CRETACEOUS PERIOD. 487 



of level ; and their thickness, — 10,000 feet in the Rocky Mountain 

 region, and half that in California, — is proof of profound subsidences 

 in progress ; but all went on regularly and without intervening dis- 

 turbances. 



In Europe, during the progress of the Mesozoic, the rocks, Triassic, 

 Jurassic, and Cretaceous, appear to have" been laid down for the most 

 part conformably, with few examples of non-concordance, yet with 

 those variations in their distribution that arise from variations of the 

 ocean's level, as a consequence of gentle heavings of the earth's crust. 

 There were thus elevations and depressions producing the varying 

 geography of the age, and successive destructions of species attending 

 them, so that only a very small number of Liassic species has been 

 foimd in the Oolyte, and less than a dozen of the Jurassic in the Cre- 

 taceous ; while also many subordinate eras were separated by epochs 

 of destruction. 



A disturbance took place, between the Triassic and Jurassic periods, 

 in the region of the Thuringian Forest and the frontiers of Bohemia 

 and Bavaria, the Jurassic beds overlying unconformably the Triassic. 

 This system of uplifts is named by De Beaumont the System of the 

 Thuringian Forest ; and the trend mentioned is N. 50° W. Again, 

 between the Jurassic and Cretaceous, was formed De Beaumont's 

 System of the Cote D' Or, having the trend N. 50° E. 



The rocks of the Cretaceous and Jurassic are very nearly hori- 

 zontal, in the great Anglo-Parisian region — the part of 'the German 

 Ocean basin now exposed to view. 



5. DISTURBANCES CLOSING MESOZOIC TIME. 



The epoch of mountain-making which took place after the Mesozoic 

 era, in North America, was delayed till the middle of the Eocene 

 period in the Tertiary age, unless the coal-bearing series of the Rocky 

 Mountains and California are true Cretaceous. This question of age 

 is still undecided ; but the evidence appears to favor most strongly the 

 view of their Eocene age. This reference of the epoch to the Middle 

 Eocene puts the North American movements of the crust nearly into 

 harmony with the European and Asiatic ; for, there, some of the 

 highest mountains date from the close of the Nummulitic section 

 of the Eocene. 



But, if the mountain-making took place at a later date, there were 

 other changes of vast influence ; for at the close of the Cretaceous 

 occurred one of the most complete exterminations of species of which 

 there is record. 



No species of the European Cretaceous is known to occur in the 

 Tertiary formation, and none of Asia or of Eastern North America. 



