AGES OF NATURE. 227 



of the bodies of vertebrae, but merely of their spinous pro- 

 cesses ; from which it must be inferred that the body of the 

 vertebra was cartilaginous, as it is in our Sturgeons. 



479. Recurring to what has been stated on that point, in 

 Chapter Twelfth, we thence conclude, that these ancient 

 fishes were not so fully developed as most of our fishes, 

 being, like the Sturgeon, arrested, as it were, in their devel- 

 opment ; since we have shown that the Sturgeon, in its or- 

 ganization, agrees, in many respects, with the Cod or Salmon 

 at an early age. 



480. Finally, there was, during the Paleozoic age, but 

 little variety among the animals of the different regions of 

 the globe ; and this may be readily explained by the pecu- 

 liar configuration of the earth at that epoch. Great moun- 

 tains did not then exist ; there were neither lofty elevations 

 ner deep depressions. The sea covered the greater part, if 

 not the whole, of the surface of the globe ; and the animals 

 which then existed, and whose remains have been preserved, 

 were all, without exception, aquatic animals, breathing by 

 gills. This wide distribution of the waters impressed a very 

 uniform character upon the whole Animal Kingdom. Be- 

 tween the different zones and continents, no such strange 

 contrasts of the different types existed as at the present 

 epoch. The same genera, and often the same species, were 

 found in the seas of America, Europe, Asia, Africa, and 

 New Holland ; from which we must conclude that the 

 climate was much more uniform than at the present day. 

 Among the aquatic population, no sound was heard. All 

 creation was then silent. 



481. THE SECONDARY AGE. Reign of Reptiles. The 

 Secondary age displays a greater variety of animals as well 

 as plants. The fantastic forms of the Palaeozoic age disap- 

 pear, and in their place we see a greater symmetry of shape. 

 The advance is particularly marked in the series of verte- 



