Leirbreen is one of very few glaciers in southern Norway at which a moraine ridge has been identified which may record a pre-'Little lee Age' Neoglacial advance. Previous attempts to date this ridge using 14C dating of buried palaeosols, lichenometry and the Schmidt hammer have produced equivocal results. This detailed Schmidt hammer study suggests that anomalously low rebound values obtained on the possibly older ridge reflect spatial variations in lithology. Comparison of R-values from boulders of carefully specified lithologies reveals that boulders on the ridge are no more weathered than those elsewhere on the foreland and considerably less weathered than those beyond the moraine limits. Results are consistent with formation during the 'Little lee Age', when other southern Norwegian glaciers reached their maximum extent.