Foraminifera of the Fens of Lincolnshire and Cambridgeshire.--Though the alluvial deposits of the fen-districts are comparatively of modern date, yet the rich assemblage of foraminifera contained in the clay of certain districts is so interesting and instructive, that a brief notice of them must not be omitted. The foraminiferous character of the Lincolnshire alluvium was first made known to me by specimens from Bolton, sent me by Professor Williamson; and their extension over a wide area in Cambridgeshire, by a liberal supply from Mr. Smith, of March. The bed that abounds in these shells, is about seven feet beneath the surface, and consists of a fine sea sand combined with carbonaceous and argillaceous matter. By washing about a gallon of this earth in water, an ounce of polythalamia and organic detritus may be obtained. The perfect shells are as fresh as if just dredged up from the sea; the soft parts--the membranous segments held together by their tubular connexion--in many instances remaining in the shell; these parts may be obtained by the solution of the shell in acid. When the Rotaliæ are rendered transparent by immersion in Canada balsam, their appearance, by transmitted light is identical with that exhibited by the fossil specimens; and if viewed by reflected light, the body may be seen occupying all the cells of the shell; but the segments are somewhat collapsed; evidently from the shrinking of the animal tissues after death.[342] [342] Two specimens are figured in my notice of fossil Foraminifera. Phil. Trans, p. iv. for 1846, pl. xxi. figs. 13, 14. The organisms of the Lincolnshire alluvium have been thoroughly investigated by Prof. Williamson; they comprise many species and genera, of the usual types; as Rotaliæ, Rosalinæ, Polystomellæ, Textulariæ, Lagenæ, Nodosariæ, &c. It is remarkable, that though a marine estuary deposit, no vestiges of diatomaceæ have been observed. The bed so rich in foraminifera, extends west and south-west of the Wash. Mr. Smith sent me a mass of sandy clay, from a well sunk in the town of March, to the depth of twenty-five feet, that was loaded with these beautiful organisms.[343] [343] The reader interested in these inquiries should peruse the highly interesting Memoir by Prof. Williamson, "On some Microscopical Objects found in the Mud of the Levant, and other Deposits." Manchester Phil. Trans, vol. viii.