CHAPTER XX 



MESOZOIC ERA: THE AGE OF REPTILES 



The Mesozoic is divided into four periods, as given below : 



Cretaceous Periods 



Jurassic Period 



Triassic Period 



Upper Cretaceous 



Lower Cretaceous 

 (Comanchean) 



The word comes from the Latin 

 creta, meaning chalk, because of 

 the great, thickness of the chalk 

 of this period in England and 

 France. 



So named because of the fine 

 development of the strata of this 

 period in the Jura Mountains. 



So named because of the three- 

 fold development in Germany 

 where the strata were first care- 

 fully studied. 





Physical Geography during the Mesozoic 



Triassic 



Atlantic and Gulf Coasts. — A number of points seem to be well 

 established concerning the distribution of land and water in North 

 America during the Triassic (Fig. 480). (1) The complete absence, 

 so far as known, of marine sediments from the eastern half of the 

 continent indicates that the coast line was farther east than now 

 and that during the entire period the lands were being reduced by 

 erosion. Indeed, it is possible that not only Newfoundland but even 

 Greenland and Iceland were united to the continent. (2) The presence 

 of Triassic rocks in long, narrow bands roughly parallel to the Atlantic 

 coast, that stretch from Nova Scotia to North Carolina, the longest of 

 which extends from the Hudson River across New Jersey, southeastern 

 Pennsylvania, through Maryland and Virginia, formerly gave rise 

 to the opinion that these deposits were formed in tidal estuaries whose 

 waters for the most part were brackish or nearly fresh. It seems 

 more probable, however, that the deposits were not formed in con- 



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