226 



indurated seams or lines I'unning tlirougli the band would indicate their 

 presence. The upper Pecten bed, on the top of No. 12, and about 

 1 ^ inches in thickness, (6 in section,) closes the upward succession of the 

 Black Shales. At Coombe Hill the shale between the lower and upper 

 Pecten beds is 8 feet in thickness, at Aust Cliflf 6 feet, and Patchway 

 7 feet. The shells are numerous in the u[)per Pecten bed, which is well 

 defined, and easily recognised by the lenticular but continuous masses 

 of pale brown earthy argillaceous Limestone, looking like indurated mud. 

 I obtained a remarkably fine centrum of Plesiosaurus from this thin 

 band when constructing the complete section of the cliff. A change 

 takes place in the character and colour of the marls and shales above 

 the black series, both on lithological and Palajontological evidence; the 

 fossils are better preserved, and we have also a larger assemblage of 

 MoUusca, both specifically and numerically. Dr. Wright, in his valuable 

 paper upon the Zone oi Avicula contorta, &c.,* notices this series, and read- 

 ing downwards, jjlaces it in his section as No. 6, stating that it contains 

 "many compressed Conchifera which have not been determined." This 

 is bed or series No. 13 in my section, and which measures 7 feet, but in 

 places may be more, owing to the in-egular capping, and peculiar nature 

 of the Estheria Zone above. I regard these grey conchoidal marly shales 

 as the most fossiliferous series in the Avicula contorta zone at Westbury, 

 but from their position in the cliff, have perhaps been little worked or 

 examined. I obtained, in a very short time, through the assistance of 

 our valued and old associate, John Jones, Esq., the following species 

 from these beds : — 



Pecten Yaloniensis, Defr. Myacites musculoides, Schl. 



Cardium Ehseticum, Merian. Avicula 



Axinus cloacinus, Ojjp. Pleurophorus angulatus, Moore. 



Anatina Suessii, 0pp. Modiola minima. Sow. 



Lima pi*ecursor, Querist. Trigonia f 



Axiniis or Schizodus. 

 and numerous casts of indefinite and doubtful forms. 



The uppermost part of this marly series culminates in a densely hard 

 grey crystalline Limestone, irregularly bedded, 3 to 5 inches in thickness, 

 (c in section,) and in which is crowded most of the Phaetic species 

 enumerated above. It is the only band of fossiliferous crystalline 

 Limestone in the whole section beneath the Monotis beds above, whereas 



* Quarterly Journal, Geological Society, vol. xvi, p. 374. 



t These all occurred in the condition of sharp casts and moulds, the true shel 

 being seldom preserved. 



