g14 ~ - STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
Russia, where it covers many thousand square miles, up to the southern 
end of the Ural chain. ‘l'o the south of the central axis in France, it 
underlies the great basin of the Garonne, flanks the chain of the Pyrenees 
on both sides, spreads out largely over the eastern side of the Spanish 
table-land, and reappears on the west side of the crystalline axis of that 
region along the coast of Portugal. It is seen at intervals along the 

* glee, 
north and south fronts of the Alps, extending down the valley of the. q 
Rhone to the Mediterranean, ranging along the chain of the Apennines 
into Sicily and the north of Africa, and widening out from the eastern 
shores of the Adriatic through Greece, and along the northern base of the | 
Balkans to the Black Sea, round the southern shores of which it ranges 
in its progress into Asia, where it again covers an enormous area. 
A series of rocks covering so vast an extent of surface must needs 
present many differences of type, alike in their lithological characters 
and in their organic contents. They bring before us the records of a 
time when a continuous sea stretched over the centre and most of the 
south of Europe, covered the north of Africa, and swept eastwards to the 
far east of Asia. There were doubtless many islands and ridges in this 
wide expanse of water, whereby its areas of deposit and biological pro- 
vinces must have been more or less sharply defined. Some of these 
barriers can still be traced, as will be immediately pointed out. 
The Cretaceous system of Europe has been subdivided as follows :? 
Senonian. 
Turonian. 
| Cenomanian. 
| Gault. 
a ets Neocomian, including a prevalent marine type, and also in some 
(rae: parts of the western districts a fluviatile (Wealden) type. 
Danian. 
Upper . | 
While there is sufficient paleontological similarity to allow a general 
parallelism to be drawn among the Cretaceous rocks of western Hurope, 
there are yet strongly marked differences pointing to very distinct con- 
ditions of life, and probably, in many cases, to disconnected areas of 
deposit. Having regard to these geographical variations, a distinct 
northern and southern province, as above stated (p. 802), can be recog- 
nized ; but Giimbel has proposed a further grouping into three great 
regions :—(1) the northern province, or area of white chalk with Belem- 
nitella, comprising England, northern France, Belgium, Denmark, West- 
phalia, &c.; (2) the Hercynian province, or area of Hxogyra columba, 
embracing Bohemia, Moravia, Saxony, Silesia, and central Bavaria; and 
(3) the southern province, or area of hippurites, including the regions of | 
France south of the basin of the Seine, the Alps, and southern Europe.” 
Britain.*—The Purbeck beds bring before us evidence of a great 
change in the geography of England towards the close of the Jurassic 
period. They show how the floor of the sea in which the thick and 
varied formations of that period were deposited came to be gradually 
1 See notes on pp. 824, 825. 
2 Geognost, Beschreib. Ostbayer. Grenzgebirg. 
* Consult Conybeare and Phillips, Geology of England and Wales, 1822; Fitton 
Ann. Philos. 2nd ser. viii. 379; Trans. Geol. Soc. 2nd ser. iv. 103; Dixon’s Geology of 
Sussex, edit. 'T. Rupert Jones, 1878; Phillips's Geology of Oxford and the Thames Valley ; 
recent papers on the English Cretaceous formations are quoted in subsequent footnotes. 
