24 



Our Native Ferns. 



country would be a valuable addition to our knowledge of geo- 

 graphical distribution : 



23. Geological Distribution.— It is well known that the plants 

 and animals now existing on the earth are not the same in 

 kind as those of former ages. Geologists have carefully studied 

 the stony heart of nature, and have drawn therefrom the story of 

 the development of land and sea, and the successive populations 

 that from time to time have held possession of our globe. Plants 

 furnishing the natural food for animals must have preceded ani- 

 mal life, yet, in the earliest geological ages, the remains of ani- 

 mals are far more numerous. The abundance of the deposits of 

 graphite and iron-ore in the earliest or Archaean rocks indicates 

 the existence of extensive plant growth, but the remains are so 

 transformed as to make it impossible to determine the character 

 of this primeval vegetation. 



In the succeeding Silurian age, the fossil remains indicate the 

 existence of algae or sea weeds in abundance, and a single small 



* Only the species and varieties recognized in this work are enumerated. 



