R. TATE ON THE LIAS ABOUT RADSTOCK. 493 



37* On the Lias about Radstock. By Ralph Tate, Esq., Assoc. 

 Linn. Soc, F.G.S., &e. (Read May 26, 1875.)j 



A recent writer* states that the geological history of Somersetshire 

 has yet to be written ; if this be true (and it is not for me to decide), 

 what a marvellous tale will have to be told! if we may judge from 

 the deeply interesting portions of that history already made known 

 to us by Mr. C. Moore, some of the results of whose labours, which 

 'cover many years, are embodied in two communications to this 

 Society f, and are illustrated by a most extensive and exquisite suite 

 of fossils deposited in the Bath Museum. 



"Without seeking to disparage the larger views set forth in the 

 last-mentioned papers, yet I consider a modified interpretation Of 

 some of the phenomena is required ; and calling to my aid an extended 

 acquaintance with Liassic species and their distribution, I believe that 

 I am in position to give a more complete account of the sequence of 

 deposits, so far as relates to the Liassic rocks in the neighbourhood of 

 Radstock, than has yet been done. 



"Wherever the Lias has been critically studied, it is found that 

 there is a parallelism in the succession of life, most especially in 

 regard to the species of Ammonites — so much so that the strata 

 admit of a grouping after their palseontological characteristics, and 

 further into regions of Ammonites, a classification as much in harmony 

 with facts as that of the Oolitic rocks into formations. 



The recognized divisions of the Lower and Middle Lias are as 

 follows : — 



Middle Lias. Zones of Ammonites spinatus, A. margaritatus, A. 

 cajpriGornus, and A. Jamesoni ; to the last are annexed an upper zone 

 of A. ibex and a lower one of A. armatus. 



Lower Lias. Zones of A. oocynotus (including the subzones of A. 

 rarieostatus, A. oocynotus, and. A. obtusus), A. Bueklandi, A. angu- 

 latus, and A. planorbis, with the Ostrea-liassica beds and the White 

 Lias. 



Mr. Moore has given sections of the Liassic rocks centering in 

 Radstock, which may be summarized as follows : — 



Middle Lias Marlstone 15 feet thick. 



v t«™» t -oc [4. -rarieostatus beds 1 , a 



Lower Lias j ^ Liag Qy , BwMondi g8ries J 16 „ „ 



White Lias series 8 „ „ 



Herein the zones of A. angulatus and A. planorbis are unrecog- 

 nized, and the medio -Liassic portion is not correlated ; nevertheless 

 I find no other than the normal arrangement to obtain. 



* H. B. Woodward, Proc. Somersetshire Nat.-Hist. Soc, vol. six. 1873. 

 t Quart. Journ. Greol. Soc. vols, x, and xxiii. 



