Strains shown by vesicles in a basaltic dyke have been factorized into components of simple shear along the dyke and shear-parallel longitudinal strain. The dyke shows high shear strains at the margins, decreasing to the axial zone. Profiles of differential displacement are almost parabolic in form, suggesting Newtonian flow of the magma. The components of longitudinal strain indicate compressional flow in the axial zone of the dyke but extensional flow at the margins. Flow profiles and hence flow rates must have varied along the length of the dyke, possibly due to temperature changes.