[Illustration: Fig. 193. Section from Hertfordshire, in England, to Sena, in France.] _White Chalk_ (2. and 3. Tab. p. 209.).--The highest beds of chalk in England and France consist of a pure, white, calcareous mass, usually too soft for a building stone, but sometimes passing into a more solid state. It consists, almost purely, of carbonate of lime; the stratification is often obscure, except where rendered distinct by interstratified layers of flint, a few inches thick, occasionally in continuous beds, but oftener in nodules, and recurring at intervals from 2 to 4 feet distant from each other. This upper chalk is usually succeeded, in the descending order, by a great mass of white chalk without flints, below which comes the chalk marl, in which there is a slight admixture of argillaceous matter. The united thickness of the three divisions in the south of England equals, in some places, 1000 feet.[211-B] The annexed section, fig. 193., will show the manner in which the white chalk extends from England into France, covered by the tertiary strata described in former chapters, and reposing on lower cretaceous beds. Among the conspicuous forms of mollusca wholly foreign to the tertiary and recent periods, and which we meet with in the white chalk, are the Belemnite, Ammonite, Baculite, and Turrilite, all genera of _Cephalopoda_, a family to which the living cuttle-fish and nautilus belong. [Illustration: Fig. 194. Portion of _Baculites Faujasii_. Maestricht and Faxoe beds and white chalk.] [Illustration: Fig. 195. Portion of _Baculites anceps_. Maestricht and Faxoe beds and white chalk.] [Illustration: Fig. 196. Turrilites. _a._ _Turrilites costatus._ Chalk marl. _b._ Same, showing the indented border of the partition of the chambers.] [Illustration: Fig. 197. Belemnites. _a._ _Belemnites mucronatus._ _b._ Same, showing internal structure. Maestricht, Faxoe, and white chalk.] Among the brachiopoda in the white chalk, the _Terebratulae_ are very abundant. These shells are known to live at the bottom of the sea, where the water is tranquil and of some depth (see figs. 198, 199, 200, 201.). With these are associated some forms of oyster (see figs. 202. and 204.), and other bivalves (figs. 203, 205, 206, 207, 208.). [Illustration: Fig. 198. _Terebratula plicatilis_, dorsal view. Upper white chalk.] [Illustration: Fig. 199. _Terebratula plicatilis_, side view.] [Illustration: Fig. 200. _Terebratula pumilus._ (_Magas pumilus_, Sow.) Upper white chalk.] [Illustration: Fig. 201. _Terebratula carnea._ Upper white chalk.] [Illustration: Fig. 202. _Ostrea vesicularis._ _Gryphaea globosa_, Min. Con. Upper chalk and upper greensand.] [Illustration: Fig. 203. _Pecten 5-costatus._ White chalk, upper and lower greensands.] [Illustration: Fig. 204. _Ostrea carinata._ Chalk marl, upper and lower greensands.] [Illustration: Fig. 205. _Crania Parisiensis_, inferior or attached valve. Upper white chalk.]