58 DPv. T. F. SIELT ON THE FAULTED IXLIEFv OF [Feb. 1912^ 



5. The Faulted Inliee of CaPvBonifePvOus _Limestoxe at Upper 

 YoBSTER (Somerset). By Thomas Feaxklin Siblt, D.Sc, 

 F.G.S. (Read December^6th, 1911.) 



[Plates II-V.] 



Contexts. 



Page 



I. Introduction 58 



XL Extent of the Inlier 59 



III. Essential Structure of the Inlier 61 



General Conclusions. 



lY. Detailed Description 62 



(a) The Isorthern Limestone Mass : Yobster Quarry. 

 (h) The Southern Limestone Mass. 

 Yobster Old Quarry. 

 Other Exposures. 



A Lamellibranch-Fauna in the Lpper Seminula- 

 Beds. 

 (c) The Grit-&-Shale Mass. 

 Y. Bibliography 72 



I. IxTFvODUCTIOX. 



The faulted inliers of Carboniferous Limestone at Luckington^ 

 Upper Yobster, and Tor Eock, Yobster, respectively, are tbree 

 small masses lying in the Coal Measures of the southernmost 

 portion of the East Somerset Coalfield, at distances varying from 

 about a mile and a quarter to half a mile north of the main outcrop 

 of the Carboniferous Limestone in the Eastern Mendips. 



The highly disturbed condition of the Carboniferous strata in 

 this coalfield is well known. Throughout the district east of 

 Nettlebridge, in which these inliers are situated, the strata of the 

 Coal Measures are overfolded and in places greatly contorted, as 

 was shown by Buckland ik Conybeare in 1824.^ 



The anomalous position of these masses of Carboniferous Lime- 

 stone has given rise to much comment and speculation by geological 

 writers. Since attention was drawn to two of them by Buckland & 

 Conybeare,^ the inliers have been the subject of several papers, 

 apart from many incidental references made to them. The con- 

 tributions of Mr. H. B. AYoodward and Mr. James McMurtrie^ are 

 particularly noteworthy, on account of the conflicting theories 

 advanced by these authors to explain the position of the masses. 

 Mr. Woodward has invoked a fan-shaped anticline broken by 



1 Buckland & Conybeare. 1824. pp. 255-56. See also McMurtrie, 1869. 

 pp. 140-44; Anstie,' 1873, pp. 55-63 & figs. 13-17; McMurtrie, 1902, 

 pp. 327-29 & pi. xiii, fig. 3. For details of references see the Bibliography, 

 §Y, p.72. 



2 Buckland k Conybeare, 1824, p. 228 & pi. xxxii, fi^. 1 c. 



- H. B.Woodward, 1871, 1876, 1891 ; Mc:\rurtrie, 1877. See alsoWinvrood, 

 1891, pp. clxxviii-clxxxvi & figs. 3-5. 



