Lateral variation in velocity beneath the low velocity layer often causes time anomalies that obscure the true structural picture. A method of correction to a deep datum has been developed to minimize the spurious anomalies without affecting those caused by structure. This method makes use of the discovery that for any particular well in Western Canada, there exists a simple exponential relationship between time and depth so that the results of relatively shallow core hole velocity surveys can often be extrapolated to predict times to much greater depths. An example is given to show how this method was applied successfully to a particular problem area in Western Canada. It has since been used in several other places.