PREFACE 



This book is intended as a comprehensive survey of the entire field of 

 geophysical exploration. The author has endeavored to present the 

 subject in broad perspective, emphasizing the relations, differences, com- 

 mon features, and, above all, the fundamentals of geophysical methods. 



The material is divided into two parts of six chapters each. The first 

 part, written in elementary language, addresses those desiring an insight 

 into the working principles and geological applications of geophysical 

 methods. It is intended for individuals in executive and geologic advisory 

 capacity and for persons not directly concerned with field or laboratory 

 operations. 



The second and major portion is written for the technical student of 

 geophysics. It presents the subject from an engineering point of view, 

 striving at a balanced discussion of theory, field technique, laboratory 

 procedure, and geological interpretations. The author has aimed at a 

 presentation that will enable the geophysicist to get an insight into the 

 geologist's reasoning in selecting geophysical methods and in interpreting 

 geophysical data, and that will acquaint the geologist with the mathematics 

 cal and physical approach to instrument and interpretation problems. 



Certain compromises were unavoidable if a volume of practical size 

 was to be arrived at. It is not possible to cover the ground in such detail 

 as a specialist, working with a particular method, may deem advisable. 

 Geophysical exploration changes rapidly; processes once in the limelight 

 have been discarded; others, seemingly forgotten, have been revived. 

 In this book the fundamental or methodical significance of a given method 

 is its chief criterion for inclusion. This has been followed even at the risk 

 of describing "older" methods. Field, office, and laboratory procedures 

 are so changeable and so subject to personal preferences that the discussion 

 of such procedures is confined to a few examples illustrative of method but 

 not of detail. Since there is a limit to the number of geophysical surveys 

 that can be illustrated, a choice was made on the basis of distinctness of 

 response to subsurface conditions, and not on the basis of survey date. 



The necessity for elementary treatment has occasioned a certain breadth 

 in the mathematical discussions, possibly at the expense of rigor and 

 elegance. In many cases formulas are given without derivation. The 



