ILLUSTRATIONS . 



Paso. 

 Plate LVI. — Diagram No. 1; showing the relative predomiuence of each prin- 

 cipal type of vegetation at each geological period (colored). - 443 

 LVII. — Diagram No. 2, showing the observed origin and development 



of the principal types of vegetation in geologic time 450 



LVIII. — Diagram No. 3, showing the assumed origin and development 



of the principal types of vegetation in geologic time 452 



361 



