Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/617

Rh that there was apparently do distinction to he made between them and detached fragments of the parent-rock or of the Lower Limestone, as the case might be. They had the aspect of having been washed and worn by marine action, and contained the fossils of the bed and many forms not found in it.

The greatest thickness of the calcareous sandstone may be a little over 200 feet.

Besides the nodule seams, interspersed throughout the bed are dense bands and nodules of chert, of a grey-brown colour and conchoidal fracture. These may take the shape of rounded masses, but are oftener seen forming thin seams in a pale-coloured sandstone towards the base of the bed. Concretionary nodules of red hæmatite and clay-ironstone are also met with throughout the bed, but in greatest abundance in the upper parts near to the marl; also in the same situation nodules of crystallized gypsum appear, even below the first nodule seam, where lumps of iron-pyrites, with sulphur in small quantities, are met with as in the overlying marl.

The Vertebrata will be noticed in the sequel.

The invertebrate fauna of the Calcareous Sandstone and the nodule seams are conspicuously represented by Pecten and Echinida, Pecten cristatus, Bronn?, P. scabellus, and P. squamulosus being plentiful. Clavagella and from 2 to 3 species of Scalaria, and Spondylus, Ostrea Boblayei, and O. Virleti are common, besides numerous other species.

Out of 21 forms met with in the Marl, about 12 affect also the Calcareous Sandstone and its nodule bands.

The Brachiopoda are Terebratula sinuosa, T. minor, Terebratulina caput-serpcntis, and Thecidium Adamsi, the first being the only one common also to the marl.

Of 22 species of Echinodermata found in the Calcareous Sandstone, 9 are common to it and the Upper Limestone, whilst 4 are also common to the Sand bed, and 2 are also found in the Marl.

Foraminifera in this bed are noticed Geol. Mag. vol. iii. p. 152.

V. The has its upper horizon marked by what I have named the "Transition or Scutella-bed".

The upper portion of this stratum passes so imperceptibly into the Calcareous Sandstone that, were it not for certain organic remains which constantly mark the point of transition, it would be difficult to define where the one ends and the other begins.

The saucer-shaped Scutella subrotunda and the Orbitoides Mantelli congregate in the above situation in great abundance.

The Lower Limestone presents considerable variability. It may be concretionary and oolitic in its composition, or irregularly compact and often semicrystalline. Large portions are made up of broken shells, Corallines and Foraminifera, whilst the structure of much of the upper parts is made of globular white nodules, strewn irregularly throughout a lamellar or concentric bedding.

The colour varies from a pure white to a cream-colour.