76 
THE FERN FORESTS OF 
For instance, the Temperate Zone throughout the 
world is characterized by certain families of trees : 
by Oaks, Maples, Beeches, Birches, Pines, etc. ; 
but the Oaks, Maples, Beeches, Birches, and the 
like, of the American flora in that latitude differ 
in species from the corresponding European flora. 
So in the Carboniferous period, when more uni- 
form climatic conditions prevailed throughout the 
world, the character of the vegetation showed a 
general unity of structure everywhere ; but it 
was nevertheless broken up into distinct botanical 
provinces by specific differences of the same kind 
as those which now give such diversity of appear- 
ance to the vegetation of the Temperate Zone in 
Europe as compared with that of America, or to 
the forests of South America as compared with 
those of Africa. 
There can be no doubt as to the true nature 
of the Carboniferous forests ; for the structural 
character of the trees is as strongly marked in 
their fossil remains as in any living plants of the 
same character. We distinguish the Ferns not 
only by the peculiar form of their leaves, often 
perfectly preserved, but also by the fructification 
on the lower surface of the leaves, and by the 
distinct marks made on the stem at their point 
of juncture with it. The leaf of the Fern, when 
falling, leaves a scar on the stem varying in shape 
and size according to the kind of Fern, so that 
