part 4] JUEASSIC chronology : LIAS. 261 



From his excellent paper I extract the following as a summary 

 of the sequence : — 



Table I. — Faunal Horizons op Lower Domerian. 



(After J. Monestier.) 



Q 1 J" Upper horizon. ^ Amaltheus gihhosa Quenstedt.' 



' \ Lower horizon. ' Seguenziceras algovianuin Oppel.' 



Subzone h. ' Cceloceras acantlioides Eeynes ' 



c, 1 r Upper horizon. • Hildoceras hoscense Reynes.' 



Subzone «."i t i. • ^ /-< ji i t ■ -a > ' 



[^ Lower horizon. Grammoceras jieldingi Keynes. 



Monestier (p. 11) gives Amaltheus Icevis as a constituent of his 

 subzone c. Perhaps this is due to local paucity of deposition, for the 

 evidence of Raasay, so far as it goes, is to the contrary ; A. IcBvis 

 is from near the top of the Scalpa Sandstone, Avhile the indication 

 of an alcjovianum fauna is near the base — some 200 feet lower. 



Over a considerable part of England it is possible that all, or 

 nearly all, of Monestier's horizons are not represented, the 

 Domerian beginning with the alc/ovianum horizon, or even later 

 than that locally. On the Dorset Coast, however, these lower 

 strata may, perhaps, be found. 



The thickness of the Domerian on the Dorset Coast exceeds, 

 according to Day's evidence,^ that of the Scottish deposits, and 

 very considerably. From the Three Tiers to the Marlstone of the 

 Junction Bed, inclusive, there are 364 feet.^ It is possible that 

 180 feet of this — the lower part — represents sti-ata missing from thff 

 Scottish deposits and from other English localities ; for it is per- 

 missible to interpret Day's record of Am. thouarsensis in the Shell 

 Bed (p. 291) as Seguenziceras aff. algovianum : this would givp 

 about 180 feet from algovianum to spinatum inclusive, which 

 compares Avell with about 200 feet of Scalpa Sandstone within the 

 same limits, leaving 180 feet below in which Monestier's pre 

 algovianum horizons may be sought — -I have seen something of a 

 hoscense style with the matrix of the Dorset Coast. 



Monestier quotes an Amalfheus fauna through all his horizons, 

 and Day gives A. margaritatus through about 330 feet of strata 

 on the Dorset Coast. It is to be regretted that investigators have 

 too often placed all the species of Amaltheus under one name ; fo- 

 Avith careful discrimination much information might have been 

 gained as to their horizons, with great advantage to correlation 

 work.3 But this range of Amaltlieus, followed by its allied genus 

 JPaltopleuroceras, induces the reflection that the strata yielding 

 these Amaltheidas ought alone to be classed as Domerian — the age 

 of Amaltheids. 



In certain cases, then, the division between Whitbian and 



1 ' Middle & Upper Lias of the Dorset Coast ' Q. J. G. S. vol. xix (1863) 

 pp. 283-85. 



' Amaltheus has been found some 2 feet below the lowest tier, W. D. Lang-, 

 Prec. Geol. Assoc, vol. xxv (1914) p. 329. 



•' Species of Amaltheus are enumerated in 'Yorkshire Type Ammonites' 

 1911, p. 25 d ; but this by no means exhausts the series. 



