414 MESOZOIC TIME — REPTILIAN AGE. 



III. MESOZOIC TIME. 



The Mesozoic or Medieval time in the Earth's history comprises 

 a single age only, — the Reptilian. 



REPTILIAN AGE. 



The Age of Reptiles is especially remarkable as the era of the 

 culmination and incipient decline of two great types in the Animal 

 Kingdom, the Reptilian and Molluscan, and of one in the Vegetable 

 Kingdom, the Cycadean. It is also remarkable as the era of the 

 first Mammals, — the first Birds, — the first of the Common or Osseous 

 Fishes, — and the first Palms and Angiosperms (p. 166). 



The Age is divided into three periods. Beginning with the ear- 

 liest, they are : — 



1. The Triassic Period. 



2. The Jurassic Period. 



3. The Cretaceous or Chalk Period. 



These periods are well denned in European Geology. But in 

 North American the separation of the first and second has not yet 

 in all regions been clearly made out. 



TRIASSIC PERIOD (16). 



The name Triassic, given to this period, alludes to a threefold 

 division which this formation presents in Germany. This division 

 is a local character, and unessential : it does not occur in other 

 remote parts of Europe, or in England, and is not to be looked for 

 in distant continents. 



1. AMERICAN. 



The formation referred to the Triassic in America may belong 

 in part to the Jurassic period. It does not reach back into the 

 Permian, because there are no Palaeozoic forms among the plants 

 or animals. It is also true that there are no species that ai*e pecu- 

 liarly Jurassic, while many of them correspond in character with 

 those of the foreign Triassic. 



I. Rocks : kinds and distribution. 



The rocks are met with in two distinct regions : — 1, in the Atlantic 

 border region, between the Appalachians and the coast; 2, in the 

 Western Interior region, over part of the slopes of the Rocky Mountains. 



On the Atlantic border the beds occur in long narrow strips 



