62 OUR NATIVE FERNS AND THEIR ALLIES. 



the story of the development of land and sea, and the succes- 

 sive populations that from time to time have held possession 

 of our globe. Plants furnishing the natural food for animals 

 must have preceded animal life, yet in the earliest geologic 

 ages the remains of animals are far more numerous. The 

 abundance of the deposits of graphite and iron-ore in the earli- 

 est or Archaean rocks indicates the existence of extensive plant 

 growth, but the remains are so transformed as to make it im- 

 possible to determine the character of this primeval vegetation. 



141. In the succeeding Silurian age the fossil remains in- 

 dicate the existence of algae or sea-weeds in abundance, and a 

 single small species of ground pine attests the existence of some 

 of the higher Cryptogamia ; no ferns, however, have been 

 found in America older than the Devonian. Over fifty species 

 of Devonian ferns have been described from the American 

 rocks chiefly, by Principal J. W. Dawson of Montreal. 



142. It is in the coal measures, however, that ferns and 

 otlier Cryptoga7nia are found in the greatest abundance and 

 profusion. Their delicate foliage is impressed on the various 

 rock strata above the beds of coal, and so perfectly are they 

 preserved that not only the methods of fructification but even 

 the microscopic spores have been detected ! In the coal meas- 

 ures of the United States and Canada (counting from the base 

 of the Catskill), 381 species of ferns have been described, 

 chiefly by Prof. Leo Lesquereux. The most abundant Ameri- 

 can genera are Neuropteris 45 species, Pecopteris 50 species, 

 Sphenopteris 31 species, Pseudopecopteris 25 species, and Rha- 

 cophyllum 24 species. 



The frontispiece gives an ideal representation of the vegeta- 

 tion of the Carboniferous age. The luxuriant tree-ferns, the 

 Lepidodendrids, ancient representatives of the diminutive club- 

 mosses or ground-pines, the Calamites, allies of the modern 

 scouring-rushes, and other forms no less wonderful, are seen in 

 their profusion. 



143. In the later geologic ages, Mesozoic and Tertiary, 

 ferns are found preserved in the rocks, with the leaves of many 

 trees and shrubs of existing genera. The indications are that 



