44 



PRINCIPLES OF PALEONTOLOGY. 



IDEAL SECTION OF THE CRUST OF THE EARTH. 

 Fig. 17. 



y Post-tertiary and Recent, 

 r Pliocene. 



Miocene. 

 Eocene. 



Cretaceous. 



Oolitic or Jurassic. 



Triassic. 

 Permian. 



Carboniferous. 



Devonian or Old Red Sand- 

 stone. 



Silurian. 



Cambrian. 

 Huronian. 



Laurentian. 



