Geological Epochs. 19 



form, in the first place, a correct idea of the period of their 

 appearance. This manner of viewing biological questions has 

 become as essential as the organization itself of living be- 

 ings, taken as the basis of their systematic arrangement. In 

 order to acquire a truly philosophical knowledge of animals 

 in general, we ought, therefore, to endeavour, before every 

 thing else, to determine the state of the animal kingdom at 

 the time of its first appearance on the surface of the globe ; 

 then to study the organic changes it has undergone in the 

 different epochs which have preceded the establishment of 

 the present order of things ; and, lastly, to specify, as far as 

 possible, the geological limits of these intermediate changes. 

 At no period have geologists made greater and more constant 

 eff'orts than in our own day, to determine the relative ages of 

 the diff^erent formations which constitute the stratified crust 

 of our globe, and the rigorous limits of formations. These 

 investigations have naturally led to a greater subdivision of 

 the epochs hitherto admitted as distinct. As the study of 

 fossils has been pursued with an always increasing accuracy, 

 so it has furnished means of characterising them, always in- 

 creasing in precision. To such a degree has this been the 

 case, that the opinion which admits many distinct and inde- 

 pendent creations, is always obtaining more and more in- 

 fluence in the minds of palaeontologists. It is even easy to 

 foresee that in a little we shall be obliged to circumscribe 

 the limits of geological formations more and more, in pro- 

 portion as the knowledge of characteristic fossils, peculiar 

 to the different stages of the formations actually admitted, 

 shall more evidently represent them to us as independent 

 systems, differing at once from those that have preceded and 

 followed them. We shall thus be led to admit a very con- 

 siderable number of independent creations, each character- 

 ised by a particular assemblage of peculiar vegetable an4 

 animal species, imbedded in a system of strata deposited dur- 

 ing the existence of these organized beings, or in conse- 

 quence of the cataclysms which attended their destruction. 

 Ere long we shall have to do, not merely with primary, se- 

 condary, or tertiary epochs, nor even simply with palaeozoic, 

 triassic, Jurassic, or cretaceous periods, but rather with cam- 



