In all seismic refraction surveys, the problem is to determine the constants in a system of equations of the type t i j = at+bj+Atj/w where at and bj are "time terms" which are characteristic of the shotpoint and seismograph station respectively, Agj is the distance between the shot point and the seismograph, t t j is the time of propagation of a refracted wave and w is the velocity of propagation of seismic waves in an underlying marker layer. I t is shown that the equations can be solved for interpenetrating networks of shot-points and seismographs provided that certain general conditions are satisfied. Factors which determine the uncertainties of the final solution are discussed, and methods of correcting for the effects of steeply dipping boundaries are included.

A three-component, short-period seismograph bas been developed in which frequency-modulated magnetic tape is used as the recording medium. The techniques for maintaining a well-calibrated system under field conditions are discussed in detail. Present methods for editing and conversion to a digital format are also described. The possibilities are explored for a modified system that produces additional long-period information from short-period seismometers.

Bott and Smith [1958] give the following formulas for three‐dimensional and two‐dimensional anomalies, respectively: d0=false(485/125false)false(ΔgT/Uxzfalse) d0=false(33/8false)false(ΔgT/Uxzfalse) where d0 is the maximum possible depth to the top of the anomaly‐producing body, ΔgT is the total anomaly and Uxz, is the maximum horizontal gradient. It should be noted that these formulas are also valid as the exact depths to a point source and an infinite horizontal line source, respectively. In the case of a 'stepped' anomaly, the derivation of maximum depth is particularly straightforward if we assume that the anomaly is due to a semi‐infinite step of depth d and thickness t (Fig. 1).

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