TEIASSIC PERIOD. 403 



m. MESOZOIC TIME. 



The Mesozoic or Mediaeval 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 cul- 

 mination and incipient decline of two great types in the Animal King- 

 dom, the Reptilian and Molluscan, and of one in the Vegetable King- 

 dom, the Cycadean. It is also remarkable as the era of the first Mam- 

 mals, — the first Birds, — the first of the Common or Osseous Fishes, 

 — and the first Palms and Angiosperms. 



The age is divided into three periods. Beginning with the earliest, 

 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. 



1. TRIASSIC PERIOD (16). 



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

 division which this formation presents in Germany. This division is 

 local and unessential : it does not occur in other remote parts of 

 Europe, or in England, and is not to be looked for in distant con- 

 tinents. 



1. American. 

 The formation in Eastern North America, here included, covers part 

 or all of the Jurassic period, and perhaps also the Wealden. It is not 

 supposed to reach back into the Permian, because there are no Paleo- 

 zoic forms among the plants or animals. 



1 Rocks : kinds and distribution. 



The rocks are met with in three 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 Moun- 

 tains ; 3, on the Pacific Border. 



1. On the Atlantic Border, the beds occur in long narrow strips, 

 parallel with the mountains or the coast-line, and occupy valleys that 



