Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/344

 their mode of occurrence. Sometimes we find a thick ferruginous rock, the bedding-planes of which are covered with thin layers of oysters ; at other times a hard blue-hearted calcareous rock, emitting a fetid odour under the hammer, and almost wholly made up of oysters and other marine shells. The oyster-beds usually contain a large quantity of carbonaceous matter, and in places, indeed, pass into what might be called impure lignite. The thickest of them measures about four feet, and it contains several interstratified bands of clay, which, like the similar beds below, contain many small oysters scattered through it.

The fossils of these oyster-beds appear to be for the most part marine. By far the most abundant are two species of oysters, one plain, the other plicated. A careful comparison of a large series of these convinces me that they are dwarfed forms of Exsoyyra sinuata Sow., and E. Boussingaultii, D'Orb. Almost all the shells found in these beds appear to be stunted in their growth, probably from having lived under unfavourable conditions. No specimens of Ammonites have been obtained from these beds, and only one small and doubtful example of a Vicarya. The following are the fossils hitherto obtained from the oyster-beds of Punfield.

Exogyra sinuata, Sow. (very abundant) Boussingaultii, If Orb.(very abundant). Pecten, sp. (very small). Cardium subhillanum, Leym. (rather rare). Corbula striatula, Sow. (abundant). Anomia laevigata, Sow. (abundant). Modiola giffreana, Pict. et Roux (rare). Several small univalves. Much carbonized wood.

In the same part of the series as the oyster-beds there occurs a bed of Sandstone containing Cyprides and casts of Cyrena.

C. " The Marine Band of Punfield." This bed, though only 21 inches thick, is of the greatest interest, presenting us as it does with a very considerable marine fauna, and thus furnishing the means of correlating this portion of the Wealden with the series of marine formations. It forms a well-marked feature in the cliff at Punfield Cove, dipping due N. at an angle of 65°. In its general characters it is very similar to the oyster-beds above. The oysters in this bed, which are of the same species as those in the oyster-beds (Exogyra sinuata and E. Boussingaultii), attain however to a larger size, and approach more nearly to their normal forms than in the latter beds. The specimens of Corbula striatula and Cardium subhillanum likewise attain to larger dimensions. But besides the shells which occur in the oyster-beds, we find in this band many which are much more decidedly marine, including Ammonites Deshayesii, several forms belonging to the new genus Vicarya, and species of Trochus, Natica, Actoeon, Actoenella, Orthostoma, Pholadomya, &c.

The upper part of the marine baud consists of a hard laminated micaceous sandstone, more or less calcareous, containing much