﻿560 ME. T. F. SIBLY ON THE CARBONIFEROUS [Aug. I905, 



The Weston-Worle ridge displays, then, a more or less inter- 

 mediate type of development in the gyring othyr is -Zone, with a 

 Mendip facies predominating to some extent. Future work in the 

 Western Mendips will doubtless furnish many new facts which may 

 throw light on this question. 



The Seminula-Zone is rather incompletely displayed in this area ; 

 but, in so far as it is seen, it presents an extremely-interesting 

 development. Until quite recently, no parallel development of S 

 had been found in the Mendips, for the Burrington section shows 

 but a poor exposure of this part of the sequence, and gives a very 

 inaccurate impression of the characters of the Seminula-Zone in 

 the Western Mendips. 



Recently, however, in the course of my present work in the 

 Mendips, I have found the same interesting development of 8 else- 

 where. At Cheddar, on the south side of the Mendips, the Seminula- 

 Zone is finely displayed in the Gorge, and shows a very striking 

 agreement with the Weston district. This applies especially to S : 

 S 2 is poorly displayed in the Weston-Worle ridge, and at Cheddar 

 it is by no means so well exposed as S a ; in both localities, however, 

 it seems to have a normal character. 



At Weston-super-Mare, the Milton-Road Quarries have yielded a 

 very rich fauna. Lithostrotion Martini, Syringopora cf. distans, 

 ' Athyris ' cf. glabristria, Spirifer cf. furcatus, and Oamarophoria 

 isorhyncha are abundant. Productus punctatus and ' Clisiophyllum ' 

 (CarcinopJiyllum) sp. are very common, and Athyris cf. plano- 

 sulcata is not infrequent. The base of the Seminula-Zone in the 

 Cheddar section contains precisely the same fauna, with one 

 apparent exception, namely, Productus punctatus. In both localities 

 this fauna is restricted to a very small vertical thickness of rocks, 

 and it undoubtedly constitutes an important horizon. 



This forms the most prominent point of agreement between S x at 

 Weston and at Cheddar; but, in addition, the general similarity is 

 complete. For example, the well-marked faunal level at the top of 

 S 1 , showing an association of Productus semireticulatus mut. (cf. Pr. 

 concinnus), Productus 6, Pr. aft", hemispliericus, Athyris cf. expansa, 

 A. aff. planosulcata, Lithostrotion Martini, and Ganinia cylindrica 

 (mut. S x ), which is so finely displayed at Cheddar, is well repre- 

 sented in the Weston-Worle ridge. 



(2) The Woodspring Ridge. 



The characters, both pakeontological and lithological, of the 

 sequence displayed here are exactly similar to those of the equiva- 

 lent part of the Clevedon development. 



Y. Summary. 



(1) The Carboniferous Limestone of the Weston-Worle ridge 

 includes the greater part of the Syringothyris-Zone [C], extending 

 from the ' Zam-mosa-dolomites ' to the base of the Seminula-Zone, 

 and a great part of the Seminula-Zone [S]. 



