﻿Yol. 6 I.] SEQUENCE m THE BEISTOL AREA. 207 



it may, however, be fixed within very narrow limits, as 

 embracing that portion of the zone in which Zaphrentis is still 

 common, but CliotJiyris glabristria becomes scarce ; the band of 

 Chonetes papilionacea may thus be taken as occurring at the base. 



Correlation with the Avon section: — 



(1) Resemblances : 



In both sections : — The maximum of Spirifer afF. dathratus 

 is followed by that of Cliothyris glabristria, while Zaphrentis 

 attains its maximum when CI. glabristria becomes scarce. 



Schizophoria is abundant, and confined to the resupinata-Biibzone. 



Chonetes cf. hardrensis is predominant in the lower part of the 

 Zone, but yields place to Chonetes papilionacea at the top. 



The same mutation of Orthotetes abounds throughout, and the 

 same species of Syringopora is found. 



(2) Differences : 



"No specimen of Zaphrentis has been found at Sodbury before 

 the upper part of the resupinata-subzone, and no Caninia, Ampleccus, 

 or Miclielinia has been discovered in any part of the Zaphrentis- 

 Zone (though specially looked for). 



The presence of Zaphrentis in the lower part of the zone and of 

 Amplexus and Miclielinia at the top might, perhaps, have escaped 

 notice, even if they occur in the same numbers as in the Avon 

 section ; but the failure to find a single Caninia at the top of the 

 zone seems to point definitely to the conclusion that the incoming 

 of this genus suffered a great retardation towards the north-east. 

 (A point of some interest is the fact that in both the Avon 

 and Sodbury sections there is, in this zone, a thick series of 

 relatively-unfossiliferous beds which are characteristically inter- 

 laced with veins and patches of calcite ; this series occurs at the 

 top of the clathratus-subzone at Sodbury, but is found in the 

 middle of that subzone in the Avon section.) 



Caninia-Zone. 



This zone includes : — 



C =The SyringotJiyris-Zone at the top of the Tournaisian ; 



and S 3 =The semireticulatus-subzone at the base of the Yisean. 



These two subzones are conveniently considered together in this 



place, in order to emphasize the palaeontological break between 



the Tournaisian and the Yisean in the northern part of the 



Bristol area, where that break is most evident. 



Lithological character:- — 



f (1) At the base relatively-unfossiliferous, massive, encri- 

 nital limestones. 

 G~( (2) A band of oolitic limestone (unfossiliferous except 

 for occasional fragments of crinoids). 

 ^ (3) A series of shales, including thick beds of dolomite 

 and an occasional bed of oolite ; ending in a 

 S x •{ prominent band of pure quartzose grit. 



(4) Massive fossiliferous limestones. 



