ZONE OF AEGOCERAS PLANORBIS. 



21 



No. 



39 

 40 

 41 

 42 

 43 

 44 

 45 

 46 

 47 

 48 



LlTHOLOGY. 



Clay. "Clear blue blocks" 



Laminated clays 



Light-coloured micaceous sandstone 



Brown clay 



Sandstone ; micaceous 



Dark sbaly clay 



Soft sandstone 



Black clay 



Ferruginous sandy vein 



Grey Keuper marls. 



Thick- 



ness. 



ft. 



in. 



' 



i 



3 











1 







2 







2 







6 







1 







3 



Paleontology. 



Pullastra arenicola, Strickl. 

 Pullastra arenicola, Strickl. 



The beds from No. 37 to N. 48 were found in situ in an escarpment at a short distance 

 from the quarry at Binton. The " Guinea-bed " is the lowest stratum seen in situ in 

 the pit, and No. 37 occupies its natural position relatively to that bed, although not 

 exposed in the Binton section. 



Lithology. — The Planorbis-beds at Brockeridge (p. 18) consist of dark, laminated 

 shales, with interstratified beds of marl and limestone. The shales split into very thin 

 laminae, between which innumerable shells of Aegoceras planorbis lie closely compressed ; 

 the white, calcareous, pulverulent material of the shells forming a strong contrast to the 

 dark shales enclosing them. In Somersetshire, at Uphill, the rock consists of shales which 

 greatly resemble those at Brockeridge ; at Watchet, of dark clays which are more 

 indurated and have the shell-structure better preserved : Aegoceras planorbis and Aeg. 

 Johnstoni are here found with the iridescent nacreous layer of their shells beautifully 

 lustrous. At Street the rock is a light-yellowish clay, with bands of greyish limestone 

 and marl beneath, and in Worcestershire at Strensham, and in Warwickshire at Binton, 

 similar lithological conditions prevail. 



The White Lias series of the section at Saltford (see p. 37) represents in part the 

 Blanorbis-heds : the relations of that zone to the Saurian beds below, and to the Buck- 

 landi-beds above, are here also well shown. In Dorsetshire the Planorbis-beds are 

 represented by the upper portion of the White Lias so well exposed in the large quarries 

 at Up-Lyme, where it is raised for caustic lime, and in the coast-sections at Charlton 

 and Pinhay Bays ; and consists of a fine-grained, cream-coloured limestone. The two 

 principal quarries afford the necessary details. Mr. Webb's quarry shows — 



In the uppermost portion, thin bands of grey limestone interstratified with shales ; in 

 these are found Aegoceras planorbis and A. Johnstoni ; in two thick beds of dark, shaly 

 clay are numerous spines and plates of sea-urchins, as Cidaris Edwardsii, Wrt., Pseudo- 

 diadema lobaium, Wrt., Hemipedina Bechei, Brod., Hemipedina Bowerbankii, Wrt. These 

 same shales are found at low-water mark at Pinhay Bay, and have yielded nearly all 

 the Echinidse said to be found in the Lower Lias at Lyme Regis. 



