128 
THE GROWTH OF CONTINENTS. 
considered as an ascertained law. What name, 
then, is most appropriate for the divisions thus 
marked by sudden and violent changes ? It 
seems to me, from their generally accepted mean- 
ing, that the word Epoch or Era, both of which 
have been widely, though indiscriminately, used 
in geology, is especially applicable here. In their 
common use, they imply a condition of things 
determined by some decisive event. In speaking 
of human affairs, we say, u It was an epoch or an 
era in history,” — or in a more limited sense, 
“ It was an epoch in the life of such or such a 
man. It at once conveys the idea of an impor- 
tant change connected with or brought about by 
some striking occurrence. Such were those di- 
visions in the history of the earth when a violent 
convulsion in the surface of the globe and a 
change in its inhabitants ushered in a new aspect 
of things. 
I have said that we owe to Elie de Beaumont 
the discovery of this connection between the suc- 
cessive upheavals and the different sets of ani- 
mals and plants which have followed each other 
on the globe. We have seen, in the preceding 
article upon the formation of mountains, that the 
dislocations thus produced show the interruptions 
between successive deposits: as, for instance, 
where certain strata are raised upon the sides of 
a mountain, while other strata rest unconformably , 
