part 4] jFEASSic cheoj^ologt : lias. 273 



The accompanjdng diagram (fig. B, p. 272) sliows the various 

 earth-movements and denudations which took place during 

 Raasayan and Deiran times, jDroducing many non-sequences. It 

 is constructed on the same principle as the previous diagram 

 (fig. A, p. 265). 



The datum-line is 1 Wessexian {Phricocloceras), proved in all 

 areas except the Scottish one. Again the continuous movement of 

 the Mendip axis is very noticeable ; for, although there are several 

 Raasayan faunas present in North Somerset, yet they are derived 

 almost entireh'', shown in the table by bracketing them with 

 7 E-aasayan. 



During Deiran times the movements were of several dates 

 not always isochronous in the difcerent areas — hence the frag- 

 mentary nature of the deposits and their lack of corre- 

 spondence. One movement produced obliteration of the early 

 Deiran deposits in Gloucestershire and the TMidlands, another the 

 obliteration of the latest deposits. Yorkshire would seem not to 

 have suffered from the first movement, but it did from the last ; 

 and, if the position of ijolyophyllum in the sequence be correct^ 

 another movement of about middle Deiran time must be postu- 

 lated : there are traces presumably of a slightly later movement — 

 local obliteration of jpolyopliyllum — in G-loucestershire. In North. 

 Somerset the first and second movements seem to have had full 

 sway and to have effected complete obliteration, but there was a 

 pause to allow the deposition of 7 Deiran, though the strata then 

 laid down suffered considerably by the latest Deiran movement 

 which continued, with perhaps occasional slight pauses, well into 

 Raasayan times. On the Dorset Coast there would seem to have 

 been continuous movement and penecontemporaneous erosion ; 

 at least the result, as I judge it, is that no Deiran deposits were 

 left : there was denudation down to 6 Mercian, but the fossils of 

 some of the later Deiran strata — laid down during short pauses — 

 were swept together and redeposited in early Raasayan. 



(3) Lyraian. 



The strata of this age are well-known and well-developed at 

 Lyme Regis, from which the name may be suitablj^ taken ; but, so 

 far as present records allow of interpretation, it seems that they 

 are not complete there. The Lymian is the time of anagenetic 

 and ttiberculate Arietids. 



The difficulty of ascertaining the number and sequence of 

 horizons in the Lymian is due to the wholly uncritical use of names 

 like Ammonites hucklandi. Instead of being a common and 

 universally distributed species as records make out, A. hucklandi 

 is a special massive form which I can only be certain of from 

 Keynsham.^ I suspect the occurrence of another horizon with a 

 fauna of smaller Coronicerates, but whether pre- or -posi-hucklandi 

 has yet to be determined : the placing of it as ])Ost-bucklandi is a 

 surmise. 



^ See Palaeontological Appendix, p. 302. « 



Q. J. O. S. No. 292. z 



