86 MR. W. J. CIAEKE ON THE TJNCONFOEMITY IN THE [Feb. IQOI, 



7. The Unconfoemitt in the Coal-Meisures of the Sheopshiee 

 Coalfields. By William James Claeze, Esq. (Communicated 

 by W. Shoke, Esq., F.G.S. Eead December 5th, 1900.) 



This unconformity, locally known as the Symon ' Fault,' has- 

 received so much attention from geologists in the past, that it would 

 almost seem superfluous to attempt any new study of the subject. 

 So far back as 1861 it was brought by the late Marcus Scott 

 before the notice of the Geological Society ^ in a very valuable paper, 

 of the facts contained in which I shall here make use, though my 

 inferences will be somewhat diflPerent from his. 



In 1863, Mr. John Eandall, in a joint paper with Mr. George E. 

 Boterts, read by Sir Andrew Ramsay before the Geological Society,^ 

 showed that the same agency which created the Symon or Great East 

 ' Fault ' in the Coalbrookdale Coalfield had removed the whole of the 

 older or lower beds of coal and accompanying seams of ironstone 

 from the Devonian rocks several miles south of the above field, and 

 that they had been replaced by two beds of inferior coal. Between 

 the upper two of these seams was a bed of limestone containing 

 Spirorbis carbonarius of sufficient thickness to repay burning for 

 lime, the whole dipping apparently beneath the Bunter Sandstone, 

 and reappearing in the same order, as Sir Roderick Murchison 

 showed, a mile farther south at Cantern Bank and Tasley near 

 Bridgnorth. Mr. Eandall, in subsequent papers read before various 

 scientific societies, and more particularly in his work on ' The Severn 

 Yalley,' published in 1882 (Madeley), showed that the same phe- 

 nomenon of the Symon or Great JEast 'Fault' was observable all 

 the way to the Forest-of-Dean Coalfield, and thence onward to the 

 Bristol Channel. 



Mr. Daniel Jones, F.G.S., in his observations on the ^oreet-of- 

 "Wyre Coalfield made in connection with . tlP^*1i)i^al^*f^m1iii^on -of 

 1871, and in various subsequent papers,^ %elduced ihuch valuable 

 evidence showing the replacement of the Lower Coal-Measures by 

 the Upper, not in Coalbrookdale alone, but in all the Shropshire 

 coalfields, laying special emphasis on the position of the JSpirorbis- 

 liraestone-bed as forming a natural datum-line near the base of the 

 Upper Measures. 



The horizon thus denoted I accept as the base of the Upper 

 Measures, but prefer not to trust to this limestone-bed as in itself 

 a sufficient datum, for the following reasons : Firstly, it is liable 

 to be confused with other Spirorbis-heds at a higher horizon in 



^ Quart. Journ. Geol. Soc. vol. xvii, pp. 457-67. 



2 Ibid. vol. xix, p. 230. 



3 'Denudation of the Coalbrookdale Coalfield' Geol. Mag. 1871, pp. 200- 

 208 ; ' On the Correlation of the Carboniferous Deposits of Cornbrook, Brown 

 Clee, Harcott, & Coalbrookdale ' Ibid. pp. 363-71 ; ' The Structure of the 

 Forest-of-Wyre Coalfield ' Trans. Fed. Inst. Min. Eng. vol. vii (1894), pp. 287- 

 300, 577, & vol. viii (1895) p. 356. 



