Part 31 (1/2)

[192-A] Cuvier, Oss. Foss., tom. iii. p. 255.

[194-A] This species is found both in the Paris and London basins.

[197-A] Coquilles caracterist. des Terrains, 1831.

[197-B] Quarterly Geol. Journal, vol. iii. p. 353.

[199-A] Prestwich, Quart. Geol. Journ. vol. iii. p. 386.

[199-B] Palaeont. Soc. Monograph. Rept. pt. ii. p. 61.

[202-A] For description of Eocene Cephalopoda, see Monograph by F. E.

Edwards, Palaeontograph. Soc. 1849.

[203-A] Annals of Nat. Hist. vol. iv. No. 23. Nov. 1839.

[206-A] Murchison, Quart. Journ. of Geol. Soc. vol. v., and Lyell, vol. vi.

1850. Anniversary Address.

[206-B] See paper by the author, Quart. Journ. Geol. Soc. vol. iv, p. 12.; and Second Visit to the U. S. vol. ii. p. 59.

[206-C] Quart. Journ. Geol Soc. vol. vi. p. 32.

[207-A] See Memoir by R. W. Gibbes, Journ. of Acad. Nat. Sci. Philad.

vol. i. 1847.

[208-A] Lyell, Quart. Journ. Geol. Soc. 1847, vol. iv. p. 15.

CHAPTER XVII.

CRETACEOUS GROUP.

Divisions of the cretaceous series in North-Western Europe--Upper cretaceous strata--Maestricht beds--Chalk of Faxoe--White chalk--Characteristic fossils--Extinct cephalopoda--Sponges and corals of the chalk--Signs of open and deep sea--Wide area of white chalk--Its origin from corals and sh.e.l.ls--Single pebbles in chalk--Siliceous sandstone in Germany contemporaneous with white chalk--Upper greensand and gault--Lower cretaceous strata--Atherfield section, Isle of Wight--Chalk of South of Europe--Hippurite limestone--Cretaceous Flora--Chalk of United States.

Having treated in the preceding chapters of the tertiary strata, we have next to speak of the uppermost of the secondary groups, called the Chalk or Cretaceous (No. 6. Table, p. 103.), because in those parts of Europe where it was first studied its upper members are formed of that remarkable white earthy limestone, termed chalk (_creta_). The inferior division consists, for the most part, of clays and sands, called Greensand, because some of the sands derive a bright green colour from intermixed grains of chloritic matter. The cretaceous strata in the north-west of Europe may be thus divided[209-A]:

_Upper Cretaceous._

1. Maestricht beds and Faxoe limestone.

2. Upper white chalk, with flints.

3. Lower white chalk, without flints, pa.s.sing downwards into chalk marl, which is slightly argillaceous.

4. Upper greensand.

5. Gault.

_Lower Cretaceous._

6. Lower greensand--Ironsand, clay, and occasional beds of limestone (Kentish rag).