858 HISTORICAL GEOLOGY. 



C. A. White has described Cretaceous fossils, from the provinces of Sergipe, 

 Pernambuco, Para, Baliia, and elsewhere, in vol. vii. of the Archives of the 

 National Museum of Bio de Janeiro (1888). Darwin found Cretaceous fossils 

 in Fuegia, on the summit of Mount Tarn and near Port Famine, in the 

 Straits of Magellan ; and the author, in 1838, obtained Belemnites, probably 

 Cretaceous, on the shores of Orange Bay, near Cape Horn.^ 



Subdivisions. 



In view of the very wide and various distribution of these continental 

 Cretaceous beds, and the diversity of conditions as to water, depth, and tem- 

 perature under which they have originated, it is not to be expected that 

 there should be uniformity in the succession of rocks, either as to kinds or 

 as to fossils, since life varies in distribution with variations in the above 

 conditions. As a consequence, the Cretaceous formation is, even in Europe, 

 a formation with or without chalk, with or without limestone, with or with- 

 out sandstones, or chiefly made up of sandstones, and with wide variations in 

 the fauna. 



The principal British subdivisions are the following : — 



I. Lower Cretaceous. — The Neocomian of Thurman (1832), so named 

 from the Latin name of Neufchatel, Neocomium; including (1) the Wealden, 

 and (2) the Lower Greensand, but restricted by some to the Wealden. 



, XL Upper Cretaceous. — (1) The Oault or Albian, consisting of clay 

 with some greensand (it is made Lower Cretaceous by most European 

 geologists) ; (2) the Cenomanian, consisting of (a) the Upper Greensand, 

 marl beds, and the Gray Chalk of Folkestone ; (3) the Turonian, the Lower 

 White Chalk without flints ; (4) the Senonian, or the Upper Chalk with 

 flints. Above comes, in Denmark, (5) the Danian, or the Maestricht beds. 



The Wealden, including the Hastings sands below and the Weald clay 

 above, is about 1500 feet thick in southern England, where it was deposited 

 in the fresh waters of a delta over 20,000 miles in area. The Gault is 100 

 feet to 200 feet thick. The chalk without flints is a prominent formation 

 across from Flamborough Head, on the east coast of England, to the southern 

 coast, in Dorset. 



The "greensand" is like that of America (page 68). The chalk con- 

 sists chiefly of Foraminifers, or the shells of Rhizopods, but contains also 

 remains of Sponges and other forms of life, which together appear to indicate 

 that the beds were formed at depths of a few hundred feet — by some made 

 300 fathoms or more ; they are similar in general character to those now 

 accumulating over the sea-bottom. The flint nodules occur in layers in the 

 chalk. The facts seem to show that the sea-bottom, on account of depth or 

 for some other reason, was in a more favorable condition for growing siliceous 

 Sponges in some places than at others. The material of a flint nodule, while 



1 For a note on the discovery, see Am. Jour. Sc, xxxv., 83, 1888. 



