256 LOWER GREENSAND. [Ch. XVIIT. 



life at this period, exerted their full intensity through the Indian, Euro- 

 pean, and American seas."^ Here, as in North and South America, the 

 cretaceous character can be recognized even where there is no specific 

 identity in the fossils ; and the same may be said of the organic type of 

 those rocks in Europe and India which occur next to the chalk in the 

 ascending and descending order, namely, the Eocene and the Oolitic. 



CHAPTER XVIII. 



LOWER CRETACEOUS AND WEALDEN FORMATIONS. 



Lower Greensand — Term " E'eocomian" — Atherfield section, Isle of Wight — 

 Fossils of Lower Greensand — Wealden Formation — Freshwater strata interca- 

 lated between two marine groups — Weald Clay and Hastings Sand — Fossil 

 shells, fish, and plants of Wealden — Their relation to the Cretaceous type — 

 Geographical extent of Wealden — Movements in the earth's crust to which the 

 Wealden owed its origin and submergence — Flora of the Lower Cretaceous and 

 Wealden Periods. 



The term " Lower Greensand" has hitherto been most commonly ap- 

 plied to such portions of the Cretaceous series as are older than the Gault. 

 But the name has often been complained of as inconvenient, and not with- 

 out reason, since green particles are wanting in a large part of the strata 

 so designated, even in England, and wholly so in some European coun- 

 tries. Moreover, a subdivision of the Upper Cretaceous group has hke- 

 wise been called Greensand, and to prevent confusion the terms Upper 

 and Lower Greensand were introduced. Such a nomenclature naturally 

 leads the uninitiated to suppose that the two formations so named are of 

 somewhat co-ordinate value, which is so far from being true, that the 

 Lower Greensand, in its widest acceptation, embraces a series nearly as 

 important as the whole Upper Cretaceous group, from the Gault to the 

 Maestricht beds inclusive ; while the Upper Greensand is but one sub- 

 ordinate member of this same group. Many eminent geologists have, 

 therefore, proposed the term "Neocomian" as a substitute for Lower 

 Greensand ; because, near ISTeufchatel (Neocomum), in Switzerland, these 

 Lower Greensand strata are well developed, entering largely into the 

 structure of the Jura mountains. By the same geologists the Wealden 

 beds are usually classed as " Lower Neocomian," a classification which 

 will not appear inappropriate when we have explained, in the sequel, the 

 intimate relation of the Lower Greensand and Wealden fossils. 



Dr. Fitton, to whom we are indebted for an excellent monograph on 

 the Lower Cretaceous (or Greensand) formation as developed in England, 

 gives the following as the succession of rocks seen in parts of Kent. 



* See Forbes, Quart. Geol. Journ, vol. i. p. 79. 



