EVOLUTION AND THE PRESENT AGE 265 
such as the Carboniferous or the Jurassic or the 
Eocene, here selected for mention, were characterized 
by such catastrophes, which swept from the face of the 
earth all existing forms of life. It was supposed that 
the introduction of a new geologic period was marked 
by a fresh introduction of living beings through some 
inexplicable act of wholesale creation. There were 
plenty of facts, indeed, which did not harmonize with 
this view, such, for example, as the continuous exist- 
ence of a certain kind of shell-fish known as trilobites 
through many successive geologic periods. The 
theory of catastrophes appeared to demand the assump- 
tion that these trilobites were wiped out and created 
over again half a dozen times; which was rather a 
shock to men’s acquired notions of probability. 
The complete overthrow of this doctrine of catas- 
trophes was effected by Sir Charles Lyell, whose great 
book was published in 1830. The difficulty with the 
catastrophizers was that while talking glibly about 
millions of years, they had not stopped to consider 
what is meant by a million years when it takes the 
shape of work accomplished. Suppose you were to 
go to the Grand Cajon of the Colorado River, and 
stand upon the fearful brink of the gorge, where it is 
more than a mile in depth, looking down at the stream 
like a tiny bright ribbon at the bottom, and were told 
that this stream is wearing off from its rocky bed about 
one-tenth of an inch every year, how your mind would 
feel staggered in the attempt to estimate the length of 
time it must have taken to excavate the whole of that 
mighty gorge! Your first impulse would certainly be 
to speak of quadrillions of years, or something of the 
sort; yet a simple calculation shows that one million 
