Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/540

374 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 9, ft. in. ft. in.

was obtained the remarkable new starfish, Stellaster Sharpii, Wright*, also Astarte minimus in clusters, Rhynchonella variabilis, Terebratula perovalis, T. ovoides, &c 1 6

7. Ironstone containing plants, Acrosalenia, &c 1 0

8. " Sand-bed " — coarsely cellular ironstone, with sandy cores — sometimes hard sandstone — containing few fossils 1 6

9. " Four-foot bed" — cellular ironstone, with ochreous and argillaceous cores, in many layers and very crumbling, alternating frequently with irregular arenaceous bands, sometimes 2 feet in thickness, and exceedingly fossiliferous — Hinnites abjectus, Pecten, Ammonites, Rhynchonella, &c 4 0 to 6 0

10. Variable beds, with very green cores, oxidized on the joint and bedding planes, in thinner bands at the top and towards the bottom, occasionally very rich in fossils, the tests sometimes preserved — Coral, Lima (various species), Pecten articulatus, wood, &c. Of the larger blocks, the iron-ore coating only is used for smelting 8 to 9

11. Much broken ferruginous beds, not worked because of water, and little known : a zone at bottom, exposed in the section of a neighbouring clay-pit, is probably equivalent to the Ammonites-bifrons zone, the bottom bed of Bass's pit. I have an example of A. bifrons said to have been obtained from this pit, but upon doubtful authority. The lowest zone contains numerous rounded pebbles or concretionary nodules about 3 0

12. Band of mixed material, as at Kingsthorpe brick -pit 0 6

Upper Lias Clay.

Although I have associated in this section certain beds with, certain fossils generally found in them, yet this association must not be understood to amount to a limitation. The more abundant fossils, such as Cardium cognatum, Isocardia cordata and a large new species, Ceromya bajociuna, Lima (various species), Cuculloea (various species), Macrodon hirsonensis, Trigonia (various species), Pecten demissus, P. lens, and some other forms, are found almost indifferently, but irregularly, in all the beds of the section.

A certain significance, however (to which I have already alluded), attaches to the position in this section of the zone of Astarte elegans, having immediately above it a bed containing Ammonites Murchisonoe and Pholadomya fidicula. It will be remembered that a similar zone occurs in the Old Duston, Old Slate Quarry, and Harlestone stone-pits (u, v, and v'), marked by the presence of the same Ammonite and bivalve — and also in the wells near Hopping Hill, at about the same distance from the surface as in the Old Duston pit. The occurrence of such a zone at these five different points, thus marked at two of them by the presence of Ammonites Murchisonoe and Pholadomya fidicula, would seem to point to the conclusion that it represents an horizon within this area, and to the equivalence within the same area of the beds (at whatever points found) lying between this zone and the Upper Lias Clay, especially as the thickness of the ferruginous beds penetrated by the wells (near y) is more than equal to the entire thickness of the Old Duston pit section down to the Astarte zone added to the thickness of the Duston ironstone pit section from the Astarte zone down to the Upper Lias clay, — that is,

Memoir.
 * Vide Note by Dr. Thomas Wright, F.R.S.E., F.G.S., appended to this