THE CARBONIFEROUS LIMESTONE OP BURRINGTON COMBE 35 
lower part of the laminosa sub-zone, i.e. the series from 
Horizon y to the base of the oolite, agrees well in faunal 
characters with the base of the main Syringothyris Zone 
at Burrington. The only point calling for notice is the 
greater abundance of Syringothyris cuspidata at Burrington. 
In the Caninia Oolite and the succeeding shales and 
dolomites there is apparently a remarkable palseon ologi- 
cal break. Orthotetes, Syringopora and Michelinia occur 
occasionally in the oolite, but are distinctly rare. 
As the Carboniferous Limestone is traced from the 
Avon towards Clevedon, this break is found to be partially 
filled in by the development of fossiliferous limestones 
(the “ Bellerophon Beds ”) in the shale series, about 150 
feet above the base of the oolite (cf , Failand and T icken- 
ham). These limestones reproduce exactly the palaeonto- 
logical characters of Horizon S as developed at Burrington, 
but they occur at a lower level in the sequence than does 
Horizon S at Burrington. 
In the Avon Section, fossiliferous beds are found again 
as we approach the top of (3), and in (4) we find a typical 
Seminula fauna, i.e. very abundant Seminula ficoidea 
and Lithostrotion. These forms are, however, associated 
with Productus semireticulatus, Syringothyris aff. laminosa, 
Caninia cylindrica (mut. Sj), and Cyathophyllum <p. 
There is, therefore, a wide overlap of the Syringothyris 
and Seminula faunas in the Bristol Area, rendering a 
subdivision of the Seminula Zone necessary ; whereas at 
Burrington, where the separation of the Tournaisian and 
Visean faunas is apparently sharp, no subdivision of the 
Seminula Zone is justifiable.^ 
^ I have recently found, in the Weston-super-Mare district, where 
the development is, in the main, very similar to that at Burrington, 
a small but distinct development of the semireticulatus sub-zone 
at the base of the Seminula Zone. Since the exposure of the base 
of the Seminula Zone, as defined in this paper, is very poor, it is 
quite possible that some such development at Burrington has not 
been revealed. Further-work in the Mendips will doubtless settle 
this important question. 
