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 Paleeontology 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. 
