part 4] JUEASSIC chronology : LIAS. 269^ 



seems to fit the Ammonite development more satisfactorily than a 

 division into two parts. Here it is proposed to adopt something 

 of the same divisions, styling them Deiran, Mercian, and Lj^mian. 



(1) Deiran. 



This is the age when the gerontic phase of the Arietidse Avas in 

 full development : it is the period of the oxycone Arietids. Its 

 stmta ar^ perhaps more developed in Yorkshire than in other 

 English areas ; and it takes its name from Deira, the ancient 

 kingdom of which Yorkshire formed a considerable part. 



The sequence of faunal horizons is suggested in the following 

 table. 



Table YI.— Deiean. 



Dates. Strata. 



r ^ X 



Hemerae. Kaasay. Ioekshiee.! Cheltenham Somerset. Dorset 



District. Coast. 



8. (?w;«e«se)? .. (X) 



7. BadstocTciceras - g Eadstock, iiortli 



% of Mendips. 



Q. Gleviceras^ ... ^ Folly Lane, (X) 



■tr Chelteuliam 



c3 (lower part). 

 b. polyophylhim . ^ 1? X Yale of (jilou- 



S cester. X 



4. oxi/notum 3 Lansdowu, 



" Cheltenham. 



3. bifeftuii r= Aston Cross, Canards 



5 • Tewkesbury. Grave, south 



's X of Mendips. 



2. simpsoni ^ 2 



1. Gagaticeras ... 3 



1 'Geol. Whitbv ' 2nd ed. Mem. Geol. Surv. ]915, p. 67. 

 • 2 See Appendix III, Faheontology, pp. 287, 289. 



[X Fauna present, position surmised. (X) Fauna present, supposed to be derived 

 and redeposited in Kaasayan (Table V, Bed 92): Mr. Lang, however, suggests 

 paucity of sediment. j 



The Deiran seems to have been a time of much earth-movement 

 and consequent non -sequences, with the result that there is little 

 correspondence of fauna in different English areas. This m.eans 

 that the sequence given is based mainh" on supposition. i 



The certain evidence is the sequence Gaf/aficeras-sinqysoni 

 m, Yorkshire with 'polyopliylhiin presumably later ; the sequence 

 oxynotum-Gleviceras in Gloucestershire with hiferum, it is 

 reasonably certain, earlier than oxynotum. There is no definite 

 correspondence here to work upon, and other areas give no help as 

 they show other dissimilar faunas. 



It is here suggested that the Yorkshire Gagnticeras-simpsoni 

 strata are earlier than the Gloucestershire deposits. 



The position in the faunal sequence of th.Q polyoj^liyllum horizon 



' See further remarks in Appendix III, Palaeontology, p. 310. 



