188 



BOTANY. 



[CHAP. vi. 



The following order of succession of Stratified Forma- 

 tions or Geological periods will enable the reader to trace 

 the gradual evolution of plant groups 



Archcean. 



Laurentian. 



CRYPTOGAMS. 



Algce. 



The Algae, or seaweeds, geologically the oldest known 

 plants, first occur in the Laurentian series, and continue 

 to the present day. 



Filices. 



The ferns first appear in the Devonian, attain their 

 maximum of development towards the end of the 

 Carboniferous age, then, with the exception of a second 



