1. A method of geophysical prospecting by transient currents utilizing a plurality of prospecting stations, each of said stations comprising a transmitter dipole for transmitting an excitation impulse and a receiver dipole for receiving numerical signals representing a subsoil transient response to said excitation wherein said numerical signals are processed to obtain a figurative representation for geophysical interpretation of said subsoil responses attributable to the geographical positioning of the prospecting stations, said processing comprising: (a) preprocessing said numerical signals to obtain a statistical composition of responses which are repeatedly registered for each of said plurality of prospecting stations; (b) determining, for each statistically composed transient response associated with a prospecting station, a local indicator function related to variations of a gradient of said transient response as a function of time; (c) determining, for several prospecting stations, a regional indicator function representing as a function of time a common mode of the local indicator functions associated with each of said several prospecting stations; (d) subtracting the regional indicator from each of the local indicators to determine a residual indicator for each of the stations concerned; and (e) producing a representation of subsoil structure features from said residual indicators determined as a function of said geographical positioning of said stations.