50 INFERIOR OOLITE AMMONITES. 



incorrectly identified (so far as British figures are concerned), and which I have 

 not yet obtained. Its claim to rank as a British species being somewhat doubtful, 

 and the actual extent of the beds which may be equivalent to the Continental " Zone 

 of Am. jurensis " being uncertain, I have preferred to use the term " Striatulum- 

 subzone " to denote the beds which in the Cotteswolds overlie the Yellow Sands 

 and form the lower part of the Cephalopoda-bed. When thoroughly developed the 

 subzone consists of two or more bands of hard stone with a dark brown marly 

 layer between, and contains certain characteristic Ammonites, among which is 

 Gramm. striatulum (p. 46). 



The thickness of the Cotteswold Sands in the Gloucestershire sections is of 

 necessity partly an estimate which gives them an average of 100 — 125 feet at 

 these localities. Oppel 1 places these sands at Frocester in the upper part of the 

 zone of Posidonomya Bronni, the " hard blue beds with Am. bifrons and Am. 

 serpentinus " forming the lower portion. I have preferred to distinguish for the 

 present their greater portion at least as the Variabilis -svibzone, since this 

 Ammonite occurs in almost the first fossiliferous band below the Striatulum-beds. 

 But the presence of Hildoceras bifrons abundantly in these sands at least forty feet 

 from their base, 2 and also at the base itself above the blue clay, 3 makes it extremely 

 hard to draw any line of demarcation between the Variabilis -subzone and the zone 

 of Hild. bifrons. H. B. Woodward, 4 using the term " Midford Sands " in its 

 widest sense to include the Yeovil and Cotteswold Sands as well as those at 

 Midford, states that they contain the zones of Am. opalinus and Am. jurensis, 5 

 and places the whole series in the Lower Oolites away from the Lias ; but, 

 as regards the latter, this occurrence of Hildoceras bifrons must be somewhat 

 hard to explain. These sands, by whatever name they are called, are very puzzling 

 to correlate with any degree of certainty ; and I feel some doubts about the 

 propriety of using the term "Midford Sands" for the whole series in the three 

 counties of Dorset, Somerset, and Gloucester until we have obtained further 



1 Oppel, op. cit., p. 296. 



2 Sections V, VI. 



3 Section VIII. 



4 ' Geology of England and Wales,' 2nd edition, p. 285, 1887. 



5 I expressed this opinion with regard to the zones of the Yeovil Sands (" Amm. Inf. Ool.," 

 ' Quart. Journ. Greol. Soc.,' vol. xxxvii, p. 608, 1881), and Oppel's statement that at Ilminster the 

 Sands of the Inferior Oolite begin above a bed filled with Am. jurensis, radians, variabilis, &c, partly 

 helped to form it (' Juraf.,' p. 253). Now I know that my determination of Lytoc. jurense was 

 incorrect, and having since seen the much clearer exposures of the Cotteswold Sands and Cephalo- 

 poda-bed, both containing a far better Ammonite fauna, I feel considerable doubts about the matter, 

 and shall be far from satisfied about the correlation of the Yeovil Sands with the Cotteswold 

 Sands and Cephalopoda-bed without working the subject up more fully in Dorset. The general 

 identity of the deposits is probable, but their exact correlation is the difficulty. 



