CHAPTER IV. 



MESOZO1C ERA. AGE OF REPTILES. 



THE Paleozoic era was very long and diversified. It 

 consisted of three ages the age of Invertebrates, the age 

 of Fishes,, and the age of Acrogens and Amphibians. 

 The Mesozoic era, on the contrary, consists of but one 

 age the age of Reptiles. Never, in the history of the 

 earth, were reptiles so abundant, of such size and variety, 

 or so highly organized, as then. 



Characteristics of the Age. The characteristics of 

 this age are the culmination of the class of reptiles, and 

 the class of cephalopod mollusks among animals, and of 

 cycads among plants ; and the first introduction of mam- 

 mals and birds, and, in the last part, of Teleost fishes and 

 Dicotyledonous trees. The most striking characteristic is 

 the culmination of reptiles, and this, therefore, gives it 

 its name. 



Subdivisions. The Mesozoic era and Reptilian age 



is divided into three periods 



C 3. Cretaceous. viz. : 1. Triassic, on ac- 



Mesozoic rocks. I 2. Jurassic. count of its distinct three- 



[ 1. Triassic. fold division in Germany, 



where first well studied. 



2. Jurassic, on account of its splendid development in 

 the folded structure of the Jura Mountains. 3. Creta- 

 ceous, on account of the chalk of England and France 

 being one of its members. 



These three are very distinct periods in Europe, but 

 in America the Trias and Juras are closely connected 

 324 



