SCIENCE OF FOSSIL LIFE 331 
slow, continuous changes that have occurred in the past and 
have molded the earth’s crust into its present condition. 
He showed, further, that organic fossils are no exception 
to this law of uniform change. He pointed to the evidences 
that ages of time had been required for the formation of the 
rocks bearing fossils; and that the regular succession of animal 
Fic. 97.—CHARLES LYELL, 1797-1875. 
forms indicates a continual process of development of animal 
life; and that the disappearance of some forms, that is, their 
becoming extinct, was not owing to sudden changes, but to 
gradual changes. When this view was accepted, it overthrew 
the theory of catastrophism and replaced it by one designated 
uniformatism, based on the prevalence of uniform natural 
laws. 
This new conception, with all of its logical inferences, 
