R. TATE ON THE LIAS ABOUT RADSTOOK. 499 



Monotis inasquivalyis, Sow. ; Bowldish ; Tirnsbury (E. B. Tawney). 



Pecten textorius, Schloth. ; Phyllis Hill (E. B. Tawney). 



■ calvus, Goldf. ; Bowldish. 



Ostrea arcuata, LamJc. ; Bowldish. 



Waldheimia sarthacensis, UOrb. ; Bowldish. 



Ehynchonella variabilis, Schloth. ; Bowldish. 



plicatissima, Quenst. ; Bowldish. 



Ditrypa quinquesulcata, Goldf. ; Bowldish. 

 Serpula deplexa, Phillips ; Bowldish. 

 Foraminifera. 



Middle Lias. 



This formation is introduced by a conglomerate bed consisting of 

 a black limestone breccia and conglomerate, and forming at Camer- 

 ton and Clan Down a separate bed, but at Eadstock, Bowldish, and 

 Munger entangled in the yellow limestone constituting the so-called 

 marlstone. These derived fragments of stone yield Ammonites rari- 

 costatus ; and associated with them are rolled or broken casts of that 

 fossil, as well as of Ammonites obliquecostatus and Pleuromya crassa. 

 The yellow matrix in which they are imbedded contains Ammonites 

 armatus, A. JEgion, and A. Taylori. Here, undoubtedly, we have a 

 commingling of Ammonites of different horizons ; but in this case an 

 explanation of the association is easy, inasmuch as the upper beds of 

 the Lower Lias have suffered denudation, even over the present tracts ; 

 probably much of the strata so removed were clays containing lime- 

 stone nodules and casts of shells in the same material, and out of 

 which they have been washed and subsequently cemented by the 

 mid-Liassic"ooze. At Clan Down theForaminiferal clay was partially 

 involved in the denudation ; and at Munger the whole of it was 

 removed. 



Thus, it seems to me that continuous and tranquil deposition 

 went on in this district from the commencement of the Lias period 

 until the accumulation of the Spiriferina bank, that through some 

 change of currents there was a hurried or disturbed deposition of 

 the Foraminiferal clay over certain areas, succeeded by a more nor- 

 mal condition, during which 2^ feet of strata at least were accumu- 

 lated; but how much more can only be known by the discovery of beds 

 in this area which will conduct us from the band with A. planicostatus 

 to the yellow limestone with A. armatus without a stratigraphical 

 break. Then there follows a most decided physical unconformity, 

 marked by the remanie fossils of the oxynotus beds and their entire 

 removal over certain spots. 



The so-called marlstone is mainly a yellow ironshot limestone of a 

 maximum thickness of 13 feet, and so much resembles some members 

 of the Inferior Oolite that it is only after recognition of the fossils 

 that one is prepared to admit its Liassic age. 



The following sections will convey the leading pala3ontological and 

 lithological features of this interesting rock-group : — 



