THE GEOLOGICAL HISTORY OF PLANTS. 



The evidence is similar to that obtained by Schlie- 

 mann on the site of Troy, where, in digging through suc- 

 cessive layers of debris, he found the objects deposited by 

 successive occupants of the site, from the time of the 

 Roman Empire back to the earliest tribes, whose flint 

 weapons and the ashes of their fires rest on the original 

 surface of the ground. 



Let us now tabulate the whole geological succession 

 with the history of animals and plants associated with it : 



SYSTEMS OF FORMATIONS. 



Age of Man and 

 Mammalia. 



Age of Reptiles. 



Age of Amphibians 



and Fishes. 

 Age of Inverte- 

 brates. 



Age of Protozoa. 



o c Modern, 

 "o Pleistocene, 



g ! Pliocene, 



5 | Miocene, 



M L Eocene. 



| f Cretaceous, 

 o ! Jurassic, 

 Triassic. 



S L 



Permian, 

 Carboniferous, 

 Erian, 

 Silurian, 

 Ordovician, 

 Cambrian, 

 . Huronian (Upper). 



^ f Huronian (Lower), 



3 I Upper Laurentian, 



o I Middle Laurentian, 



^ I Lower Laurentian. 



ozoic. 



Angiosperms and 

 Palms dominant. 



Cycads and Pines 

 dominant. 



Acrogens and Gym- 

 nosperms domi- 

 nant. 



Protogens and 

 Algae. 



It will be observed, since only the latest of the sys- 

 tems of formations in this table belongs to the period of 

 human history, that the whole lapse of time embraced in 

 the table must be enormous. If we suppose the modern 

 period to have continued for say ten thousand years, and 

 each of the others to have been equal to it, we shall re- 

 quire two hundred thousand years for the whole. There 

 is, however, reason to believe, from the great thickness of 

 the formations and the slowness of the deposition of many 



