Under certain simplified but realistic physical assumptions, the basic data from continuous velocity surveys in wells can be used to simulate the variations in acoustic impedance in the ground which give rise to seismic reflections. An analogue computer is described which makes use of the basic well data to produce synthetic seismic records which resemble actual seismograms from shothole explosions. This process provides an interesting insight into the requisite physical conditions, as well as the physical processes, whereby seismic reflections are set up in the earth. The close relationship between seismograms and well logs is brought out. Illustrations are given of field results.