736 GEOLOGY 



THE LOWER CRETACEOUS IN OTHEK CONTINENTS* 



Europe. The deposits in some of the lakes, marshes, estuaries, 

 and other lodgment basins which resulted from the geographic 

 changes at the close of the Jurassic period in Europe, record the 

 transition from that period to the early Cretaceous. The inter- 

 ruption of marine sedimentation in Southern Europe was not so 

 general, and over considerable areas the Lower Cretaceous succeeds 

 the Jurassic conformably, both being marine. In Russia, it is 

 difficult in many places, to define the upper limit of the Jurassic, 

 so complete is the gradation into the (Lower) Cretaceous. 



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

 is there used, is divisible into two major parts, a lower and an upper, 

 as distinct as successive systems usually are. As in North America, 

 the lower division is much more restricted in its distribution than 

 the upper, and is, to a large extent, of non-marine origin. 



During the initial stages of the Lower Cretaceous, the areas of 

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

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

 them by bringing them beneath a common sea. The Lower Creta- 

 ceous formations embrace all sorts of clastic rocks, together with 

 limestone, glauconitic beds, beds of coal (northwestern Germany), 

 and iron ore. They embrace, indeed, about all varieties of sedi- 

 mentary rock except chalk, the rock from which the name "Creta- 

 ceous" was derived. In southern Europe, much of the system is 

 limestone. 



Other continents. In other continents, the Lower and Upper 

 Cretaceous have been less clearly differentiated; yet enough is 

 known to show that the Lower and Upper Cretaceous systems are, 

 in general, markedly different, both in origin and distribution. 

 Lower Cretaceous formations of marine origin are wide-spread in 

 Siberia, Japan, and the southern part of Asia, but in limited areas 

 only in most other parts. The system is believed to have slight 

 development in the mountain regions of northwestern A /rim. where 

 it is really an extension of the Lower Cretaceous of southern Europe 



1 The term Comanchean is not applied to the Lower Cretaceous forma- 

 tions outside of North America. 



