140 
THE GROWTH OF CONTINENTS. 
It will be noticed by those who have any knowl- 
edge of geological divisions, that in this diagram 
I consider the Carboniferous epoch as forming a 
part of the Secondary age. Some geologists have 
been inclined, from the marked and peculiar 
character of its vegetation, to set it apart as form- 
ing in itself a distinct geological age, while oth- 
ers have united it with the Palaeozoic age. For 
many years I myself adopted the latter of these 
two views, and associated the Carboniferous epoch 
with the Palaeozoic age. But it is the misfortune 
of progress that one is forced not only to unlearn 
a great deal, but, if one has been in the habit of 
communicating his ideas to others, to destroy 
much of his own work. I now find myself in 
this predicament ; and after teaching my students 
for years that the Carboniferous epoch belongs to 
the Palaeozoic or Primary age, I am convinced, — 
and this conviction grows upon me constantly as 
I free myself from old prepossessions and bias on 
the subject, — that with the Carboniferous epoch 
we have the opening of the Secondary age in the 
history of the world. A more intimate acquaint- 
ance with organic remains has shown me that 
there is a closer relation between the character 
of the animal and vegetable world of the Carbo- 
niferous epoch, as compared with that of the Per- 
mian and Triassic epochs, than between that of 
the Carboniferous epoch and any preceding one. 
