Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/562

396 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 23, go far to establish a broad line of demarcation between the Lower and Middle Lias.

The species enumerated in Table I. (p. 397) from the zones of A. oxynotus and A. raricostatus have occurred at Cheltenham, with the following exceptions, Bel. excavatus and B. elegans (Yorkshire), and Montlivaltia mucronata, M. mammiformis, and M. radiata (Fenny Compton). Those in Table II. (p. 398) have chiefly been obtained from near Cheltenham and at Aston Magna ; the species recorded by Drs. Oppel and Wright, Mr. Day, and Prof. Phillips, from the zone of Ammonites Jamesoni in Yorkshire and Dorsetshire, are introduced.

At Cheltenham the zone of Ammonites Jamesoni is exposed in the clay-pits by the Leckhampton Road ; it consists of a mass of blue shaly clay with a few thin bands of compacted shells. With the exception of Ammonites ibex, A. Valdani, A. Henleyi, the Belemnites, and Inocerami, the fossils are of small size, but most of the species enumerated occur in great numbers. The most abundant species are Ammonites Valdani, Belemnites clavatus, B. umbilicatus, B. oxyconus, Dentalium minimum, Cerithium Slatteri, Chemnitzia liassica, C. Blainvillei, Turbo admirandus, Nucula cordata, Leda Galatea, Arca Stricklandi, Pentacrinus basaltiformis, Waldheimia numismalis. The totality of the species correlates these beds with the Belemnite schist or Numismalis-beds of Hanover, Wurtemberg, and France, the most complete list of fossils from which is that given by Schlonbach*. He records, eliminating synonyms, seventy-five species from this zone as developed in the north of Germany ; of these, thirty-nine are peculiar, thirty-three pass to the zone above, six are found in the Lower Lias, and thirty-six occur in beds of the same horizon in England.

The species recorded from Aston Magna were obtained by Mr. Thomas Slatter in the railway-cutting near that village : the exact relation of the bed yielding the fossils was not ascertained ; but that gentleman informs me that it is a soft blue clay underlying five or six feet of blue shaly clay, literally filled with broken pieces of Spiriferina verrucosa and Belemnites. The specific identity of the greater number of the fossils from this section with those from the zone of Ammonites Jamesoni at Cheltenham requires the Aston beds to be referred to that horizon.

From Table I. I deduce that of the fifty species recorded from the zones of Ammonites raricostatus and A. oxynotus, chiefly in the neighbourhood of Cheltenham, eight pass to the zone of A. Jamesoni, whilst thirteen occur in lower horizons, and twenty-nine are peculiar to these horizons in England.

Table II. records one hundred and fifteen species in the zone of Ammonites Jamesoni, sixty of which pass to higher zones, whilst eleven make their first appearance in the Lower Lias. Of the species common to the Lower and Middle Lias, five have been enumerated in the first table, so that there are fourteen species in common to the two formations.

But other species of the Lower Lias, not given in the above tables, reappear in higher stages of the Middle Lias. Such migrated species


 * Deutsch. geol. Ges. vol. xv. 1863.