The Principles of Palaeontology. 143 



of the same age can be distinguished from the mutations the 

 species has undergone when found in more recent deposits. The 

 association of faunas is taken into account in reconstructing the 

 average conditions in which they existed,]and we can form an 

 idea regarding the zoologic and botanic geography of the diverse 

 epochs of geologic periods. 



Finally, scientists at the present day much prefer the synthetic 

 method in treating of the results acquired, and endeavor to 

 affiliate the countless forms of extinct creatures which are con- 

 stantly being brought to light. This new science, Phylogeny, 

 rests in great measure on palaeontologic data, and in return sup- 

 plies these with their greatest attraction. Its importance in the 

 present condition of our knowledge is such that we are obliged 

 to examine in some detail the principles on which it is based and 

 the problems which it solves. 



This brief historic sketch makes manifest the fact that 

 Palaeontology, like every other science, but in a more pronounced 

 degree, remained for long centuries in an almost rudimentary 

 state. Some men of genius, in the early part of this century, 

 stated the principles which have raised the study of fossils to an 

 independent science. At the present day Palaeontology is pro- 

 gressing with rapid steps. It proceeds, by successive approxima- 

 tions, as its object naturally indicates. We shall have occasion, 

 in the course of this work, to make manifest the importance of 

 the results achieved, and to point out the problems which still 

 remain to be solved. 



