For a number of years geophysical methods of subsurface surveys have been employed in geology, locating of petroleum and ore bodies, ground water studies, foundation studies for many types of structures, and other fields. These methods have utilized field apparatus, such as seismic and electrical resistivity, to locate or plot these unknown subsurface formations. These two methods are probably the most commonly used. Many public and private agencies, as well as individuals, have adopted the electrical resistivity apparatus as standard equipment, among them many state highway departments, consulting geologists, governmental engineering agencies such as the Bureau of Reclamation, water districts, soil engineers, and oil companies. Highlights in the usefulness of this tool as reported by these agencies, include the economical determination of borrow pit sources, ground water, soundness and faulting of rock formations, depths of bed rock, and oil well logging. The electrical device utilizes the principle that soil and rock of different character offer varying resistances to the flow of electrical current, whereas other methods employ basic principles such as the passage of sound vibration, etc.