186 3IE. E. WETHEEED OX IXSOLTJBLE EESIDUES FE0:M 



16. Oil IxsoLrELE Eesidues obtained from the CARBOxiPEEors- 

 LI:kIESIO^'E Seeies at Cliftox. By Edwaed Wetheeed, Esq., 

 E.G.S., F.C.S., E.E.M.S. (Eead Eebmary 8, 1888.) 



[Plate YIII.] 



The Ccirboniferous-Limestone rocks at Clifton are Trell known and 

 have been the subject of several communications to the Geological 

 and other Societies. Among the authors of such communications I 

 may mention Sir H. de la Beche, Sir A. Eamsay, Dr. Buckland, 

 Mr. Conybeare, Mr. Etheridge, Mr. Tawney, and Mr. Stoddart ; the 

 papers and monographs written by the investigators just named 

 deal mostly with the physical, stratigraphical, or paheontological 

 ]3roblems which the rocks of the gorge of the Avon have presented 

 for solution : I am not aware that any one has examined the residues 

 obtained from the limestone after boiling portions in strong acid. 



Outlines of the Formation. 



The thickness of the Carboniferous-Limestone series at Clifton 

 is thus stated by Sir H. de la Beche * : — 



feet. 

 Upper mixture of Sandstones, Marls, and Limestones 400 



Central portion of series 1438 



Lower Shales 500 



2338 



Professor HuU t, in his classification of the Carboniferous series, 

 puts the Bristol and Somersetshire coal-fields under one head, and 

 gives the thickness of the Limestone as follows : — 



feet. 



Stage C. Yoredale Shales (thin) 100 



Stage B. Carboniferous Limestone 2330 



Stage A. Lower Limestone Shales 100 



2530 



Professor Hull's classification of the Carboniferous series seems to 

 me to be the most comprehensive yet produced; but there may be 

 some difference of opinion as to the term Yoredale when applied to 

 the Upper Limestone of the Bristol and Somersetshire coal-fields. If 

 Professor Hull means, by the term Yoredale, the beds which mark 

 those physical conditions which closed the Limestone Period and 

 ushered in the Millstone Grit and Coal-measures, then he is correct 

 in saying that there is at Clifton a series of deposits, represented 

 by a thickness of about 100 feet, which mark the close of the 

 Limestone Period and the coming in of the MiUstone G-rit. They 



* Mem, Geol. Survey, vol. i. p. 129. 

 t Quart, Joum. Geol. Soc. vol. xxxiii. p. 631 (1877). 



