Among the formations alluded to, the Thanet Sands of Prestwich have been sufficiently described in the last chapter, and classed as Lower Eocene. To the same tertiary series belong the Belgian formations, called by Professor Dumont, Landenian. On the other hand, the Maestricht and Faxoe limestones are very closely connected with the chalk, to which also the Pisolitic limestone of France is referable. Classification of the Cretaceous Rocks.—The cretaceous group has generally been divided into an Upper and a Lower series, the Upper called familiarly _the chalk,_ and the Lower _the greensand_; the one deriving its name from the predominance of white earthy limestone and marl, of which it consists in a great part of France and England, the other or lower series from the plentiful mixture of green or chloritic grains contained in some of the sands and cherts of which it largely consists in the same countries. But these mineral characters often fail, even when we attempt to follow out the same continuous subdivisions throughout a small portion of the north of Europe, and are worse than valueless when we desire to apply them to more distant regions. It is only by aid of the organic remains which characterise the successive marine subdivisions of the formation that we are able to recognise in remote countries, such as the south of Europe or North America, the formations which were there contemporaneously in progress. To the English student of geology it will be sufficient to begin by enumerating those groups which characterise the series in this country and others immediately contiguous, alluding but slightly to those of more distant regions. In the table (p. 283) it will be seen that I have used the term Neocomian for that commonly called “Lower Greensand;” as this latter term is peculiarly objectionable, since the green grains are an exception to the rule in many of the members of this group even in districts where it was first studied and named. UPPER CRETACEOUS OR CHALK PERIOD. Maestricht Beds and Faxoe Limestone. Upper White Chalk, with flints. Lower White Chalk, without flints. Chalk Marl. Chloritic series (or Upper Greensand). Gault. LOWER CRETACEOUS OR NEOCOMIAN. Marine Fresh-water Marine: Upper Neocomian, see p.308 Marine: Middle Neocomian, see p.312 Marine: Lower Neocomian, see p.312 Wealden Beds (upper part). Belemnitella mucronata. Belemnitella mucronata, Maestricht, Faxoe, and White Chalk. _a/_ Entire specimen, showing vascular impression on outer surface, and characteristic slit. _b._ Section of same, showing place of phragmocone.[1]