126 GEOLOGY. 



converted into dry land, while other areas emerged from the sea, but 

 were not so situated as to be drained. In the deposits of some of 

 the lakes, marshes, estuaries, and other lodgment basins which resulted 

 from these geographic changes, the transition from the Jurassic period 

 to the Early Cretaceous x is recorded. The oldest deposits in these 

 non-marine waters in England (Purbeck beds) are classed as Jurassic, 

 while later but conformable beds (Wealden) are generally regarded 

 as Cretaceous. The interruption of marine sedimentation in southern 

 Europe at the close of the Jurassic was less general, and over con- 

 siderable areas the Lower Cretaceous succeeds the Jurassic conform- 

 ably, both being marine. In Russia, the gradation from Jurassic 

 to Lower Cretaceous is often so complete that no plane of division 

 can be drawn between them. 



The European areas of deposition may be grouped in two principal 

 provinces, a northern and a southern. To the former belong the Cre- 

 taceous beds of England, central Europe, and Russia; to the latter, 

 those of southern France, Spain, Italy, and the Balkan peninsula. 

 The two provinces were separated by a series of islands which now 

 form the highlands of France, southern Germany, and Austria. The 

 northern province seems also to have been partly shut off from the 

 Atlantic to the west. The southern province was continued east over 

 the corresponding latitudes of Asia, and south over the northern border 

 of Africa. 



In Europe, as in North America, the Cretaceous, as that term has 

 been used, is divisible into two major parts, a Lower and an Upper, 

 as distinct as successive systems usually are. In general, the Lower 

 is much more restricted in its distribution than the Upper, and is, 

 to a larger extent, of non-marine origin. In both these respects, 

 the Lower Cretaceous of Europe is in harmony with the Comanchean 

 of North America. 



During the initial stages of the Early Cretaceous period, the areas 

 of sedimentation were more or less isolated; but later, advances of 

 the sea enlarged some of these separated areas, and finally united 

 many of them by bringing them beneath a common sea. The expan- 

 sion of the epicontinental sea was still greater at the opening of the 



1 Early Cretaceous is here used instead of Comanchean for the time during which 

 the strata corresponding to the Comanchean of the North American continent were 

 laid down. 



