part 4] 



JURASSIC CHRONOLOGY. 



441 



^ thin layer of sandj^ cW is beginning to come in beneath the 

 ' marlstone,' and it thickens rapidly towards Doghus Cliff. 



Section III illustrates the thinning-out and change in lithic 

 character of the lenticle of clay 0. 



Section III — The Junction-Bed, measured in a Block on the Talus 

 AT THE Eastern End op Down Clief. 



Hemerse. Strata and Fauna. Feet inches. 



Sifrons. '■ L. Massive mottled limestone. Hildoceras hifrons. 



i Obscure parting. 



FaJciferum. \ M. Whitish ;ind pink, conglomeratic, mottled lime- 

 stone; ferruginous near the base. 

 Apparently transitional from 

 Pre- 0. Greyish-white, nodular, earthy store, with marly 



falciferum?\ streaks and patches. 



Apparently transitional from 

 Spinatum. R. Oolitic conglomeratic 'marlsrone.' JBeJeinnifes 



spp., Paltoplenroceras i^Y). [_ol(?S, Pal to pi euro- 

 ceras cf. piseudocostatiim Hyatt, but more spi- 

 nose.J Seen to 



The 'marlstone' here is almost certainl}^ the lower or pre-S6^rr«j^« 

 layer, and the ''J^Jeuroiomaria Bed' Q is midoubtedly absent: hence 

 the appearance of a transition from K to M must be considered 

 illusor3\ In formations where ' contemporaneous ' erosion has been 

 active (especially if the materials be at all soft) so much inter- 

 mixture of matrices has taken place along the line of contact of 



Section IV- — The Junction-Bed, measured in a Block on the 

 Talus below Doohus Cliff. 



Hemerse, 

 Pifrons. 



Falciferum. 



Pleurotomaria ? 



'Spinatum. 



Strata and Fauna. Feet inches. 



L. Pinkish-3'ellow mottled limestone. Hildoceras 

 bifrons, rolled fragments of Harpoceras sp., 

 Phynchonella cf. moorei. 

 Obscure parting. 

 M. Similar, but harder, limestone. Ver}'^ large 

 JELarpoceras falciferum, Dactylioceras spp., 

 ' Aulacothi/ris ' sp. 

 [An inverted Terebratulid (5218) a little like 

 T. aspasia Meneghini & Zittel, but rounder, 

 not nearly so sulcate, and possessing a smaller 

 beak.] 

 Obscure parting. 

 Q. Impersistent earthy ferruginous seam. Vleuro- 

 tomarice, Amherleya, Ci/lindrites, Trochus ; 

 Plicatula cf. spinosa. 

 Besting upon a rather irregular surface of 

 R. Rough conglomeratic ' marlstone.' Palto- 

 pletu'oce7'as spinatum, Discohelix sinister, 

 Pteria ^ incequivalvis,'' Pseudopecten cequi- 

 valvis, Modiola, Ostrea, etc. ; llhynclioneUa 

 acuta, Hh. furcillata. Ph. tetraedra, Tere- 

 bratida punctata, Zeilleria cornuta, Z. 

 quadrijida, Spiriferina oxygona. 

 [6137, Paltopleuroceras cf. pseudospinatum 

 Hyatt, but has many more ribs ; 5689 (2 ex). 

 Homoeorhynchia acuta, medium size ; 5361, 

 F'urcirhi/nchia ftu^cata S. B. ; 1830, Tetra- 

 rhynchia cf. tetraedra/\ 



1-2 



