2Dart 4J Jurassic cheonologt : lias. 309 



but much variation in this respect ma}' be expected as well as, the 

 more minutel}'' subdivision is carried on, a great increase in local 

 non-sequences. 



The position of the Le2)tcilfioceras and^. nautiJiformis horizons 

 in regard to the faunal sequence discussed in the stratigraphical 

 portion of this paper (p. 26(3). may be surmised to this extent — 

 they are ^ve-gihhosa — a spinous species near to, perhaps as used 

 by Monestier including, Amcdtlieus armiger. Whether they are 

 pre- or ^ost-algovicoium as now restricted is uncertain ; but it 

 may be surmised that they do not correspond to this algovianum 

 horizon, because the localities yielding the respective faunas seem 

 to be geographically separate. 



Evidence for other -^ve-gibhosa horizons in this country and 

 their relation to the Mediterranean sequence will chie% depend on 

 certain Amalthei. Lytocerata, and an occasional Hildoceratid. On 

 the Dorset Coast very low down in the Domerian — in the strata just 

 above the Three Tiers — are Amalthei of the clevelandicus pattern, 

 and the same occur low down in marls at Lightpill, near Stroud 

 (Gloucestershire). Large Amalthei of the stokesi pattern occur in 

 sandy strata at South Petherton — perhaps the A. margaritatus of 

 Woodward's Bed 2^ ; but whether this is pre- or ])Ost-aIgov iauicm 

 in its restricted sense is uncertain. The origiiial Ammonites stolcesi 

 came from the Dorset Coast ; but there is the same doubt about 

 its position : one can only judge from the colouring of Sower by 's 

 plate that it is from blue marls. Fine Lytocerates occur in the 

 Marlstone Series at Dudbridge, near Stroud, and at two horizons 

 on the Dorset Coast : there are various species, recorded incorrectly 

 as A. Jimhriafiis. Day cites the good specimens from his JS'Largari- 

 fafus stone- where I have found them, and he places others lower.^ 

 Whether the Dudbridge species are on the same horizon as either 

 of the Dorset species cannot yet be said : there may be three 

 horizons. 



All this evidence, faulty though it may be, seems to suggest 

 that there are the following ^re-gibbosa horizons in the English 

 Domerian to deal with : — 



Leptaleoceras. 



Sphffirocones (A. naiitiliformis). 



Amalthei (of stol-esi pattern). 



Seguenziceras (and small Amalthei). 



Lytocerata. 



Amalthei of clevelandicus pattern. 



Lytocerata. 



These divisions may not all be separable, and it is not claimed 

 that they are in correct descending order ; but a table of some sort 

 is required as a preliminar}^ to making out our home sequence. 

 Only when that is understood will it be possible to correlate with 

 the Mediterranean sequence, and bring all into one hemeral time- 

 scale. 



^ Loc. cit. 



2 Q. J. G. S. vol. xix (1863) p. 292. » Ihid. p. 291. 



