314 F. Dixey — The Coal-measures of Clapton, Somerset 



Unconformity between the Coal-measures and the Lower Car- 

 boniferous has recently been demonstrated in the Titterstone Clee 

 Hills by Mr. E. E. L. Dixon, 1 and in the Forest of Dean Coal-field by 

 Professor T. Franklin Sibly. 2 



This investigation was undertaken at Professor Sibly's suggestion, 

 and I have great pleasure in recording my indebtedness to him for 

 advice and helpful criticism. 



Review of Field Evidence. 



Eastern District (The Clapton Coal-field). 



This area has been mapped on the scale of 6 inches to 1 mile. It 

 furnishes conclusive evidence of unconformity between the Coal- 

 measures and the older strata. On the north the Coal-measures 

 sink beneath the Trias, but on the east and south they are bounded 

 by the Old Red Sandstone and the Carboniferous Limestone Series. 

 The unconformity maybe demonstrated in three ways: (1) By the 

 overstep of the Coal-measures from the Carboniferous Limestone 

 across the Lower Limestone Shales on to the Old Red Sandstone. 

 (2) By the occurrence of small ' islands ' of Carboniferous Limestone 

 which rise through a covering of Coal-measures. (3) By angular 

 discordance between the Coal-measures and Carboniferous Limestone ; 

 this is suggested by the general northerly dip of the Coal-measures 

 and southerly dip of the older rocks, and it is proved by small 

 exposures in the neighbourhood of Clapton Church (St. Michael's). 



1 . The southern and eastern boundary of tbe Coal-measures has 

 been carefully traced. Its transgressiye nature is quite evident from 

 the map, and the overstep can be definitely proved on the ground 

 immediately south and east of Eaish House. Near Naish House the 

 boundary gradually crosses from the Carboniferous Limestone, the 

 base of which continues as a low escarpment due east towards Moat 

 House Farm, on to the Lower Limestone Shales. It extends 

 a short distance eastwards along the little strike valley in the Lower 

 Limestone Shales (where a spring is thrown out from the Pennant 

 Grit by the underlying Lower Limestone Shales), and then swings 

 northward somewhat suddenly until the Coal-measures rest directly 

 upon the Old Red Sandstone. 



2. The ' islands ' of Carboniferous Limestone usually form little 

 rounded and wooded knolls. The largest, that immediately west of 

 Clapton village, lies on the margin of the Coal-measures, and is for 

 the most part surrounded by Trias. The other knolls, five in 

 number, are situated within less than a mile to the south-west; 

 three of them are entirely, and a fourth is partly, enclosed by Coal- 

 measures. The small knoll upon which St. Michael's Church stands 

 is bounded on all sides by the Coal-measures, which are clearly seen 

 in several places to rest upon the Limestone. 



3. The unconformable junction between the Coal-measures and 

 the Carboniferous Limestone is best seen in a small excavation on 

 the eastern side of the field path which leads northwards from the 



1 Geol. Mag., Dec. V, Vol. VII, p. 458, 1910. 



2 Geol. Mag., Dec. V, Vol. IX, p. 420, 1912. 



