448 



JUEASSIC CHRONOLOGY. 



[vol. Ixxviii, 



Section IX — The Junction-Bed and Contiguous Deposits, measured 

 in sitii AT THE Western P]kd of Watton Cliff. 



Hemerse. Strata sni Fauna, Feet inches. 



Dumortieria. A+B. Blue sandy ' Upper Lias' clay. 



Marked iion-seq uence. 

 Falciferum ? M (?). Very hard mottled limestone, witli large Sarpo- 

 ceras falciferiim common at the top. [5230, 

 Harpoceras cf. mulgravium.'\ 

 . Top much iron-stained and planed off smooth. 8-9 



Transitional from 

 Mi(?). Harder, conglomeratic, mottled limestone. Small 

 Sarpoceras ? sp. near the top. [Micromorpli, 

 not Sarpoceras.'] 10-11 



Irregular parting. 

 '[Thoi'ncombi- U (?). Soft, earth}', j'ellowisli ' marlstone.' Belemnites 

 ensi&.] sp., Syncyclonema sp., JRliynclionella sp. [5232, 



Tetrarhynchia thorncombiensis], 6 



A p p a r e n 1 1 3^ transitional from 

 Ui (?). Rough lumpy ' marlstone,' soft and highl}' 

 ferruginous. 

 Apparentl}^ transitional from 

 U2(?). Soft earth}' 'marlstone' crowded with crinoid 



fragments. 2-3 



Apparently transitional from 

 Lumpy ironshot marlstone, somewhat oolitic. 

 U3 (?). Obscure fragment of Sarpoceras in friable 

 condition. Seen to 

 (About 1 foot obscured by slipped material.) 

 T. Soft yellow sands. 



The most interesting feature of this section is the absence of 

 the lithographic and other limestones of layers D to J).. That all 

 these beds should have disappeared in so short a distance is a good 

 example of the remarkably sudden variations to be met with in the 

 Junction-Bed. 



Layers M (?) and M^ (P) are almost certainly the continua- 

 tion of layers M and M^ (?) in Section VIII. Presumably layer 

 M (?), at least, is of falciferum date — unless the specimens of 

 Sarpoceras falciferum are redeposited. 



Layers U (?) to U3 (?) are only separable with uncertainty, as 

 ihe deposit is very irregular, lumpy, and confusedly mingled. The 

 fossils characf eristic of the ' marlstone ' of the Western Cliffs 

 •appear to be absent, and much of the rock is more like the Tetra- 

 rhyncJiia-tJiorncombiensis Bed and other hard bands in the Yellow 

 Sands than the true ' marlstone.' Mr. Buckman considers that the 

 whole of layers U(?) to ^^(P) is pre-spinaticiu material redeposited. 



[During further work in 1921 I discovered a block of the 

 J^UBction-Bed (about 8 feet long) lying partly embedded in talus 

 fiome few feet west of the group of three blocks measured in 

 ^Section VIII. At the eastern end, the 'Upper Lias ' clay A-f-B 

 Tests upon the earthy limestone C (4 to 5 inches) and the litho- 

 rgraphic stone D (7 to 8 inches) ; at the western end it rests upon 

 the grey limestone D^, C and D having been removed by denudation 

 iprior to the deposition of the ' Upper Lias ' clay.] 



