Beautiful Cidarites and their spines may be collected in the Oolitic strata at Calne, Chippenham, Bath, &c.; and in the coralline Oolite near Faringdon; and of Saleniæ, in the Greensand gravel-pits near that town. The Upper Greensand near Warminster, and at Chute Farm, near Heytesbury, abounds in small Cidaritidæ and other echinites. The large sinuated Clypeus is found in great perfection in the Oolite at Malton, Cheltenham, Gloucester, &c. The cretaceous echinites are to be met with in most localities of the white chalk. The chalk-pits in Kent, especially at Gravesend, Northfleet, Chatham, &c. are rich in Cidarites, and their spines. The Galerites, and Ananchytes, are also very fine and numerous; and the softness of the chalk renders their extrication from the stone a delightful task for the young geologist. Specimens of the common kinds of fossil Echinoderms may be obtained at moderate prices of the dealers named in the Appendix. There is a matchless suite of fossil Echinidæ in the British Museum, which has been arranged and named by Mr. S. P. Woodward, and is now the most instructive and interesting collection extant. It contains examples of the following genera, viz., Ananchytes, Echinocorys, Echinolampas, Holaster, Galerites, Cidaris, Diadema, Acrosalenia, Glypticus, Disaster, Pygurus, Clypeaster, Scutella, Salmasis, Echinocyanus, &c. There is also a good series of echinital spines. CHAPTER X. FOSSIL FORAMINIFERA--MICROSCOPICAL EXAMINATION OF CHALK AND FLINT. "Where is the dust that has not been alive?" Young. That those infinitesimal forms of animal existence which swarm throughout the waters of the ocean, but whose presence can only be made manifest by the aid of the microscope, are preserved in a fossil state,--that their durable remains constitute mountain ranges, and form the subsoil of extensive regions,--and that the most stupendous monuments erected by man are constructed of the petrified relics of beings invisible to the unassisted eye,--are facts not the least astounding of those which modern Geology has revealed.