•iOS ME. s. s. BrcK:siAX ox Lvol. Ixxviii, 



This is an exact reversal of their true sequence. The possi- 

 bility of such inversion had been already surmised from consider- 

 ation of other cases. ^ 



The important j)oint is, however, that the evidence of anmionites 

 is not to be trusted too implicitly in certain cases : it shows that 

 special care has to be taken in reading records. That there was 

 such an inversion might be explained on the supposition that, as 

 the latest bed (that of striatulum date) was destroyed, its removal 

 exposed an earlier bed {hifrons) which, in turn being removed, gave 

 opportunity for the denudation of fcdciferum. But this is only 

 a part of the history : it is faii'ly evident that strata of these dates 

 and of others Avere all exposed to denudation at the same time. 

 ^\\\x% fcdciferum contributed to the fauna of the lower part of one 

 fallen block; hifrons (so far as the evidence of pink matrix goes) 

 was laid under contribution for layer 9 ; thoriiconibiensis provided 

 materials for layer 3, and for various earlier layers. While the 

 middle and upper part of the bed was being laid down, however, a 

 stratum which yielded striatulum forms was being considerably 

 raided to provide materials, though it was not the only bed from 

 which they Avere obtained. 



The latest date for the deposition of the AVatton Bed is deter- 

 mined by the date of the superimposed areno-argillaceous stratum 

 (Xo. 13) - : the Watton Bed was laid down before that date. 

 This sandy stratum is, fi-om its position, presumably a less argilla- 

 ceous representative of the Down-CliiP: Clay which caps the 

 Junction-Bed in the cliffs west of Eypesmouth ; or it may be the 

 equivalent of the basal part of the Bndport Sands, which in 

 Burton Cliff assume a bluish colour in their lower part. But, 

 again, these basal Bridport Sands may be really a less argillaceoas 

 condition of Down-Cliff Clay. 



The Down-Cliff Clay has yielded i)?//>'?o;'Z'/(^/7V^-^ the irony scale at 

 the base of the AVarton- Cliff sandy stratum has also yielded Dumor- 

 tieria, the basal Bridport Sands at Burton have given no evidence. 

 The Watton Bed is, therefore, earlier than the Dumortieria 

 hemera. in the main. But an early form of Durnortieria occurs 

 in the AVatton Bed, layer 3 ; the irony scale which caps that bed 

 and the complete lithic change between the AVatton Bed and 

 the sandy stratum point to a non-sequence of greater or less dura- 

 tion. It is to be concluded that the Durnortieria hemera contains 

 really more episodes than oui* present time-scale allows for: first, an 

 episode of early Du/nortieria, during which calcareous conditions 

 of lithographic -stone deposition obtained — a tranquil deposition of 

 fine sediment resembling paper-shales ; secondly, an episode of 

 j)ossible denudation while a lithic change was accomplished ; thirdly, 

 the episode of argillaceous or areno-argillaceous conditions of the 

 Down- Cliff Clay and its equivalents, passing higher up into 



^ I, 9. p. 74, footnote 1. 



^ Section I. p. 382. 



3 I, 2. p. 519; I. 5. p. 64. 



