part 3] THE LITHOLOGICAL SUCCESSION AT CJ.IETON. 213 



10. The LiTHOLO&iCAL Succession of the Caebonifeeous 

 Limestone (Atonian) of flie Ayon Section at Clifton. 

 By Sidney Hugh Reynolds, M.A., Sc.D., F.Gr.S., Professor 

 of Greology in the University of Bristol. (Head January 5th, 

 1921.) 



[Plates VIII-XIV.] 



Contents. 



Page 

 I. Introduction and Previous Work 213 



II. Description of the Rocks 21(. 



(A) The Cleistopora Beds. 



(B) The Zaplirentis Beds. 



(C) The Syringothyris Beds. 



(D) The Semimda Beds. 



(E) The DibrinojyJiylluni Beds. 



III. Changes which have aifected certain of the Rocks 236 



IV. Modiola Phases of the Avon Section 237 



V. Summary and Conclusions 238 



VI. Vertical Section of the Right Bank of the Avon 239 



[Note. — The cost of certain of the illustrations and of preparing thin 

 rock- sections, some 200 in number, examined in connexion with this 

 paper, was defrayed by grants from the University of Bristol Colston 

 Society. The numbers (A 11, etc.) refer to slides in the University 

 collection.] 



I. Inteoduction and Peeyious Woek. 



Although a very large amount of information concerning the 

 lithology of the Carboniferous Limestone is now available, that of 

 no section has hitherto been described in detail, and it seemed 

 that a full account of the rocks of the classical Avon Section 

 might prove of value. The first full account of the composition 

 or structm-e of one of the rocks of that section Avas W. W. 

 Stoddart's description of the ' Bryozoa-Bed ' ^ (' Microzoal Bed ') 

 in 1861 and 1865. In one of his papers on the Geology of the 

 Bristol Coalfield, he ^ further gave a considerable am^ount of in- 

 formation concerning the Avon rocks. 



Sorby,3 in his Presidential Address to the Greological Society 

 in 1879, briefly alluded to some of the oolites from the Avon 

 Section, but it was not until Mr. E. B. Wethered turned his atten- 

 tion to the subject that any detailed work was done. Mr. 

 Wethered's investigations referred, on the one hand, to the chemical 

 and mineralogical features, and on the other, to the faunal 

 and microscopical characters. His paper on ' Insoluble Residues 



1 Ann. & Mag. Nat. Hist. ser. 3, vol. viii (1861) pp. 486-90 ; also Geol. Mag 

 1865, pp. 83-85. 



2 Proc. Bristol Nat. Soc, n.s. vol. 1(1874-76) pp. 313 et seqq. 

 ^ Q. J. G. S. vol. XXXV (1879) Proc. p. 86. 



