308 ME. s. s. BUCKMAN 0]!>r [vol. Ixxiii, 



Such Hildoceratids find their home in the Mediterranean area : 

 whether their rarit}^ here is due to stratal failure or inequality 

 of zoological distribution is for future work to determine. 



An attempt to ascertain the position of Leptaleoceras in the 

 Domerian may be made by comparison of its matrix with that of 

 other Ammon ites. Taking the Gloucestershire area first — the matrix 

 of A. nautiliformis J. Buckman,! from a neighbouring Marlstone 

 eminence, Alderton-Dumbleton, a few miles north of Gretton, is 

 light blue, compact, arenaceo-calcareous (micaceous?) non-ooHtic — 

 ver}^ suggestive of the ' bluish gray calcareous grit ' mentioned 

 for a bed of ' Marlstone ' ^ (lower Domerian, below the Kock-Bed). 

 The matrix of Leptaleoceras is blue, less compact, calcareous and 

 shelly. That of specimens of Amaltheiis armiger'^ {Am. amaltheus 

 spinosus Quenstedt, 2K(rs\ from Gretton and Alderton is feebly 

 blue, oolitic, very shelly ; while that of Paltopleurocerates from 

 the latter place varies from somewhat similar, not so shelly, to 

 yellow, not shelfy, not oolitic. 



On the 2)rinciple that the blue colour and the arenaceous 

 character are indices of lower beds, the following Gloucestershire 

 sequence may be surmised : — ■ 



5. Paltopleiiwceras. 



4. Amalthei (spinous forms). 



3. Leptaleoceras. 



2. A. nautiliformis. 



1. ? 



In regard to South Petherton, colour fails to make distinction 

 between the matrices of such ammonites : all are a yellowish, 

 more or less ironshot oolite, with only the distinction of larger 

 browner limonitic grains in the cases of the Amaltheids. The 

 absence of blue colour and of micaceous grains with presence of 

 ironshot oolite seems to show that all come not lower — and it may 

 be in, the Bock-Bed — equivalent to Bed 4. 8 to 12 feet thick, of 

 Woodward's section from the neighbourhood^ — this Bock-Bed 

 being some loO feet from the base of the Marlstone Series of 

 which the lower 100 feet is described as ' blue and gre}^ micaceous 

 marls.' In this Bock-Bed it may be assmned that the Amaltheids 

 occupy the higher part, and the other ammonites the lower ; and 

 now that the Gloucestershire district has suggested somewhat of a 

 clue, perhaps the differentiation of the Somerset Bock-Bed into 

 zones can be made : there is room enough for several, and the need 

 is obvious. 



This interpretation with regard to nautili for mis audits matrices 

 would mean, if correct, that in the Ilminster district of Somerset 

 the Marlstone Bock-Bed began earlier than in Gloucestershire ; 



^ 'Yorkshire Type Ammmonites ' 1911, No. 37. 



2 'Geology of Clieltenham ' new ed. 1844, p. 38, Bed 2. 



^ 'Yorkshire Type Ammonites' 1911, p. 25 d. As one finds this and like 

 spinous Amalthei labelled Am. spinatus on occasion, a clue may be afforded 

 to some old records. 



■* • Lias of Engl.: Jur. Eocks' vol. iii, Mem. Geol. Surv. 1893, p. 202. 



