PREFACE 
the evidences of immense time that looked out from 
their gray and crumbling fronts. I was in the pre- 
sence of Geologic Time, and was impressed by the 
scarred and lichen-coated veteran without knowing 
who or what he was. But he put a spell upon me 
that has deepened as the years have passed, and 
now my boyhood ledges are more interesting to me 
than ever. 
If one gains an interest in the history of the earth, 
he is quite sure to gain an interest in the history of 
the life on the earth. If the former illustrates the 
theory of development, so must the latter. The 
geologist is pretty sure to be an evolutionist. As 
science turns over the leaves of the great rocky 
volume, it sees the imprint of animals and plants 
upon them and it traces their changes and the ap- 
pearance of new species from age to age. The bio- 
logic tree has grown and developed as the geologic 
soil in which it is rooted has deepened and ripened. 
I am sure I was an evolutionist in the abstract, or 
by the quality and complexion of my mind, before 
I read Darwin, but to become an evolutionist in 
the concrete, and accept the doctrine of the ani- 
mal origin of man, has not for me been an easy 
matter. 
The essays on the subject in this volume are 
the outcome of the stages of brooding and think- 
ing which I have gone through in accepting this 
doctrine. I am aware that there is much repeti- 
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