GENEEAL RELATIONS OF PLANTS TO TIME. 439 



This distinguislied observer, in dividing the series of stratified 

 deposits in accordance -vvith the fossil plants contained in 

 them, named the Palteozoic period the " Age of Acrogens," 

 the Secondary period (exclusive of the Cretaceous) the " Age 

 of Gymnosperms," and the Cretaceous and Tertiary periods the 

 '■' Age of Angiosperms." This generalisation, though still ex- 

 pressing a general truth, can only be accepted Tvith consider- 

 able reservation. Gymnosperms, and perhaps even Angio- 

 sperms, are not unknown in the Palaeozoic period; and if 

 the Sigillarioids should be referred to the former group of 

 plants, then the later Palceozoic period would have as good 

 claim to be called the " Age of Gymnosperms " as the 

 Secondary period. Again, as pointed out by Sir Charles 

 Lyell, the Lower and Upper Cretaceous floras differ from 

 one another in the most striking manner, the Lower Creta- 

 ceous agreeing in this respect with the Jurassic series, whilst 

 the L'pper Cretaceous series is linked on by its plants to 

 the Tertiary formations. The line, therefore, between the 

 Age of Gymnosperms and the Age of Angiosperms must be 

 drawn between the Lower and L'pper Cretaceous, and not at 

 the base of the Cretaceous series. 



