374 HISTORICAL PALAEONTOLOGY. 



been effected, to what extent it has taken place, under what 

 conditions and laws it has been carried out, and how far it 

 may be regarded as merely auxiliary and supplemental to some 

 deeper law of change and progress, are questions to which, in 

 spite of the brilliant generalisations of Darwin, no satisfactory 

 answer can as yet be given. In the successful solution of this 

 problem if soluble with the materials available to our hands 

 will lie the greatest triumph that Palaeontology can hope to 

 attain ; and there is reason to think that, thanks to the guiding- 

 clue afforded by the genius of the author of the ' Origin of 

 Species,' we are at least on the road to a sure, though it may 

 be a far-distant, victory. 



