122 THE GROWTH OF CONTINENTS. 
partment also, and there will be no hesitation as 
to the use of words for which we shall then ha\o 
a positive, definite meaning. 
Although the fivefold division of Werner, by 
which he separated the rocks into Primitive, 
Transition, Secondary, Alluvial, and "V olcanic, 
proved to be based on a partial misapprehension 
of the nature of the earth-crust, yet it led to 
their subsequent division into the three great 
groups now known as the Primary, or Palasozoic, 
as they are sometimes called, because here are 
found the first organic remains, the Secondary, 
and the Tertiary. I have said in a previous arti- 
cle that the general unity of character prevailing 
throughout these three divisions, so that, taken 
from the broadest point of view, each one seems 
a unit in time, justifies the application to them 
of that term, Age , by which we distinguish in 
human history those periods marked throughout 
by one prevailing tendency ; — as we say the age 
of Egyptian or Greek or Roman civilization, — 
the age of stone or iron or bronze. I believe that 
this division of geological history into these great 
sections or chapters is founded upon a recogni- 
tion of the general features by which they are 
characterized. 
Passing over the time when the first stratified 
deposits were accumulated under a universal 
ocean in which neither animals nor plants ex- 
