﻿Vol. 6 1.] SEQUENCE IN THE BRISTOL AEEA. 251 



I have hastened to make this correction, for the assistance of 

 those who are working in neighbouring areas, in the hope that, the 

 horizons of the two flows being now very definitely fixed, they may 

 find some trace of volcanic ejectamenta at the same levels. 



I am deeply indebted to Mr. Sibly, who has placed his knowledge 

 of the area and its fossils entirely at my service, and it was under 

 his guidance that I first visited the Woodspring- Cliff section. 



(iii) The Chepstow and Forest-of-Dean Outcrop. 



Although I have not yet completed the examination of this large 

 area, the agreement of the faunal succession with that in the Bristol 

 area is practically complete whenever paleeontological evidence can 

 be found. A great portion of the fauna! sequence is, however, 

 entirely obscured by the extensive development of dolomites in the 

 Upper Tournaisian and by the early entrance of the ' Millstone-Grit ' 

 facies before the end of Visean time. 



It will be sufficient, for my present purpose, to describe briefly 

 . the development in the south and in the extreme north-east of the 

 area. 



A. The Chepstow Area (including Chepstow near 

 its north-eastern corner and Magor at the extreme south-west). 



1. The Lower Cleistopora-Zone contains the typical K x fauna, 

 immediately following upon a series of transitional beds in which 

 fossils are extremely scarce. 



2. The base of Z x is represented by the characteristic forms, in 

 their usual abundance. 



3. For some distance above this level the beds are extensively 

 dolomitized, and fossils are consequently rare. 



4. There is, however, a well-marked fossiliferous band, which 

 extends throughout the district, and contains a typical assemblage 

 of Z 2 forms. 



5. For some distance above this level there is a great lack of 

 exposures, and the next higher beds which are met with belong to 

 the Seminula-ZGue. 



6. As in the Bristol area, this zone is thick ; it contains the 

 typical assemblage of fossils. The Seminula- Zone is splendidly 

 displayed in the large quarries on the left bank of the Wye, 

 immediately north of Chepstow. 



7. I. have seen no trace of the Dibunophyllum-Zone. 



B. The Mitcheldean District. 



The main interest of this region, which I have recently examined 

 with great care, lies in the interpretation of the rock-facies rather 

 than in the faunal sequence. The faunal succession is quite normal, 

 and the different fossiliferous levels can be assigned to their correct 

 horizons without any difficulty or question. All the fossils that 



