The Principles of Palaeontology. 189 



laws are complicated, and their application presents considerable 

 difficulties. We have sought to place these difficulties in a clear 

 light, in order that the student may not be surprised at the" un- 

 certainty which still exists in regard to many points of this great 

 problem ; the discussions which still constantly arise, and the 

 discordance among the theories propounded, should not be in- 

 voked as an argument against the doctrine of evolution itself. 

 The method of the natural sciences is unfortunately subordinate 

 to the acquisition of the necessary materials, and in Palaeon- 

 tology more, than in any other science, progress depends on the 

 increase of collections. 



