EVOLUTION AND THE PRESENT AGE 267 
cations and explanations. It is not believed that 
the earth’s surface was always so quiet as at present, 
because it is an accepted opinion among men of 
science that the earth was once a vaporous body 
immensely hotter than at present and to some extent 
self-luminous, as Jupiter and Saturn are to-day. Such 
a state of things was a state of more or less curious 
commotion such as may now be witnessed upon the 
surfaces of those planets which are so big that they 
still remain hot. Obviously, the cooling of the earth’s 
surface, with the formation of a crust, must have en- 
tailed increasing quiet, and it was of course not until 
long after the formation of a solid crust with liquid 
oceans that organic life could have begun to exist. 
Even after the introduction of plants and animals, the 
energies of the heated interior, imperfectly repressed, 
broke forth from time to time in local catastrophes 
upon the surface, though doubtless never in one that 
could be called universal. 
In early geologic ages there were doubtless earth- 
quakes and floods more violent than any recorded in 
history, but the chief agencies of change were the quiet 
ones, and in general, if at any time you had visited the 
earth, you would have found a peaceful scene where 
gentle showers and quickening sunshine coaxed forth 
the sprouting herbage, with worms crawling in the 
ground and quadrupeds of some sort browsing on the 
vegetation, and never would there just come a time 
when you could say that the old age had gone and a 
new one succeeded it. How does one generation of 
men succeed another? The fathers are not swept 
away in a body to make room for the children, but one 
by one the old drop off and the young come on till a 
