414: MESOZOIC ERA— AGE OF REPTILES. 



CHAPTER IV. 

 MESOZOIC ERA— AGE OF REPTILES. 



The Palaeozoic era, we have seen, was very long, and very diversi- 

 fied in dominant types, of both animals and plants. It was during this 

 long era that originated nearly all the great branches, and even sub- 

 branches, of the organic kingdom. We have during this era, therefore, 

 three very distinct ages : an age of Invertebrates, an age of Fishes, and 

 an age of Acrogens and Amphibians. The Mesozoic was far less long 

 and far less diversified in dominant types. It consists of only one age, 

 viz., the age of Reptiles. Never in the history of the earth, before or 

 since, did this class reach so high a point in numbers, variety of form, 

 size, or elevation in the scale of organization. 



General Characteristics. — The general characteristics of the Meso- 

 zoic era are the culmination of the class of Reptiles among animals, and 

 of Oycads among plants, and the^rs^ appearance of Teleosts (common 

 osseous fishes), Birds ; Mammals among animals, and of Palms and 

 Dicotyls among trees. 



Subdivisions. — The Mesozoic era is divided into three periods, viz. : 

 1. Triassic, because of its threefold development where first studied in 

 Germany ; 2. Jurassic, because of the splendid development of its 

 strata in the Jura Mountains ; 3. Cretaceous, because the chalk of Eng- 

 land and France belongs to this period. 



Mesozoic Era. - 



" 3. Cretaceous period. 



2. Jurassic period. 



1. Triassic period. 



In this country the Triassic and Jurassic are not so distinctly sepa- 

 rable as they are in Europe, nor as' they are from the Cretaceous. They 

 form, in fact, one series, and if the Mesozoic had been studied first in 

 this country, the whole would probably have been divided into only two 

 periods. We shall therefore speak of the Mesozoic of this country as 

 consisting of two periods, viz., the Jura- Trias and the Cretaceous. On 

 account of their fuller development in Europe, it will be best to speak, 

 first, of the Triassic generally, then of the Jurassic generally, taking 

 our illustrations mainly from European sources, and then of the Jura- 

 Trias in America. Also, on account of the comparative poverty of the 

 Trias in remains, we will dwell much less on this period than on the 

 subsequent Jurassic ; for in this latter period culminated all the dis- 

 tinctive characters of the Reptilian age. 



