THE MESOZOIC AGES. 



189 



teristic feature. In the Trias, as in the Permian, 

 the continents of the northern hemisphere presented 

 large land areas, and there were lagoons and land- 

 locked seas in which gypsum, magnesian limestones, 

 and rock salt were thrown down, a very eminent 

 example of which is afforded by the great salt deposits 

 of Cheshire. There were also tremendous outbursts 

 of igneous activity along the margins of the con- 

 tinents, more especially in Eastern America. But with 

 all this there was a rich land flora and a wonderful 

 exuberance of new animal life on the land; and in 

 places there were even swamps in which pure and 

 valuable beds of coal, comparable with those of the 

 old coal formation, were deposited. 



The triple division of the Trias as a cycle of the 

 earth's history, and its local imperfection, are well 

 seen in the European development of the group, 

 thus : 



The Trias is succeeded by a great and complex 

 system of formations, usually known as the Jurassic, 

 from its admirable development and exposure in the 



