1870.] TATE — GLOUCESTERSHIRE LIAS. 395
That the zone of Ammonites capricornus is intimately connected
with the Marlstone there cannot be a doubt, and in the Yorkshire
Lias it has for many years been grouped with it ; but as the zones of
Ammonites Jamesoni and A. ibex, in this country, have usually been
regarded as imperfectly fossiliferous, the necessary data for comparison
being absent, the position of these zones in the Middle Lias has,
with some degree of reasonableness, been questioned, more especially
because the lithological conditions of the upper zones of the Lower
Lias (sensu stricto) are repeated in the zone of Ammonites Jamesoni.
Professor Ramsay, in his Anniversary Address to the Geological Society in 1864, leads us to infer that the divisional line between the Lower and Middle Lias is one of convenience; he shows by tables the number of species which pass upwards through the zones of the Lias, and in a resume states that from the zone of Ammonites raricostatus, which forms the top of the Lower Lias, six species (eighteen species only are recorded), or about thirty-three per cent., pass upwards into the Middle Lias, whilst from the zone of Ammonites Davoei (here equivalent to the zones of A. Jamesoni, A. ibex, and A. capricornus) thirty-one species pass upwards, or very nearly thirty-eight per cent. The facts from which the above results have been obtained, if examined in detail, show that, as regards the species of Ammonites, their range is trenchant, but that common species of fossils graduate upwards from one division to another.
The number of species recorded in England from the several zones is given as follows : — zone of A. oxynotus, 6 ; A. raricostatus, 18 ; A. Henleyi and A. Davoei, 82 ; and considering the paucity of fossils from these zones bordering on the junction of the Middle and Lower Lias, it would be unphilosophical to lay too much stress upon their palaeontological affinities and differences.
The scanty published information we possess relative to the organic remains of the lowermost zone of the Middle Lias is given by Oppel and Wright. The former author estimates the thickness of the zone of Ammonites Jamesoni in Robin Hood's Bay at 100 feet, and mentions the following fossil species : — Ammonites Jamesoni, A. Taylori, Belemnites elongatus, Gryphoea obliqua, Pholadomya decorata, and Pinna folium. He also notices the development of this zone at Charmouth, but gives no list of fossils ; Mr. C. H. Day, however, has enumerated twenty-eight species of Mollusca from it. In the neighbourhood of Cheltenham, Dr. Oppel did not determine the occurrence of the zone of Ammonites Jamesoni ; but Dr. Wright says* "in Gloucestershire the beds representing this zone are found only in some deep brick-pits near Leckhampton, whence I obtained fragments of Ammonites Jamesoni and Gryphoea obliqua, with Rhynchonella rimosa."
Having during a series of years made a comparatively extensive collection of fossils from the " Belemnite beds" of the neighbourhood of Cheltenham, and being aided by several collectors and other sources of information, I am enabled to record from the zones of Ammonites oxynotus and A. raricostatus fifty species, and from the zone of Ammonites Jamesoni one hundred and sixteen species ; these data
- Mon. Brit. Asteriadae, Pal. Soc. p. 78 (1864).
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