part 8] succEssioisr of the atoniajst at clifto]n'. 215 



as ' lagoon-phase deposits,' and the conditions under which they 

 accumulated are discussed in detail. Vaughan's later papers often 

 refer to the A. von Section, and contain a record of the development 

 of his opinions concerning it. Thus, in the Brit. Assoc. Report 

 (Winnipeg, 1909) on ' The Faunal Succession of the Lower Car- 

 boniferous (Avonian) of the British Isles,' Table II gives his 

 views as to phasal equivalents of the Avonian and the physical 

 conditions under which the rocks accumulated, and these views are 

 further developed in the Burrington paper ^ (1911). In this paper 

 several rock-types are described and figured which are charac- 

 teristic also of the Avon Section. Miss M. B. Chapman, ^ in the 

 course of her enquiry into the mode of origin of the purer lime- 

 stones, has analysed a number of rocks from the Avon Section ; and 

 Mr. L. M. Parsons's^ paper on ' Dolomitization & the Leicestershire 

 Dolomites ' is of much interest, in view of the widespread dolo- 

 mitization of the Avon rocks. Lastly, a brief account of the Avon 

 lithology is contained in a paper read before Section C at the 

 Bournemouth meeting of the British Association for the Advance- 

 ment of Science. An abstract was reprinted in the ' Geological 

 Magazine ' ^. 



The following account deals primarily with the exposures on the 

 right bank of the Avon ; but those on the left bank are briefly 

 mentioned, and are described when any particular horizon is badly 

 exposed on the right bank. 



While, at the time of the publication of the Bristol and Avon 

 papers, Vaughan drew the line between the Upper and the Lower 

 Avonian at the top of the Syringotliyris Zone, it later became 

 clear that C^ was more closely related to y and C^ to S^, and that 

 the dividino^-line should be drawn in the middle of C. The reasons 

 for this are stated in the Gower paper, pp. 542-43, and in the 

 Burrington paper, pp. 307-308. 



Vaughan's latest views on the correlation of the rocks of this 

 horizon are contained in his paper on the ' Correlation of Dinantian 

 & Avonian'^. In this paper he revives the term 'horizon A,' 

 first used in the Avon paper, and extends it to include all the strata 

 from Upper C, {laminosa dolomites) to Lower S^. As the present 

 paper is not concerned with questions of correlation, but deals 

 solely with the lithological succession, and also in view of the 

 f i-equent references to the * Bristol ' and ' Avon ' papers which it 

 contains, it has seemed best to describe the rocks undei* Vaughan's 

 original subdivisions. The quarries are referred to under the 

 names or numbers adopted by Vaughan. Topographical details 

 a]'e only given in cases where they are not likely to be obliterated 

 by later quarrjdng operations. 



1 Q. J, G. S. vol. Ixvii (1911) pp. 385-88. 



2 Geol. Mag. 1912, pp. 498-503. 



3 lUd. 1918, pp. 246-58. 



4 Ihid. 1919, pp. 523-24. 



5 Q. J. G. S. vol. Ixxi (1915) pp. 1-49. 



