Vol. 67.] THE AVONIAN OF BURRINGTON COMBE. 385 



(2) Spiriferina per acuta de Kon. op. cit. pp. 101-102 & pi. xxii, 



figs. 56-61. 

 This species is very abundant in Z x of Belgium ; the specimen 

 figured in the Bristol Paper is probably the same. 



Comparison with Spiriferina octoplicata (J. de C. 

 Sow.). — Sp. per acuta has tall and narrow ribs, the furrows being 

 relatively broad ; so that a cross-section of a single valve lying on 

 its ribs is castellated with narrow slits. The cardinal angles are 

 never rounded, and the hinge-line is the greatest width of the 

 shell. 



Sp. octoplicata has ribs and furrows equal and similarly angular, 

 so that the cross-section, made as above, is sharply maxillate. The 

 hinge-line is often shorter than the width of the shell, and the 

 cardinal angles are then rounded. 



The history of Spiriferina in the Avonian is as yet unknown. 



V. (a) Physiographical Comparison of the Burrington Sequence 



WITH THAT AT OTHER POINTS OF THE SoTJTH- WESTERN AND 



Belgian Provinces. (A. Y.) 



These two provinces may be considered to form together a single 

 large province, to which the name Bristol-Dinant Province 

 will be applied. 



Pre- Avonian. (Old Red Sandstone.) 



Burrington, in common with the whole South-Western Province, 

 formed part of a great inland lake, whereas the Belgian Province 

 and North Devon were covered by the Devonian Sea. 



Km. 



In the South-Western Province, fresh water gave place to very 

 shallow marine conditions. 



In the Belgian Province, the sea became shallow. Hence in Km 

 conditions became similar over the whole Bristol-Dinant Province. 



In North Devon a Carboniferous fauna was evolving in the 

 Productella-productoides Beds of the Pilton Series. 



This is the base-line of the Avonian and the bottom of the 

 Cleistopora Zone. 



K x and K 2 . 



The Carboniferous fauna became established throughout the 

 South - Western Province, whereas Km conditions persisted in 

 the Belgian Province. 



This portion of the sequence is consequently classed as Carboni- 

 ferous in England, but as Devonian in Belgium. Since it is a 

 matter of impossibility to separate our K beds from Z under two 

 distinct formations, whereas it is merely a conventional division in 

 Belgium, we may hope that the young Belgian geologists will come 

 into line. 



