A local unconformity separating the chalk and gault in parts of East Anglia points to another local uplift with its accompanying complications in the characters of the strata. After the uplift had ceased, general depression must have occurred, and the various divisions of the chalk were accumulated in a fairly open sea, though, for reasons to be given presently, this was probably of no great lateral extent, save when united with the open ocean, probably in a manner similar to the connexion between the Gulf of Mexico and the Atlantic.

The general variations in the lithological characters of the various members of the Cretaceous system will probably be rendered clearer by reference to the accompanying diagram ([Fig. 24]) representing the variations when traced across England from south to north[101].

[101] For information concerning the British Cretaceous beds, see Topley and Foster, "Geology of the Weald," Mem. Geol. Survey, 1875; Bristow and Strahan, "Geology of the Isle of Wight," Mem. Geol. Survey, 1889; Lamplugh, "On the Speeton Clay," Q. J. G. S., vol. XLV. p. 575, and "The Speeton Series in Yorkshire and Lincolnshire," ibid., vol. LII. p. 179; Barrois "Recherches sur le Terrain Crétacé supérieur de l'Angleterre et d'Irlande," Lille, 1876; and various papers by Messrs Hill and Jukes-Browne, in the Quarterly Journal of the Geological Society and Geological Magazine of recent years. For the Scotch deposits consult a paper by Prof. Judd, Q. J. G. S., vol. XXXIV. p. 736, and for those of Ireland, see Hume, Q. J. G. S., vol. LII. p. 540.

Fig. 24.

The clue to the physical geography of Britain during Cretaceous times is furnished to a considerable extent by study of the foreign deposits. In Northern Europe the Cretaceous beds of England are met with in Northern France, and there the characters are generally speaking similar to those of our British deposits. In Germany shallower water conditions prevailed, the lower beds gradually disappear, and the upper beds are replaced by mechanical sediments of various degrees of coarseness, becoming on the whole coarser, as one travels eastward, so that in Saxony the chalk is partly replaced by arenaceous deposits (the 'Quader' sandstones) which are responsible for the remarkable scenery of the Elbe district above Dresden. In passing northwards, indications of similar change are noted in the deposits of Denmark and Scania, whilst to the south, we get a complete change in the character of the rocks, after crossing the Loire in France, and a similar change is observable in districts lying further east. Furthermore, as will be noted more fully in a subsequent paragraph, the character of the Upper Cretaceous flora indicates the existence of a large tract of land lying to the north and north-west of Europe, so that it would appear that the Cretaceous rocks of Northern Europe were deposited in a gulf-like expansion of a western ocean, bounded on the north by Scandinavia, on the west by eastern Germany, and on the south by a ridge running eastward from the mouth of the Loire[102]. We may speak of this gulf as the Chalk gulf. To the south of the presumed ridge the character of the strata alters, and also that of the included organisms. This southern type of Cretaceous rocks is one which is very widely spread, being found in Europe south of the Loire, and of the Alps, and in Greece and Turkey, while it also occurs in the northern parts of Africa. The beds of this type are traceable through Asia Minor into India and to the shores of the Indian Ocean, indicating the existence of a widespread Cretaceous ocean, which is sometimes spoken of as the Hippurite-limestone sea, for reasons which will eventually appear. The deposits are largely formed of hard limestone which is very different in its character from the soft chalk of the northern gulf.

[102] The reader will find the existence of this gulf maintained and supported by a considerable mass of detail in Mr A. R. Wallace's Island Life.

The climatic conditions which prevailed during Cretaceous times were apparently similar in most respects to those of the preceding Jurassic period, and as already stated the climatic zones which Neumayr defined for Jurassic times are also maintained by him to have existed during the Cretaceous period. The existence of cold has sometimes been inferred from the presence of large foreign blocks in the chalk, especially at its base, but if these are due to the transport, they might well be caused by masses of floating ice, which are often found at considerable distances from the coast in temperate regions after the break-up of the frost which succeeds an unusually hard winter. The flora and fauna are not suggestive of severe conditions.