The assistance of Dr. C. Max Bauer, Chief, Geology Branch (retired),
National Park Service and of Chief Park Naturalist David de L. Condon in
making criticisms and suggestions on the material presented here is
acknowledged. The cooperation of the Yellowstone Library and Museum
Association in publishing the book is appreciated and I wish to thank
Yellowstone National Park for the use of copies of original paintings by
E. J. Sawyer for some of the illustrations. I also wish to acknowledge
the aid rendered by all others who participated in the editing and
completion of the manuscript for publication.