The preferred orientation of phyllosilicates in a sample of slate from North Wales causes anisotropy of X ray absorption. The linear absorption coefficient μ should be replaced by what is probably a second-rank tensor quantity, μij, with principal values of <1.31¿0.08, 1.34¿0.06, 1.57¿0.10>¿10-2. The maximum absorption is normal to the slaty cleavage, the intermediate absorption axis lies in the cleavage and is normal to the lineation, and the least absorption is parallel to the lineation. Based on March's theory, transmission pole figure X ray data, corrected for anisotropy of X ray absorption and for the irradiated volume, variable with sample orientation, give principal strains of <0.79¿0.03, 0.30¿0.02, -0.57¿0.00>. This differs from empirically corrected results of <0.81, 0.38, -0.60> but little from the results, <0.80, 0.31, -0.57>, of measurements on ellipsoidal strain indicators. ¿ American Geophysical Union 1991