LIOCERAS OPALINUM. 49 



An analysis of the Cotteswold sections shows us that, while the beds which 

 actually contain Lioc. opalinum do not vary so very greatly, yet the thickness of what 

 is called the Cephalopoda-bed increases very much at North Nibley. This we see 

 chiefly occurs in the middle part, or the beds lying between those below in 

 which I have noted Gramm. striatulum and those above with Lioc. opalinum, 

 and there is also a certain increase in the beds with Gramm. striatulum. Calling 

 these horizons C", C", C, the result may be stated in a tabular form, thus : 





Haresfield. 



Coaley Wood. 



North Nibley. 





Ft. In. 



Ft. In. 



Ft. In. 



C" 



1 4 



1 10 



1 11 



0" 



8 



8 



10 10 



c 



10 



11 



2 9 



Total .., 



2 10 



3 7 



15 6 1 



C", as I have said, are the beds where Lioc. opalinum actually occurs in the 

 Cotteswolds, while C" are the beds below, in which I have not detected it though 

 I have found in them a somewhat similar, but I believe generically different, 

 Ammonite. If we use the name " Zone of Am. opalinus " it would seem correct to 

 place C" and C" in that zone, and, as I have previously remarked, the upward 

 extension of the zone is a matter of uncertainty. It is, however, well to consider 

 that Oppel 2 makes two zones, the one of Trigonia navis and the other of Am. toru- 

 losus, and states that Am. opalinus occurs throughout both zones (pp. 297, 

 367). Perhaps C" and part of the " Sandy Ferruginous " beds D' may be 

 respectively the zones of Am. torulosus and Trigonia navis, and C" should be 

 parted between them. C, or the lower part of the Cephalopoda-bed in Gloucester- 

 shire, I have provisionally called the Striatulum-subzone because of the presence 

 of Ammonites striatulus so abundantly in the beds which directly overlie the yellow 

 micaceous Cotteswold Sands that are lithologically so different. From Hares- 

 field Beacon to Little Sodbury, a distance of nearly seventeen miles direct, I 

 have found this Ammonite always in this position. Oppel, 3 when treating of 

 Frocester Hill, places beds of this horizon (i. e. lying on the top of the Yellow 

 Sands) in the zone of Am. jurensis, a species which has hitherto, I think, been 



1 This is the greatest development o£ the " Cephalopoda-bed " which I know, viz. fifteen feet 

 six inches. Dr. Wright, on the authority of Sir A. C. Bamsay, states (' Monogr. Lias Amnion.,' 

 p. 95) that at Wotton-under-Edge the series is sixteen feet thick. With my late friend Mr. E. 

 Witchell I tested this point by actual measurement, and found it to be only eleven feet. In other 

 respects the section agrees with North Nibley. 



2 Oppel, ' Juraformation,' pp. 293 and 305 ; and at p. 321 he states that these two zones 

 sometimes attain a thickness of 300 feet in the Swabian Alps. 



3 Oppel, op. cit., p. 296. 



7 



