Field measurements with the EM16 instrument, in several areas definitely confirm the usefulness of the VLF method for mapping shallow geological structure. Results obtained across a portion of the Gloucester fault southeast of Ottawa indicate that this technique is particularly suitable in areas where the geology is simple. The field results generally agree rather well with theoretical model data. The latter, however, indicates that mapping with the EM16 alone produces little quantitative information, although the relative positions of the high and low resistivity beds are generally clear. For this reason, it is desirable to supplement the EM16 data occasionally with surface impedance measurements to obtain apparent resistivities on both sides of the contact. This is especially true where it is suspected that the observed anomaly is caused by an accident in the bedrock topography rather than by the opposition of beds of differing resistivity.