THE CARBONIFEROUS LIMESTONE OF BURRINGTON COMBE 39 
Red Sandstone to the level at which Zaphrentis is first 
recorded. Shales predominate in the lower part of the 
zone, but more and more limestone occurs as we ascend 
the series. Limestones containing characteristic Cleistopora 
fossils occur very near the base, and in ascending the zone we 
find the gradual establishment of the Cleistopora fauna. 
No subdivision of this zone is justifiable on the evidence 
obtained. The exposure of the upper two-thirds of the 
zone is very unsatisfactory, and our knowledge of the 
faunal characters of this part is therefore very limited, 
but the following outstanding features are important : — 
(i) In the lower part of the zone, ‘ Modiola-Ostracod ’ shales 
alternate with thin limestones which contain characteristic 
fossils of the zone. 
(ii) In the middle of the zone, Chonetes ‘ Buchiana ’ is abundant, 
and Productus cf. hassus occurs occasionally. 
(iii) The upper part of the zone is marked by the increasing abun- 
dance of certain forms, and the entrance of others ; all these 
forms persist into the Lower Zaphrentis Zone, where the 
majority attain their maxima. 
B. Zaphrentis Zone. 
This zone, which is very finely developed, having a 
total thickness of 800 feet, exhibits the maximum develop- 
ment of the Tournaisian fauna. The lower part of the 
zone consists mainly of thin-bedded limestones with thin 
shale partings ; the upper half is formed chiefiy of massive 
limestones. Horizon y consists of thin-bedded limestones. 
Nodular chert occurs in the massive limestones near the 
middle of the zone. The basal beds are poorly exposed, 
and in the failure to recognize Horizon |8 the lower limit 
of the zone has been fixed at the level where Zaphrentis 
is first recorded. 
The main clathratus sub-zone is finely displayed and 
shows all its characteristic faunal features. 
The base of the resupinata sub-zone is well displayed, 
but the succeeding beds are not well exposed until Hori- 
