red shales—the Caninia Dolomites and Shales. The uppermost 
beds of this group are more massive than the lower and less shale is developedinthem. 
Shales and thick bands of dolomite with occasional oolites form the lowest beds of 
the Seminula Zone. They are essentially similar in lithology to the underlying 
Caninia Dolomites. They are followed by massive blue-grey limestones, which are 
frequently dolomitised, and by thin shales, which are succeeded in turn by calcite 
mudstones, which weather white. The shales become less conspicuous higher in the 
section, where grey Lithostrotion-bearing limestones predominate. The upper beds 
of the Seminula Zone, the Sz Subzone, consist of oolites and pisolites at the base and 
the Concretionary Beds at the top. The latter are fine-grained, argillaceous lime- 
stones, the upper surfaces of which are undulating. They are underlain by black 
shales, which ramify into the overlying limestone bands. The Concretionary Beds, 
which sometimes contain algae and ostracods, are interbedded with chinastones and 
occasional oolitic limestones. 
