GENEUAl LAWS OF ORIGIN AND MIGRATION. 271 



back on the theory of periods of rapid origin, as we liave 

 already seen suggested by Saporta in the case of the '"'re- 

 taceous dicotyledons. Such abrupt and plentiful intro- 

 duction of species over large areas at the same time, by 

 whatever cause effected — and we are at present quite igno- 

 rant of any secondary causes — becomes in effect something 

 not unlike the old and familiar idea of creation. Science 

 must indeed always be balfled by questions of ultimate 

 origin, and, however far it may be able to trace the chain 

 of secondary causation and development, must at length 

 find itself in the presence of the great Creative Mind, 

 who is ** before all things and in whom all things con- 

 sist." 



