198 H. B. Woochcard and J. H. Blake — 



red marls become more variegated, and frequently alternate with 

 green and grey marls now in rapid succession, then in alternate 

 masses, until we lose the red entirely, and enter upon the hard aad 

 soft green, grey, white, and buff-coloured marls which constitute the 

 base of the Khgetic series. Sometimes one or two bands of red marl 

 occur several feet up in these latter marls. It is therefore impossible 

 to fix a boundary, save that of colour, which is liable to so much 

 variation, that the same horizon cannot be accurately determined m 

 different sections. 



Evidences of unconformability between these beds have, however, 

 been put forward, and these we must proceed to notice. Mr. Moore ^ 

 alludes to the frequent unconformability of the Lower Lias, Eh^tic, 

 and New Eed Marl, due to •'' the absence of some of their members." 

 Whilst at Queen's Camel, where the section is complete, he observes 

 that there is " a clear passage upwards, without any break, from the 

 upper beds of the Keuper, through the Ehtetic and White Lias 

 series into the Lower Lias,'^ yet to the North of the Mendips this is 

 not the case. In this area he finds a total absence of the zones of 

 Ammonites planorbis and of A. angulahis ; but the latter occurs in the 

 zone of A. BucMandi, which thus rests directly on the White Lias. 

 Although he has " no special faith in precise Ammonite or other 

 zones of life," '^ Mr. Moore regards the absence of the zones as evidence 

 of unconformability ; and this feature extends as far as Bath.^ Mr. 

 Moore alludes also to the paucity of Saurian remains in this area. 



As we have mentioned, the junction of the Lias with the Ehgetic 

 beds on this side of the Mendips is more distinctive than it is to the 

 south, there being no difficulty in determining it ; but the stratifica- 

 tion of the beds is always conformable, and there is no evidence of 

 any marked lapse of time between the deposition of the two series. 

 Certainly the Planorbis-heds were never deposited in this area and 

 subsequently removed ; the thinning out of the Lower Lias appears 

 to be due to a suspension of sediment or slowness of deposition. 

 Mr. Moore accounts for the attenuation of many of the Secondary 

 beds in this area on the ground that the Mendip Hills formed a 

 barrier against the incursion of sedimentary matter to the north. If 

 this be true, they may have formed a barrier to check the migration 

 of the Ammonites planorbis. 



At all events, we do not see that this feature in any way affects 

 the general conformability of the Ehastic and Lower Lias, or indeed 

 of any of the other Secondary strata, some of which show a striking 

 attenuation. 



Neither can we admit that ''the absence of some of their members," 

 whether lithological or palseontological, necessarily constitutes a 

 proof of unconformability. It would be most unreasonable to sup- 

 pose that the same operations and conditions were in force forming 



^ Quart. Journ. Geol. Soc, vol. xxiii., p. 459, etc. 



- Quart. Journ. Geol. Soc, vol. xvii., p. 487 ; vol. xxiii., p. 471. 



^ Ammonites planorbis occurs at Keynsham, and we have noticed it in the cutcing 

 near Bitton Station on the Midland Eailway. We have also obtained it in the cherty 

 beds of the Lias at Harptree Hill. 



