LIOCERAS OPALINUM. 51 



knowledge. According to Oppel neither the zone of Jurensis nor of Opalinus 

 occurs in the Cotteswold Sands. He places the lower part of the Cephalopoda-bed 

 in the zone of Am. jurensis, and he claims the Sands as the upper part of the zone 

 of Posidonomya Bronni. 



If the term " Midford Sands " is to include the Opalinum-zone, it must be taken 

 to be equivalent not to the Cotteswold Sands alone but to the Cephalopoda-bed as 

 well, and may in that case even include a considerable part of the " Sandy 

 Ferruginous " beds, which would be an anomalous state of things. According to 

 Mr. Hudleston 1 there is no trace of the fauna of the Cephalopoda-bed of 

 Gloucestershire in the Midford Sands themselves at Midford, and therefore I 

 think that it would be unwise to use the term so as to include that deposit. My 

 idea would rather be to place some name on the Sands occurring in the three 

 Counties that would signify the horizon equivalent only to what lies between 

 the Upper Lias Clays below and the Striatulum-beds above, equal in fact to the 

 Cotteswold Sands, but not to include the lithologically very different strata of the 

 Gloucestershire Cephalopoda-bed in the term Sands. It may be that the Midford 

 Sands are equivalent either to the Cotteswold Sands only, or to those Sands and 

 more. In the former case the term would do, but the proper zonal constituents 

 would have to be determined ; in the latter case I think that it would be preferable 

 to use some other name to indicate the Sands alone in other counties. 2 



As will be seen from the extract from Mr. Hudleston's section given at p. 47, 

 a bed only three inches thick containing Lioc. opalinum occurs at the base of the 

 Inferior Oolite Limestone at Burton Bradstock. This bed I take to be the exact 

 equivalent of the one at Haresfield, above the Cephalopoda-bed, viz. No. 15, and 

 there are at Burton Bradstock some seven feet of sandy grits just underneath, 

 which must be reckoned to the lower part of the Opalinum-zone, and from which 

 probably my specimens of Lytoceras torulosum, Schiibler, were obtained. A 

 similar position is occupied by the sandy marls and sandstone beds which occur at 

 Stoke Knap near Broad Windsor, Dorset, near Haselbury, Somerset, and at some 

 other places, and which are from two to five feet thick. They are, I imagine, 

 below the actual bed with Lioc. opalinum at Burton Bradstock, but are the 

 equivalent of the beds Nos. 17 and 18, at Haresfield, and therefore, like those, 



1 ' Gasteropoda,' Pal. Soc, volume for the year 1886, p. 56. 



2 Having visited Midford since I wrote the above, and finding that the Parlcinsoni- zone there rests 

 directly upon yellow sands, I prefer to consider all the intervening beds to be absent, and to imagine 

 these sands to be the equivalent of those below the Striatulum-beds in Gloucestershire, rather than as 

 doubtful representatives of the lower members of the Inferior Oolite. In that case the sands at Midford 

 do not contain the zone of Am. opalinus, and, according to Oppel's opinion about the Cotteswold 

 Sands, they would be below the zone of Am. jurensis. If Oppel is right, their inclusion in the Inferior 

 Oolite is a mistake. 



