78 ME, S. S. JiUCKM'A.N' OX [vol. lxxvi, 



If the Dorset and Yorkshire evidence of this table he considered, 

 the first impression is that Ammonites tubellus occurs at three 

 horizons — with strong -ribbed JEchiocerata of rarieostatoides 

 pattern, with E. macdonnellii, and later than E. aplanatnm. As 

 such repetitive occurrence is quite unusual with ammonite species, 

 much more evidence would be necessary before it could be accepted. 

 Other surmises may certainly be put forward meanwhile; and 

 what seems likely is, that the record of A. tubellus in Bed 17 of 

 Yorkshire is due either to nomenclature failure, which is known to 

 have occurred and has been already recorded by me, 1 or to zonaliza- 

 tion failure — a mistake as to horizon, for both beds 17 and 20 of 

 Yorkshire are described as 'Blue Shale.' ~ 



If the upper record of A. tubellus can be disposed of in this 

 manner, then the Yorkshire record might be brought into line 

 with that of Dorset on the supposition that Bed 20 of Yorkshire 

 is an incomplete polyhemeral deposit, containing in its 85 feet, 

 which is a greater thickness than that of many proved pofyherneral 

 deposits, fragments of Raasayan 3, 1, and 5. But, if that be 

 accepted, it involves the corollary that the number of sequential 

 faunal episodes in Raasayan 4 is greater than has been supposed, 

 and that some of these episodes are missing from Yorkshire. 



It certainly .seems as if the multiplication of faunal episodes, 

 with consequent non-sequences in various areas, is assuming undue 

 proportions. But, as I remarked in my former paper, 3 



i It is unlikely that the remarkable sequence disclosed at Raasay with the 

 large adjustment which it involves will be the oidy discovery of its kind.' 



And the future may show that, instead of being too bold, I have 

 actually been too timid in dealing with the evidence of Raasay 

 itself. However, the evidence of the dissimilar faunas of other 

 areas will show what further adjustment is required. The im- 

 portant point is to record the evidence, and to give it unprejudiced 

 consideration. 



If, then, the supposition about the record in Bed 17 of York- 

 shire can be confirmed, and that about the character of Bed 20 be 

 accepted, the faunal sequences may be numbered so as to separate 

 the various episodes. Then it might be possible to present the 

 records in the following manner (Table VII), which brings Ammo- 

 nites tubellus into line without doing any violence to the evidence, 

 except in regard to that of Bed 17. 



The Gloucestershire evidence is particularly instructive : it 

 seems to indicate that there was an episode of Ammonites tubellus 

 distinct from that of strong-ribbed Echiocerates, which again is 

 to a certain extent confirmed by the order in which Dr. Lang finds 

 these faunas preserved in Bed 100 of the Dorset Coast. There 

 was, in Gloucestershire, entombment of Ammonites tubellus and 

 presumably preservation of its strata : just before and just after- 

 wards there is faunal failure. This faunal failure is presumably 



1 II, 6, p. 70, footnote 1. 2 Ibid. loc. cit. 



3 n, 8, p. 263. 



