Chap. IX. 
GEOLOGICAL KECOED. 
303 
started into life all at once, the fact would be fatal to 
the theory of descent with slow modification through 
natural selection. For the development of a group 
of forms, all of which have descended from some one 
progenitor, must have been an extremely slow pro¬ 
cess; and the progenitors must have lived long ages 
before their modified descendants. But we continually 
over-rate the perfection of the geological record, and 
falsely infer, because certain genera or families have 
not been found beneath a certain stage, that they did 
not exist before that stage. We continually forget 
how large the world is, compared with the area over 
which our geological formations have been carefully 
examined; we forget that groups of species may else¬ 
where have long existed and have slowly multiplied 
before they invaded the ancient archipelagoes of Europe 
and of the United States. We do not make due allow¬ 
ance for the enormous intervals of time, which have 
probably elapsed between our consecutive formations,— 
longer perhaps in most cases than the time required 
for the accumulation of each formation. These intervals 
will have given time for the multiplication of species 
from some one or some few parent-forms; and in the 
succeeding formation such species will appear as if sud¬ 
denly created. 
I may here recall a remark formerly made, namely 
that it might require a long succession of ages to adapt 
an organism to some new and peculiar line of life, for 
instance to fly through the air ; but that when this had 
been effected, and a few species had thus acquired a 
great advantage over other organisms, a comparatively 
short time would be necessary to produce many di¬ 
vergent forms, which would be able to spread rapidly 
and widely throughout the world. 
I will now give a few examples to illustrate these 
