Relations of the Rhcetic Beds in Somersetshire. 199 



sediment of a like nature, synchronously, over the extensive area 

 where these formations are known to occur. So, likewise, with 

 respect to their entombed organic remains, " we may expect that 

 species found in some places may not be discovered in others, since 

 we can scarcely anticipate that it would be otherwise, or that all 

 the creatures existing even upon a moderately-sized area in the 

 waters beneath which this mass of calcareous matter and mud was 

 accumulated would be found in one locality." ^ 



Mr. Moore ^ points out what he considers to be a possible uncon- 

 formability between the Eed Marl and the Ehaetic beds in the 

 sections at Watchet, Aust, and Penarth, because there the Ehaetic 

 beds are seen to lie almost immediately upon gypseous marls, 

 Avhereas at Hatch, near Taunton, a different series of marls intervenes. 



To this we need only reply that the occurrence of gypsum is very 

 local, being sometimes present and sometimes absent in the same 

 series of marls only a short distance apart. Thus to the west of 

 Watchet, gypsum is very abundant, whereas to the east it is absent, 

 although the general lithological character of the beds is the same. 

 Gypsum also occurs at different horizons, as may be seen in the in- 

 structive coast section to the west of Watchet, where it occurs in the 

 Eed Marls of the Keuper, and likewise in the thin-bedded grey, black 

 and buff-coloured marls of the Ehaetic series, commencing about 30 

 feet above the junction of the latter with the Eed Marls, and extend- 

 ing to within a few feet of the black Avicula contorta shales. It is 

 equally abundant in both series of marls, occurring in nodules, 

 nodular bands and fibrous veins, of various thickness, the latter 

 intersecting the beds in every conceivable direction. Thus the 

 formation of the gypsum is evidently of posterior date to the deposi- 

 tion of the marls, and instead of tending to prove unconformability 

 between the Ehsetic beds and New Eed Marl, rather points to the 

 intimate relations of the two series of conformable beds.^ 



Professor Eamsay* regards the Lias and Ehaetic beds as conform- 

 able, but he mentions "symptoms of erosion" which have been 

 observed between them at Penarth and Curry Eivell. The Sun-bed 

 at Curry Eivell presents an irregular surface, and the same feature 

 is present on the surfaces of other beds of the White Lias below. 

 Eegarding the Ehsetic beds as "formed in shallow water under 

 brackish semi-estuarine conditions," he remarks that estuarine or 

 tidal sea-currents would have been sufficient to produce these phe- 

 nomena when the Lias-sea first came across a slowly sinking area. 



We have never met with any evidences of erosion due to exposure 

 at the time to atmospheric influences. Evidences of shallow water 

 and of pauses in deposition occur at all horizons in the Ehaetic 

 series, though they are not to be frequently observed. They consist 



1 De la Beche's Geological Report on Cornwall, Devon and West Somerset, p. 232. 



^ Quart. Journ. Geol. Soc, vol. xxiii., p. 468. 



3 I am inclined to tkink that the veins were formed after the beds were con- 

 solidated, the strise being always at right angles to the walls of the same, whereas 

 the nodules may have been formed by segregation or otherwise when the beds were 

 unconsolidated, and perhaps shortly after their deposition. — J.H.B. 



* Quart. Journ. Geol. Soc, vol. xxvii., p. 197. 



