A HISTORY OF BEDFORDSHIRE a cycadian stem, Cycadoidea yatesii* amongst other forms, have been found there. One of the most abundant of the derived fossils is Ammonites biplex. The bed has long been worked for the phosphate of lime which its coprolitic nodules contain, but all the workings in the county are now closed. At a higher horizon are beds of fullers' earth which have formed an item of local commerce for the last two centuries. This earth occurs in ' tabular lenticular masses,' 2 the areas and thicknesses of which vary considerably. It is an ' earthy hydrated silicate of alumina ' possessing saponaceous and detergent qualities which render it of use in certain industrial operations. Its colour varies in the different seams, its hues being sometimes sharply defined and at other times graduated ; the variations in shade are not accompanied by important alterations in chemical composition. A peculiarity of this mineral is that although it has an argillaceous base it has no coherent properties, being quite un- suited for the manufacture of pottery. For a long period it was obtained by sinking ' earth-wells,' usually unprotected by masonry or brickwork. This method was superseded about the year 1890, when two companies were formed for working the bed. The most modern machinery was employed and extensive mining operations were carried on for some time, but the concerns did not prove a financial success and the works were closed in 1901. Quite recently 3 a fossiliferous band of much interest has been dis- covered at the summit of the series in pits which have been opened on Shenley Hill near Leighton in order to obtain the silver sand before mentioned. The fossils occur in blocks of ' hard, horny-looking, gritty limestone ' between two undulating floors of iron-grit at the junction of the Lower Greensand with the Gault. These blocks, as well as the iron- grit bands, afford evidence of having been ' uncovered on the sea-floor,' where they have been eroded by current-action, but ' the shells embedded in the limestone, although fragile, are in splendid preservation, and rarely show even the slightest traces of abrasion.' Brachiopods are by far the most numerous ; next come the pectens ; spines of echinoderms are rather plentiful ; and amongst other fossils are joints of a crinoid, cara- paces of a crustacean, and polyzoa with which many fossils are encrusted. The chief interest in this discovery lies in the fact that the fauna has a decidedly Upper Greensand facies ; so much so that were not the strati- graphical position of the bed so clearly defined it might have been con- cluded to be of Upper Greensand age. Similar forms of life doubtless appear under similar conditions, but the connection is here so close that it leads to the inference that the Lower and Upper Greensand must some- where be continuous, the fauna of the Lower Greensand migrating under 1 Carruthers, Geo/. Mag. iv. 199, pi. ix. (1867). a A. C. G. Cameron, The Geology of the Fullers' Earth (1893). Mr. Cameron has added greatly to our knowledge of the geology of Bedfordshire, and this is the best account we possess of fullers' earth as it occurs in the county. 3 G. W. Lamplugh and J. F. Walker, ' On a Fossiliferous Band at the Top of the Lower Green- sand near Leighton Buzzard,' £>uart. Journ. Geol. Soc. lix. 234-65 (1903). 12
