THE TERTIARY SYSTEM. 



737 



Mount Parnassus. 



N geological chronology, the cretaceous deposits conclude the 

 secondary series of strata; and, glancing back at the formations 

 included in the vast interval extending from the close of 

 the primary age, when the gneissic rocks and mica schists had been produced, to the 

 termination of the chalk era, we have indubitable evidence of a grand general revo 

 lution being in progress in the physical condition of our planet, originating sedimentary 

 deposits, which, mineralogically, differ more or less from the earliest strata, according as 

 their relative antiquity is inferior. During the secondary period we have marked the 

 dawn and development of organic life upon the globe as its leading characteristic ; the 

 abundant flora of the carboniferous era, and fauna of the oolite ; and the development of 

 life in numerous organisms of the animal and vegetable kingdoms, which have now no 

 living representative in field, or flood, or forest : but during the tertiary epoch, so called 

 from its deposits being of newer date than the secondary, we are presented with strata 

 still more diverse in composition from the ancient rocks, and with fossil contents which 

 assimilate to the forms of living existence. Before proceeding farther, it may be well 

 to recapitulate the leading botanical and zoological changes which mark the interval 

 reaching from the first appearance of organic life to the close of the cretaceous era. 

 Two extensive groups of land plants had flourished and passed away. The luxuriant 

 vegetation of the carboniferous system, with its sigillariaB, lepidodendra, and calamites, 

 vanished with it, and the new races of zamias and cycadene, which appear in the weald, 

 departed from the northern sites before the completion of the chalk. The inhabitants of 

 the ocean, of many races zoophyta, mollusca, and cartilaginous fishes came into being, 

 and became extinct, during the period under notice, some enduring for a longer interval 



