part 4] 



JURASSIC CHRONOLOGY. 



381 



the position of the Junction-Bed. A consideration of the post 

 Inferior-Oolite strata will be reserved for a later communication. 



Section I — Watton Cliff, between Eypesmouth and West Bay 

 (Bbidpoet), Dorset.^ 



Beds 1-4 in Thickness. 



the middle part Sequence of Strata. (approximate) 



of the Cliff. in feet 



1. Forest Marble : massive shelly blocks with clay- 



partings 30 



2. Upper Grey Marls 30 



3. a. MiCROMORPH OsTREA Bed : a mass of smalF 



oysters rarely 5 mm. long. Pedicle-valve of 

 Dictyothyris ; fragments of Acanthothiris (A. 

 hradfordiensis Walker ?). 

 b. The ^ BO UETi' or ^ Riiyxchonella Bed': about 

 16 inches thick, mainly brown, crumbly, but 

 white and compact for about 2 to 3 inches J- 

 from the bottom. Full of specimens of Gonio- 

 rhynchia,'^ often crushed ; also occasional ex- 

 amples of Ornithella sp., crushed. Rarely 

 Terebratula langtonensis Walker. 

 Lower Grey Marl. 

 White Marl. J 



c. 

 d. 



4. Large Conchoidal Bed : clays which break into 



large pieces. Measured up the cliff from 5 

 to 3 cZ 



5. OSTREA-ACUillXATA Cl AYS 



G. Brachiopod-Beds '^ -. stone bands 6 to 12 inches 

 thick separated by clays 18 to 30 inches thick. 

 The contents of the stone-bands vary, and their 



sequence is somewhat supposititious 



a. Orxithella Bed. 



6. Large s3Iithii Bed : Rhynchonelloidea aff. 

 S7nithii, rather large examples without other 

 brachiopods. 



c. AcAyTHOTiiiRis 'B:ei> : A. poiverstockensis, Rhyn- 

 chonelloidea smithii, and a large ammonite 

 {ParMnsonites ?).'* 



d. The globata Bed or Terebratula Bed : Stiph- 

 rothyris ^^'p,-^ Terebratula ci.tuinida Davidson 

 (T. globata auctt. non Sow.) + r. cf. nunney' 

 ensis S. Buckman. Rhynchonelloidea cf . smithii. 



e. Shelly Bed : small forms of Rhy^ichonelloidea 

 cf . smithii. 



125 

 20 



25 



^ See diagram 1, p. 383. 



^ For these and other brachiopod names see Bibliography, I, 6. 



•^ Details of the Brachiopod-Beds were mostly obtained from blocks 

 scattered on the beach during 1916. In 1917 and 1919 these blocks were 

 nearly all buried; towards the end of my visit in 1920 a high tide removed 

 shingle, disclosing the upturned edges of some stone-bands along the line of 

 fault immediately east of Eypesmouth. These gave some help in the inter- 

 pretation of the succession ; but, owing to faulting and dislocation, they are 

 not too reliable. A detailed section will be given in a later communication. 



"• Now in the Museum of the Geological Survey, Jermyn Street, London. 



2d2 



