The Great Glen Fault in the Shetland Area

Abstract

WE apologize to Dr Flinn for any disquiet we may have caused by omitting to refer to his recent paper¹. We agree with him that the aeromagnetic map² distinguishes regions of shallow and deep magnetic basement by the smoothness of the contours. We disagree, however, with his use of the general anomaly level as an indication of sediment thickness, which is the distinction between his pattern A anomalies which “probably overlie deep sedimentary basins” and pattern B which “covers sedimentary basins less deep than those of pattern A”. The usual geophysical approach is to estimate the depth to the basement using well established quantitative techniques³. One of the main points of our report⁴ was to present evidence for three deep Mesozoic basins marked C, D and E on our map. These basins are not delineated in Flinn's interpretation, although they do occur within wider tracts which he interprets as sediment covered.