Vi PREFACE
The work would hardly have been possible without the
material help that has been generously given by many members of
the staff of the Geophysical Section of the Gulf Research Labora-
tory. Various parts of the manuscript have been read by indi-
viduals particularly familiar with the subject matter. It is a
pleasure to acknowledge the help thus given by James Affleck,
Thomas Bardeen, Milton Dobrin, C. H. Drcsbach, L. W. Gard-
ner, 8. Hammer, G, B, Lamb, M. Muskat, B. Perkins, Jr., 0. F.
Ritzmann, W. B. Robinson, C. A. Swartz, V. V. Vacquier, and
R. D. Wyckoff. Special acknowledgment is due to T. A.
Elkins, who read most of the manuscript and provided part
of the bibliography, to W. L, Dowler, who mode all the drawings,
and to Elmina Lewis for all the stenographic work. Finally,
I wish to express my appreciation to Dr. Paul D. Foote, director
of the Gulf Research Laboratory, for his interest and for the
stenographic and other facilities provided by the laboratory
and to him and Dr. E. A. Eckhardt for permission to undertake
this work.
L. L. NETTLETON.
Gulf Research and Development Company,
Pittsburgh, Pa.,
July, 1940.