FORMATIONS AND PHYSICAL HISTORY 527 



Lower Cretaceous in Other Continents l 



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 interrup- 

 tion of marine sedimentation in Southern Europe was not so general, 

 and over considerable areas the Lower Cretaceous succeeds the 

 Jurassic conformably, both being marine. 



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

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

 the sea united many of them. The Lower Cretaceous formations 

 include 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 sedimentary rock except 

 chalk, the rock from which the name "Cretaceous" 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 gen- 

 eral, markedly different, both in origin and distribution. Marine 

 Lower Cretaceous is well developed in the western part of the 

 Andes Mountains. It is widespread also in the northern part of 

 South America, but not elsewhere east of the Andes. It is generally 

 absent about the borders of the South Atlantic. On the other hand, 

 marine Lower Cretaceous beds occur in many places about the 

 southern Pacific and Indian Oceans. Lower Cretaceous formations 

 of marine origin are widespread also in Siberia and Japan. The 

 system is believed to have slight development in the mountains 

 of northwestern Africa, where it is really an extension of the Lower 

 Cretaceous of southern Europe, and is unconformable beneath the 

 Upper Cretaceous, and in South Africa. 



Geographic changes of importance occurred in various parts of 

 the earth at the close of the early Cretaceous period, as shown by 

 (i) the unconformities between the Lower (Comanchean) and 

 Upper Cretaceous systems, as at some points in Europe, north 

 Africa, Australia, and South America, and (2) in the differences in 

 their distribution. 



1 The term Comanchean is not applied to the Lower Cretaceous formations 

 outside of North America. 



